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description | The invention relates generally to infrared marking devices and methods and, in particular, to infrared marking devices visible through thermal imaging cameras and methods of using the infrared marking devices. When firefighters and other emergency personnel arrive at a smoke-filled or burning building or structure, a search and rescue operation is conducted in which each room of the burning structure is systematically searched for persons trapped by the structure fire or otherwise unable to escape from the burning structure. Typically, the firefighters don protective survival gear (e.g., self contained breathing apparatus) and search in teams by following the structural walls. Dense smoke and darkness severely limit the visibility inside the burning structure and hamper firefighter search and rescue operations, sometimes at the risk of the firefighter's safety. After each room in the burning structure is searched and before searching the next room, a conventional type of marker may be used to mark the entrance leading into the searched room. These markers indicate to subsequent firefighters that the room has been previously searched during the search and rescue operation. Marking searched rooms expedites the search and rescue operation as rooms are not needlessly searched multiple times by different firefighters or by even the same team of firefighters disoriented by the dense smoke and darkness. Searched rooms may be indicated by, for example, placing a chair in the doorway or by marking the door with a crayon or chalk mark. Another conventional type of marker may be applied to a door at the entrance leading into the room. These conventional markers may rely on a visible indicator, such as a visible strobe light, a reflector, or a colored object, to alert the firefighters that a particular room in the burning structure has been searched. However, smoke has a large component of micron-sized carbon soot particles in it, making it very absorbing at the visible-light wavelengths. Hence, visual indicators are inadequate under conditions of dense smoke and darkness in which vision is obscured. Conventional markers may also rely on an audible signal, such as sound emitted from a speaker, to alert the firefighters that a particular room in the burning structure has been searched. However, the firefighter's ability to discern markers emitting audible signals may be indistinguishable from other environmental noises or may be muffled and muted by the survival gear worn by the firefighter. Verbal communications to communicate searched rooms is also obscured by the environmental noises and the firefighter's survival gear. Thermal imaging cameras (“TICs”) permit firefighters to penetrate heavy smoke and overcome the handicap of darkness to visualize heat sources in situations of limited visibility during search and rescue operations. Typically, a fireman carries a portable, hand-held thermal imaging camera into a burning structure and relies on thermal patterns visible in the camera display that indicate the presence of a person, a hot spot which may be the source of the fire, or some other thermal characteristic or heat emitting object of interest. The thermal imaging camera converts infrared radiation emitted by the heat source, which is not visible to the human eye, into a visible image viewable on the camera's display. The thermal imaging camera detects the frequency or wavelength of the radiation, which is related to a specific temperature. The wavelength of the emitted infrared radiation increases as the temperature of the heat source increases. On the display of the thermal imaging camera, heat sources are displayed with a color or gray scale in which the displayed brightness increases with temperature. The detection threshold of the electronics in the thermal imaging camera is typically adjusted so that low temperature objects are not visible in the displayed image. This improves the image contrast between heat sources of interest and background objects. Conventional markers that rely on the emission of visible light or sensing by the unaided human eye are not imaged by the thermal imaging camera as visible wavelengths are outside of the infrared band of the electromagnetic spectrum. Moreover, the temperature of objects emitting visible light lack a sufficient heat signature to be plainly visible in a thermal imaging camera. In addition, the range of the visible light emitted from the object and the ability to see a visual indicator is limited by an inability to penetrate the dense smoke. Conventional markers that rely on reflection are ineffective in the absence of an infrared radiation source for reflection. Thermal imaging cameras are passive devices in that they do not carry such infrared radiation sources. Even if an infrared source were married with a thermal imaging camera, the high directionality of the infrared light beam projected from the camera would dramatically restrict the firefighter's ability to successfully reflect infrared radiation from the reflector. Colored objects cannot be visualized using a thermal imaging camera because of the invisibility of light in the visible band of the electromagnetic spectrum to the camera's imaging system. If firefighters are compelled by the nature of the structure fire to crawl during the search and rescue operation, conventional room markers may be difficult to distinguish visually. Obviously, sound emitting markers cannot be imaged by the thermal imaging camera. What is needed, therefore, is a marker for a room door that may operate in conjunction with a thermal imaging camera during search and rescue operations conducted by firefighters inside a smoke-filled or burning structure that overcomes these and other deficiencies of conventional markers. In accordance with an embodiment of the present invention, an infrared marking device comprises a ring-shaped, elasticized outer sleeve having a tubular sidewall and an amount of a self-heating material confined inside the tubular sidewall of the outer sleeve. The self-heating material emits infrared radiation when activated to initiate an exothermic chemical reaction. The infrared marking device, which may be used as a marker for a room door during search and rescue operations conducted by firefighters inside a smoke-filled or burning structure, has a heat signature of infrared radiation that is imageable in a thermal imaging camera. In certain embodiments, the sidewall of the outer sleeve is permeable to oxygen and the self-heating material reacts exothermally when exposed to the oxygen permeating through the sidewall. In other embodiments, the infrared marking device may further comprise a ring-shaped elastic band positioned inside the outer sleeve and extending circumferentially about the outer sleeve. The elastic band operates to elasticize the outer sleeve. In accordance with an embodiment of the present invention, a method is provided for marking an object, such as a door, inside a structure, such as a smoke-filled or burning structure. The method comprises activating a self-heating material confined inside a marking device to initiate an exothermic reaction that emits infrared radiation and applying the marking device to the object inside the structure. The present invention is generally directed to infrared marking devices visible inside a smoke-filled or burning structure to firefighters using a thermal imaging camera. The infrared marker preferably contains an oxygen-activated exothermic composition that emits heat when activated. The infrared marking devices, when activated and attached to the knobs of a door, are used to subsequently signal firefighters that a room has been searched and cleared. The infrared marking devices may also be attached to a tool handle for advantageously locating a dropped tool. The present invention will now be described in greater detail by referring to the drawings that accompany the present application. With reference to FIG. 1 and in accordance with an embodiment of the present invention, an infrared marking device or infrared marker 10 is deployed by attachment to door levers or knobs 12 and 13 (FIG. 7) of a door 12, 13 providing access to a doorway leading into a room inside a smoke-filled or burning structure 16. A firefighter 18, who is performing a search and rescue operation inside the burning structure 16, is carrying a thermal imaging camera 20 that is adapted to detect heat sources emitting radiation in the infrared band of the electromagnetic spectrum. The thermal imaging camera 20 permits the firefighter 18 to penetrate heavy smoke and overcome darkness to visualize infrared emitting sources inside the burning structure during the search and rescue operation. Thermal imaging cameras 20 may, for example, detect infrared radiation in the 8,000 nm to 14,000 nm range, which is significantly outside of the visible light range of 400 nm to 700 nm. The infrared marker 10 is visible to the firefighter 18 as an image 21 in a display 22 of the thermal imaging camera 20. The presence of the infrared marker 10 on the knobs 12, 13 of the door 14 alerts the firefighter 18 that the room has searched and cleared during the search and rescue operation and, consequently, the room accessible through the door 14 does not require another search. This improves firefighter safety in that searched rooms bearing the infrared marker 10 on the door 14 are not needlessly searched multiple times, which speeds the search and rescue operation. The image 21 of the infrared marker 10 visible on the display is crescent shaped or C-shaped based on the shape of the deployed infrared marker 10, although the invention is not so limited as the marker 10 may have a different deployed imageable configuration. With reference to FIGS. 2-4, the infrared marker 10 comprises an outer tube or sleeve 24, an amount of an exothermic, self-heating material 25 (FIG. 2A) confined in a plurality of air-permeable packs or pouches 26 confined inside the outer sleeve 24, and an extensible elastic band 28 disposed inside the sleeve 24. Advantageously, the composition of the self-heating material 25 inside the pouches 26 may be selected such that, upon activation, the temperature of the self-heating material 25 may be approximately 135° F. to approximately 175° F. At these temperatures, the infrared marker 10 emits heat energy as infrared radiation that may be readily detectable by the thermal imaging camera 20 and displayed on display 22 with a clear contrast level relative to background objects visible to the firefighter 18. The heat or infrared signature emitted by the infrared marker 10 advantageously does not require an electrical power source for heat generation. The composition of the self-heating material 25 in pouches 26 may include one or more chemicals and chemical compounds that oxidize to generate heat when exposed to an oxidant, such as oxygen from the air. One common variety of self-heating material 25 has a composition that generates heat based upon iron oxidation triggered by the presence of an oxidant, such as oxygen from the ambient air, inside the outer sleeve 24. Pouches 26 suitable for use in the present invention are disclosed in U.S. Pat. No. 5,918,590, which is hereby incorporated by reference herein in its entirety, as an oxygen permeable container holding a particulate exothermic composition consisting of amounts of iron powder, activated carbon, non-activated carbon, and mixtures thereof, a metal salt such as sodium chloride, and water held in a water holding material like vermiculite. Another useable composition for the self-heating material 25 may consist of iron powder, carbon, salt, and vermiculite as a water holding material or any similar oxidizing ingredients. Still other compositions for the self-heating material 25 may require the rupture of a frangible barrier to allow different chemicals to mix to initiate the exothermic chemical reaction of the infrared marker 10. The outer sleeve 24, which is shaped like a ring or toroid, has a tubular construction with a tubular sidewall 35 consisting of one or more layers of woven or nonwoven fabric or cloth, as best shown in FIG. 3A. The fabric constituting the tubular sidewall 35 is porous to air, which permits air to permeate the tubular sidewall 35 and enter the space inside the outer sleeve 24 in which the pouches 26 of self-heating material 25 are confined. Advantageously, the fabric or cloth of the outer sleeve 24 may be formed from threads or fibers of a flame-resistant or flame-retardant material, or may be formed from threads or fibers of a cotton or cotton blend to which a chemical treatment is applied to make the material flame-resistant or flame-retardant. Advantageously, the fabric or cloth constituting the outer sleeve 24 may be water repellant if the self-heating material 25 is negatively impacted by water exposure. Of course, self-heating materials 25 capable of initiating and sustaining the chemical reaction in the absence of oxygen may impose different requirements on the properties of the fabric or cloth in the outer sleeve 24 as understood by a person having ordinary skill in the art. The outer sleeve 24 may be formed from a rolled length of fabric material having the free open ends and side edges sewn together, after the elastic band 28 and pouches 26 are inserted, to form seams that define the tubular sidewall 35. To that end, opposite side edges of the outer sleeve 24 may be joined together by a line of stitches 41 and the ends of the outer sleeve 24 may be joined by another set of stitches (not shown). The invention contemplates that the outer sleeve 24 may be formed from a stretchable elasticized fabric made with elastic strands, instead of the elastic insert defined by the elastic band 28 that elasticizes the outer sleeve 24. As best shown in FIG. 2A, the pouches 26 may be stationed at spaced-apart locations distributed about the circumference of the outer sleeve 24. Each of the pouches 26 includes at least one air permeable wall 26a that, when the infrared marker 10 is activated, permits the passage of oxygen-containing air from the space inside the tubular sidewall 35 of the outer sleeve 24 to the self-heating material 25. The wall 26a of the pouch 26 may also regulate the transfer of water across its thickness for purposes of controlling the loss of water from the self-heating material 25 through the sidewall 26a for those self-heating materials 25 that rely on moisture during the exothermal chemical reaction. The pouches 26 may be unattached and free to move circumferentially within the outer sleeve 24. To provide confinement, the outer sleeve 24 may include a plurality of transverse seams 32 defined by stitching that compartmentalize the outer sleeve 24 to an extent sufficient to confine each of the pouches 26 within an arc length of the circumference of the outer sleeve. In a specific embodiment, the outer sleeve 24 may include a plurality of, for example, two transverse seams 32 that define compartments 33 each holding one or more of the pouches 26 and confining circumferential movement of each individual pouch 26 within each half of the circumference. In various embodiments, there may be two (2) to six (6) transverse seams 32 compartmentalizing the outer sleeve 24. Alternatively, the pouches 26 may be directly attached to the tubular sidewall 35 of the outer sleeve 24 and/or directly attached to the elastic band 28 so that the transverse seams 32 are not required. In other alternative embodiments of the present invention, the outer sleeve 24 may lack transverse seams 32 such the interior of the outer sleeve 24 constitutes a single continuous space in which the unattached pouches 26 are free to move. In these embodiments, the lumen defined by the outer sleeve 24 would supply an air passage for transferring heat about the entire circumference of the infrared marker 10. Advantageously, the pouches 26 are positioned in the outer sleeve 24 at circumferential locations such that, regardless of how the infrared marker 10 is applied to the knobs 12, 13 and if the door 14 is either open or closed, the heat emission from at least one of the pouches 26 is visible in the thermal imaging camera 20 from the exterior of the door 14. The confinement of the heat emission from the pouches 26 by the outer sleeve 24 may result in heat confinement along the entire circumference of the outer sleeve 24, as opposed to discrete hot spots only at the location of the pouches 26. As a result, the entire length of the infrared marker 10 will be visible in the display 22 of the thermal imaging camera 20. The elastic band 28, which may be formed from any suitable continuous or endless strip elastic material having a loop shape, is circumferentially disposed inside the outer sleeve 24. When relaxed, the elastic band 28 causes the outer sleeve 24 to bunch, wrinkle or shirr when the outer sleeve 24 contracts in dimension to conform to the elastic band 28. Advantageously, the length of the outer sleeve 24 and elastic band 28 are selected such that the infrared marker 10 may be easily applied by a firefighter 18 to the knobs 12, 13 of substantially all conventional doors 14 and, after application, the elastic band 28 supplies tension sufficient to keep the infrared marker 10 secured to the knobs 12, 13. One suitable material for the elastic band 28 is latex rubber, which may elongate to several times its relaxed length when stretched. Generally, the elastic band 28 may be formed from any material that, upon application of a force to its relaxed, initial length, can stretch or elongate to its elongated length without rupture and breakage, and which can substantially recover its initial length upon release of the applied force. The elastic band 28 may have any desired cross-sectional shape, such as rectangle, trapezoid, round, oval, irregular or the like, as well as any combination thereof. The outer sleeve 24 has a relaxed circumference substantially determined by the circumference of the elastic band 28 and a maximum stretched circumference limited by the physical dimensions of the outer sleeve 24. In an exemplary embodiment of the present invention, the elastic band 28 of latex rubber may have a length of about twelve (12) inches and the outer sleeve 24 may have a maximum stretched circumference of about twenty-four (24) inches to thirty-six (36) inches. These lengths are specified such that the infrared marker 10 may be deployed on the door knobs 12, 13 and such that one or more of the infrared markers 10 may be carried either securely wrapped about the palm of the firefighter's gloved hand 38 (FIG. 4) or securely wrapped about the handle of a tool, such as a fire axe 30 (FIG. 5). Carrying one or more the infrared markers 10 on the fire axe 30 may advantageously permit the firefighter 18 to easily locate and grasp the fire axe 30 if the fire axe 30 is dropped during the search and rescue operation. Infrared markers 10 are carried on the firefighter's gloved hand 38 may be used to locate the firefighter 18. With reference to FIG. 6, the infrared marker 10 is normally confined in a sealed bag or other sealed enclosure 36. In embodiments in which the self-heating material 25 is activated by oxygen, the sealed enclosure 36 has walls that are formed from a material that prevents oxygen from the air from reaching the self-heating material 25 confined inside the pouches 26. As a result, the infrared marker 10 is stored for use inside the sealed enclosure 36 in a latent or dormant state in a substantially oxygen deprived ambient atmosphere in which the self-heating material 25 is not generating heat. The present invention contemplates that a plurality of the infrared markers 10 may be provided inside a single sealed enclosure 36 in the form of a kit. The sealed enclosure 36 may include a resealable closure 37 or may include another type of access mechanism, such as a frangible seal. In use and with reference to FIGS. 1-7, the firefighter 18 removes the infrared marker 10 from the sealed enclosure 36 in route to the burning structure 16 or after arriving at the site of the burning structure 16. Air permeates through the fabric or cloth of the outer sleeve 24 and through the air permeable walls of the pouches 26 to the self-heating material 25 in the pouches 26. The self-heating material 25 is exposed to oxygen in the air, which initiates a chemical reaction with the self-heating material 25 that causes heat emission from the pouches 26. The properties, including but not limited to amount, distribution, and composition, of the self-heating material 25 inside the pouches 26 are selected to provide heat emission, which provides a heat signature visible in the display 22 of the thermal imaging camera 20, that persists for several hours. The firefighter 18 wraps one or more of the infrared markers 10 about the palm of his gloved hand 38 (FIG. 4) or about the handle of the fire axe 30 (FIG. 5) in a double-wrapped manner before entering the burning structure 16. After the firefighter 18 searches each of the rooms inside the burning structure 16, one of the infrared markers 10 is deployed on the door knobs 12, 13 of the door 14 providing access to the room. If the infrared markers 10 are carried across the firefighter's palm, a simple swiping may be used to engage a portion of the sleeve 24 with, for example, the outer knob 12 on the door's exterior face and then stretched to extend the elastic band 28 to engage, for example, the inner knob 13 on the door's interior face. The stretched elastic band 28 relaxes to a stretched state that secures the infrared marker 10 to the knobs 12, 13 of the door 14. The infrared marker 10 may deployed such that a bolt 34 of a latch of the door 14 is unobstructed by the marker 10. This permits the door 14 to be closed and secured by extending the bolt 34 into a strike (not shown) in the door facing. Alternatively and as shown in FIG. 7, the infrared marker 10 may be deployed in a wrapped configuration such that the bolt 34 is occluded by a portion of the infrared marker 10 and, when the door 14 is shut, fails to latch. Alternatively and as shown in FIG. 7A, one of the infrared markers 10 may be individually wrapped about each of the door knobs 12, 13 of door 14. The invention contemplates that the infrared marker 10 may be wrapped about only the exterior door knob 12 of door 14. The self-heating material 25 in the pouches 26 provides a heat signature in the infrared band of the electromagnetic spectrum that is visible to the firefighter 18 in the display 22 of the thermal imaging camera 20. The presence of the infrared marker 10 indicates to subsequent firefighters 18 that the room behind the door 14 has been previously searched and cleared by another firefighter 18. The infrared marker 10 is also visible in the thermal imaging camera 20 from a perspective inside the room. This may guide the firefighter in finding the door 14 through which he entered the room, if the room is dark and filled with smoke, if the firefighter becomes disoriented, or if self-contained breathing apparatus is exhausted. After use, the infrared marker 10 is left on the door 14 and eventually the chemical reaction of the self-heating material 25 goes to completion at which time heat emission ceases. The invention contemplates that other types of objects inside a burning structure may be marked with the infrared marker 10, such as the fire axe 30. The infrared marker 10 may also be used as a locating device for the firefighter 18 when attached to the firefighter's gloved hand 38. With reference to FIGS. 8-10 in which like reference numbers refer to like features in FIGS. 1-7 and in accordance with an alternative embodiment of the present invention, an infrared marking device or infrared marker 40 may include a self-heating material 42 in the form of loose particulate or powder confined inside the outer sleeve 24. The self-heating material 42 is similar or identical in composition to the self-heating material 25 confined in the pouches 26 (FIGS. 1-7). The fabric or cloth constituting the outer sleeve 24 may control the transfer of water across its thickness to prevent the entry of water into the space holding the self-heating material 42 and to regulate the loss of water through the tubular sidewall 35 for those self-heating materials 42 that rely on moisture during the exothermal chemical reaction. Therefore, the properties of the fabric or cloth are tailored to eliminate the need for pouches 26 (FIGS. 2, 2A). Transverse seams 32 compartmentalize the outer sleeve 24 such that the self-heating material 42 does not aggregate in one location inside the outer sleeve 24. The compartmentalization is illustrated as dividing the outer sleeve 24 such that an amount of self-heated material 42 is confined within each quadrant of the circumference. During manufacture, every other transverse seam 32 is stitched closed and an opening in the outer sleeve 24 is left at the future location of every other transverse seam 32, as shown in FIG. 10, for loading the self-heating material 42 into the specific compartments 33 of the infrared marker 40. After the self-heating material 42 is introduced into the outer sleeve 24, transverse seams 32 are stitched to close the openings, as shown in FIG. 9, to define the plurality of, for example, four compartments 33 each confining an amount of the self-heating material 42. The compartmentalization serves to keep the self-heating material 42 distributed evenly about the circumference of the outer sleeve 24, although the self-heating material 42 disposed loosely within each individual compartment may aggregate to some extent. With reference to FIG. 11 in which like reference numbers refer to like features in FIGS. 1-10 and in accordance with an alternative embodiment of the present invention, the outer sleeve 24 of the infrared marker 40 may also have a dual lumen configuration in which the self-heating material 42 is confined inside one circumferential lumen 44 and the elastic band 28 is disposed in the other circumferential lumen 46. The individual lumens 44, 46 are separated by a circumferential partition 48 to define a side-by-side arrangement, although the present invention is not so limited. For example, the lumens 44, 46 may have a concentric arrangement in which the elastic band 28 is placed inside the radially innermost one of the lumens 44, 46 and the self-heating powder 42 is confined in the radially outermost one of the lumens 44, 46. In this instance, at least the radially innermost of the lumens 44, 46 would supply an air passage for heat transfer about the entire circumference of the infrared marker 40 when the infrared marker 40 is activated. This may promote uniform infrared emission about the circumference of the infrared marker 40. With reference to FIG. 12 in which like reference numbers refer to like features in FIGS. 1-11 and in accordance with an alternative embodiment of the present invention, an infrared marker 50 may be formed from an outer sleeve 52 constructed from a material that has pores 56 that are sealed when the outer sleeve 52 is in a relaxed state. When the outer sleeve 24 is stretched for use, the pores 56 open to permit the passage of oxygen in the ambient air to the self-heating powder 42, which activates the marker 50. For clarity, the outer sleeve 52 is shown in the stretched condition in FIG. 12. so that the pores 56 are plainly visible. In this instance, the sealed enclosure 36 (FIG. 6) may be optionally required to store the infrared marker 50 in the latent or dormant oxygen-deprived state. With reference to FIG. 13 in which like reference numbers refer to like features in FIGS. 1-12 and in accordance with an alternative embodiment of the present invention, an infrared marker 60 may be formed from an outer sleeve 62, similar to outer sleeve 24, that is lined with a liner 64. The outer sleeve 62 and liner 64 are overlaid, rolled into a tube-shape, and joined by a longitudinal seam 66. The free open ends of the outer sleeve 62 and liner 64 are then joined together to form a ring-shaped infrared marker 60. The liner 64 may be, for example, constituted by a moisture impervious material that is pierced by pores or openings at the locations at which the stitching of the longitudinal seam 66 penetrates the liner 64. The infrared marker 60 is stored in the latent or dormant oxygen-deprived state inside the sealed enclosure 36 (FIG. 6). After removal from the sealed enclosure 36, the openings formed in the outer sleeve 62 and liner 64 by the longitudinal seam 66 permit the passage of oxygen in the ambient air to the self-heating powder 42, which activates the marker 60. In alternative embodiments, the openings in the outer sleeve 62 and liner 64 may be provided separate from, or in addition to, the openings of the longitudinal seam 66. With reference to FIG. 14 in which like reference numbers refer to like features in FIGS. 1-13 and in accordance with an alternative embodiment of the present invention, the liner 64 of infrared marker 60 may stitched at different circumferential locations to define transverse seams, of which transverse seam 70 is representative, that are similar to transverse seams 32 (FIGS. 2 and 8). The transverse seams 70 compartmentalize the liner 64 for confining the movement of the self-heating powder 42 (FIG. 13). Preferably, a portion of self-heating powder 42 is confined within each of the compartments (not shown) that are similar to compartments 33 (FIGS. 2 and 8). The elastic band 28 is placed inside the inner diameter of the liner 64. The outer sleeve 62 does not participate in the transverse seams 70 and, as a result, an air passage 72 is defined for heat transfer about the entire circumference of the infrared marker 60 when the infrared marker 60 is activated. This may promote uniform infrared emission about the circumference of the infrared marker 60. The infrared markers 40, 60 are each sealed inside the air-tight enclosure 36 and used in the same manner as infrared marker 10, as described above. While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept. |
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description | This application claims benefit under 35 USC 119(e) of U.S. Provisional Patent Application No. 61/024,903, filed Jan. 30, 2008, entitled “METHODS, APPARATUS, AND COMPUTER-PROGRAM PRODUCTS FOR INCREASING ACCURACY IN CONE-BEAM COMPUTED TOMOGRAPHY,” the content of which is incorporated herein by reference in its entirety. Cone beam (CB) computed tomography (CT) involves the imaging of the internal structure of an object by collecting several projection images (“radiographic projections”) in a single scan operation (“scan”), and is widely used in the medical field to view the internal structure of selected portions of the human body as well as in the industrial and security fields to perform non-destructive inspection and to detect contraband and weapons in security screening. Typically, several two-dimensional projections (which are images) are made of the object, and a three-dimensional representation of the object is constructed from these projections using various tomographic reconstruction methods. From the three-dimensional data sets, conventional CT slice images through the object can be generated. The two-dimensional projections are typically created by transmitting radiation from a “point source” through the object, which will absorb some of the radiation based on its size and density, and collecting the non-absorbed radiation onto a two-dimensional imaging device, or imager, which comprises an array of pixel detectors (simply called “pixels”). Such a system is shown in FIG. 1. Typically, the point source and the center of the two-dimensional imager lie on a common axis, which may be called the projection axis. The source's radiation emanates toward the imaging device in a volume of space approximately defined by a right-circular cone, with roughly circular- or ellipse-shaped cross sections perpendicular to the axis (where deviations are caused by non-ideal aspects that include the heel effect in X-ray sources), having its vertex at the point source and its base at the imaging device. This is the reason the radiation is often called cone-beam (CB) radiation. The imagers in state-of-the-art CBCT systems measure around 30 cm by 40 cm, having approximately 750 rows of pixels with approximately 1,000 pixels in each row, for approximately 750,000 pixels. Generally, when no object is present within the cone, the distribution of radiation is substantially uniform on any roughly circular or elliptical area on the imager that is centered about the projection axis, and that is within the cone. However, the shape of the radiation boundary on the imager may be non-uniform, from a large number of perturbations, so that there is no perfect rotational symmetry about the projection axis. In any event, any non-uniformity in the distribution can be measured in a calibration step and accounted for. The projection axis may not be at the center of the imager or the center of the object. It may pass through them at arbitrary locations including very near the edge. In an ideal imaging system, rays of radiation travel along respective straight-line transmission paths from the source, through the object, and then to respective pixel detectors without generating scattered rays. However, in real systems, when photons of X-radiation in rays interact with a portion of the object (including photoelectric, Compton and pair production interactions), one or more scattered rays are often generated that deviate from the transmission path of the incident radiation. These scattered rays are often received by “surrounding” pixel detectors that are not located on the transmission path that the initial photon-containing-rays of radiation was transmitted on, thereby creating errors in the electrical signals of the surrounding pixel detectors. Also, in typical two-dimensional imagers, the radiation meant to be received by a pixel is often scattered by various components of the source-imager system (e.g., scintillation plate, bow tie filters, radiation hardening filters, the metal anode that electrons hit in the source to produce X-rays etc.), and received by surrounding pixels. These effects are often characterized, in part, by a point-spread function (PSF), which is a two-dimensional mapping of the amount of error caused in surrounding pixels by a given amount of radiation intended for a central pixel. The surface of the PSF is similar to the flared shape of a trumpet output, with the greatest amount of error occurring in pixels adjacent to the central pixel. Each of the above non-ideal effects creates spatial errors in the pixel data generated by the two-dimensional imager. In turn, the spatial errors cause artifacts (e.g., phantom images) and loss of resolution and contrast and blurring in the CBCT image slices produced by the radiation imaging system. As part of making his inventions, the inventor has recognized that, while radiologists and physicians use CBCT imaging to obtain broad images of a patient's torso during the initial portion of the diagnostic phase, they often focus their attention to specific areas of the images, such as to parts of specific organs, during the latter portion of the diagnostic phase and/or treatment phase. As also part of making his inventions, the inventor has discovered that the accuracy of the images generated from CBCT can be greatly improved by obscuring portions of the radiation source so that the radiation only passes through the specific areas of the patient related to the regions-of-interest to the doctor. The obscuring action causes less radiation to pass through the patient's body, which in turn causes the radiation to undergo less scattering through the patient's body, thus reducing a major source of error in the image accuracy. The obscuring action may be performed with bodies of material that absorb at least 60 percent of the incident radiation (and up to 100 percent); total absorption of the incident radiation is not necessary although it is sometimes preferred. Thus, as used herein, the action of obscuring a portion of a radiation beam means absorbing at least 60 percent of the incident radiation, or initial value, of that portion, and up to 100 percent thereof. The obscuring action also causes the radiation to strike a smaller portion of the two-dimensional imager. The use of less than the full area of the two-dimensional imaging device is contrary to conventional wisdom and practice in the art, which teaches artisans, physicians, and radiologists to use the full extent of the two-dimensional imager. For this reason, the prior art teaches against the present invention. The obscuring action may be done along either or both of the axial and trans-axial dimensions of the imager (the axial dimension is parallel to the rotation axis of the gantry, and the trans-axial dimension is perpendicular to the axial dimension). If the obscuring action is only done along the axial dimension, then standard 3-D reconstruction methods may be used; this is often the preferred manner of obscuring the beam. If the obscuring action is done along the trans-axial dimension (also called the lateral dimension), then truncated 3-D reconstruction methods may be used to just reconstruct limited volumes of the object being imaged. In further preferred implementations of the present inventions, an estimate of the scattered radiation may be generated from the measured pixel data of selected pixels that lie outside of the illuminated area. The scatter estimate may be subtracted from, or otherwise factored out of, the CT data set to further improve the accuracy of the data. A first general invention of the present application is directed to a method of operating a cone-beam CT scanning system, the system having a two-dimensional pixel array with a number Xpix of pixels in a first dimension that is perpendicular to the system's axis of rotation and a number Ypix of pixels in a second dimension that is parallel to the system's axis of rotation, Xpix being greater than one hundred and Ypix being greater than ten. The system further has a source of radiation that emits a cone-beam of radiation that normally covers all of the pixels of the pixel array. Broadly stated, the method comprises positioning an object between the source of radiation and the pixel array, obscuring a portion of the cone beam of radiation such that direct rays of the radiation cover less than 85 percent of the area of the pixel array and span at least three percent of the second dimension in a portion of the pixel array, and obtaining a plurality of projections of the object with the cone beam obscured, the plurality of projections being taken at a corresponding plurality of relative angles between the object and the source of radiation. The obscuring action may be done by placing a collimator (e.g., one or more sets of fan blades) between the radiation source and the object. A second general invention of the present application is directed to a method of operating a cone-beam CT scanning system, the system having a two-dimensional pixel array with a number Xpix of pixels in one of the dimensions and a number Ypix of pixels in the other dimension, Xpix being greater than one hundred and Ypix being greater than ten. The system further has a source of radiation that emits a cone-beam of radiation that normally covers all of the pixels of the pixel array. Broadly stated, the method comprises determining an extent of the pixel array that will receive direct-path radiation passing through a target volume of the object during a rotational scan of the object, the rotation scan including a plurality of projections of the object taken at a corresponding plurality of relative angles between the object and the source of radiation, the extent of the angles being equal to or greater than 180 degrees, and the target portion being smaller than the size of the object. The method further comprises obscuring a portion of the cone beam of radiation such that direct rays of the radiation cover at least the determined extent, but less than 85 percent of the pixel array. The obscuring action may be done by placing a collimator (e.g., one or more sets of fan blades) between the radiation source and the object. Further embodiments of the method may include obtaining a plurality of projections of the object with the cone beam obscured, the plurality of projections being taken at a corresponding plurality of relative angles between the object and the source of radiation. A third general invention of the present application is directed to a method of operating a cone-beam CT scanning system, the system having a two-dimensional pixel array with a number Xpix of pixels in a first dimension that is perpendicular to the system's axis of rotation and a number Ypix of pixels in a second dimension that is parallel to the system's axis of rotation, Xpix being greater than one hundred and Ypix being greater than ten. The system further has a source of radiation that emits an un-obscured cone-beam of radiation that normally covers all of the pixels of the pixel array. Broadly stated, the method comprises obtaining a first scan of the object with the direct rays of the radiation covering at least 85 percent of the pixel array; and obtaining a second scan of the object with the direct rays of the radiation covering less than 85 percent of the pixel array and spanning at least three percent of the second dimension in a portion of the pixel array. Further preferred embodiments of this method may include generating a three-dimensional CT data set of the object from the projections of the scans using a truncated reconstruction method. A related computer-program product invention may comprise acquiring the sets of radiographic projections of these two scans and generating a three-dimensional CT data set of the object with a truncated reconstruction method. A fourth general invention of the present application is directed to a method of reconstructing projection data comprising acquiring a set of radiographic projections of an object that has been taken with a portion of the pixels being obscured from the cone-beam radiation, acquiring an indication of which pixels have been obscured, and performing a truncated reconstruction of the object using the radiographic projection and the indication of which pixels have been obscured. The action of acquiring the sets of radiographic projections may comprise receiving the sets from another entity or process, and may comprise instructing a cone-beam CT scanning system to generate the sets. The action of acquiring the indication of which pixels have been obscured may comprise receiving the indication from another entity or process, and may comprise analyzing the pixel values of the scans to determine which pixels have been obscured. Further preferred embodiments of this method may include generating estimates of scattered radiation from the data of the obscured pixels and generating corrected radiographic projections from the acquired radiographic projections and the estimates of the scattered radiation. A related computer-program product invention comprises instruction sets that direct a data processor to perform the above actions. A fifth general invention of the present application is directed to a method of processing projection data comprising acquiring a set of radiographic projections of an object that have been taken with a portion of the pixels being obscured from the cone-beam radiation, obtaining an indication of which pixels have been obscured, and generating estimates of scattered radiation from the values of the obscured pixels. The action of acquiring the sets of radiographic projections may comprise receiving the sets from another entity or process, and may comprise instructing a cone-beam CT scanning system to generate the sets. The action of acquiring the indication of which pixels have been obscured may comprise receiving the indication from another entity or process, and may comprise analyzing the pixel values of the scans to determine which pixels have been obscured. Further preferred embodiments of this method may include generating corrected projections from the radiographic projections and the estimates of the scattered radiation. A related computer-program product invention comprises instruction sets that direct a data processor to perform the above steps. A sixth general invention of the present application is directed to a cone-beam CT scanning apparatus. Broadly stated, the apparatus comprises a two-dimensional pixel array with a number Xpix of pixels in an axial dimension and a number Ypix of pixels in a trans-axial dimension, Xpix being greater than one hundred and Ypix being greater than ten, a source of radiation that emits a cone-beam of radiation that normally covers all of the pixels of the pixel array, a collimator disposed closer to the source of radiation than the two-dimensional pixel array and that is selectively moveable to obscure at least one portion of the cone-beam, a first positioner that positions the collimator in response to a first set of at least one control signal, and a controller that generates the first set of at least one control signal. In one preferred embodiment, the collimator comprises a first set of fan blades that are selectively moveable to obscure one or both sides of the cone-beam, and the first positioner positions the first set of fan blades in response to the first set of at least one control signal. The edges of the fan blades of the first set are oriented substantially perpendicular to the scan axis, and are substantially parallel with the trans-axial dimension of the imaging device. With this configuration of this preferred embodiment, the first set of fan blades can selectively obscure pixels in the axial (Ypix) dimension. Further preferred embodiments further comprise a second set of fan blades that are selectively moveable to obscure one or both sides of the cone-beam along the trans-axial dimension, and a second positioner that positions the second set of fan blades in response to a second set of at least one control signal, wherein the controller further generates the second set of at least one control signal. In this further preferred embodiment, the edges of the fan blades of the second set are oriented substantially parallel to the scan axis, and are substantially perpendicular to the axial dimension of the imaging device. The obscuring of the cone beam according to the present invention reduces the field of view of the image, but improves image accuracy in the field of view. A reconstructed three-dimensional CT data set models the radiation attenuation coefficient of the object's material at a three dimensional array of locations, called voxels (which is shorthand for “volume pixels”). As a ray of radiation passes through the voxels of the object, its intensity decreases exponentially along the beam path. It is the small differences in the attenuation coefficients of the voxels that produce the subtle contrasts that physicians and radiologists use to image, identify, and diagnose problems. When there is a lot of scattering of the radiation rays, there is a lot of noise in the projection data, and this noise decreases the accuracy of reconstructing, and thereby measuring, each voxel's attenuation coefficient. The scattered radiation represents noise because it has been generated at unknown points in the object being imaged, and has been attenuated by unknown materials along unknown paths through the object. As part of making his invention, the inventor has recognized that scattered radiation generated at a point of the object can be dispersed over a wide area of the pixel array. The present invention reduces the overall magnitude of the scattered radiation by decreasing radiation in areas where it is not needed for the physicians and radiologists to see the subtle contrasts that they seek to examine. The improvement in the imaging quality results in more accurate Hounsfield units for the voxels. A Hounsfield unit is essentially a resealing of the attenuation coefficient of a voxel, where a Hounsfield unit value of 0 represents the attenuation coefficient of water, and a Hounsfield unit value of −1000 represents the attenuation coefficient of air. Voxels that are more dense than water have Hounsfield units that are greater than zero, and materials that are less dense than water have Hounsfield units that are less than zero. The Hounsfield unit system provides physicians and radiologists with higher contrast perspective to see finer details since the human body is mostly water. The present inventions improve the accuracy of measured Hounsfield units by reducing radiation scattering and reducing the field of view. These and other inventions are described below in greater detail. The inventions disclosed herein may be used separately to together in various combinations, and one or more elements and features of each invention may be used in the other inventions. The inventions of the present application will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the inventions are shown. This inventions may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough and complete and fully conveys the scope of the inventions to one skilled in the art. In the drawings, the relative dimensions of some elements may be exaggerated for clarity. The same reference numerals are used to denote the same elements throughout the specification. The elements may have different interrelationships and different positions for different embodiments. The terms used herein are for illustrative purposes of the present inventions only and should not be construed to limit the meaning or the scope of the present inventions. As used in this specification, a singular form may, unless definitely indicating a particular case in terms of the context, include a plural form. Also, the expressions “comprise” and/or “comprising” used in this specification neither define the mentioned characteristics, numbers, steps, actions, operations, members, elements, and/or groups of these, nor exclude the presence or addition of one or more other different characteristics, numbers, steps, operations, members, elements, and/or groups of these, or addition of these. Spatially relative terms, such as “over,” “above,” “upper,” “under,” “beneath,” “below,” “lower,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of an apparatus in use or operation in addition to the orientation depicted in the figures. For example, if an apparatus in the figures is turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “over” or “above” the other elements or features. Thus, the exemplary term “above” may encompass both an above and below orientation. As used herein, terms such as “first,” “second,” etc. may be used to describe one or more members, components, characteristics, etc. However, it is obvious that the members, components, characteristics, etc. should not be defined by these terms. The terms are used only for distinguishing one member, component, characteristic, etc. from another. Thus, a first member, component, characteristic, etc. that is described may also refer to a second member, component, characteristic, etc. without departing from the scope of the present invention. System Overview. FIG. 2A is a schematic diagram of a first exemplary imaging system 100 according to the system inventions of the present application. System 100 comprises a radiation source 110, a two-dimensional imaging device 120 disposed opposite to radiation source 110 along a projection line, a first set of fan blades 130 disposed between the radiation source and the two-dimensional imaging device, a first fan-blade drive 135 that holds fan blades 130 and sets their positions. The edges of fan blades 130 are oriented substantially perpendicular to the scan axis (defined below), and are substantially parallel with the trans-axial dimension (defined below) of imaging device 120. As an option, system 100 may further comprise a second set of fan blades 140 disposed between the radiation source and the two-dimensional imaging device, and a second fan-blade drive 145 that holds fan blades 140 and sets their positions. The edges of fan blades 140 are oriented substantially parallel with the scan axis (defined below), and are substantially parallel to the axial dimension (defined below) of imaging device 120. The fan blades are examples of a collimator, and are disposed closer to radiation source 110 than imaging device 120. Examples of other collimators are provided below. System 100 further comprises a gantry 150 that holds radiation source 110, imaging device 120, and fan-blade drives 135 and 145 in fixed or known spatial relationships to one another, a mechanical drive 155 that rotates gantry 150 about an object disposed between radiation source 110 and imaging device 120, with the object being disposed between fan blades 130 and 140 on the one hand, and imaging device 120 on the other hand. The term gantry has a broad meaning, and covers all configurations of one or more structural members that can hold the above-identified components in fixed or known (but possibly movable) spatial relationships. For the sake of visual simplicity in the figure, the gantry housing, gantry support, and fan-blade support are not shown. These components do not form part of the present inventions. Also not shown is a support table for the object (i.e., an object support member), which does not form a part of the present inventions related to System 100. Additionally, system 100 further comprises a controller 160 and a user interface 165, with controller 160 being electrically coupled to radiation source 110, mechanical drive 155, fan-blade drives 135 and 145, imaging device 120, and user interface 165. User interface 165 provides a human interface to controller 160 that enables the user to at least initiate a scan of the object, to collect measured projection data from the imaging device, and to adjust the positions of fan blades 130 and 140. User interface 165 may be configured to present graphic representations of the measured data. In imaging system 100, gantry 150 is rotated about the object during a scan such that radiation source 110, fan blades 130 and 140, fan-blade drives 135 and 145, and two-dimensional imaging device 120 circle around the object. More specifically, gantry 150 rotates these components about a scan axis, as shown in the figure, where the scan axis intersects the projection line, and is typically perpendicular to the projection line. The object is aligned in a substantially fixed relationship to the scan axis. The construction provides a relative rotation between the projection line on the one hand and the scan axis and an object aligned thereto on the other hand, with the relative rotation being measured by an angular displacement value θ. Mechanical drive 155 is mechanically coupled to gantry 150 to provide rotation upon command by controller 160. The two-dimensional imaging device comprises a two-dimensional array of pixels that are periodically read to obtain the data of the radiographic projections. Imaging device 120 has an X-axis and a Y-axis, which are perpendicular to each other. Imaging device 120 is oriented such that its Y-axis is parallel to the scan axis. For this reason, the Y-axis is also referred to as the axial dimension of imaging device 120, and the X-axis is referred to as the trans-axial dimension, or lateral dimension, of device 120. The X-axis is perpendicular to a plane defined by the scan axis and the projection line, and the Y-axis is parallel to this same plane. Each pixel is assigned a discrete X-coordinate (“X”) along the X-axis, and a discrete Y-coordinate (“Y”) along the Y-axis. In typical implementations, the size of the array is 1024 pixels by 768 pixels, with the longer dimension of the array being oriented parallel to the X-axis. As used herein, the discrete X-coordinates start at 1 and end at Xpix (e.g., Xpix=1024), and the discrete Y-coordinates start at 1 and end at Ypix (e.g., Ypix=768). A smaller number of pixels are shown in the figure for the sake of visual clarity. The imaging device may be centered on the projection line to enable full-fan imaging of the object, may be offset from the projection line to enable half-fan imaging of the object, or may be movable with respect to the projection line to allow both full-fan and half-fan imaging of objects. As an example of a half-fan configuration, the imaging device may be offset from the center by 16 centimeters in its X-dimension when the imaging device has a span in the X dimension of 40 centimeters. FIG. 3 shows a perspective view of a first exemplary implementation of fan blades 130 and fan-blade drive 135. Each fan blade 130 may have a thin rectangular shape, and may comprise a material that absorbs the radiation of source 110. Such a material may comprise lead (Pb). Each fan blade 130 absorbs at least 60% of the incident radiation from radiation source 110. In preferred implementations, a fan blade absorbs at least 90 percent, and more preferably at least 99 percent, of the radiation incident upon it. Fan-blade drive 135 may comprise two mechanical positioners. In one exemplary implementation, each mechanical positioner is mechanically coupled to a respective fan blade to cause the fan blade to move in a controlled and measurable (e.g., predictable) manner. In another implementation, one of the mechanical positioners is mechanically coupled to the fan blades to cause the blades to move relative to one another so as to vary the distance of the gap between the blades in a controlled and measurable manner, and the other positioner is mechanically coupled to the blades to cause the blades to move as a group in a controlled and measurable manner. In the latter exemplary implementation, the first positioner and the fan blades may be mechanically disposed on a carriage, and the second positioner may be mechanically coupled to the carriage. Each positioner may comprise a linear motor servo, a rotating motor servo with rotation-to-linear translation mechanism, or the like. The construction of fan blades 140 and fan blade drive 145 may be the same as that of fan blades 130 and fan-blade drive 135, respectively. FIG. 4 shows a perspective view of a second exemplary implementation of fan blades 130 and fan-blade drive 135. Each fan blade 130 may comprise an eccentric cam, and may comprise a material that absorbs at least 60% of the incident radiation from radiation source 110. Such a material may comprise lead (Pb). In preferred implementations, a fan blade absorbs at least 90 percent, and more preferably at least 99 percent, of the radiation incident upon it. Each fan-blade drive 135 may comprise a rotating servo motor, preferably with a set of reduction gears, which drives the eccentric cam. Fan blades 130 may be placed in an overlapping relationship so that each may obscure more than 50% of imaging device 120. The construction of fan blades 140 and fan blade drive 145 may be the same as that of fan blades 130 and fan-blade drive 135, respectively. As used herein, the term “fan blades” has broad meaning, and covers all configurations of structural members that can provide a primary region (e.g., gap, aperture, etc.) through which radiation may pass with relatively little attenuation compared to one or more surrounding regions, and where a dimension of the primary region may be controlled and/or where the primary region may be selectively disposed toward or away from the projection line so that the primary region can be selectively disposed inside or outside of the source's radiation field that is collected by the imaging device. Also as used herein, the terms “fan-blade drive” and “positioners” have broad meanings, and cover all configurations of electromechanical elements that can provide the above positioning of the fan blades and other collimators. Each fan blade 130 and 140 is disposed closer to radiation source 110 than imaging device 120, and is adapted to significantly attenuate the radiation that strikes it, and to preferably substantially block it. The distal edges of fan blades 130 are preferably parallel to the X-axis of imaging device 120 and are selectively moveable, by way of fan blade drive 135, to obscure one or both sides of the cone-beam along the axial dimension. An example of the obscuring action is shown in FIG. 5, where pixels having Y coordinate values less than Y1 and greater than Y2 are substantially shielded from the radiation emitted by source 110, where Y1<Y2, and where both Y1 and Y2 are greater than 1 and less than Ypix. This is typically the preferred obscuring configuration, and leaves an imaging window through which direct-path radiation from source 110 may be received. The window is defined by the four points: (1,Y1), (1,Y2), (Xpix,Y1), and (Xpix,Y2). Similarly, the distal edges of fan blades 140 are preferably parallel to the Y-axis of imaging device 120 and are selectively moveable, by way of fan blade drive 145, to obscure one or both sides of the cone-beam along the trans-axial dimension. An example of the obscuring action is shown in FIG. 6, where pixels having X coordinate values less than X1 and greater than X2 are substantially shielded from the radiation emitted by source 110, where X1 <X2, and where both X1 and X2 are greater than 1 and less than Xpix. This leaves an imaging window through which direct-path radiation from source 110 may be received, where the window is defined by the four points: (X1,1), (X1,Ypix), (X2,1), and (X2,Ypix). FIG. 7 shows an example where both sets of fan blades are positioned to obscure portions of the imaging device, leaving an imaging window through which direct-path radiation from source 110 may be received. The window is defined by the four points: (X1, Y1), (X1,Y2), (X2, Y1), and (X2,Y2). In preferred embodiments, controller 160 can send control signals to fan-blade drives to select any location and size of window desired by the operator. Referring back to FIG. 2A, when controller 160 receives a request from the user to begin a scan of an object, controller 160 instructs fan-blade drives 135 and 145 to set the fan blades 130 and 140, respectively, in given positions (as described in greater detail below), instructs mechanical drive 155 to begin a scan rotation of gantry 150, and instructs radiation source 110 to begin emitting radiation. As it rotates, mechanical drive 155 provides controller 160 with an indication of the angular displacement value θ. Controller 160 uses this information to read the values of imaging device 120's pixel detectors at selected angular displacement values θ to obtain the data for the radiographic projections. Typically, there are between 250 and 1000 projections taken in the 360-degree scan rotation, with each projection being spaced from adjacent projections by a set increment Δθ of angular displacement. The controller stores the data from each projection in a memory storage device, along with the angular displacement value θ at which the projection was taken. Controller 160 comprises a processor, an instruction memory for storing instruction sets that direct the operation of the processor, a data memory that stores pixel and other data values used by the present inventions implemented by the imaging system, and an I/O port manager that provides input/output data exchange between processor 160 and each of radiation source 110, mechanical drive 155, fan-blade drives 135 and 145, and imaging device 120. The instruction memory and data memory are coupled to the main processor through a first bidirectional bus, and may be implemented as different sections of the same memory device. Because of the large amount of data provided by the two-dimensional imaging device, the I/O port manager is preferably coupled to the main processor through a second bidirectional bus. However, the I/O port manager may be coupled to the main processor by way of the first bidirectional bus. The operation of the processor is guided by a group of instruction sets stored in the instruction memory, which is an exemplary form of computer-readable medium. Exemplary instruction sets are illustrated below. In exemplary imaging system 100 shown in FIG. 2A, the gantry rotates about the object, which means that the projection line rotates about the object and the scan axis. Instead, it may be appreciated that the object and the scan axis may be rotated while the gantry and the projection line are stationary. A second exemplary imaging system which rotates the object is shown at 100′ in FIG. 2B. System 100′ comprises all of the components of system 100, with the components being coupled to one another in the same way, except that the mechanical drive is coupled to an object support member, which holds the object being scanned. In system 100′, the gantry remains stationary while the mechanical drive rotates the object support member and the object. System 100′ is suitable for industrial uses (e.g., scanning non-human objects), whereas system 100 is suitable for medical uses (e.g., scanning human objects). Methods and Computer-Program Products. A first general invention of the present application is directed to a method of operating a cone-beam CT scanning system, such as systems 100 and 100′, and is illustrated by the flow diagram of an exemplary method 200 in FIG. 8. The exemplary method comprises positioning an object between the radiation source 110 and the imaging device 120, obscuring one or more portions of the cone-beam radiation from source 110 such that direct rays of the radiation cover 85 percent or less of the area of the pixel array and span at least three percent of the array's axial dimension (Y-axis) in at least a portion of the pixel array. These limitations can be stated mathematically as:(X2−X1)*(Y2−Y1)≦0.85*Xpix*Ypix, and(Y2−Y1)≧0.03*Ypix over at least a portion of the X-axis.The obscuring action may be done before or after the positioning action. A lamp emitting visible light may be substantially co-located with radiation source 110 to facilitate performing the obscuring action by illuminating the imaging window onto the object support table before the positioning action, or onto the object during the positioning action. In typical implementations, the obscuring action is performed such that direct rays of the radiation span at least fifteen percent of the array's axial dimension (Y-axis) in at least a portion of the pixel array, and more typically at least twenty percent. Also, in many typical implementations, direct rays of the radiation may cover 75 percent or less of the area of the pixel array, and 50 percent or less. In some cases, it can be lower than 35 percent. The exemplary method further comprises obtaining a plurality of projections of the object with the cone beam obscured, with the plurality of projections being taken at a corresponding plurality of relative angles θ between the object and radiation source 110. The number of projections is preferably sufficient to perform at least a truncated reconstruction of the voxel attenuation coefficients, being at least 250, preferably at least 400, more preferably at least 500, and most preferably at least 600. The actions of method 200 may be performed by an operator of system 100 (or 100′), such as a radiologist, physician, technologist, etc., and the projections may be stored in the data memory of controller 160. From there, the projections may be processed by a truncated reconstruction procedure to generate CT images of the imaged area of the object, as described below in greater detail, or may be exported to another data processor for processing. To assist the operator with performing the above obscuring and obtaining actions, the instruction memory of data processor 160 may be loaded with an exemplary computer-program product 210 shown in FIG. 9. Product 210 comprises a computer-readable medium and a plurality of instruction sets embodied on the computer-readable medium. Instruction set #1 directs data processor 160 to receive input from the operator on the desired extents of the imaging window and to set fan blades 130 and 140 at respective positions. These instructions may include a subset of instructions that direct processor 160 to receive the values of the imaging window (e.g., the values of X1, X2, Y1, and Y2); they may include a subset of instructions that direct data processor 160 to provide a graphical representation of the pixel array of device 120 to the user, and to receive inputs from the user, such as in the form of mouse clicks, to define an imaging window on the graphical representation, and to draw a representation of the imaging window on the graphical representation. The subset of instructions may further direct the data processor 160 to receive inputs from the user to modify the position of the defined imaging window. In further embodiments, this subset of instruction set #1 may include instructions that direct data processor 160 to take a projection of the object (such as with θ=0), and to display the projection on the graphical representation. This enables the operator to identify features of the object, such as bones of a patient, and to locate the imaging window with respect to the identified features. The operator can also temporarily place radiation-absorbing markers on the object (e.g., patient) that indicate the desired extent of the imaging window during this initial projection. The markers will appear on the initial scan, and the operator can set the imaging window relative to the shown markers. Instruction set #2 of product 210 directs data processor 160 to receive input from the operator to start a scan of the object. Instruction set #3 directs data processor 160 to perform the scan of the object and obtain a plurality of radiographic projections of the object at a corresponding plurality of angular displacement values θ between the object and the radiation source. Under the direction of instruction set #3, data processor 160 preferably instructs mechanical drive 155 to begin a scan rotation of gantry 150, instructs radiation source 110 to begin emitting radiation, receives indications of the angular displacement value θ from mechanical drive 155, and reads the values of imaging device 120's pixel detectors at selected angular displacement values θ to obtain the data for the radiographic projections. Instruction set #4 of computer-program product 210 directs data processor 160 to store the radiographic projections (i.e., pixel data and corresponding angular displacement value θ), in a computer-readable medium, such as the data memory of data processor 160, which may include a disk storage unit. Instruction set #4 may be performed in parallel with instruction set #3, storing each projection as it is read from imaging device 120. Product 210 may include an optional instruction set #5 that directs data processor 160 to store indications of the locations of fan blades 130 and 140 along with the projection data. This information can be stored as the extent of the imaging window (e.g., as X1, X2, Y1, and Y2), and can be useful to a truncation reconstruction procedure, which is described in greater detail below. However, the reconstruction procedure may comprise processing actions that deduce the extent of the imaging window, in which case the results of instruction set #5 are not needed. Typically the operator wishes to set the imaging window to a target area of the object (e.g., patient), such as an organ of the patient, which is generally contained within a three-dimensional volume. It is important for the operator to recognize that the position of the object and the extent of the imaging window have to be collectively set so that the target volume is irradiated during the scan of the object. In one implementation, the values X1 and X2are set to the full extent of the imager's x-dimension (X1 =1 and X2=Xpix), and fan blades 130 are adjusted with the help of the previously described illumination lamp to illuminate the desired cross section of the object. Since the rays of the cone-beam radiation diverge, this action is generally sufficient to capture the target region as long as the scan axis runs through the object (the reader may visually verify this by looking ahead to FIG. 11). The position of the object support table and/or the height of the object over the table may be adjusted to bring the scan axis within the volume of the object. In another implementation, the object is positioned such that the target volume at θ=0 is centered on the scan axis, such as by adjusting the trans-axial position of the object to center the lateral extent of the target volume about the scan axis, and adjusting the height of the object support table to center the thickness of the target volume about the scan axis. In this case, the axial extent of the target volume need only be located within the axial extent of imaging device 120. However, if desired and if possible, the axial position of the object may be adjusted so as to center the axial extent of the target volume about the position of the projection axis at θ=0. These adjustment actions may be done by the operator as a further embodiment of method 200, described above. Once the target volume has been centered about the scan and projection axes, the extent of the imaging window may be determined as follows, and as illustrated by the trans-axial cross section of the system shown in FIG. 10. The target area measures 2Δx by 2Δy by 2Δz, where Δx, Δy, and Δz can have different values, and where the dimension 2Δy is perpendicular to the page. In order to provide reconstructed voxel values in the target volume, the width of the imaging window in the X-dimension should be set to 2ΔX=2rD/d, where r=[Δx 2+Δz2]1/2, where D is the shortest distance between radiation source 110 and imaging device 120, and where d is the distance between radiation source 110 and the scan axis. This can be deduced by applying geometric principles to the construction shown in the figure. X1 and X2 may then be set to X1 =(Xpix/2−ΔX) and X2=(Xpix/2+ΔX). If it is not possible to center the x- and z-dimensions of the target value about the scan axis, then one may expand the size of the volume shown in the figure, in either one or both of the x- and z-dimensions, so as that the expanded volume encompasses the target volume, and then work with the expanded volume instead of the target volume. This approach can be taken when it is not possible to adjust the height of the object with respect to the support table. FIG. 11 shows the axial cross section of the system with the target volume centered about the scan axis and the projection axis. During the scan of the object, there will be angles at which the some edges of the target volume will be at a distance of (d−r) from radiation source 110, as illustrated by dashed lines in the figure. In order to provide reconstructed voxel values in the target volume, the width of the imaging window in the Y-dimension should be set to 2ΔY=2ΔyD/(d−r), which can be deduced by applying geometric principles to the construction shown in the figure. Y1 and Y2 may then be set to Y1 =(Ypix/2−ΔY) and Y2=(Ypix/2+ΔY). The value of r may be based on the dimensions of the target volume, or the above-described expanded volume if it is not possible to center the target volume about the scan axis. If it is not possible or desirable to center the y-dimension of the target volume about the projection axis, an offset may be added to the Y1 and Y2 values. For example, if the y-dimension of the target value is offset by a value Δb from the projection axis, then a value of ΔB may be added to both Y1 and Y2, such as Y1 =(Ypix/2−ΔY+ΔB) and Y2=(Ypix/2+ΔY+ΔB), where ΔB=ΔbD/(d−r). Δb has a positive value when the target volume is offset toward Y=Ypix, and a negative value when the target volume is offset toward Y=1. As a point of generality, we may refer to the point (Xpix/2, Ypix/2) as (Xc,Yc), where the latter is defined as the point where the projection axis intersects the pixel array. If y1 and y2 are the extend of the target volume, as measured relative to the center point where the projection axis and scan axis intersect, then Δy may be generated as the absolute value of the difference between y1 and y2, and Δb may be generated as (y1 +y2)/2. Instruction set #1 of product 210 described above may comprise a subset of instructions that receives the extent of the target volume from the operator and computes the values X1, X2, Y1, and Y2 of the imaging window. The extent of the x- and y-dimensions of the target volume may be input by numeric values relative to a predefined measuring point, or may be obtained through the above-described graphical interface that shows the user an initial projection at θ=0 and enables the user to define a box on the graphical interface (the subset of instructions may then back-project the box to the plane of the scan axis using simple geometric operations). The z-dimension may be input as numeric values relative to the top of the object support table by the operator, and corrected for the distance between the scan axis and the table top. In some implementations, the subset of instructions may take a second projection of the object at θ=90, and provide the operator with a graphic representation of the second projection and graphic interface that enables the operator to define the z-dimension (the subset of instructions may then back-project this input to the plane of the projection axis using simple geometric operations). With this information, the subset of instructions may expand the target volume to account for any off-centering of the target volume, and then compute the image window with the actions previously described above. The paragraphs describing FIGS. 10 and 11 illustrated various actions that can be taken to determine (e.g., find) the extent of the pixel array that will receive direct-path radiation passing through a target volume of the object during a rotational scan of the object. This determination action actually comprises a part of another invention of the present application, which is described next with reference to the method flow diagram illustrated in FIG. 12. This invention relates to a method of operating a cone-beam CT scanning system, such as systems 100 and 100′, which is illustrate by exemplary method 220 (FIG. 12). Method 220 comprises determining an extent of the pixel array that will receive direct-path radiation passing through a target volume of the object during a rotational scan of the object, the rotation scan including a plurality of projections of the object taken at a corresponding plurality of relative angles between the object and the source of radiation, the extent of the angles preferably being equal to or greater than 180 degrees, and the target portion being smaller than the size of the object. The extent may be determined by taking actions described in the three previous paragraphs. Method 220 further comprises obscuring one or more portions of the cone beam of radiation such that direct rays of the radiation cover at least the determined extent, but 85 percent or less of the pixel array. The obscuring action may be done by placing a collimator and/or one or more fan blades (e.g., fan blades 130 and/or 140) between the radiation source and the object. This action typically further comprises providing an imaging window in which the direct rays span at least three percent of the array's axial dimension, and more typically at least 15 to 20 percent of the array's axial dimension. Also, in many typical implementations, direct rays of the radiation may cover 75 percent or less of the area of the pixel array, and 50 percent or less. In some cases, it can be lower than 35 percent. The exemplary method 220 further comprises obtaining a plurality of projections of the object with the cone beam obscured, with the plurality of projections being taken at a corresponding plurality of relative angles θ between the object and radiation source 110. The number of projections is preferably sufficient to perform at least a truncated reconstruction of the voxel attenuation coefficients. The actions of method 220 may be performed by an operator of system 100 (or 100′), such as a radiologist, physician, technologist, etc., and the projections may be stored in the data memory of controller 160. From there, the projections may be processed by a truncated reconstruction procedure to generate CT images of the imaged area of the object, as described below in greater detail, or may be exported to another data processor for processing. Truncated reconstruction methods have been widely developed and used in the art for the case where the object is larger than the area of the two-dimensional imaging device. While these truncated reconstruction methods were not developed with the present inventions in mind, they may be readily adapted to process the projection data collected by the present inventions without undue experimentation by those of ordinary skill in the art. Papers and patents describing truncated reconstruction methods can be readily located by searching the Internet and free-access patent databases with the search terms “truncated reconstruction” and “tomography.” U.S. Pat. Nos. 5,640,436 and 6,542,573, and published PCT application WO-2005-104038 A1 provide examples of truncated reconstruction methods, and are incorporated herein by reference. Yet another general invention of the present application is directed to a method of operating a cone-beam CT scanning system, such as systems 100 and 100′, the system having a two-dimensional pixel array with a number Xpix of pixels in a first dimension that is preferably perpendicular to the system's axis of rotation and a number Ypix of pixels in a second dimension that is preferably parallel to the system's axis of rotation, Xpix being greater than one hundred and Ypix being greater than ten. The method is illustrated at 240 in FIG. 13, and comprises obtaining a first scan of the object with the direct rays of the radiation covering at least 85 percent of the pixel array, and obtaining a second scan of the object with the direct rays of the radiation covering less than 85 percent of the pixel array and spanning at least three percent of the second dimension in a portion of the pixel array. This action typically further comprises providing an imaging window in the second scan in which the direct rays span at least three percent of the array's axial dimension, and more typically at least 15 to 20 percent of the array's axial dimension. Also, in many typical implementations, direct rays of the radiation in the second scan may cover 75 percent or less of the area of the pixel array, and 50 percent or less. In some cases, it can be lower than 35 percent. The first and second scans may be performed in any order, and they may be performed in succession without having the object move from the support table, or they may be performed with a sufficiently long span of time, such as on different days, to allow the object to be away from the support table for a period of time. The projection data may be stored in a computer-readable medium. This action may be performed in an interleaved manner, with a portion of the action being performed after each scan, or contemporaneously with each scan. Further preferred embodiments of this method may include generating a three-dimensional CT data set from these projections using a truncated reconstruction method, as described below in greater detail. Data of the first scan may be used to estimate the missing data of the second scan. The obscured regions of either or both of the first and second scans may be used to generate estimates of the scattered radiation (as described below in greater detail), and these estimates may be subtracted out of the projection data, or otherwise factored out, prior to the reconstruction procedure. Reconstruction Computer-Program Products. Related to the above inventions are a plurality of computer-program product inventions related to reconstructing three-dimensional CT data (e.g., voxels) from the two-dimensional projection data collected above. These products are described next. A first exemplary product is shown at 300 in FIG. 14. Product 300 comprises a computer-readable medium and a plurality of instruction sets embodied on the computer-readable medium, as shown in the figure. Instruction set #1 directs the data processor to acquire the projection data that was collected in the above-described inventions, such as by methods 200 and 220. In one embodiment, the instruction set may direct the data processor to receive the data, such as by reading it from a computer-readable medium. In another embodiment, product 300 may be loaded onto controller 160 and this instruction set may direct the data processor of controller 160 to instruct system 100 (or 100′) to obtain the projection data. Typically, product 300 only uses one of instruction sets 2A and 2B, and may only comprise one or the other. Instruction set #2A directs the data processor to read the values of the imaging window (e.g., X1, X2, Y1, and Y2) from the stored projection data. Instruction set #2B directs the data processor to infer the extents of the imaging window (e.g., X1, X2, Y1, and Y2) from the stored projection data. This may be done by detecting the step change in pixel value that occurs at the boundaries of imaging window, such as convolving one or more of the projections with the sum of two orthogonal spatial derivative operators, which essentially generate the sum of dF/dx+dF/dy, where F represents the pixel data, and thereafter least-squares fitting four lines to the convolved data. It may also be done by a histogram analysis of the data to identify the group of pixels within the imaging window by their high value, differentiating them from the pixels outside the window by their low value, and then fitting a rectangle to pixels found to be within the window. Instruction set #3 directs the data processor to identify truncated projection data from the projection data and the values of the imaging window, as found by instruction set #2A or #2B. Instruction set #3 may create arrays of the truncated data, and copy the pixel values within the imaging window to the new array for each projection. It may also merely set index ranges to the full projection data, to which further instructions may refer. As an option component of product 300, instruction set #4 directs the data processor to generate estimates of the scattered radiation from the projection data outside of the imaging window, and to generate corrected truncated projection data from the truncated projection data and the estimates. Exemplary instructions for this are described in a dedicated section below. Instruction set #5 directs the data processor to perform a truncated reconstruction with the truncated projection data, or the corrected truncated projection data, if available, to generate a set of three-dimensional CT data. These instructions may implement the methods described in U.S. Pat. Nos. 5,640,436 and 6,542,573, or similar methods found in the art. The particulars of the reconstruction are not essential to the invention of product 300. Instruction set #6 directs the data processor to store the generated three-dimensional CT data in a computer-readable medium. From the three-dimensional CT data, a number of cross sections of the target volume may be constructed. Product 300 may comprise additional instruction sets that receive input from an operator to select a cross section for display, and that in turn display the requested cross section. The particulars of such cross section display instructions are not essential to the invention of product 300. Product 300 may be run by data processor 160 (shown in FIGS. 2A and 2B), or another data processor. A second general reconstruction product is illustrated by the exemplary produce 340 shown in FIG. 15. Product 340 comprises a computer-readable medium and a plurality of instruction sets embodied on the computer-readable medium, as shown in the figure. It is similar to product 300, but is intended to process the dual-scan data collected by method 240, described above. Instruction set #1 directs the data processor to acquire the projection data that was collected with method 240, or the like, from the appropriate computer-readable mediums. In one embodiment, the instruction set may direct the data processor to receive the data, such as by reading it from a computer-readable medium. In another embodiment, product 300 may be loaded onto controller 160 and this instruction set may direct the data processor of controller 160 to instruct system 100 (or 100′) to obtain the projection data. Instruction set #2A directs the data processor to read the values of the imaging window (e.g., X1, X2, Y1, and Y2) for each of the scans from the stored projection data. Instruction set #2B directs the data processor to infer the extents of the imaging window (e.g., X1, X2, Y1, and Y2) for each of the scans from the stored projection data. This may be done as described above for method 300, the actions of which are incorporated herein by reference. Typically, product 340 only uses one of instruction sets 2A and 2B, and may only comprise one or the other. Instruction set #3 directs the data processor to identify truncated projection data for both of the scans from the projection data and the values of the imaging window, as found by instruction set #2A or #2B. Instruction set #3 may create arrays of the truncated data, and copy the pixel values within the imaging window to the new array for each projection. It may merely set index ranges to the full projection data, to which further instructions may refer. As an option component of product 340, instruction set #4 directs the data processor to generate estimates of the scattered radiation from the projection data outside of the imaging window, and to generate corrected truncated projection data from the truncated projection data and the estimates. This is preferably done for both scans. Exemplary instructions for this are described in a dedicated section below. If the imaging window for the scan of the larger pixel area covers the entire pixel array, this step is omitted for the larger-area scan, or is modified to use estimates from the smaller-area scan. Instruction set #5 directs the data processor to perform a truncated reconstruction with the truncated projection data, or the corrected truncated projection data, if available, to generate a set of three-dimensional CT data. These instructions may implement the methods described in published PCT application WO-2005-104038 A1, or similar methods found in the art. The method essentially finds where each projection of the smaller-area scan matches the corresponding projection of the larger-area scan (which may be done by a two-dimensional auto-correlation of the original data or the scatter-corrected data), and then replaces the data of the larger-area scan in the matched area with the corresponding data of the smaller-area scan, in the matched area. The particulars of the reconstruction are not essential to the invention of product 340. Instruction set #6 directs the data processor to store the generated three-dimensional CT data in a computer-readable medium. From the three-dimensional CT data, a number of cross sections of the target volume may be constructed. Product 340 may comprise additional instruction sets that receive input from an operator to select a cross section for display, and that in turn display the requested cross section. The particulars of such cross section display instructions are not essential to the invention of product 340. Product 340 may be run by data processor 160 (shown in FIGS. 2A and 2B), or another data processor. It may be appreciated that each of the above computer-program products performs a corresponding method, which may be separately recited herein as a set of independent and dependent method claims. Scatter-Estimation Methods and Computer-Program Products. FIG. 16 shows the pixel values of an axial line of pixels from Y1 to Ypix for some value of X that crosses through the imaging window. Image data and scattered radiation are present within the imaging window (the scattered radiation being much less compared to the case of a full-width imaging window), and scatter radiation is present at the extremes of the axial line (near Y=1 and Y=Ypix). At the edges of the imaging window, there are transition regions due to the penumbra of radiation source 110. As is know in the art, the source is not a perfect point, but has some width. This width interacts with the edges of fan blades 130 to create a tapering of the incident radiation, rather than a step change, and this tapering causes tapered regions of width Δp between the edges of the imaging window and the scatter radiation profiles at the extremes. The likely profile of the scattered radiation within the imaging window can be estimated by human eye as the dot-dashed line shown in the figure. A good estimate of the likely profile can be generated at the dashed straight line, which is constructed as a straight line from two pixel values just outside of the two penumbra regions, such as at (Y1 −Δp) and (Y2+Δp). This is a simple linear interpolation form. More complex interpolation forms may be used, such as splines. Because the pixel data often has spurious noise, it is preferred to average the value of (Y1 −Δp) with the corresponding values of adjacent axial lines, and to average the value of (Y2+Δp) with the corresponding values of adjacent axial lines, before constructing the interpolation. This will lessen the effects of spurious noise. This interpolation may be done for each axial line traversing the imaging window. While the above methods of estimating the scatter radiation have been done along the axial lines, it may be done along the trans-axial lines as well, particularly if the trans-axial width of the imaging window is narrower than the axial width of the imaging window. Once the estimates of the scatter radiation inside the imaging window are generated by such an interpolation, they may be subtracted directly from the corresponding pixel values in the imaging window to generate corrected projection data. However, because of possible spurious noise, it may be preferred to perform a truncated subtraction rather than a direct subtraction. The truncated subtraction is generated by forming the ratio between the scatter estimate for a pixel and the pixels value, limiting the maximum value of this ratio to a predetermined ceiling value a that represents a reasonable expected upper bound for scattering ratio, multiplying the limited ratio by the pixel's value, and thereafter subtracting the resulting multiplication from the pixel value. This may be mathematically expressed as PVc=PV−PV*limit(SE/PV, α), where PVc is the scatter-corrected pixel value, PV is the pixel value, SE is the scatter estimate for the pixel, and limit(*,*) is the limit function. In view of the above discussion, an exemplary computer-program product 400 for scatter correction is provided in FIG. 17. Product 400 is suitable for stand-alone use or use with products 300 and 340 as instruction set #4. Product 400 comprises a computer-readable medium and a plurality of instruction sets embodied on the computer-readable medium, as shown in the figure. Instruction set #1 directs the data processor to acquire the projection data of a scan and the values of the imaging window (e.g., X1, X2, Y1, and Y2). In one embodiment, the instruction set may direct the data processor to receive the data, such as by reading it from a computer-readable medium. In another embodiment, product 400 may be loaded onto controller 160 and this instruction set may direct the data processor of controller 160 to instruct system 100 (or 100′) to obtain the projection data. Instruction set #2 directs the data processor to generate one or more interpolated profiles of the estimated scattered radiation across the imaging window suitable for each projection of the scan. Instruction set #2 preferably includes averaging pixel values outside of the imaging window, and generating the interpolations from the averaged values. Instruction set #3 directs the data processor to generate a set of corrected projection data for each projection from the projection data itself and the interpolated profile(s) of the estimated scattered radiation across the imaging window for the projection. This may be generated as a direct subtraction of the estimated scatter profile from the pixel values, or as the truncated subtraction of the estimated scatter profile from the pixel values, as described above. Instruction set #4 directs the data processor to store the corrected projection data for each projection in a computer-readable medium. It may be appreciated that the above computer-program products perform corresponding methods, which may be separately recited herein as sets of independent and dependent method claims. For projection data collected from method 240 for the large-area scan, if the imaging window covers the entire area of the large area scan, then the interpolation profiles of estimated scattered radiation generated for each projection of the small-area scan may be applied to the corresponding projection of the large area scan, with the profiles being extrapolated to the regions outside of the imaging window, and optionally scaled by a factor greater than 1 to account for the additional radiation received by the object during the large area compared to the small area scan. (The additional radiation received by the object cases more scattered radiation in the large area scan than compared to the small area scan.) The instruction sets of the above-described computer-program products may be combined together, either in whole or various sub-combinations, to provide additional computer-program products. The actions of the methods performed by the instruction sets may be similarly combined to provide additional methods. Additional Collimator Structures. In addition to fan blades, the present inventions may be practiced with various collimator structures. An exemplary collimator structure 500 is shown in FIG. 18. It comprises a plate of radiation attenuation material, with the properties described above for fan blades 130 and 140, a central aperture 510 through the plate to allow radiation to pass without attenuation, and a plurality of slits 520 disposed along the axial and trans-axial dimensions, crossing at the center of aperture 510. Collimator 500 may replace fan blades 130 and 140 in systems 100 and 100′, and may be moved in the axial and trans-axial directions by linear motor servos and the like. Collimator 500 produces a circular or oval-shaped image window on imaging device 120, and it may also be moved along the projection axis by another linear motor servo to vary the diameter of the image window. Slits 520 also allow radiation to pass through the plate without attenuation, and generate projection slices of the object which may be found and used by truncation reconstruction programs to better estimate the missing projection data. Slits 520 do not appreciably increase the scatter radiation. Slits 520 may be incorporated into fan blades 130 and 140. Any recitation of “a”, “an”, and “the” is intended to mean one or more unless specifically indicated to the contrary. As used herein, computer-readable medium includes, but is not limited to, volatile memory, such as a data memory of a data processor, non-volatile memory (such as EPROMs, EEPROMs, “jump drives”), magnetic disk drive storage (including fixed media and removable media), floppy disks, optical discs (such as CD-ROM discs and writable DVD discs), magnetic tape, optical tape, magnetic drums, optical drums, holograms, and any other tangible medium to which data may be written, and from which data may be read, at the request of a computer, microprocessor, data processor, and the like. The pixel arrays used here preferably have X-and Y-dimensions of at least 100 pixels in each dimension, and more preferably at least 400 pixels in each dimension, and most preferably at least 700 pixels in each dimension. The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described, it being recognized that various modifications are possible within the scope of the invention claimed. Moreover, one or more features of one or more embodiments of the invention may be combined with one or more features of other embodiments of the invention without departing from the scope of the invention. While the present invention has been particularly described with respect to the illustrated embodiments, it will be appreciated that various alterations, modifications, adaptations, and equivalent arrangements may be made based on the present disclosure, and are intended to be within the scope of the invention and the appended claims. |
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description | This application claims priority on Japanese Patent Application 2006-009281 filed Jan. 17, 2006. This invention relates to factor estimating device, method and program for estimating factor of a result that takes place in a target system under diagnosis, as well as a recording medium for recording such a factor estimating program. In particular, this invention relates to a production process management device for managing production processes of target products. Processes for improving production steps are being required for factory production lines in order to improve the yields. In such an improvement process, steps that cause defective products are identified and apparatus are adjusted and cleaned so as to eliminate factors that cause such defective products. In a production process including a large number of steps, however, a variety of candidates are considered as factors of causing defective products such as defective components of the production apparatus, problems involved in the setting of the production apparatus and the problems related to the routes of transportation. For example, the processes of a system for surface-mounting circuit boards may be divided into the printing, mounting and reflow steps. The printing step is where a solder paste is applied to a substrate, and the mounting step is where components are set on the substrate. In the final reflow step, heat is applied to melt the solder to attach the components. If a bridge defect occurs in such a surface-mounting system, displacement of the mask and the unclean female mold may have contributed as the cause of the defect but one or more of them may be the basic factor. When a phenomenon that becomes a factor of a defect appears, not only does a symptom of the defect appear in the products, but there also appear some effects in the operation history of the production apparatus and the inspection history of the inspection apparatus. The amount of data related to the symptoms of these defective products and to the operation history of the production apparatus and the inspection history of the inspection apparatus becomes enormous, making it very difficult to carry out any analysis on the occurrence of the defects. Persons in charge of production management with a lot of experience in production management may know empirically the relationship among the effects of such factors on the production and inspection apparatus and how to interpret such effects and may be able to effectively improve the production steps. Inexperienced production managers will have to examine many candidate factors one at a time to finally identify a real factor, and it turns out to be a very time-consuming effort to improve the production steps. It is therefore being desired to provide a method of highly accurately and efficiently estimating factors of any abnormal situation independently of the level of skill of the production manager. Japanese Patent Publication Tokkai 6-196900, for example, disclosed a method of obtaining data from inspecting apparatus individually provided to each of the printing, mounting and reflow steps and making an estimate based on such data. In the case of a surface-mounting system, however, there is no guarantee that all data necessary for estimating a factor can be obtained from such inspecting apparatus. Although the area of solder as seen from the front of the substrate may be obtained by an image processing technology, for example, data on the warping of the substrate can be obtained only by a visual observation by a viewer from the side. Although a device for detecting the warping of the substrate may be considered, it is not desirable to allow the total cost of the inspecting apparatus to increase unnecessarily. In other words, it is preferable to input data from human observers in addition to data obtained from an inspection apparatus. This is to say that cooperation between an inspection apparatus and a human observer is preferable for estimating factors. In general, knowledge data are of a network structure and a search is carried out from a root node along a path. In order to make an efficient estimate, therefore, it is necessary to optimize this network structure. This may be done, for example, by making an important item for the estimate as a node on an upstream side, but it will involve large amounts of labor and cost. In addition, so-called important items may change, depending on the circumstances of making the estimate. In summary, it is extremely difficult to form a network structure capable of efficiently making an estimate according to a variety of circumstances. It is therefore an object of this invention in view of the problems described above to provide a factor estimating device capable of efficiently making an estimate, independent of the network structure. A factor estimating device according to this invention is for estimating a factor from a result generated in a target system for diagnosis and is characterized as comprising an estimate knowledge recording part for recording factor estimating knowledge data that correlate one or more candidates for factor to each of a plurality of results that may be generated in the target system and show factor estimating paths from each of the results to each of the candidates corresponding to each result as knowledge of a network structure having condition branches, inference processing means for carrying out factor estimating process based on the factor estimating knowledge data recorded in the estimate knowledge recording part, item data obtaining means for obtaining data on input item corresponding to conditions contained in the factor estimating knowledge data while the inference processing means carries out the factor estimating process, fitness calculating means for calculating fitness factors based on the data obtained by the item data obtaining means, the fitness factors being indicative of degrees to which the conditions are satisfied, certainty calculating means for calculating for each of the factors a representative value of an assembly of fitness factors corresponding to a condition contained in the factor estimating paths as certainty factor, and influence calculating means for calculating influence factor for each of input items indicative of degree of influence on the certainty factor when the data on the input item are obtained regarding a certain input item. In the above, the item data obtaining means obtains data on a selected input item by considering the influence factors. A factor estimating method of this invention is for estimating a factor from a result generated in a target system for diagnosis by means of a factor estimating device provided with an estimate knowledge recording part for recording factor estimating knowledge data that correlate one or more candidates for factor to each of a plurality of results that may be generated in the target system and show factor estimating paths from each of the results to each of the candidates corresponding to each result as knowledge of a network structure having condition branches. The method is characterized as comprising an inference step of carrying out factor estimating process based on the factor estimating knowledge data recorded in the estimate knowledge recording part, an item data obtaining step of obtaining data on input item corresponding to conditions contained in the factor estimating knowledge data during the factor estimating process in the inference step, a fitness calculating step of calculating fitness factors based on the data obtained in the item data obtaining step, the fitness factors being indicative of degrees to which the conditions are satisfied, a certainty calculating step of calculating for each of the factors a representative value of an assembly of fitness factors corresponding to a condition contained in the factor estimating paths as certainty factor, and an influence calculating step of calculating influence factor for each of input items indicative of degree of influence on the certainty factor when the data on the input item are obtained regarding a certain input item. In the above, the item data obtaining means obtains data on a selected input item by considering the influence factors. According to this invention, a factor estimating process is carried out based on factor estimating knowledge data which show the factor estimating paths from each result to each of the factors corresponding to that result as knowledge in a network structure having condition branches. This factor estimating process is carried out by obtaining data on input items corresponding to the conditions contained in the factor estimating knowledge data. Fitness factors indicative of the degrees to which conditions are satisfied are calculated during this process, and a value representing the group of fitness factors corresponding to the conditions contained in the factor estimating paths is calculated as certainty factor for each factor. For each input item, an influence factor for indicating the degree of influence on the certainty factor when data on that input item are obtained is calculated, and data on input item having a high influence factor are obtained. Thus, since data are obtained from input items with a high influence factor, or input items that are important in estimating factors, independent of the factor estimating paths, factors can be estimated efficiently. The network structure can be constructed easily, furthermore, since the network structure need not be optimized for carrying out the factor estimating process. The influence factor may be calculated, for example, by obtaining predicted values which would be the influence factors if data were set for input items for which data are not obtained yet, calculating for each factor the difference between this predicted value and the current influence factor and calculating the total sum of these differences. Although it is preferable to obtain data from the input item with the highest influence factor, data may be obtained from an input item with such influence factor that estimated factors can change when data are obtained. Examples of the value which represents the group of fitness factors include the minimum value and the average value. As data are obtained from an input item with a high influence factor, however, consistency may be lost in the questions to be asked to the user for obtaining data from input items because there is no relationship to the factor estimating paths. For this reason, the factor estimating device of this invention may preferably further comprise an aimed node determining means for determining as an aimed node, when data obtained by the item data obtaining means satisfy a condition, the node to which the satisfied condition branches, and the item data obtaining means obtains data of an input item with a high (or highest) influence factor selected out of those of input items corresponding to the aimed node and nodes on the downstream side of the aimed node. With the device thus structured, the search area for input item on which data are to be obtained becomes limited to the downstream side of the aimed node. If the obtained data on the input item satisfy the condition, the node to which the condition branches is determined as the aimed node. In this way, the search area becomes further narrowed down. Thus, when questions are posed to the user in order to obtain data on input items, the questions will be corresponding to the input items within the gradually narrowing search area and hence the consistency in the flow of questions is not adversely affected. If the aimed node moves gradually in the downstream direction, there finally ceases to exist any input item on which data are to be obtained. If the aimed node is then returned to a root node, there is the possibility of selecting an input item that corresponds to a condition on a completely different path. In such a situation, the question made to the user for obtaining data on input item may become completely different, the flow of questions becoming interrupted. Thus, it is preferable that the aimed node determining means be adapted to determine an earlier determined aimed node as the aimed node if there is no input item with influence factor higher than a specified value. In this situation, since the search area returns to that immediately before the narrowing down, a flow of similar questions can be maintained. For this purpose, a memory device becomes necessary for recording the history of aimed nodes. A memory device of the last-in, first-out type is preferred for this purpose. For maintaining the consistency in the flow of questions, the factor estimating device of this invention may further comprise a related item recording part for grouping and recording data on a plurality of related input items and the item data obtaining means obtains not only data on a selected input item by considering the influence factors but also data on input items that belong to same group as the selected input item. When data of a selected input item with a high influence factor are obtained with a factor estimating device thus structured, data of other input items related to this selected input item are also obtained. In such a situation, the questions to the user asked for obtaining data on the related input items are likely to be also related and hence consistency of the flow of the questions can be maintained. The factor estimating device of this invention may further comprise a related item recording part for grouping and recording data on a plurality of related input items, the item data obtaining means obtaining not only data on the selected input item by considering the influence factors but also data on input items that belong to the same group as the selected input item and have influence factors higher than a specified value. In this case, data on input items can be obtained efficiently because data on input items with low influence factors are not obtained. The factor estimating device of this invention may still further comprise input control means for obtaining a user's response to a question corresponding to a condition contained in the factor estimating knowledge data, the item data obtaining means obtaining the data on the input item based on the response obtained by the input control means. In this case, the user and the factor estimating device can cooperate in estimating factors since data on input items are obtained based on responses from the user. The factor estimating device of this invention may still further comprise inspection result inputting means for receiving inspection result data from an inspection device that inspects the target system, an inspection result recording part that records the inspection result data received by the inspection result inputting means and an obtaining method recording part for recording data on an obtaining method indicating whether the data on the input item are obtained either from a user or from the inspection result data or from both of them, as well as the data on the input item, the item data obtaining means obtaining the data on the input item based on the data on the obtaining method corresponding to the input item. In this case, the user, the inspection device and the factor estimating device can cooperate in estimating factors since data on input items are obtained based on the inspection result data from the inspection device. The factor estimating device of this invention is particularly useful for a process managing device adapted to estimate causing factors of defects from a defective result generated in a processing system for carrying out processes on a target object. The factor estimating device of this invention may be realized by a computer. In such a case, program storage devices readable by a machine, tangibly embodying a program of instructions executable by such computer are also considered to be within the scope of this invention. In summary, the factor estimating device of this invention is capable of estimating a factor because data are obtained from input items with high influence factors, that is, input items that are important in estimating factors. Since the network structure need not be optimized for estimating factors efficiently, the network structure can be constructed easily according to this invention. The invention is described next by way of one of its embodiments with reference to figures. It will be described as being applied to a process management system for a production system including a production line for printed circuit boards but it goes without saying that this is not intended to limit the scope of the invention. The present invention is applicable to the whole management of processing steps for target products. In the above, the processing steps for target products include, for example, production steps for industrial products, inspection steps for mining, industrial and agricultural products or materials, processing steps of discarded objects (such as industrial wastes and drain, offgas and refuse), inspection steps for wastes, inspection steps for equipment and recycling steps. FIG. 2 shows a production (processing) system 1 for printed circuit boards to which a process managing system according to the embodiment of this invention is applied. The production system 1, as shown in FIG. 2, includes each of the steps necessary for the producing printed circuit boards such as the printing, mounting and reflow steps and is provided with a printing device 11 for carrying out the solder printing step whereby a solder is pasted on a substrate, a mounting device 12 for carrying out a component mounting step whereby electronic components are mounted to the substrate, a soldering device 13 for carrying out a reflow step whereby the electronic components on the substrate are soldered, and a process managing device (a factor estimating device) 10 for managing the production system 1. The printing device 11, the mounting device 12 and the soldering device 13 are arranged in this order from the upstream side to the downstream side with reference to the flow of products by this production system 1. A printing inspection device 14a, a mounting inspection device 14b and a soldering inspection device 14c are disposed respectively near the printing device 11, the mounting device 12 and the soldering device 13. The printing inspection device 14a is for inspecting the quality of a substrate processed by the printing device 11, the mounting inspection device 14b is for inspecting the quality of a substrate processed by the mounting device 12, and the soldering inspection device 14c is for inspecting the quality of a substrate processed by the soldering device 13. In the following, the printing inspection device 14a, the mounting inspection device 14b and the soldering inspection device 14c may each be referred to simply as an inspection device 14 when there is no need to distinguish among them. The process managing device 10 serves not only to manage the production system 1 as a whole but also to carry out the factor estimating process and the analyzing process to be described below. It is adapted to receive various data and instructions from the user as the production manager and to carry out various operations. The process managing device 10, the printing device 11, the mounting device 12, the soldering device 13, the printing inspection device 14a, the mounting inspection device 14b and the soldering inspection device 14c are connected together by a communication line to together form a communication network. As a communication network, it may be of any type such as a LAN (local area network) as long as the devices can communicate among themselves. Apart from the process managing device 10, a terminal device which may be operated by the user for an input operation may be provided and connected to this communication network such that inputs of data to the process managing device 10 and displays of various images may be effected through this terminal device. Although FIG. 2 shows a particular example with each of the printing device 11, the mounting device 12 and the soldering device 13 being provided with a corresponding inspection device 14, the process managing device 10 as a whole may be provided with only one inspection device 14. For example, if the process managing device 10 is provided only with the soldering inspection device 14c, it is possible to detect defects occurring in the final production result. FIG. 1 is referenced next to explain the structure of the process managing device 10. As shown in FIG. 1, the process managing device 10 is provided with a control part 30, an inspection result input part (inspection result inputting means) 40, an input part 21, a display part 22, an estimate knowledge recording part 23, a question data recording part 24, an inference process temporary recording part 25, a step status database (inspection result recording part) 26, an aimed node stack recording part 27, a related item recording part 28, and an item data obtaining method recording part 29. The input part 21 is for receiving instructions from the user and the data inputs and may comprise key input means such as a keyboard and buttons and a pointing device such as a mouse. The display part 22 is for displaying the details of various processes by the process managing device 10 and may comprise a display device such as a liquid crystal display device or a CRT (cathode ray tube). The inspection result input part 40 is for receiving data related to the inspection results of production process by the production system 1 and is provided with a printing result input part 41, a mounting result input part 42, a soldering result input part 43 and a production device history input part 44. The printing result input part 41 is for receiving the results of inspection by the printing inspection device 14a. The mounting result input part 42 is for receiving the results of inspection by the mounting inspection device 14b. The soldering result input part 43 is for receiving the results of inspection by the soldering inspection device 14c. The production device history input part 44 is for receiving data related to the production history from the printing device 11, the mounting device 12 and the soldering device 13. The inspection result input part 40 needs only to be adapted to receive data related to the inspection results from at least one selected from the printing device 11, the mounting device 12, the soldering device 13, the printing inspection device 14a, the mounting inspection device 14b and the soldering inspection device 14c. For example, if it is adapted to receive only the inspection result data related to the result of soldering from the soldering inspection device 14c, it is still possible to detect defects occurring in the final production result. The estimate knowledge recording part 23 is for recording factor estimating knowledge data. The factor estimating knowledge data are for searching for factors for each of defective results and are recorded as a causality network. Details of the causality network will be explained farther below. The question data recording part 24 is for recording, as a question database, question data shown to the user when estimating factors. Each item of the question data contained in this question database is linked to an input item recorded in the item data obtaining method recording part 29. Details of this question database will be explained farther below. In the above, the input item is an item corresponding to the conditions between the nodes of the causality network. Its details also will be explained farther below. The inference process temporary recording part 25 is for recording inference process data which are being obtained with the progress in inference during an inference process being carried out by an inference part 32. Details of the inference process data will be explained farther below. The step status database 26 is a database recording data (inspection result data) related to the results of inspection in the production process by the production system 1 received by the inspection result input part 40. In other words, the results of inspection by the printing inspection device 14a, the mounting inspection device 14b and the soldering inspection device 14c as well as data related to the production history from the printing device 11, the mounting device 12 and the soldering device 13 are recording in the step status database 26. The aimed node stack recording part 27 is for recording data on the node, which becomes a specified point (specifically, the node ID which identifies the node) in a stack format. The related item recording part 28 is for grouping the data on a plurality of related input items and recording them as a group database. The item data obtaining method recording part 29 is for recording data on the method of obtaining data of each input item as an item data obtaining method database. Details of the aforementioned group database and the item data obtaining method database will be explained farther below. The estimate knowledge recording part 23, the question data recording part 24, the step status database 26, the related item recording part 28, and the item data obtaining method recording part 29 may be realized as a non-volatile memory medium such as a hard disk device. The inference process temporary recording part 25 may be realized as work memory such as a RAM (random access memory). The aimed node stack recording part 27 may be realized as a memory device for queuing data by the last-in, first-out method. The control part 30 is for controlling the processes by the process managing device 10 and is provided with an input display control part 31, the inference part 32, a knowledge conversion part 33, a question generating part 34, a characteristic quantity calculating part (or simply “quantity calculating part”) 35 and a related item selecting part (or simply “item selecting part”) 36. The knowledge conversion part 33 is for reading out the factor estimating knowledge data recorded in the estimate knowledge recording part 23 and generating a production rule as inference knowledge. The production rule means information in a data form convenient for causing a computer to carry out the inference process for estimating factors. Details of the production rule will be explained farther below. The question generating part 34 is for reading out question data corresponding to each step of the inference process from the question data recording part 24 in response to a request from the inference part 32 and generating questions. The characteristic quantity calculating part 35 is for reading out the inspection result data recorded in the step status database 26 in response to a request from the inference part 32 and calculating necessary characteristic quantities by carrying out statistical calculations and the like. The related item selecting part 36 is for selecting input items related to those selected by the inference part 32. This is done by reading out data on the input data of the same groups as the input items selected by the inference part 32 from the related item recording part 28 and selecting therefrom data on the input items having an influence factor greater than a specified value. The input display control part 31 is for receiving input data from the input part and carrying out a display control for the display part 22 and is provided with a question input-output control part (input control means) 51 and a factor output control part 52. The question input-output control part 51 is for displaying questions on the display part 22 in response to an instruction from the inference part 32 and carrying out the processes of receiving response inputs to these questions and transmitting them to the inference part 32. The factor output control part 52 is for displaying candidates of estimated factors and data on each factor in response to an instruction from the inference part 32. The inference part 32 is for carrying out an inference process by estimating factors and is provided with an inference process part (inference processing means) 61, a fitness calculating part (fitness calculating means) 62, a certainty calculating part (certainty calculating means) 63, an influence calculating part (influence calculating means), an item data obtaining part (item data obtaining means) 65 and an aimed node determining part (aimed node determining means) 66. The inference process part 61 is for generally controlling the factor estimating process. The aimed node determining part 66 is for carrying out the process of determining the aimed node, or the node to be considered on the causality network. The downstream side from the aimed node becomes the range of search for input items. In the following, the downstream side of the aimed node on the causality network will be referred to as the sub-network. The fitness calculating part 62 is for calculating, when data are obtained for an input term corresponding between specified nodes on the sub-network, the fitness factor with respect to the nodes connected to the downstream side corresponding to these data. The certainty calculating part 63 is for calculating the certainty factor regarding each estimated factor, based on fitness factor obtained by the factor estimating process. The influence calculating part 64 is for calculating the influence factor which indicates the change in the certainty factor when data on a certain input item are obtained. The item data obtaining part 65 is for obtaining the data of the input item with the highest influence factor in the sub-network. Factors can thus be estimated efficiently because data are obtained from input terms with high influence factor, that is, the input terms which are important in estimating factors without regard to the factor estimating paths. It also makes it easier to build a network structure because it is not necessary to optimize the network structure for estimating factors efficiently. Details of the aforementioned inference process, aimed node determining process, fitness calculating process, certainty calculating process, influence calculating process and item date obtaining process will be described farther below. The causality network as the factor estimating knowledge data recorded in the estimate knowledge recording part 23 will be explained next. The causality network is the data that show the details of the inference from each no-good result to the factors of this no-good result (hereinafter referred to as the “no-good factors”) as the knowledge of the network structure. The causality network includes a plurality of nodes on the diagnostic paths from a no-good result to its no-good factors. Diagnostic branches are formed at these nodes so as to form the diagnostic paths from a specific no-good result to a plurality of no-good factors. The causality network may be data showing knowledge having a tree structure with only one parent node. Each node represents a specific phenomenon. If a factor of the phenomenon corresponding to a certain node has a high probability of being a phenomenon corresponding to a node on the downstream side of this node on the diagnostic path, the fitness factor is high between these two nodes. FIG. 3 is a schematic drawing of an example of causality network, dl indicating a no-good result, c1-c4 indicating no-good factors, and s1-s5 indicating phenomena corresponding to nodes. In the case of this example, four no-good factors c1-c4 are estimated as candidates corresponding to the specific no-good result dl, and diagnostic paths s1-s5 corresponding to the individual no-good factors are formed as chains of nodes. In the case of this causality network, the five diagnostic paths shown in FIG. 4 are included. If the knowledge structure were such that the no-good factors c1-c4 are directly connected to no-good result dl, the conditions for judging the fitness factor for each no-good factor would become extremely complicated. If the knowledge structure is as shown by the network structure of FIG. 3, on the other hand, the conditions for judging the fitness factor of the no-good factors of the phenomena that cause the no-good result, the phenomena that cause each of the phenomena and the no-good factors of each of these phenomena become relatively simple if considered individually. Thus, it becomes possible to carry out the inference process for estimating factors by examining relatively simple conditions and hence that even a relatively inexperienced user can properly narrow down on factors. Next, the process of generating a production rule from the diagnostic paths of a causality net work by the knowledge conversion part 33 will be explained. As explained above, the production rule means information in a data form convenient for causing a computer to carry out the inference process for estimating factors. The knowledge conversion part 33 functions to read out data on target diagnostic paths from the data on causality network recorded in the estimate knowledge recording part 23 and to generate a production rule corresponding to these diagnostic paths. The production rule contains not only data on conditions between the nodes from a no-good result to a no-good factor along a specific diagnostic path but also data on the no-good factor which becomes TRUE when these conditions are all satisfied. Thus, it becomes possible to judge whether or not this no-good factor is TRUE by making the simple judgment whether or not all of the conditions between each node are satisfied, which is convenient for processing by a computer. FIG. 5A shows an example of diagnostic path from no-good result dl through nodes as phenomena s1-s3 in this order to reach no-good factor c1. In addition, data on conditions related to f1-f4 as diagnostic knowledge corresponding to the conditions between the nodes are also set. Explained more in detail, condition f1=LARGE must be satisfied in other to estimate that no-good result dl is due to phenomenon s1, the condition for estimating s2 from s1 is f1=LARGE, the condition for estimating s3 from s2 is f3=LARGE, and the condition for estimating c1 from s3 is f4=LARGE. Based on such diagnostic path data, the knowledge conversion part 33 generates a production rule as shown in FIG. 5B. The production rule represents the data that the corresponding no-good factor is TRUE when the condition connecting all conditions between nodes contained in the diagnostic path from the no-good result to the no-good factor by AND is satisfied. The production rule of FIG. 5B shows the data that c1 is TRUE when all of the conditions f1=LARGE, f2=LARGE, f3=LARGE and f4=LARGE are satisfied. When a plurality of conditions connected by AND are set as condition between nodes, the production rule represents that the corresponding no-good factor is TRUE when the condition connecting all conditions between nodes contained in the diagnostic path from the no-good result to the no-good factor inclusive of this plurality of conditions connected by AND is satisfied. In the case of the example shown in FIG. 6A, the condition for estimating from s1 to s2 is f2=LARGE AND f5=LARGE. In this case, the production rule represents the data that c1 is TRUR when all the conditions f1=LARGE, f2=LARGE, f5=LARGE, f3=LARGE and f4=LARGE are satisfied. When a plurality of conditions connected by OR are set as condition between nodes, production rules corresponding individually to the conditions connected by OR are generated. In other words, each production rule represents the data that the corresponding no-good factor becomes TRUE when all of the conditions between nodes other than those between nodes for which a plurality of conditions contained in the diagnostic path from the no-good result to the no-good factor and connected with OR and the condition connecting with AND any one of the conditions connected with OR are satisfied. The number of production rules that are generated is the same as the plural number of conditions connected with OR. FIG. 7A shows an example wherein the condition for estimating from s1 to s2 is f2=LARGE OR f5=LARGE. In this case, as shown in FIG. 7B, two production rules are generated, one providing that c1 is TRUE when all of the conditions f1=LARGE, f2=LARGE, f=LARGE and f4=LARGE are satisfied and the other providing that c1 is TRUE when all of the conditions f1=LARGE, f5=LARGE, B=LARGE and f4=LARGE are satisfied. When a supplementary path exists, a production rule connecting the conditions contained in this supplementary path with AND to the production rule corresponding to the production path leading to the same no-good factor is generated. The nodes on the supplementary path are for defining intermediate phenomena from a no-good to a factor. There may be knowledge, however, describing a phenomenon that is not an intermediate phenomenon but a phenomenon related directly to a factor such as an overall trend. Such knowledge is described as a supplementary path. FIG. 8A shows an example with a diagnostic path from phenomenon s4 to no-good factor c1 as a supplementary path and its condition is f5=LARGE. In the situation of this example, a production rule representing that s1 is TRUE when all of the conditions f1=LARGE, f2=LARGE, f=LARGE, f4=LARGE and f5=LARGE are satisfied is generated, as shown in FIG. 8B. Next, the process of calculating fitness by the fitness calculating part 62 is explained. Fitness factor means the degree to which the conditions set between the nodes of a production rule are satisfied. Fitness is expressed by a number between 0 and 1. The larger the number representing fitness, the higher is the degree to which a condition is satisfied. If there are only two selection branches and a condition can be either completely satisfied or completely unsatisfied, the fitness factor can be only either 0 or 1. According to the present embodiment of the invention, the fuzzy theory is used such that answers are allowed to conditions for which the fitness factor may be greater than 0 and smaller than 1. Thus, in a situation where the response to a condition becomes ambiguous, it is possible to obtain a result of estimate reflecting this ambiguous condition. Since it becomes unnecessary to force an ambiguous response into an extreme response, it is possible to prevent inappropriate estimates from being made. Since the value of the fitness factor is indicative of the certainty factor of the estimate of the next node, the fitness factor can be used for judging the appropriateness of an estimate. Specifically, a membership function is set to each of language values that become candidates of a response to the corresponding condition. The fitness factor for each language value is calculated according to the language value inputted as response by referencing the membership function. Explained more in detail, the fitness factor of a language value inputted as response becomes 1.0. The fitness factor of a language value other than those inputted as response is obtained by taking the smaller (min) of the membership function corresponding to that language value and the membership function corresponding to the inputted language value and calculating its maximum value (max). If the membership function corresponding to the language value inputted as response and that membership function corresponding to the inputted language value do not cross each other, the fitness factor is set to 0.0. The language values that become the candidate for response to each condition and the data related to each membership function are recorded in the estimate knowledge recording part 23. The fitness calculating part 62 reads out these data recorded in the estimate knowledge recording part 23 and thereby calculates the fitness factor. The fitness calculating part 62 also serves to record the data related to the calculated fitness factor together with the data on the conditions corresponding to this fitness factor in the inference process temporary recording part 25. Let us consider next a calculation process for the fitness factor wherein, as an example, a condition “Is XXX large?” is set and three responses LARGE, MEDIUM and SMALL may be imagined. FIGS. 9A and 9B are examples of membership function for these three responses. FIG. 9A is an example wherein if the response is LARGE, the fitness of LARGE is 1.0, that of MEDIUM is 0.5 and that of SMALL is 0.0. FIG. 9B is another example wherein if the response is LARGE, the fitness of LARGE is 1.0, that of MEDIUM is 0.7 and that of SMALL is 0.3. Next, the process of calculating the certainty factor by the certainty calculating part 63 is explained. Certainty is a value which is set corresponding to each no-good factor, indicating the possibility that this no-good factor is really the causing factor of the no-good result that is the object to be estimated. To obtain the value of certainty, a production rule corresponding to the diagnostic path leading to the corresponding no-good factor from the no-good result to be estimated is extracted first. Next, conditions for which fitness factor has been calculated are extracted from the conditions contained in this extracted production rule and, the one of them having the smallest value of fitness is set as the certainty factor. If a plurality of production rules exist, corresponding to the diagnostic path from the target no-good result to be estimated from the corresponding no-good factor, certainty is calculated for each of these production rules and the largest of the calculated certainty factors is set as the certainty factor for this no-good factor. The certainty calculating part 63 also serves to read out data on fitness factors recorded in the inference process temporary recording part 25 as well as data on the conditions corresponding to these fitness factors to thereby obtain required fitness factors and to calculate the certainty factor. The calculated certainty factor is recorded in the inference process temporary recording part 25 together with the data on the corresponding no-good factor. In the case of the example shown in FIGS. 7A and 7B, the certainty factor for no-good factor corresponding to c1 is calculated as follows. First, fitness factors g1-g5 corresponding to all of the conditions f1-f5 are extracted. Certainty factor for no-good factor c1 is then given as follows: Certainty factor (c1)=max(min(g1, g2, g3, g4), min(g1, g2, g3, g4, g5)). Although the smallest of the fitness factors of the conditions contained in the extracted production rule according to the example described above, this is not intended to be always the case. It may be another value representative of the assembly of the fitness factors included in the production rule, such as their average value. The certainly factor need not be set as a representative value of fitness factors but any score which may look reasonable may be used such as an after-the-fact probability, a score based on an after-the-fact probability or a score based on a distance such as the Euclid distance. Next, the process of calculating the influence factor by the influence calculating part 64 is explained. The influence factor is a value which is set corresponding to each input item, being the value that shows the total sum of changes in the certain factors for all input items. Thus, the influence factor may be expressed as follows:(Influence factor)=Σc|(current certainty factor)−(predicted certainty factor)|where Σc indicates the total sum over the no-good factors. Explained more in detail, the influence calculating part 64 obtains the required certainty factors by reading out data on the current certainty factors recorded in the inference process temporary recording part 25. FIG. 10 shows an example of current certainty factors recorded in the inference process temporary recording part 25. As shown, certainty factors are recorded for each no-good factor. Next, the influence calculating part 64 causes the fitness calculating part 62 to calculate fitness factor on the assumption that data on a certain input item have been obtained. The fitness factor thus obtained becomes what is referred to as the predicted certainty factor above. Next, the influence calculating part 64 uses the formula given above to calculate the influence factor. This process is repeated for each of the input items contained in the sub-network, and the calculated influence factor is recorded in the inference process temporary recording part 25 together with data on the corresponding input item (or its item ID). Next, the process of obtaining data on input items by the item data obtaining part 65 is explained. The item data obtaining part 65 reads out the influence factor corresponding to each input item within the sub-network from the inference process temporary recording part 25 and identifies the input item with the highest influence factor. If no input item exists within the sub-network or if there is no input item with influence factor higher than a specified threshold value, the item data obtaining part 65 completes the process for obtaining data and reports to this effect to the aimed node determining part 66 because there would be no effect or little effect on the certainty factor even if more data on input items within this sub-network were further obtained. The item data obtaining part 65 transmits data on the identified input item (hereinafter referred to as the identified item) to the item selecting part 36. The item selecting part 36 reads out the input items related to the identified item (hereinafter referred to as the related item) from the related item recording part 28. FIG. 11 shows an example of group database recorded in the related item recording part 28. As shown, the group database contains for each group the group ID for distinguishing the group and the item IDs of the input items included in the group. In other words, the item selecting part 36 serves to receive the item ID of the identified item from the item data obtaining part 65, to identify the group ID including the received item ID and to read out other item IDs included in the identified group ID. The item IDs that have been read out are transmitted to the item data obtaining part 65 as data on the related item. Thus, when data on the identified item are obtained, data on the related items are also obtained. In this situation, there is a high possibility that the questions to be asked to the user for obtaining the data on the identified item and those for obtaining the data on the related items be related. Consistency in the flow of questions can thus be maintained. The item selecting part 36 may preferably read out of the inference process temporary recording part 25 the influence factor corresponding to the item ID which has been read out and exclude those item IDs with influence factors lower than a specified value from the item IDs to be transmitted to the item data obtaining part 65 such that useless data of input items can be prevented from being obtained. Thereafter, the item data obtaining part 65 reads out data on the method of obtaining data corresponding to the identified and related items from the obtaining method recording part 29. FIG. 12 shows an example of item data obtaining method database recorded in the obtaining method recording part 29. As shown, the obtaining method recording part 29 stores for each input item the item ID for distinguishing the input item, data showing whether data on the input item are to be obtained either from a person or from the inspection result or they are to be obtained from both, a question ID for distinguishing a question when it is to be done by a person and data on a calculation algorithm when it is done by an inspection result. When the data on input item are obtained only from a person, NULL is entered as data on calculation algorithm. When the data on input item are obtained only from an inspection result, NULL is entered as question ID. In other words, the item data obtaining part 65 references the item data obtaining method database and obtains a question ID and/or a calculation algorithm corresponding to each of the identified and related items. When the data are to be obtained only either from a person or from an inspection result, the item data obtaining part 65 has only to judge whether they should be obtained from a person or from an inspection result based on the cost and the time of labor. Next, the item data obtaining part 65 obtains data on the identified and related items. This is to say that if a question ID is obtained from the obtaining method recording part 29, the item data obtaining part 65 transmits the question ID to the question generating part 34. The question generating part 34 generates a question by reading out from the question data recording part 24 data corresponding to the question ID received from the item data obtaining part 65. FIG. 13 shows an example of question database recorded in the question data recording part 24. As shown, the question database stores for each question the question ID, the content of the question and the selection branches of the response to the question. In other words, the question generating part 34 reads out the question and the selection branches corresponding to a question ID from the question data recording part 24. The question and the selection branches that have been read out are displayed on the display part 22. The response from the user is transmitted through the input part 21 and the question input-output control part 51 to the item data obtaining part 65. The item data obtaining part 65 generates data on the input item based on the received response. If data on calculation algorithm are obtained from the obtaining method recording part 29, the item data obtaining part 65 transmits the data on calculation algorithm to the characteristic quantity calculating part 35. The characteristic quantity calculating part 35 serves to obtain a characteristic quantity by carrying out a calculation based on the received data on calculation algorithm and transmits the obtained characteristic quantity to the item data obtaining part 65. The item data obtaining part 65 generates data on the input item based on the received characteristic quantity. The item data obtaining part 65 further serves to record the generated data on the input item together with the corresponding item ID in the inference process temporary recording part 25. FIG. 14 shows an example of data on input items recorded in the inference process temporary recording part 25. As shown, the data format of the input items is determined for each input item such as TRUE and FALSE corresponding to responses YES and NO, LARGE, MEDIUM and SMALL corresponding to responses large, medium and small, and numeral values corresponding to characteristic quantities. NULL is entered where data are not inputted yet. From the above, it can be easily judged whether or not data corresponding to each of the input items have been inputted. Next, the process of determining the aimed node by the aimed node determining part 66 is explained. If the data on an input item obtained by the item data obtaining part 65 satisfy the condition corresponding to this input item, the aimed node determining part 66 determines the node to which the condition branches as the aimed node. The aimed node determining part 66 pushes the node ID of the aimed node thus determined to the aimed node stack recording part 27. In this manner, the sub-network can be narrowed down. When questions are asked to the user for obtaining data on the input items, consistency in the flow of questions is not adversely affected because questions are asked corresponding to the input items in the sub-network which is sequentially narrowed down. If there is no input item on which the data are not worth obtaining by the item data obtaining part 65, the aimed node determining part 66 returns the aimed node back by popping it from the aimed node stack recording part 27. In this way, it is possible to return to the earlier wider sub-network and to search for an input item for which it is worth obtaining data. A similar flow of questions can be maintained by returning to the sub-network immediately before narrowed down. The process of inference is terminated when node IDs recorded in the aimed node stack recording part 27 cease to exist because of the popping since this means that there is no longer any input item in the causality network for which data are worth obtaining. The results of the diagnosis are displayed on the display device 22 through the factor output control part 52. Next, an example of causality network is explained with reference to FIG. 15. FIG. 15 shows a causality network for no-good result “defective bridge” for which the following eight no-good factors are candidates: “mounting displacement”, “bent lead”, “low flux activity of paste”, “oxidized component”, “dirty component”, “large paste area”, “paste displacement”, and “high heater temperature setting”. Diagnostic paths from no-good result “defective bridge” to these eight no-good factors are set as the knowledge of the network structure. In the case of the example of FIG. 15, the production rules obtained from the diagnostic paths leading to the three no-good factors “mounting displacement”, “bent lead” and “low flux activity of paste” are respectively as follows: IF ((lead and land contacting)=Yes & (component displacement)=(LARGE)) then (mounting displacement); IF ((lead and land contacting)=Yes & (component displacement)=(MEDIUM)) then (bent lead); and IF ((land with no paste)=Yes & (land with wetting problem)=Yes & (flux activity of paste)=(LOW)) then (low flux activity of paste). In the example of FIG. 15, since there are two diagnostic paths that lead to no-good factor “large paste area”, there are the following two production rules that are obtained: IF ((heat slump outside normal range)=Yes & (amount of paste)=(too much)) then (area of paste is too large); and IF ((paste wetting up to shoulder of lead)=Yes & (temperature of reflow oven)=(medium) then (area of paste is too large). In the example of FIG. 15, since the diagnostic path that leads to no-good factor “high heater temperature setting” includes a supplementary path, the production rule obtain obtained therefrom becomes as follows: IF ((paste wetting up to shoulder of lead)=Yes & (temperature of reflow oven)=(high) & (heater setting)=(high) & (paste wetting up all over substrate)=Yes) then (large paste area). Next, the flow of the factor estimating process is explained with reference to the flowchart shown in FIG. 16. As this process is started, the input display control part 31 causes a question screen to be displayed on the display part 22 (Step S1). An area for inputting a no-good result is provided to the question display area on this question screen. The user inputs a no-good result in this area and the inputted data area received by the question input-output control part 51 (Step S2), and the no-good result data are recorded in the inference process temporary recording part 25 by means of the inference process part 61. As a no-good result is inputted, the inference process part 61 extracts data on the causality network corresponding to this no-good result from the estimate knowledge recording part 23 (Step S3). At the time, the inference process part 61 obtains data on the causality network converted to a production rule by the knowledge conversion part 33, and the inference part 32 carries out the inference process based on the extracted causality network (Step S4). After the inference process is finished, the screen of the result of diagnosis is displayed on the display part 22 by the factor output control part 52 (Step S5). The factor estimating process is thereafter finished. Next, the flow of the inference process in Step S4 will be explained with reference to the flowchart of FIG. 17. As the inference process is started, the data of various kinds recorded in the inference process temporary recording part 25 are cleared first (Step S11), together with the data recorded in the aimed node stack recording part 27. Next, the aimed node determining part 66 treats a root node (node of a no-good result) as the aimed node and pushes the corresponding node ID to the aimed node stack recording part 27 (Step S12). Next, the data on input items recorded in the inference process temporary recording part 25 (as shown in FIG. 14) are referenced and it is judged whether or not there is any input item not having data obtained within the sub-network (Step S13). If such an input item exists (YES in Step S13), the influence calculating part 64 calculates the influence factor of each input item contained in the sub-network and records it in the inference process temporary recording part 25 (Step S14). The input items having data obtained are excluded because their influence factors are zero. Next, the item data obtaining part 65 judges whether or not there are input items with influence factor higher than a specified value (Step S15). If such an input item exists (YES in Step S15), the item data obtaining part 65 identifies the input item with the highest influence factor as the identified item (Step S116) and selects the input items that are in the same group as this identified item and have an influence factor higher than the specified value as related items (Step S117). Next, the item data obtaining part 65 obtains data on the identified and related items (Step S18). Next, the fitness calculating part 62 calculates the current fitness factor and the certainty calculating part 63 calculates the certainty factor based on the obtained data (Step S19). The corresponding node ID is then pushed to the aimed node stack recording part 27 with the node corresponding to the identified node as the aimed node (Step S20). The program returns thereafter to Step S13 and repeats the operations described above. If there is no input item not having data obtained within the sub-network (NO in Step S13) or if there is no input item with influence factor higher than the specified value (NO in Step S15), the aimed node determining part 66 judges whether the aimed node is a root node or not (Step S21). If the aimed node is not a root node (NO in Step S21), the aimed node determining part 66 returns the aimed node by popping it from the aimed node stack recording part 27 (Step S22), and the program returns thereafter to Step S13. If the aimed node is a root node (YES in Step S21), the inference process is terminated (Step S23) because this amounts to having no input item for which data are worth obtaining, and the program returns to the beginning, causing the factor output control part 52 to have an image of the result of the inference on the display part 22 (Step S5) and terminating the factor estimating process. Examples of display of diagnostic results are explained next with reference to FIGS. 18 and 19. The display screen according to these examples is provided with a question display area and a result display area. The question display area is for displaying the history of questions offered to the user during the course of the factor estimating process and the user's responses thereto. The question input-output control part 51 displays the history by reading out the history recorded in the inference process temporary recording part 25. The result display area is for displaying the diagnostic paths leading to the selected no-good factor. These diagnostic paths are extracted from the causality network by the inference process part 61, and the extracted diagnostic paths are displayed in the result display area by the factor output control part 52. On these diagnostic paths, numeral data on the fitness factors corresponding to the paths between nodes are displayed. Each path may be displayed with a thickness representing the corresponding fitness. It goes without saying, however, that this is not the only way to represent the fitness. Any display mode is usable if the user can easily recognize the degree of fitness. Thus, since the history of questions and responses regarding identified no-good factors and data on diagnostic paths are displayed, it is possible to demonstrate to the user the justification of the result of estimating factors. FIG. 18 shows an example of diagnostic result on no-good factor c1 corresponding to no-good result dl, and FIG. 19 shows another diagnostic result on no-good result “dirty component” corresponding to no-good result “defective bridge”. As indicated by these examples, a diagnostic result may be displayed even if data on all input items included in diagnostic paths are not obtained. A diagnostic result may be displayed under the condition where data on all input items included in diagnostic paths are obtained. It depends on the influence factor of each of the input items whether or not data on the input items can be obtained. Although an embodiment of the invention was shown above wherein the item data obtaining part 65 identifies the input item with the highest influence factor and obtains data on the identified and related items by selecting other input items which are in the same group as the identified item or the identified input item, the item data obtaining part 65 may instead calculate the total sum of the influence factors of the input items belonging to each group and obtain the data on the input items included in the group having the largest total sum of influence factors. Although the group database recorded in the related item recording part 28 according to the embodiment described above contains item IDs of the related input items for each group, the order of obtaining data of each input item may be contained. In such a case, the item data obtaining part 65 follows this order to ask questions to obtain responses or to obtain characteristic quantities from inspection data. The aforementioned group database may include the order in which an analysis is carried out after data on each input item are obtained. In such a case, the item data obtaining part 65 follows this order to calculate the fitness and certainty factors after obtaining data of each input item. Since important input items may be analyzed first, it is preferable for the aimed node determining part 66 to push the aimed node stack recording part 27 in the reverse order. In this case, the node corresponding to the input item which is the first in the order becomes the aimed node. According to the embodiment described above, the aimed node determining part 66 considers the root node as the first aimed node. In this case, the sub-network becomes the same as the causality network, making the search area large such that it becomes time-consuming to obtain the influence factor of each input item. For this reason, the input items may be preliminarily classified on the basis of a specified condition such as the type of the steps such that the search area of the sub-network may be somewhat narrowed down by the user specifying a class. FIG. 20 shows another example of causality network related to the substrate mounting process. The substrate mounting process consists roughly of the following three steps, the printing step, the mounting step and the reflow step, and input items are preliminarily classified into these steps. In this example, nodes P1, P2, P5 and P9-P12 and input items T1, T2 and T6-T13 are classified into the printing step, nodes P3, P6, P7 and P13-P15 and input items T3, T4, T9 and T14-T19 are classified into the mounting step and nodes P4, P8 and P16-P18 and input items T5, T15, T16 and T18-T21 are classified into the reflow step. If the user guesses that the no-good factor is in the printing step and specifies the classification of the printing step, it is possible to narrow down to the sub-network including nodes P1, P2, P5 and P9-P12 and input items T1, T2 and T6-T13 and to reduce the time for obtaining the influence factor of each of the input items in the sub-network. When the aimed node returns again to the root node, those related to the printing step can be excluded from the search area and the time for obtaining the influence factor of each input item can be prevented from significantly increasing. The description given above is not intended to limit the invention. Many modifications and variations are possible within the scope of the invention. For example, although the invention was described above as applied to a process managing system for estimating no-good factors for a production line, the invention is not limited to process managing systems but may also be applied to different kinds of software as an aid to responding to a claim process, aid systems for workers carrying out periodic inspections and devices of different kinds for estimating factors such as tools for aiding the sale of customized products. Each block of the control part 30 of the process managing device 10 may be formed by hardware logic or may be realized by software by using a CPU. Explained more specifically, the control part 30 may comprise a CPU for carrying out instructions of a control program for realizing various functions, a ROM for storing this program, a RAM for the development of the program and memory media such as memory device for recording the program as well as data of various types. The object of the present invention can be accomplished by supplying the control part 30 with a memory medium recording the program code (executable program, intermediate code program and source program) of the control program of the control part 30, or the software for carrying out the aforementioned functions, in a computer-readable form and causing this computer (CPU or MPU) to read out the program code recorded on the memory medium and execute it. Examples of the aforementioned tangible memory medium include tapes such as magnetic tapes and cassette tapes, disks such as magnetic disks including floppy and hard disks and optical disks including CD-ROM, MO, MD, DVD and CD-R, cards such as IC cards (inclusive of memory cards) and optical cards and semiconductor memories such as mask ROM, EPROM, EEPROM and flash ROM. The control part 30 may be structured to be connectable to a communication network such that the program code can be supplied through the communication network. There is no particular limitation as to the kind of communication network. Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone network, mobile communication network and satellite communication network may be used. There is no particular limitation as to transmission medium forming the communication network. Lines such as IEEE1394, USB, power transmission, cable TV lines, telephone lines and ADSL lines and wireless means such as IrDA and remote control infrared lines, Bluetooth®, 802.22 wireless, HDR, portable telephone network, satellite lines and ground wave digital network may be utilized. The present invention can be realized also in the form of computer data signal buried in carrier waves. Factor estimating devices of this invention are useful to a process managing system for estimating no-good factors for a production line but this does not limit the invention. They are applicable to apparatus of different types for estimating factors such as software for aiding claim processing, systems for aiding workers carrying out periodic inspections and tools for aiding the sale of customized products. |
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041939530 | claims | 1. A method of producing breeder or fuel and breeder kernels for fuel elements of nuclear reactors comprising the steps of: making a hydrosol containing a dispersed particle phase selected from the group consisting of thorium oxide and mixtures thorium oxide and uranium (VI) oxide which mixtures have a hexavalent uranium content not exceeding 25% by weight of the aggregate amount of heavy metal, and hydrosol having a heavy metal concentration between 1.5 and 3 moles per liter, and injecting said hydrosol substantially horizontal in the form of drops into a gas phase enriched with ammonia gas overlying an ammonium hydroxide containing precipitation bath held at a pH value between 8 and 9, so that said drops fall by gravity through said gas phase while being affected by the ammonia content thereof and are immersed in said precipitation bath and hardened therein. 2. A method as defined in claim 1 in which said precipitation bath contains ammonium nitrate at a concentration of at least 3 moles per liter. 3. A method as defined in claim 1 or 2 in which the injection of said hydrosol into said gas phase in the form of drops is carried out at a hydrosol temperature between 30.degree. C. and 60.degree. C. |
abstract | A radioactive material sequestration system may include a radionuclide containment composition dispenser and a sorption based media container. The radionuclide containment composition dispenser may be configured for holding a radionuclide containment composition and be capable of dispensing the radionuclide containment composition to remove radionuclides from a radioactive material. The radionuclide containment composition is a mixture of a clay mineral and water. The sorption based media container may be configured for holding a sorption based media; receiving dispensed radionuclide containment composition; and sequestering the radionuclides. The radioactive material sequestration system may also include a probe. |
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claims | 1. A method of inspecting an underwater pipeline to determine wall thickness or information about contents of the underwater pipeline, the method comprising:interposing the underwater pipeline between a gamma radiation source and an array of detector units, the gamma radiation source and the array of detector units being mounted in a fixed relationship with each other on a support so that radiation emitted by the gamma radiation source passes along a plurality of paths through a portion of the underwater pipeline and impinges upon the array of detector units;rotating the support, the gamma radiation source, and the array of detector units around a circumference of the underwater pipeline and acquiring data at a plurality of radially offset positions around the underwater pipeline to acquire density data at a variety of angles through the underwater pipeline; andpresenting a representation of the underwater pipeline or contents of the underwater pipeline using the density data;wherein the support, the gamma radiation source, and the array of detector units are provided on an apparatus that comprises a buoyancy material. 2. The method according to claim 1, wherein the apparatus is hinged so that the apparatus is configured to be opened and closed around the underwater pipeline. 3. The method according to claim 1, wherein the representation is a representation of a composition of the underwater pipeline or its contents. 4. The method according to claim 1, wherein presenting a representation comprises building the representation using tomography algorithms. 5. The method according to claim 1, further comprising detecting a void in the underwater pipeline. 6. The method according to claim 1, further comprising detecting a crack in the underwater pipeline. 7. The method according to claim 1, further comprising detecting wall thinning in the underwater pipeline. 8. The method according to claim 1, further comprising detecting a gas hydrate within the underwater pipeline. 9. The method according to claim 1, further comprising detecting scale within the underwater pipeline. 10. The method according to claim 1, further comprising detecting a change in density relative to a reference value. 11. The method according to claim 10, wherein the reference value is a calculated value. 12. The method according to claim 10, wherein the reference value is a value from an adjacent portion of the underwater pipeline. |
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047391731 | abstract | A collimator apparatus (10 or 100) including one or more bundles of nested rods (11, 11a or 101 or 101a or 201) which define a surface (112, 112a) which interferes with a beam of radiation is described. The apparatus particularly uses coil spring (48) between and along the axis (a--a or c--c) of the rods which are compressed by blocks (13, 14, 13a and 14a or 103, 104, 103a and 104a) to lock the rods in position in holes in the blocks. The apparatus is particularly useful for shaping radiation beams for patient treatment. |
claims | 1. A seal apparatus for a jet pump slip joint in a boiling water nuclear reactor pressure vessel, the jet pump comprising a jet pump inlet mixer and a jet pump diffuser joined by a slip joint, the diffuser comprising a plurality of guide ears spaced circumferentially around the diffuser, said seal apparatus comprising: a split seal ring; and a segmented diaphragm spring having a first side, a second side, an inner circumference, and an outer circumference, said diaphragm spring engaging said split seal ring at said inner circumference of said diaphragm spring, said diaphragm spring comprising a plurality of latch assemblies spaced circumferentially around said outer circumference, each said latch assembly configured to engage a diffuser guide ear. 2. A seal apparatus in accordance with claim 1 wherein said diaphragm spring further comprises: claim 1 a seal ring engagement portion depending from said second surface and extending around said inner circumference, said seal engagement portion configured to engage said seal ring; a support portion depending from said second surface and extending around said outer circumference, said plurality of latch assemblies coupled to said support portion; and a plurality of slots extending from said inner circumference to said support portion, said slots spaced circumferentially around said inner circumference. 3. A seal apparatus in accordance with claim 1 wherein each said latch assembly comprises a latch bolt and said diaphragm spring comprises a plurality of latch bolt openings, each said latch bolt extending through a corresponding latch bolt opening. claim 1 4. A seal apparatus in accordance with claim 3 wherein said latch bolt comprises a head and a plurality of ratchet teeth spaced around the periphery of said latch bolt head. claim 3 5. A seal apparatus in accordance with claim 4 wherein said diaphragm spring further comprises a locking spring coupled to said first surface of said diaphragm spring, said locking spring engaging said ratchet teeth of said latch bolt. claim 4 6. A seal apparatus in accordance with claim 3 wherein said latch assembly further comprises at latch arm, said latch arm comprising a threaded latch bolt opening, said latch bolt extending through and threadedly engaging said latch bolt opening, said latch arm configured to engage a diffuser guide ear. claim 3 7. A seal apparatus in accordance with claim 6 wherein said latch arm comprises a slot sized to receive a diffuser guide ear. claim 6 8. A jet pump for a boiling water nuclear reactor, said jet pump comprising: an inlet mixer; a diffuser coupled to said inlet mixer by a slip joint, the diffuser comprising a plurality of guide ears spaced circumferentially around the diffuser; and a seal apparatus comprising a split seal ring, and a segmented diaphragm spring having a first side, a second side, an inner circumference, and an outer circumference, said diaphragm spring engaging said split seal ring at said inner circumference of said diaphragm spring, said diaphragm spring comprising a plurality of latch assemblies spaced circumferentially around said outer circumference, each said latch assembly configured to engage a diffuser guide ear. 9. A jet pump in accordance with claim 8 wherein said diaphragm spring further comprises: claim 8 a seal ring engagement portion depending from said second surface and extending around said inner circumference, said seal engagement portion configured to engage said seal ring; a support portion depending from said second surface and extending around said outer circumference, said plurality of latch assemblies coupled to said support portion; and a plurality of slots extending from said inner circumference to said support portion, said slots spaced circumferentially around said inner circumference. 10. A jet pump in accordance with claim 8 wherein each said latch assembly comprises a latch bolt and said diaphragm spring comprises a plurality of threaded latch bolt openings, each said latch bolt extending through a corresponding latch bolt opening. claim 8 11. A jet pump in accordance with claim 10 wherein said latch bolt comprises a head and a plurality of ratchet teeth spaced around the periphery of said latch bolt head. claim 10 12. A jet pump in accordance with claim 11 wherein said diaphragm spring further comprises a locking spring coupled to said first surface of said diaphragm spring, said locking spring engaging said ratchet teeth of said latch bolt. claim 11 13. A jet pump in accordance with claim 10 wherein said latch assembly further comprises a latch arm, said latch arm comprising a threaded latch bolt opening, said latch bolt extending through and threadedly engaging said latch bolt opening, said latch arm configured to engage a diffuser guide ear. claim 10 14. A jet pump in accordance with claim 13 wherein said latch arm comprises a slot sized to receive a diffuser guide ear. claim 13 15. A method of repairing a jet pump slip joint, the jet pump comprising a jet pump inlet mixer and a jet pump diffuser joined by a slip joint, the diffuser comprising a plurality of guide ears spaced circumferentially around a first end of the diffuser, said method comprising the steps of: coupling a seal apparatus to the slip joint, the seal apparatus comprising a split seal ring and a segmented diaphragm spring having a first side, a second side, an inner circumference, and an outer circumference, said diaphragm spring configured to engage the split seal ring at the inner circumference of the diaphragm spring, the diaphragm spring comprising a plurality of latch assemblies spaced circumferentially around the outer circumference, each latch assembly configured to engage a diffuser guide ear. 16. A method in accordance with claim 15 wherein the diaphragm spring further comprises a seal ring engagement portion depending from the second surface and extending around the inner circumference, the seal engagement portion configured to engage the seal ring, a support portion depending from the second surface and extending around the outer circumference, the plurality of latch assemblies coupled to the support portion, and a plurality of slots extending from the inner circumference to the support portion, the slots spaced circumferentially around the inner circumference, and coupling a seal apparatus to the slip joint comprises the steps of: claim 15 positioning the split ring seal on the first end of the diffuser; and positioning the diaphragm spring on the first end of the diffuser with a spring slot engaging each of the diffuser guide ears. 17. A method in accordance with claim 16 wherein each latch assembly comprises a latch bolt and the diaphragm spring comprises a plurality of threaded latch bolt openings, each latch bolt extending through a corresponding latch bolt opening, the latch bolt comprising a head and a plurality of ratchet teeth spaced around the periphery of the latch bolt head. claim 16 18. A method in accordance with claim 17 wherein the latch assembly further comprises a latch arm, the latch arm comprising a threaded latch bolt opening, the latch bolt extending through and threadedly engaging the threaded latch bolt opening, the latch arm further comprising a slot sized to receive a diffuser guide ear, and coupling a seal apparatus to the slip joint further comprises the steps of: claim 17 tightening the latch bolt of each latch assembly so that latch arms swing into position and engage a corresponding guide ear; installing the inlet mixer through the split ring seal and diaphragm spring and into the diffuser to form the slip joint; tightening the latch bolt further to capture the latch arm slot against the guide ear to engage the seal ring with the seal engagement portion of the diaphragm spring; and locking the latch bolt. 19. A method in accordance with claim 18 wherein the diaphragm spring further comprises a locking spring coupled to the first surface of the diaphragm spring, the locking spring configured to engage the ratchet teeth of the latch bolt, and locking the latch bolt comprises the step of engaging the ratchet teeth of the clamp bolt head with the locking spring. claim 18 20. A method in accordance with claim 15 further comprising the step of disassembling the inlet mixer from the diffuser prior to coupling the seal apparatus to the slip joint. claim 15 |
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047599049 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite of FIGS. 1A and 1B is an elevational view, partly in cross-section, of a pressurized water reactor 10 comprising a pressure vessel 12 including an upper dome, or head assembly, 12a, cylindrical sidewalls 12b and a bottom closure 12c comprising the base of the reactor 10. Plural radially oriented inlet nozzles 11 and outlet nozzles 13 (only one (1) of each appearing in FIGS. 1A and 1B) are formed in the sidewall 12b, adjacent the upper, annular end surface 12d of the sidewall 12b. Whereas the cylindrical sidewall 12b may be integrally joined, as by welding, to the bottom closure 12c, the head assembly 12a is removably received on the upper, annular end surface 12d of the sidewall 12b and secured thereto. The sidewall 12b further defines an inner, generally annular mounting ledge 12e for supporting various internals structures as later described. Within the bottom closure 12c, as schematically indicated, is so-called bottom-mounted instrumentation 14. The lower barrel assembly 16 comprises a generally cylindrical sidewall 17 affixed at its lower end to a lower core plate 18, which is received on mounting support 18b, as generally schematically illustrated. The cylindrical sidewall 17 extends substantially throughout the axial height of the vessel 12 and includes an annular mounting ring 17a at the upper end thereof which is received on the annular mounting ledge 12e thereby to support the assembly 16 within the vessel 12. As will be rendered more apparent hereafter, the sidewall 17 is solid in the vicinity of the inlet nozzles 11, but includes an aperture 17b having a nozzle ring 17c mounted therein which is aligned with and closely adjacent to the outlet nozzle 13. An upper core plate 19 is supported on a mounting support 17d affixed to the interior surface of the cylindrical sidewall 17 at a position approximately one-half the axial height thereof. Fuel rod assemblies 20 are positioned in generally vertically oriented, parallel axial relationship within the lower barrel assembly 16 by bottom mounts 22 carried by the lower core plate 18 and by pin-like mounts 23 carried by, and extending through, the upper core plate 19. Flow holes 18aand 19a(only two of which are shown in each instance) are provided in predetermined patterns, extending substantially throughout the areas of the lower and upper core plates 18 and 19, the flow holes 18a permitting passage of a reactor coolant fluid into the lower barrel assembly 16 in heat exchange relationship with the fuel rod assemblies 20 defining the reactor core, and the flow holes 19a permitting passage of the core output flow into the inner barrel assembly 24. A neutron reflector and shield 21 is mounted interiorly of the cylindrical sidewalls 17, in conventional fashion. The inner barrel assembly 24 includes a cylindrical sidewall 26 which is integrally joined at its lower edge to the upper core plate 19. The sidewall 26 has secured to its upper, open end, an annular mounting ring 26a which is received on an annular hold-down spring 27 and supported along with the mounting ring 17a on the mounting ledge 12e. The sidewall 26 further includes an aperture 26b aligned with the aperture 17b and the output nozzle 13. Within the inner barrel assembly 24, and densely packed within the cylindrial sidewall 26, are positioned a plurality of rod guides in closely spaced, parallel axial relationship; for simplicity of illustration, only two such rod guides are shown in FIGS. 1A and 1B namely rod guide 28 housing a cluster of radiation control rods 30 (RCC) and a rod guide 32 housing a cluster of water displacement rods 34 (WDRC). The rods of each RCC cluster 30 and of each WDRC cluster 34 are mounted individually to the respectively corresponding spiders 100 and 120. Mounting means 36 and 37 are provided at the respective upper and lower ends of the rod guide 28 and, correspondingly, mounting means 38 and 39 are provided at the respective upper and lower ends of the rod guide 32, the lower end mounting means 37 and 39 mounting the respective rod guides 28 and 32 to the upper core plate 19, and the upper mounting means 36 and 38 mounting the respective rod guides 28 and 32 to a calandria assembly 50, and particularly to a lower calandria plate 52. The calandria assembly 50, disclosed in greater detail in FIG. 3 and subsequently discussed in relation thereto, includes, in addition to the lower calandria plate 52, an upper calandria plate 54 which is the main support plate of the calandria assembly 50, and is joined to an annular flange 50a which is received on the flange 26a to support the calandria assembly 50 on the mounting ledge 12e. A plurality of parallel axial calandria tubes 56 and 57 are positioned in alignment with corresponding apertures in the lower and upper calandria plates 52 and 54, to which the calandria tubes 56 and 57 are mounted at their respective, opposite ends. More specifically, calandria extensions 58 and 59 extend through corresponding apertures in and are secured to the lower calandria plate 52, and the corresponding calandria tubes 56 and 57 are respectively secured to the extensions 58 and 59. Similarly, the upper ends of the calandria tubes 56 and 57 are connected to the upper calandria plate 54. The specific configuration of the connections of the calandria tubes 56 and 57 are significant to the present invention and are discussed with reference to FIGS. 3 and 4-7. For the specific configurations of the respective calandria extensions 58 and 59 as illustrated, only the calandria extensions 58 project downwardly from the lower calandria plate 52 and connect to corresponding mounting means 36 for the upper ends, or tops, of the RCC rod guides 28. The upper end mounting means 38, associated with the WDRC rod guides 32, may be interconnected by flexible linkages to the mounting means 36 of the RCC rod guides 28, in accordance with the invention of the U.S. Pat. No. 4,687,628 entitled: "FLEXIBLE ROD GUIDE SUPPORT STRUCTURE FOR INNER BARREL ASSEMBLY OF PRESSURIZED WATER REACTOR"--Gillett et al., assigned to the common assignee hereof. Alternatively, the WDRC rod guides 32 may be connected independently to the lower calandria plate 52 by the top end support structure of the invention disclosed in the copending application, entitled: "TOP END SUPPORT FOR WATER DISPLACEMENT ROD GUIDES OF PRESSURIZED WATER REACTOR"--Gillett et al., Ser. No. 798,194, filed Nov. 14, 1985, and allowed July 22, 1987 assigned to the common assignee hereof; in the latter instance, the calandria extensions 59 likewise project downwardly from the plate 52, similarly to the extensions 58, to engage and laterally support the WDRC mounting means 38. Extending upwardly beyond the upper calandria plate 54 and, more particularly, within the head assembly 12a of the vessel 12, there are provided plural flow shrouds 60 and 61 respectively aligned with and connected to the plural calandria tubes 56 and 57. A corresponding plurality of head extensions 62 and 63 is aligned with the plurality of flow shrouds 60, 61, the respective lower ends 62a and 63a being flared, or bell-shaped, so as to facilitate assembly procedures and, particularly, to guide the drive rods (not shown in FIG. 1) into the head extensions 62, 63 as the head assembly 12a is lowered onto the mating annular end surface 12d of the vessel sidewall 12b. The flared ends 62a, 63a also receive therein the corresponding upper ends 60a, 61a of the flow shrouds 60, 61 in the completed assembly, as seen in FIG. 1. The head extensions 62, 63 pass through the upper wall portion of the head assembly 12a and are sealed thereto. Control rod cluster (RCC) displacement mechanisms 64 and water displacement rod cluster (WDRC) displacement mechanisms 66 are associated with the respective head extensions 62, 63 flow shrouds 60, 61 and calandria tubes 56, 57 which, in turn, are associated with respective clusters of radiation control rods 30 and water displacement rods 34. The RCC displacement mechanisms (CRDM's) 64 may be of well known type, as are and have been employed with conventional reactor vessels. The displacer mechanisms (DRDM's) 66 for the water displacer rod clusters (WDRC's) 34 may be in accordance with the disclosure of U.S. Pat. No. 4,439,054--Veronesi, assigned to the common assignee hereof. The respective drive rods associated with the CRDM's 64 and the DRDM's 66 are structurally and functionally the equivalent of an elongated, rigid rod extending from and in association with the respective CRDM's 64 and DRDM's 66 to the respective clusters of radiation control rods (RCC's) and water displacements rods (WDRC's) 30 and 34 and particularly, are connected at their lower ends to the spiders 100 and 120. The CRDM's and DRDM's 64 and 66 thus function through the corresponding drive rods to control the respective vertical positions of, and particularly, selectively to lower and/or raise, the RCC's 30 and the WDRC's 34 through corresponding openings (not shown) provided therefore in the upper core plate 19, telescopingly into or out of surrounding relationship with the respectively associated fuel rod assemblies 20. In this regard, the interior height D.sub.1 of the lower barrel assembly 16 is approximately 178 inches, and the active length D.sub.2 of the fuel rod assemblies 20 is approximately 153 inches. The interior, axial height D.sub.3 is approximately 176 inches, and the extent of travel, D.sub.4, of the rod clusters 30 and 34 is approximately 149 inches. It follows that the extent of travel of the corresponding CRDM and DRDM drive rods is likewise approximately 149 inches. While the particular control function is not relevant to the present invention, insofar as the specific control over the reaction within the core is effected by the selective positioning of the respective rod clusters 30 and 34, it is believed that those skilled in the art will appreciate that moderation or control of the reaction is accomplished in accordance with the extent to which the control rod clusters 30 are inserted into or withdrawn from the core and with the effective water displacement which is achieved by selective positioning of the water displacement rod clusters 34. The RCC's 30 are adjusted in position relatively frequently, compared to the WDRC's 34, to achieve the desired power output level from the reactor. Conversely, the WDRC's 34, initially, are lowered, or inserted, fully into the lower barrel assembly 16 at the initiation of each fuel cycle. The WDRC's 32, through their respective drive rods (not shown in FIG. 1) and DRDM's 66, then are selectively removed as the excess reactivity is depleted, over the fuel cycle. Typically, this is performed by simultaneously removing a group of four such WDRC's 34 from their fully inserted positions in association with the fuel rod assemblies 20, to a fully raised position within the corresponding WDRC guides 32 and thus within the inner barrel assembly 24, in a continuous and controlled withdrawal operation. More specifically, the four WDRC's 34 of a given group are selected so as to maintain a symmetrical power balance within the reactor core, when the group is withdrawn. Typically, all of the WDRC's 34 remain fully inserted in the fuel rod assemblies 20 for approximately 60% to 70% of the approximately 18 month fuel cycle. Groups thereof then are selectively and successively moved to the fully withdrawn position as the excess reactivity is depleted, so as to maintain a nominal, required level of reactivity which can sustain the desired output power level, under control of the variably adjustable RCC's 30. The reactor coolant fluid, or water, flow through the vessel 10 proceeds generally from a plurality of inlet nozzles 11, one of which is seen in FIG. 1, downwardly through the annular chamber 15 is between an outer generally cylindrical surface defined by the interior surface of the cylindrical sidewall 12b of the vessel 12 and an inner generally cylindrical surface defined by the cylindrical sidewall 17 of the lower barrel assembly 16. The flow then reverses direction and thereafter passes axially upwardly through flow holes 18a in the lower core plate 18 and into the lower barrel assembly 16, from which it exits through a plurality of flow holes 19a in the upper core plate 19 to pass into the inner barrel assembly 24, continuing in parallel axial flow therethrough and finally exiting upwardly through flow holes 52a in the lower calandria plate 52. Thus, parallel axial flow conditions are maintained through both the lower and inner barrel assemblies 16 and 24. Within the calandria 50, the flow in general turns through 90.degree. to exit radially from a plurality of outlet nozzles 13 (one of which is shown in FIG. 1). The inlet coolant flow also proceeds into the interior region of the head assembly 12a through perimeter bypass passageways in the mounting flanges received on the ledge 12e. Particularly, a plurality of holes 170, angularly spaced and at a common radius, are formed in the flange 17a and provide axially-directed flowpaths from the annular chamber 15 into the annular space 172 intermediate the spring 27 and the interior of the sidewalls of the vessel 12; further, a plurality of aligned holes 174 and 176 extend through the flanges 26a and 50a, the holes 174 being angularly oriented, to complete the flow paths from the annular space 172 to the interior of the head assembly 12a. The flow of coolant proceeds from the head region through annular downcomer flow paths defined interiorly of certain of the flow shrouds 60, 61 and calandria tubes 56, 57, as later described, from which the head coolant flow exits into the top region of the inner barrel assembly 24, just below the lower calandria plate 52, to mix with the core outlet flow and pass through the calandria 50, exiting from the outlet nozzles 13. The head coolant flow maintains the head assembly 12a at a significantly reduced temperature, relative to the rest of the vessel 12, as is required for the equipment mounted thereon, such as the CRDM's 64. As later discussed, the head region also serves as a coolant reservoir, from which the coolant may flow rapidly through downcomer flow paths, in a so-called blowdown operation, to cool the nuclear core of fuel rod assemblies 20, in the event of a LOCA. The pressure of the cycle water, or reactor coolant, within the head region typically is in the range of about 2,250 psi, and provides the energy source, i.e., fluid pressure, to the DRDM's 66 for raising the DRDM drive rods from a fully inserted to a fully withdrawn, or up position, as described more fully in the related, above-identified patent. In this regard, the core outlet flow is at a relatively reduced pressure, due to pressure drops imposed by the passage of the coolant through the lower and upper barrel assemblies 16 and 20 and especially the fuel assemblies 20. FIG. 2 is a cross-sectional, schematic bottom planar view of the lower calandria plate 52 at a position in FIGS. 1A and 1B intermediate the mounting means 36 and 38 for the RCC and WDRC rod guides 28 and 32, respectively, and the plate 52; further, FIG. 2 is on an enlarged scale, and represents only a fragmentary quadrant of the internal structure of the calandria 50 for illustrating diagramatically the dense packing of the arrays of plural control and water displacer rod clusters 30 and 34 within the inner barrel assembly 24. Each of the circles labelled "D" designates an aperture, or hole, in the calandria plate 52 through which is received a corresponding DRDM drive rod, associated with a corresponding WDRC cluster 34; similarly, each of the circles marked "C" designates an aperture in the calandria plate 52 through which is received a corresponding CRDM drive rod, associated with a corresponding RCC cluster 30. These apertures C and D, along with the corresponding RCC and WDRC calandria tubes 56 and 57, and the corresponding shrouds 60 and 61 define downcomer flow paths, relative to the drive rods received therethrough. Further, the circles 52a in the lower calandria plate 52 in FIG. 2 correspond to the apertures 52a shown in FIG. 1, which provide for passage of the reactor coolant output flow from the inner barrel assembly 24 into the calandria assembly 50. Elements 74 comprise leaf springs which are mounted by bolts 76 to the calandria lower plate 52 in oppositely oriented pairs, generally in alignment with the diameters of the RCC associated apertures "C," in an alternating, orthogonally related pattern. The free ends of the springs 74 bear downwardly upon the upper surfaces of the RCC mounting means 36 of a next-adjacent aperture "C," so as to provide a frictional force opposing lateral displacement thereof and accordingly of the associated rod guide 28, while affording a degree of flexibility to the axial position of the rod guide. While the use of springs 74 is one preferred structural mounting means for the RCC guides, in accordance with the disclosure of the above noted, U.S. Pat. No. 4,687,628 entitled: "FLEXIBLE ROD GUIDE SUPPORT STRUCTURE FOR INNER BARREL ASSEMBLY OF PRESSURIZED WATER REACTOR," alternative mounting means may be employed for this purpose and thus the foregoing described structure is not to be deemed limiting in any sense, but merely illustrative. As will be apparent by comparison of FIGS. 1 and 2, the RCC clusters and WDRC clusters are disposed in densely packed, interleaved arrays, substantially across the entire cross-sectional area of the inner barrel assembly 24. The RCC and WDRC rod clusters 30 and 34 are supported by corresponding spiders 100 and 120, as illustratively shown in FIG. 1, in turn connected through corresponding drive rods to the CRDM's 64 and DRDM's 66, as hereafter described. FIG. 3 is an enlarged, elevational and cross-sectional, fragmentary view of the calandria 50, as removed from the vessel 12 and including the shrouds 60, 61 associated with the calandria tubes 56, 57, respectively. The connections of the lower ends of the calandria tubes 56 and 57 through the extensions 58, 59 to the lower calandria plate 52 are shown in greater details in FIGS. 4 and 5, respectively; the connections of the upper ends of the calandria tubes 56 and 57, and of the lower ends of the respectively associated shrouds 60 and 61, to the upper calandria plate 54 are shown in greater detail in FIGS. 6 and 7. Each of FIGS. 4 through 7 is in vertical cross-section as in FIG. 3, and on a greatly enlarged scale relatively thereto. Concurrent reference will be had in the following to FIGS. 3 through 7. The calandria assembly 50, as now seen more clearly in FIG. 3, comprises a generally cylindrical, flanged shell 150 formed of a composite of the flange 50a, an upper connecting cylinder 152 which is welded at its upper and lower edges to the flange 50a and to the upper calandria plate 54, respectively, and a lower connecting cylinder, or skirt, 154 which is welded at its upper and lower edges to the upper and lower calandria plates 54 and 52, respectively. The lower connecting cylinder, or skirt, 154 includes an opening 154a aligned with each of the outlet nozzles 13 such that the axial core outlet flow received within the calandria 52 through the openings 52a in the lower calandria plate 52 may turn through 90.degree. and exit radially from within the calandria 52 through the opening 154a to the outlet nozzle 13. As best seen in FIGS. 4 and 5, the extensions 58 and 59 for the calandria tubes 56 and 57 are received through corresponding mounting holes 158 and 159 in the lower calandria plate 52, and which are counterbored so as to define "J-shaped" cross-sectional annuli 158a and 159a surrounding the circumferences of the corresponding extensions 58 and 59. Full penetration welds 158b and 159b then are formed in the interfaces of the J-shaped annuli 158a and 159a and the contiguous circumferential surfaces of the respective extensions 58 and 59, respectively, affording flexible annular weld joints therebetween. The respective calandria tubes 56 and 57 are then butt welded at their lower ends to the inclined, upper end surfaces 58a and 59a of the respective extensions 58 and 59. The extensions 58 and 59 in conjunction with the annuli 158a and 159a and the flexible annular weld joints 158b and 159b thus afford a flexible connecting means between the lower ends of the calandria tubes 56 and 57 and the lower calandria plate 52. As before noted, the extensions 59 associated with the WDRC drive rods 201 and the WDRC rod guides 38, rather then being flush with the lower surface of the lower calandria plate 52, instead may be elongated and project axially downwardly, similarly to the extensions 58 associated with the RCC rod guides 36, to engage independent mounting means 38 for the WDRC rod guides 32, where the latter are not flexibly linked to the mounting means 36 for the RCC rod guides 28, all in accordance with the disclosures of the above identified copending applications. The means for connecting the calandria tubes 56 and 57 with the upper calandria plate 54 are illustrated in FIGS. 6 and 7, respectively, to which reference is now had. Mounting holes 160 and 161 are formed through the upper calandria plate 54, within which are received respective connectors 162 and 163 which are butt welded at their lower ends 162a, 163a to the upper ends of the corresponding calandria tubes 56, 57, and at their upper ends 162b, 163b, to the lower ends of the corresponding shrouds 60, 61. The connectors 162, 163 have respective annular mounting collars 164, 165, which are radially enlarged so as to be juxtaposed in contiguous relationship with the sidewalls of the holes 160, 161 adjacent the upper surface of the upper calandria plates 54, and corresponding full penetration welds 166, 167 are formed therebetween. As seen from FIGS. 4 and 6, and FIGS. 5 and 7, respectively, RCC drive rod 200 and WDRC drive rod 201 are received through the respective calandria tubes 56 and 57, the corresponding extensions 58 and 59, the connectors 162 and 163, and the shrouds 160 and 161 respectively, for interconnecting the corresponding RCC and WDRC drive mechanisms 64 and 66 with the respective spiders 100 and 120 and the corresponding, associated RCC rod clusters 30 and WDRC rod clusters 34. From FIG. 3, it will be particularly clear that the calandria assembly 50 is a redundant structure, in that the spacing of the upper and lower calandria plates 54 and 52 is defined by both the connecting cylinder, or skirt, 154 and the calandria tubes 56, 57, all of which are connected at their respective upper and lower ends to the calandria plates 52 and 54, as hereinbefore described and specifically illustrated and discussed with reference to FIGS. 3 through 7. The rigidity of the structure is necessary to afford adequate structural stability and to withstand flow induced vibration forces thereby to prevent excessive wear of internal components and, particularly, the drive rods 200 and 201 and the attached rod clusters 30 and 34. However, due to thermal transients and steady state differentials produced by the core outlet flow relative to the low temperature coolant in the head assembly 12a, significant thermal stresses may develop within the calandria assembly 50, which may cause some degree of bending or distortion of the main support, upper calandria plate 54. Due to the respectively different configurations of an temperature distributions on the plates 52 and 54, the connecting cylinder, or skirt, 154 and the calandria tubes 56, 57, and the tendency of the plate 54 to be distorted, significant axial thermal stresses potentially could develop. The present invention affords a structure which minimizes those thermal stresses and limits same to an acceptable level. Particularly, the lower calandria plate 52 is of approximately 1.50" in thickness and is provided with a generally symmetrical pattern of flow holes 52a disposed about each of the mounting holes 158 and 159, as before described; as a result, the lower calandria plate 52 is relatively flexible, especially in comparison to the upper calandria plate 54. Moreover, the J-shaped annuli 158a and 159a provide adequate integrity of the welded joints 158b and 159b and lateral rigidity, or stiffness, yet afford axial flexibility. These combined factors thus compensate for the axially-directed thermal stresses and associated bending stresses which otherwise would develop. Within the head assembly 12a, the flow shrouds 60, 61 protect the drive rods 200, 201 from the head coolant flow which, if the drive rods 200, 201 were directly subjected thereto, could produce vibration due to the long, unsupported lengths of the drive rods 200, 201 passing through that region. The presence of the flow shrouds 60, 61, while necessary for this purpose, introduces a problem with regard to the coolant flow from the head region during blowdown. Particularly, in the event of a loss of coolant accident (LOCA), the entirety of the coolant in the interior of the head assembly 12a, i.e., the head region, must be available to pass through the downcomer flow paths and reach the nuclear core of fuel rod assemblies 20 within the lower barrel assembly 16, for cooling same. As before noted, the downcomer flow paths 210 and 211 are defined by the spacing annuli between the respective drive rods 200, 201 and, variously, the associated flow shrouds 60, 61, the calandria tubes 56, 57 and their associated connecting structures, and thence through the inner barrel assembly 24 and the apertures 19a of the upper core plate 19 into the core region, comprising the fuel assemblies 20 of the lower barrel assembly 16. In this regard, it will be understood that the flow shrouds 60, 61, while received within the flared ends 62a, 63a of the head extensions 62, 63, are not sealed thereto. However, since the flow shrouds 60, 61 necessarily have solid cylindrical sidewalls, once the head region drains to the tops of the flow shrouds 60, 61 during blowdown, the remaining coolant is trapped in the head region and can no longer enter the downcomer flowpath and drain into the core. The present invention affords a solution to this problem, by providing flow holes 221 at the base of each flow shroud 61, extending radially through the sidewalls of the connectors 163, which thus permit substantially the entire volume of coolant within the head region to enter each annular downcomer flow path 211. While illustrated as employed only with the WDRC related flow shrouds 61, if a larger flow is required, corresponding flow holes and related structure, to be described, may be employed as the connectors 162 for the RCC-related flow shrouds 60 and calandria tubes 56, as well. The provision of the flow holes 221, requires that the drive rods 201 be shielded from the jetting effect of the coolant entering through the flow holes 221 and impinging thereon; further, it is important to guard against the potential of flashing of steam which could block the flow of coolant through the flow holes 221. Particularly, as is well known in the art, steam may become trapped within the head region of the head assembly 12a, for example as a result of a LOCA. During blowdown, when the liquid coolant level within the head region drops below the tops of the flow shrouds 61, steam could enter the annular flow paths 211 in the so-called "flashing" phenomenon and thus block the flow of further liquid coolant through the flow holes 221. The present invention prevents these problems from occurring, through the provision of a flow diverter 222 which is positioned coaxially within each connector 163 and which comprises an annular flange 223 received on and welded to an annular ledge 163c and an integral, tubular extension 224 having a smaller outer diameter than the inner diameter of the connector 163 and thus defining an annular downcomer flow path 211a through which the coolant entering the flow holes 221 passes, for joining or merging with the blowdown flow through the general, annular downcomer flow path 211. The flow diverter 222 furthermore includes a flow restrictor 225 which preferably is formed integrally as a radially inward collar within the diverter 222, having an inner surface spaced closely from the outer surface of the drive rod 201. In one practical application, employing a drive rod of approximately 1.75", the inside diameter of the annular flow restrictor 225 is approximately 2.00" and the axial length is approximately 1.25". The flow restrictor 225 thus provides sufficient flow resistance to flashing of steam entering through the open top of the flow shroud 61, such that the steam does not choke off the flow of coolant through the flow holes 221. In fact, in view of the required presence of the flow restrictors 225 to preclude clogging of the downcomer flow due to flashing, substantially all of the downcomer flow from the head region passes through the flow holes 221, even during normal operation. The flow diverter 222 and the associated, integral flow restrictor 225 combine to provide a structure whereby the drive rods 210 are shielded completely from crossflow of coolant within the head region, and in fact are so protected, extending from the head region and throughout the lengths thereof to the tops of the rod guides, without impairment of the head cooling flow to the core during blowdown. The improved calandria assembly of the present invention thus affords sufficient structural strength and rigidity to provide requisite support functions, including shielding of the drive rods from flow-induced vibrational forces, while additionally providing coolant downcomer flow paths through the annuli between the RCC drive rods and the associated flow shrouds and calandria tubes, which remain functional during blowdown operation, but which do not expose the drive rods to axially directed coolant jetting and which prevents potential blockage of the downcomer flow paths by flashing of steam, as may accompany a LOCA. From the clear teaching herein of the preferred calandria assembly embodiment having specific structures for achieving these requisite functions, numerous modifications and adaptations will be apparent to those of skill in the art and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the true spirit and scope of the invention. |
049838482 | abstract | X-ray intensifying screens that can be conveniently and easily used in book cassettes and automatic changer systems are described. These screens have an improved surface made by bonding a thin, clear, transparent, tough, flexible, dimensionally stable polyamide film thereon. The screens display a very low average dynamic coefficient of friction, very good resistant to wear (e.g., gouging and abrasion) and a low static susceptibly which permits long term use in book cassettes and rapid handling incurred in said changer systems. |
description | This application is a 35 U.S.C. 371 national stage filing from International Application No. PCT/KR2007/005053 filed Oct. 16, 2007, which claims priority to Korean Application No. 10-2006-0100415, filed Oct. 16, 2006, the teachings of which are incorporated herein by reference. The present invention relates, in general, to a liquid-metal cooled fast reactor, and more particularly, to a nuclear fuel assembly and a core for a liquid-metal cooled fast reactor, in which the nuclear fuel assembly has nuclear fuel rods having different cladding thicknesses in reactor core regions, includes a nuclear fuel assembly in an inner reactor core region, a nuclear fuel assembly in a middle reactor core region, which surrounds the nuclear fuel assembly of the inner reactor core region, and a nuclear fuel assembly in an outer reactor core region, which surrounds the nuclear fuel assembly of the middle reactor core region, and is installed in a hexagonal duct with nuclear fuel materials surrounded by respective claddings, and in which the claddings of a nuclear fuel rod in the inner reactor core region, a nuclear fuel rod in the middle reactor core region and a nuclear fuel rod in the outer reactor core region are formed at different thicknesses, thereby being able to effectively flatten power distribution using a single-enrichment nuclear fuel in the liquid-metal cooled fast reactor. Growing interest has recently been taken in the development of fourth generation nuclear reactors, which alleviate international resistance to nuclear proliferation (i.e. the spread of nuclear weapons). Among them, it has been reported that a sodium cooled fast reactor has entered the step just before commercialization, because the technology thereof has been considerably developed. Thus, in several countries, including the USA, Japan and Russia, nuclear reactor design concepts that obviate a blanket and use a single-enrichment nuclear fuel in order to alleviate resistance to the spread of liquid-metal nuclear reactors, have been suggested. Each blanket contains depleted uranium or natural uranium, and is characterized by the production of nuclear-grade plutonium when loaded into a reactor core. However, since the blanket increases the breeding ratio of nuclear fuel, the obviation of the blanket has an advantage in that it basically blocks the production of nuclear-grade plutonium, thus alleviating resistance based on fears of nuclear proliferation, but has a disadvantage in that it has a lower breeding ratio. The use of the single-enrichment nuclear fuel maintains a constant breeding ratio in each reactor core region, and thus limits the frequency of changes in power distribution over time. Accordingly, the single-enrichment nuclear fuel facilitates the design of an orifice required for flow distribution. In Korea, a sodium-cooled reactor of 600 MWe has already been designed, thus both obviating the blankets and using the single-enrichment nuclear fuel. In a core of the sodium-cooled reactor, in order to flatten the power distribution using the single-enrichment nuclear fuel, a non-nuclear fuel rod, such as a B4C rod, a ZrH2 rod, or a vacancy rod, has been used for a nuclear fuel assembly. However, the design of such a nuclear fuel assembly is complicated compared to that of a known nuclear fuel assembly. When the B4C or ZrH2 rod is irradiated at high temperature, the soundness of this non-nuclear fuel rod containing this compound becomes a problem. Particularly, in the case of the ZrH2 rod, because hydrogen is emitted at a high temperature of 550° C., the soundness of cladding has become a known problem. The general concept of a high-capacity sodium-cooled fast reactor is based on the use of the blankets and variation of fuel enrichment in each reactor core region in order to flatten power distribution. In the case where the single-enrichment nuclear fuel is used, a method of properly disposing the blankets in the middle of the reactor core as well as in the reactor core has been used. In a lead-cooled fast reactor, BREST, which has recently been proposed in Russia, a method of varying the outer diameter of the nuclear fuel rod in each reactor core region instead of avoiding variation in fuel enrichment has been adopted. Further, an attempt has been made to alleviate resistance to nuclear proliferation by obviating the blanket. The concept of the BREST is based on the use of lead as a coolant and nitride as a nuclear fuel. However, with this method, it is difficult to maintain the size of the nuclear fuel assembly consistent due to the difference between the outer diameters of the nuclear fuel rods, when applied to the case of using a sodium-cooled reactor, particularly, a duct and a wire wrap. The Japan Nuclear Cycle Development Institute (JNC) has proposed a method of maintaining both the outer diameter of the nuclear fuel rod and the thickness of the cladding uniform and of varying the content of zirconium (Zr) in the nuclear fuel surrounded by the cladding in each reactor core region. Regarding this method, however, the predominant opinion is that the performance and production of the nuclear fuel become a problem. The reason is as follows. According to results released from the US Argonne National Laboratory, the optimal content of Zr is generally 10 wt %, and when the content of Zr is less than 10 wt %, eutectic and melting temperatures of a metal fuel do not become sufficiently high, and re-distribution of elements may create a region where the content of Zr is abruptly reduced. In contrast, when the content of Zr is more than 10 wt %, the melting temperature of a fuel core becomes higher than that of a quartz tube when the nuclear fuel is produced. JNC has also proposed a method of simultaneously varying the content of Zr in each reactor core region and adjusting the smear density of the metal fuel. However, according to a study on the smear density of the metal fuel, reported by US Argonne National Laboratory, the optimal smear density of the metal fuel is 75% TD, and when it is higher than this value, the soundness of the nuclear fuel become a problem. According to the design concepts of an encapsulated nuclear heat source (ENHS), a small-size ultra-long cycle lead-cooled fast reactor, which is being studied under the control of California State University at Berkeley in the USA, an attempt has been made to maintain the size and components of the nuclear fuel rod uniform in all of the reactor core regions, and to adjust the power distribution by increasing the area of a non-nuclear fuel region in the middle of the fuel core. In this case, however, it is found that the area of the non-nuclear fuel region in the middle of the fuel core is increased such that the peak power factor is maintained less than 1.5, and thus the breeding ratio is considerably reduced. According to the ENHS design concepts, another method of maintaining the design specification and components of each nuclear fuel rod in each reactor core region uniform and of varying only the distance between the nuclear fuel rods has been released. This method, however, is suitable for a small-size reactor core that makes no use of a duct and a wire wrap, but not for a large-size reactor core, which uses the duct and the wire wrap. Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a nuclear fuel assembly having nuclear fuel rods of different cladding thicknesses in reactor core regions in a liquid-metal cooled fast reactor, in which the nuclear fuel assembly has nuclear fuel rods, each of which has a cladding thicknesses varied in each reactor core region, and in which claddings of the nuclear fuel rod in an inner reactor core region, the nuclear fuel rod in a middle reactor core region and the nuclear fuel rod in an outer reactor core region are formed at different thicknesses without using any non-nuclear fuel rods, thereby being able to effectively flatten power distribution using a single-enrichment nuclear fuel in the liquid-metal cooled fast reactor. In order to achieve the above object, according to one aspect of the present invention, there is provided a liquid-metal cooled fast reactor, in which claddings of a nuclear fuel rod in an inner reactor core region, a nuclear fuel rod in a middle reactor core region and a nuclear fuel rod in an outer reactor core region are formed at different thicknesses, thereby being able to effectively flatten power distribution using a single-enrichment nuclear fuel. According to the present invention, the claddings of the nuclear fuel rods in the respective reactor core region of the liquid-metal cooled fast reactor are formed at different thicknesses, and more particularly, the thicknesses of the claddings are formed to be decreased in the order of the inner, middle and outer reactor core regions, and thus the diameters of the nuclear fuel materials are formed to be increased in the order of the inner, middle and outer reactor core regions, so that the present invention can flatten the power distribution by simplifying the method of realizing a single enrichment, improve the soundness of the nuclear fuel assembly by simplifying the design of the nuclear fuel assembly and the soundness of each nuclear fuel rod, thus resulting in improved economy. 1: nuclear fuel assembly 2: cross section of nuclear fuel rod 3: duct 4: structure of nuclear fuel rod 5: loaded model of reactor core 6: reflector assembly 7: B4C shield assembly 8: IVS (In-Vessel Storage Unit) 9: shield assembly 10: wire wrap According to one aspect of the present invention, there is provided a liquid-metal cooled fast reactor, in which claddings of a nuclear fuel rod in an inner reactor core region, a nuclear fuel rod in a middle reactor core region and a nuclear fuel rod in an outer reactor core region are formed at different thicknesses, thereby being able to effectively flatten power distribution using a single-enrichment nuclear fuel. The cladding of the nuclear fuel rod in the inner reactor core region has a thickness of 1.02 mm. The nuclear fuel material portion of the nuclear fuel rod in the inner reactor core region has a diameter of 6.03 MM. The cladding of the nuclear fuel rod in the middle reactor core region has a thickness of 0.74 mm. The nuclear fuel material portion of the nuclear fuel rod in the middle reactor core region has a diameter of 6.51 mm. The cladding of the nuclear fuel rod in the outer reactor core region has a thickness of 0.59 mm. The nuclear fuel material portion of the nuclear fuel rod in the outer reactor core region has a diameter of 6.77 mm. Reference will now be made in greater detail to exemplary embodiments of the invention with reference to the accompanying drawings. FIG. 1 is a sectional view illustrating a nuclear fuel assembly. FIG. 2 is a top plan view illustrating an assembly duct model. FIG. 3 is a top plan view illustrating a nuclear fuel rod model. FIG. 4 is a schematic diagram illustrating the loaded state of a reactor core in each reactor core region in accordance with the present invention. FIG. 5 is a sectional view illustrating a nuclear fuel rod in an inner reactor core in accordance with the present invention. FIG. 6 is a sectional view illustrating a nuclear fuel rod in a central reactor core in accordance with the present invention. FIG. 7 is a sectional view illustrating a nuclear fuel rod in an outer reactor core in accordance with the present invention. FIG. 8 is a table showing the major design specification of a reactor core in accordance with the present invention. As illustrated in FIGS. 1, 2 and 3, a nuclear fuel assembly 1 is made up of 271 nuclear fuel rods 4. At this time, the nuclear fuel rods 4 are installed in a hexagonal duct 3, and sodium coolant is provided between the ducts 3. The duct 3 has a thickness of 3.7 mm, the distance between the outer faces of the duct 3 is 18.31 cm, and the distance between the inner faces of the duct 3 is 17.57 cm (see FIG. 8). A sodium region between the ducts 3 has a thickness of 4 mm, and a pitch of the nuclear fuel assembly 1 is 18.71 cm (see FIG. 8). The duct 3 makes uniform the flow resistance of all channels therein and in a bundle of the nuclear fuel rods 4, mitigates a by-pass phenomenon, in which the sodium coolant flows along a path having low flow resistance, and forces the sodium coolant to flow around all of the nuclear fuel rods 4 in the bundle of the nuclear fuel rods 4 such that the sodium coolant uniformly flows. Thereby, the duct 3 of the nuclear fuel assembly 1 makes it possible to function as an orifice. Further, the duct 3 structurally supports the bundle of nuclear fuel rods 4, and 271 nuclear fuel rods 4 form a hexagonal bundle in a triangular arrangement in the duct 3. Each nuclear fuel rod 4 is mounted on a mounting rail through mechanical connection. The mounting rail is mechanically connected to the upper end of a nose piece 3e. The nose piece 3e supports the lower portion of the nuclear fuel assembly 1, and provides an inlet for the sodium coolant. When the nuclear fuel rods 4 are arranged in a triangular shape in the duct 3, a wire wrap 10 is used to maintain an interval between the nuclear fuel rod 4 and the nuclear fuel rod 4. The wire wrap 10 is bonded and welded to upper and lower end plugs at opposite ends of each nuclear fuel rod 4 so as to be wound around each nuclear fuel rod 4 at regular intervals, thereby functioning to maintain the interval between the nuclear fuel rods 4 and the interval between the nuclear fuel rods 4 and the duct 3, and increase the flow mixture of the sodium coolant. The wire wrap 10 has a diameter of 1.4 mm, and each nuclear fuel rod 4 has an outer diameter of 9.0 mm. Further, the ratio of the pitch P of a grid and the diameter D of each nuclear fuel rod 4 is 1.1667 (see FIG. 8). Each nuclear fuel rod 4 has a shielding region 4e for the bottom end cap at a lower end thereof and for a Mod. HT9 cladding, and the shielding region 4e has a length of 111.76 cm. The upper side of the shielding region 4e is a nuclear fuel region 4d, the length of which is 100 cm. The nuclear fuel material in the nuclear fuel region 4d is surrounded by a cladding, and a sodium bonding agent is disposed between the nuclear fuel material and the cladding. Sodium of the sodium bond has good compatibility with other material as well as good thermal conductivity, and thus serves to maintain low temperature distribution of the nuclear fuel core. Among the sodium that is present between the nuclear fuel material and the cladding while the nuclear fuel is burnt, some penetrates the nuclear fuel material due to the expansion of the nuclear fuel material, and the rest moves in an upward direction. Each nuclear fuel rod has a gas plenum region 4c at the upper portion thereof, which holds gas generated by nuclear fission and lowers the pressure in a cladding tube. The gas generated from the nuclear fuel by nuclear fission goes up to the gas plenum region 4c together with the sodium. The gas plenum region 4c has a length of 156.25 cm. The upper side of the gas plenum region 4c is an upper end plug 4a, the length of which is 2.54 cm. Thus, the total length of each nuclear fuel rod 4 is 370.55 cm (see FIG. 8). As illustrated in FIG. 4, the reactor core region having the nuclear fuel is divided into three regions: inner, middle and outer. The inner, middle and outer reactor core regions have 114, 78 and 138 nuclear fuel rods 4 respectively, which constitute the nuclear fuel assembly 1. 72 reflector assemblies 6 are disposed at the outer boundary of the reactor core region having the nuclear fuel, and 78 B4C shield assemblies 7, 114 in-vessel storage units (IVSs) 8, and 90 shield assemblies 9 are disposed outside the reflector assemblies 6 in that order. As illustrated, at this time, the reactor core completely obviates a blanket assembly in order to alleviate resistance based on fears of nuclear proliferation. Among the reactor core regions, the inner reactor core region constitutes a nuclear fuel assembly 1a, the middle reactor core region surrounding the nuclear fuel assembly 1a of the inner reactor core region constitutes a nuclear fuel assembly 1b, and the outer reactor core region surrounding the nuclear fuel assembly 1b of the middle reactor core region constitutes a nuclear fuel assembly 1c. In the nuclear fuel assembly 1 of the liquid-metal cooled fast reactor, which is installed in the hexagonal duct 3 with the nuclear fuel materials 2-2a, 2-2b and 2-2c surrounded by the claddings 2-1a, 2-1b and 2-1c, the claddings 2-1a, 2-1b and 2-1c of the nuclear fuel rod 2a in the inner reactor core region, the nuclear fuel rod 2b in the middle reactor core region and the nuclear fuel rod 2c in the outer reactor core region are formed at different thicknesses. In this manner, by forming the claddings 2-1a, 2-1b and 2-1c of the nuclear fuel rods 2a, 2b and 2c in the reactor core regions at different thicknesses, the power distribution can be flattened. Here, the thickness of the cladding 2-1a of the nuclear fuel rod 2a in the inner reactor core region is most preferably 1.02 mm. The thickness of the cladding 2-1b of the nuclear fuel rod 2b in the middle reactor core region is most preferably 0.74 mm. The thickness of the cladding 2-1c of the nuclear fuel rod 2c in the outer reactor core region is most preferably 0.59 mm. However, the outer diameters of the nuclear fuel rods 2a, 2b and 2c are equally maintained in order to equally maintain areas of the channels in all reactor core regions. Further, the nuclear fuel makes use of an ordinary TRU-U-10Zr metal fuel, and the smear density of the metal fuel is 75% TD, and is maintained consistent in all of the reactor core regions. To the end, the diameter of the nuclear fuel material 2-2a of the nuclear fuel rod 2a in the inner reactor core region is most preferably 6.03 mm. The diameter of the nuclear fuel material 2-2b of the nuclear fuel rod 2b in the middle reactor core region is most preferably 6.51 mm. The diameter of the nuclear fuel material 2-2c of the nuclear fuel rod 2c in the outer reactor core region is most preferably 6.77 mm. In other words, the main feature of the present invention is that in order to flatten the power distribution using the single-enrichment nuclear fuel, the cladding 2-1a of the nuclear fuel rod 2a in the inner reactor core region is thickest, whereas the cladding 2-1c of the nuclear fuel rod 2c in the outer reactor core region is thinnest. Thus, the liquid-metal cooled fast reactor having the nuclear fuel assembly 1 in accordance with the present invention can secure good reactor-core performance, and can simultaneously flatten power distribution using the single-enrichment nuclear fuel. In the drawings and specification, typical exemplary embodiments of the invention have been disclosed, and although specific terms are employed, they are used in a generic and descriptive sense only and not for the purposes of limitation, the scope of the invention being set forth in the following claims. As described above, according to the present invention, the claddings of the nuclear fuel rods in the respective reactor core region of the liquid-metal cooled fast reactor are formed at different thickness, and more particularly, the thicknesses of the claddings are formed so as to decrease in the order of the inner, middle and outer reactor core regions, and the diameters of the nuclear fuel materials are formed so as to increase in the order of the inner, middle and outer reactor core regions, so that the power distribution can be flattened by simplifying the method of realizing single enrichment, so that the soundness of the nuclear fuel assembly and the soundness of each nuclear fuel rod can be improved by simplifying the design of the nuclear fuel assembly, and so that the improvement of economy can be realized. |
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055526128 | description | DETAILED DESCRIPTION OF THE EMBODIMENTS Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Containers for transporting radiation shield members according to embodiments of the present invention are described below with reference to the drawings. A transport container 1 for transporting a radiation shield member according to an embodiment of the present invention is cylindrical as shown in FIG. 3, and is 37 mm in its diameter (C) and approximately 106 mm in its height (H1). The transport container 1 for transporting a radiation shield member comprises a sheath container 2 cup-shaped and made of plastic; and a cover 3, cup-shaped and made of plastic, covering an opening of the sheath container 2, thus closing the opening end thereof. The cover 3 has a sealing mechanism which is unrestorable when the cover 3 is removed from the sheath container 2. The sealing mechanism will be described later in detail. The transport container 1 for transporting the radiation shield member according to the embodiment accommodates in the sheath container 2 a first radiation shield member 100 having a syringe, in which radiopharmaceutical liquid is filled, inserted thereinto as shown in FIG. 12. The radiation shield member 100 to be accommodated in the sheath container 2 containing the syringe has been on the market. Two wing-shaped holding members 102 extending in opposed directions to each other in a diametrical direction of the syringe and perpendicular to the axial direction of the syringe is formed on one side of the radiation shield member 100 from which a plunger 101 connected with a gasket provided in the syringe projects. When the radiation shield member 100 shown in FIG. 12 is accommodated in the transport container 1 for transporting the radiation shield member 100, the radiation shield member 100 does not have the plunger 101 or a needle 103 mounted thereon, but a radiation shield member having a plunger mounted thereon may be accommodated in the transport container 1 for transporting the radiation shield member. In this case, needless to say, a cover is formed in conformity to the length of the plunger and the configuration thereof. As shown in FIGS. 2 and 7, an annular projection 4 is formed circumferentially on the entire outer peripheral surface of the sheath container 2 in the vicinity of the edge of the opening thereof. An annular groove 5 to engage the annular projection 4 is formed circumferentially on the entire inner peripheral surface of the cover 3 in correspondence to the annular projection 4. The cover 3 keeps the sealing performance of the transport container 1 for transporting the radiation shield member by means of a so-called snap-on method due to the engagement between the annular projection 4 and the annular groove 5 and is removable from the sheath container 2. Mountain-shaped guide projections 8 as disclosed in Japanese Laid-Open Utility Model Publication No. 55-170262 are formed in the circumferential direction of the sheath container 2 at regular intervals on the peripheral surface thereof in the vicinity of the edge of the opening thereof. In this embodiment, the guide projections 8 are formed at four positions at intervals corresponding to a central angle of 90.degree.. Each guide projection 8 has two inclined slide surfaces 8a. A groove 6 for installing a holding ring 12 which will be described later is formed circumferentially on the entire inner peripheral surface of the sheath container 2 in the vicinity of the edge of the opening thereof, as shown in FIG. 7. Further, at a position where a bottom plate 2a of the sheath container 2 is disposed, two plates 7 are erected in parallel with each other at a predetermined interval along the inner peripheral surface of the sheath container 2. As shown mainly in FIGS. 8 through 10, a cup-shaped radiation shield container 9 is mounted in the sheath container 2. The radiation shield container 9 is made of lead material or the like and shields radiation which has been emitted from the radiopharmaceutical liquid contained in the syringe accommodated in the sheath container 2 and then transmitted through the radiation shield member 100. The outer diameter of the radiation shield container 9 is so set as to generally allow the radiation shield container 9 to contact the inner peripheral surface of the sheath container 2. When the radiation shield container 9 is mounted in the sheath container 2, the end surface 9a of the opening of the radiation shield container 9 is situated at a shorter distance toward the bottom of the sheath container 2 than the end surface 2b of the opening of the sheath container 2 is situated toward the bottom of the sheath container 2, as shown in FIG. 7. As will be described later, the radiation shield container 9 can be prevented from being removed from the sheath container 2 by mounting the holding ring 12 on a stepped portion formed between the end surface 2b and the end surface 9a and mounting the holding ring 12 on the sheath container 2. When the sheath container 2 is cylindrical as in the case of this embodiment, in order to prevent the radiation shield container 9 from rotating circumferentially in the sheath container 2, a groove 10 having a width a little smaller than the interval between the two plates 7 is formed on the bottom of the radiation shield container 9 so as to press the plates 7 into the groove 10. If the sheath container 2 is not cylindrical, it is unnecessary to form the groove 10. Concave recesses 11 to be engaged by the wing-shaped holding members 102 which constitutes a part of the radiation shield member 100 when the radiation shield member 100 is accommodated in the radiation shield container 9 are formed on the end surface 9a of the radiation shield container 9. The depth of each concave recess 11 is equal to the thickness of the wing-shaped holding member 102, and the configuration of the concave recess 11 is the same as that of the wing-shaped holding member 102 which contacts the end surface 9a. The radiation shield member 100 is fixed in position in the radiation shield container 9 by the engagement between the concave recess 11 and the wing-shaped holding member 102. Although the concave recess 11 is adopted in this embodiment as a position-fixing portion for fixing the wing-shaped holding member 102 in position, the position-fixing portion for fixing the wing-shaped holding member 102 in position is not limited to a portion having a concave configuration. For example, as shown in FIGS. 13 and 14, a portion may be constituted by projections 411 erected on the end surface 9a and capable of contacting the other peripheral surface of the wing-shaped holding members 102. As shown in mainly FIGS. 5 through 7, the holding ring 12 is an annular member approximately U-shaped in section and having a through-hole in the center thereof. As shown in FIG. 7, the holding ring 12 comprises a cylindrical portion 12b engaging the inner peripheral surface of the sheath container 2; an approximately ring-shaped shield container removal-preventing portion 12a extending from the cylindrical portion 12b toward the center of the holding ring 12; and an approximately T-shaped shield member removal-preventing portion 12c extending from two positions, opposed to each other, of the shield container removal-preventing portion 12a toward the center of the holding ring 12. An annular projection portion 12d which engages the holding ring-installing groove 6 formed on the inner peripheral surface of the sheath container 2 is circumferentially formed on the entire outer peripheral surface, of the cylindrical portion 12b, which contacts the inner peripheral surface of the sheath container 2. Considering a possible removal of the holding ring 12 from the sheath container 2, preferably, the projection portion 12d is semicircular in section as shown in the drawings. The holding ring 12 is mounted on the opening of the sheath container 2 by engaging the cylindrical portion 12b with the inner peripheral surface of the sheath container 2 and by engaging the projection portion 12d with the holding ring-installing groove 6. A projection portion 12e projecting radially and outwardly from the cylindrical portion 12b contacts the end surface 2b of the sheath container 2. As a result of the mounting of the holding ring 12 on the sheath container 2, the shield container removal-preventing portion 12a is brought into contact with the end surface 9a of the opening of the radiation shield container 9, thus preventing the radiation shield container 9 from being removed from the sheath container 2 and in addition, the shield member removal-preventing portion 12c prevents the radiation shield member 100 from being removed from the radiation shield container 9, because the shield member removal-preventing portion 12c extends in such a direction and a configuration as to cover and contact the wing-shaped holding members 102 engaged by the concave recesses 11 of the radiation shield container 9, as shown in FIG. 4. Although in the illustration, the thickness of the shield container removal-preventing portion 12a is equal to that of the shield member removal-preventing portion 12c, actually, for example, the thickness of the shield container removal-preventing portion 12a is 0.5 mm and that of the shield member removal-preventing portion 12c is 0.3 mm. That is, the thickness of the shield member removal-preventing portion 12c is very small. As shown in FIGS. 1 and 11, the cover 3 is cup-shaped and mounted on the edge of the opening of the sheath container 2, thus closing the opening of the sheath container 2. A projection 3a approximately half-elliptic in section is formed circumferentially on the entire inner peripheral surface of the cover 3 in the vicinity of the upper end of the cover 3. A cup-shaped radiation shield member 13 made of lead material and having a projection 13a, engaging the projection 3a, formed on the outer peripheral surface thereof is held inside the cover 3. That is, with the upper surface 13b of the top portion of the cup-shaped lead radiation shield member 13 in contact with the inner surface 3b of the top portion of the cover 3, the projection 3a of the cover 3 engages the projection 13a of the cup-shaped lead radiation shield member 13, thus holding the cup-shaped lead radiation shield member 13 inside the cover 3. In order to separate the cup-shaped lead radiation shield member 13 from the cover 3 more easily, a gap 16 having an appropriate amount of space is formed between the outer peripheral surface 13d of the cup-shaped lead radiation shield member 13 and the inner peripheral surface 3c of the cover 3. The gap 16 performs a function of allowing the cover 3 to be flexible, thus facilitating the opening and closing of the cover 3. In order to separate the cover 3 from the cup-shaped lead radiation shield member 13, for example, a thumb of one hand is inserted into the inside of the cup-shaped lead radiation shield member 13 and a forefinger of the hand contacts the outer side surface of the cover 3 to pick them to reduce the gap between the cup-shaped lead radiation shield member 13 and the cover 3, thus easily taking out the cup-shaped lead radiation shield member 13 from the cover 3. Inverted mountain-shaped cover side-guide projections 17 having two inclined slide surfaces 17a is formed on the inner peripheral surface 3c disposed in the vicinity of the opening edge of the cover 3, in correspondence with the guide projections 8 formed on the outer peripheral surface of the sheath container 2. By rotating the cover 3 in the circumferential direction thereof, one of the slide surfaces 8a of each guide projection 8 and one of the slide surfaces of each cover side-guide projection 17 slide in contact with each other, thus outwardly moving the cover 3 in the axial direction of the sheath container 2 and separating the cover 3 from the sheath container 2. The height H2 of the cup-shaped lead radiation shield member 13 is so set that when the annular groove 5 formed on the cover 3 and the annular projection 4 formed on the sheath container 2 are in engagement with each other, the lower end surface 13c of the cup-shaped lead radiation shield member 13 contacts the shield container removal-preventing portion 12a of the holding ring 12 as well as the shield member removal-preventing portion 12c thereof. Thus, the wing-shaped holding members 102 of the radiation shield member 100 are held firmly by means of the cup-shaped lead radiation shield member 13 and the radiation shield container 9 via the shield container removal-preventing portion 12a and the shield member removal-preventing portion 12c, with a force being applied to the wing-shaped holding members 102 of the radiation shield member 100 in the axial direction thereof. In the cover 3, an annular notch 13e is formed circumferentially on the entire outer peripheral surface of the cover 3 in correspondence to the annular groove 5, and the thickness of a portion, of the cover 3, sandwiched between the annular groove 5 and the annular notch 13e is much smaller than the thicknesses of other portions of the cover 3. The opening side of the cover 3 disposed below the annular notch 13e is denoted as the sealing connection portion 14. The art of the sealing connection portion proposed by the present applicant and disclosed in Japanese Utility Model Publication No. 5-24078 is adopted in forming the sealing connection portion 14. That is, the knob 15 is pulled to the cover 3 and rotated around the cover 3, and then the sealing connection portion 14 is separated from the cover 3 at the annular notch 13e to break the seal between the cover 3 and the sheath container 2 to take out the cover 3 from the sheath container 2. The sealing connection portion 14 prevents danger that the cover 3 is loosened from the sheath container 2 or the cover 3 is opened or closed by accident during transport. The sealing connection portion 14 is separated from the cover 3 at the annular notch 13e, and hence the cover 3 can be removed from the sheath container 2 by pulling a knob 15 formed on the sealing connection portion 14. In addition, the break of the sealing connection portion 14 from the cover 3 indicates that the radiopharmaceutical liquid has been used. In the transport container 1 for transporting the radiation shield member, according to this embodiment, having the above-described construction, the radiation shield member 100 containing the syringe is accommodated in the transport container 1 by engaging each wing-shaped holding member 102 with each concave recess 11 formed on the end surface 9a of the radiation shield container 9 and by preventing the movement of the radiation shield member 100 in the axial direction of the transport container 1 by means of the holding ring 12. Further, as a result of the mounting of the cover 3 on the sheath container 2 so as to close the opening of the sheath container 2 by the cover 3, the end surface 13c of the cup-shaped lead radiation shield member 13 inside the cover 3 is brought into contact with the holding ring 12, and then the opening of the sheath container 2 is sealed by the cover 3. In this state, the radiation shield member 100 is held firmly in the transport container 1. That is, in the state in which the opening of the sheath container 2 is sealed by the cover 3, the radiation shield member 100 is prevented from moving in the axial direction of the transport container 1 and further, the leading end of the radiation shield member 100 is prevented from pivoting on the wing-shaped holding members 102 in the radiation shield container 9. In taking out the radiation shield member 100 from the transport container 1, the knob 15 of the sealing connection portion 14 is pulled to break and remove the sealing connection portion 14 from the cover 3 by cutting the sealing connection portion 14 at the annular notch 13e. In this manner, the transport container 1 sealed by the cover 3 which has closed the sheath container 2 is unsealed. By rotating the cover 3 in the circumferential direction thereof, the slide surfaces 8a of the guide projections 8 of the sheath container 2 and the slide surfaces 17a of the cover side-guide projections 17 of the cover 3 slide in contact with each other, thus moving the cover 3 in the axial direction of the sheath container 2 and separating the sheath container 2 from the cover 3. As a result of the removal of the cover 3 from the sheath container 2, the head of the radiation shield member 100 is exposed to the outside. By pulling the head in the axial direction of the transport container 1, the wing-shaped holding members 102 press the shield member removal-preventing portion 12c of the holding ring 12 upward. In this manner, the radiation shield member 100 is removed from the transport container 1. As described above, in the container for transporting the radiation shield member according to this embodiment, the radiation shield member 100 can be held in the transport container 1 reliably and stably by providing a radiation shield container 9 having an inner diameter shorter than the length of the total of the two wing-shaped holding members 102 of the radiation shield member 100 and by providing on the radiation shield container 9 the concave recesses 11, having the same configurations in plan view as those of the wing-shaped holding members 102, to be engaged by the wing-shaped holding members 102. Thus, it is unnecessary to provide a cushioning material for supporting the radiation shield member 100 in the transport container 1, and the outer diameter of the radiation shield container 9 can be reduced and thus a compact and light transport container 1 can be provided. Further, since each concave recess 11 has the same plan configuration as that of each wing-shaped holding member 102, the radiation shield member 100 can be taken out from the radiation shield container 9 easily. Since the cup-shaped lead radiation shield member 13 is mounted in the cover 3 by engaging the projection 3a of the cover 3 with the projection 13a of the cup-shaped lead radiation shield member 13, the cup-shaped lead radiation shield member 13 can be easily mounted on the cover 3 in the manufacturing operation, and the cup-shaped lead radiation shield member 13 mounted in the cover 3 can be removed from the sheath container 2 together with the cover 3 by removing the cover 3 from the sheath container 2. In order to separate the cover 3 from the cup-shaped lead radiation shield member 13, for example, a thumb of one hand is inserted into the inside of the cup-shaped lead radiation shield member 13 and a forefinger of the hand contacts the outer side surface of the cover 3 to pick them to reduce a gap between the cup-shaped lead radiation shield member 13 and the cover 3, thus easily taking out the cup-shaped lead radiation shield member 13 from the cover 3. Accordingly, the cup-shaped lead radiation shield member 13 can be reused. Moreover, since the gap 16 is formed between the inner peripheral surface 3c of the cover 3 and the outer peripheral surface 13d of the cup-shaped lead radiation shield member 13, the cover 3 is allowed to be flexible and thus can be easily installed on the sheath container 2 or removed therefrom. As apparent from the above description, the present invention can provide the transport container which has a favorable operability and allows a reusable material and a non-reusable material to be easily separated from each other for classified refuse. Furthermore, since the shield member removal-preventing portion 12c is formed on the holding ring 12, and a part of each wing-shaped holding member 102 of the radiation shield member 100 is covered with the shield member removal-preventing portion 12c, the radiation shield member 100 accommodated in the sheath container 2 can be prevented from popping out therefrom even though the sheath container 2 upsets in the state in which the cover 3 has been removed from the sheath container 2. Since the shield member removal-preventing portion 12c is constituted by a thin plate, the shield member removal-preventing portion 12c is bent by pulling the head of the radiation shield member 100 in the axial direction of the transport container 1 and consequently, the radiation shield member 100 can be taken out from the transport container 1. In addition, since the holding ring 12 is mounted on the sheath container 2 by the engagement between the projection portion 12d and the holding ring-installing groove 6 of the sheath container 2, the holding ring 12 can be removed from the sheath container 2, and the radiation shield container 9 can be separated from the sheath container 2 for the disposal of the sheath container 2 by removing the holding ring 12 from the sheath container 2 and pulling the radiation shield container 9 in the axial direction of the transport container 1. Thus, the radiation shield container 9 can be reused. Further, the sheath container 2 and the radiation shield container 9 are provided with the plates 7 and the groove 10 engaging the plates 7, respectively so as to prevent the radiation shield container 9 from rotating relative to the sheath container 2. Thus, the position relationship between the shield member removal-preventing portion 12c and the wing-shaped holding members 102 is maintained. That is, the state in which the shield member removal-preventing portion 12c covers a part of the wing-shaped holding members 102 is prevented from being altered. FIGS. 15-18 show a transport container for transporting a radiation shield member according to another embodiment of the present invention. In this embodiment, there is no holding ring 12 and instead, a plurality of approximately trapezoidal engaging projections 427 are integrally formed to project inwardly from the inner peripheral surface of the opening end of the sheath container 2 to contact the engaging projections 427 with the end surface of the opening end of the radiation shield container 9 to prevent the radiation shield container 9 from being removed from the sheath container 2. The two wing-shaped holding members 102 of the radiation shield member 100 are engaged in the concave recesses 11 serving as the position-fixing portion and provided at the end surface 9a of the radiation shield container 9 in the sheath container 2 to fix the radiation shield member 100 between the cover 3 and the cup-shaped lead radiation shield member 13. The depth of the concave recess 11 is smaller than the thickness of the wing-shaped holding member 102, and thus the wing-shaped holding members 102 engaged in the concave recesses 11 are held between the cup-shaped lead radiation shield member 13 of the cover 3 and the radiation shield container 9 of the sheath container 2 to reliably fix the radiation shield member 100 in the transport container. On the other hand, as a result of the provision of the engaging projections 427, in order to prevent it from being difficult that the radiation shield container 9 is taken out from the sheath container 2, an opening is formed at the bottom of the sheath container 2 and a bottom cover 420 is provided to cover the opening. Then, the bottom cover 420 is taken out from the sheath container 2 to easily take out the radiation shield container 9 through the opening of the bottom of the sheath container 2. The bottom cover 420 is made of elastic synthetic resin and has a female screw 421 at its body portion for engaging a male screw 422 formed at the outer side surface in the vicinity of the bottom opening of the sheath container 2. The bottom cover 420 also has a ring portion 423 connected to the body portion of the bottom cover 420 via a plurality of connecting portions 424 for easily cutting out from the body portion. The ring portion 423 has four wedges 425 at its inside to engage the four wedges 425 with wedges 426 of the male screw 422 of the sheath container 2. That is, when the female screw 421 of the bottom cover 420 is engaged with the male screw 422 of the sheath container 2 to mount the bottom cover 420 onto the sheath container 2, an inclined slide surface 425a of each wedge 425 of the bottom cover 420 is slid on an inclined slide surface 426a of each wedge 426 of the sheath container 2. When the bottom cover 420 is rotated and taken out from the sheath container 2, an engaging surface 425b of each wedge 425 of the bottom cover 420 contacts an engaging surface 426b of each wedge 426 of the sheath container 2 to prevent rotation. Then, when the bottom cover 420 is further rotated to the sheath container 2, the connecting portions 424 between the ring portion 423 and the body portion of the bottom cover 420 are cut to leave the ring portion 423 on the side of the sheath container 2 and take out the bottom cover 420 from the sheath container 2. A sealing connection mechanism similar to the sealing connection mechanism between the cover 3 and the sheath container 2 is formed between the bottom cover 420 and the sheath container 2. The engaging projections 427 are not limited to be integrally fixed to the sheath container 2 but may be removably fixed thereto. According to this embodiment shown in FIGS. 15-18, the two wing-shaped holding members 102 of the radiation shield member 100 are fixedly held between the cup-shaped lead radiation shield member 13 of the cover 3 and the radiation shield container 9 of the sheath container 2, and thus it is unnecessary to provide a cushioning material in conformity with the outer diameter of the radiation shield member 100 which is provided in the conventional transport container and the outer diameter the entire transport container can be reduced and the transport container can be light in weight and have favorable operability. FIG. 19 shows a transport container for transporting a radiation shield member according to a further embodiment of the present invention with the radiation shield member 100 being inserted therein. In this embodiment, there is provided the holding ring 12 but the holding ring 12 has only the shield member removal-preventing portion 12c and does not have the shield container removal-preventing portion 12a. A mechanism for preventing the shield container 9 from being removed from the sheath container 2 is provided on the side of the bottom of the sheath container 2. That is, an annular projection 460 is provided at the inner surface of the bottom of the sheath container 2 and the projection 460 is engaged with an annular projection 461 formed on the outer surface of the bottom of the shield container 9 to engage the shield container 9 with the sheath container 2 for preventing removal thereof. In order to release the engagement between the projections 460 and 461 of the shield container 9 and the sheath container 2, a mechanism similar to the sealing connection mechanism between the cover 3 and the sheath container 2 is provided. That is, the knob 15 and the sealing connection portion 14 etc. are provided at a portion in the vicinity of the bottom of the sheath container 2. The sealing connection is broken by the knob 15 to separate the bottom-side portion 462 of the sheath container 2 from the body portion-side portion 463 thereof, and thus the engagement between the two projections 460 and 461 is released. After releasing the engagement between the two projections, when the holding ring 12 is removed from the sheath container, the shield container 9 can be easily taken out from the sheath container 2. In this embodiment, such a mechanism that the two wing-shaped holding members 102 of the radiation shield member 100 are fixedly held between the cup-shaped lead radiation shield member 13 of the cover 3 and the shield container 9 of the sheath container 2 can be adopted. The shield member removal-preventing portion 12c is not limited to be provided at the holding ring 12 but may be integrally fixed to the sheath container 2 or may be removably fixed thereto. When the shield member removal-preventing portion 12c is integrally fixed to the sheath container 2, the portion 12c is broken or the sheath container 2 itself is broken to take out the shield container 9 for disposal. Although the mountain-shaped and inverted mountain-shaped guide projections 8, 17 are formed on each of the sheath container 2 and the cover 3 in the above-described embodiment, the cover 3 and the sheath container 2 may be fixed to each other with screws. Further, each of the cup-shaped sheath container 2, the radiation shield container 9, and the cover 3 according to the above-described embodiment is not limited to a cylindrical member having a bottom, i.e. a member having a ring-shaped section and having a bottom, but may be a member having a rectangular, square, or polygon frame-shaped section and having a bottom. If the sheath container 2, the radiation shield container 9, and the cover 3 are rectangular, square, or polygon, preferably, the holding ring 12 has a configuration in conformity with the configuration thereof. In addition to plastic having a high degree of hardness, metal such as stainless steel, aluminum, tungsten or the like may be preferably used as the material of the wing-shaped holding member 102 of the radiation shield member 100. Preferably, a sheet made of liquid absorbing polymer such as ethylene-acrylate copolymer is provided in a space between the radiation shield container 9 and the radiation shield member 100. Instead of lead, heavy metal such as tungsten having radiation-shielding capability may be used as the material of the radiation shield container 9 and that of the cup-shaped lead radiation shield member 13 of the cover 3. The means for fixing the cup-shaped lead radiation shield member 13 to the cover 3 and the means for fixing the radiation shield container 9 to the sheath container 2 are not limited to the construction of the embodiments described but may use an adhesive double coated tape or an adhesive. In this modification, a gap between the members to be fixed to each other is preferably formed so as to easily separate them from each other for disposal. When ABS resin, polyethylene, polystyrene, vinyl chloride resin, or elastic material, most preferably ABS resin, is used for the material of the cover 3 and the sheath container 2, the cup-shaped lead radiation shield member 13 and the radiation shield container 9 can easily be taken out from the cover 3 and the sheath container 2, respectably, and the cover 3 and the sheath container 2 can easily be cut and torn. When the sheath container has a thin notch, it is easy to tear the sheath container 2 at the thin notch and separate the radiation shield container 9 from the sheath container 2, irrelevant to the fixing with an adhesive. Furthermore, compared with the conventional transport container, the container for transporting a radiation shield member according to the embodiment of the present invention can have the longer cover 3 and an appropriate weight, can be easy to grip, can be so devised as to allow the cover 3 to be flexible, and in addition, so devised based on human engineering as to easily remove the cover 3 from the sheath container 2. As described above, according to the container for transporting a radiation shield member of the present invention, the position-fixing portion (for example, concave recesses 11, projections 411, end surface 9a) for fixing the wing-shaped holding members of the radiation shield member including the syringe is formed on the radiation shield container to hold the wing-shaped holding members thereof, and thus the wing-shaped holding members can be reliably fixed in the radiation shield container and the diameter of the radiation shield container can be reduced. When the container for transporting a radiation shield member of the present invention includes the holding frame (for example, holding ring 12), the shield member removal-preventing portion (for example, 12c) can be formed on the holding frame to prevent the radiation shield member from being removed from the radiation shield container. Thus, the radiation shield container and the holding frame can be light in weight and can prevent the radiation shield member accommodating the syringe in which radiopharmaceutical liquid has been filled from popping out therefrom by accident. The radiation shield container and the sheath container can be easily separated from each other by providing the holding frame for disposal. Furthermore, when the transport container includes the fifth engaging portion (for example, projection 3a) and the sixth engaging portion (for example, projection 13a), the fifth and sixth engaging portions allow the radiation shield member to be mounted in the cover, and thus the cover is taken out from the sheath container and at the same time the radiation shield member provided at the cover is also taken out from the sheath container to provide a transport container having favorable operability and easily separate the radiation shield member from the cover for disposal. Moreover, when the position-fixing portion for fixing the wing-shaped holding members of the radiation shield member including the syringe is provided on the radiation shield container and the shield member removal-preventing portion for preventing the radiation shield member from being removed from the radiation shield container is provided on the holding frame, the radiation shield member can be prevented from being rotated and moved in its axial direction in the radiation shield container. This construction eliminates the other constituent members for fixing the radiation shield member to the interior of the radiation shield container. Thus, the transport container can be light in weight and can prevent the radiation shield member accommodating the syringe in which radiopharmaceutical liquid has been filled from popping out therefrom by accident. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modification are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom. |
description | The present invention relates to an exhaust heat recovery boiler (hereinafter, also referred to as a heat recovery boiler) to be used in a commercial or industrial combined cycle power generation plant, more specifically, a construction method for a heat recovery boiler by fabricating a module of a heat exchanger tube bundle panel, and a heat exchanger tube bundle panel module to be used for construction of the exhaust heat recovery boiler. A combined cycle power generation plant comprising of a combination of a gas turbine and a heat recovery boiler has a power generation efficiency higher than that of other thermal power generation plants, it mainly uses natural gas as a fuel, and it has less production of sulfur oxide and ash dust, so that its exhaust gas purification load is small, for which it has attracted a lot of attention as a successful power generation system. In addition, a combined cycle power generation plant is excellent in load responsiveness since it can quickly change its power generation output according to power demand, and its startup time is comparatively short (it rises quickly), so that it has attracted attention as a power generation method suitable for peaking operation (daily start daily stop) with starts and stops made according to daily power demand cycles. A combined cycle power generation plant comprises of a power generating gas turbine, a heat recovery boiler that generates steam by using exhaust gas of the gas turbine, and a steam turbine that generates power by using steam obtained by the heat recovery boiler. FIG. 1 is a schemic view of a horizontal heat recovery boiler equipped with a supplementary firing burner inside. The heat recovery boiler has a casing 1 as a gas duct in which an exhaust gas G from the gas turbine flows horizontally. A supplementary firing burner 2 is located inside the casing 1 in the vicinity of the inlet into which the gas turbine exhaust gas is led, and a number of heat exchanger tubes are located inside the casing 1. The casing 1 is supported by structural members mainly consisting of main columns 33 and main beams 34. In comparison to components that form conventional high-capacity thermal power generation plants that generate power by burning fossil fuels such as coal, petroleum, or natural gas, etc., the components of a combined cycle power plant including a heat recovery boiler are smaller in capacity and transportable only by sea after being assembled to a nearly completed state in a component manufacturing factory. When the construction site is relatively near the manufacturing factory and near the sea, the installation at the construction site is comparatively easily performed as described above. Therefore, the installation can be completed in shorter time than in the case of high-capacity components of thermal power generation plants. However, in combined cycle power generation, power generation efficiency higher than the conventional is required. Also required is a high-speed startup and stop operation. Hence the heat recovery boiler is made out of a large number of components, and when the conditions of the construction site are different from the above-mentioned conditions and the degree of completion in the factory is low, its installation requires great labor and time. For example, for a heat recovery boiler, a group of approximately one-hundred heat exchanger tubes and its header are set as one unit and are transported to the construction site, and the heat exchanger tube bundle panels are hung down on a unit basis from structural members (main frames) including the main columns 33 and the main beams 34 of the heat recovery boiler which have been constructed in advance at the construction site with intermediate beams located on the ceiling wall of the casing 1 supported by the structural members. Repetition of such operations of hanging and installing the one-hundred heat exchanger tube bundle panels results in an increase of operations at high elevations and it carries increased safety risks. In addition, the construction period is longer, and the construction costs are higher. Therefore, by considering transportation and installation of the heat exchanger tube bundle panels 23 of the heat recovery boiler, a technical development has been earnestly demanded which makes the heat recovery boiler construction easy by fabricating modules, wherein a number of heat exchanger tube bundle panels 23 are defined as one block (hereinafter, referred to as a heat exchanger tube bundle panel module). The entire heat recovery boiler is divided into several modules and the modules are completed as one unit within the component manufacturing factory. Installation is completed by assembling the modules at the construction site. Particularly, when considering that it is difficult to obtain the heat recovery boiler construction parts and secure skilled personnel necessary for construction outside Japan, the module construction method is very effective. The components are completed as partial products divided into a number of modules in the factory in Japan. Quality control or process control systems are adequate and many skilled workers are available in Japan. The modules are transported to the construction site to possibly minimize the operations at the construction site where they are assembled. The method in which the entire heat recovery boiler is manufactured by dividing it into several modules within the factory and then assembled at the construction site is known by, for example, U.S. Pat. No. 859,550 (Patent family: Japanese Published Unexamined Patent Application No. S62-266301). The U.S. Pat. No. 859,550 discloses a construction method in which modules of heat exchanger tube bundle panels are protected by being housed in a frame body formed of a rigid member when they are transported, and the frame body can be used as it is as a main frame of the heat recovery boiler at the construction site. [Patent Document 1] U.S. Pat. No. 859,550 [Patent Document 2] Japanese Published Unexamined Patent Application No. S62-266301 However, in the construction method of the U.S. Pat. No. 859,550, the frame body housing the modules of the heat exchanger tube bundle panels becomes large in size since it can be used as it is as a main frame of the heat recovery boiler at the construction site. Therefore, the costs for transporting the modules of the heat exchanger tube bundle panels increase. An objective of the invention is to provide a construction method for a heat recovery boiler which can reduce the transportation costs, prevent damage to the heat exchanger tube bundle panels during transportation, reduce the installation costs, and minimize waste material after installation, and a heat exchanger tube bundle panel module to be used for this method. An additional objective of the invention is to provide a construction method for a heat recovery boiler that is most economical since the components forming the heat recovery boiler are formed into several modules and manufactured in the factory and transported to the site and assembled, and a heat exchanger tube bundle panel module to be used for this method. When constructing a heat recovery boiler, in order to improve the installation performance and operation safety by labor reduction, in particular, reduction of high level work at the construction site of the heat recovery boiler by dividing the heat exchanger tube bundle panel part including a heat exchanger tubes 6 and upper header and lower header thereof into several modules for the entire heat recovery boiler, it is desirable that structural members for the heat recovery boiler such as main columns 33, main beams 34, bottom wall columns 36, etc., are incorporated into the module. However, the modules with the structural members incorporated have a longer cross sectional area at the exhaust gas duct, and become large in size. In the case of the large modules, the heat recovery boiler construction site is limited to a site such as a coastal area near a pier wherein a large barge can approach alongside due to transportation conditions, whereby installation outside Japan of the modules manufactured in Japan is poor in adaptability. Therefore, in the invention, members (module frames 24 and 25, described later, and so on) that become a part of the structural members such as the main columns 33 and the main beams 34 of the heat recovery boiler are used as components of the heat exchanger tube bundle panel module 20. Thereby, the module frames 24 and 25 can reinforce the heat exchanger tube bundle panel module during transportation. In the invention, the module frames 24 and 25 are coupled to the heat recovery boiler main frames such as the main columns 33 and the main beams 34, etc., after construction of the heat recovery boiler, so that the transportation costs are reduced according to the heat recovery boiler main frames such as the main columns 33 and the main beams 34, etc., that are not transported, and members are rarely wasted after construction. (1) The invention relates to an exhaust heat recovery boiler construction method constituted as follows. A construction method for an exhaust heat recovery boiler that generates steam by disposing a number of heat exchanger tubes 6 in a gas duct in that an exhaust gas flows almost horizontally, wherein, a heat exchanger tube bundle panel module 20 including: a plurality of heat exchanger tube bundle panels 23 disposed along the gas flow including a number of heat exchanger tubes 6, upper and lower headers 7, 8 of the heat exchanger tubes 6, and vibration restraining supports 18 that are disposed at predetermined intervals to prevent contact between adjacent heat exchanger tubes 6 in the direction crossing the lengthwise direction of the heat exchanger tubes 6; a casing 1 that forms the gas duct which is attached inside with a thermal insulating material 13 to cover the outer periphery consisting of the ceiling wall, the bottom wall, and both-side walls along the gas flow of the plurality of heat exchanger tube bundle panels 23; heat exchanger tube bundle panel support beams 22 located outside the ceiling wall of the casing 1 to become the ceiling wall at the time of installation at the boiler construction site; header supports 11 that penetrate the ceiling wall of the casing 1 and connect the upper headers 7 and the heat exchanger tube bundle panel support beams 22 to hang the upper headers 7 down; vertical module frames 24 as vertical support members of the heat exchanger tube bundle panels 23 located outside both side walls of the casing 1 to become both side walls at the time of installation at the boiler construction site; and horizontal module frames 25 as horizontal support members of the heat exchanger tube bundle panel 23 located outside the ceiling wall and bottom wall of the casing 1 to become the ceiling wall and the bottom wall at the time of installation at the construction site, is set as one module unit and a necessary number of modules are prepared in a proper size according to the design specifications of the exhaust heat recovery boiler, main frames for supporting the heat exchanger tube bundle panel module 20 including the main columns 33, the main beams 34 and the bottom wall columns 36 are constructed in advance at the construction site of the exhaust heat recovery boiler, the heat exchanger tube panel modules 20 are inserted between adjacent two main columns 33 and the heat exchanger tube panel support beams 22 of the heat exchanger tube bundle panel modules 20 are set at the setting height of the main beams 34 at the exhaust heat recovery boiler construction site, and the vertical module frames 24 and the main columns 33, the horizontal module frame 25 on the ceiling wall side and the main beam 34, and the horizontal module frame 25 on the bottom wall side and the bottom wall columns 36 are connected and fixed to each other. At the exhaust heat recovery boiler construction site, it is possible that bottom wall columns 36 having surfaces orthogonal to the gas flow and the widths of which in the horizontal direction of the plane are made wider than those of the main columns 33 are disposed by a number enabling the bottom wall corners of the heat exchanger tube bundle panel modules 20 to be placed thereon, and at least on the wide width portions of the bottom wall columns 36 of both side walls, the main columns 33 and the lower ends of the vertical module frames 24 are placed. In addition, when transporting the heat exchanger tube bundle panel modules 20 of one module unit, vibration restraining fixing members 26 and 61 are disposed between the vibration restraining supports 18 and the casing 1 which becomes both side walls and between the lower headers 8 and the casing 1, whereby damage during transportation can be prevented. When each heat exchanger tube bundle panel module 20 is formed into a size that enables two or more modules to be disposed in the horizontal direction of a plane orthogonal to the gas flow of the exhaust heat recovery boiler, and the vertical module frames 24 are formed of a vertical module frame 24a disposed on the casing 1 side and a vertical module frame 24b disposed on the adjacent heat exchanger tube bundle panel module 20 side, a construction method for the exhaust heat recovery boiler is employed in which the vertical module frame 24a and the horizontal module frame 25 of the heat exchanger tube bundle panel module 20 are connected to the main frames for supporting the module 20 including the main columns 33, the main beams 34 and the bottom wall columns 36, the module frame 24b is removed, and furthermore, when several reinforcing module frames 24c that are located at positions facing the heat exchanger tube bundle panel 23 on the front surface side and/or the back surface side in the gas flow direction of each heat exchanger tube bundle panel module 20 and connect the vertical module frames 24a and 24b to each other, the reinforcing module frames 24c are also removed. When each heat exchanger tube bundle panel module 20 is formed into a size enabling two or more modules to be disposed in the horizontal direction of a plane orthogonal to the gas flow of the exhaust heat recovery boiler, and when first aseismic braces 59a and 59a that connect the end portion inner side of the casing 1 to become the ceiling wall and the central portion inner side of the casing 1 to become the side wall of the heat exchanger tube bundle panel module 20 respectively, are located at positions facing the heat exchanger tube bundle panels 23 on the surface side and/or the back surface side in the gas flow direction, and the second aseismic braces 59b and 59b that connect the end of the casing 1 to become the bottom wall side and the central portion inner side of the casing 1 to become the side wall of the heat exchanger tube bundle panel module 20 respectively, are located at positions facing the heat exchanger tube bundle panels 23 on the surface side and/or the back surface side in the gas flow direction, the first and second aseismic braces 59a and 59b are used not only during transportation and installation at the boiler construction site of the heat exchanger tube bundle panel modules 20, but also are used even after completion of the boiler installation without removing the braces. When transporting the heat exchanger tube bundle panel modules 20, the first and second aseismic braces 59a and 59b and a transporting spacer 63 that maintains the gap between the surface and/or the back surface in the gas flow direction of the heat exchanger tube bundle panel 23 are disposed, whereby the first and second aseismic braces 59a and 59b can be commonly used as transporting reinforcing members, so that it becomes unnecessary to newly located transporting reinforcing members. When each heat exchanger tube bundle panel module 20 is formed into a size that enables two or more modules to be located in the horizontal direction of a plane orthogonal to the gas flow of the exhaust heat recovery boiler, the end of the casing 1 to become the ceiling wall side and the end of the casing 1 to become the bottom wall side of the heat exchanger tube bundle panel module 20 respectively are coupled to each other by first transporting reinforcing member 70 by a removable coupling method, and the first transporting reinforcing member 70 and the casing 1 to become the side wall side are coupled to each other by a plurality of second transporting reinforcing members 71 by a removable coupling method, at the time of transporting the heat exchanger tube bundle panel modules 20 and at the time of installation at the boiler construction site, the first transporting reinforcing member 70 and the second transporting reinforcing members 71 are left as they are, and these are removed after completion of installation, whereby the exhaust heat recovery boiler is constructed. (2) In addition, the invention relates to a heat exchanger tube bundle panel module for constructing an exhaust heat recovery boiler constituted as follows. A heat exchanger tube bundle panel module for constructing an exhaust heat recovery boiler which generates steam by disposing a number of heat exchanger tubes 6 inside a gas duct in that an exhaust gas flows almost horizontally, comprises: a plurality of heat exchanger tube bundle panels 23 disposed along the gas flow, each including a number of heat exchanger tubes 6, upper and lower headers 7 and 8 of the heat exchanger tubes 6, and vibration restraining supports 18 located at predetermined intervals to prevent contact between adjacent heat exchanger tubes 6 in a direction crossing the lengthwise direction of the heat exchanger tubes 6, and a casing 1 that forms the gas duct and has a thermal insulating material 13 attached inside to cover the outer periphery formed by the ceiling walls, the bottom walls, and both side walls along the gas flow of the plurality of heat exchanger tube bundle panels 23, heat exchanger tube bundle panel support beams 22 located outside the ceiling wall of the casing 1 to become the ceiling wall when installing at the boiler construction site, header supports 11 that penetrate the ceiling wall of the casing 1 and connect the upper headers 7 and the heat exchanger tube bundle panel support beams 22 to hang the upper headers 7 down, vertical module frames 24 that are vertical support members of the heat exchanger tube bundle panels 23 located outside the casing 1 to become both side walls when installing at the boiler construction site, and horizontal module frames 25 that are horizontal support members of the heat exchanger tube bundle panels 23 located outside the ceiling wall and outside the bottom wall of the casing 1 to become the ceiling wall and the bottom wall when installing at the boiler construction site, wherein when installing an exhaust heat recovery boiler at the construction site, a heat exchanger tube bundle panel module 20 with a size enabling two or more modules to be disposed adjacent to each other in the horizontal direction of a plane orthogonal to the gas flow of the boiler is set as one module unit, and the main columns 33 and the vertical module frames 24 in the main frames for supporting the module including the main columns 33, the main beam 34, and the bottom wall column 36 to be constructed in advance at the exhaust heat recovery boiler construction site, the main beam 34 and the horizontal module frame 25 on the ceiling wall side, and the bottom wall column 36 and the horizontal module frame 25 on the bottom wall side can be connected and fixed to each other. The vertical module frames 24 consist of a vertical module frame 24a located on the casing 1 side and a vertical module frame 24b located on the heat exchanger tube bundle panel module 20 side, and is further located with a plurality of reinforcing module frames 24c that are positioned to face the heat exchanger tube bundle panels 23 on the surface side and/or the back surface side in the gas flow direction of each heat exchanger tube bundle panel module 20, and connect the vertical module frames 24a and 24b and are removed after installing the boiler. In this case, after installing the boiler of the modules 20, the vertical module frame 24b and the reinforcing module frame 24c are removed. In addition, it is possible that the vertical module frames 24 consist of a vertical module frame 24a disposed on the casing 1 side, and includes the first aseismic braces 59a and 59a that connect the end portion inner side of the casing 1 to become the ceiling wall side and the central portion inner side of the casing 1 to become the side wall, and are positioned to face the heat exchanger tube bundle panels 23 on the surface side and/or back surface side in the gas flow direction of the heat exchanger tube bundle panel modules 20, and the second aseismic braces 59b and 59b that connect the end of the casing 1 to become the bottom wall side and the central portion inner side of the casing 1 to become the side wall side, and are positioned to face the heat exchanger tube bundle panels 23 on the surface side and/or back surface side in the gas flow direction. In this case, the heat exchanger tube bundle panels 23 can be protected when the modules 20 are transported and installed, and simultaneously, the first and second aseismic braces 59a and 59b can be used as reinforcing members of the heat exchanger tube bundle panels 23 without being removed after the heat exchanger tube bundle panel modules 20 are installed in an exhaust heat recovery boiler. Furthermore, the vertical module frames 24 can be located with the first transporting reinforcing member 70 that couples the end of the casing 1 to become the ceiling wall side and the end of the casing 1 to become the bottom wall side to each other, and is removed after completion of installation in the boiler, and a plurality of second transporting reinforcing members 71 that couple the first transporting reinforcing member 70 and the casing 1 to become the side wall side to each other and are removed after completion of installation in the boiler, positioned to face the heat exchanger tube bundle panel modules 23 on the surface side and/or the back surface side in the gas flow direction of the respective heat exchanger tube bundle panels 20. Herein, for the coupling portion between both ends of the casing 1 to become the ceiling wall side and the bottom wall side and the first transporting reinforcing member 70 and the coupling portions between the side wall side casing 1 and the second transporting reinforcing members 71, a fitting type coupling method is used for a coupling portion where a compressive load is applied, and a bolt coupling method is used for a coupling portion where a tensile load is applied, whereby enabling the first transporting reinforcing member 70 and the second transporting reinforcing members 71 to be easily removed after installing the heat exchanger tube bundle panel modules 20 in the exhaust heat recovery boiler. In addition, even when bolt coupling is used for both the coupling portion between both ends of the casing 1 to become the ceiling wall side and the bottom wall side and the first transporting reinforcing member 70 and the coupling portions between the casing 1 to become the side wall side and the second transporting reinforcing members 71, the first transporting reinforcing member 70 and the second transporting reinforcing members 71 can be easily removed after installing the heat exchanger tube bundle panel modules 20 in the exhaust heat recovery boiler. In addition, it is allowed that the reinforcing module frame 24c, the first and second aseismic braces 59a and 59b, and the second transporting reinforcing members 71 are disposed on either the surface side or the back side in the gas flow direction of the heat exchanger tube bundle panels 23 as long as protection of the modules 20 is possible at the time of transportation, etc. Furthermore, gas passing preventive baffle plates 28 and 28 are attached to both side surfaces of the plane (gas path width plane) orthogonal to the gas flow direction of the heat exchanger tube bundle panel 23 of each heat exchanger tube bundle panel module 20, and between the respective heat exchanger tube bundle panels 23 of two modules 20 and 20 adjacent to each other in the horizontal direction of the surface orthogonal to the gas flow, a gas short pass preventive plates 29 which are connected at one side surface to the baffle plate 28 of one heat exchanger tube bundle panels 23, and come into contact at the other side surface with the baffle plate 28 of the other heat exchanger tube bundle panel 23, are attached, whereby one side wall of the gas short pass preventive plate 29 is strongly pressed by the baffle plate 28 in contact with it due to the gas flow, eliminates the gap between the two heat exchanger tube bundle panels 23 disposed adjacent to each other, and prevents generation of gas that does not pass the insides of the heat exchanger tube bundle panels 23 (gas short pass). Particularly, by folding the side surface of the gas short pass preventive plate 29 to come into contact with the baffle plate 28 of the heat exchanger tube bundle panel 23 toward the upstream side of the gas flow inside the gas duct, the gas flow is engulfed by the folding portion, the folding portion is more strongly pressed against the baffle plate 28, and the gas short pass preventive effect increases further. A modulation construction method of a horizontal exhaust heat recovery boiler that forms a gas duct in the horizontal direction according to embodiments of the invention is described with reference to the drawings. FIG. 1 is a schemic view of the horizontal exhaust heat recovery boiler, FIG. 2 shows a section orthogonal to the gas flow direction of the heat recovery boiler of an exhaust gas G flow horizontally shown in FIG. 1, and FIG. 3 shows a section in the gas flow direction. FIG. 2 is equivalent to a sectional view on the arrow A-A of FIG. 1, and FIG. 3 is equivalent to a sectional view on the arrow S-S of FIG. 2. The heat exchanger tube bundle panel 23 of the exhaust heat recovery boiler includes, as shown in FIG. 2 or FIG. 3, a number of heat exchanger tubes 6, an upper header 7, a lower header 8, an upper connecting duct 9, and a lower connecting duct 10, and the heat exchanger tube panel 23 is supported onto a heat exchanger tube bundle panel support beam 22 via header supports 11. The outer periphery of the heat exchanger tube bundle panels 23 is enclosed by a thermal insulating material (thermal insulator) 13 and a casing 1 covering the outer periphery of the thermal insulating material. The casing 1 is made of a steel plate, and its plate thickness is approximately 6 millimeters. Inside the thermal insulating material 13, a liner 12 (also referred to as an inner casing) for retaining the thermal insulating material is located (the casing 1 including the lamination of the liner 12 and the thermal insulating material 13 is simply referred to as a casing 1 in some cases). On the outer surface of the heat exchanger tube 6, a fin 16 (partially shown in FIG. 2 and FIG. 3) is wound, and a plurality of fin-attached heat exchanger tubes 6 are arranged in the exhaust gas flow direction in zigzags, that is, in staggered arrangement. When the exhaust gas G passes between the heat exchanger tubes 6 and the speed reaches a certain extent or more, the fluid force of the passing exhaust gas G and the rigidity of the heat exchanger tubes 6 forming the passage of the exhaust gas G interfere with each other, and may cause a phenomenon called flow induced vibration in that self-excited vibration of the heat exchanger tubes 6 occurs. In order to prevent the flow induced vibration and avoid contact between forward and rearward and left and right heat exchanger tubes 6, the tubes are bundled by vibration restraining supports 18 located in a direction orthogonal to the tube axis. As shown in FIG. 3, between the lower header 8 and a wall face structure formed of the lower casing 1, the liner 12, and the thermal insulating material 13, a panel aseismic device 31 having a structure that adapts to vertical thermal elongation and prevents vibrations in the forward and rearward directions is located. FIG. 4 is a side view of a heat exchanger tube bundle panel module 20 of a first embodiment of the invention. One through several heat exchanger tube bundle panels 23 each including a plurality of fin-attached heat exchanger tubes 6, the upper header 7, and the lower header 8, etc., are arranged in parallel to the gas flow direction to form a module, and are integrated with vertical module frames 24 (24a, 24b) and horizontal module frames 25 that are commonly used as transporting frames are integrated together to obtain each heat exchanger tube bundle panel module (hereinafter, may be simply referred to as a module) 20. The number of panels in the heat exchanger tube panel module 20 is set by considering the limits in transportation to the construction site, installation efficiency at the installation site, and limitations due to system performance, etc. Therefore, in one heat exchanger tube panel module 20, heat exchanger tube bundle panels 23 including many (for example, 600) heat exchanger tubes 6, their upper and lower headers 7 and 8, and upper and lower connecting ducts 9 and 10, and around these, a wall face structure that forms each part of the casing 1, the liner 12, and the thermal insulating material 13 which construct the ceiling wall face, and the side wall face, and the bottom wall face of the heat recovery boiler are located, and these are integrated together by being housed in the module frames 24 and 25. FIG. 5 is a schemic perspective view including a partial section of a supporting structure from which the upper header 7 portion of one heat exchanger tube bundle panel module 20 consisting of four heat exchanger tube bundle panels 23 are hung down via the ceiling wall of the casing 1 as an example. FIG. 3 shows a state where two heat exchanger tube bundle panel modules 20 each consisting of five heat exchanger tube bundle panels 23 are installed along the gas flow direction of the boiler. To the peripheral portions on the four corners of the ceiling of the casing 1 of each heat exchanger tube bundle panel module 20, horizontal module frames 25 are fixed, and on the casing 1 on the inner side of the horizontal module frames 25, a plurality of heat exchanger tube bundle panel support beams 22 are fixed. The heat exchanger tube bundle panel support beams 22 support the upper headers 7 of the heat exchanger tube bundle panels 23 via the header supports 11, and both ends of the heat exchanger tube bundle panel support beams 22 are weld-connected to the horizontal module frames 25 (the horizontal module frame 25 on the near side is not shown in FIG. 5). As shown in FIG. 4, the vertical module frames 24 (24a and 24b) and the horizontal module frames 25 are weld-connected to the casing 1 in advance. The module frames 24 and 25 are formed of wide flange beams, etc., with widths narrower than the widths of the main columns 33 and the main beams 34 located in advance at the construction site. These are integrated with the main beams 33 and the main columns 34 located outside the casing 1 and serve as structural members of the casing 1 of the heat recovery boiler. The vertical module frames 24 are connected to the main columns 3 at the construction site, the ceiling wall side horizontal module frame 25 is connected to the main beams 34 at the construction site, and the bottom wall side horizontal module frames 25 are connected to the bottom wall columns 36. The module frames 24 and 25 are located at positions of a part of the main columns 33 and the main beams 34 of the heat recovery boiler at the construction site, and the module frames 24 and 25 become reinforcing members when transporting the modules 20. In addition, the lengths of the module frames 24 and 25 projecting to the outside of the casing 1 that are comparatively narrower than the main columns 33 and the main beams 34 are shorter than the widths of the main columns 33 and the main beams 34, so that the increase in transportation costs due to location of the module frames 24 and 25 can be negligible. Of the two vertical module frames 24a and 25b of the module 20 shown in FIG. 4, the module frame 24b is positioned at the center of the gas duct of the heat recovery boiler when two modules 20 are arranged parallel to the width direction of the gas duct (the horizontal direction of the plane orthogonal to the gas flow), and the two module frames 24a and 24b are attached with a number of reinforcing module frames 24c on the surface in the width direction of the module 20 for reinforcement during transportation, and brackets 24d for connecting the module frames 24c to the module frame 24b are attached to the module frame 24b. These module frames 24b and 24c and the brackets 24d are removed after installing the modules 20. In this embodiment, in order to prevent the modules 20 from being damaged by vibrations during transportation, it is possible that, as shown in FIG. 6, between the vibration restraining support 18 and a wall face structure formed by the casing 1, the liner 12, and the thermal insulating material 13, a vibration restraining fixing bolt 26 is located. After pressing the vibration restraining fixing bolt 26 that can be pressed toward the end of the vibration restraining support 18 from the outside of the wall face structure (may be simply referred to as the casing 1), the bolt is tightened by a lock nut 27 to fix the heat exchanger tube bundle panel 23 to the wall face structure via the vibration restraining support 18 (FIG. 6(a)). When installing the module 20 at the heat recovery boiler construction site, the tightened lock nut 27 is loosened to release the pressing of the fixing bolt 26 against the vibration restraining support 18, whereby removing the module 20 from the wall face structure (FIG. 6(b)). It is also possible that a fixing member having a plate with a length corresponding to the distance between the casing 1 and the end of the vibration restraining support 18 is welded to both the wall face structure and the vibration restraining support 18 and this fixing member is cut after transportation although this is not shown. Furthermore, it is also possible that a plate such as one made of wood with a thickness corresponding to the gap between the casing 1 and the end of the vibration restraining support 18 is inserted in the gap, and this plate is removed after transportation. Furthermore, it is also possible that a filler such as sand or gel material, etc., is filled in necessary points of the heat exchanger tube bundle panel 23 inside the wall face structure so as to prevent the heat exchanger tube bundle panel 23 from vibrating and this filler is extracted after transportation. Moreover, although this is not shown, it is also possible that a vibration restraining fixing member having a pair of rods that have changeable widths and can temporarily fix the set widths is sandwiched between the wall face structure and the vibration restraining support 18 during transportation to prevent the heat exchanger tube bundle panel 23 from being damaged during transportation. A heat recovery boiler for a combined cycle power generation plant with a gas turbine burning temperature of the 1300° C. class is divided into two or three modules 20 in the width direction of the gas duct (direction orthogonal to the gas flow) (FIG. 2 is a sectional view of modules 20 that are two-divided in the gas flow direction and assembled to the main columns 33 and the main beams 34), and in the gas flow direction, each module 20 contains one to twelve heat exchanger tube bundle panels 23, and this quantity is determined based on layout of the panels 23 and restrictions on transportation. The modules 20 may be different in size depending on their positions inside the heat recovery boiler. One module 20 has a size of, for example, 26 m in the up and down direction of the paper surface of FIG. 4, 3 to 4.5 m in the paper depth direction, and 1.5 to 4 m in the paper surface transverse direction. FIG. 7 shows a heat exchanger tube bundle panel module 20 of a second embodiment of the invention. This module 20 is transported by laying the side wall face horizontally, so that the side view of the horizontally laid state is shown in FIG. 7. Inside the casing 1 (the casing 1 including a lamination of the liner 12 and the heat reversing material 13 inside may be simply referred to as a casing) including a lamination of the liner 12 and the thermal insulating material 13 inside, a plurality of heat exchanger tube bundle panels 23 each including a number of heat exchanger tubes 6, an upper header 7 and a lower header 8 thereof, and vibration restraining supports 18, etc., are housed. Between the heat exchanger tube bundle panels 23 and the casing 1, transporting spacers 61 that fix the heat exchanger tube bundle panels 23 are set between the vibration restraining support 18 and the casing 1 and between the lower header 8 and the casing 1. In addition, lugs 60a and 60b are attached to the inner surfaces of both ends of the ceiling wall side casing 1 and the bottom wall side casing 1, a lug 60c is attached to the central portion inner surface of the side wall casing 1, a aseismic brace 59a is attached between the lugs 60a and 60c, and a aseismic brace 59b is attached between the lugs 60b and 60c. The lugs 60a and 60b are located with a transporting hole 64 and a boiler driving slot 65, respectively, and when transporting, the first and second aseismic braces 59a and 59b are attached into the transporting holes 64. Therefore, the first and second aseismic braces 59a and 59b are roughly integrated with the casing 1. Since a trianglar shape is formed for the ceiling wall side casing 1, the sidewall side casing 1, and the first aseismic brace 59a and a trianglar shape is formed for the bottom wall side casing 1, the sidewall side casing 1, and the second aseismic brace 59b, the casings 1 on the respective wall faces are reinforced to become a firm structure by the first and second aseismic braces 59a and 59b, so that it is unnecessary to located the reinforcing module frame 24c of FIG. 4. In addition, as shown in FIG. 9 (view on the section along S-S of FIG. 2), after installing the heat exchanger tube bundle panel module 20 to the main columns 33 and the main beams 34 of the main frames, transporting spacers 63 are located for maintaining the distances between the heat exchanger tube bundle panels 23 on the surface side and/or back surface side and the first and second aseismic braces 59a and 59b facing each other in the gas flow direction, whereby the module 20 can be prevented from deforming during marine transportation without vibrations of the heat exchanger tube bundle panels 23. In addition, the module 20 shown in FIG. 7 is a firm structure, so that marine transportation is possible even when the vertical module 24b shown in FIG. 4 is not located. FIG. 8 shows a state in that the module 20 of FIG. 7 is lifted by a crane in the direction of arrow A. In this case, a trianglar shape is also formed by the casing 1 and the first and second aseismic braces 59a and 59b, so that the casing 1 does not deform due to the lifting load, and it is not necessary to add a new structural member. FIG. 10 is a side view of an arrangement in the horizontal direction (gas path width direction) of a plane orthogonal to the gas flow when two modules 20 and 20 and structural members supporting the modules are integrated together to assemble an exhaust heat recovery boiler. After assembling the modules 20 and 20, pairs of braces 59a and 59b and 59a and 59b are inserted in the driving slots 65 of the lugs 60a and 60b and 60a and 60b. The driving slots 65 are rectangular slots, and the first and second aseismic braces 59a and 59b and 59a and 59b can be movable along the slots 65 when the boiler is driven, so that even when the first and second aseismic braces 59a and 59b and 59a and 59b thermally expand, this thermal expansion can be absorbed by the driving slots 65. Therefore, thermal expansion of the first and second aseismic braces 59a and 59b and 59a and 59b is not restricted, and after assembling the modules 20 and 20 to the boiler main body, the work of cutting and removing the first and second aseismic braces 59a and 59b and 59a and 59b is not necessary. In addition, the four first and second aseismic braces 59a and 59b and 59a and 59b form a diamond shape, and play a role in preventing deformation of the casing 1 when the exhaust heat recovery boiler receives a seismic force in the horizontal direction of the arrow B. FIG. 9 shows an example of one module 20 that is a block of five heat exchanger tube bundle panels 23. Each heat exchanger tube bundle panel 23 is formed by joining the upper header 7 and the lower header 8 by three-row heat exchanger tubes 6. The heat exchanger tubes 6 are fixed by hanging supports 11 that link the lug 57 attached to the upper header 7 and the casing 1. In addition, the transporting spacer 63 prevents the heat exchanger tube bundle panels 23 from moving in the paper surface transverse direction of FIG. 9. Between the lower header 8 and the wall face structure formed by the lower casing 1, the liner 12, and the thermal insulating material 13, a panel aseismic devices 31 that have a structure for adapting to vertical thermal elongation and preventing vibrations in the forward and rearward directions are located. FIG. 11 is a side view of the entire structure of an exhaust heat recovery boiler to which the heat exchanger tube bundle panel module 20 is applied according to this embodiment. In the example shown in FIG. 11, in order from the upstream side to the downstream side of the inside of the exhaust gas duct, a superheater A, a high-pressure evaporator B, denitration equipment C, a high-pressure economizer D, a low-pressure evaporator E, and a low-pressure economizer F are located. For the superheater A and the high-pressure evaporator B, one heat exchanger tube bundle panel module 20 is located each forward and rearward of the gas flow direction, respectively, and also for the high-pressure economizer D and the low-pressure economizer F, one heat exchanger tube bundle panel module 20 is each located forward and rearward of the gas flow direction, respectively. In the front side of the gas flow direction of the module 20 of the superheater A, the first and second aseismic braces 59a and 59b are located, and on the rear side of the gas flow direction of the module 20 of the high-pressure evaporator B, the first and second aseismic braces 59a and 59b are located. Likewise, the first and second aseismic braces 59a and 59b are located on the front side of the gas flow direction of the module 20 of the high-pressure economizer D, and on the rear side of the gas flow direction of the module of the low-pressure economizer F, the first and second aseismic braces 59a and 59b are located. The necessary number of the first and second aseismic braces 59a and 59b for the entire heat recovery boiler are installed, and in the forward and rearward of the gas flow direction of the low-pressure evaporator E of this embodiment, it is not necessary to dispose the first and second aseismic braces 59a and 59b, so that these are not located. Furthermore, in the forward and rearward of the gas flow direction of the denitration equipment C, as a denitration equipment module different from the heat exchanger tube bundle panel module 20 of the invention, the first and second aseismic braces 59a and 59b are located, or different type aseismic braces are used. As described above, when an exhaust heat recovery boiler is constructed by using the module 20 of FIG. 7 and FIG. 9, the first and second aseismic braces 59a and 59b and 59a and 59b are located, so that the first and second aseismic braces 59a and 59b and 59a and 59b can be commonly used as reinforcing members when transporting or lifting. The material costs and manufacturing costs of the reinforcing members of the module 20 and cutting and removing costs of the reinforcing members after the boiler is constructed become unnecessary, and the costs of the exhaust heat recovery boiler can be significantly lowered. Thereby, the construction costs of the combined cycle power generation facilities can be reduced, and this leads to reduction in power generation unit costs. It is also possible that the module 20 of FIG. 7 and FIG. 9 and the module 20 from which the module frames 24b, 24c, and 24d shown in FIG. 4, have been removed, are mixed to assemble the heat exchanger tube bundle panels 23 of the exhaust heat recovery boiler. FIG. 12 is a side view of a heat exchanger tube bundle panel module 20 of a third embodiment of the invention. This module 20 is transported by laying the side wall face horizontally, so that a horizontally-laid side surface is shown in FIG. 12. Inside the casing 1 including a lamination of the liner 12 and the thermal insulating material 13 inside (the casing 1 formed by laminating the liner 12 and the thermal insulating material 13 may be simply referred to as a casing), heat exchanger tube bundle panels 23 each including a number of heat exchanger tubes 6, an upper header 7 and a lower header 8 thereof, and vibration restraining supports 18, etc., are contained. Between the heat exchanger tube bundle panels 23 and the casing 1, transporting spacers 61 for fixing the heat exchanger tube panels 23 during transportation are installed between the vibration restraining support 18 and the casing 1 and between the lower header 8 and the casing 1. On the inner surfaces of the ceiling side casing 1 and the bottom side casing 1, transporting reinforcing members 70 and 71 having truss structures are installed. The end portion inner surface of the ceiling wall side casing 1 and the end portion inner surface of the bottom wall side casing 1 are connected by the first transporting reinforcing member 70, and the inner surface of the bottom wall side casing 1 and the first transporting reinforcing member 70 are connected by a plurality of ladder-shaped and cater-cornered second transporting reinforcing members 71. To the first transporting reinforcing member 70 that couples the ends of the ceiling wall side casing 1 and the bottom wall side casing 1, a pair of lugs 72 and 72 are attached, and the module 20 becomes able to be lifted in the direction of the arrow A by the wire 73 connected to the lugs 72 and 72. A detailed view of the part A of FIG. 12 is shown in FIG. 13. The support plate 75 located on the ceiling wall side casing 1 and the first transporting reinforcing members 70 are attached with transporting reinforcing member fixing flanges 75a and 70a, respectively, and the first transporting reinforcing member 70 is bolt-coupled to the ceiling wall side casing 1 by the transporting reinforcing member fixing flanges 75a and 70a. The bottom wall side casing 1 and the transporting reinforcing member 70 are also bolt-coupled at the flange portions although this is not shown. FIG. 14 is a detailed view of the part B of FIG. 12. To the side wall side casing 1, the supporting plate 76 is fixed, and to the other end of the supporting plate 76 and the second transporting reinforcing member 71, flanges 76a and 71a are attached, respectively, and the second transporting reinforcing member 71 is bolt-coupled to the side wall side casing 1 by the flanges 16a and 71a. FIG. 15 shows the details of the part C of FIG. 12. To the side wall side casing 1, a transporting reinforcing member fixing guide 66 is attached, and into this guide 66, a second transporting reinforcing member 71 is fitted, and the second transporting reinforcing member 71 is restricted in movement other than movements in the axial direction. The heat exchanger tube bundle panel module 20 shown in FIG. 12 is transported by laying it horizontally, and during transportation, great vibration loads are applied forward and rearward, leftward and rightward, and upward and downward, and the reinforcing members 70 and 71 are integrated with the ceiling wall side, the bottom wall side, and the side wall side casings 1 by the fitting type transporting reinforcing member guide 66 and the reinforcing member fixing flanges 70a and 75a and 71a and 76a, and it can be prevented that the casing 1 deforms or is damaged by the vibration loads. During transportation of the module 20, as shown in FIG. 12, in some cases, the wire 73 is hooked on the lug 72 and the modules are lifted, and the load that acts at this time reaches the maximum when the boiler of the modules 20 is installed. As shown in FIG. 12, the results of investigation regarding the loading directions that act on the transporting reinforcing members 70 and 71 when the module 20 is lifted are shown in FIG. 16. In FIG. 16, the arrow T indicates that an axial force is generated in the tension direction, and the arrow C indicates that an axial force is generated in the compression direction. In this embodiment, the method of coupling the reinforcing members 70 and 71 and the casing 1 so as to make the removal of the transporting reinforcing members 70 and 71 easiest by considering the directions of the two axial forces is determined. Namely, for the part C of FIG. 12 where only a compressive load acts, a fitting type coupling method is used. Since only a compressive load acts on the part C, the transporting reinforcing member 70 does not come out of the side wall casing 17, and it becomes possible to remove the transporting reinforcing members 70 and 71 from the casing 1. Since a tensile axial force acts on the part B, bolt coupling is used which can resist against a tensile load and is most easily removed. To remove the transporting reinforcing members 70 and 71 after the modules 20 are installed into the main frames (main columns 33, main beams 34, and bottom columns 36, etc.) of the boiler structure, the bolts of the transporting reinforcing member fixing flanges 70a and 75a and 71a and 76a shown in FIG. 12 are loosened and removed, whereby the transporting reinforcing members are easily removed. FIG. 17 shows an example in which bolt coupling using a flange structure is employed for all connecting portions between the transportation reinforcing members 70 and 71 and the casing 1 shown in FIG. 12. In this case, since bolt coupling is applied to all connecting portions between the transportation reinforcing members 70 and 71 and the casing 1, the reinforcing members 70 and 71 and the casing 1 are firmly connected regardless of the direction the module 20 is turned toward during transportation, in particular, when it is lifted, and these connecting portions are disconnected by only removing the bolts, and therefore, the transportation reinforcing members 70 and 71 can be easily removed. Thus, in this embodiment, it becomes possible to easily remove the transporting reinforcing members 70 and 71 after the heat exchanger tube bundle panel modules 20 are installed into the main frames of the boiler structure of the exhaust heat recovery boiler, and the construction costs of the exhaust heat recovery boiler can be reduced. Thereby, the construction costs of the combined cycle power generation facilities can be reduced, so that an effect of reduction in power generation unit costs is obtained. Next, procedures for installing the heat exchanger tube bundle panel modules 20 to the main frames such as the main columns 33, the main beams 34, and the bottom columns 36, etc., at the heat recovery boiler construction site are described. At the heat recovery boiler construction site, as shown in the perspective view of FIG. 18, wide bottom columns 36 are located in advance, and on the bottom columns 36, the main columns 33 and the main beams 34 are constructed. When the installing positions of the main columns 33 and the main beams 34 are determined, the side supports 37 that connect adjacent main columns 33 to each other are located to make the retaining of the main columns 33 and the main beams 34 more firm. The width in the horizontal direction (gas path width direction) of the bottom wall column 36 is set wider than the width of the main column 33 to be disposed above it, and when two modules 20 are disposed adjacent to each other in the width direction of the gas duct shown in FIG. 18, the bottom wall corners of the two modules 20 can be simultaneously placed on the central bottom wall column 36. On the two bottom wall columns 36 on the side wall side, the other side bottom wall corners of the two modules 20 adjacent to each other in the gas flow direction are placed, respectively. Next, as shown in the perspective view of FIG. 19, before installing the modules 20 into the heat recovery boiler structural members including the main columns 33, the main beams 34, the bottom wall columns 36, and the side supports 37, some of the main beams 34 are removed and appropriate points of the ceiling wall side and the bottom wall side of the module frames 24 and 25 are lifted by a crane 42 and the modules 20 are located between the adjacent main columns 33 in order as shown in the plan view of FIG. 21 and the perspective view of FIG. 22. Also in this case, the module frames 24 and 25 of the modules which become a part of the main columns 33 and the main beams 34 are located outside the casing 1, so that there is no possibility that the modules 20 deform due to structural shortage when they are lifted by the crane 42. However, when lifting the modules 20, if they are lifted while a part of the modules 20 is in contact with the ground, an unexpected load is applied to the ground contact portion and it may deform, so that it is necessary that the module 20 is inserted between the two main columns 33 as shown in FIG. 21 and FIG. 22 while being lifted so that the ceiling wall and the bottom wall of the casing 1 of the module 20 do not come into contact with the ground together with the crane 42, and then hang down from the main beam 34. As shown in FIG. 21 and FIG. 22, the module 20 is inserted between the two main columns 33 disposed in the forward and rearward direction as the gas flow direction, where no side support 37 is located, and disposed at a predetermined position as shown in FIG. 23, and the upper part of the module 20 is connected to the main beam 34 on the rear side. Next, as shown in the perspective view of FIG. 24, the module 20 to be located adjacent to the above-described module 20 is also inserted between two main columns 33 and connected to the main beam 34 on the rear side in the same manner. Thereafter, the upper parts of the two modules 20 are connected to the main beams 34 on the front side. Since FIG. 22 through FIG. 24 show the case where the heat exchanger tube bundle panel modules 20 shown in FIG. 4 are installed, and after the upper parts of the two modules 20 structured as shown in FIG. 4 are connected to the main beams 34 of the front side in the state of FIG. 24, the reinforcing module frames 24c and the brackets 24d must be removed. When the modules 20 structured as shown in FIG. 7 are connected to the main columns 33 and the main beams 34, the first and second aseismic braces 59a and 59b are not removed but are used as they are as structural members of the exhaust heat recovery boiler. Furthermore, when the modules 20 structured as shown in FIG. 12 are connected to the main columns 33 and the main beams 34, after the upper parts of the two modules 20 are connected to the main beams 34 on the front side in the state of FIG. 24, the first transporting reinforcing member 70 and the second transporting reinforcing member 71 must be removed. At a proper position shown in FIG. 25 (perspective view of the section cut along the D-D line of FIG. 2), the vertical module frame 24 is connected to the main column 33 by bolt and nut 38 and welding, and as shown in FIG. 26 (perspective view including sections cut along two vertical directions inside the module 20 of the oval area B of FIG. 2), the horizontal module frame 25 is connected to the main beam 34 by bolt and nut 38 and welding. Furthermore, as shown in FIG. 27 (perspective view including a section cut vertically inside the module 20 of the oval area A of FIG. 2) that shows the adjacent portions to each other of the horizontal module frames 25 of the two modules 20 arranged in the direction (referred to as the width direction) orthogonal to the gas flow of the gas duct, the horizontal module frames 25 of the modules 20 are placed on one bottom wall column 36 together. In FIG. 28 (perspective view including the sections cut along two vertical directions inside the module 20 of the oval area C of FIG. 2), two modules 20 to be located in parallel in the width direction of the gas duct and horizontal module frame 25 portions of the two modules 20 to be disposed adjacent to each other in the gas flow direction of the gas duct are shown. In the perspective views of FIG. 25 through FIG. 28, the vertical and horizontal module frames 24 and 25 are connected to the main columns 33 and the main beams 34 by welding or the like, and in the gap between the adjacent modules 20, a thermal insulating material 13′ and/or a casing 1′ (the liner 12 is not shown) is filled. A side view from the gas flow direction after the two modules 20 to be disposed in parallel in the width direction of the gas duct are welded and connected to the heat recovery boiler structural members (the main columns 33, the main beams 34, the bottom wall columns 36, and the side supports 37) is as shown in FIG. 2. Thus, when the heat exchanger tube bundle panel modules 20 are installed at the heat recovery boiler construction site, installation of the heat exchanger tube bundle panels 23 is completed as well as the casing 1 of the heat recovery boiler. According to this embodiment, dangerous construction work at the inner upper side of the casing 1 of the heat recovery boiler is omitted, scaffolding setting and removal become unnecessary, and the heat exchanger tube bundle panels 23 can be installed inside the heat recovery boiler casing 1 easily and quickly, so that a heat recovery boiler can be constructed in a short period. Only the heat exchanger tube bundle panels 23 arranged parallel in the gas path width direction of the exhaust heat recovery boiler of an embodiment of the invention are shown by the perspective view of FIG. 29 and the sectional view in the plane direction of FIG. 30, wherein on the side surfaces of the heat exchanger tube bundle panels 23 along the gas flow, baffle plates 28 are located, and furthermore gas short pass preventive plates 29 that prevent gas short pass are located. On both side surfaces of the heat exchanger tube bundle panels 23, baffle plates 28 are located to prevent gas short pass from the gaps between the heat exchanger tube bundle panels 23 and the casing 1, however, the gaps between the heat exchanger tube bundle panels 23 arranged in parallel to each other in the gas path width direction of the exhaust heat recovery boiler cannot be filled only by the baffle plates 28 as in the case of this embodiment. The reason for this is that gaps are necessary between adjacent heat exchanger tube bundle panels 23 when considering the installation operations of the heat exchanger tube bundle panels 23 and thermal elongation of the panels 23. If the gaps are left as they are, gas passes through the gaps, and as a result, the gas to pass through the heat exchanger tube bundle panels 23 is reduced and the recovery heat amount is reduced. Therefore, conventionally, for the gaps of the heat exchanger tube bundle panels 23, after installing the heat exchanger tube bundle panels 23, as shown in the sectional view in the plane direction of FIG. 31, gas short pass preventive plates 30 are set at the gas inlet and the gas outlet between the baffle plates 28 of adjacent panels 23. However, to set the gas short pass preventive plates 30 after setting scaffolding in the height direction including a high place, the installing period becomes long since safety measures such as prevention of workers falling during working at a height are taken. Therefore, in this embodiment, the gas short pass preventive plates 29 are attached in advance at the factory or the like to the baffle plates 28 of the heat exchanger tube bundle panel 23 on one side positioned corresponding to the gas inlet and gas outlet of the heat exchanger tube bundle panel 23, and then brought to the construction site, and the heat exchanger tube bundle panel 23 attached with the gas short pass preventive plates 29 is installed first. One side surface of the rectangular gas short pass preventive plate 29 is attached to the baffle plate 28, and the opposite side surface is left free. After the heat exchanger tube bundle panel 23 attached with the gas short pass preventive plates 29 is installed at the construction site, the other side heat exchanger tube bundle panel 23 without the gas short pass preventive plates 29 to be arranged in parallel is installed, and at this point, the other side heat exchanger tube bundle panel 23 is installed so that the gas short pass preventive plates 29 come into contact with the baffle plates 28 of the other side heat exchanger tube bundle panel 23. Thereby, when the gas flows, the free side surfaces of the gas short pass preventive plates 29 are press-contacted with the baffle plates 28 of the other side heat exchanger tube bundle panel 23 at the gas inlet side, so that the gap between the two heat exchanger tube bundle panels 23 is eliminated, whereby gas short pass does not occur. In addition, when the free side surfaces of the gas short pass preventive plates 29 are bent, the gas flow is efficiently caught up into the bent portions, so that the gas short pass preventive plates 29 are more securely pressed against the baffle plates 28 of the other side heat exchanger tube bundle panel 23, the gap is eliminated, and gas short pass is more reliably prevented. Thus, by attaching the gas short pass preventive plates 29 to the baffle plates 28 located on both side surfaces of each heat exchanger tube bundle panel 23 in advance at the component manufacturing factory or the like, it becomes unnecessary to set up scaffolding for attachment at the heat recovery boiler construction site, whereby the installing period of the gas short pass preventive plates 29 is shortened and the installing operations are improved in safety. According to the invention, by using the construction in that the module frames 24 and 25 that become a part of the main frames as structural members such as the main columns 33 and the main beams 34 of the heat recovery boiler are used as components of the heat exchanger tube bundle panel modules 20, the transportation costs are reduced according to the omission of the main frames such as the main columns 33 and the main beams 34 of the heat recovery boiler, and there is almost no member wasted after construction. Furthermore, when the heat exchanger tube bundle panel modules 20 of the exhaust heat recovery boiler are installed at the construction site, a structure with high installation performance at the heat recovery boiler construction site can be applied to the joint portions between the modules 20 and between the modules 20 and the main frames of the heat recovery boiler. In addition, by making the bottom wall columns 36 of the structural members located in advance at the heat recovery boiler construction site wider than the main columns 33, the operations for installing the heat exchanger tube bundle panel modules 20 can be reduced, the combined cycle power generation plant construction process can be rationalized, and the local installation costs can be reduced. Furthermore, after constructing the heat recovery boiler, the module frames 24 and 25 become a part of the main frames such as the main columns 33 and the main beams 34 of the heat recovery boiler, so that almost no member is wasted after construction. In addition, when transporting the heat exchanger tube bundle panel modules 20, vibration restraining fixing members 26 and 61 are located between the vibration restraining supports 18 located at predetermined intervals to prevent contact between adjacent heat exchanger tubes 6 and the casing 1, so that the heat exchanger tube bundle panel modules 20 can be prevented from being damaged, and transportation of the heat exchanger tube bundle panel modules 20 to a distant site becomes easy. Furthermore, between two heat exchanger tube bundle panels 23 to be disposed adjacent to each other in the gas path width direction (direction orthogonal to the gas flow), gas short pass preventive plates 29 that are connected at one-side surfaces to the baffle plates 28 of one side heat exchanger tube bundle panel 23 and come into contact at the other side surfaces with the baffle plates 28 of the other heat exchanger tube bundle panel 23 are attached, and in particular, the side surfaces of the gas short pass preventive plates which come into contact with the baffle plates 28 of the heat exchanger tube bundle panel 23 are bent toward the gas flow upstream side inside the gas duct, whereby gas short pass between the two heat exchanger tube bundle panels 23 does not occur, so that gas reserving heat can be effectively recovered. In addition, by connecting one-side surfaces of the gas short pass preventive plates 29 to the baffle plates 28 of one heat exchanger tube bundle panel 23 in advance, the heat exchanger tube bundle panel 23 with the gas short pass preventive plates 29 can be installed without scaffolding inside the furnace at the heat recovery boiler construction site, and this is preferable in view of safety in installing operations since it shortens the installing construction period and omits the work at a height. |
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051715180 | description | DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a segment of tubing having a first conductivity is removed from a heat exchanger. A thermally conductive material is supported on one of the inner side and the outer side of the tubing segment in thermal contact with the tubing segment wall. A thermocouple is placed in contact with a portion of the thermally conductive material which is not close to the tube wall. Temperature measurement points T.sub.1 and T.sub.2 that are not within the melting temperature range or vaporization temperature range of the thermally conductive material are selected. Preferably, T.sub.1 and T.sub.2 are selected such that the thermally conductive material is a melt at one of T.sub.1 and T.sub.2 and a solid at the other of T.sub.1 and T.sub.2. The tubing segment is brought to an initial temperature T.sub.i that is either higher or lower than both T.sub.1 and T.sub.2, and is kept at the initial temperature T.sub.i for a measured or known period of time. A heating or cooling medium having a temperture appropriate to bring the temperature of the thermally conductive material to T.sub.1, and subsequently to T.sub.2, is placed on the other of the inner and outer sides of the tubing segment in thermal contact with the tubing segment wall. Thermal contact includes direct physical contact, as well as indirect contact that is sufficiently close to provide a measurable amount of heat transfer between the substances. Preferably, the thermally conductive material and the heating or cooling medium are in direct physical contact with the tubing segment wall and are directly opposite each other, separated only by the tubing segment wall. While the tubing segment is in thermal contact with both the thermally conductive material and the heating or cooling medium, the time required for the temperature of the portion of the thermally conductive material in contact with the thermocouple to change from T.sub.1 to T.sub.2 is measured. Optionally, the tubing segment is then removed from contact with the medium after a known amount of time and is placed in contact with another heating or cooling medium having a temperature T.sub.c which will effect a temperature change in the opposite direction, i.e. from T.sub.5 to T.sub.6. The time required for the thermally conductive material to undergo a temperature change in this direction also can be timed. Time measurements of the heating and/or cooling processes preferably are made repeatedly until consistent, reliable data has been obtained. A tubing segment having a wall with different physical and/or heat transfer characteristics than the wall of the original tubing segment is then obtained, either by altering the physical and/or heat transfer characteristics of the original tubing segment or by selecting a different tubing segment. If the original tubing segment is altered, the thermally conductive material and thermocouple preferably, although not necessarily, remain in contact with the tubing segment during the alteration process. If a different tubing segment is used, the thermally conductive material is disposed in thermal contact with the wall of the tubing segment in the same manner as for the original tubing segment, and a thermocouple is placed in contact with the thermally conductive material, away from the tube wall. The time required for the thermally conductive material to undergo a predetermined temperature change from T.sub.3 to T.sub.4 is then measured by contacting the other of the inner and outer wall of the tubing segment, i.e, the wall that is not in contact with the thermally conductive material, with an appropriate heating or cooling medium having a temperature T.sub.b and measuring the time required for the temperature of the thermally conductive material to change from T.sub.3 to T.sub.4 in the same manner as with the original tubing segment. Measurements optionally can be made of temperature changes in an opposite direction, i.e., from T.sub.7 to T.sub.8 after placing a medium having a temperature T.sub.d in thermal contact with the tubing segment or the side of the tubing segment opposite to the thermally conductive material. Time measurements preferably are repeated until consistent and reliable data have been obtained. The same temperature measurement points and heating and/or cooling mediums preferably are used before and after alteration of the tubing segment, i.e. T.sub.a =T.sub.b, T.sub.1 =T.sub.3, and T.sub.2 =T.sub.4, and when applicable, T.sub.c =T.sub.d, T.sub.5 =T.sub.7 and T.sub.6 =T.sub.8 The tubing segment or segments used according to the method of the invention can be formed from any conductive metal or non-metal tubing material. Because the method of the invention does not require calculations based upon tube geometry, the tubing segment or segments can have any shape, thickness and composition. The invention is particularly useful for comparing the heat transfer characteristics of various types of thin-walled metal tubing useful in and/or removed from nuclear reactor steam generators, such as used and unused or cleaned Inconel 600 (International Nickel Company) tubing. The thermally conductive material preferably has a higher conductivity than the tubing segment wall within the temperature ranges T.sub.1 -T.sub.2 and T.sub.3 -T.sub.4 in order that the limiting factor in the rate of temperature change will be the heat transfer coefficient of the wall rather than the heat transfer coefficient of the thermally conductive material. The thermally conductive material preferably melts and crystallizes within narrow temperature ranges between T.sub.1 and T.sub.2 and between T.sub.3 and T.sub.4, and has a melting point well below the melting point of the tubing material. For example, low melt metal alloys comprising bismuth and lead and which have melting ranges of less than one degree Fahrenheit are particularly useful. Cerrobend.RTM. (Cerro Metal Products Co.), which contains 50.00% bismuth, 26.70% lead, 13.30% tin and 10.00% cadmium has been used successfully, as it melts in a narrow temperature range well below the melting point of a heat exchanger tube, i.e. at 158.degree. F. The thermally conductive material is conveniently kept at about atmospheric pressure, although the method of the invention can be carried out with the thermally conductive material maintained at another pressure. The thermally conductive material preferably is in the form of a melt when it is placed in contact with the inner or outer wall of the tubing segment. The amount of thermally conductive material that is required will depend in part upon the desired accuracy of the measurements which are made. Preferably, when the thermally conductive material is placed inside the tubing segment, the inner side of the tubing segment is filled almost completely, leaving only a small air space (about 1-5%) to allow for expansion of the thermally conductive material. As a minimum, a sufficient amount of thermally conductive material must be used to ensure that the temperature-sensitive point on the thermocouple is always in contact with only the thermally conductive material and does not contact the tube wall. When the thermally conductive material is placed on the outer side of the tube segment, it is desirable to have a thickness of about 0.25 inch or more along the entire length of the tube. In order to measure the temperature of the thermally conductive material, a thermocouple is positioned in contact with a portion of the thermally conductive material. The thermocouple should not touch the wall of the tubing segment. When the thermally conductive material is placed inside the tubing segment, a particularly useful way for preventing the thermocouple from touching the tube wall is to place the thermocouple at the end of a wire which is bent in an S-shaped curve. In this manner, the thermocouple can be positioned near the center of the tube, with the curves of the "S" abutting opposite side walls of the tube. Preferably, the thermocouple is positioned as far as possible from the ends of the tube, as heat transfer through the seals on the ends of the tube can therefore be considered negligible. When the thermally conductive material is placed inside the tubing segment, the tube preferably is sealed in any manner that will prevent leakage into or out of the interior of the tubing segment. Proper sealing of the tubing segment is particularly important for situations in which the inner walls of the tube may have been in contact with radioactive material, as escape of radioactivity into the heating and cooling mediums is thereby prevented. The tubing segment can be sealed with welded caps, locking fittings, or other airtight and watertight means. When the thermally conductive material is positioned outside the tubing segment, it is preferable to place the thermally conductive material in a sealed enclosure which encompasses the outer wall of the tubing segment, as such an arrangement will allow for the thermally conductive material to be melted. However, it also is possible to use a thermally conductive material on the inner or outer side of the tubing segment which remains in a solid phase throughout the measurement process, and under such circumstances a sealed enclosure is not necessarily required, assuming that the thermocouple is in contact with only the thermally conductive material. In order to bring about temperature changes of the thermally conductive material, heating and/or cooling mediums such as liquid baths are prepared. While a single measurement of the time required for a temperature change between a pair of temperatures T.sub.1 and T.sub.2 can be made using a single medium having a temperature that is higher or lower than both T.sub.1 and T.sub.2, it is preferable to have at least two baths, e.g. a first bath at a temperature T.sub.a that is warmer than both T.sub.1 and T.sub.2 and a second bath at a temperature T.sub.c that is cooler than both T.sub.1 and T.sub.2. By transferring the tubing segment repeatedly between the first and second baths, temperature increases and/or decreases of the thermally conductive material can be measured repeatedly. Optionally, the warmer bath has a temperature above the melting point of the thermally conductive material and the cooler bath has a temperature below the melting point of the material. Furthermore, the tubing segment preferably is repeatedly transferred from one bath directly to the other bath at a consistent interval of time, e.g. every 5 minutes, in order to ensure that multiple measurements are made under identical conditions. While a variety of types of mediums can be used, including gases and liquids, water and air are preferred for economic reasons. Preferably, the heating and/or cooling baths are the same substance that the tube is in contact with during its normal use, as the amount of improvement in heat transfer rates resulting from tube alteration may depend upon the type of medium that is used. For example, when the surface of the tubing segment has pores, different mediums may enter the pores at different rates, thereby affecting heat transfer rates through the tube wall. The temperature measurement points T.sub.1 and T.sub.2 are temperatures at which the slope of the applicable temperature versus time heating or cooling curve for the thermally conductive material is relatively steep. For example, T.sub.1 and T.sub.2 preferably are points of maximum slope on a temperature versus time heating curve for the thermally conductive material when T.sub.1 <T.sub.2 T.sub.1 and T.sub.2 preferably are points of maximum negative slope on a temperature versus time cooling curve for the thermally conductive material when T.sub.1 >T.sub.2. When a conventional thermocouple is used, the thermally conductive material preferably will have a rate of temperature change of at least about 2-3 degrees per minute at the temperature measurement points, and more preferably at least 3.5 degrees per minute. The melting and vaporization temperatures of the thermally conductive material are generally not suitable measurement points, as the temperature of the thermally conductive material will change very little, if at all, during the phase change. The same temperature measurement points preferably are used in connection with the original tubing segment and the second tubing segment, as otherwise normalization of one set of data relative to the other may be necessary. Also, it is preferable to use the same heating and/or cooling mediums for measurements made before and after alteration of the tubing segment, in order to avoid having to normalize one set of data relative to the other. Furthermore, use of a generally constant-temperature heating or cooling medium is preferred in order to avoid having to take into account changes in the temperature of the medium, and differences in volume of the medium used for time measurements of tubing segments having different conductivities. It has been found useful in practice to make time measurements between one pair of temperatures, e.g., T.sub.1 and T.sub.2 during heating of the thermally conductive material, and another pair of temperatures, e.g., T.sub.5 and T.sub.6, during cooling of the thermally conductive material, as the temperatures at which the rate of change in temperature of the thermally conductive material is highest can be different during thermally conductive material heating and cooling processes. When Cerrobend.RTM. alloy is used, useful temperature measurement points when the thermally conductive material is heated are about 155.degree. F. and 170.degree. F. During a corresponding cooling process, useful temperature measurement points are 160.degree. F. and 147.degree. F. The method of the present invention can be carried out under boiling conditions, preferably using water as a cooling medium and using a hot oven as a heating medium. When measurement of changes in heat transfer rates at or near the boiling point of water are desired, T.sub.1 preferably is greater than 212.degree. F., T.sub.2 is greater or less than 212.degree. F., and the tubing segment preferably contains a thermally conductive material that melts at a temperature greater than 212.degree. F. The tubing segment can be heated in an oven to a temperature above 212.degree. F. and subsequently cooled in a bath having a temperature of less than 212.degree. F. According to one embodiment of the invention, alteration of the heat transfer characteristics of the tubing segment includes any type of change that will impact the overall heat transfer coefficient of the tubing segment and/or the heat transfer area of the tube wall. Preferably, tubing segment alteration constitutes removal of deposits from the wall of the tubing segment, such as by chemical cleaning techniques. While the tubing segment preferably is cleaned on at least the outer surface, the inner surface of the tubing segment also can be cleaned. It is preferable to avoid temporarily removing the thermally conductive material from the tubing segment for purposes of cleaning. Thus, in situations in which the outer surface of the tubing segment is to be cleaned, the thermally conductive material preferably is placed inside the tube. Conversely, when the inner surface of the tubing segment is to be cleaned, the thermally conductive material preferably contacts the outer side of the tube. In practicing the method of the invention, time measurements which are accurate to at least the nearest second usually will provide for a useful comparison of heat transfer rates before and after cleaning of the tube walls. The times that are measured are inversely proportional to the overall rate at which heat is conducted from the medium surrounding the tube, through the tube wall and into the thermally conductive material, or in the opposite direction. The time measurements obtained before and after alteration of the segment can be compared qualitatively and/or quantitatively in a variety of ways. In this connection, the percentage change in heat transfer rate due to chemical cleaning can be calculated by taking the difference between the heat transfer times before and after chemical cleaning as measured under identical conditions, dividing this difference by the heat transfer time before alteration of the tubing segment, and multiplying the result by 100. Having generally described the invention, the following examples are included for purposes of illustration so that the invention may be more readily understood and are in no way intended to limit the scope of the invention, unless otherwise specifically indicated. EXAMPLE 1 Filling of Tubing Segment; Selection of Temperature Measurement Points A straight segment of Inconel 600 (International Nickel Company) tubing having an outer diameter of 5/8", and a mass of 450.04 g was obtained. One end of the tube was sealed with a Swagelok.RTM. tube fitting (Crawford Fitting Co.) end cap through which a thermocouple was wired. The tip of the thermocouple was bent to an S-shape with the tip of the thermocouple firmly located in the center of the tube. The sealed end of the tube was placed in a hot water bath having a temperature of 200.+-.5.degree. F. About 40% of the tube was immersed in the hot water bath. Cerrobend.RTM. (Cerro Metal Products Co., Bellefonte, Pa.) alloy was heated to above 210.degree. F. and was poured into the tilted tube. The upper end of the tube was sealed, and the tube was heated in the hot water bath in a generally vertical position until the thermocouple indicated that the thermally conductive material was at a temperature of 180.degree. F. This heating process took about ten minutes. The tube was then lifted vertically from the bath and was air cooled at room temperature, thereby allowing a void to form at the top and allowing air bubbles to be removed from the melt. The tube was opened and a 3/4" void was observed at the upper end of the tube. This void space was desirable in order to allow for expansion or contraction of the Cerrobend.RTM. material. The tubing segment was then transferred repeatedly from a hot bath having a temperature of 190.degree.-200.degree. F. to a cooler bath having a temperature of about 149.degree. F., and measurements of the time required for the temperature of the thermally conductive material to change from 155.degree. F. to 151.degree. F. and from 155.degree. F. to 150.degree. F. were made. The following day, similar measurements were made as the tubing segment was alternately heated from 150.degree. F. to 175.degree. F. in a constant temperature hot bath at 192.2.degree. F. and cooled to room temperature. It was found that repeated measurements of heating time between 150.degree. F. and 175.degree. F. were consistent. Repeated measurements of cooling time lacked consistency, and it was concluded that the inconsistency was a result of subcooling during crystallization of the Cerrobend.RTM. material. It was further concluded that the most accurate results can be obtained when the temperature measurement points are temperatures at which the slope of the temperature-versus-time curve is steepest. The temperature-versus-time curve is relatively flat during a phase change. EXAMPLE 2 Measurement of Time Required for Temperature Change of Thermally Conductive Material Before Cleaning A U-tube 10, shown in FIG. 1, having a 5" radius of curvature was obtained. A wire thermocouple 12 was inserted in the tube, with the temperature-sensing end of the thermocouple extending to the bottom of the curve of the U. The thermocouple 12 was bent into an S-shaped curve in order to keep the temperature-sensing end away from the tube wall. The tube 10 was filled to within 1/2" of each end with melted Cerrobend.RTM. alloy having a temperature of about 210.degree. F. The tube was sealed. Wires 14 were affixed to each end of the tube and were connected to a horizontal immersion control rod 16. The thermocouple 12 was clamped to the rod to prevent the U-tube 10 from swinging from the wires 14. A Primeline Stripchart Recorder #EL195 (Esterline Corp.) (not shown) was calibrated and loaded with chart paper. A first water bath 18 was prepared and kept at a constant temperature of 144.2.degree. F., and an agitator 20 was arranged to heavily agitate the bath. A thermocouple 22 was placed in the bath to continually monitor its temperature. A second water bath was prepared and kept at a constant temperature of about 186.5.degree. F. with an agitator set for minimum agitation. The tube was placed in the first constant-temperature bath overnight in order to ensure that it reached equilibrium with the bath. The next day, the tube was placed in the second bath for about 15 minutes in order to melt the Cerrobend.RTM., and was subsequently cooled in the first bath for 5.0 minutes. Temperature measurement points were selected at which the rate of change in temperature of the thermally conductive material was found to be high when it was subjected experimentally to heating processes and cooling processes, i.e. 155.degree. F. and 170.degree. F. were selected for the heating process and 160.degree. F. and 147.degree. F. were selected for the cooling process. Temperature measurements were then taken as the tubing segment was repeatedly heated in the second bath from 155.degree. F. to 170.degree. F. and subsequently cooled in the first bath from 160.degree. F. to 147.degree. F. The tubing segment remained in each bath for 5 minutes before being transferred to the other bath. The heating and cooling time in seconds for each measured temperature range are provided on Tables 1 and 2 below, along with average times for the heating and cooling processes. Differences in the times required for heating the thermally conductive material and the times required for cooling the material were attributed to both the difference in .DELTA.T for the heating and cooling processes, and to the differences in the conductive properties of liquid metal and solid metal in the tube. EXAMPLE 3 Measurement of Time Required for Temperature Change of Thermally Conductive Material After Cleaning The U-shaped tube used in Example 2 was cleaned on a polishing wheel to remove the magnetite coating from its outer surface, and was buffed with a moist cloth. The tests conducted in Example 2 were then repeated, using the same constant-temperature water baths, temperature measurement points and Stripchart Recorder. The temperature of the first bath was maintained at 144.2.degree. F. The temperature of the second bath was maintained at 186.6.degree. F. Before time measurements were taken, the tube was warmed in the first bath for about 90 minutes and was then placed in the second bath for about 15 minutes in order to melt the Cerrobend.RTM.. The tubing segment was subsequently cooled in the first bath for five minutes. The measurements of temperature and time collected are shown on Tables 1 and 2 below. Calculations of the percent decrease in heat transfer time based both on (1) total average times, and (2) average times with the highest and lowest data points excluded, are also provided. As indicated in Tables 1 and 2, the percent decrease in heat-transfer time due to the chemical cleaning of the tube used in Examples 2-3 was between 5 and 6%, indicating that it would be economically beneficial to clean the steam generator tubes. Furthermore, in a power-limiting situation, cleaning the tubes could result in a 5-6% increase in power generation. Similar results were obtained for measurement taken of heating and cooling processes. As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims. TABLE 1 ______________________________________ HEAT TRANSFER TIME FOR TEMPERATURE INCREASE OF U-SHAPED HEAT EXCHANGER TUBE Heating Time Test Number 155-170.degree. F. ______________________________________ Heat Transfer Time Before Cleaning 1 114 2 116 3 117 4 122 5 117.5 6 117 7 115.5 8 116 9 119 10 118 11 118 12 116 13 118.5 AVG 117.3 AVG w/o HI/LO 117.1 Heat Transfer Time After Cleaning 14 111.5 15 109 16 110 17 111 18 107 19 113 20 111 21 114 22 108 23 109.5 24 106 25 112 26 113 27 111 28 117 AVG 110.9 AVG w/o HI/LO 110.8 Decrease in Heat Transfer Time AVG 5.5 AVG w/o HI/LO 5.4 ______________________________________ TABLE 2 ______________________________________ HEAT TRANSFER TIME FOR TEMPERATURE DECREASE OF U-SHAPED HEAT EXCHANGER TUBE Cooling Time Test Number 160-147.degree. F. ______________________________________ Heat Transfer Time Before Cleaning 1 187 2 181 3 193 4 184 5 181 6 192 7 183 8 184 9 183.5 10 181 11 186 12 184 13 179.5 AVG 184.5 AVG w/o HI/LO 184.2 Heat Transfer Time After Cleaning 14 175 15 175 16 176 17 175.5 18 178 19 171 20 173.5 21 172 22 176 23 181 24 167 25 178 26 174 27 172 28 177 AVG 174.7 AVG w/o HI/LO 174.8 Decrease in Heat Transfer Time AVG 5.3 AVG w/o HI/LO 5.1 ______________________________________ |
046844988 | summary | CROSS REFERENCE TO RELATED APPLICATIONS Reference is hereby made to the following copending applications dealing with related subject matter and assigned to the assignee of the present invention: 1. "Nuclear Reactor Fuel Assembly With A Removable Top Nozzle" by John M. Shallenberger et al, assigned U.S. Ser. No. 644,758 and filed Aug. 27, 1984, which is a continuation-in-part of U.S. Ser. No. 537,775, filed Sept. 30, 1983, now abandoned. 2. "Locking Tube Removal And Replacement Tool And Method In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 670,418 and filed Nov. 9, 1984. 3. "Top Nozzle Removal And Replacement Fixture And Method In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 670,729 and filed Nov. 13, 1984. 4. "Locking Tube Removal Fixture And Method In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 695,762 and filed Jan. 28, 1985. 5. "Locking Tube Insertion Fixture And Method In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 689,656 and filed Jan. 8, 1985. 6. "Reusable Locking Tube In A Reconstitutable Fuel Assembly" by John M. Shallenberger et al, assigned U.S. Ser. No. 719,108 and filed Apr. 2, 1985. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to fuel assemblies for nuclear reactors and, more particularly, is concerned with improvements for releasably locking the top nozzle on the upper ends of the control rod guide thimbles and a method of carrying out the locking and unlocking of the top nozzle to and from the guide thimbles. 2. Description of the Prior Art In most nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include a plurality of fuel rods and control rod guide thimbles held in an organized array of grids spaced along the fuel assembly length and attached to the control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the guide thimbles which extend slightly above and below the ends of the fuel rods. At the top end of the fuel assembly, the guide thimbles are attached in passageways provided in the adapter plate of the top nozzle. The guide thimbles may each include an upper sleeve for attachment to the top nozzle. During operation of such fuel assembly in a nuclear reactor, a few of the fuel rods may occasionally develop cracks along their lengths resulting primarily from internal stresses, thus establishing the possibility that fission products having radioactive characteristics may seep or otherwise pass into the primary coolant of the reactor. Such products may also be released into a flooded reactor cavity during refueling operations or into the coolant circulated through pools where the spent fuel assemblies are stored. Since the fuel rods are part of the integral assembly of guide thimbles welded to the top and bottom nozzles, it is difficult to detect and remove the failed rods. Until recently, to gain access to these rods it was necessary to remove the affected assembly from the nuclear reactor core and then break the welds which secure the nozzles to the guide thimbles. In so doing, the destructive action often renders the fuel assembly unfit for further use in the reactor because of the damage done to both the guide thimbles and the nozzle which prohibits rewelding. In view of the high costs associated with replacing fuel assemblies, considerable interest has arisen in reconstitutable fuel assemblies in order to minimize operating and maintenance expenses. The general approach to making a fuel assembly reconstitutable is to provide it with a removable top nozzle. One reconstitutable fuel assembly construction, devised recently, is illustrated and described in the first U.S. patent application cross-referenced above. It incorporates an attaching structure for removably mounting the top nozzle on the upper ends of the control rod guide thimbles. The attaching structure includes a plurality of outer sockets defined in an adapter plate of the top nozzle, a plurality of inner sockets with each formed on the upper end of one of the guide thimbles, and a plurality of removable locking tubes inserted in the inner sockets to maintain them in locking engagement with the outer sockets. Each outer socket is in the form of a passageway through the adapter plate which has an annular groove. Each inner socket is in the form of a hollow upper end portion of the guide thimble having an annular bulge which seats in the annular groove when the guide thimble end portion is inserted in the adapter plate passageway. A plurality of elongated axial slots are provided in the guide thimble upper end portion to permit inward elastic collapse of the slotted portion so as to allow the larger bulge diameter to be inserted within and removed from the annular circumferential groove in the passageway of the adapter plate. In such manner, the inner socket of the guide thimble is inserted into and withdrawn from locking engagement with the outer socket. The locking tube is inserted from above the top nozzle into a locking position in the hollow upper end portion of the guide thimble forming the inner socket. When inderted in its locking position, the locking tube retains the bulge of the inner socket in its expanded locking engagement with the annular groove and prevents the inner socket from being moved to a compressed releasing position in which it could be withdrawn from the outer socket. In such manner, the locking tubes maintain the inner sockets in locking engagement with the outer sockets, and thereby the attachment of the top nozzle on the upper ends of the guide thimbles. Furthermore, to prevent inadvertent escape due to vibration forces and the like, heretofore the locking tubes have been secured in their locking positions. After insertion of the locking tubes into their locking positions within the inner sockets of the hollow upper end portions of the guide thimbles, a pair of bulges are formed in the upper portion of each locking tube. These bulges fit into the circumferential bulge in the upper end portion of the guide thimble and provide an interference fit therewith. When reconstitution of the fuel assembly is undertaken, these locking tubes must first be removed from the top nozzle. The locking tubes must be handled as "loose parts", either individually or together using an appropriate removal fixture, which require storage, retention and accountability during performance of underwater nuclear fuel assembly reconstitution activities. Then, after the failed fuel rods have been removed and replaced and following remounting of the top nozzle, handling is again required when either the same locking tubes are reused a second time by inserting them back into the guide thimble upper ends and re-deforming them to secure them at their locking positions or a full complement of new locking tubes are inserted on the guide thimble upper ends and secure them by bulging. This practice has a number of disadvantages. First, a large number of locking tubes must be handled and a large inventory thereof must be maintained. Second, provision must be made for disposal of the discarded irradiated locking tubes. Third, after each locking tube is inserted, a deforming operation must be carried out remotely to produce the bulges in each tube. And, fourth, an inspection of bulges must be carried out remotely to ascertain whether the bulges were made to the correct dimension. Consequently, notwithstanding the overall acceptability of the use of the above-described attaching structure in reconstitutable fuel assemblies, these recently recognized disadvantages have created a need for further improvement of the reconstitution operation so as to enhance commercial acceptance thereof. SUMMARY OF THE INVENTION The present invention provides a reconstitutable fuel assembly with improved features for locking the top nozzle upon and unlocking it from the guide thimbles which are designed to satisfy the aforementioned needs. The present invention introduces a push-down locking tube concept in which the locking tube is not removed from the fuel assembly guide thimbles during underwater reconstitution activities. This push-down concept improves the reconstitution operation in several ways. First, it eliminates the need to track separate pieces during the reconstitution operation. Second, it reduces the time required to reconstitute the fuel assembly by eliminating the locking tube deforming operation after remounting the top nozzle. Third, by retaining the locking tubes within the guide thimbles and reusing them, provisions are not necessary for handling and disposal of the irradiated locking tubes. To summarize, by the design change in the locking tube concept contemplated by the present invention, an easier, more trouble-free removal and remounting of the top nozzle during reconstitution is achieved which result in an overall more efficient and reliable reconstitution operation without impacting the highly desirable basic design and integrity of the top nozzle/guide thimble attaching structure described and illustrated in the first patent application cross referenced above. Accordingly, the present invention sets forth in a reconstitutable fuel assembly including a top nozzle with an adapter plate having at least one passageway, at least one guide thimble with an upper end portion, and an attaching structure for mounting the top nozzle adapter plate in releasable locking engagement upon the guide thimble upper end portion, the improvement which comprises: (a) a push-down locking tube mounted within the guide thimble upper end portion for movement relative thereto between an upper locking position wherein the adapter plate and guide thimble upper end portion are maintained in the locking engagement and a lower unlocking position wherein the adapter plate is releasable from the guide thimble upper end portion; and (b) cooperating means defined on the locking tube and the guide thimble for retaining the locking tube at either of its upper and lower positions in the guide thimble. More particularly, the cooperating means on the guide thimble includes a pair of upper and lower circumferential bulges defined on the guide thimble upper end portion and located below the adapter plate when the latter is in locking engagement upon the guide thimble upper end portion. The bulges are axially spaced from one another along the guide thimble upper end portion such that the upper bulge is located to retain the locking tube at its upper locking position and the lower bulge is located to retain the locking tube at its lower unlocking position. Still further, the cooperating means on the locking tube includes a circumferential bulge defined on a lower portion of the locking tube which is seatable in either of the upper and lower circumferential bulges defined on the guide thimble upper end portion. Additionally, the locking tube cooperating means defines at least one slot in the locking tube extending axially upwardly along the lower portion of the locking tube from a lower edge thereof. The axial slot allows radial compression and expansion of the lower portion of the locking tube upon movement of the locking tube between and positioning of the tube at its upper and lower positions for seating and unseating of the circumferential bulge of the locking tube into and from the respective upper and lower circumferential bulges of the guide thimble upper end portion. The present invention also relates to a method of locking the top nozzle adapter plate on and unlocking it from the guide thimble upper end portion, which comprises the steps of: (a) selectively moving a locking tube within the guide thimble upper end portion to an upper locking position wherein the adapter plate and guide thimble upper end portion are maintained in locking engagement; and (b) selectively moving the locking tube within the guide thimble upper end portion to a lower unlocking position displaced below the upper locking position wherein the adapter plate is releasable from the guide thimble upper end portion. |
summary | ||
description | This application is a divisional of U.S. patent application Ser. No. 10/879,065 filed on Jul. 30, 2004 now abandoned. The disclosure of the above application is incorporated herein by reference in its entirety. 1. Field of the Invention The present invention relates generally to a vibration mitigation device for a nuclear reactor component, and to a method of mitigating vibration in a nuclear component. 2. Description of the Related Art Boiling water reactors (BWRs) have emerged as a reliable type of nuclear reactor for producing electrical energy. However, some BWRs have experienced cracking in various components of the BWR. One contributing factor to component cracking in a BWR may be due to high cycle fatigue. Typically, a BWR may operate from about one to two years on a single core loading of fuel. Upon completion of a given period (known as an energy cycle or fuel cycle), approximately ¼ to ½ of the least reactive fuel (oldest or most burnt) may be discharged from the reactor. The number of cycles which may constitute a substantially high number of cycles may vary from BWR to BWR, as other factors may affect cycle time, such as design, operating conditions, etc. High cycle fatigue may be caused, for example, by a substantially high acoustic frequency vibration, for example a frequency above 100 Hz, and/or a substantially low acoustic frequency vibration, for example a frequency below 100 Hz. It should be understood that the frequency which constitutes a high and/or a low acoustic frequency may vary based on the application. The amplitude of a vibration in a BWR may directly influence or exacerbate high cycle fatigue, which in turn may cause the cracking of a component of the BWR. The amplitude of the vibration in the BWR experienced by a component of the BWR may be directly proportional to the stress in the component. High amplitude of the vibration in the BWR may lead to a high stress level, which may cause the cracking of a component of the BWR. FIG. 1 is a cut-away to illustrate an upper portion of a conventional reactor pressure vessel (RPV) of a BWR. Typically, and referring to FIG. 1, a BWR may include an upstanding reactor pressure vessel 10 which incorporates a lower reactor core structure beneath which are control rod drive mechanisms (not shown for clarity). Above the core may be a steam separator assembly 25 and a steam dryer assembly 30 leading to a steam outlet 35. One or more reactor components of the steam separator assembly 25 or steam dryer assembly 30 may experience vibration due to increased vibration amplitude due to the stresses from the aforementioned high cycle fatigue. This may accelerate cracking of the reactor component. An exemplary embodiment of the present invention is directed to a device for mitigating vibration in a component in a nuclear reactor. The device may include a spring mechanism and a mass attached to the spring mechanism. The spring mechanism and mass may be in operative engagement with each other so as to reduce vibration effects in the component. Another exemplary embodiment of the present invention is directed to a method of reducing vibration in a component within a nuclear reactor. A device operatively connected to the component and including a magnet and conductive cylinder, may be actuated. This actuation may generate one or more eddy currents providing a damping function for removing vibration energy from the component. FIGS. 2A and 2B illustrate a vibration mitigation device (VMD) according to an exemplary embodiment of the present invention. FIG. 2A is a cross-sectional view of the VMD 200, and FIG. 2B is an exploded view. VMD 200 may be operatively attached or connected to a reactor component within the BWR such as a component of the steam dryer assembly 30. As shown, the VMD 200 may include an acoustic shield 210. The acoustic shield 210 may be comprised of stainless steel and/or any other material suitable for an environment of the BWR. The acoustic shield 210 may be provided to reduce vortexes which may excite an acoustic room mode. For example, acoustic shield 210 may be configured to provide a relatively smooth steam flow across the VMD 200. A smooth steam flow may help to avoid and/or possibly prevent excitation of acoustic room modes, which may also be referred to as acoustic cavity modes, in the steam plenum of the steam dryer assembly 30, which may be in the vicinity of the component the VMD 200 is attached to, such as a component surface 30A of a steam dryer assembly 30, as shown in FIG. 2A. An acoustic room mode is an acoustic standing wave pattern. Acoustic room modes may be excited when a vortex crosses the mouth of a cavity at a frequency that is close to an acoustic frequency. A vortex may be created when a boundary layer of a fluid in contact with a structure passes across the cavity. A portion of the fluid in contact with the structure may move slower than a portion of the fluid not in contact with the structure. The difference in the velocity between the portions may create circulation which becomes the vortex. When the vortex crosses the mouth of the cavity, an acoustic room mode may be excited. The excited acoustic room mode may increase the vibration energy in the component. Accordingly, acoustic shield 210 may facilitate a relatively smooth steam flow across the VMD 200 so as to avoid and/or possibly prevent excitation of the aforementioned acoustic room modes in the component to which the VMD 200 is attached. VMD 200 may include a top end cap 220 and a bottom end cap 260. Caps 220 and 260 may provide a structure to which a spring mechanism 232 may be attached. A base plate 270 may provide support for the VMD 200 and may be attached to or secured on the steam dryer, such as at component surface 30A, for example. Caps 220, 260 and base plate 270 may be comprised of stainless steel and/or any other material suitable for an environment of the BWR, for example. VMD 200 may further include a cylinder 230 with adjacent permanent magnets 240. The cylinder 230 may be either conductive or nonconductive. The permanent magnets 240 may be comprised of Alnico, Samarium Cobalt, Ceramic, and/or any other magnetic material, for example. The spring mechanism 232 may be embodied as coil springs, and/or may include a spring force provided by cantilever beams attached to a conductive core 250. The conductive core 250 may be comprised of steel, copper and/or any material having electrically conductive properties. In an example, cylinder 230 may be stationary with respect to the acoustic shield 210, the top end cap 220, the bottom end cap 260, the adjacent permanent magnets 240, and the base plate 270 of the VMD 200. Alternatively, the conductive core 250 may oscillate with the spring mechanism 232. The spring mechanism 232 may be attached such that a first spring 235 is connected from the conductive core 250 to the top end cap 220, and a second spring 245 is connected from the conductive core 250 to the bottom end cap 260. For example, the conductive core 250 may oscillate with the spring mechanism with respect to the cylinder 230 with adjacent magnets 240, in such a way that eddy currents are induced in the conductive core 250. Eddy currents are created when a conductor moves within a magnetic field. This relative motion may induce a voltage in an electrical conductor. The induced voltage is proportional to an induced current, which is the eddy current. A material resistance of the conductive core 250 may convert the eddy currents into heat. Heat is created when current passes through an object with material resistance. Thus, the eddy currents in the conductive core 250 create a magnetic field which acts as a resistance to the oscillatory motion of the conductive core 250. This resistance may thus reduce the potential vibration effects induced by the component(s) to which the VMD 200 is connected. FIG. 3 illustrates a VMD according to another exemplary embodiment of the present invention. Several of the components are somewhat similar in nature to FIG. 2. For example, VMD 300 may include an acoustic shield 310 of stainless steel and/or any other material suitable for an environment of the BWR. The acoustic shield 310 is provided to reduce vortexes which may excite an acoustic room mode, as described above. VMD 300 may include a top end cap 320 and a bottom end cap 350 to which a spring mechanism 332 may be attached. A base plate 360 of stainless steel and/or any other material suitable for an environment of the BWR may provide support for the VMD 300 and may be attached to or secured on the steam dryer. The spring mechanism 332 may be embodied as coil springs, and/or may include a spring force provided by cantilever beams attached to a magnetic core 340. The magnetic core 340 may be comprised of Alnico, Samarium Cobalt, Ceramic, and/or any other magnetic material, for example. The conductive cylinder 330 may be stationary with respect to the acoustic shield 310, the top end cap 320, the bottom end cap 350, and the base plate 360 of the VMD 300. The conductive cylinder 330 may be comprised of steel, copper and/or any other material having electrically conductive properties. Alternatively, the magnetic core 340 may oscillate with the spring mechanism 332. The spring mechanism 332 may be attached such that a first spring 335 is connected from the magnetic core 340 to the top end cap 320, and a second spring 345 is connected from the magnetic core 340 to the bottom end cap 350. The magnetic core 340 may oscillate with the spring mechanism with respect to the conductive cylinder 330 such that eddy currents are induced in the conductive cylinder 330. The material resistance of the conductive cylinder 330 may convert the eddy currents into heat, as described above. The eddy currents in the conductive cylinder 330 may create a magnetic field which may act to resist the oscillatory motion of the magnetic core 340, thereby reducing the potential vibration effects induced by the component(s) to which the VMD 300 is connected. A system designer may modify one, several and/or all of the physical dimensions of the constituent components of the VMD 200/300, in an effort to obtain a desired result. For example, increasing the magnetic flux of the permanent magnets 240 (or magnetic core 340) may decrease the amplitude of the frequency response by increasing the damping factor, while reducing the magnetic flux of the permanent magnets 240/magnetic core 340 may increase the amplitude of the frequency response by decreasing the damping factor. In another example, increasing the distance between the permanent magnets 240 and the conductive core 250 (or magnetic core 340 and conductive cylinder 330) may increase the amplitude of the frequency response by decreasing the damping factor. Decreasing this distance may reduce the amplitude of the frequency response by increasing the damping factor. In another example, increasing the mass of the conductive core 250 (or conductive cylinder 330) may increase the frequency difference between the new damped natural frequencies, while decreasing the mass of the conductive core 250/cylinder 330 may decrease the frequency difference between the new damped natural frequencies. In another example, changing the stiffness of the spring mechanism 232 or 332 may change the magnitude of newly created damped natural frequencies. In accordance with the exemplary embodiments, two new damped natural frequencies may be induced by the VMD 200/300, in place of an original natural frequency. The spring mechanisms attached to VMD 200/300 may induce the two new damped natural frequencies. One of the new damped natural frequencies may have a frequency which is lower than the original natural frequency, and the other may have a frequency which is higher than the original natural frequency. Further, each of the two new damped natural frequencies may have an amplitude lower than an amplitude of the original natural frequency. Therefore, as the VMD 200/300 provides amplitude reduction of the original natural frequency with damping, and the two new damped natural frequencies have amplitudes lower than the original natural frequency, the maximum amplitude of the frequency response may be reduced for a component configured with the VMD 200/300. FIG. 4 is a graph for comparing an original natural frequency with damped natural frequencies introduced by the exemplary embodiments of the present invention. The graph shows the dynamic amplification of the system response as a function of the non-dimensional frequency. This graph represents the vibration frequency response of a nuclear reactor component with and without the inclusion of a VMD. As shown in FIG. 4, the original natural frequency 400 has a peak which reaches the top of the scaled x-axis at a frequency represented by “1” on the y-axis. In contrast, the peaks of the two damped natural frequencies 410 and 420 introduced by application of VMD 200/300 to a reactor component may occur at frequencies both above and below the original natural frequency, and further at reduced amplitudes, as compared to the amplitude of the original natural frequency 400. Therefore, the amplitude of the original natural frequency 400 has been reduced with damping, and the two new damped natural frequencies 410 and 420 have amplitudes lower than the original natural frequency 400, so the maximum amplitude of the frequency response has been reduced for a component with the VMD 200/300. The dynamic amplification of each natural frequency and the non-dimensional frequency at which the maximum amplification occurs are functions of the values chosen for the specific design parameters such as magnetic field strength, mass, stiffness, gap, etc. The exemplary embodiments of the present invention being thus described, it will be obvious that the same may be varied in many ways. For example, the VMD may be applied to reactor components other than the steam dryer assembly, such as a jet pump assembly, for example. With respect to FIG. 1, the jet pump assembly may be attached to the BWR with a riser brace. The riser brace may experience cracking similar to the steam dryer assembly. The VMD described above may be similarly attached to a riser brace supporting a jet pump assembly in an effort to prevent cracking. The VMD 200/300 may also be applicable to any system which utilizes a tuned mass damper (TMD), for example. Such variations are not to be regarded as a departure from the spirit and scope of the exemplary embodiments of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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claims | 1. A method of measuring a number of environmental conditions with a transmitter device, said transmitter device comprising a neutron detector, a capacitor electrically connected in parallel with said neutron detector, a gas discharge tube comprising an input end and an output end, and an antenna electrically connected to said output end, said input end being electrically connected with said capacitor, the method comprising the steps of:detecting neutron flux with said neutron detector;storing energy in said capacitor until a breakdown voltage of said gas discharge tube is reached; andemitting a signal with said antenna corresponding to the neutron flux. 2. The method of claim 1 wherein said transmitter device further comprises an oscillator circuit electrically connected with said output end and said antenna; and wherein the method further comprises:pulsing said antenna with said oscillator circuit. 3. The method of claim 2 wherein said oscillator circuit comprises a second capacitor, an inductor electrically connected to said second capacitor, and a resistance temperature detector electrically connected in series with said inductor; wherein said second capacitor and said inductor are each electrically connected with said antenna; and wherein the method further comprises:altering the signal emitted by said antenna with said resistance temperature detector. 4. The method of claim 2 wherein said oscillator circuit comprises a second capacitor, an inductor electrically connected to said second capacitor, and a second inductor electrically connected in series with said inductor; wherein said second capacitor and said inductor are each electrically connected with said antenna; and wherein the method further comprises:altering the signal emitted by said antenna with said second inductor. |
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062434330 | claims | 1. A nuclear fuel element, comprising: a central core of a body of nuclear fuel material selected from the group consisting of compounds of uranium, plutonium, thorium and mixtures thereof; and, an elongated composite container having a hollow central bore, the container comprised of an outer metallic tubular portion and an inner metallic barrier metallurgically bonded to the outer metallic tubular portion, the inner metallic barrier having a combination of crack resistance and corrosion resistance consisting essentially of commercially pure zirconium microalloyed with iron in the range of about 850-1500 ppm and the balance incidental impurities. 2. The nuclear fuel element of claim 1 wherein the inner metallic barrier having a combination of acceptable cracking resistance and superior corrosion resistance consists essentially of iron in a range of about 1000.+-.150 ppm. 3. The nuclear fuel element of claim 1 wherein the corrosion resistance of the inner metallic barrier as measured by the modified ASTM G2 steam test is less than about 5 mg/dm.sup.2 /day. 4. The nuclear fuel element of claim 1 wherein the thickness of the inner metallic barrier is about 10-20% of the total thickness of the elongated composite cladding container. 5. The nuclear fuel element of claim 1 wherein the cracking resistance of the inner metallic barrier measured by PCI resistance testing at 315.degree. C. has a failure rate of 50% or less. 6. The nuclear fuel element of claim 1 wherein the nuclear fuel material is selected from the group consisting of compounds of uranium, plutonium, thorium and mixtures thereof. 7. The nuclear fuel element of claim 1 wherein the microstructure of the inner metallic barrier is recrystallized, having a grain size in the range of ASTM 9 to ASTM 11. 8. The nuclear fuel element of claim 2 wherein the microstructure of the inner metallic barrier is recrystallized, having a grain size in the range of ASTM 9 to ASTM 12. 9. The nuclear fuel element of claim 1 wherein the outer metallic tubular portion is selected from the group consisting of zirconium and its alloys, stainless steel, aluminum and its alloys, niobium and magnesium alloys. 10. The nuclear fuel element of claim 9 wherein the outer metallic tubular portion is comprised of zirconium and its alloys. 11. The nuclear fuel element of claim 10 wherein the inner metallic barrier consists essentially of iron in the range of about 850-1500 ppm, and the weight percent of zirconium in the inner metallic barrier is greater than the weight percent of zirconium in the outer metallic tubular portion. 12. The nuclear fuel element of claim 1 in which the inner metallic barrier consists essentially of iron in the range of about 1000-1500 ppm. 13. The nuclear fuel element of claim 12 wherein the microstructure of the inner metallic barrier is recrystallized, having a grain size in the range of ASTM 9 to ASTM 12. 14. The nuclear fuel element of claim 12 wherein the cracking resistance of the inner metallic barrier measured by PCI resistance testing at 315.degree. C. has a failure rate of 10% or less. 15. The nuclear fuel element of claim 14 wherein the corrosion resistance of the inner metallic barrier as measured by the modified ASTM G2 steam test is about 2 mg/dm.sup.2 /day. 16. The nuclear fuel element of claim 15 wherein the inner metallic barrier comprises about 10 to about 20% of the total composite container thickness. |
055286542 | claims | 1. A multilayer film for X-rays comprising: a substrate; and first and second films formed alternately on said substrate; wherein, one of the first and second films has a smaller refractive index than the other film, and consists of an alloy containing Co and Cr. a substrate; and a multilayer of first and second films formed alternately on said substrate, wherein, one of the first and second films has a smaller refractive index than the other film, and consists of an alloy containing Co and Cr. an optical system including an optical element for exposing an object with X-rays, said optical element comprises; a substrate; and a multilayer of first and second films formed alternately on said substrate; wherein, one of the first and second films has a smaller refractive index than the other film, and consists of an alloy containing Co and Cr. providing an X-ray optical system including an optical element; said optical element being formed by forming a multilayer of first and second films alternately on said substrate, wherein one of the first and second films consists of an alloy containing Co and Cr; providing a mask having a pattern and a wafer; and exposing the mask and the wafer to radiation to transfer the pattern of the mask onto the wafer by using said X-ray optical system. a substrate; and a multilayer of first and second films formed alternately on said substrate; wherein one of the first and second films has a smaller refractive index than the other film, and consists of an alloy containing Co and Cr. 2. A multilayer film according to claim 1, wherein said alloy is represented by the formula: Co.sub.x Cr.sub.1-x, where, x=0.3 to 0.8 mole fraction of Co. 3. A multilayer film according to claim 1, wherein the thickness of said film having the smaller refractive index is 30 .ANG. or less. 4. A multilayer film according to claim 1, wherein one of said films having a greater refractive index contains an element selected from the group consisting of Ba, Mg, Be, Sb, V, Te, Sc, Ti, Ca, C, B, and Zr. 5. A multilayer film according to claim 1, wherein one of said film having the greater refractive index contains a material selected from the group consisting of V, Sc, CaF.sub.2, and B.sub.4 C. 6. An optical element for X-rays, comprising: 7. An optical element according to claim 6, wherein the optical element is an X-ray reflection mirror. 8. An optical element according to claim 6, wherein the optical element is a reflection-type X-ray mask. 9. An optical element according to claim 6, wherein said alloy is composed of Co.sub.x C.sub.1-x, where, X=0.3-0.8 mole fraction of Co. 10. An optical element according to claim 6, wherein the thickness of said film having the smaller refractive index is 30 .ANG. or less. 11. An optical element according to claim 6, wherein one of said films having a greater refractive index contains an element selected from the group consisting of Ba, Mg, Be, Sb, V, Te, Sc, Ti, Ca, C, B, and Zr. 12. An optical element according to claim 6, wherein one of said films having a greater refractive index contains a material selected from the group consisting of V, Sc, CaF.sub.2, and B.sub.4 C. 13. An X-ray exposure apparatus comprising: 14. An apparatus according to claim 13, wherein said object comprises a wafer, and a pattern printed onto the wafer by exposure. 15. An apparatus according to claim 13, wherein said alloy is composed of Co.sub.x Cr.sub.1-x, where, X=0.3-0.8 mole fraction of Co. 16. An apparatus according to claim 13, wherein the thickness of said film having the smaller refractive index is 30 .ANG. or less. 17. An apparatus according to claim 13, wherein one of said films which has a greater refractive index contains a material selected from the group consisting of Ba, Mg, Be, Sb, V, Te, Sc, Ti, Ca, C, B, and Zr. 18. An apparatus according to claim 13, wherein one of said films having the greater refractive index contains a material selected from the group consisting of V, Sc, CaF.sub.2, and B.sub.4 C. 19. A method of manufacturing a mirco-device, comprising the steps of: 20. An optical element, comprising: |
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summary | ||
claims | 1. A simplified nuclear reactor system for commercially generating electricity, the system comprising:a nuclear reactor;a primary coolant loop connecting to the nuclear reactor;a containment surrounding the nuclear reactor; anda depressurization system including,a coolant tank and a filter pool vertically above the nuclear reactor outside the containment and including no flow path opening into the containment outside the nuclear reactor,an injection line crossing the containment and connecting the coolant tank and the nuclear reactor, wherein the injection line includes a closable and openable valve,a relief line crossing the containment and connecting the filter pool and the nuclear reactor, anda rupture disk connecting the relief line to the nuclear reactor, wherein the rupture disk is integral in a wall of the nuclear reactor so as to have material continuity with the wall, and wherein the rupture disk is configured to open the reactor at a pressure setpoint below failure of the reactor. 2. The system of claim 1, whereinthe relief line is configured to carry coolant away from the reactor following opening of the rupture disk. 3. The system of claim 2, further comprising:wherein the relief line extends into and opens below a surface of the filter pool so as to exhaust the coolant into the filter pool for condensation and/or scrubbing. 4. The system of claim 3, wherein the filter pool includes a particulate filter configured to filter particulate matter out of gas exiting the filter pool to the atmosphere. 5. The system of claim 4, wherein the containment and the reactor are below ground, wherein the filter pool is above ground outside the containment, and wherein the relief line extends through the containment from the reactor to the filter pool. 6. The system of claim 1, wherein the depressurization system includes a plurality of the rupture disks in series, and wherein the pressure setpoint is about 120% of the operating pressure of the nuclear reactor. 7. The system of claim 1, wherein the rupture disk is configured to open the reactor by failure due to stress at the pressure setpoint. 8. The system of claim 1,wherein the depressurization system further includes a valve on the injection line and integral with the nuclear reactor, wherein the valve permits only injection of coolant from the coolant tank into the nuclear reactor. 9. A simplified nuclear reactor system for commercially generating electricity, the system comprising:a nuclear reactor;a primary coolant loop connecting to the nuclear reactor;a containment surrounding the nuclear reactor; anda gravity-driven injection system including,a coolant tank and a filter pool vertically above the nuclear reactor outside the containment and including no flow path opening into the containment outside the nuclear reactor,an injection line crossing the containment and connecting the coolant tank and the nuclear reactor, wherein the injection line includes a closable and openable valve, and wherein the valve and a wall of the nuclear reactor are integral so as to have material continuity, anda relief line crossing the containment and connecting the filter pool and the nuclear reactor, wherein the relief line is connected to the nuclear reactor by a rupture disk. 10. The system of claim 9, wherein the valve permits only injection of coolant from the coolant tank into the nuclear reactor. 11. The system of claim 10, wherein the valve is configured to passively open at detection of a low liquid level in the nuclear reactor. 12. The system of claim 9, wherein the nuclear reactor is completely underground and the coolant tank is above ground. 13. The system of claim 9,wherein the rupture disk is configured to open the reactor at a pressure setpoint below failure of the reactor. 14. The system of claim 13, wherein therelief line is configured to carry coolant away from the reactor following opening of the rupture disk. 15. The system of claim 14, wherein the injection line flows into the nuclear reactor at the valve at a first vertical position of a downcomer annulus in the nuclear reactor, and wherein the relief line flows out of the nuclear reactor at the rupture disk at a second vertical position of the reactor above a core of the nuclear reactor and above the first vertical position. 16. The system of claim 14, wherein the relief line extends into the filter pool so as to exhaust the coolant into the filter pool for condensation and/or scrubbing. 17. The system of claim 16, wherein the containment and the reactor are below ground, and wherein the filter pool and coolant tank are outside containment and above ground. 18. The system of claim 13, wherein the injection system is configured to lower a pressure of the nuclear reactor to a level where coolant will be injected from the coolant tank due to gravity. 19. A simplified nuclear reactor system for commercially generating electricity, the system comprising:a nuclear reactor;a primary coolant loop connecting to the nuclear reactor;a containment surrounding the nuclear reactor; anda gravity-driven injection system including,a coolant tank and a filter pool vertically above the nuclear reactor outside the containment and including no flow path opening into the containment outside the nuclear reactor,an injection line crossing the containment and connecting the coolant tank and the nuclear reactor, wherein the injection line includes a closable and openable valve, anda relief line crossing the containment and connecting the filter pool and the nuclear reactor, wherein the relief line is connected to the nuclear reactor by a rupture disk. |
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abstract | A method for identifying a drifted dose integrator in an implantation system and an implantation system are provided. The implantation system includes a first dose integrator and a second dose integrator. The first dose integrator includes a first input configured to receive a first current generated from charges carried by implanted ions in a wafer, and a first output configured to output a first accumulated dosage value. The second dose integrator includes a second dose integrator including a second input configured to receive a second current generated from the charges carried by the implanted ions in the wafer, and a second output configured to output a second accumulated dosage value. The implantation system further includes a processing unit comparing the first accumulated dosage value and the second accumulated dosage value to detect a drift in one of the first and the second dose integrators. |
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059129360 | summary | FIELD OF THE INVENTION This invention relates generally to nuclear reactors and, more particularly, to assemblies and methods for coupling piping within reactor pressure vessels of such reactors. BACKGROUND OF THE INVENTION A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Boiling water reactors have numerous piping systems, and such piping systems are utilized, for example, to transport water throughout the RPV. For example, core spray piping is used to deliver water from outside the RPV to core spargers inside the RPV and to cool the core. Typically, core spray piping is coupled between a nozzle in the RPV and a shroud connection in the shroud. Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds, exposed to high temperature water. The reactor components are subject to a variety of stresses associated with, e.g., differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to SCC. Reactor internal piping, such as core spray lines inside the reactor pressure vessel, occasionally require replacement as a result of SCC. One known method of replacing a core spray line requires draining the RPV and taking field measurements of the precise distance, e.g., horizontal and vertical, between the nozzle and the shroud connection. A replacement core spray line is then cut utilizing the measurements, and such replacement line is then welded in place. Replacing a core spray line typically requires considerable down time, and is tedious. It would be desirable to provide an assembly which facilitates replacing a core spray line without requiring detailed field measurements and cutting. It also be desirable to provide such an assembly which would enable a core spray line to be replaced without requiring any welding. SUMMARY OF THE INVENTION These and other objects are attained by an assembly which, in one embodiment, includes a pipe connector assembly for replacing a core spray line in a nuclear reactor without field cutting, measuring, or welding such line. The pipe connector assembly includes a first coupling member, a second coupling member, and at least one locking element. The first coupling member includes a flange, a substantially cylindrical pipe engaging portion extending from a first surface of the flange and a spherical convex seat portion extending from a second surface of the flange. The second coupling member includes a flange having a spherical concave seat portion for receiving the convex seat portion of the first coupling member and a substantially cylindrical pipe engaging portion extending from a first surface of the second coupling member flange. The locking element includes at least one spherical washer and a crimp mechanism and couples the first coupling member and the second coupling member. To replace core spray lines, three pipe sections and three pipe connector assemblies are typically used. The pipe sections are sized so that their total length matches or slightly exceeds the total length of the core spray line to be replaced. Generally, the first pipe assembly couples the first pipe section to a the second pipe section, the second pipe assembly couples the second pipe section to the third pipe section, and the third pipe assembly couples the third pipe section to a RPV nozzle. More particularly, and referring to the first pipe connector assembly only, a second end of the first pipe section is inserted into the first coupling member bore. Similarly, a first end of the second pipe section is inserted into the second coupling member bore. The coupling members are then positioned so that their respective bores are aligned, and the first coupling member seat is seated on the second coupling member seat. The locking elements are then extended through the respective stud bores to couple the first and second coupling members, and thus the first and second pipe sections, together. The second pipe connector assembly couples a second end of the second pipe section to the first end of the third pipe section in the same manner. The third pipe connector assembly couples a second end of the third pipe section to the RPV nozzle junction in the same manner. Before fully securing the locking elements, a first end of the first pipe section is coupled to a shroud connector. Thereafter, the second and third pipe sections are positioned so that any excess core spray line length is accommodated by the rotational misalignment of the pipe sections and the pipe connector assemblies. Particularly, the first and second coupling members of each pipe connector assembly are rotated with respect to each other so that the various pipe sections move relative to each other. Thereafter the locking elements are fully secured. The resulting connection is essentially leak tight and is able to resist significant shear, axial, moment, and torsion loads. The above-described pipe connector assembly is particularly suitable for use in nuclear reactor applications and facilitates replacing a core spray line without draining the reactor or welding. In addition, such assembly facilitates replacing a core spray line without requiring precise field measurements or cutting. |
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claims | 1. A correlation tolerance limit setting system using repetitive cross-validation, the system comprising a controller including at least one of electronic logic circuits or processor-executable instructions stored on a non-transitory machine-readable medium, the controller being configured to implement:a variable extraction algorithm randomly classifying data of an initial database (DB) set into training data and validation data at a specific rate, and then matching each of the training data and the validation data with each run identifier (ID) assigned thereto and storing them in a training initial set and a validation initial set, respectively, thereby extracting variables for determining a departure from nucleate boiling ratio (DNBR) limit by optimizing coefficients of a selected correlation based on the data stored in the training initial set;a normality test algorithm performing a normality test for data of a training set and data of a validation set after extracting the variables; anda DNBR limit algorithm determining the DNBR limit by a parametric method or a nonparametric method depending on a result of the normality test,wherein the DNBR limit algorithm includes:an output module determining whether the data of the training set and the data of the validation set have a same population or not by the parametric method or the nonparametric method depending on a result of the normality test for a measured/predicted value (M/P) of a run ID of the training set and an M/P of a run ID of the validation set derived for each case, and performing the normality test for an M/P of a run ID of a poolable set which is combined with the training set and the validation set or the M/P of the run ID of the validation set by the parametric method or the nonparametric method depending on the result of whether the data of the training set and the data of the validation set have the same population or not; anda limit determination module deriving a distribution of 95/95 DNBR values for all N cases after calculating the 95/95 DNBR values by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of the run ID of the poolable set or the M/P of the run ID of the validation set from the output module for each case, and determining a 95/95 DNBR limit using the derived distribution of the 95/95 DNBR values;wherein the selected correlation expresses a relationship between each of dependent variables and a reactor core trip setpoint in order to derive the reactor core trip setpoint from measured values of dependent variables instrumented at a predetermined location of a reactor core, and a relationship of a critical heat flux (CHF) and the measured value of each of the instrumented dependent variables; andwherein a measured value of the instrumented dependent variables and a CHF which is an independent variable derived from a selected correlation are set as one data, and then the one data is assigned with a run ID and stored in an initial DB set. 2. The system of claim 1, wherein the variable extraction algorithm includes:an initialization module classifying the data of the initial DB set into the training data and the validation data, and then matching the training data and the validation data with each run ID assigned thereto and storing them in the training initial set and the validation initial set, respectively, wherein the data for which the run ID of a full DB set and the run ID of the training initial set are the same to each other is stored in the training set, and the data for which the run ID of the full DB set and the run ID of the validation set are the same to each other is stored in the validation set;a correlation coefficient optimization module optimizing for fitting of the coefficients of the selected correlation using the data of the training initial set;an extraction module deriving the M/P for each run ID of the training set by applying optimized coefficients of the selected correlation to the data of the training set, and then extracting a maximum M/P for each run ID of the training set among the derived MP's;a location and statistics change determination module determining whether a measurement location of the core is changed or not with each run ID, having the extracted maximum M/P, of the training set or the statistics are changed or not with an average value of the derived M/P of each run ID of training initial set, wherein the optimized coefficients of the selected correlation are output when there is no change of the core measurement location, having the extracted maximum M/P, or statistics on the average value of the derived M/P's by iteratively performing optimization of the coefficients of the selected correlation until there is no change of the core measurement location, having the extracted maximum M/P, or_statistics on the average value of the derived M/P's; anda variable extraction module applying the optimized coefficients of the selected correlation to each data of the validation set, and then extracting dependent variables, having the maximum M/P, of the data of the validation set as the variables for determining the DNBR limit. 3. The system of claim 1, wherein, when the data of the training set and the data of the validation set have the same population by the parametric method depending on a result of the normality test for the data of the training set and the data of the validation set, the normality test algorithm performs the normality test for the M/P of each run ID of the poolable set by the parametric method or the nonparametric method. 4. The system of claim 1, wherein the normality test algorithm determines whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set, and when the data of the training set and the data of the validation set have the same population, the normality test algorithm performs the normality test for the M/P of each run ID of the poolable set by the parametric method or the nonparametric method; andthe normality test algorithm determines whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set, and when the data of the training set and the data of the validation set do not have the same population, the normality test algorithm performs the normality test for the M/P of each run ID of the validation set by the parametric method or the nonparametric method. 5. A correlation tolerance limit setting method using repetitive cross-validation, the method comprising:step a) of randomly classifying data of an initial database (DB) set into training data and validation data at a specific rate, and then matching each of the training data and the validation data with each run identifier (ID) assigned thereto and storing them in a training initial set or a validation initial set, respectively, thereby extracting variables for determining a departure from nucleate boiling ratio (DNBR) limit by optimizing coefficients of a selected correlation based on the data stored in the training initial set;step b) of performing a normality test for data of a training set and a validation set after extracting the variables; andstep c) of determining the DNBR limit by a parametric method or a nonparametric method depending on a result of the normality test,wherein the step c) includes:substep c-1) of determining whether the data of the training set and the data of the validation set have a same population or not by the parametric method or the nonparametric method depending on a result of the normality test for a measured/predicted value (M/P) of a run ID of the training set and an M/P of a run ID of the validation set derived for each case, and performing the normality test for an M/P of the run ID of a poolable set which is combined with the training set and the validation set or the M/P of the run ID of the validation set by the parametric method or the nonparametric method depending on the result of whether the data of the training set and the data of the validation set have the same population or not; andsubstep c-2) of deriving a distribution of a 95/95 DNBR value for all N cases after calculating the 95/95 DNBR value by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of the run ID of the poolable set or the M/P of each run ID of the validation set from the output module for each case, and determining a 95/95 DNBR limit using the derived distribution of the/a 95/95 DNBR value;wherein the selected correlation expresses a relationship between each of dependent variables and a reactor core trip setpoint in order to derive the reactor core trip setpoint from measured values of dependent variables instrumented at a predetermined location of a reactor core, and a relationship of a critical heat flux (CHF) and the measured value of each of the instrumented dependent variables; andwherein a measured value of the instrumented dependent variables and a CHF which is an independent variable derived from a selected correlation are set as one data, and then the one data is assigned with a run ID and stored in an initial DB set. 6. The method of claim 5, wherein the step a) includes:initialization substep a-1) of classifying the data of the initial DB set into the training data and the validation data, and then matching the training data and the validation data-with each run ID assigned thereto and storing them in the training initial set and the validation initial set, respectively, wherein the data for which the run ID of a full DB set and the run ID of the training initial set are the same to each other is stored in the training set, and the data for which the run ID of the full DB set and the run ID of the validation set are the same to each other is stored in the validation set;correlation coefficient optimization substep a-2) of optimizing for fitting of the coefficients of the selected correlation using the data of the training initial set;extraction substep a-3) of deriving an M/P for each run ID of the training set by applying optimized coefficients of the selected correlation to the data of the training set, and then extracting a maximum M/P for each run ID of the training set among the derived MP's;location and statistics change determination substep a-4) of determining whether a measurement location of the core is changed or not with each run ID, having the extracted maximum M/P, of the training set or the statistics are changed or not with an average value of the derived M/P of each run ID of training initial set, wherein the optimized coefficients of the selected correlation are output when there is no change of the core measurement location, having the extracted maximum M/P, or statistics on the average value of the derived M/P's by iteratively performing optimization of the coefficients of the selected correlation until there is no change of the core measurement location, having the extracted maximum M/P, or statistics on the average value of the derived M/P's; andvariable extraction substep a-5) of applying the optimized coefficients of the selected correlation to each data of the validation set, and then extracting the dependent variables, having the maximum M/P, of the data of the validation set as the variables for determining the DNBR limit. 7. The method of claim 5, wherein, at the step b), when the data of the training set and the data of the validation set have the same population by the parametric method depending on a result of the normality test for the data of the training set and the data of the validation set, the normality test for the M/P of each run ID of the poolable set is performed by the parametric method or the nonparametric method. 8. The method of claim 5, wherein, at the step b), it is determined whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set, and when the data of the training set and the data of the validation set have the same population, the normality test for the M/P of each run ID of the poolable set is performed by the parametric method or the nonparametric method;it is determined whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set; andwhen the data of the training set and the data of the validation set do not have the same population, the normality test for the M/P of each run ID of the validation set is performed by the parametric method or the nonparametric method. |
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051125692 | abstract | An intrinsic-safety nuclear reactor of the pressurized water type, having:. a reactor vessel (2) equipped with a core (4), a lower header (5) and an upper header (6), at least one heat exchanger (3) with a secondary fluid, means of hydraulic connection (9, 10) between said headers and said heat exchanger and at least one circulation pump (11), PA0 a pressurized container (1) surrounding the reactor vessel (2) and which defines a tank (15) full of a cold, neutron-absorbing liquid; PA0 pipes (20) allowing communication between the lower area of said tank and the lower header of the vessel, as well as pipes (21) allowing communication between the upper area of said tank and the upper header,. in which the pressure drop in the primary fluid across the core is substantially equal to the difference in head between the cold column of said tank and the hot column of the vessel.. The pressurized container (1) is immersed in a pool (18) containing a neutron-absorbing liquid at atmospheric pressure.. Furthermore, the wall of the vessel (2) is insulated, while the wall of the container (1) has no insulation, so as to achieve the greatest possible heat exchange between said container wall and the water of the surrounding pool (18). |
041475917 | abstract | This invention relates to fuel assembly for Fast Breeder Reactor, such as wire spacer fuel assembly, in which the thickness of cladding tubes in the upper end portion of fuel pins positioned in the peripheral region of the assembly is made larger than that of the remaining portion. Thus, according to the present invention, a bundle of the fuel pins can be restrained from displacement in one direction in the assembly when the fuel pins are deformed by heat and neutron radiation in operation of a nuclear reactor, and further the sectional portion of the fuel pins can be prevented from deformation caused by a load externally operated on the fuel pins. Furthermore, the thickness of the cladding tubes can be prevented from reduction caused by fretting corrosion which is caused by the contact of the cladding tubes with a wrapper tube. |
claims | 1. A charged-particle beam apparatus, the apparatus comprising:at least one source for generating a charged-particle beam;a first deflector configured to scan the charged-particle beam in a first dimension; anda second deflector configured to deflect the scanned beam such that the scanned beam impinges telecentrically upon a surface of a target substrate,wherein the second deflector comprises a Wien filter elongated and oriented lengthwise along the first dimension, andwherein the elongated Wien filter comprises an electric comb deflector applying an electric field along the first dimension and a static magnetic deflector applying a magnetic field perpendicular to the first dimension. 2. The apparatus of claim 1, further comprising a beam separator configured to deflect secondary electrons emitted from the target substrate towards a detector system. 3. The apparatus of claim 2, wherein the beam separator comprises pairs of electrodes oriented lengthwise along the first dimension. 4. The apparatus of claim 2, further comprising a de-scanner to further deflect the secondary electrons such that the secondary electrons converge upon a detector. 5. The apparatus of claim 1, further comprising a Wehnelt electrode configured to control charge at the surface of the target substrate, the Wehnelt electrode including a slot oriented lengthwise along the first dimension. 6. The apparatus of claim 5, further comprising an additional electrode positioned further away from the surface of the target substrate than the Wehnelt electrode, the electrode having a positive potential with respect to the target substrate. 7. The apparatus of claim 1, wherein the elongated Wien filter is configured to deflect secondary electrons emitted from the target substrate so as the secondary electrons converge at a position of a detection system. 8. The apparatus of claim 1, wherein the detection system comprises an energy analyzer. 9. The apparatus of claim 1, further comprising an array of multiple sources for generating charged-particle beams. 10. The apparatus of claim 9, wherein the charged-particle beams from the multiple sources are deflected simultaneously such that each beam impinges telecentrically upon the surface of the target substrate. 11. The apparatus of claim 1, further comprising circuitry to detect a substrate current. 12. The apparatus of claim 11, wherein the detected substrate current is used to provide a signal for forming an image of the target substrate. 13. A method of electron beam inspection, the method comprising:generating a primary electron beam;scanning the primary electron beam in a first dimension; anddeflecting the scanned beam such that the scanned beam impinges telecentrically upon a surface of a target substrate,wherein said deflecting is performed using a Wien filter elongated and oriented lengthwise along the first dimension, andwherein the elongated Wien filter comprises an electric comb deflector applying an electric field along the first dimension and a static magnetic deflector applying a magnetic field perpendicular to the first dimension. 14. The method of claim 13, further comprising separating secondary electrons emitted from the target substrate from the primary electron beam by deflecting the secondary electrons towards a detector system. 15. The method of claim 14, wherein said separating is performed using pairs of electrodes oriented lengthwise along the first dimension. 16. The method of claim 13, further comprising controlling charge at the surface of the target substrate using a Wehnelt electrode, said Wehnelt electrode including a slot oriented lengthwise along the first dimension. 17. The method of claim 13, wherein the elongated Wien filter deflects secondary electrons emitted from the target substrate so that the secondary electrons converge at a position of a detection system. 18. The method of claim 17, further comprising generating an energy spectrum of the secondary electrons. 19. The method of claim 13, wherein the target substrate is translated in a direction perpendicular to the first dimension. 20. A method of electron beam lithography, the method comprising:generating a primary electron beam;scanning the primary electron beam in a first dimension;controllably blocking the primary electron beam so as to generate a programmed pattern; anddeflecting the scanned beam such that the scanned beam impinges telecentrically upon a surface of a target substrate,wherein said deflecting is performed using a Wien filter elongated and oriented lengthwise along the first dimension, andwherein the elongated Wien filter comprises an electric comb deflector applying an electric field along the first dimension and a static magnetic deflector applying a magnetic field perpendicular to the first dimension. |
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description | This invention was made with Government support under contract number DE-AC02-98CH10886, awarded by the U.S. Department of Energy. The Government has certain rights in the invention. The invention relates to nuclear technology, and to irradiation targets and their preparation. Such targets can be irradiated by an intensive accelerator beam to obtain various radioactive isotopes from Sb-containing targets. For example, 117mSn in a no-carrier-added (NCA) form may be produced. Targets and methods for target preparation from Ga—Ni alloys have been used for production of 68Ge using a proton beam accelerator (C. Loch et al., “A New Preparation of Germanium-68”, Int. J. Appl. Radiat. Isot., 33, 261-270 (1982); N. R. Stevenson et al., A New Production Method for Germanium-68, Synthesis and Application of Isotopically Labelled Compounds, Ed. J. Allen, John Willey & Sons, 1995, p. 119-223; A. A. Razbach et al., “Production of Germanium-68 in Russia”, Proc. 6th Workshop on Targetry and Target Chemistry, Vancouver, Canada, 1995, p. 5114)). The Ga—Ni alloys were electrodeposited onto copper backing or pressed onto a copper block heated after or during pressing. Tin-117m cannot be produced from such target material. A target was prepared from thick pure antimony monolith in a target shell to provide 117mSn (B. L. Zhuikov et al., Process and targets for production of no-carrier added radiotin, Russian patent No. 2313838 (published Dec. 27, 2007)). However, pure Sb has a low heat conductivity and thermal stability. This can result in melting and sublimation of the pure Sb during exposure to intensive proton beams and can result in destruction of the target shell. Additional targets and methods for their preparation are thus desirable, The present invention relates to nuclear technology, and to irradiation targets and their preparation. Some embodiments provide for the production of a target for irradiation by an intensive accelerator beam to obtain various radioactive isotopes from Sb-containing targets. One embodiment of the invention is a target for redionuclide production wherein the target comprises an intermetallic composition of natural or enriched antimony. Suitable alloys include antimony and titanium, antimony and copper, antimony and nickel, or antimony and aluminum. The composition can be welded to a copper target backing which is cooled during irradiation. The target surface facing the accelerator beam can be covered with a thin layer of a metal. In another embodiment, the intermetallic composition is encapsulated in a metallic shell and can be cooled by water during irradiation. The shell can be made of metallic niobium, stainless steel, nickel, or titanium. The shell can be plated with nickel The composition can be welded to a copper backing block by means of diffusion welding in vacuum at pressure 80-160 kG/cm2 and temperature of 360-440° C. The block can be cooled with water during the target irradiation at the accelerator. According to another embodiment, the composition may be attached to the target shell of the above mentioned materials by means of diffusion welding in vacuum performed with pressure 200-300 KG/cm2 on the target square and at a temperature of 600-1000° C. In still another embodiment, the target shell can be made of titanium plated with nickel by means of diffusion welding of nickel foil, or electroplating by copper and then by nickel, or decomposing of nickel carbonyl at the heated target shell in dynamic vacuum. In still another embodiment, Ti—Sb composition is electroplated directly with nickel of thickness 40-100 μm. These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims and accompanying drawings wherein: This invention relates to irradiation targets and their method of preparation. In one embodiment, an antimony containing target comprises an intermetallic composition of antimony which can then be irradiated with a beam of charged particles, such as protons. The beam can be a high current beam. Radioactive no-carrier-added (NCA) tin-117m can be produced using a proton beam. Other radioactive isotopes of tin, tellurium, iodine, or other elements can be produced using Sb-containing targets irradiated with protons, deuterons, or alpha-particles. In exemplary embodiments, the target can contain intermetallic compounds of natural antimony or enriched antimony (e.g., 123Sb). Thermal stability, heat conductivity, content of the element to produce the desired isotope in nuclear reactions, as well as interaction with a target shell are some of the parameters that can provide a stable and useful target that can be irradiated by a high beam current. A number of intermetallic compositions can provide stable and useful targets, including for example, intermetallic compounds or eutectic solid solutions. The intermetallic compositions can comprise compounds or eutectic solutions of Sb combined with another metal, including, for example, Ti, Ni, Cu, Ag, or Al. For example, TiSb, NiSb, and AlSb are thermally stable; the melting points of these compounds are 1160° C., 1147° C., and 1058° C., and the heat of formation 167, 32-66 and 49 kJ/mol, respectively. Thermally stable compounds, including the above three compounds, do not decompose to the extent that could provide an unstable or useless target. Pure Sb, which has a melting point of 630° C., sublimes and can destroy the target shell. The heat conductivity of TiSb is higher than pure Sb and Ti. A number of other intermetallic compounds and alloys can also be used for target preparation, including, for example Ag—Sb and TiSb2. In the formation of TiSb, the intermetallic composition contains antimony not less than 40 atomic % (63 weight %) and not more than 50 atomic % (72 weight %). A higher concentration of Sb may lead to the presence of pure antimony at heating, while a lower concentration of antimony reduces the production rate of radioactive isotopes from irradiated antimony-containing target. An antimony concentration of not less than 48 atomic % (70 weight %) and not more than 49 atomic % (71 weight %) is preferable. The ratio of Ti:Sb which is close to 50 atomic % also provides higher melting point, i.e., 1160° C., in the composition, which is important for temperature stability. The antimony may be natural enriched antimony (121Sb or 123Sb) for future isotope production. In an exemplary embodiment, intermetallic TiSb-composition forms a massive block comprising monolith with density not less than 95% of X-ray density of the compound. Lower densities lead to a lower heat conductivity and mechanical strength. The eutectic solid solutions can comprise Cu and Sb. For example, a eutectic solid solution of Cu with Sb (63 atomic % of Cu, melting point 526° C.) has a greater heat conductivity (56±5 W/m·K) compared to pure Sb (17-21 W/m·K). Targets based on these intermetallic compositions can be irradiated at a high beam current. The intermetallic may also comprise NiSb, AlSb or TiSb. The heat conductivity of TiSb is greater than Ti or Sb. The intermetallic composition can be welded (e.g., using diffusion welding to a backing block prior to irradiation. FIG. 1 shows an embodiment of a target design with an intermetallic compound welded to the cooled copper backing 12 and irradiated at an accelerator. The irradiated target material 10 is covered with a thin layer of a metal. The backing block is cooled with water going in channels 14. The water is sealed with a radiation stable gasket 16. This backing block can be cooled during the irradiation. This design can be used, for example, with targets (such as thin targets) that will be irradiated for 117mSn production at low proton inlet energies (e.g., 30-40 MeV). In some instances, the backing block design can be used with 1-2 mm targets in the beam direction or with a thinner target if the beam is directed to the target surface with a smaller beam angle (e.g., 6-12°). The backing block can be made from a number of materials including for example, metals with a high heat conductivity, metallic silver, various copper alloys, and copper. Diffusion welding can be performed, for example, in a vacuum at 80-160 kG/cm2 (or at 90-110 kG/cm2) and at a temperature of 360-440° C. The target surface facing the beam can be covered with a thin layer of a metal. In some instances, this thin layer can protect the target or lessen Sb evaporation in the accelerator vacuum. A number of different materials can be used to form this thin layer including for example, nickel or other inorganic materials. This thin layer can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 microns thick. In another exemplary embodiment, the intermetallic composition, can be encapsulated in a shell prior to irradiation. The shell can be a hermetic shell. The shell can be cooled by water flowing around one or more sides of the target. FIG. 2 shows an embodiment of a target design with an Sb-containing intermetallic composition encapsulated in a metallic shell cooled outside by water during irradiation. The composition 20 is encapsulated into metallic shell 22. Inlet and outlet target windows 24 (100 μm foils) can be plated with Ni-layer (50-100 μm thickness) and can be welded by means of diffusion welding to the intermetallic composition 20. Metallic rings 26 (0.5 mm thickness) can strengthen the design and can provide a reliable electron beam welding with joint 28. Dimensions are given in mm. This design can be used, for example, during 117mSn production using a proton beam with an inlet proton energy of 55 MeV or higher. The shell can be made from any number of metals, alloys or the like, including for example, metallic niobium, nickel, stainless steel, or titanium. The shell can be closed (e.g., sealed or hermetically sealed) by welding, such as diffusion welding. For example, diffusion welding can be performed in a vacuum under pressure of 200 kG/cm2 or more, or 300 kG/cm2 or less on the target square (or, for example, 250-280 kG/cm2), and at temperature from 600° C. to 1000° C. (or 800-900° C.). The shell can be additionally closed (e.g., sealed or hermetically) around the periphery of the target shell by means of electron beam or laser welding; this can provide more reliable encapsulation. Cooling water under a high intensity proton beam can become more chemically active (due to, for example, radiolysis) and can, in some instances, deteriorate or destroy some materials. In some embodiments, the outer surface of the shell can withstand cooling water under a high intensity proton beam, and thus may be more suitable for the shell. For example, stainless steel, niobium, and nickel can be used for the shell material. Inconel (austenitic nickel-based superalloys) or other nickel- and chromium-base alloys can also be used as the shell material. Materials that may not be stable on their own can be plated, e.g., nickel plating, to reduce or prevent interaction with water under the proton beam. In some embodiments, the shell material can be plated with nickel. Shell materials that can be plated include, for example, AlSb, TiSb, NiSb, titanium, molybdenum, tungsten, aluminum, zinc, graphite, copper and tantalum. In some embodiments, the plated nickel thickness can be from 40 μm to 100 μm. A shell that excludes elements that produce undesirable radionuclides upon proton beam exposure can be useful. Undesirable radionuclides can be implanted in the composition material as recoil atoms and can sometimes require an additional chemical purification of 117mSn from the other radionuclides. For example, Ti does not produce additional undesirable radionuclides upon proton beam exposure and thus the Ti—Sb shell material can provide a useful shell material. TiSb can be encapsulated in a titanium shell by means of welding, such as diffusion welding. For example, diffusion welding can be performed in a vacuum under pressure of 200-300 kG/cm2 on the target square (or, for example, 250-280 kG/cm2), and at temperature from 600° C. to 1000° C. (or 800-900° C.). Under these temperature and pressure conditions, the titanium is adequately welded and good contact between the titanium shell and Ti—Sb composition is provided; this can improve target cooling during irradiation. The target shell can be additionally closed around the periphery of the target shell by means of electron beam or laser welding; this can provide more reliable encapsulation. The titanium shell can be plated by nickel to aid in the protection from the interaction with water during irradiation. It can be difficult to directly electroplate titanium with nickel because titanium can form a stable oxide film on its surface. In these and other such situations, other methods can be used to plate with nickel. For example, three methods can be used to provide titanium plating with nickel: (1) preliminary electroplating of titanium with copper layer and then with nickel as it is described for example in (V. I. Lainer. Galvanic plating of light alloys. Moscow. Metallurgizdat, 1959); (2) plating by means of nickel carbonyl decomposing at the heated target shell in dynamic vacuum at temperature not less than 400° C. when the oxide film is not sufficiently strong, nickel sputtering in vacuum is also possible; and (3) diffusion welding of nickel foil with titanium shell, that can be performed in the same process of diffusion welding of titanium shell with the foregoing pressure and temperature parameters, before, or after titanium shell welding. The targets fabricated by the above methods can be irradiated at high intensity beams of accelerated particles to produce 117mSn and other radionuclides generated from natural or enriched antimony. The invention will be further appreciated in light of the following examples. A plate of a copper alloy containing 62 atomic % Sb (76% in weight) thickness 0.4 mm was welded by means of diffusion welding to a copper backing block, as shown in FIG. 1. The diffusion welding was performed at unit pressure 100 kG/cm and temperature 400° C. (melting pressure of the alloy is 526° C.). The copper block from the back side had channels for cooling water; the water velocity was 4 m/s. The target was oriented to the beam at an angle of 11°. The target was irradiated by a proton beam having an energy range of 40-26 MeV, a beam current of 500 μA, and a beam spot area was of 12 cm2. Energy release in the target material was 580 W/cm2, and the maximum calculated temperature on the target surface was 350° C. The production rate of 117mSn was 3.2 mCi/h. A round plate of Ti—Sb composition, containing 44 atomic % Sb (67% in weight), thickness 2.2 mm, diameter 45 mm was electroplated with nickel (layer thickness is 40 μm). The target cooled in all sides by water flow was irradiated with a proton beam (beam angle was 26°) with a beam current of 100 μA in the energy range 55-30 MeV. The production rate of 117mSn on the target material containing natural Sb was 2.3 mCi/h. There were no considerable admixtures of 113Sn. Using enriched 123Sb material in a similar target, the production rate was 3.6 mCi/h. A ring plate of TiSb composition 5.8 mm thick inside titanium body ring (outer diameter is 50 mm, inner diameter is 40 mm), as shown in FIG. 2, was covered from the both sides by titanium (100 μm) and then nickel (50 μm) foils. The foils were welded to the plate by means of diffusion welding in vacuum under press 5200-5500 kG at 850° C. during 25 min. When the temperature was 600-650° C. the titanium foil was welded well to the titanium body ring but not to the TiSb composition. The obtained detail was additionally enhanced with 0.5 mm titanium rings and welded around by electron beam for a better sealing. The resulting target was irradiated on proton beam (at angle 26°) in energy range 120-85 MeV with beam current 100 μA and the target was cooled from all sides by water flow. The production rate of 117mSn was 20 mCi/h. Considerable amounts of 113Sn were also produced in this target. This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should only be defined by the appended claims. |
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abstract | This invention relates to a composite material for neutron shielding and maintenance of sub-criticality comprising a matrix based on vinylester resin and an inorganic filler capable of slowing and absorbing neutrons. |
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description | The present application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 12/966,315, entitled “Radiation Shield Device and Associated Method” filed on Dec. 13, 2010, the contents of which are incorporated herein in their entirety. Embodiments of the present disclosure relate generally to methods and devices for shielding an area from radiation and, more particularly, to a cryogenically cooled radiation shield device and an associated method. The sun occasionally releases significant amounts of charged particles during events known as coronal mass ejectas (“CMEs”). The charged particles released during CMEs include electrons, protons, and heavy ions. Each CME may last for about one or two days in the vicinity of earth, but their effects may linger for up to a week. Such proton and heavy ion radiation can cause cell damage to humans exposed to such radiation. Additionally, sensitive electronic components and other devices may be adversely affected by such radiation. Therefore, even though CMEs are relatively uncommon occurrences, the amounts of radiation they could potentially inflict upon a crew and equipment of a spacecraft suggests that consideration be given to shielding part or all of a spacecraft from such radiation. Similarly, comparable radiation protection may be desirable in other environments as well, such as habitats for celestial bodies such as the moon and Mars. Shielding from proton and heavy ion radiation may generally be accomplished by either absorbing the particles or by deflecting the particles. To absorb the radiation, materials of a thickness sufficient for the amount of energy expected from the radiation, can be provided around an area that houses the crew and/or sensitive equipment during a CME. However, because of the significant amount of weight such a housing would require, the use of radiation absorbing material is not practical for space exploration and other applications. Additionally, the absorption of high energy particles may release a different form of radiation such as gamma rays and X-rays that pass through the shielding material and create other difficulties for the crew and/or equipment. It may therefore be preferable to deflect the particles of radiation rather than absorb them. In order to deflect particles of radiation, active radiation shield devices have been proposed. An active radiation shield device may include one or more coils that extend about an area to be shielded, such as about a spacecraft or the like. By passing current through the coil(s) of the radiation shield device, a magnetic field may be generated that deflects particles of radiation that may otherwise impinge upon the spacecraft. In order to facilitate the generation of the protective magnetic field, a radiation shield device may include coils formed of a superconductive material. The coils formed of the superconductive material must therefore be maintained at a temperature below its critical superconducting temperature onset level and as close to absolute zero as practical. As such, the coils formed of a superconductive material may be initially cooled from an ambient temperature and then maintained at a temperature below its critical superconducting temperature onset level by electrical refrigeration units. However, the electrical refrigeration units may be relatively heavy and may consume a substantial amount of electrical power. In addition, the electrical refrigeration unit may require electrical power generation and distribution, which also disadvantageously adds to the overall weight of the system. As it is often desirable to reduce the weight of a spacecraft, it may therefore be undesirable to include an electrical refrigeration unit and the associated electrical power generation distribution system in order to cool the coils formed of a superconducting material to a temperature near absolute zero. As such, radiation shield devices, including coils formed of a superconductive material, may alternatively immerse the coils in liquid helium, which lowers the temperature of the coils from an ambient temperature, such as about 23° C., to a temperature required for superconducting operations, such as −269° C., as a result of the boil-off vaporization of the liquid helium. Since the latent heat of the liquid helium is relatively low, however, an excessive amount of liquid helium, as measured in terms of the weight and volume of the liquid helium, may need to be boiled off in order to cool the coils. As such, a substantial quantity of liquid helium may be required to be provided in order to sufficiently cool the coils formed of a superconductive material, thereby disadvantageously increasing the weight of the spacecraft or the like. A cryogenically cooled radiation shield device as well as an associated method are provided according to embodiments of the present disclosure in order to shield an area, such as the capsule of a space vehicle, from radiation, such as the charged particles released during CMEs. In this regard, the cryogenically cooled radiation shield device and associated method of one embodiment are configured to deflect the particles of radiation in a manner that is lighter and/or consumes less cryogen liquid than some prior approaches. In one embodiment, a cryogenically cooled radiation shield device is provided that includes at least one first coil comprised of a superconducting material extending about an area to be shielded from radiation. The cryogenically cooled radiation shield device also includes a first inner conduit extending about the area to be shielded from radiation. The at least one first coil is disposed within the first inner conduit. The cryogenically cooled radiation shield device also includes a first outer conduit extending about the area to be shielded from radiation. The first inner conduit is disposed within the first outer conduit. The cryogenically cooled radiation shield device also includes a first cryogen liquid disposed within the first inner conduit and a second cryogen liquid, different than the first cryogen liquid, disposed within the first outer conduit. The cryogenically cooled radiation shield device may also include thermal insulation surrounding the first inner conduit and positioned between the first inner conduit and the first outer conduit. The first cryogen liquid may have a lower boiling point than the second cryogen liquid. For example, the first cryogen liquid may comprise liquid helium, and the second cryogen liquid may be liquid oxygen, liquid nitrogen or liquid hydrogen. In one embodiment, the cryogenically cooled radiation shield device also includes at least one second coil comprised of a superconductive material and extending about the area to be shielded from radiation, second inner and outer conduits extending about the area to be shielded from radiation with the at least one second coil being disposed within the second inner conduit and the second inner conduit being disposed within the second outer conduit, and first and third cryogen liquids disposed within the second inner and outer conduits, respectively, with the third cryogen liquid being different than the first and second cryogen liquids. In this embodiment, the second cryogen liquid may comprise liquid hydrogen, and the third cryogen liquid may comprise liquid oxygen. Further, the cryogenically cooled radiation shield device of this embodiment may also include a fuel cell configured to receive boil-off of the second and third cryogen liquids. The cryogenically cooled radiation shield device may also include a first intermediate conduit extending about the area to be shielded from radiation. In this embodiment, the first inner conduit is disposed within the first intermediate conduit, while the first intermediate conduit is disposed within the thermal insulation and the first outer conduit. In another embodiment, a space vehicle is provided that includes a capsule and a radiation shield device. The radiation shield device includes at least one first coil comprised of a superconductive material extending about the capsule. The radiation shield device also includes a first inner conduit and a first outer conduit extending about the capsule. The at least one first coil is disposed within the first inner conduit. The first inner conduit is, in turn, disposed within the first outer conduit. The radiation shield device of this embodiment also includes first and second cryogen liquids disposed within the first inner conduit and the first outer conduit, respectively. In one embodiment, the radiation shield device may also include thermal insulation surrounding the first inner conduit and positioned between the first inner conduit and the first outer conduit. The first cryogen liquid of one embodiment has a lower boiling point than the second cryogen liquid. For example, the first cryogenic liquid may be liquid helium, and the second cryogen liquid may be liquid oxygen, liquid nitrogen, or liquid hydrogen. The radiation shield device of one embodiment may also include at least one second coil comprised of a superconductive material and extending about the capsule, second inner and outer conduits extending about the capsule with the at least one second coil disposed within the second inner conduit, and the second inner conduit disposed within the second outer conduit. The radiation shield device of this embodiment also includes first and third cryogen liquids disposed within the second inner and outer conduits, respectively, with the third cryogen liquid being different than the first and second cryogen liquids. In this regard, the second cryogen liquid may be liquid hydrogen, and the third cryogen liquid may be liquid oxygen. The space vehicle of one embodiment may also include a fuel cell configured to receive boil-off of the second and third cryogen liquids. In a further embodiment, a method of cryogenically cooling a radiation shield device is provided that includes cryogenically cooling at least one first coil comprised of a superconductive material. The cryogenic cooling includes circulating a first cryogen liquid through a first inner conduit in which at least one first coil is disposed and circulating a second cryogen liquid, different than the first cryogen liquid, through a first outer conduit in which the first inner conduit is disposed. The method of this embodiment also generates a protective magnetic field by providing current flow through the at least one first coil while the at least one first coil is cryogenically cooled. In one embodiment, the at least one first coil may be pre-cooled prior to commencement of the mission, thereby reducing the quantity of cryogen liquid that must be carried during the mission. The first cryogen liquid may have a lower boiling point than the second cryogen liquid. For example, the first cryogen liquid may be liquid helium, and the second cryogen liquid may be liquid oxygen, liquid nitrogen, or liquid hydrogen. In one embodiment, the circulation of a second cryogen liquid may include the sequential circulation of a plurality of different cryogen liquids through the first outer conduit. In this embodiment, the plurality of different cryogen liquids may be sequentially circulated through the first outer conduit in order of descending boiling point. Accordingly, the circulation of the first cryogen liquid through the first inner conduit may commence following the sequential circulation of a plurality of different cryogen liquids through the first outer conduit. In accordance with embodiments of the present disclosure, a cryogenically cooled radiation shield device and an associated method are provided in order to deflect particles of radiation in a manner that is conservative in terms of its weight and its consumption of liquid cryogen. However, the features, functions and advantages that have been discussed may be achieved independently and the various embodiments of the present disclosure may be combined in the other embodiments, further details of which may be seen with reference to the detailed description and drawings. Embodiments of the present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. Indeed, these embodiments may 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 satisfy applicable legal requirements. Like numbers refer to like elements throughout. Referring now to FIG. 1, the radiation shield device 10 in accordance with one embodiment of the present disclosure is illustrated. The radiation shield device 10 is generally described herein as providing protection from radiation for a manned space vehicle or a habitat for celestial bodies, particularly during CME events. However, further embodiments of the present disclosure may include radiation shield devices for any situation in which protection from particle radiation is desired beyond the earth's magnetosphere. The radiation shield device 10 of the illustrated embodiment includes first and second shells 12, 14 that at least partially surround an area 16 to be shielded from radiation. In the illustrated embodiment, a space vehicle defines the area 16 to be shielded from radiation. A space vehicle may have various configurations, but the space vehicle of the illustrated embodiment has a cylindrical center portion and tapered end portions. A space vehicle may house one or more crew members as well as equipment, such as electronics, that may be sensitive to particle radiation. As shown in the illustrated embodiment, the first and second shells 12, 14 at least partially surround the space vehicle. As such, the first and second shells may somewhat follow the shape of the space vehicle. In this regard, the first and second shells 12, 14 of the illustrated embodiment have a medial cylindrical portion that encircles the cylindrical central portion of the space vehicle and opposed end portions that are tapered radially inward from the medial cylindrical portion so as to generally follow the tapered end portions of the space vehicle. The tapered end portions of the first and second shells 12, 14 may taper in a curved fashion as shown in the embodiment of FIG. 1. Alternatively, the end portions of the first and second shells 12, 14 may taper linearly or otherwise so as to more closely follow or conform to the tapered end portions of the space vehicle. As shown in FIG. 1, the second shell 14 is spaced apart from the first shell 12 in such a manner that the second shell is further away from the area 16 to be shielded, such as the space vehicle, than the first shell. In this regard, the first shell 12 may be adjacent to the area 16 to be shielded and, in one embodiment, is attached or connected thereto, while the second shell 14 is spaced further from the area to be protected. As such, the radiation shield device 10 may include a truss network 18 between the first and second shells 12, 14 for connecting the second shell to the first shell and positioning the second shell relative to the first shell. In one embodiment, the truss network 18 is formed of a plurality of truss members extending between and connected to the first and second shells 12, 14. Although the truss network 18 may be formed of various materials, the truss elements of one embodiment may be formed of a composite material, such as a carbon reinforced matrix material in order to provide sufficient strength while limiting the weight of the truss network. The second shell 14 may be larger than the first shell 12 as a result of the second shell being spaced further from the area 16 to be shielded and having, for example, a larger effective radius from the central axis 20 of the area to be shielded. However, the second shell 14 of one embodiment has the same or a comparable shape to that of the first shell 12, as shown in FIG. 1. The first shell 12 includes a plurality of conductive coils that encircle the area 16 to be shielded. With respect to the embodiment of FIG. 1, the circles that graphically represent the first shell 12 are intended to be generally representative of one or more of the coils that encircle the area 16 to be shielded. Likewise, the second shell 14 includes a plurality of conductive coils that encircle the area 16 to be shielded from radiation as well as encircling the first shell 12. Again, the circles that graphically represent the second shell 14 in FIG. 1 are intended to be generally representative of one or more of the coils that encircle the area 16 to be shielded. Indeed, in one embodiment, both the first and second shells 12, 14 may include a substantially greater number of coils than the number of circles shown in FIG. 1. As described below in conjunction with the thermal control system, the coils of each of the first and second shells 12, 14 may be arranged in coil groupings. In one embodiment, the coil groupings of the first shell 12 are paired with respective coil groupings of the second shell 14. Additionally, while the coil planes of the first and second shells 12, 14 of the illustrated embodiment are shown to be parallel and offset form one another, the coil planes of the first and second shells of other embodiments may be rotated with respect to one another, either with or without an offset. The coils of one embodiment are formed of superconductive material. For example, the coils may be formed of a niobium titanium (NbTi) copper matrix multifilament superconducting wire winding. However, other embodiments of the present disclosure may include coils formed of alternative superconductive materials. In order to have superconductive properties, the superconductive material must be maintained at a temperature below its critical superconducting temperature onset level and as close to absolute zero as practical, preferably 36 K or lower, more preferably less than 25 K and most preferably less than 10 K. As such, the radiation shield device 10 may include a thermal control system in thermal communication with the superconductive material of the coils to lower the temperature of the superconductive material to a desired temperature below its critical superconducting temperature onset level. In operation, current is flowed through the coil groupings of the first shell 12 in one direction, such as a counterclockwise direction when looking down on the area 16 to be shielded from above. Conversely, current is flowed through the coil groupings of the second shell 14 in the opposite direction, such as in a clockwise direction when viewed down on the area 16 to be shielded from above. As a result of the current flow through the coils, a magnetic field is generated by each of the first and second shells 12, 14 which function as first and second solenoids, respectively. As a result of the current flowing through the first and second shells 12, 14 being in opposite directions, however, the north and south poles of the coil groupings of the first shell are correspondingly oriented opposite the north and south poles of the paired coil groupings of the second shell. With reference to the illustrated embodiment, for example, the north pole of the coil groupings of the first shell 12 may be at the upper end of the area 16 to be shielded and the south pole of the coil groupings of the first shell may be at the lower end of the area to be shielded, while the north pole of the coil groupings of the second shell 14 may be at the lower end of the area to be shielded and the south pole of the paired coil groupings of the second shell may be at the upper end of the area to be shielded. Representative magnetic flux lines generated by the first and second shells 12, 14 are shown in FIG. 1. As a result of the opposite direction of the current flow through the coils of the first and second shells 12, 14, the magnetic fields generated by the current flow through the coils of the first and second shells offset one another within the area 16 to be shielded such that little or no magnetic field is generated therewithin. Thus, the radiation shield device 10 need not include an internal magnetic shield device to protect the interior of the area to be shielded from the magnetic fields generated by the radiation shield device itself. Accordingly, the weight of a space vehicle or the like may be reduced relative to space vehicles that require such an internal magnetic shield device. In the region between the first and second shells 12, 14, the magnetic fields generated by the current flowing in opposite directions through the coils are directed in the same direction and are additive, thereby resulting in a stronger magnetic field between the first and second shells than that generated by either the first or the second shell individually. Further details regarding the radiation shield device 10 and the resulting magnetic field are provided by U.S. patent application Ser. No. 12/966,315 entitled “Radiation Shield Device and Associated Method”, filed concurrently herewith, the entire contents of which are incorporated by reference herein. As noted above, the radiation shield device 10 includes a thermal control system for establishing and maintaining the temperature required for superconducting operation of the coils. In this regard, FIG. 2 illustrates one example embodiment of aspects of the thermal control system for controlling the temperature of the coils. It is noted, however, that the truss network is not shown in FIG. 2 so as to more clearly illustrate aspects of the thermal control system. Although each shell 12, 14 could be treated as a single unit for thermal control purposes, the plurality of coils of each shell may be broken into a plurality of groupings, such as the three groupings depicted in FIG. 2. Each grouping may, in turn, be separately cooled to temperatures sufficient to allow for superconducting operations. Although three groupings are shown for each shell in the embodiment of FIG. 2, a shell may include more or fewer coil groupings in other embodiments. The thermal control system includes an inner conduit 24 that extends about the area 16 to be shielded from radiation. In an embodiment in which the coils of a shell include two or more coil groupings, the thermal control system may include a first inner conduit, a second inner conduit, a third inner conduit, etc. (hereinafter generally referenced as “an inner conduit” and designated as 24), one of which is associated with each coil grouping. As shown in FIG. 2 and, in more detail, in FIG. 3, the inner conduit 24 houses the coils 22 for the respective coil grouping. The inner conduit 24 is generally slightly larger than the coils 22 disposed therein such that a cryogen liquid may be circulated therethrough as described below. The inner conduit 24 may be formed of various materials but, in one embodiment, is formed of material that does not react with the cryogen liquid, such as aluminum. An inner conduit 24 may also have various shapes and configurations but, in the illustrated embodiment, has a length in the axial direction that is greater than its radial width such that the coils 22 housed within the inner conduit may relatively uniformly encircle that portion of the area 16 to be shielded from radiation about which the inner conduit extends. As shown in FIG. 2 and, in more detail, in FIG. 3, the thermal control system also includes an outer conduit 26 extending about the area 16 to be shielded from radiation. In an embodiment in which the coils of a shell include two or more coil groupings, the thermal control system may include a first outer conduit, a second outer conduit, a third outer conduit, etc. (hereinafter generally referenced as “an outer conduit” and designated as 26), one of which is associated with each coil grouping. As shown, each inner conduit 24 is disposed within a respective outer conduit 26. As such, the outer conduit 26 is generally larger than the inner conduit 24, such as by having a greater length in the axial direction and a greater radial width, so that a cryogen liquid may be flowed therethrough. Although not necessary, the outer conduit 26 may also have a shape that is consistent with or, in one embodiment, identical to that of the inner conduit 24. The outer conduit 26 may also be formed of various materials but, in one embodiment, is formed of a material that does not react with the cryogen liquid, such as the same material as the inner conduit 24, e.g., aluminum. The thermal control system may also include intermediate thermal insulation 28 surrounding each inner conduit 24 and positioned between the inner conduit and the outer conduit 26 for limiting thermal transfer between the outer conduit and the inner conduit. Although the intermediate thermal insulation 28 may be formed of various materials, the intermediate thermal insulation of one embodiment is formed of a layered composite insulation with paper. Additionally, the thermal control system may include outer thermal insulation 29 surrounding each outer conduit 26 for limiting thermal transfer between the environment and the outer conduit. Although the outer thermal insulation 29 may be formed of various materials, the outer thermal insulation of one embodiment is also formed of a layered composite insulation with paper. With the exception of predefined inlets and outlets for controllably introducing and removing cryogen liquids, the inner and outer conduits 24, 26 are watertight such that a cryogen liquid circulated through the inner conduit remains within the inner conduit and does not leak into the outer conduit. Likewise, a cryogen liquid circulated within the outer conduit 26 exterior of the inner conduit 24 does not leak into the inner conduit and, instead, remains within the outer conduit. In operation, cryogen liquids may be circulated through the inner and outer conduits 24, 26 in order to lower the temperature of the superconductive material of the coils 22 to a temperature below the critical superconducting temperature onset level and to thereafter maintain the temperature of the superconductive material of the coils at that relatively low temperature. As a result of the thermal control system and associated method of operation of embodiments of the present disclosure, the coils 22 may be efficiently cryogenically cooled in a manner that is sensitive to the weight that is required to be carried by the space vehicle. As described above, the thermal control system may include two nested conduits, with each inner conduit 24 disposed within a respective outer conduit 26. However, other embodiments of the thermal control system of the present disclosure may include additional conduits arranged in a nested fashion with one or more intermediate conduits positioned between the inner conduit 24 and the outer conduit 26. By way of example, FIGS. 2 and 3 illustrate an embodiment of a thermal control system that has three nested conduits, namely, a first conduit 24 in which the coils 22 are disposed, an intermediate conduit 30 within which the inner conduit is disposed and an outer conduit 26 within which both the inner and intermediate conduits are disposed. The outer conduit 26 may, in turn, be surrounded by outer thermal insulation 29, such as a layered composite insulation with paper. In the illustrated embodiment, the intermediate conduit 30 is also surrounded by intermediate thermal insulation 28 such that the intermediate and outer conduits are spaced apart from one another by the intermediate thermal insulation. As described below, cryogen liquids may be circulated through each of the conduits in order to efficiently cool the coils 22 to a temperature sufficiently low for superconducting operations. Although any additional conduits may be formed to have different shapes and to be formed of different materials, the intermediate conduit 30 of the embodiment illustrated in FIGS. 2 and 3 has a common shape with those of the inner and outer conduits 24, 26 and is formed of the same material as the inner and outer conduits, such as a material that does not react with the cryogen liquid, e.g., aluminum. Although the radiation shield device 10 may be configured in various fashions, the radiation shield device of one embodiment includes a power source 34 as shown in FIG. 4. The power source 34 is in communication with the first and second shells 12, 14, such as the plurality of coils of the first and second shells such that actuation of the power source causes current to flow through the coils of the first and second shells in the desired directions. The radiation shield device 10 of one embodiment is an active device such that the power supply 34 may alternately cause current to flow through the coils of the first and second shells 12, 14 in order to generate a protective magnetic field or cease the current flow through the coils of the first and second shells in order to no longer generate the protective magnetic field. As such, the power supply 34 may be configured to be actuated in instances in which approaching particle radiation is detected such that current flow is initiated and the protective magnetic field is generated prior to the particle radiation impinging upon the area 16 to be protected, such as a space vehicle. Once the particle radiation has dissipated, however, the power supply 34 may be deactuated, thereby conserving energy until the next time that a protective magnetic field is to be generated. The radiation shield device 10 of the embodiment of FIG. 4 may also include a source 36 of the cryogen liquids, the controlled circulation of which lowers the temperature of the superconductive material of the coils to a temperature below its critical superconducting temperature onset level prior to or concurrent with the flow of current therethrough. In one embodiment, a separate source, such as a tank, is provided for each cryogen liquid. In one embodiment, however, the sources of the cryogen liquids are combined. In this regard, the cryogen liquids are maintained separate from one another, but the tanks that store and supply the different cryogen liquids are nested in a comparable fashion to the conduits. In this regard, the cryogen liquid having the lowest boiling point, such as liquid helium, may be stored in an innermost tank 36a. The innermost tank 36a may be disposed within a second tank 36b that stores the cryogen liquid having the next lowest boiling point, such as liquid hydrogen. The source 36 of this embodiment would generally have the same number of nested tanks as the number of different cryogen liquids. Thus, while the source 36 of cryogen liquids of the embodiment of FIG. 4 has two nested tanks 36a, 36b, the source may include three or more nested tanks in other embodiments such that the first and second tanks may, in turn, be disposed within a third tank that stores the cryogen liquid having the third lowest boiling point, such as liquid nitrogen. If additional cryogen liquids are utilized by the thermal control system, the source 36 may have additional tanks for storing the cryogen liquids with the sequence or nesting of the tanks based upon the relative boiling points of the cryogen liquids with the tanks ranging from an innermost tank 36a storing the cryogen liquid having the lowest boiling point to an outermost tank storing the cryogen liquid having the highest boiling point. Each tank may be individually connected to the conduit(s) through which the respective cryogen liquid is to circulate. Each of the tanks may be surrounded by a thermal insulation layer. The radiation shield device 10 may also include a controller 38 for controlling the valves or other control devices that selectively allow the flow of cryogen liquids through the different conduits. In one embodiment, the thermal control system is active in that the thermal control system is alternately activated and inactivated with the thermal control system being activated in response to predefined events, such as the detection of approaching particle radiation. In this regard, the thermal control system may be activated so as to lower the temperature of the coils 22 to enable superconducting operation and the generation of a protective magnetic field about the area 16 to be protected prior to the arrival of the particle radiation. Once the particle radiation has dissipated, the thermal control system may be deactivated, thereby conserving energy and reducing the quantity and, therefore, the weight of the cryogen liquid required to cool the coils 22. As shown in FIG. 2, the thermal control system of one embodiment may divide the coils into two or more groupings, each of which is surrounded by two or more conduits carrying cryogen liquids. Although each coil grouping may be cooled in the same fashion utilizing the same cryogen liquids in each respective conduit, different coil groupings may be cooled utilizing different cryogen liquids in some embodiments. For example, the thermal control system of one embodiment may circulate a second cryogen liquid, e.g., liquid hydrogen, from tank 36b through the outer conduit 26 associated with one coil grouping and a third cryogen liquid, e.g., liquid oxygen, from tank 36c through the outer conduit associated with another coil grouping. While the circulation of either liquid hydrogen or liquid oxygen reduces the temperature of the coils 22 within the respective inner conduit 24, the boil-off of the liquid hydrogen and the liquid oxygen that it caused as a result of the absorption of heat from the coils and/or the environment may be combined and utilized productively, as shown in the embodiment of FIG. 4. In this regard, the boil-off of the liquid oxygen from one coil grouping of the thermal control system and the boil-off of the liquid hydrogen from another coil grouping of the thermal control system may be provided to a fuel cell 40. The fuel cell 40, in turn, may combine the boil-off of the liquid oxygen and the boil-off of the liquid hydrogen to generate electricity and/or to generate drinking water which may be utilized to facilitate operation and habitation of the space vehicle. A radiation shield device 30 of another embodiment is shown in FIGS. 5 and 6. In this embodiment, the radiation shield device 10 does not include first and second shells. Instead, the radiation shield device 10 includes two or more cylindrical coils 42 extending about and encircling the center cylindrical portion of an area 16 to be shielded, such as a space vehicle, and a pair of trapezoidal coils 44 extending about and encircling portions of the opposed trapezoidal end portions of the area to be shielded. Each of the coils may include a plurality of coils formed of a superconductive material. In operation, current may be caused to flow and through the coils in the same direction and a magnetic field may be generated as shown by the magnetic flux lines of FIG. 5. The magnetic field generated by the radiation shield device 10 of this embodiment also protects against particle radiation. However, the magnetic field generated by the radiation shield device 10 of this embodiment extends through and creates a magnetic field within the area 16 to be shielded, such as within the space vehicle. As shown in cross-section FIG. 6, the radiation shield device 10 of this embodiment may also include a thermal control system with the windings that comprise each respective coil being disposed within a respective inner conduit 24. As before, each of the inner conduits 24 is disposed within a respective outer conduit 26 which, in turn, is surrounded by outer thermal insulation 29. Intermediate thermal insulation 28 may also be disposed about the inner conduit 24 between the inner conduit and the outer conduit 26. By circulating cryogen liquids through the respective conduits, the coils may be cooled so as to facilitate superconducting operation. The nested conduits of the thermal control system may be configured in a variety of manners in accordance with embodiments of the present disclosure. As shown in FIG. 7, for example, the thermal control system may include an inner conduit 24 within which the coils are disposed and an outer conduit 26 within which the inner conduit is disposed. While the outer conduit 26 may be surrounded by outer thermal insulation 29, the inner conduit 24 may be disposed within the outer conduit without any surrounding intermediate thermal insulation and without any intermediate conduit such that the cryogen liquid circulating through the outer conduit is in direct contact with the inner conduit. Referring now to FIG. 8, a method of cryogenically cooling a radiation shield device 10 is illustrated. In one embodiment, the coils of the radiation shield device 10 may be pre-cooled as shown in operation 50, such as to a temperature capable of supporting a superconducting operation or to a temperature at least cooler than ambient, prior to commencement of a mission, such as prior to launch of the space vehicle. Although the coils need not be pre-cooled in all embodiments, pre-cooling the coils reduces the cooling that is subsequently required during the mission and may therefore reduce the amount of cryogen liquids that are required to be carried onboard the space vehicle, thereby advantageously reducing the weight. Once the mission has begun, and regardless of whether the coils were pre-cooled prior to the mission, a determination may be made, such as by the controller 38, that the coils are to be cooled to a sufficiently low temperature to support superconducting operation. For example, the controller 38 may detect or otherwise determine that particle radiation is approaching the space vehicle and may desire to generate a protective magnetic field. Thus, prior to the arrival of the particle radiation, the controller 38 may issue instructions to the thermal control system regarding the circulation of a cryogen liquid required to cryogenically cool the coils. In the embodiment illustrated in FIG. 8, one or more second cryogen liquids are initially circulated through at least one of the conduits. See operation 52. Although the second cryogen liquid may be circulated through the outer conduit 26, the second cryogen liquid of one embodiment is circulated through the inner conduit 24. Although the second cryogen liquid may be selected to reduce the coils to a sufficient low temperature to support superconducting operation, the second cryogen liquid may be selected to cool the coils, but not to a sufficiently low temperature to support superconducting operations. While a variety of second cryogen liquids may be circulated through the conduit(s), such as the inner conduit 24, examples of second cryogen liquids that may be circulated include liquid oxygen, liquid nitrogen and liquid hydrogen. In order to increase the efficiency with which the coils are cooled, the thermal control system may be configured to sequentially circulate different cryogen liquids through the conduit(s), such as the inner conduit 24. In this embodiment, the cryogen liquids that are sequentially circulated through the conduit(s), such as the inner conduit 24 may be sequenced based upon the respective boiling points of the cryogen liquids and, in particular, in order of descending boiling point. As such, from among the cryogen liquids to be circulated through the conduit(s), such as the inner conduit 24, the cryogen liquid having the highest boiling point is initially circulated through the conduit(s), the cryogen liquid having the next highest boiling point is next circulated through the conduit(s), and so on until the cryogen liquid having the lowest boiling point is circulated through the conduit(s). In one example in which liquid oxygen, liquid nitrogen, and liquid hydrogen are circulated through the conduit(s), such as the inner conduit 24, liquid oxygen having a boiling point of −183° C. may initially be circulated through the conduit(s). Once the liquid oxygen has lowered the temperature of the coils to about −183° C., the liquid oxygen may be replaced with liquid nitrogen having a boiling point of about −198° C. Once the liquid nitrogen has lowered the temperature of the coils to about −198° C., the liquid nitrogen may be replaced with liquid hydrogen having a boiling point of about −253° C., with the circulation of the liquid hydrogen continuing until the temperature of the coils has been lowered to about −253° C. As shown in operation 54 of FIG. 8, a first cryogen liquid may also be circulated through the inner conduit 24 in which the coils 22 are disposed. Although the first cryogen liquid may be circulated through the inner conduit 24 concurrent with the circulation of a second cryogen liquid in instances in which the second cryogen liquid is circulated through the outer conduit 26, the circulation of the first cryogen liquid through the inner conduit is initiated, in one embodiment, once the circulation of the second cryogen liquids through the conduit(s) has lowered the temperature of the coils 22, such as to or near the boiling point of the second cryogen liquid, e.g., to at or near the lowest boiling point of the second cryogen liquids, such as −253° C. in an instance in which liquid hydrogen is circulated through the conduit(s). By initially lowering the temperature of the coils 22 by circulation of the second cryogen liquid through the conduit(s) prior to introducing the first cryogen liquid into the inner conduit 24, the coils are more efficiently cooled due to significant differences between each cryogen liquid's enthalpy of vaporization, also referred to as the latent heat of vaporization, or most simply termed latent heat. In this regard, although the second cryogen liquids circulated through the conduit(s) may have higher boiling points than the first cryogen liquid, such as liquid helium, circulating through the inner conduit 24, the latent heat of the second cryogen liquids circulated through the conduit(s) may be larger than the latent heat of the first cryogen liquid circulated through the inner conduit such that the second cryogen liquids may absorb more heat from the coils and cool the coils more efficiently and more rapidly than the first cryogen liquid. In this regard, the latent heat of second cryogen liquids such as liquid oxygen, liquid nitrogen, and liquid hydrogen are 213 kJ/kg-K, 200 kJ/kg-K, and 455 kJ/kg-K, respectively, while the latent heat of a first cryogen liquid such as liquid hydrogen is about 21 kJ/kg-K. Thus, the bulk of the cooling may be performed with the second cryogen liquids that can efficiently lower the temperature of the coils 22 a substantial amount, even though the second cryogen liquids may not be able to completely lower the temperature of the coils to the desired temperature for superconducting operations. Once the second cryogen liquids have lowered the temperature of the coils 22 a substantial amount, such as to or near the lowest boiling point of the second cryogen liquids, such as −253° C. in one embodiment, the first cryogen liquid may be circulated through the inner conduit 24 in order to further reduce the temperature of the coils to a temperature sufficient for superconducting operations, such as to −269° C. in an instance in which the first cryogen liquid is liquid helium. This efficient multi-stage cooling of the coils to the desired temperature for superconducting operations also permits the coils to be cooled in a manner that requires less coolant in terms of weight and/or volume, thereby reducing the quantity of coolant that the space vehicle, for example, must transport. Once the temperature of the coils 22 has been lowered so as to support superconducting operation, current may be provided to the coils by the power source 34 as shown in operation 56 with the direction of the current through the coils being controlled as described above. Based upon the flow of current through the coils and the direction of the current flow, a protective magnetic field may be generated about the space vehicle. See operation 58 of FIG. 8. With reference to FIG. 3, in order to maintain the coils 22 at a temperature that is sufficiently low to support superconducting operations, the first and second cryogen liquids may be circulated through the inner and outer conduits 24, 26 with the boil-off of the first cryogen liquid serving to overcome the internal heat or the heat transported into the first cryogen liquid through the intermediate thermal insulation 28 positioned between the inner and outer conduit, while the boil-off of the second cryogen liquid serves to overcome the heat absorbed through the outer thermal insulation 29 from the ambient environment. As described above, one or more second cryogen liquids may be sequentially circulated through the inner conduit 24 to lower the temperature of the coils. The second cryogen liquids may then be flushed from the inner conduit 24 and a first cryogen liquid may be circulated through the inner conduit to further lower the temperature of coils to a temperature that is sufficiently low to support superconducting operations. Concurrent with the circulation of the first cryogen liquid through the inner conduit 24, a second cryogen liquid may be circulated through the outer conduit 26. Alternatively, the one or more second cryogen liquids may be sequentially circulated, not through the inner conduit 24, but through the outer conduit 26 in the embodiment of FIGS. 2 and 3 or through the intermediate conduit 30 (and optionally also the outer conduit) in the embodiment of FIG. 7 with the first cryogen liquid being circulated through the inner conduit 24, either concurrent with the circulation of the second cryogen liquid through the other conduit(s) or following the circulation of the second cryogen liquid through the other conduit(s). As such, the area 16, such as a space vehicle, may be shielded from radiation utilizing coils formed of a superconductive material that are efficiently cooled in a manner that limits the quantity of coolant that is required. Further, the method may shield an area 16 from radiation without requiring substantial energy for operation. In this regard, the method of shielding an area 16 from radiation may be activated in response to detection of approaching particle radiation, but may be deactuated, thereby conserving energy, in instances in which particle radiation is not imminent. Many modifications and other embodiments of the present disclosure set forth herein will come to mind to one skilled in the art to which these embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the present disclosure is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. |
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053414071 | claims | 1. A cladding tube having a cross-section, the cladding tube comprising: an outer circumferential substrate having an inner surface; a zirconium barrier layer bonded to the inner surface of the outer circumferential substrate and itself having an inner surface; and an inner circumferential liner bonded to the inner surface of the zirconium barrier layer, wherein the inner circumferential liner comprises a zirconium alloy having less than about 1.2% tin by weight. an outer circumferential substrate having an inner surface; a zirconium barrier layer bonded to the inner surface of the outer circumferential substrate and itself having an inner surface; and an inner circumferential liner bonded to the inner surface of the zirconium barrier layer, wherein the inner circumferential liner comprises a zirconium alloy having less than about 1000 ppm oxygen by weight. an outer circumferential substrate having an inner surface; a zirconium barrier layer bonded to the inner surface of the outer circumferential substrate and itself having an inner surface; and an inner circumferential liner of zirconium alloy bonded to the inner surface of the zirconium barrier layer, wherein the inner circumferential liner is less than about 20 micrometers thick. a cladding tube including an outer circumferential substrate having an inner surface, a zirconium barrier layer bonded to the inner surface of the outer circumferential substrate and itself having an inner surface, and an inner circumferential liner of zirconium alloy bonded to the inner surface of the zirconium barrier layer, wherein the inner circumferential liner contains less than about 1.2% tin by weight; nuclear fuel material disposed within said tube; and means for sealing the respective ends of said tube with said nuclear material therein. a lower tie plate for supporting an upstanding matrix of fuel rods and permitting the entry of water moderator; an upper tie plate and permitting the exit of water and generated steam moderator; a plurality of fuel rods, said fuel rods including a cladding tube including an outer circumferential substrate having an inner surface, a zirconium barrier layer bonded to the inner surface of the outer circumferential substrate and itself having an inner surface, and an inner circumferential liner of zirconium alloy bonded to the inner surface of the zirconium barrier layer, wherein the inner circumferential liner comprises less than about 1.2% tin by weight; nuclear fuel material disposed within said zirconium alloy cladding tube; means for sealing the respective ends of said tube with said nuclear material therein one or more spacers disposed within said fuel bundle at varying elevations on said fuel bundle, said spacers surrounding and holding said array of fuel elements in designed center to center spacing; and, means for tying said upper and lower tie plates together. an outer circumferential substrate having an inner surface; a zirconium barrier layer bonded to the inner surface of the outer circumferential substrate and itself having an inner surface; and an inner circumferential liner bonded to the inner surface of the zirconium barrier layer, wherein the inner circumferential liner comprises a zirconium alloy having less than about 0.12% iron by weight. 2. The cladding tube of claim 1 wherein the inner circumferential liner is less than about 30 micrometers thick. 3. The cladding tube of claim 2 wherein the inner circumferential liner is less than about 20 micrometers thick. 4. The cladding tube of claim 3 wherein the inner circumferential liner is between about 10 and 15 micrometers thick. 5. The cladding tube of claim 1 wherein the zirconium barrier layer is between about 50 and 130 micrometers thick. 6. The cladding tube of claim 1 wherein the inner circumferential liner contains less than about 1000 ppm oxygen by weight. 7. The cladding tube of claim 6 wherein the inner circumferential liner contains less than about 600 ppm oxygen by weight. 8. The cladding tube of claim 1 wherein the substrate comprises a zirconium alloy selected from the group consisting of Zircaloy-2, Zircaloy-4, Zirlo, zirconium/2.5% niobium, NSF alloy, Valloy, Excel, and Excellite. 9. The cladding tube of claim 8 wherein the substrate comprises Zircaloy-2. 10. The cladding tube of claim 8 wherein the substrate comprises Zircaloy-4. 11. The cladding tube of claim 1 wherein the zirconium barrier layer is comprised of a material selected from the group consisting of crystal bar zirconium and sponge zirconium. 12. The cladding tube of claim 1 wherein the inner circumferential liner comprises at least about 98% zirconium by weight, between about 0.07 and 0.24% iron by weight, and less than about 1.2% tin by weight. 13. The cladding tube of claim 12 wherein the inner circumferential liner comprises a modified Zircaloy having a low tin content. 14. The cladding tube of claim 12 wherein the inner circumferential liner comprises between about 0.5 and 1.2% tin by weight. 15. The cladding tube of claim 12 wherein the inner circumferential liner comprise about 0.8% tin by weight. 16. The cladding tube of claim 1 wherein the inner circumferential liner comprises at least about 98% zirconium by weight, less than about 0.2% iron by weight, about 1% niobium by weight, and about 1% tin by weight. 17. The cladding tube of claim 1 wherein the inner circumferential liner comprises zirconium, about 0.07 to 0.24% iron and about 0.05 to 0.15% chromium by weight. 18. The cladding tube of claim 17 wherein the inner circumferential liner is comprised of a zirconium alloy having about 0.1% iron by weight and another alloying material selected from the group consisting of about 0.05% chromium by weight, about 0.04% nickel by weight, and a combination of about 0.04% nickel by weight plus about 0.05% chromium by weight. 19. The cladding tube of claim 1 wherein the inner circumferential liner comprises at least about 98% zirconium by weight and between about 0.5 and 2.5 weight percent bismuth. 20. A cladding tube having a cross-section, the cladding tube comprising: 21. The cladding tube of claim 20 wherein the inner circumferential liner is less than about 20 micrometers thick. 22. The cladding tube of claim 21 wherein the inner circumferential liner is less than about 15 micrometers thick. 23. The cladding tube of claim 22 wherein the inner circumferential liner is between about 10 and 15 micrometers thick. 24. The cladding tube of claim 20 wherein the zirconium barrier layer is between about 50 and 130 micrometers thick. 25. The cladding tube of claim 20 wherein the inner circumferential liner contains less than about 800 ppm oxygen by weight. 26. The cladding tube of claim 25 wherein the inner circumferential liner contains less than about 600 ppm oxygen by weight. 27. The cladding tube of claim 20 wherein the substrate comprises a zirconium alloy selected from the group consisting of Zircaloy-2, Zircaloy-4, Zirlo, zirconium/2.5% niobium, NSF alloy, Valloy, Excel, and Excellite. 28. The cladding tube of claim 20 wherein the substrate comprises Zircaloy-2 or Zircaloy-4. 29. The cladding tube of claim 20 wherein the zirconium barrier layer is selected from the group consisting of crystal bar zirconium and sponge zirconium. 30. The cladding tube of claim 20 wherein the inner circumferential liner comprises at least about 98% zirconium by weight, between about 0.07 and 0.24% iron by weight, and less than about 1.1% tin by weight. 31. The cladding tube of claim 30 wherein the inner circumferential liner comprises a modified Zircaloy having a low tin content. 32. The cladding tube of claim 30 wherein the inner circumferential liner comprises between about 0.5 and 1.2% tin by weight. 33. The cladding tube of claim 20 wherein the inner circumferential liner comprises at least about 98% zirconium by weight, less than about 0.2% iron by weight, about 1% niobium by weight, and about 1% tin by weight. 34. The cladding tube of claim 20 wherein the inner circumferential liner comprises zirconium, about 0.07 to 0.24% iron and about 0.05 to 0.15% chromium by weight. 35. A cladding tube having a cross-section, the cladding tube comprising: 36. The cladding tube of claim 35 wherein the inner circumferential liner is less than about 15 micrometers thick. 37. The cladding tube of claim 36 wherein the inner circumferential liner is between about 10 and 15 micrometers thick. 38. The cladding tube of claim 35 wherein the inner circumferential liner comprises at least about 98% zirconium by weight, between about 0.07 and 0.24% iron by weight, and less than about 1.2% tin by weight. 39. The cladding tube of claim 35 wherein the inner circumferential liner comprises a modified Zircaloy-2 having a low tin content. 40. The cladding tube of claim 35 wherein the inner circumferential liner comprises a modified Zircaloy-4 having a low tin content. 41. The cladding tube of claim 35 wherein the inner circumferential liner of zirconium alloy contains less than about 1000 ppm oxygen by weight. 42. The cladding tube of claim 35 wherein the zirconium barrier layer is selected from the group consisting of crystal bar zirconium and sponge zirconium. 43. A fuel element comprising: 44. The fuel element of claim 43 wherein the cladding tube has a defined cross-section and wherein said inner circumferential liner is less than about 20, micrometers thick. 45. The fuel element of claim 43 wherein said inner circumferential liner comprises less than about 1000 ppm oxygen by weight. 46. The fuel element of claim 43 further comprising a pressurized gas within said nuclear fuel element. 47. The fuel element of claim 43 wherein the barrier layer is selected from the group consisting of crystal bar zirconium and sponge zirconium. 48. A nuclear fuel bundle comprising: 49. The nuclear fuel bundle of claim 48 further comprising a channel, said channel surrounding said fuel bundle from the vicinity of said lower tie plate to the vicinity of said upper tie plate to define a flow channel between said tie plates around said fuel elements. 50. A cladding tube having a cross-section, the cladding tube comprising: 51. The composition of claim 50 wherein the inner circumferential liner comprises a modified Zircaloy-2 having a between about 0.02 and 0.1% iron by weight. 52. The composition of claim 50 wherein the inner circumferential liner comprises a modified Zircaloy-4 having a between about 0.02 and 0.12% iron by weight. 53. The cladding tube of claim 50 wherein the inner circumferential liner is less than about 15 micrometers thick. 54. The cladding tube of claim 50 wherein the inner circumferential liner contains less than about 600 ppm oxygen by weight. 55. The cladding tube of claim 50 wherein the substrate comprises a zirconium alloy selected from the group consisting of Zircaloy-2, Zircaloy-4, Zirlo, zirconium/2.5% niobium, NSF alloy, Valloy, Excel, and Excellite. 56. The cladding tube of claim 50 wherein the zirconium barrier layer is comprised of a material selected from the group consisting of crystal bar zirconium and sponge zirconium. 57. The cladding tube of claim 50 wherein the inner circumferential liner comprises a modified Zircaloy. 58. The cladding tube of claim 50 wherein the inner circumferential liner comprises less than about 1.2% tin by weight. |
summary | ||
claims | 1. A method for reducing deposition of charged particulates on a conductive surface defining a wetted portion of a coolant flow passage in a nuclear reactor, comprising the steps of:forming a base dielectric layer by exposing the conductive surface to a first organometallic precursor compound under conditions sufficient to decompose the precursor compound and form a substantially continuous base dielectric layer on the conductive surface, the base dielectric layer consisting essentially of at least one tantalum (Ta) compound; andforming an outer dielectric layer by exposing the base dielectric layer to a second organometallic precursor compound under conditions sufficient to decompose the precursor compound and form a substantially continuous outer dielectric layer on the base dielectric layer, the outer dielectric layer consisting essentially of at least one titanium (Ti) compound. 2. A method for reducing deposition of charged particulates on a conductive surface defining a wetted portion of a coolant flow passage in a nuclear reactor according to claim 1, wherein:forming the base dielectric layer utilizes a chemical vapor deposition (CVD) process with the conductive surface being maintained at a first deposition temperature of between about 400° C. and about 500° C. and a first deposition pressure of no more than about 20 mTorr; andforming the outer dielectric layer utilizes a CVD process with the base dielectric layer being maintained at a second deposition temperature of between about 400° C. and about 500° C. and a second deposition pressure of no more than about 20 mTorr. 3. A method for reducing deposition of charged particulates on a conductive surface defining a wetted portion of a coolant flow passage in a nuclear reactor according to claim 1, wherein:forming the base dielectric layer utilizes deposition process with the conductive surface being maintained at a first deposition temperature of between about 400° C. and about 500° C. and a first deposition pressure of no more than about 20 mTorr; andforming the outer dielectric layer utilizes a CVD process with the base dielectric layer being maintained at a second deposition temperature of between about 400° C. and about 500° C. and a second deposition pressure of no more than about 20 mTorr. 4. A method for reducing deposition of charged particulates on a conductive surface defining a wetted portion of a coolant flow passage in a nuclear reactor according to claim 1, wherein:the base dielectric layer is formed using a method selected from a group consisting of atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced physical vapor deposition (PEPVD), sputtering, plasma spray coating (APS, VPS and LPPS) and high velocity oxy-fuel (HVOF) processes; andthe outer dielectric layer is formed using a method selected from a group consisting of atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced physical vapor deposition (PEPVD), sputtering, electric arc spraying (EAS), plasma spray coating (APS, VPS and LPPS) and high velocity oxy-fuel (HVOF) processes. 5. A method for reducing deposition of charged particulates on a conductive surface defining a wetted portion of a coolant flow passage in a nuclear reactor according to claim 2, wherein:the base dielectric layer consists essentially of Ta2O5 and is formed to a first layer thickness Tb of between about 0.1 and about 2 μm; andthe outer dielectric layer consists essentially of TiO2 and is formed to a second layer thickness To of between about 0.5 μm and about 3 μm. 6. A method for reducing deposition of charged particulates on a conductive surface defining a wetted portion of a flow passage within a Boiling Water Reactor (BWR), comprising the steps of:forming a base dielectric layer by exposing the conductive surface to a first organometallic precursor compound under conditions sufficient to decompose the precursor compound and form a substantially continuous base dielectric layer on the conductive surface, the base dielectric layer consisting essentially of at least one tantalum (Ta) compound; andforming an outer dielectric layer by exposing the base dielectric layer to a second organometallic precursor compound under conditions sufficient to decompose the precursor compound and form a substantially continuous outer dielectric layer on the base dielectric layer, the outer dielectric layer consisting essentially of at least one titanium (Ti) compound. 7. A method for reducing deposition of charged particulates on a conductive surface defining a wetted portion of a flow passage, comprising the steps of:forming a base dielectric layer by exposing the conductive surface to a first organometallic precursor compound under conditions sufficient to decompose the precursor compound and form a substantially continuous base dielectric layer on the conductive surface, the base dielectric layer consisting essentially of at least one tantalum (Ta) compound; andforming an outer dielectric layer by exposing the base dielectric layer to a second organometallic precursor compound under conditions sufficient to decompose the precursor compound and form a substantially continuous outer dielectric layer on the base dielectric layer, the outer dielectric layer consisting essentially of at least one titanium (Ti) compound, andwherein the first organometallic precursor compound includes a first metal; and the second organometallic precursor compound includes a second metal, wherein the first metal and the second metal are different metals. 8. The method for reducing deposition of charged particulates on a conductive surface according to claim 7, wherein:the base dielectric layer consists essentially of a first refractory metal oxide and has a thickness of between about 0.1 and about 2 μm; andthe outer dielectric layer consists essentially of a second refractory metal oxide and has a thickness of between about 0.5 μm and about 3 μm, wherein the first and second refractory metals are different. 9. The method for reducing deposition of charged particulates on a conductive surface according to claim 8, wherein:the base dielectric layer consists essentially of Ta2O5 and has a thickness of between about 0.1 and about 2 μm; andthe outer dielectric layer consists essentially of TiO2 and has a thickness of between about 0.5 μm and about 3 μm. |
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summary | ||
042344484 | claims | 1. A method for treating aqueous solutions and suspensions of radioactive waste containing sodium sulfate, which comprises heating and drying the aqueous solutions and suspensions of radioactive waste in a drier thereby obtaining radioactive waste powders; transfering the powders from the drier to a hopper; measuring a water content of the powders retained in said hopper; when the measured water content satisfies a predetermined condition, transfering the powders from the hopper to a pelletizer; and pelletizing the powders therein; or when the measured water content of the powders fails to satisfy the predetermined condition, introducing a washing solution comprising hot water under pressure to the bottom of the hopper, thereby causing a stirring action between the washing solution and the powders and forming an admixture of an aqueous solution of the powders and an aqueous slurry of the powders; then discharging the washing solution and the radioactive waste powders from the hopper in the form of the admixture of the aqueous solution of the powders and the aqueous slurry of the powders; and thereafter drying the inside of the hopper whereby the hopper is made ready for storage of another batch of radioactive waste powders. 2. A method according to claim 1, wherein hot water at 32.degree. C. or higher is used as the washing solution, when solid matters of the aqueous solutions and suspensions of radioactive waste are comprised mainly of Na.sub.2 SO.sub.4. 3. A method according to claim 2, wherein the hot water is introduced to the hopper at the bottom from a washing tank by a pump, and recycling of the hot water is carried out through the pump, the hopper, the washing tank, and said pump. 4. A method according to claim 2, wherein the hopper is located below said drier and wherein the hot water is introduced up through the hopper to the inside of the drier to wash the hopper and the drier simultaneously, and then the resulting washing solution and powders are discharged therefrom. 5. A method according to claim 1, wherein the washing solution is introduced to the hopper at the bottom from a washing tank by a pump, and recycling of the washing solution during a washing operation is carried out through the pump, the hopper, the washing tank, and said pump. 6. A method according to claim 1, wherein the hopper is located below said drier and wherein the washing solution is introduced up through the hopper to the inside of the drier to wash the hopper and the drier simultaneously, and then the resulting washing solution and powders are discharged therefrom. 7. A method according to claim 6, wherein the washing solution is introduced into the hopper and drier and allowed to partially fill the hopper during dissolution and washing to form said admixture and thereafter the resulting admixture is discharged from the hopper. 8. A method according to claim 1 further comprising the step of introducing a gas into the bottom of the hopper together with said washing solution to promote dissolution and washing of the powders within said hopper by increasing the stirring action. 9. A method according to claim 8 wherein the gas introduced into the bottom of the hopper is compressed air. 10. A method according to claim 1 further comprising transfering the washing solution and the powders discharged from the hopper to the washing sump and thereafter recycling the resulting washing solution containing the powders to an inlet of the drier for retreatment therein said predetermined condition being satisfied when the powders have a water content below a definite limit content of a few percent. 11. A method according to claim 1 wherein drying the inside of the hopper is effected by introducing a dry gas into said hopper. 12. A method according to claim 11 wherein the dry gas introduced into the hopper is compressed air. 13. A method according to claim 1 wherein the washing solution and the radioactive powders are discharged from the top of said hopper and then passed to a washing tank and the resultant solution is recycled to the hopper for a predetermined period of time to complete the washing operation and thereafter the final resulting washing solution is discharged to a washing sump. 14. A method according to claim 1 wherein said radioactive waste is comprised mainly of Na.sub.2 SO.sub.4 and said washing solution is hot water at a temperature of at least 60.degree. C. whereby said powders are converted into a slurry state without the formation of crystals of Na.sub.2 SO.sub.4. 15. An apparatus for treating aqueous solutions and suspensions of radioactive waste which comprises a drier for evaporating and drying solutions and suspensions of radioactive waste to provide radioactive waste powders, a closed hopper connected to said dryer for receiving the powders therefrom and for storing a batch of powders therein, a pelletizer means for pelletizing the powders contained within said hopper, said pelletizer means being located downstream of said hopper and connected to said hopper via conduit means, means for measuring a water content of the batch of powders to determine whether the water content of the powders within the hopper satisfies a predetermined condition, means for transfering the powders from the hopper to said pelletizer means via said conduit means when the powders satisfy said predetermined condition, means for supplying a washing solution under pressure into the bottom of said hopper when the measured water content of the powders fails to satisfy said predetermined condition thereby causing a stirring action between the washing solution and the powders and forming an admixture of an aqueous solution of the powders and an aqueous slurry of the powders within said hopper, means for discharging the admixture containing the washing solution and the powders from the hopper, and means for introducing a drying gas into the inside of the hopper after discharge of the admixture containing the washing solution and said powders, whereby the inside of the hopper is dried and made ready for the storage of another batch of dried radioactive waste powders. 16. An apparatus according to claim 15 wherein said means for discharging the washing solution and the powder from said hopper is connected to a washing sump for receiving said washing solution and said powders and means for recycling the washing solution and powders to an inlet of the drier for retreatment therein. |
claims | 1. Apparatus for use with an X-ray system comprising:an X-ray anti-scatter grid comprising:at least a first layer of elongate radiopaque septa arranged such that longitudinal axes of each the septa belonging to the first layer are disposed along a first direction, in parallel to each other, spaces between the septa of the layer being filled with air;a rigid frame configured to support the elongate septa;two or more slotted plates coupled to the rigid frame, each of the slotted plates defining a plurality of slots, each of the septa passing through a respective pair of slots defined by a pair of the slotted plates disposed on opposite sides of the frame from each other, such that an orientation of each of the septa with respect to the frame is determined by an orientation of the corresponding pair of slots with respect to the frame; anda pulling mechanism disposed upon the frame, the pulling mechanism being configured to permanently apply tension to the plurality of septa that are arranged in parallel to each other, such that tension is applied to the plurality of septa by the pulling mechanism during use of the X-ray anti-scatter grid; anda controller configured to:receive an input indicating a focal length of the X-ray system, andin response thereto, to adjust orientations of the septa within the first layer. 2. The apparatus according to claim 1, wherein the controller is configured to adjust orientations of the septa within the first layer such that the septa are parallel to a primary X-ray beam generated by the X-ray system. 3. The apparatus according to claim 1, wherein the X-ray system includes an X-ray system processor, and wherein the controller is configured to automatically receive the input indicating the focal length of the X-ray system from the X-ray system processor. 4. The apparatus according to claim 1, wherein the controller is configured to manually receive the input indicating the focal length of the X-ray system. 5. The apparatus according to claim 1, wherein the controller is configured to adjust orientations of the septa within the first layer by adjusting orientations of the slotted plates with respect to the frame. 6. The apparatus according to claim 5, further comprising one or more stepper motors, wherein the controller is configured to adjust orientations of the septa within the first layer by adjusting orientations of the slotted plates with respect to the frame using the stepper motor. 7. Apparatus for use with an X-ray system comprising:an X-ray anti-scatter grid comprising:at least a first layer of elongate radiopaque septa arranged such that longitudinal axes of each the septa belonging to the first layer are disposed along a first direction, in parallel to each other, spaces between the septa of the layer being filled with air;a rigid frame configured to support the elongate septa;two or more slotted plates coupled to the rigid frame, each of the slotted plates defining a plurality of slots, each of the septa passing through a respective pair of slots defined by a pair of the slotted plates disposed on opposite sides of the frame from each other, such that an orientation of each of the septa with respect to the frame is determined by an orientation of the corresponding pair of slots with respect to the frame; anda pulling mechanism disposed upon the frame, the pulling mechanism being configured to permanently apply tension to the plurality of septa that are arranged in parallel to each other, such that tension is applied to the plurality of septa by the pulling mechanism during use of the X-ray anti-scatter grid,wherein each of the septa comprises a foil core that is coated with a metal that has an atomic number that is greater than an atomic number of the foil core. 8. The apparatus according to claim 7, wherein the rigid frame and the elongate septa are not formed as an integral unit. 9. The apparatus according to claim 7, wherein the rigid frame and the elongate septa are not formed via a three-dimensional printing process. 10. The apparatus according to claim 7, wherein the X-ray anti-scatter grid comprises a single layer of elongate radiopaque septa. 11. The apparatus according to claim 7, wherein the X-ray anti-scatter grid further comprises a second layer of elongate radiopaque septa, arranged such that longitudinal axes of each the septa belonging to the second layer are disposed along a second direction, in parallel to each other, the second direction being perpendicular to the first direction, such that, when viewed along a third direction that is perpendicular to the first and second directions, the first and second layers of radiopaque septa define a grid. 12. The apparatus according to claim 7, wherein a thickness of each of the septa is between 0.04 mm and 0.1 mm. 13. The apparatus according to claim 7, wherein a height of each of the septa is between 10 mm and 20 mm. 14. The apparatus according to claim 7, wherein, within the layer of septa, a distance between each of the septa and adjacent septa is between 0.5 mm and 1.5 mm. 15. The apparatus according to claim 7, wherein the foil core comprises a copper foil core. 16. The apparatus according to claim 7, wherein the metal coating comprises tin. 17. The apparatus according to claim 7, wherein each of the septa comprises phosphor bronze. 18. A method comprising:driving an X-ray system to direct X-rays from an X-ray source to an X-ray detector; anddirecting the X-rays via an X-ray anti-scatter grid that includes:at least a first layer of elongate radiopaque septa arranged such that longitudinal axes of each the septa belonging to the first layer are disposed along a first direction, in parallel to each other, spaces between the septa of the layer being filled with air;a rigid frame configured to support the elongate septa;two or more slotted plates coupled to the rigid frame, each of the slotted plates defining a plurality of slots, each of the septa passing through a respective pair of slots defined by a pair of the slotted plates disposed on opposite sides of the frame from each other, such that an orientation of each of the septa with respect to the frame is determined by an orientation of the corresponding pair of slots with respect to the frame, anda pulling mechanism disposed upon the frame, the pulling mechanism being configured to permanently apply tension to the plurality of septa that are arranged in parallel to each other, such that tension is applied to the plurality of septa by the pulling mechanism while the X-ray system directs X-rays from an X-ray source to an X-ray detector; andin response to an indication of a focal length of the X-ray system, causing orientations of the septa within the first layer to be adjusted. 19. The method according to claim 18, wherein causing orientations of the septa within the first layer to be adjusted comprises causing the orientations of the septa within the first layer to be parallel to a primary X-ray beam generated by the X-ray system. 20. The method according to claim 19, wherein causing orientations of the septa within the first layer to be adjusted comprises automatically causing orientations of the septa within the first layer to be adjusted in response to an input indicating the focal length of the X-ray system from the X-ray system processor. 21. The method according to claim 19, wherein causing orientations of the septa within the first layer to be adjusted comprises causing orientations of the septa within the first layer to be adjusted in response to a manual input indicating the focal length of the X-ray system. 22. The method according to claim 19, wherein causing orientations of the septa within the first layer to be adjusted comprises adjusting orientations of the slotted plates with respect to the frame. 23. The method according to claim 22, wherein causing orientations of the septa within the first layer to be adjusted comprises adjusting orientations of the slotted plates with respect to the frame using a stepper motor. 24. A method comprising:driving an X-ray system to direct X-rays from an X-ray source to an X-ray detector; anddirecting the X-rays via an X-ray anti-scatter grid that includes:at least a first layer of elongate radiopaque septa arranged such that longitudinal axes of each the septa belonging to the first layer are disposed along a first direction, in parallel to each other, spaces between the septa of the layer being filled with air;a rigid frame configured to support the elongate septa;two or more slotted plates coupled to the rigid frame, each of the slotted plates defining a plurality of slots, each of the septa passing through a respective pair of slots defined by a pair of the slotted plates disposed on opposite sides of the frame from each other, such that an orientation of each of the septa with respect to the frame is determined by an orientation of the corresponding pair of slots with respect to the frame, anda pulling mechanism disposed upon the frame, the pulling mechanism being configured to permanently apply tension to the plurality of septa that are arranged in parallel to each other, such that tension is applied to the plurality of septa by the pulling mechanism while the X-ray system directs X-rays from an X-ray source to an X-ray detector,wherein directing the X-rays via the X-ray anti-scatter grid comprises directing the X-rays via an X-ray anti-scatter grid in which each of the septa comprises a foil core that is coated with a metal that has an atomic number that is greater than an atomic number of the foil core. 25. The method according to claim 24, wherein directing the X-rays via the X-ray anti-scatter grid comprises directing the X-rays via an X-ray anti-scatter grid that includes a single layer of elongate radiopaque septa. 26. The method according to claim 24, wherein directing the X-rays via the X-ray anti-scatter grid comprises directing the X-rays via an X-ray anti-scatter grid that further includes a second layer of elongate radiopaque septa, arranged such that longitudinal axes of each the septa belonging to the second layer are disposed along a second direction, in parallel to each other, the second direction being perpendicular to the first direction, such that, when viewed along a third direction that is perpendicular to the first and second directions, the first and second layers of radiopaque septa define a grid. 27. The method according to claim 24, wherein directing the X-rays via the X-ray anti-scatter grid comprises directing the X-rays via an X-ray anti-scatter grid in which a thickness of each of the septa is between 0.04 mm and 0.1 mm. 28. The method according to claim 24, wherein directing the X-rays via the X-ray anti-scatter grid comprises directing the X-rays via an X-ray anti-scatter grid in which a height of each of the septa is between 10 mm and 20 mm. 29. The method according to claim 24, wherein directing the X-rays via the X-ray anti-scatter grid comprises directing the X-rays via an X-ray anti-scatter grid in which, within the layer of septa, a distance between each of the septa and adjacent septa is between 0.5 mm and 1.5 mm. 30. The method according to claim 24, wherein each of the septa comprises phosphor bronze. 31. The method according to claim 24, wherein the metal coating of each of the septa comprises tin. |
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description | This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. JP2006-128199 filed May 2, 2006, the entire content of which is hereby incorporated by reference. The invention relates to a semiconductor mask correcting device and a semiconductor mask correcting method of correcting a defective portion of a photo mask, which is used in the process of fabricating a semiconductor device, into a non-defective photo mask. Since a photo mask used in the process of fabricating a semiconductor device is an original form of a pattern, an existence of a defective portion is necessarily inspected and the defective portion is appropriately corrected as needed, after a mask pattern is drawn on a mask substrate. In a fabrication method of a usual photo mask, first, design data of the mask pattern is designed by using a computer, and then the designed data is transformed into drawing data for a drawing device. Next, a drawing of the mask pattern is performed on a mask substrate by the drawing device on the basis of the drawing data. Due to this, the photo mask a mask pattern of which is drawn on the mask substrate can be made. Additionally, after making the photo mask, it is possible to check an existence of a defect of the photo mask or a location of the existence of that by using a defect inspecting device, and when the defect exists, a semiconductor mask correcting device performs the defect correction before transferring an image of the mask to a wafer. As for the defects of the mask pattern, there are examples such as an extrusion which is projected as an extra protrusion from a desired pattern, and an intrusion which is a concave portion such as an empty on the desired pattern. The mask correction device specifies a location by finding the defective portions, and appropriately corrects them. In methods of the correction, for example, when the protrusion is found, the protrusion portion is corrected by a focused ion beam to be cut off (i.e. an etching process). Additionally, when the concave is found, the concave portion is corrected by gas assist method so that a predetermined material is deposited therein (i.e. a deposition process). In addition, as for a method of inspecting the mask pattern, there are usually two ways available. That is, systems of a die to die and a die to database are available. The die to die system is a method which is used when the same mask pattern of at least two or more is drawn on the mask substrate, and finds the defective portion from differences between the patterns by matching them to each other. The die to die system has advantages that an inspection time is short and comparatively performed in a simple way, while the system does not cope with the defective portion occurring in the same way on all patterns and the case of drawing only one pattern on the mask substrate. Particularly, a pattern shape which is subjected to the correction becomes a fine size and a complicated shape in company with a decrease in size of a semiconductor device, recently. Therefore, it is difficult to compare the pattern shape with an original design of that. That's reason why a die to database system is required more and more instead of the die to die system. The die to database system is a method comparing a mask image acquired by scanning a mask pattern which is actually drawn on the mask substrate with drawing data stored as CAD data, by using a pattern matching. Using this method, an actual pattern and a designed pattern can be compared by being directly matched (piled up) to each other, and thus the defective portion such as the protrusion or the concave portion is detected in high accuracy. Thanks to this, the die to database system will be a mainstream as an inspection method from now on. Recently, accompanied with a decrease in size of the semiconductor circuit, an optical proximity effect correction (i.e. OPC) which is one of the kinds of a resolution enhancement technology (i.e. RET) such as phase shift mask technology is just applied in the semiconductor mask fields. That is a technology using a mask for improving a transfer characteristic by controlling a phase and a transmittance of light, and OPC patterns such as a serif, a jog, and a hammer head are added on the mask pattern. In this way, even if the mask pattern is a fine pattern, it is possible to obtain a desired transfer image by using exposure. Particularly, the transfer image transferred by the mask pattern is mostly used in a semiconductor circuit. Hence, such a method is also employed to obtain a high-accuracy semiconductor circuit. Additionally, in addition to the OPC pattern recently, a method adding an assist pattern which is an application of the OPC pattern is contrived to expose an edge of the mask pattern more accurately (see, for example, Benjamin G. Eynon, Jr.: “Photomask Fabrication Technology”, McGraw-Hill ELECTRONIC ENGINEERING, 2005, Chapter 7: Resolution Enhancement Techniques, P457-P467). The assist pattern which is occasionally called a different name as SRAF (i.e. Sub Resolution Assist Feature) is mostly arranged to surround a vicinity of the main pattern to become a circuit pattern. The assist pattern has a characteristic that it is formed excessively thinner than the main pattern, and the pattern itself does not resolve during exposure, but when the main pattern around which the assist pattern is disposed is exposed, highly accurate transfer is enabled by solving fluctuation of the edges of the main pattern. That is, the assist pattern functions as auxiliary of the main pattern. As mentioned above, to fabricate the fine semiconductor circuit in high accuracy, a method using a mask pattern which combines the assist pattern with the main pattern is just employed recently. The assist pattern is disposed in accordance with a shape of the main pattern, and thus design data of the main pattern is designed first, then the assist pattern is inserted by being designed in accordance with the main pattern. Next, the pattern designs of the main pattern and the assist pattern are employed as final circuit diagram data, and then the final circuit diagram data is transformed into the mask data which is drawing data. The photo mask is fabricated by drawing on the mask substrate in accordance with the mask data. After making the photo mask, the photo mask and the mask data is compared by the die to database system which is directly matched to each other, and the correction is appropriately performed along with the inspection of the defective portion such as the protrusion and the concave portion. However, there are the following problems that still remain in the assist pattern mentioned above. First, the final circuit diagram data adding the assist pattern to the main pattern transforms into the mask data which is the drawing data through a process usually called a fracturing. Because of the reason, all pattern data of the final circuit diagram data is minutely partitioned in the form of a trapezoid and a rectangle. In particular, as shown in FIG. 9, a recent main pattern MP is formed in a complicate shape by adding the OPC pattern thereto as mentioned above. Therefore, through the fracturing process, the main pattern on data is recognized as an aggregate of a plurality of the trapezoid or the rectangular shape partitioned as shown in FIG. 10. On the contrary, as shown in FIG. 9, the assist pattern AP is arranged around the main pattern MP in a comparatively thin and rectangular shape with a certain width, but it has a simple shape compared with the main pattern MP, and thus the assist pattern is recognized as just own shape itself as shown in FIG. 10 after the processing. By the way, since the main pattern MP is recognized as an aggregate of shapes such as a rectangle, the main pattern can not be distinguished from the assist pattern AP on data. That is, as shown in FIG. 10, a part of figure mp forming the main pattern MP takes the same shape by comparison with the assist pattern AP, so there is a concern about an error recognizing the part of figure mp as the assist pattern AP. Accordingly, in a step of mask data, the main pattern MP and the assist pattern AP can not be clearly recognized to be distinguished between them. Additionally, the mask data is stored into a mask data file in a partitioned state. Accordingly, when the die to database system is attempted to inspect the photo mask after drawing on a substrate in actual situation, it is difficult to match the mask data with a photo mask image in high accuracy, and thus the inspection of the defective portion can not be performed. Above all, since, as for the main pattern of the photo mask, the transfer image becomes semiconductor circuit when exposure is performed, it is necessary to match with the main pattern MP of the mask data in high measurement accuracy and location accuracy to inspect the defective portion, and properly correct by specifying the defective portion. However, since the main pattern MP can not be distinguished from the assist pattern AP on the mask data as mentioned above, it is not possible to inspect the main pattern which is required after the drawing. In addition, even if it is possible to distinguish the main pattern MP of the mask data from the assist pattern AP, it is difficult to match the main pattern in high accuracy in an actual situation. In detail, since the assist pattern AP stored as the mask data is mostly designed as a fine line shape different with the main pattern MP (to prevent resolving in the process of exposure), it is easily affected by a distortion during drawing on the mask substrate. Therefore, the assist pattern drawn in actual situation becomes distorted shape, and mostly, does not necessarily match with the assist pattern AP of the mask data. However, the assist pattern is not resolved even though the exposure is performed, so it is allowed even if there are some defective portions or errors. Accordingly, there is commonly no correction for the drawn assist pattern. That is, the correction of the photo mask is commonly performed for only the main pattern. Because of that, when the photo mask image is matched with the mask data, it is required to inspect the defective portion by matching between locations of both main patterns only in high accuracy. However, when the photo mask image and the mask data is subjected to the pattern matching, the high distorted assist pattern is formed on the photo mask as mentioned above, whereupon it adversely affects matching of the main pattern. For example, it is attempted to perform as the high distorted assist pattern of the photo mask is compulsory matched with the assist pattern AP of mask data, or the high distorted assist pattern of the photo mask is compulsory matched with the main pattern MP of the mask data since it is failed to correctly recognize the assist pattern. As mentioned above, the assist pattern AP of the photo mask is one of the noise factors in the process of matching, whereupon an accuracy of matching decreases. Accordingly, the matching of the main pattern can not be performed in high accuracy, and it is not possible to exactly perform the inspection and the correction on the defective portion. In is an object of the invention which is contrived in consideration of the situations mentioned above to provide a semiconductor mask correcting device and a semiconductor mask correcting method capable of performing the pattern matching process which matches the photo mask having the assist pattern with the mask data in high accuracy by using a die to database system, and fabricating the photo mask with high quality by performing the mask correction in high accuracy. To solve the problems, the invention provides units which will be described below. According to the invention, a semiconductor mask correcting device for inspecting a defective portion of a photo mask, which has a mask substrate and a mask pattern drawn on the mask substrate on the basis of mask data in which a main pattern and an assist pattern are previously stored as drawing data, and correcting the defective portion, the device includes a stage on which the photo mask is placed to be movable in parallel to the surface of the mask substrate, an image acquiring unit acquiring a mask image of the mask pattern, an extraction unit extracting only the main pattern from the mask data, an inspection unit matching and comparing the extracted main pattern with a drawn main pattern which is obtained from the mask image, along with inspecting whether the defective portion exists in the drawn main pattern in accordance with differences between both main patterns, and specifying the location of the defective portion, and a correction unit correcting the defective portion specified by the inspection unit by using a focused ion beam. In the invention, the extraction unit includes a recognition section recognizing the main pattern and the assist pattern as figures surrounded by only an outline, respectively, a specification section specifying a figure, which has a predetermined space from the nearest figure and of which at least a width and a length satisfy predetermined values, among the recognized figures as the assist pattern, and a main pattern extracting section extracting as the main pattern the figures other than the figure specified as the assist pattern. According to the invention, a semiconductor mask correcting method of inspecting a defective portion of a photo mask, which has a mask substrate and a mask pattern drawn on the mask substrate on the basis of mask data in which a main pattern and an assist pattern are previously stored as drawing data, and correcting the defective portion, the method includes an image acquiring process of acquiring a mask image of the mask pattern drawn on the mask substrate, a recognition process of recognizing the main pattern and the assist pattern stored in the mask data as figures surrounded by only an outline, respectively, a specification process of specifying a figure, which has a predetermined space from the nearest figure and of which at least a width and a length satisfy predetermined values, among the recognized figures as the assist pattern, after the recognition process, an extraction process of extracting as the main pattern the figures other than the figure specified as the assist pattern, after the specification process, an inspection process of matching and comparing the extracted main pattern with a drawn main pattern which is obtained from the mask image, along with inspecting whether the defective portion exists in the drawn main pattern in accordance with differences between both main patterns, and specifying the location of the defective portion, and a correction process of correcting the specified defective portion by using a focused ion beam after the inspection process. In the semiconductor mask correcting device and the method of semiconductor correction according to the invention, the photo mask on which the mask pattern including the main pattern and the assist pattern on the mask substrate is drawn is placed on the stage at the beginning. At this time, the mask pattern is drawn by a drawing device on the basis of the mask data. The mask data is exchanged for data of a drawing application by performing the fracturing process on final circuit diagram data adding the assist pattern to the main pattern. So, the pattern data stored in the mask data is stored as an aggregate of figures in a trapezoid, a rectangular shape or the like which is divided by plurality on data. After the photo mask is placed on the stage, an image acquiring process is performed which acquires a mask image, that is, an image of the mask pattern drawn on the mask substrate by the image acquiring unit. During this time, by properly moving the stage, it is possible to scan on the mask substrate and surely acquire the mask image. On the other hand, the extraction unit distinguishes and extracts only the main pattern from the main pattern and the assist pattern stored in the mask data. In detail, first, the recognition section performs a recognition process which recognizes the main pattern and the assist pattern, the patterns being stored as an aggregate of figures which is divided by plurality on data, as figures surrounded by only an outline, respectively. Due to the recognition process, the main pattern stored as an aggregate of figures which is divided by plurality on data by the fracturing process becomes the condition of being reconnected to each other, thereby being recovered in the condition of final circuit diagram data which is originally designed. Specifically, even if the main pattern is designed for any complicated shape by an addition of an OPC pattern, the effect of the fracturing process is cancelled by the above-described outline and it is possible to recover as the condition of a designing step. The assist pattern is also recovered as the state of the final circuit diagram data, but the pattern is stored in the mask data as a figure which is not affected by the fracturing process since it is originally a simple shape. Hence, the recovered figure is the same as the figure stored in the mask data. Continuously, the specification section performs a specification process specifying a figure which is disposed in a satisfied state of a predetermined space apart from the nearest figure as the assist pattern, when at least a width and a length of each figure recognized as an independent figure by the recognition section satisfy a predetermined value. Usually, the assist pattern has a size which is not resolved during exposure and disposed on vicinity of the main pattern. Therefore, the figure satisfying aforementioned qualifications is defined as the assist pattern. Subsequently, the main pattern extracting section specifies as the main pattern a figure other than the figure which is specified as assist pattern in the process of the specification among the figures recognized in the process of the recognition process, and performs the extraction process which extracts only the main pattern. As mentioned above, the extraction unit can exactly extract the data of only the main pattern from the mask data which is processed by the fracturing. The inspection unit performs matching the main pattern which is extracted in the extraction unit with a mask image which is obtained by the image acquiring process mentioned above. Specifically, the unit performs matching the extracted main pattern with a main pattern which is obtained from the mask image after a drawing. Additionally, the inspection unit performs the inspection process inspecting whether the defective portion (such as the extrusion or the intrusion) exists or not on the drawn main pattern, from the differences between both of them, in company with comparing between both patterns. Simultaneously, if the defective potion exists, the inspection unit specifies the location. Especially, since only the main pattern is exactly extracted by distinguishing the assist pattern with the main pattern from the mask data processed by the fracturing, the assist pattern which is the known noise factor can be removed from original reference data of the die to database system. Accordingly, it is possible to match the main patterns only which should be originally corrected. As a result, it is possible to match locations of the patterns in high accuracy by using the die to database system and more accurately perform an inspecting on the defective portion and specifying locations. Additionally, the correction unit performs the correcting process which corrects the specified defective portion by using FIB (i.e. focused ion beam). On this occasion, the existence of the defective portion is exactly inspected as mentioned above, and the position of the defective portion is exactly specified, thereby being capable of performing the mask correction in high accuracy. As the result, it is possible to fabricate the photo mask with high quality having the assist pattern. By using the photo mask fabricated as mentioned above, it is also possible to accurately fabricate a microscopic semiconductor circuit and the like where fluctuation of edges and the like is suppressed. As mentioned above, due to the semiconductor mask correcting device and the semiconductor mask correcting method according to the invention, it is possible to perform the pattern matching process which matches the photo mask having the assist pattern with the mask data in high accuracy by using die to database system, and fabricate the photo mask with high quality by performing the mask correction in high accuracy. Additionally, as for the semiconductor mask correcting device of the invention, in the semiconductor mask correcting device according to the invention, the correction unit corrects the defective portion by using an etching process or a formation of deposition film depending on kinds of the defective portion. As for the semiconductor mask correcting method of the invention, in the semiconductor mask correcting method according to the invention, the step of correcting corrects the defective portion by using an etching process or a formation of deposition film depending on kinds of the defective portion. In the semiconductor mask correcting device and the semiconductor mask correcting method according to the invention, when the correcting process is performed, the defective portion is corrected by the etching process using a FIB irradiation, in the case that the defective portion is a protrusion. Contrary, in the case that the defective portion is an intrusion, a deposition film is formed by supplying a gas which is a raw material of the deposition film and irradiating the FIB, thereby correcting the defective portion. Therefore, the correction unit can perform a reliable mask correction, since the etching process or the formation of deposition film is suitably used depending on the kinds of the defective portion. Thanks to a semiconductor mask correcting device and a semiconductor mask correcting method according to the invention, it is possible to perform a pattern matching process which matches a photo mask having an assist pattern with mask data in high accuracy by using a die to database system, and fabricate the photo mask with high quality by performing a mask correction in high accuracy. Hereinafter, an embodiment of a semiconductor mask correcting device and a semiconductor mask correcting method according to the invention will be described with reference to FIGS. 1 to 8. A semiconductor mask correcting device 1 of the embodiment, as shown in FIG. 1, inspects a defective portion of a photo mask 3 which has a mask substrate 2 and a mask pattern P drawn on the mask substrate 2 by a drawing device or the like, and corrects the defective portion. The mask pattern P includes the main pattern MP1 and the assist pattern AP1 which are drawn on the basis of the mask data D1 mentioned later which is previously stored as the drawing data. As shown in FIG. 2, the semiconductor mask correcting device 1 includes a XY stage 10 (stage) on which the photo mask 3 is placed to be movable in parallel direction (XY direction) to the surface of the mask substrate 2, an image acquiring unit 11 acquiring a mask image of the mask pattern P drawn on the mask substrate 2, an extraction unit 12 extracting data (Hereinafter, the data is referred to as a main pattern MP0. Likewise, data of the assist pattern AP1 is referred to as an assist pattern AP0.) of the main pattern MP1 only from pattern data stored in the mask data D1, an inspection unit 13 comparing the extracted main pattern MP0 with a main pattern MP1 which is obtained from the mask image after a drawing by matching (being piled up) to each other, and specifying the location along with inspecting whether the defective portion exists on the main pattern MP1 after the drawing in accordance with differences between both of them and specifying the location of the defective portion, and a correction unit 14 correcting the defective portion specified by the inspection unit 13 by using FIB (i.e. a focused ion beam). As shown in FIG. 2, an upper side of the XY stage 10 includes an ionizer 15 generating ion, and an ion optical system 16 such as an object lens used in FIB by narrowly focusing the generated ion so as to form an image on the surface of the mask substrate 2. Accordingly, the FIB is set to be irradiated toward the surface of the mask substrate 2. Scan electrodes 17 including an X electrode and a Y electrode are disposed between the ionizer 15 and the ion optical system 16, and an irradiation spot of the FIB can be scanned in the predetermined range of an XY plane. Additionally, upon the mask substrate 2, a gas gun 18 supplying gas G1 for an etching to the vicinity of the surface of the mask substrate 2 on which the FIB is irradiated, a gas gun 19 supplying raw gas (for example, phenanthrene and the like) G2 which forms a deposition film, and a secondary electron detector 20 detecting an intensity of a secondary electron which is generated by the irradiation of the FIB are disposed. A planar distribution of the secondary electron intensity corresponds to the mask pattern P which is drawn on the mask substrate 2. The electron intensity detected by the secondary electron detector 20 is transformed into digital data by an A/D transforming circuit 21 and inputted to a PC (i.e. a personal computer) 22. Due to this, it is possible to obtain the mask image of the mask pattern P which is drawn on the mask substrate 2. Consequently, the image acquiring unit 11 includes the secondary electron detector 20, the A/D transforming circuit 21 and the PC 22. In the PC 22, the display unit 23 displaying the acquired mask image is connected to the scan circuit unit 24 controlling the scan electrodes 17 and determining the irradiation range of the FIB, by receiving an order from the PC 22. As shown in the FIG. 3, the PC 22 is equipped with a control unit 30 including CPU or various kinds of memories and performing a transfer or a temporal store of data along with integrally controlling all components of the PC, an image forming unit 31 forming the mask image on the basis of the secondary electron intensity transformed into digital data by the A/D transforming circuit 21, an image output unit 32 making the mask image formed by the image forming unit 31 display on the display unit 23, and the inspection unit 13 and the correction unit 14. The inspection unit 13 inputs the extracted main pattern MP0 from a memory 38 which is mentioned later of the extraction unit 12 in company with the main pattern MP1 after the drawing from the mask image formed by the image forming unit 31. The inspection unit 13 inspects whether the defective portion exists and notifies the correction unit 14 of the location and a kind (for example, the extrusion, the intrusion or the like) of the defective portion if the defects exist. The correction unit 14 suitably controls the scan circuit unit 24 or the gas guns 18 and 19 on the basis of information sent from the inspection unit 13, and the unit corrects the defective portion of the mask by performing the etching process or the deposition process which forms the deposition film. The extraction unit 12 includes a recognition section 35 reading the main pattern MP0 and the assist pattern AP0 from the mask data D1 which is previously stored as the drawing data and recognizing them as figures surrounded by only an outline, respectively, a specification section 36 specifying a figure which is disposed in a satisfied state of a predetermined space S apart from the nearest figure as the assist pattern AP0 when at least a width W and a length H of recognized figures satisfy a predetermined value, a main pattern extracting section 37 extracting as the main pattern MP0 a figure other than the figure which is specified as assist pattern AP0, and the memory 38 storing the extracted main pattern MP0. Regarding to the extracting method, it will be described in detail, later. Next, it will be described about an inspection of the photo mask 3 performed by using the semiconductor mask correcting device 1 mentioned above, and the case of the mask correction for the defective portion. As illustrated in FIG. 3, the mask data D1 is transformed for the drawing through the fracturing process from the final circuit diagram data D2 adding the assist pattern AP0 to the main pattern MP0. As a result, the pattern data of the main pattern MP0 stored in the mask data D1 is stored as an aggregate of a trapezoid shape, a rectangular shape or the like divided by a plurality of that on data, as shown in FIG. 4. However, since the assist pattern AP0 of the pattern data is formed as a simple shape, the pattern is stored in the mask data as a figure which is not affected by the fracturing process. The correction method of the semiconductor mask in the embodiment includes an image acquiring process acquiring a mask image of the mask pattern P drawn on the mask substrate 2, a recognition process recognizing the main pattern MP0 and the assist pattern AP0 stored in the mask data D1 as figures surrounded by only an outline, respectively, a specification process specifying a figure which is disposed in a satisfied state of a predetermined space S apart from the nearest figure as the assist pattern AP0 when at least a width W and a length H of each recognized figure satisfy a predetermined value, after the recognition process, an extraction process extracting a figure other than the figure which is specified as the assist pattern AP0 as the main pattern MP0, after the specification process, an inspection process comparing the extracted main pattern MP0 with a main pattern MP1 which is obtained from the mask image after a drawing by matching to each other, and specifying the location along with inspecting whether the defective portion exists on the main pattern MP1 after the drawing in accordance with differences between both of them (MP0 and MP1), and a correction process correcting the specified defective portion by using FIB after the inspection process. Hereinafter, it will be described about these processes in detail. First of all, the photo mask 3 is placed on the XY stage 10 as shown in FIG. 1, and the mask pattern P which is provided with the main pattern MP1 and the assist pattern AP1 on the mask substrate 2 is drawn thereon. The image acquiring process is performed which acquires a mask image, that is, an image of the mask pattern P drawn on the mask substrate 2 by the image acquiring unit 11. Specifically, the FIB is irradiated toward the surface of the mask substrate 2 which is placed on the XY stage 10. By irradiating the FIB, the secondary electron intensity of which is corresponded to a distribution on a plane of the mask pattern P is radiated from the surface of the mask substrate 2. The secondary electron detector 20 performs an intensity detection of the radiated secondary electron. At that time, the XY stage 10 is suitably moved to scan on the mask substrate 2, and a detection of the secondary electron is performed. The detected secondary electron intensity is transformed into digital data by the A/D transforming circuit 21, and then the data is inputted to the image forming unit 31 of PC 22. The image forming unit 31 forms the mask image on the basis of the inputted secondary electron intensity. As a result, it is possible to obtain the mask image. The formed mask image is displayed on the display unit 23 by the image output unit 32 and sent to the inspection unit 13. On the other hand, the extraction unit 12 extracts the main pattern MP0 only of the main pattern MP0 and assist pattern AP0 which is previously stored in the mask data D1 by distinguishing the assist pattern AP0 from the main pattern. In detail, first, the recognition section 35 reads the data of the main pattern MP0 and assist pattern AP0 which is stored as an aggregate of figures divided by plurality on data, from the mask data D1, as shown in FIG. 4. And then, it performs a recognition process which recognizes the main pattern and the assist pattern as figures surrounded by only an outline, respectively, as shown in FIG. 5. Due to the recognition process, the main pattern MP0 stored as an aggregate of figures which is divided by plurality on data by the fracturing process becomes the condition of being reconnected to each other, thereby being recovered in the condition of final circuit diagram data D2 which is originally designed. Specifically, even if the main pattern MP0 is designed for any complicated shape by an addition of an OPC pattern, the effect of the fracturing process is cancelled by the above-described outline and it is possible to recover as the condition of a designing step. The assist pattern AP0 is also recovered as the state of the final circuit diagram data D2, but the pattern is stored in the mask data as a figure which is not affected by the fracturing process since it is originally a simple shape, as mentioned above. Therefore, the recovered figure is the same as the figure stored in the mask data D1. Continuously, as shown in FIG. 6, the specification section 36 numbers a figure recognized as an independent figure by the recognition section 35 for identification (FIG. 6 is illustrated by putting an identification number in brackets). Due to this, next processes can be recognized by the identification number, whereby dealing with the processes becomes easy. After the numbering, the specification section 36 performs a specification process specifying a figure which is disposed in a satisfied state of a predetermined space S apart from the nearest figure as the assist pattern AP0, when at least a width W and a length H of figures satisfy a predetermined value. Usually, the assist pattern AP0 has a size which is not resolved during the exposure and disposed on the vicinity of the main pattern MP0. Therefore, the figure satisfying aforementioned qualifications is defined as the assist pattern AP0. For example, in FIG. 7, when a rectangular pattern is sequentially defined as P1, P2 and P3 from the left of the paper, the figure P2 satisfying the condition that the width W of the rectangular pattern figure P2 is in the predetermined range of the minimum width WMin to the maximum width WMax, the length H of the figure P2 is not less than the predetermined minimum length HMin, and the space S which is narrow one of spaces between the figure P2 and the nearest one of a figure P1 or P3 when seen in perpendicular to the longitudinal direction of the figure P2 is in the range of the minimum space SMin to the maximum space Smax is specified as the assist pattern AP0. Since there is used the space S from the nearest figure as a judge condition, the assist pattern AP0 can be exactly specified in either case that another figure exists only one side or both. As a result, two figures P1 and P2 are specified as the assist pattern AP0 in the case illustrated in FIG. 7. On the basis of the definitions, the specification section 36 specifies totally 6 figures the identification number of which is “1” to “3”, “5”, “7” and “8” among figures illustrated in FIG. 6 as the assist pattern AP0. Subsequently, the main pattern extracting section 37 specifies, as the main pattern MP0, a figure other than the figures (totally 6 figures as mentioned above) which is specified as the assist pattern AP0 in the specification section 36 among totally 8 figures recognized during the recognition process. The main pattern extracting section also performs the extraction process extracting the main pattern MP0 only. Consequently, as shown in FIG. 8, figures of the identification number “4” and “6” are extracted as the main pattern MP0. As mentioned above, the extraction unit 12 performs the recognition process, the specification process and the extraction process, whereby only the main pattern MP0 can accurately extract from the mask data D1 processed by the fracturing. The extracted main pattern MP0 is stored in the memory 38. The inspection unit 13 performs reading the main pattern MP0 which is extracted in the extraction unit 12 from the memory 38, and then matching the main pattern MP0 with the mask image which is sent from the image forming unit 31. Specifically, the unit performs matching the extracted main pattern MP0 with a main pattern MP1 which is obtained from the mask image after the drawing. Additionally, the inspection unit 13 performs the inspection process inspecting whether the defective portion exists on the main pattern MP1 after the drawing, from the differences between both of them, in company with comparing between both patterns. As a result, if the defective potion exists, the inspection unit specifies the kinds (such as the extrusion or the intrusion) and the location of the defective portion. Particularly, due to the definition added to the assist pattern by the outlining and the predetermined condition, the assist pattern AP0 and the main pattern MP0 are clearly distinguished from each other in the mask data D1 processed by the fracturing, and only the main pattern MP0 is accurately extracted. Accordingly, it is possible to remove the assist pattern AP0 which is the known noise factor from the original reference data in the die to database system. Hence, only the main patterns which are original targets of the correction can be subjected to the matching process. As the result, it is possible to match the location in high accuracy by using the die to database system and accurately perform the inspection and the location specification of the defective portion. Additionally, the correction unit 14 is suitably controls the scan circuit unit 24 or the gas guns 18 and 19 on the basis of information sent from the inspection unit 13, and the correction unit performs the correction process correcting the defective portion of the mask by performing the etching process or the deposition process which forms the deposition film. To clarify, when the defective portion is the extrusion, the FIB is irradiated while supplying the gas G1 for the etching from the gas gun 18. Using this method, the correction can be performed on the defective portion by the etching process. Conversely, when the defective portion is the intrusion, the FIB is irradiated while supplying the raw gas G2 from the gas gun 19. Using this method, the correction can be performed on the defective portion by the deposition process forming the deposition film in the intrusion portion. Therefore, the correction unit 14 performs the accurate mask correction since the correction is performed by selectively using the etching process or the deposition process in accordance with the kinds of the defective portion. When the correction is performed, the existence of the defective portion is accurately inspected as mentioned above, and the location of the defective portion is accurately specified, and thus the high accurate mask correction can be performed. Accordingly, the photo mask 3 with high quality which has the assist pattern AP1 can be fabricated. Using the photo mask 3 fabricated as mentioned above, it is possible to accurately fabricate the microscopic semiconductor circuit where the fluctuation of edges and the like is suppressed. In the semiconductor mask correcting device 1 and the method using the same of the embodiments mentioned above, the photo mask 3 having the assist pattern AP1 can be matched with the mask data D1 by the pattern matching in high accuracy, using the die to database system and it is possible to fabricate the photo mask 3 with high quality by performing the accurate mask thereon. Technology range of the invention is not limited to the embodiment mentioned above, and may be modified to various forms of the embodiment in the range of the object of the invention, if necessary. For example, to extract the main pattern from the pattern data which is stored in the mask data, first, the assist pattern is specified. At that time, even adding more minute conditions to a width, a length, and a space from an adjacent figure of the figure, it does not matter that the definition added to the assist pattern is performed. Adding more minute conditions, the pattern design is more complicated, but it is still possible to perform the extraction of the main pattern by clearly specifying the assist pattern. However, since the extraction process speed decreases depending on the added conditions, it is better for efficiency to specify the assist pattern in the condition of at least a width, a length, and a space as mentioned above. |
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claims | 1. An optical detection apparatus for detecting image signals of a labeled sample, comprises:at least a laser generator for providing an excitation light and transmitting the excitation light; anda scan module for continuously reflecting the excitation light and introducing the excitation light to provide a linear scanning light by changing a reflection angle;a carrier for carrying the laser generator and the scan module, so that the laser generator and the scan module move together in a direction nonparallel to a linear direction of the linear scanning light so as to provide a two-dimensional testing zone in which the labeled sample is placed and is excited by the linear scanning light to emit an emission light; anda light receiver for receiving the emission light and forming the image signals of the labeled sample according to the emission light. 2. The optical detection apparatus of claim 1, wherein the scan module comprises:a polygon mirror for reflecting the excitation light; anda motor for rotating the polygon mirror to changing the reflection angle of the polygon mirror so that the excitation light is reflected into scanning light. 3. The optical detection apparatus of claim 2, wherein the polygon mirror comprises a polyhedron rotor and a plurality of scanning mirrors respectively embedded on a plurality of surfaces of the polyhedron rotor. 4. The optical detection apparatus of claim 2, wherein the polygon mirror is formed with a plurality of mirrors. 5. The optical detection apparatus of claim 1, wherein the scan module is a galvanometer which comprises a reflective mirror having one reflective surface and a driving unit driving the reflective mirror so that the reflective mirror oscillates and simultaneously reflects the excitation light to form a scanning light. 6. The optical detection apparatus of claim 1, further comprising:a mirror, which is carried by the carrier to move with the scan module, for reflecting the excitation light to the scan module. 7. The optical detection apparatus of claim 1, further comprising:a collimation and coupling lenses connected to the laser generator for collimating and guiding the excitation light so as to transmit to the scan module. 8. The optical detection apparatus of claim 1, further comprising:a collimation and coupling lenses connected to the laser generator for collimating and guiding the excitation light; anda mirror, which is carried by the carrier to move with the scan module, for reflecting the excitation light from the collimation and coupling lenses to the scan module. 9. The optical detection apparatus of claim 1, further comprises:at least a mirror for guiding the emission light from the labeled sample to the light receiver, wherein the testing zone, the mirror and the light receiver are serially arranged in an emission light path. 10. The optical detection apparatus of claim 9, wherein the excitation light passes aside the mirror. 11. The optical detection apparatus of claim 1, further comprises:a light generator for providing an illumination to the labeled sample. 12. The optical detection apparatus of claim 11, wherein the light generator has a plurality of light-emitting diodes. 13. The optical detection apparatus of claim 1, wherein the preferred direction, in which the carrier moves, is perpendicular to the linear direction of the linear scanning light. 14. The optical detection apparatus of claim 1, wherein the carrier comprises an actuator for generating scanning motion. 15. The optical detection apparatus of claim 1, wherein the light receiver comprises:an image lens for receiving the emission light from the labeled sample;a filter for getting a certain wavelength emission light; andan image-sensing module for forming image signals of the labeled sample corresponding to the filtered emission light. 16. The optical detection apparatus of claim 15, wherein the image-sensing module is a charge-coupled device (CCD). |
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abstract | An electronic emission device including plural electron beams including a first structure having a plurality of emission sources of electron beam, hybridized with a second structure including a plurality of diaphragm openings. |
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description | The present invention relates generally to nuclear reactors and more specifically to control rods for a nuclear reactor. Controls rods are used in nuclear reactors to control the rate of fission. In pressurized water reactors (PWRs), the control rods typically are arranged in control rod clusters. As shown in FIG. 1, each control rod cluster 10 can include a spider 12 with the control rods 14 vertically extending downwardly from the spider 12. The control rods 14 have a cladding 16, typically made of stainless steel or Ni-based alloy, fastened to the spider 12. The cladding 16 can have a bottom end cap 20 and a top end cap 22 to define a cavity 18. The cavity 18 is filled with one or more absorber bars 30, which are typically cylindrical and held by mean of a spring 24. The absorber bars for the control rod for a PWR often are made of silver, indium and cadmium, AgInCd. Absorber pellets, made for instance of B4C, may be interposed between the absorber bar 30 and the spring 24. The control rod cluster 10 can be lowered via the spider 12 into guide thimbles of the fuel assembly of a PWR to regulate the reactivity of the nuclear reactor core. During nuclear power reactor operation, the neutrons penetrate the control rod cluster 10 and the absorber bar material is activated and transmuted to other elements. The activation level depends on the accumulated irradiation of the material and the bottom section of the absorber bar 30 nearest the bottom end cap 20 introduced more deeply in the reactor core than the top section, has the highest neutron-activated radioactivity. U.S. Pat. Nos. 4,928,291, 5,183,626 and 5,889,832 describe control rod clusters and are hereby incorporated by reference herein. U.S. Pat. No. 4,650,606 describes cutting off used poison rods secured to a holder by a cutter and then storing them in a storage container. U.S. Pat. No. 4,383,394 describes a cutting device for irradiated components such as nuclear fuel assembly parts. Korean Patent Application Abstract 2006-0027472 describes an apparatus for automatically cutting a nuclear fuel control rod using a plurality of cutters that can reduce the time required for cutting the nuclear fuel control rod. Japanese Patent Application No. 06-182414 describes a nuclear reactor spent guide tube cutting device. An object of the present invention is to permit recycling of absorber bar material from control rods. The present invention provides a method for recycling AgInCd control rod absorber bar material from a used control rod comprising an AgInCd absorber bar, the method comprising: sectioning the AgInCd absorber bar from a used control rod into a first section and a second section, the first section having a higher radioactivity than the second section; and recycling the material of the second section of AgInCd absorber bar. By sectioning the first section, for example that of a highly radioactive lower end of the absorber bar nearest the bottom end cap 20, the remaining second section of lower radioactivity advantageously can be recycled. Recycling can include: reusing the second section unprocessed in a new control rod; processing the material of the second section into a new control rod; processing the material of the control rod for another use; or storing the second section for a future undetermined use. The AgInCd absorber bars being costly, particularly the precious metals components Ag and In, the cost for manufacturing new control rods can be significantly reduced, or the second section sold or recycled in other ways to reduce overall operating costs. Other uses of this material can be considered, such as use of In for LCD manufacturing, after separating out Ag, In or Cd, for instance by chemical separation. FIG. 2 shows a first embodiment where the absorber bar 30 of the control rod 14 is constituted of three absorber bars 32, 34, 36 made of AgInCd located between a top end cap 22 and a bottom end cap 20. The control rod 14 can remain attached to the spider 12, or be removed from the spider 12 by a top cut or a physical detachment process, for example as discussed in incorporated-by-reference U.S. Pat. No. 5,889,832. While the control rod 14 is held from the top either via the spider 12 or a separate gripper, a cutting device 50 can make a cut 52 through both the cladding 16 and the bar 36 to create a first section 60 of absorber bar 30 with a higher radioactivity corresponding to the lowermost portion of the absorber bar, and a second section 62 of absorber bar 30 for recycling. Here second section 62 includes absorber bars 32, 34 and the section of absorber bar 36 above cut 52. However, second section 62 for recycling need not include all of the absorber bar 30 other than first section 60. Cutting device 50 is shown schematically, but may be for example similar in construction to cutting devices described in U.S. Pat. Nos. 4,650,606, 4,383,394, Korean Patent Application Abstract 2006-0027472, or Japanese Patent Application No. 06-182414, all of which are hereby incorporated by reference herein. The first section 60, together with bottom end cap 20 and the cladding 16 below cut 52 can be transferred via a bottom gripper to a storage container 82 in the spent fuel pool 80 of the nuclear reactor from which the used control rod 14 was taken, as shown schematically. Due to diametric expansion of the absorber bar 30 under cumulative effects of creep and swelling of the absorber bar material during nuclear power reactor operation, first section 60 of the absorber bar 30 may have interacted with cladding 16. However, the section of absorber bar 36 above cut 52, and the absorber bars 32, and 34 should not have expanded to create an interaction with the cladding 16. Thus, once cut 52 is made, second section 62 of lower radioactivity may simply fall out of cladding 16. During the cut, the spider 12 or top gripper, together with the bottom gripper, can hold for example both the top of control rod 14 and the bottom of control rod 14 together, for example over a recycling depot 90. After the cut is complete, the bottom gripper can move the first section 60 together with bottom end cap 20 and the cladding 16 below cut 52 to storage container 82 in the spent fuel pool 80, while the section of absorber bar 36 above cut 52 and the absorber bars 34 and 32, i.e. the second section 62, fall into recycling depot 90. FIG. 4A for example shows how, in one example of a control rod 14, at after about 8 centimeters from the bottom end cap connection, diameter expansion of the control rod substantially ceases. In the example of FIG. 4B, relating to another control rod 14, the expansion of the diameter of the control rod is substantial until about 15 centimeters from the bottom of the absorber bar and ceases at after about 50 centimeters from the bottom of the absorber bar. Cut 52 preferably is above the location where any substantial expansion has occurred, to ensure that the absorber bar 30 above cut 52 can be easily removed from cladding 16. Preferably, the method thus includes determining an expansion of the absorber bar 30 in the cladding 16 at at least one location along the used control rod 14. The location of cut 52 then can be a function of the determined expansion. The location of cut 52 need not to be based on an actual measurement of that specific control rod 14 and may be based on analytical predictions or on a combination of controls and analytical predictions. For example, a profilometry report or an analytical prediction for at least one of the control rods 14 of the cluster 10 may be run, and this report then used for all the control rods 14 of that cluster 10 or even for all the control rods 14 of a corresponding bank of clusters 10 to determine the expansion. However, a report or a prediction can be run for each individual control rod 14 as well. Depending on the foreseen use of the second section 62 of the absorber bar 30, the location of cut 52 may also be a function of the radioactivity of the absorber bar 30. FIG. 5A shows a gamma scan of a lower part of a control rod 14 from a shutdown bank of cluster 10; after about 40 centimeters, and clearly by 60 centimeters, the radioactivity of the absorber material has leveled off. FIG. 5B shows a gamma scan of a lower part of a control rod 14 from a temperature regulation bank of cluster 10. The radioactivity of the absorber material decreases more gradually and levels off by 100 centimeters. The actual location where the radioactivity levels off will depend on design, type of service for cluster 10, reactor type, and length of decay time. For example, control rods 14 of clusters 10 used in a main control bank of clusters may never be recyclable because the inserted and thus activated part of the absorber bar 30 through its service life may be too long, while other control rods 14 of clusters 10 used in other banks of clusters may solely have tip exposure. The capability of the control rod 14 handling and recycling facility to deal with various levels of activity can also be a factor, and if the capability exists, the cut may be made even before the radioactivity leveling off occurs. Also, the cluster 10 may be shipped to the recycling facility and then the control rods 14 separated from the spider 12 or the control rods 10 may be separated at the reactor plant and then handled by the recycling facility. Preferably, the cut 52 is made at a location where the second section 62 near the cut 52 will have a radioactivity level of less than or equal to 0.05 Curies/mm. The cut 52 also preferably occurs so that the first section 60 has a length of about 100 cm or less, and most preferably at about 50 cm or less. However, a length of at least 10 cm is desired. These lengths help maximize the amount of recyclable material. As shown in FIG. 2, the AgInCd absorber bars 32 and 34 and the section of absorber bar 36 above cut 52, i.e. the second section 62, can then be recycled, for example for the same nuclear power plant at a recycling station 100 where a new cladding 110 with a welded new bottom end cap 120 can be provided. Bars 32 and 34 together with another similarly sized bar can be placed in the new cladding 110. The partial section from bar 36 can also be reused, by adding additional material to bar 36, or adding a new bar of the size of the missing material, so that for example four bars may be in the new cladding 110. The partial section from bar 36 may for instance be positioned in the topmost portion in the new cladding 100. A new top end cap can be supplied at recycling station 100 and welded to the new cladding 110 after loading of the spring 24, if any. The new control rod is then connected to a cluster. It should be noted that the second section 62 with cladding 16 above cut 52 may be moved together to recycling station 100 as well, for example by providing a provisional plug after cut 52, or cutting the used control rod 14 while control rod 14 is upside down. Alternately to reusing second section 62 in a new control rod, the absorber bars 32, 34 and the section of absorber bar 36 above cut 52 may also be stored for later use, or reprocessed. FIG. 3 shows a second embodiment where the control rod 14 is cut solely through the cladding 16 at a cut 152. When a gripper moves the lower cladding section below cut 152 away, the entire bar 36 may move with it and defines first section 160 of absorber bar 30. Due to creep and swelling and interaction between the lower portion of bar 36 and cladding 16, bar 36, cladding 16 below cut 152 and bottom end cap 20 likely will move as a group. Even if not, bar 36 will remain in the cut section of cladding 16 if held upright. This embodiment is useful solely when a plurality of bars is provided, and may permit a quicker cutting and processing. Bars 32 and 34 can then define second section 162 of absorber bar 30 and be recycled, for example as described with respect to FIG. 2. In addition topmost portion of bar 36 may be cut with another tool positioned in the spent fuel pool or in the recycling station and recycled with bars 32 and 34 or separately. In addition, with the second embodiment, analytical studies can be used to pre-determine the control rod 14 irradiation and evaluate the corresponding diametric expansion and radioactivity level at at least one location along the absorber bar, for example for a given or expected duration of use as illustrated on FIG. 6. The absorber bars can then be designed as a function of the analytical studies to determine a desired length of absorber bar 36 of the first section 160, and of one or more absorber bars of second section 162. The absorber bars can then be manufactured, shipped and used in a cluster. The cladding can then be sectioned at the end of the use of the control rod 14, and the material of the second section 162 recycled. It should be noted that the absorber bar material may be in a single bar, or any number of a plurality of bars. Also, while the preferred embodiment describes cutting, the term sectioning can include other ways of sectioning other than cutting. |
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summary | ||
abstract | A duct-type spacer grid for nuclear fuel assemblies is disclosed. In this spacer grid, a plurality of duct-shaped grid elements, individually having an octagonal cell, are closely arranged in parallel and are welded together, thus forming a matrix structure. The grid elements do not pass across the center of the subchannel of the assembly, thus effectively reducing pressure loss. Each of the grid elements is formed as an independent cell, and so they effectively resist against a lateral impact. A plurality of integral type swirl flow vanes, having different heights or same height, axially extend from the top of the grid to be positioned within each subchannel. The swirl flow vanes are bent outwardly, and so they do not contact the fuel rods during an insertion of the fuel rods into the cells. In the spacer grid, the fuel rods are supported within the cells by line contact springs without using any dimple. The spacer grid thus uniformly distributes its spring force on the fuel rods and almost completely prevents damage of the fuel rods due to fretting wear. |
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summary | ||
054669430 | abstract | An evacuated testing device (100) including a housing (106) providing a test chamber (101) therein, a first mechanism (102) for retaining an object (116) under test in relation to an aperture (112), a second mechanism (104) positioned within the test chamber (101) for generating and transmitting uniform electromagnetic radiation to the object (116), and a third mechanism (122) disposed within the test chamber (101) in thermal communication with the second mechanism (104) for varying the temperature thereof. In a preferred embodiment, a test dewar (102) and an infrared blackbody radiating source (104) are enclosed within a test chamber (101) of the evacuated testing device (100). A focal plane array (116) is mounted on a cold finger (114) within the test dewar (102) in close proximity to an emissive surface (126) of the blackbody radiating source (104). A thermoelectric cooler (122) varies the temperature of the emissive surface (126) which generates and transmits the infrared radiation. An aperture (112) formed within a cold shield (110) and the temperature of the blackbody radiating source (104) determine the amount of radiation impinging upon the focal plane array (116). The blackbody radiating source (104) simulates typical terrestrial background radiation levels over a temperature range of from -40.degree. C. to +80.degree. C., is controlled and calibrated to within 0.05.degree. C. and can be slewed between different temperatures in a brief period. |
abstract | A radiation case having a radiation-proof door, and having a radiation-proof main section that has a back portion, a floor portion, a ceiling portion and side portions, vertical cavities formed in the back portion, the vertical cavities being a distance from a surface of a back wall of the back portion, radiation rods located in the vertical cavities, each radiation rod containing cobalt-60 pellet, the distance between the vertical cavities and the surface of the back wall of the back portion being less than a penetration distance for gamma rays coming out of each cobalt-60 pellet. |
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040177378 | description | GENERAL DESCRIPTION Referring now to the drawings, in FIG. 1, a preferred form of x-ray apparatus 30 of this invention is illustrated as including an upright frame and housing 31 and base frame 31a forming a box-like structure, and a box-like patient elevator pedestal 32 mounted in front of housing 31. Elevator pedestal 32 includes an elevator apparatus 33 movable in and out (i.e., towards and away from housing 31) as indicated by the arrow 34, and a patient support platform 35 mounted on elevator apparatus 33 for movement up and down as indicated by the arrow 36. As shown in FIG. 9, platform 35 is in the form of a hollow box and includes a top plate 35a pivotally mounted on a bottom plate 35b by brackets 35c mounted on each side of bottom plate 35b (only one bracket 35c is shown in FIG. 8). A slotted block 37 is mounted on platform 35, and includes an elongated slot 38 therein for controlling the movement of a belt on a patient conveyor cart as illustrated in FIGS. 7-12. Block 37 is movable towards and away from housing 31 as indicated by arrow 39. Platform 35 also includes an elongated slot 40 for interconnection with a bar on the front of a patient conveyor cart as hereinafter described. Extending from platform 35 and towards housing 31 is a patient headrest 41 which is also movable to adjust the tilt of the patient's head as hereinafter described. The apparatus for raising and lowering the respective members of pedestal 32 described is illustrated in FIGS. 7-12 and will hereinafter be described in detail. Elevating apparatus 33 on pedestal 32 functions to support the patient at the proper elevation and in the proper position within the x-ray apparatus for the x-raying operation. A rotatable disc 42, defining a generally circular opening 43, is mounted in x-ray apparatus 30 as hereinafter described. A cylindrical member 42a extends from the edge of disc 42 defining opening 43 into apparatus 30. As illustrated in FIG. 1, an x-ray source 44 and an x-ray film holder or housing 45 including a cylindrical film cassette 46 are mounted on the opposite sides of disc 42 adjacent opening 43 so that they face each other, and are spaced apart a sufficient distance to permit the head of a patient to be inserted between them. The mounting and operation of disc 42 and source 44 are shown in FIGS. 2, 6, 23A, 23B, 24A and 24B, and the configuration and operation of the film holder 45 is illustrated in FIGS. 13-17. A retractable tape measure 47 may be mounted on the inside of housing 45 for measuring the correct patient head to film distance during operation of apparatus 30. Disc 42 is mounted to rotate in an opening in a front plate 48 which is, in turn, mounted on a suitable frame which is illustrated in detail in FIG. 2. During operation, the head of a patient to be x-rayed is supported on headrest 41 between x-ray source 44 and film housing 45 so that as disc 42 rotates, it carries x-ray source 44 and film housing 45 about the head of a patient in a manner similar to the apparatus in U.S. Pat. Nos. 2,798,953 and 3,045,118, except that the patient is upright in those patents instead of horizontal. Also, while the shift required to provide a panoramic x-ray through certain areas to be x-rayed in those patents is provided by shifting the position of the patient with respect to the center of rotation of the x-ray source and film, this shift, when required, is provided in the present invention by shifting the center of rotation of disc 42, and providing for variations in the degree of this shift. Suitable control apparatus 49 for providing the required electrical switching and control functions to operate the elements described of x-ray apparatus 30 is shown as being mounted in the upper righthand portion of housing 31, as, for example a removable sub-panel. Details of this apparatus are illustrated in FIGS. 3-5 and 18-22. Of course, an x-ray apparatus constructed in accordance with the principles of this invention may take many different forms, other than the general arrangement described with respect to apparatus 30. GIMBAL SHIFT AND DISC DRIVE APPARATUS As noted, an important feature of the present invention is the provision for shifting the center of rotation of disc 42 during operation rather than shifting the patient. Referring now to FIG. 2, preferred apparatus for providing this shift is shown as including a pivoted gimbal or operating frame 50 mounted inside housing 31 for supporting disc 42 for rotation. As illustrated, frame 50, which may be made of lightweight aluminum tubing, has its lower end 50a in the form of an apex of a triangle and this end is provided by a tubular sleeve 51a mounted by spaced bearings 51b (see FIG. 9) to pivot on a rigid pivot pin 51c which is, in turn, mounted in base frame 31a of apparatus 30. By this arrangement, frame 50 can pivot about pin 51c to shift between the dotted line positions 50b and 50c inside of housing 31, which are on either side of the center shift position illustrated by the solid line position of frame 50 in FIG. 2. As illustrated in FIG. 2, single, V-grooved rollers 52 and 53 are rotatably mounted on the upper portion of the frame 50 and on opposite sides thereof by arms 54a and 55a, respectively, and each of arms 54a and 55a are respectively pivotally supported on frame 50 by brackets 54b and 55b. Also, opposed pairs of V-grooved rollers 56 and 57 are rotatably mounted on opposite sides of frame 50, below rollers 52 and 53, on opposed plates 58a and 59a, respectively, and plates 58a and 59a are in turn respectively pivotally mounted on brackets 58b and 59b connected to gimbal frame 50. Rotatable disc 42, which may be made of a piece of flat aluminum with opening 43 in the center, includes a beveled outer edge 60 having converging beveled surfaces 60a and 60b, and disc 42 is mounted between and supported on rollers 52, 53, 56 and 57 with edge 60 supported in the grooves of the rollers as shown in FIG. 6. An adjustable rod 61, which may be adjusted in length by a turnbuckle 62, may be connected between arms 54a and 55a to adjust the force with which rollers 52 and 53 engage beveled edge 60 of disc 42. A pulley 65 may be rigidly connected to each of rollers 57, and mounted to rotate with the roller, and pulleys 65 may be driven by a constant speed motor 63 through an endless belt 64 connected to pulleys 65 (see FIG. 6). Of course, if desired, rollers 56 can be driven instead of rollers 57. As illustrated in FIG. 6, the V-groove of each of rollers 57 includes converging surfaces 57a and 57b, so that these surfaces are engaged with a corresponding surface of edge 60 of disc 42 to provide a ripple free, precision drive which is highly responsive and capable of withstanding continuous directional changes during rotation of the disc and the structures mounted on it. To accomplish this, the relationship between V-groove surfaces 57a and 57b of rollers 57 and beveled edge 60 of disc 42 is such that the circumferential speed of the mating members agrees at a center line 66 representing the true pitch diameter of the disc. On either side of line 66, the circumferential speed of the mating members is in conflict, but of opposing character so that the direction of their components of motion cancel each other. Thus, in the area represented by the arrows 69, the circumferential speed of disc 42 exceeds that of rollers 57, and in the area represented by the arrow 68 the opposite is true. As a result, although disc 42 supports a relatively heavy stationary load, driving rollers 57 are not subject to compression so that relatively small rollers, which can be made of phenolic or similar material, can effectively and efficiently rotate a relatively large disc carrying a relatively heavy weight, for example, in the order of 120 pounds, at a constant speed of, for example, 2 rpm. Referring again to FIG. 2, the preferred apparatus illustrated for shifting the position of gimbal frame 50 within housing 31 includes a double acting hydraulic cylinder 70, which is controlled by a four-way, three-position solenoid valve 71, illustrated in detail in FIG. 19. A shift control means is preferably mounted in the lower portion of housing 31 for responding to the shift in position of frame 50 to control the extent of the shift. A preferred form of this means is illustrated as including a lever arm 72 pivotally mounted at one end 72a to a linkage rod 73, and pivotally mounted at its other end 72b to an upwardly extending rod 74. Linkage rod 73 is also pivotally mounted at its lower end to the base frame 31a of housing 31. At a point 76, intermediate its ends, arm 72 is pivotally connected to an actuator rod 75 which is connected to frame 50 so that the motion of frame 50 between its respective shift positions is identically tracked at intermediate pivot point 76. Intermediate pivot point 76 is located so that the distance between the end pivot points 72a and 72b of lever arm 72 is four times the distance between pivot point 76 and the end pivot point connected to linkage 73, so that the motion of rod 74 in a vertical direction is four times the motion of arm 75 in response to the shift of frame 50. As shown in FIGS. 3 and 4, rod 74 is connected at its upper end, in the upper portion of housing 31, to operate a shift selector mechanism generally designated by the numeral 77. A preferred form of such a selector mechanism is illustrated as including a switch actuator 78 which is mounted in an elongated slot 78a in the center of a plate 79, and switch actuator 78 is connected to the upper end of rod 74 to follow the movement thereof. Elongated slots 80 and 81 are also located in plate 79 on either side of slot 78a and function as guides for microswitches 82 and 83, respectively, which are mounted to be actuated by actuator 78 and to move back and forth in the slots to different positions representing different desired shifts of gimbal frame 50, with switch 82 representing the left limit of shift and switch 83 representing the right limit of shift. A third microswitch 78b is mounted to be actuated by actuator 78 on the back of plate 79, adjacent the center of slot 78a, and switch 78b represents the center position of shift of frame 50. As illustrated in FIG. 3, an endless cable 84 is connected between spaced pulleys 85 and 86 mounted, respectively, on the upper and lower ends of plate 79, and each of switches 82 and 83 is rigidly connected to cable 84 to move in its respective guide slot under control of cable 84. Pulley 85 is mounted on a shaft 87 which is, in turn, connected to operate a rotary switch 88, and shaft 87 extends through housing 31 to be actuated by a pointer knob 89 as illustrated in FIGS. 4 and 5. By adjusting the rotary position of shaft 87 by knob 89, switches 82 and 83 can be moved from a position representing the maximum shift of frame 50 in one direction, wherein switch 82 is adjacent to the upper end of slot 80 and switch 83 is adjacent the lower end of slot 81, to a central position in which switches 82 and 83 are located in their respective slots directly across from each other, and to a position representing the maximum shift of frame 50 in the opposite direction, wherein switch 82 is located adjacent the lower end of slot 80 and switch 83 is located adjacent the upper end of slot 81. Of course, switches 82 and 83 may be set at positions between the described extreme positions, and center position. As indicated in FIG. 5, the extreme positions of switches 82 and 83 may be represented by positions 1 and 15 indicated for pointer knob 89, the center position by knob position 8, with intermediate positions represented by knob positions 2-7 and 9-14. Referring to the area marked generally by the numeral 90 in the top of FIG. 2, maximum shift positions of the axis of rotation of disc 42 are indicated, along with intermediate positions corresponding to the numbers 1-15 as in FIG. 5. In the illustration given, numeral 8, which would represent a position wherein switches 82 and 83 are located near the center of slot 80 and 81 and are across from each other, represents zero or no shift. Thus, during operation of the apparatus of FIG. 2, knob 89 can be set to provide a desired degree of shift within the limits described. Also, pulleys 85 and 86 can be sized so that each of positions 1-15 is a 20.degree. step of shaft 87 and causes a one centimeter movement of each of switches 82 and 83, which in turn causes a one-half centimeter shift of the center of rotation of disc 42. Thus, the amount of shift of frame 50 can be accurately controlled. The electrical schematic of switch 88 is shown in FIG. 20, and the hydraulic schematic of the valve 71 for controlling shift cylinder 70 is shown in FIG. 19. PATIENT CONVEYOR AND ELEVATOR MECHANISM Referring now to FIGS. 7-12, a patient conveyor cart 100, supported on wheels for portability, is illustrated as including a patient P lying on a belt conveyor 101 on top of the cart. In FIG. 7, elevator apparatus 33 is shown extended away from x-ray apparatus 30 and in its lower position for receipt of cart 100. Cart 100 also includes a guide bar 102 located underneath the front end of the cart, and the cart also includes a second bar 103 spaced towards the rear of the cart from bar 102, which, as described in FIG. 11, operates a mechanism for moving belt conveyor 101 to shift the patient from a position shown in FIGS. 7 and 8 to a position such as shown in FIG. 9. As shown in FIGS. 8 and 9, patient elevator apparatus 33 includes apparatus for moving belt conveyor 101 in and out to move the patient from a position on cart 100, to the position wherein his head is lying on headrest 41; apparatus for moving cart 100 and the patient to the correct elevation for movement of the patient into machine 30; apparatus for moving patient P and cart 100 inwardly and outwardly from machine 36 when the patient is at the proper elevation; and apparatus for tilting headrest 41 for proper positioning of the patient's head. As illustrated in FIG. 8, the apparatus for moving belt conveyor 101 includes block 37 which is connected through piston rods 104 (only one shown) to spaced hydraulic cylinders 105 mounted inside of platform 35. As shown in FIG. 8, conveyor 100 is lifted to insert bar 102 in slot 40 of platform 35 and bar 103 in slot 38 of movable block 37, with cylinders 105 retracted as shown in FIG. 7. As shown in FIG. 10, platform 35 is supported by parallel arms 106 which telescope into tubular members 107 mounted on a generally rectangular platform 108 which is, in turn, pivotally mounted at their lower ends to the lower frame of pedestal 32 so that arms 109 supporting platform 35 form a parallelogram movable between the positions shown in FIGS. 8 and 9. A hydraulic cylinder 110 is vertically mounted on platform 108 in the approximate center thereof, and includes a piston rod 111 standing upwardly and secured to lower plate 35b of platform 35 for moving it up and down between the lower position shown in FIG. 8 to the upper position shown in FIG. 9. Thus, when patient conveyor cart 100 has been supported on extendable block 37 and platform 35, as shown in FIG. 8, cylinder 110 can be actuated to raise the platform 35 to a position in which a patient can be moved inwardly towards machine 30, and this operation will raise cart 100 off the ground so that it is no longer supported by its front wheels. The apparatus for moving elevator mechanism 33, and thus patient P, towards and away from machine 30 includes a hydraulic cylinder 112 mounted inside of pedestal 32 and connected to a cross member 112a connected between the lower end of tubular members 107. As shown in FIG. 8 when cylinder 112 is extended, apparatus 33 is in its outward position and when cylinder 112 is retracted, as shown in FIG. 9, apparatus 33 is in its inward position wherein the patient is located with his head between x-ray source 44 and film housing 45. Headrest 41 is mounted on an angled plate 41a which is pivotally supported by parallel plates 113 on the back wall of platform 35 (see FIG. 1). Plate 41a is pivotally connected at a pivot point 114 to parallel plates 113 and extends from pivot point 114 to the piston rod of a hydraulic cylinder 115 mounted inside of platform 35, so that as piston rod is extended or retracted, headrest 41 pivots to provide different positions of tilt for a patient's head. As previously noted, top plate 35a of platform 35 and block 37 is pivotally mounted with respect to bottom plate 35b to follow the horizontal level of cart 100 when elevated off of its front wheels. The electrical control and hydraulic control apparatus for controlling the operation of hydraulic cylinders 105, 110, 112 and 115 are illustrated in FIGS. 19 and 20 and their operation is hereafter described in detail. Referring now to FIG. 11, a preferred form of a patient conveyor mechanism for cart 100 is illustrated for driving belt conveyor 101 which may be an endless belt made of a flexible material preferably with a low coefficient of friction mounted for rotation about rollers (not shown) on the opposite ends of cart 100. The conveyor mechanism includes a slide mechanism 120 having bar 103 at one end connected to parallel spaced apart rods 120a and 120b, which are in turn slidably mounted inside slotted, parallel guides 121a and 121b mounted on each side of conveyor belt 101 and adjacent its longitudinal edges. The other ends of rods 120a and 120b are connected to a cross member 122, parallel with and spaced from bar 103, so that as bar 102 is moved in the direction of arrow 123, cross member 122 follows the movement of bar 103. Means is also provided which is connected to conveyor belt 101 and amplifies the motion of bar 103 while causing movement of conveyor 101 in the desired direction. As illustrated, this means includes a closed linkage mechanism 124 including opposed parallel members pivotally connected with their ends to form a closed diamond. Mechanism 124 is pivotally connected at one apex 125 to a cross member 126 which is rigidly connected to cart 100, and is pivotally connected at the opposite apex 127 to conveyor belt 101. A cross member 128 is pivotally connected between opposite members of linkage mechanism 124, and cross member 128 is pivotally connected at an intermediate point 129 to cross member 122 at approximately its center. Thus, as cross member 122 is moved in conjunction with bar 103, moving pivot point 129 in the direction shown, linkage mechanism 124 is caused to move apex pivot point 127 with respect to apex pivot point 125, thus moving conveyor 101 with respect to cart 100. In FIG. 11, mechanism 124 is shown extended as it would be with the patient loaded in machine 30, and mechanism 124 is retracted with cross member 122 adjacent cross member 126 as shown in dotted lines when the patient is lying fully on cart 100. In the arrangement described, the relative movement of apex pivot point 127 with respect to apex pivot point 125 is greater than the movement of pivot point 129, for example 3-4 times depending on the relationship of the elements described, thus providing significant amplification of the movement of bar 103 in response to hydraulic cylinders 105, and reducing the stroke length requirement for the cylinders. The amount of amplification provided can be increased or decreased as desired by varying the size of linking mechanism 124, although it is desirable that linkage mechanism 124 not be so large that it extends beyond the sides of cart 100 when retracted. Conveyor belt 101 can be marked with the proper patient position so that full travel of piston rods 104 will carry him from the position of FIG. 8 to the position of FIG. 9. PATIENT ELEVATOR LIMIT SWITCHES During elevation and positioning of a patient in apparatus 30, care must be taken to avoid hitting the patient's head or headrest 41 against x-ray source 44. Also, care must be taken to ensure that the patient's head is properly positioned between source 44 and film holder 45 so that the patient is not struck by either of these objects when disc 42 is rotated. Further, it is highly desirable that the patient be fully withdrawn from apparatus 30 and fully on cart 100 before the cart is fully lowered to where it can be removed from elevator apparatus 33. In view of these requirements, it is preferred that certain limit switches be provided in association with elevator apparatus 33 and patient conveyor cart 100 to automatically limit the movement of the patient or disc 42 when the danger of interference is present. Examples of such limit switches which have been established to be desirable for this purpose are shown in FIGS. 9, 10, and 12. Of course, the number and location of such switches can vary depending on the degree to which the operator is to be entrusted to operate apparatus 30 within safe limits. As shown in FIG. 10, one of tubular arms 107 includes a rectangular window 130 in it and an actuator plate 131 is mounted on telescoping arm 106 adjacent window 130 so that as arm 106 moves up and down, plate moves up and down in window 130. Also, a hollow tube 132 is mounted on lower plate 35b of platform 35 and extends through plate 108 to a position parallel to and adjacent arm 107 and window 130. A limit switch LS1, which can be connected to inhibit the operation of cylinders 110 and 112, is mounted on arm 107 adjacent the lower end of window 130 and includes a long actuator arm 133 extending down from it at an angle with respect to arm 107. Tube 132 includes an elongated slot 132a in its lower end, and a pin actuator 134, having a pin 134a extending through slot 132a, is slidably mounted in tube 132, and urged towards the bottom of tube 132 by a spring 135. A cable 136 is connected to pin actuator 134 and extends up through tube 132, about an amplifying idler wheel 136a (see FIG. 9) to the lower end of headrest 41 so that as headrest 41 is tilted about its pivot point, pin actuator 134 moves up and down in slot 132a to change the vertical position of pin 134a with respect to actuator arm 133. Wheel 136a functions to amplify the motion of the headrest. Also, as platform 35 moves up and down tube 132 moves up and down with it also changing the vertical position of pin 134a with respect to actuator arm 133. Thus, the actuation of arm 133 by pin 134a depends both on the amount of tilt of headrest 41 and the vertical position of elevator platform 35 so that when the headrest is up, the patient can be moved in to apparatus 30 with platform 35 at a lower position than is possible when the headrest is down and could strike x-ray source 44. The operating parameters of limit switch LS1 can be set to make sure that headrest 41 always clears source 44 at any elevation of platform 35. For example, if headrest 41 moves vertically up to 2 inches, and platform 35 moves vertically up to 8 inches, then arm 133 must be at least 10 inches long to cover the possible total vertical movement of 10 inches. The angle of arm 133 and length of pin 134a should be such that switch LS1 is actuated whenever source 44 would be struck by headrest 41 when moving inward. However, when the patient is all the way out of x-ray apparatus, or out a sufficient distance that danger of hitting source 44 is not present, then a limit switch LS2, mounted in association with one of arms 109 (see FIG. 9) can be actuated to override switch LS1 and permit up and down movement of platform 35. The vertical elevation of platform 35 can also be detected by limit switches LS3 and LS4 which are mounted adjacent window 130 so that they can be actuated by plate 131. Switch LS3 can be mounted at a position so that it can be utilized to sound an alarm when the elevation of platform 35 is such that with headrest 41 up, a normal sized head would be struck by film holder 45 during rotation about the front of the head. Switch LS4 can be mounted at a position so that it can be utilized to sound an alarm when the elevation of platform 35 and headrest 41 is such that the headrest 41 would be struck by film holder 45 during rotation about the back of the head. If desired, a vertical scale (not shown) can be provided to show the vertical position of platform 35 and red markings provided to indicate danger zones. A limit switch LS5 is mounted adjacent window 130 to be engaged by plate 131 for interrupting the vertical down motion of elevator apparatus 33 when the front wheels of cart 100 are a fixed distance from the ground, for example 1/4 inch, and permit the belt conveyor to be driven to its home position (all the way out). Another limit switch LS6 is mounted in platform 35 to sense when conveyor 101 is home and permit the completion of the vertical descent of elevator apparatus 33. Another limit switch LS7 may be mounted in platform 35 adjacent slot 40 so that it can be actuated by bar 102 when properly inserted and interrupt any elevating operation or operations of conveyor belt 101 until it is properly actuated. Thus, with the conveying apparatus described, a patient can be safely and rapidly brought to the proper position in apparatus 30. Since his head rests firmly on headrest 41, the patient can relax and does not need to try to hold his head steady at an unnatural position. In adjusting the position of the patient's head in apparatus 30, the operator need only site the portion to be x-rayed in the line of sight of the x-rays, and adjust the elevation of the head to the proper distance from film holder 45 by use of tape means 47. The electrical connections of the limit switches described and their function in controlling the application of power to the various solenoid valves of the patient elevating and conveying apparatus are shown in FIG. 20, and the hydraulic system is shown in FIG. 19. As shown in FIG. 9, the hydraulic system for operating cylinders 70, 105, 110, 112 and 115 can be mounted inside of pedestal 32 as represented by the dotted box 190. Referring to FIG. 19, this apparatus includes a hydraulic pump 191 connected between a low pressure inlet 192 to a source of hydraulic fluid generally represented by the number 193, and at its high pressure outlet 194 to a fluid distribution manifold 195 including a plurality of fluid inlets and outlets. The fluid return 196 from manifold 195 is connected to source 193 to establish a closed cycle fluid system. A controlled bypass 197 may be connected across conduits 194 and 196 to pump a portion of the fluid output of pump 191 into source 193 to reduce the flow rate of the pump under control. Fluid inlets and fluid outlets of manifold 195 are connected to conduct fluid to and from a series of three position, four way, solenoid operated spool valves. In addition to valve 71, previously described, a solenoid operated valve 198 is provided for controlling cylinder 110, a solenoid valve 200 is provided for controlling cylinder 112, and a solenoid valve 201 is provided for controlling cylinder 115. Valves 71, 198 and 200 are identical as shown, and valves 199 and 201 are modified to permit use of pilot operated check valves 202 and 203, respectively, as shown in FIG. 19. Both cylinder 110, which controls the up and down motion of apparatus 33, and cylinder 115, which controls headrest 41, must hold a vertical load for a certain length of time, and pilot check valves 202 and 203 are provided to prevent fluid leakage or seepage which would otherwise cause the supported mechanism to slowly decline in elevation. In all other respects, the hydraulic system described is conventional. Referring now to FIG. 20, the electrical switching is illustrated for operating solenoid valves 71, and 198-201. As shown, four double pole, double throw bat handle switches BS1, BS2, BS3, and BS4, which may be mounted on control panel 49 for operation by the operator, are illustrated as being connected at their pole terminal to line L1 providing a source of AC current along with line L2 which forms the AC common. Actuation of switches BS1-BS4 in one direction provides electrical current to the solenoid on one side of the respective solenoid valve, and actuation of the switches in the other direction provides current to the solenoid on the other side of the respective valve, thus effecting movement of the cylinders controlled thereby in both of their directions. As illustrated, switch BS1 is connected to supply power to lines Z4 and Y4 connected to the solenoid relays of valve 198 for controlling belt 101; switch BS2 is connected to supply power to lines Z2 and Y2 connected to the solenoid relays of valve 200 for controlling the in-out movement of elevator 33; switch BS3 is connected to supply power to lines Z3 and Y3 connected to the solenoid relays of lines Z1 and Y1 connected to the solenoid relays of valve 201 for controlling the angle of tilt of headrest 41. Limit switches LS1, LS2, LS5, LS6 and LS7 are also illustrated in FIG. 20 and are connected to interrupt the operation of the various solenoid valves when actuated. As illustrated, limit switches LS1 and LS2 are connected in series with the coil of an interference relay K7 so that the relay is actuated when an interference condition exists. Limit switch LS1 is normally open, and limit switch LS2 normally closed so that both switches LS1 and LS2 must be closed in order to permit relay K7 to be actuated. As noted, switch LS1 is closed when the inward movement of headrest 41 would cause it to strike source 44, and switch LS2 is closed when apparatus 33 is far enough out that this interference can't occur. Relay K7 includes terminal K7a which is connected to light an interference lamp 204 when actuated to provide a visual indication of an interference condition, and a contact K7b connected to switch A.C. power from line Z2 causing solenoid valve 200 to move the elevator in to line Z3 to cause solenoid valve 199 to be actuated to move the elevator up. Thus, when limit switch LS1 indicates interference during movement of elevator apparatus 33, and switch LS2 is not activated, the elevator apparatus is automatically caused to move upwardly until limit switch LS1 drops out when the interference condition is passed. Limit switches LS5 and LS6 are connected between switch BS3 and the elevator up-down solenoid valve 199 (line Y3) so that the downward motion of the elevator is stopped when limit switch LS5 is actuated, and until limit switch is actuated by conveyor belt 101 moving to its home position. Also relay K7 includes a contact K7c which is connected to switch the power on line Y3 normally operating solenoid valve 199 to move the elevator down, to the elevator in-out solenoid valve 200 (line Y2) to automatically move the elevator out when relay K7 is actuated until it is out a sufficient distance to avoid interference. As illustrated, limit switch LS7, which senses when the patient conveyor cart 100 is in position on platform 35, is connected in line Z4 between switch BS1 and solenoid valve 198, thus deactivating the belt in-out action until LS7 is actuated. Also, as illustrated, limit switches LS3 and LS4 may be connected between a source of voltage and a suitable alarm (not shown) by contacts of a section F of a mode switch MS so that, for example, if two separate modes of operation of x-ray apparatus are employed, having different safe limits, limit switch LS3 is actuated in one mode and limit switch L4 is activated in the other mode. THE FILM DRIVE MECHANISM Referring now to FIGS. 13-17, a preferred form of film drive mechanism of this invention is illustrated for advancing the x-ray film as it is moved around the object being x-rayed. As illustrated in FIG. 13, a cylindrical film cassette 46 is utilized in the present apparatus for supporting a partially folded x-ray film 140 inside of an opaque, removable film pouch 141, and film cassette 46 is rotated to advance film 140 as disc 42 is rotated to provide a panoramic x-ray. If the object to be x-rayed were a perfect circle, then the speed of rotation of film cassette 46 would have to be equal to that of disc 42. However, during operation of x-ray apparatus 30, while x-raying through the skull, for example, the speed of rotation of film cassette 46 must, due to the configuration of the cross section of the skull, vary slightly from the speed of rotation of disc 42 in order to compensate for different circumferential speeds at different positions along a desired focal trough. In the past, such as in the Vertical Panorex apparatus maufactured and sold by the assignee of the present invention, this slight variation in film speed has been provided by utilization of a basis cam 142 shown in FIG. 14a which includes lobe portions which closely follow the contour of the skull. During operation of that machine, the drive mechanism for driving the x-ray source is directly coupled to the basic cam 142 which is, in turn, coupled to drive an x-ray film, mounted in a flat film holder, past a slot at a speed which is proportional to the shape of the cam. However, this direct drive mechanism requires mechanical linkage by thin wire and is subject to mechanical problems and film jitter, and an important feature of the present invention is the provision of a drive mechanism for moving the x-ray film at the required speed while moving disc 42, which employs no mechanical linkage between the drive mechanisms. In x-ray apparatus 30, disc 42 may be driven by motor 63 at a constant speed of 2 rpm and the film speed mechanism of this invention to be described permits programmed speed variations in a 2 rpm motor utilized to drive film cassette 46 in order to synchronize the film speed to the circumferential speed of the outline of the object being x-rayed which, as noted, is other than a perfect circle. In a constant speed motor, the effective output revolution is the shaft rotation with respect to its stator, normally a stationary housing. Conversely, if the housing is allowed to rotate, its speed would increase or reduce the differential speed between the rotating shaft and an external fixed base, depending on the direction of movement of the housing with respect to direction of rotation of the rotating shaft. The present invention uses this technique to satisfy the requirements of a variable speed film drive which is accurately responsive to speed variation of fractional revolutions without introducing jitter. To accomplish this, basic cam 142 is redesigned utilizing variations in the radius of the basic cam to provide a sloped cam 143 illustrated in FIG. 14B. Whereas the basic cam shape closely follows the shape of the desired focal trough, and its circumferential speed at any excursion point is the desired film speed, the sloped cam must provide for differentials in radius at adjacent excursion positions proportional to the required change in film speed. To accomplish this, the change in radius of the basic cam between adjacent excursion positions (for example, 15.degree. apart) is determined and converted directly to a plus or minus change in rotational speed between adjacent 15.degree. positions to provide a required change in slope for the translated cam. In starting with a basic radius for sloped cam 143, then the change in slope can be translated into a minus or a positive increase or decrease in radius of the new cam to provide the desired slope. In order to utilize sloped cam 143 as a mechanism for varying the speed of the film drive motor, means is provided by the present invention for rotating the housing of the motor in response to change in slope of the sloped cam as the cam and the shaft of the motor are rotated in synchronism. In this manner, the motor shaft, which can be coupled to drive cylindrical film cassette 46 will have a variable speed with respect to the motor housing as determined by the slope of the cam of FIG. 14B. The film drive means utilizing the concept is illustrated in FIGS. 15-17. Film cassette 46 and the drive mechanism therefor are mounted inside housing 45 which includes an x-ray slit 144 in its lower portion as shown in FIG. 15, x-ray slit 144 being aligned with an x-ray beam from x-ray source 44. Thus, as film cassette 46 is rotated to rotate unexposed x-ray film 140 past slit 144, film 140 is exposed to the x-rays in the conventional manner. As show in FIG. 16, a constant speed electric motor 145 having an output shaft 146 may be connected to a suitable bushing 147 mounted on the rear plate 45a of film holder housing 45 so that shaft 146, or an extension thereof, extends through an opening in plate 45a. The housing of motor 145 is free floating as hereinafter described. Shaft 146 extends inside housing 45 to support a pulley 148, a motor housing lever arm 149, and a magnetic clutch mechanism 150, having spaced permanent magnets 151 on it (see FIG. 15). Cylindrical film cassette 46 includes a metal plate 152 located on the rear thereof so that film cassette 46 may be mounted on clutch 150 and supported thereon for rotation by force of magnets 152, and yet be easily removed when required. A guide rod 153 may be provided at the center of clutch 150 which fits in an opening in the center of the rear plate of film cassette 46, to properly position film cassette 46 on clutch 150, and film cassette 46 may include a central handle 154 extending from the center of its bottom plate, for aiding in placing and removing film cassette 46 on magnetic clutch 150. Thus, with the apparatus described, as motor 145 rotates it functions to rotate film cassette 46 at the speed of rotation of shaft 146. Cam 143 is rotatably mounted on the rear plate 45a of housing 45 by a shaft 155 on which a pulley 156 is mounted. A timing belt 157 is connected between pulleys 148 and 156 so that these pulleys and sloped cam 143 rotate in synchronism with shaft 146 as motor 145 is operated. However, the housing of motor 145 is connected by a pair of rods 158 through a slotted opening 158a in rear plate 45a, and rods 158 are rigidly connected to an end of a lever arm plate 149. As illustrated in FIG. 15, lever arm 149 is pivotally mounted intermediate its ends about shaft 146 so that it can pivot with respect to the shaft, and a cam follower idler wheel 159 is mounted at the end of lever arm 149 opposite the end to which rods 158 are connected, for following the rotation of sloped cam 143. A spring 160 is connected between the end of lever arm 149 on which idler wheel 159 is mounted and the backwall 45a of housing 45 so that idler wheel 159 is resiliently urged against sloped cam 143 as the cam is rotated. Since lever arm 149 is free to pivot about shaft 146, and since the housing of motor 145 is rigidly connected through rods 158 to the opposite end of lever arm 149, as lever arm 149 pivots about shaft 146 between the dotted line positions 149a and 149b shown in FIG. 15, the housing of motor 145 rotates with respect to shaft 146 to increase or decrease the relative rotational speed of the shaft. As illustrated in FIG. 15, when cam 143 is at its minimum diameter 143a at the point where it is engaged by idler wheel 159, plate 149 is in the dotted line position 149a, and when cam 143 is at its maximum diameter 143b at the point where it is engaged by idler wheel 159, plate 149 is in the position 149b. In order to control the rotation of film cassette 46 and cam 143, a microswitch 161 is mounted on a plate 162 extending between shaft 155 and a slotted opening 163 in wall 45a. A notch 164 may be provided in pulley 156 so that the contact arm of switch 161 moves in and out of the notch as pulley 156 is rotated. The operation of switch 160 in controlling the operation of motor 145 is described with reference to FIG. 22. By mounting plate 161 in the manner shown in FIG. 17, it can be pivoted about shaft 155 to adjust the position of switch 161 with respect to notch 164 when film cassette 46 is at a desired stopping position. Suitable distinctive marks may be provided on film cassette 46 and on housing 45 for ensuring that the operator properly orientates the film cassette when it is installed. Also, a friction brake (not shown) can be provided on shaft 155 to place a constant drag on the rotation of shaft 146 to reduce the chances of backlash or jitter. With the arrangement described utilizing sloped cam 143, the direction of the slope of the cam is responsible for an increase or decrease in the speed of rotation of shaft 146, while the degree of the slope is responsible for the magnitude of the speed variation as the shaft rotates. The range of speed variation is limited by the physical size of the sloped cam and the cam follower wheel 159. By use of a maximum 6 inches diameter cam, speed variations up to plus or minus thirty percent can be provided, if required. Also, it is preferred that film holder 45 be slidably mounted on two spaced apart rods 165 mounted on disc 42 so that film holder can be moved between and positioned at the dotted and solid line positions shown in FIG. 9. ELECTRICAL AND HYDRAULIC CIRCUITRY Referring now to FIGS. 18-22, the electrical and hydraulic circuitry for controlling the operation of x-ray apparatus 30 is illustrated. FIG. 18 illustrates a block diagram of the overall electrical system of apparatus 30 and the heart of this system is a multi-position, multi-step programmer 170 which is stepped between its respective steps by a stepper motor 171. Programmer 170 controls the sequence of operation of the various components of apparatus 30 in response to an operator command and automates this operation as much as possible to avoid the necessity of operator intervention in any desired sequence of operations. In the example shown of the present invention, prorammer 170 has at least 26 separate switching positions, each of which may be programmed to be either an open circuit or closed circuit in one or more of a series of 60 consecutive steps from a home position back to the home position, representing a complete cycle of a programmer. In addition to the programmer, the electrical control circuitry of FIG. 18 includes a remote control circuit 172 which permits the operator to remotely control the operation of the x-ray apparatus without being exposed to high voltage x-rays, and x-ray circuits for 173 for controlling the application of high voltage to x-ray source 44. As illustrated in FIG. 18, switch positions 1, 2, 4, 5, 6 and 7 of programmer 170 may be utilized to control the sequence of operation of the x-ray circuits 173 as the programmer moves between its sequential steps. Also, a disc drive and camera shift circuitry 174 is connected to positions 8, 9, 10, 24 25 and 26 of programmer 170 for controlling the rotation and direction of movement of disc 42, and the orientation of source 44 during various steps of the x-ray cycle and during the different modes of operation. Details of a preferred form of circuitry 174 are illustrated in FIG. 21. Position 11 of programmer 170 may be used to control the application of an electrical brake 175a provided from a D.C. source 175b to motor 63 for stopping the rotation of disc 42 at a desired position. A film cam drive circuit 176, illustrated in detail in FIG. 22, is connected to programmer switch 12, and programmer switches 13-19 are connected to the gimbal shift control circuitry 177, illustrated in detail in FIG. 20, for controlling shifting of gimbal frame 50. Switch positions 20-23 of programmer 170 are utilized to control the sequence of operation of a control circuit and mode switch (shown in FIGS. 20 and 21 by the reference MS) which in turn controls the operation of programmer 170 and the mode of operation of x-ray apparatus 30. In a preferred form of x-ray apparatus described, two modes of operation are provided, referred to herein as mode 1 and mode 2. Mode 1 represents the operation of x-ray apparatus in x-raying the frontal portion of the head or skull, including the dental arch, whereas mode 2 represents application of the x-ray apparatus 30 to x-raying the back portion of the skull. The operation and structure of the present invention is shown and described herein as in mode 1 except as otherwise noted. Thus, by the provision of these two modes of operation, along with the ability to adjust the position of the subject being x-rayed in the machine and select a desired shift within the limits described tomographs of a desired portion or adjacent portions of the skull can be readily provided by the apparatus of this invention. The principles utilized by the invention to accomplish this can also be readily adapted to providing tomographs of other selected portions of the human body. As a matter of convenience, and in order to establish the sequence of operation for a programmer 170 and the apparatus of this invention, switch positions 1-27 can be utilized for mode 1 operation with position 60 being the home position, and switch positions 28-54 can be utilized for mode 2 operation, again with step 60 as a home position. Positions 55-59 are not used except that position 59 may provide an event signal signalling that one more step is required to move the programmer to home position 60. An event signal is provided by switch position 3 on programmer 170 to operate an event counter which keeps count of the programmer cycles. In the following description and in FIGS. 20-22 each of the switch positions of programmer 170 is represented by the letter S followed by the number of the switch position. Also, L1 represents one side of an A.C. input voltage, L2 the other side (or common), and X represents switched voltage L1, which may be provided by a push button remote switch permitting the operator to operate apparatus 30 from behind a protective shield. Programmer 170 may include an internal control relay (not shown) and an external micro-switch SS1 which is actuated mechanically each step to ensure that the programmer has made a complete step. In the preferred embodiment of this invention illustrated switch positions 20-23 may be utilized to control the stepping of programmer 170. Also, a micro-switch SA may be mounted on frame 50 adjacent the top of disc 42 (see FIG. 2) and switch actuators may be located at the -9.degree., -60.degree., -120.degree., +9.degree., +60.degree. and +120.degree. positions of disc 42 for actuating switch SA, which is connected to ensure the full stepping of programmer 170 when actuated. The relationship of the positions of the switch actuator or disc 42 to the operation of apparatus 30 is explained with reference to the description of FIGS. 23A, 23B, 24A and 24B. The manner in which shift selector switch 88 controls shift solenoid 71, through lines Z5 and Y5 is also illustrated in FIG. 20. Switch 88 is shown as a rotary switch having three sections, 88a, 88b, and 88c, each with positions 1-15 corresponding to the position of knob 89. Micro-switches 78b, 82 and 83 are connected in series between a source of electrical current (lines X and L2) and the solenoid coils of solenoid valves 71, and are shunted by programmer switches S18, S17 and S19, respectively, so that the programmer can selectively override the action of the micro-switches to cause a shift limit to be passed. Programmer switches S13 and S14 are also connected to the circuit through a section of a mode switch MS to switch power to the shift circuit during either mode 1 or mode 2 of operation, and the duration of shift is controlled by programmer switches S15 and S16 which switch the current to either section 88a or 88b of switch 88 to in turn control which of llines Z5 or Y5 is actuated. During any shifting operation of frame 50 of x-ray apparatus 30, it is preferrd that the high voltage to source 44 be cut off, and programmer switch S7 provides this function. Section 88c of switch 88 is used to shunt programmer switch S7 to override the cut off of the x-ray source when no shift is selected by the operator (i.e., knob 89 is set at the mid position 8). Referring now to FIG. 21, wherein the control circuitry for excursion motor 63 is illustrated, the direction, movement, and braking of motor 63 are provided by relays K3, K4, K6 and K8. Relay K3 is connected to conduct D.C. voltage from a conventional A.C. to D.C. power supply 210 to apply a D.C. brake to motor 63 when switch contact S11 of programmer 170 is actuated. Relay K4 is connected to reverse the polarity of the line voltage driving motor 63 when switch contact S10 of programmer 170 is actuated. Relay K8 functions as a camera shift relay which is latched by one of its terminals and switch S24 to control the shifting of disc 42 between the respective starting positions in the two modes of operation. Relay K6 enables control switch S25 of programmer 170 which permits selected shifting of the camera during selected steps of the program. The function of these relays and their associated switches are explained with respect to the description to follow of the operation of apparatus 30 in FIG. 23A, 23B, 24A and 24B. Referring now to FIG. 22, the preferred form of control circuitry for operating film drive motor 145 is illustrated. A double pole, double throw relay K9 is provided and this relay switches the input terminals of motor 145 between a source of running current between lines X and L2 and a capacitor brake illustrated generally by the numeral 211. Programmer switch S12 is in series with the control voltage of motor 145, as is limit switch 161 which is mounted on plate 162 to be actuated by pulley 156 as shown in FIG. 17. Switch 161 is shown in FIG. 22 in the position it is in when its actuator arm is in notch 164. Thus to start the movement of motor 145 with switch 161 in this position, it is necessary for programmer 170 to move to a position where switch S12 is closed. This causes relay K9 to switch to actuate motor 145 which, in turn, causes notch 164 to move away from the actuator of switch 161, thus closing switch 161 to continue to operate motor 145. Motor 145 runs until a complete cycle is completed (i.e., the film is fully exposed) at which time the actuator arm of switch 161 again drops in notch 164, releasing relay K9 to apply a D.C. braking voltage to motor 145. As illustrated, brake 211 includes bridge rectifier 212 for converting voltage between lines X and L2 to a D.C. voltage, and a capacitor C1 connected across bridge rectifier 212 and to motor 145 when relay K9 is released. Thus, during operation of motor 145, capacitor C1 is charged and this charge is utilized to apply a braking current to motor 145 to cause it to accurately stop each time a complete cycle of rotation for film cassette 46 is provided, or if excursion is to be stopped at will at any time during the excursion. OPERATION OF THE X-RAY APPARATUS Referring now to FIGS. 2, 23A, 23B, 24A and 24B, operation of x-ray apparatus 30 will be explained with reference to the two mode of operation provided by the preferred embodiment illustrated. In this description it is assumed that patient P has been properly positioned in x-ray apparatus 30 for the start of operation in the selected mode and that the desired gimbal shift for frame 50 has been selected, and that only initiation of a cycle start button (generally a remote pushbotton, dead man type switch) is required. In positioning the head of the patient in the dental mode a clear plastic, L-shaped guide plate 250, with lines 251 on it at about 20.degree. with respect to the vertical may be placed against film holder 45 is shown in FIG. 9 to permit the inferior border of the mandible to be lined up with one of lines 251. This ensures that the dental arch will be x-rayed without projecting x-rays through bone structure that would cast shadows on the image. Also, reference herein to the angular position of the disc 42 refers to the angular positions shown in FIG. 2. At the start of any cycle of operation in mode 1, programmer 170 is in its home position 60 so that the next adjacent position of the programmer is step position 1. Also, in this position of the programmer, by completion of a previous cycle disc 42 has automatically been driven to position where source 44 and film holder 45 are in line with vertical centerline CL (the solid line position of source 44 and film holder 45 in FIG. 2). In response to an operator command, such as by actuation of an "initiate" switch, programmer 170 is caused to move from its home position to step position 1, the start of mode 1. By energizing a remote pushbutton switch, the mode 1 cycle begins at which time the programmer switches 8 and 10 are actuated for driving the excursion motor in the counterclockwise direction to move the film holder 45 and source 44 to the solid line position shown in FIG. 23A where film holder 45 is at -120.degree., while film 140 is started to rotate in holder 45 past slot 144. Also, since the cycle started with frame 50 at the 0.degree. shift position, programmer switch S13, which activates the gimbal shift in mode 1, and programmer switch S15 which causes the shift to move in a clockwise direction, are actuated along with programmer switch S18 bypassing center limit switch 78b. Also, actuation of shift control switch S13 (S14 in mode 2) supplied power to line W (FIG. 20) interrupting fluid bypass 197 so that shift cylinder 70 is operated at a higher speed than the rate of the other cylinders. This causes cylinder 70 to move frame 50 for one-half of the full amount of the selected shift so that its vertical centerline is now located at line CL' in FIG. 23A. This shift is disabled as film holder 45 reaches the -9.degree. position (FIG. 2) where microswitch SA is actuated to cause programmer 170 to step from positions 1 to 2. The disc excursion continues to move film holder 45 through the -60.degree. position (FIG. 2) to the -120.degree. position shown in solid lines in FIG. 23A where the counterclockwise motion of the disc is stopped, and the x-ray source filament is turned on by a programmer switch S5. Programmer 170 automatically steps to the next step portion 5 and programmer switch S10 is released to change the polarity of the excursion drive motor to cause rotation of disc 42 in a clockwise direction. The programmer goes through steps 6, 7 and 8 and at step 8, the clockwise run of disc 42 is started by again actuating programmer switch 8 and turning on the high voltage (done at stepper position 9 by programmer switch S7) to start the x-ray cycle. Film holder 45 moves from the -120.degree. to position through the -60.degree. position to the -9.degree. position during stepper positions 9-11, at which time the high voltage to the x-ray is cut off by releasing programmer switch S7, and the full shift of gimbal frame 50 is initiated by actuation of programmer switches S13 and S16. Limit bypass switches S18 and S19 are actuated during this step so that switch actuator 78 moves from right limit switch 83 to left limit switch 82, which has not been bypassed, at which time the shift is cut off. Thus, the positions of switches 82 and 83 with respect to each other determines the extent of the shift. When this shift occurs, frame 50, x-ray source 44 and film holder 45 are moved to the solid line positions shown in FIG. 23B, where the vertical centerline of frame 50 is indicated as being the line CL". During shifting the excursion motor is kept running so that film holder 45 passes through the 0.degree. position of FIG. 2, and when the +9.degree. position is reached, the x-ray high voltage source is again turned on by actuation of programmer switch S7. As the programmer steps from step positions 12 to 14, film holder 45 moves respectively through the +60.degree. and to the +120.degree. position. At stepper position 14, the high voltage and filament to x-ray source 44 is cut off by deactivating programmer switches S4, S5 and S7, and the clockwise excursion of disc 42 is disengaged. In steps 15 through 18 of the programmer, the polarity of the A.C. driving of excursion motor 63 is reversed, and in stepper positions 19 and 20 the excursion motor is driven back in a counterclockwise direction until film holder 45 reaches the +9.degree. position at which time the left limit bypass provided by programmer switch S17 is activated, and the center line switch 78b bypass provided by programmer switch S18 is removed, permitting a one-half shift of frame 50 back to its original starting position. Positions 22 through 26 of stepper are utilized to stop the excursion of disc 42 and the shift and to set the apparatus for the start of the next cycle. Step positions 26 and 27 are utilized to automatically step programmer under control of programmer switch S21 to the home position 60 as soon as the remote pushbutton switch is released. Thus, as illustrated in FIGS. 23A and 23B, a panoramic radiograph of the front portion of the head of patient P may be provided, with a first half section being x-rayed by rotating disc 42 120.degree. about one center of rotation C', and a second half being x-rayed by rotating disc 42 120.degree. about another center of rotaton C". FIG. 25 illustrates an example of such a radiograph taken in mode 1 through the dental arch. The center, unexposed area 140a represents the movement of film 140 and disc 42 through the -9.degree. to +9.degree. excursion described. FIGS. 24A and 24B illustrate the sequence of operation of apparatus 30 in mode 2 wherein the back of the head of patient P is x-rayed. As noted, stepper positions 28 through 54 are utilized for mode 2 operation and at the start of the mode 2 cycle film holder 45 must be shifted to the -60.degree. position in order to permit proper placement of the patient in the apparatus so as disc 42 rotates to the start position, the patient's head will not be struck. This placement is different in mode 2 because in this mode the film holder 45 passes round the back of the head of the patient and the x-ray source 44 passes about the front of the head. For sake of convenience, when mode switch MS is switched to mode 2, and prior to the mode 2 run, programmer 170 can be caused to run the excursion motor in a counterclockwise motion until film holder 45 is just prior to the -60.degree. position. At this time film holder 45 will be in a start mode 2 position and the patient may be loaded into the apparatus. At the initiation of the mode 2 cycle, programmer 170 will step to position 28, the start of mode 2. Energizing the remote pushbutton switch will cause disc 42 to rotate in the counterclockwise direction to move x-ray source 44 and film holder 45 to the dotted line position shown in FIG. 24A where film holder 45 is at the +60.degree. position which is the position at which the x-raying of the back of the head begins. During this rotation of disc 42 which is controlled by stepper positions 18-38, when film holder 45 passes from the -171.degree. position to the+171.degree. position, one-half of the alloted shift for frame 50 is provided to move line CL to CL' as shown in FIG. 24A. When the +60.degree. position for film holder 45 is reached, the polarity of excursion motor 63 is reversed at stepper position 39, the x-ray source turned on, and disc 42 is rotated clockwise to move film holder 45 back past the +171.degree. and -171.degree. positions, between which the full shift of gimbal frame is provided (at the solid line position of FIG. 24A) moving centerline CL from line CL' to line CL" as shown in FIG. 24B. Again, the high voltage source is disabled at the +171.degree. position of film holder 45 and enabled again at the -171.degree. position of film holder 45 so that no x-rays are provided as the apparatus passes about the center of its rotation, generally at a time when the spinal cord of the patient would be in line with the x-rays. As shown in FIG. 24B, after shifting, source 44 and film holder 45 (now in the dotted line position) move in the clockwise direction to the solid line position shown for x-raying the last half of the portion of the skull being x-rayed. When the solid line position of FIG. 24B is reached, represented by return of film holder 45 to the -60.degree. position, the x-ray source is cut off and disc 42 is automatically caused by programmer 170 to move to its home position as programmer 170 moves to home position 60 after the remote pushbotton switch is released. This is to prepare x-ray apparatus 30 for the start of another cycle of operation. Also, the one-half shift is initiated to bring line CL back to its starting position at vertical dead center. In both mode 1 and mode 2, at the time that the cycle is initially turned on, programmer switch 12 is actuated to bypass microswitch 161 and start the rotating of film 140 and this rotation continues at least for the time during the x-ray scan when source 44 is on, but generally longer as shown by the unexposed portions of the film on either side of the exposed portions. The position of switch 161 with respect to notch 164 can be adjusted to cause the movement of film 140 to stop upon completion of a full cycle of operation. Of course, the sequence of operation of the various components of x-ray apparatus 30, and the various positions of disc 42, source 44, and film holder 45 can be varied as required for a specific x-ray operation. However, with the two modes of operation described, x-ray can be provided of both the front portion of the patient's skull, including the dental arch, and of the back portion with appropriate shift provided for providing a desired focal trough or avoiding the passage of x-rays through the patient's spinal cord, or other objects which would provide shadows that decrease the clearness of the x-rays. As shown in FIG. 9, by the dotted line positions for x-ray source 44 and film holder 45, the line of sight of source 44 and holder 45 with respect to each other can be changed during the different modes of operation to direct the x-ray beams through a desired portion of the skull, once the position of headrest 41 is set (which, of course, can also be adjusted). As noted in FIG. 9, x-ray source 44 may be mounted to swivel on a bracket 44a, and the solid line position shown represents orientation of x-ray source 44 at a 7.degree. angle with respect to vertical. This position, which is suitable for x-raying a dental arch, requires that film holder 45 be located in the solid line position shown. For mode 2 operation, where the back of the head is being x-rayed, x-ray source 44 can be positioned in the vertical dotted line position, and film holder 45 positioned in the outer dotted line position as illustrated in FIG. 9. Also, while the x-ray source is normally cut off during shifting of frame 50, when selector switch 88 is in position 8 and no shift is provided, programmer switch S7 can be actuated to bypass the x-ray cut off function and provide a continuous x-ray without the unexposed center area 140a. An important feature of the present invention is that adjustments by the operator to properly set the apparatus for a desired operation are minimized. In the usual situation, other than setting the orientation of the x-ray source with respect to vertical and positioning of film holder 45, which settings may remain fixed through a large number of x-raying operations, the operator needs only to dial in the direction and amount of shift for frame 50 and orientate and position the patient's head at the correct object-to-film distance, by use of tape measure 47. With reference to FIG. 2, position 8 on scale 90 represents zero shift of frame 50; positions 1-7 represent negative shifts in one-half centimeter increments where the left half (0.degree. to -120.degree. ) of the rotational scan is taken from a shifted center of rotation C" (shown at the extreme negative shift provided at position 1 for knob 89); and positions 9-15 represent positive shifts in one-half centimeter increments where the left half of the rotational scan is taken from shifted center of rotation C' and the right half scan is taken from shifted center of rotation C" (shown at the extreme positive shift provided at position 15 for knob 89). FIGS. 26-28 illustrate the manner in which the proper shift may be provided to obtain the best line of focus of a portion of the skull to be radiographed. In FIG. 26, a preferred form of a slide rule profile projector 220 is illustrated which includes two members 221 and 222 mounted in any suitable manner to slide with respect to each other, such as by a pin and slot arrangement. Members 221 and 222 may be made of transparent plastic and one of the members includes a scale 223 on it which is numbered from 1 to 15 (corresponding to the numbers of knob 89 and scale 90) and the other member includes an arrow 224 on it which is adapted to move along scale 223 as members 221 and 222 slide with respect to each other. For example, in the preferred embodiment illustrated of projector 220, member 222 can be moved back and forth on member 221. As illustrated in FIG. 26, member 221 includes an arcuate section 221a which is shaped generally to conform with the outline of a cross section through the left half of the skull of a human, particularly through the dental arch. A similar arcuate section 222a is provided on section 222 for the right half skull cross section. These curved sections are similar to the curved faces of basic cam 142 since they represent the actual line of focus of apparatus 30. Thus, as illustrated in FIG. 27, wherein a cross section of a human skull is illustrated through the dental arch, with the spine S shown in the approximate center thereof, slide rule profile projector 220 can be overlayed on the cross section with arcuate section 221a located along the left side of the dental arch and arcuate section 222a located along the right section of the dental arch. When this is done, the position of arrow 224 with respect to scale 223 can be read on scale 223, for example, between positions 5 and 6 as shown in FIG. 26, representing a negative shift of the center of rotation C from position C' to position C". Switch selector switch 88 can be correlated with these readings in a manner so that by selecting switch position 6 on knob 89 the required shift for providing the full x-ray of the dental arch shown in FIG. 27 can be provided. Because of the relatively wide focal trough 225 and 226 provided (represented by the dotted lines in FIG. 27) and the overlap between the left half and right half scans, the shift of frame 50 does not have to be precise and 1/2 to 1 cm. steps between shift provides satisfactory resolution. By appropriate selection of the center of rotation of disc 42, a slight overlap between the left side and right side x-ray scans or radiograph 140 can be provided so that a full picture of the dental arch is illustrated. FIG. 28 represents the use of projector 220 to determine the setting for knob 89 to x-ray selected portions of the lower portion of a skull, represented in cross section in FIG. 28. As shown, a positive shift sufficient to move center of rotation C from position C' to C" is indicated by scale position 10.4, or position 10 for knob 89. Thus, the best line of focus outline can be determined with projector 220 by sliding arrow 224 on movable portion 222 toward a greater position number on scale 223 (9-15) for an increasing focal diameter, or toward a smaller number on scale 223 (1-7) for a decreasing focal diameter. The curved outlines 221a and 222a represent, in either case, the resulting line of best focus. The center gap, at a position for arrow 224 greater than 8, indicates the area missed by the radiograph. Conversely, the center overlap of the two curved sections represents the object overlap on position numbers smaller than 8 when the corresponding shift number is dialed into the shaft selector switch 88. A center white stripe will show on the radiograph as a result of the x-ray cutoff during shift, except during no shift position 8. Also, as shown in FIG. 26, a ruler 230 scaled, for example, in centimeters (assuming that tape measure 47 is similarly scaled) may be mounted on projector 220 for determining the correct object-to-film distance when positioning the head of the patient in apparatus 30. As shown in FIGS. 27 and 28, this distance would be about 81/2 cm. when projector 220 is overlayed on the skull cross sections illustrated. Persons with a larger or smaller head would provide different readings. The reading on ruler 230 can be read on tape measure 47 to set the distance to the outer extremity of the portion of the skull from slit 144 in film holder 45. The skull dimensions of the patient for determining the size of the skull cross section section shown in FIGS. 27 and 28 can be readily determined in a conventional manner by the radiologist or technician. As illustrated in FIGS. 27 and 26 by focal troughs 225 and 226, and in FIG. 26 by a representative radiograph actually provided by use of an x-ray apparatus constructed in accordance with this invention, the resulting radiographs from this invention are provided of a continuous curved plane having a depth of focus of, for example, 1/2 cm. Thus, a zone of focus suitable for tomography and zone laminography is provided to provide a definitive picture of the examined area. By offsetting successive radiographs at, for example, in 1/2 cm. steps, on either side of an area being examined, the effective depth of focus can be increased and a three dimensional picture of the examined area can be provided to improve the diagnostic use of the radiographs. Also, while in the embodiment illustrated, the best line of focus is represented by curved section 221a and 222a, which are determined by the configuration of sloped cam 143 (which is, in turn, determined by the configuration of basic cam 142), different configurations of cam 143 can be used and corresponding different lines of focus provided by proper shaping of sections 221a and 222a. This is accomplished again by translating the shape of a basic cam corresponding to desired lines of focus to the required sloped cam shape as heretofore explained. Thus, by providing effective means for changing the shape of the focal trough, by providing for changing the width of the focal trough by selecting different shifts for gimbal frame 50, and by providing for relatively easy selection of different orientations of the object being examined and the object-to-film distance, a highly versatile x-ray apparatus with a wide range of capability for medical and dental application is provided. Further, by the use of an automated programmer and automatic limit switching during patient placement and positioning, the chances of operator error or misjudgment are greatly reduced. The capabilities of the x-ray apparatus of this invention compare very favorably with x-ray apparatus that are a good deal more complex and many times more expensive. From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus. It will be understood that certain features and subcombinations are of utility and may be employed with out reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense. |
047724455 | abstract | A system which measures direct current drift and noise in sensor signals from redundant sensors utilizing a parity-space algorithm. Parity vector signals produced by the parity-space algorithm are averaged to provide a direct current (DC) drift signal. An instantaneous noise signal is found by subtracting the direct current drift signal from a parity vector signal for one of the samples of the sensor signals. The RMS value of the instantaneous noise signals are averaged to provide sensors noise signals. |
abstract | ||
description | 1. Field This invention pertains generally to electrical generators and more particularly to a solid state assembly that generates electricity in response to a relatively low radiation environment. 2. Related Art Events in Japan's Fukushima Dai-ichi Nuclear Power Plant reinforced concerns of the possible consequences of a loss of power over an extended period to the systems that cool the nuclear reactor core and spent fuel pools. As the result of a tsunami there was a loss of off-site power which resulted in station blackout periods. The loss of power shut down the reactor and spent fuel pool cooling systems. The water in some of the spent fuel pools dissipated through vaporization and evaporation due to a rise in the temperature of the pools heated by the highly radioactive spent fuel assemblies submerged therein. Without power, over an extended period, to pump replacement water into the reactor and into the spent fuel pools the fuel assemblies could potentially become uncovered, which could, theoretically, raise the temperature of the fuel rods in those assemblies, possibly leading to a breach in the cladding of those fuel rods and possible escape of radioactivity into the environment. The total loss of power for the equipment and sensors experienced by the Fukushima Dai-ichi units following the devastating tsunami resulted in an inability to control the valve functions needed to maintain fuel assembly cooling. It is an object of this invention to provide a device capable of passively providing the electrical current required to greatly extend the ability of the nuclear station batteries to control the core cooling and monitoring systems, enabling them to continue to perform the required critical functions during a station blackout. These and other objects are achieved by a solid state electrical generator having an electrically conductive housing with a radiation responsive material supported within the electrically conductive housing. The radiation responsive material is responsive to background radiation within a nuclear power generating facility, outside of the nuclear reactor, but within the vicinity of nuclear fuel rods, to generate sufficient electricity to operate or substantially fully charge batteries that operate emergency equipment within the facility. An insulator is situated between the radiation responsive material and the housing. In one embodiment, the electrical output of the radiation responsive material increases over a given period of time within a field of the background radiation. After a first given number of operating cycles of the nuclear reactor, the electricity produced by the radiation responsive material is sufficient to operate or substantially fully charge the batteries that operate the emergency equipment even with the reactor shut down. Preferably, the radiation responsive material is not radioactive until it is placed within the background radiation. In addition, the electrically conductive housing can be thin enough to fit within a space between a wall of the reactor cavity within which the nuclear reactor is supported and the outside of the pressure vessel that houses the core of the nuclear reactor. In one embodiment, the radiation responsive material is a gamma radiator substantially sandwiched against a gamma and electron radiator. In one such embodiment, the radiation responsive material is a combination of Co-59 and tungsten. Preferably, the electrically conductive housing and the radiation responsive material are flexible. In still another embodiment, an electrical insulator seal gasket is supported between a backside of the housing and the gamma radiator and electrically insulates the backside of the housing from a front side of the housing which forms a collector. The invention also contemplates a nuclear power generating facility including such a solid state electrical generator. FIG. 1 shows a side view and FIG. 2 shows a front view of a schematic representation of one exemplary preferred embodiment of the principles claimed hereafter. The electrical current generator illustrated in FIGS. 1 and 2 is a solid state device having an outer housing 12 with an electrically conductive front end 14 which is sealed from a back end 16 by an insulator seal gasket base plate 18. A radiation responsive material 20 is disposed between the front end of the housing 14 and the insulator seal gasket face plate 18, with insulation 26, such as Al2O2 disposed on both sides of the radiation responsive material 20 between the radiation responsive material and the front of the housing 14 and between the radiation responsive material 20 and the insulator seal gasket face plate 18. The insulator seal gasket faceplate 18 keeps electrons being “pushed” into the device from the face nearest the external gamma radiation source (e.g., the reactor vessel) from canceling out the electrons generated by the internal gamma emitter. The radiation responsive material 20, in this embodiment, is formed from a gamma radiator material, such as, for example, Co-59 that is substantially sandwiched against a gamma and electron radiator such as tungsten with an electrical lead 28 forming an emitter that conducts the electron path between the utilization device that is to be powered and the current generator 10. The front portion of the housing 14 forms the collector. The term “gamma radiator” is used to denote a material that emits gammas in response the decay or capture within the material of either neutrons or gamma as a result of incident radiation. Similarly, the term “gamma and electron radiator” is used to denote a material that emits electrons in response to the decay or capture within the material of gammas or neutrons. FIG. 3 shows a schematic representation of the electrical current production mechanism of this exemplary embodiment of the invention claimed hereafter. When the device 10 is irradiated by a neutron and/or gamma source 30, some of the radiation decays and is captured within the radiation responsive material, which emits electrons that are collected by the front end of the aluminum housing 14, to establish an electrical current 32 which flows from the emitter 28 to the collector 14. The surface area and thickness of the gamma radiator, (e.g., Co-60) and the corresponding surface area and desired thickness of the gamma and electron radiator, e.g., tungsten, may be adjusted by those skilled in the art to achieve the desired electrical current generation within the expected neutron and gamma radiation fields. The thickness of the insulation 26 between the radiator elements 20 and the outer collector 14 may also be optimized by those skilled in the art to produce the maximum current without suffering from shorting between the two regions within the expected operating temperature range of the device. As FIG. 3 indicates, the primary source of electric current in this device is a function of time, I(t). Generated within the device are Compton and photo-electrically scattered electrons produced in the tungsten plate 24 adjacent to the cobalt-59 plate 22, by the gamma radiation produced by Co-60 generated by neutron interactions with Co-59 in the Co-59 plate. In addition to this mechanism for electric current production, the prompt capture gamma radiation released when a neutron is captured by a material such as tungsten will also produce Compton and photo-electrical scattered electrons that have sufficient energy to cross the gap between the radiator 20 and the collector 14. The surface area of the device can be made very large. The device can also be very thin and flexible. FIG. 4 shows an example of a potential application. A reactor vessel 34 is supported within the reactor cavity 36 and encloses a reactor core 38 housing the nuclear fuel assemblies. The cavity walls 40 extend around the vessel 34 over the height of the core 38 and the walls 40 support the device 10 of this invention over at least a portion of the height of the reactor core 38. Thus, the device can be used to line the reactor vessel cavity and utilize the wasted neutrons and gamma radiation that leaks out of the reactor vessel 34 to generate valuable electrical current. FIG. 5 shows a plan view of a cross section of the reactor cavity having the device 10 wrapped around at least a portion of the cavity walls 40. FIG. 6 shows another potential application for this device to a spent fuel pool 42 having racks of spent fuel assemblies 44 suspended within a coolant 46. The device 10 can be supported by the pool walls below the coolant 46 water level as shown at location 50 or it may be suspended from the walls above the coolant level as indicated by the locations 48. Multiple devices 10 can be spread around the spent fuel pool 42 and connected in series or parallel as needed to meet the requirements of equipment that it is intended to power. The device 10 may be used, for example, to power valves 52 for replenishing coolant 46 that may have evaporated from the pool or a recirculation system 54 for removing heat from the coolant 46. This operating principle can be achieved using materials other than cobalt and tungsten. An important feature of this design is the use of materials that are able to produce electrical power when placed inside a relatively low neutron and gamma radiation field and will essentially breed material to enhance the power produced by the device sufficiently to allow the device to provide sufficient power to the batteries that supply power to critical instrumentation and safety equipment, even though the reactor or other source of neutron and gamma radiation has shut down. Preferably, the device is not initially radioactive. An estimate of the amount of electric current that may be generated from ex-vessel deployment of this device in a twelve foot by twelve foot, by 0.5 inch device for the AP1000 nuclear reactor system available from Westinghouse Electric Company LLC, can be generated from information on the nominal neutron flux and gamma radiation dose inside the vessel cavity, the Co-60 generation rate, the capture gamma production rate in tungsten and the available current production sensitivity of tungsten (Mirion IST). The results of this simple calculation indicate that the device will output at least a steady three Amps of current following reactor shutdown after one cycle of operation. This amount can easily be increased by a factor of ten with proper optimization of the thickness of the gamma radiator and the gamma and electron radiator. This amount increases linearly with time until a significant amount of the Co-59 is converted to Co-60. After two cycles of operation, the output current will be twice as much. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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description | This application claims priority from U.S. Provisional Application Ser. No. 61/473,998 filed Apr. 11, 2011, which is incorporated herein by reference in its entirety. The invention is related to the field of nuclear power plant inspection, and in particular to a wireless underwater robot for nuclear power plant inspection. There is an increasing need for stringent inspection of nuclear power plants. In particular, the inside structure of a reactor and its associated equipment and instrument are of high priority. Many of these internal structures are currently inaccessible for the human and have been left uninspected. Prior work on underwater robots for nuclear reactor inspection exists, but these robot systems are not wireless; a long cable wire is used for communication and control as well as for powering the robot. Cables not only prevent the robot freely move within the reactor and adjacent area, but also get contaminated with radioactive materials, which make the maintenance and storage of the robot system more difficult and costly. The invented wireless robot is simple, compact, and disposable, and is able to move freely without a tether. According to one aspect of the invention, there is provided an inspection robot for inspecting a nuclear reactor. The inspection robot includes a hull and an on-board control mechanism that controls the operation of the inspection robot. The on-board control mechanism controls one or more sensors used to inspect one or more structures in the nuclear reactor as well as the movement by the inspection robot. A gimbal mechanism rotates the inspection robot hull by shifting the center-of-mass so that gravity and buoyancy forces generate a moment to rotate the hull in a desired direction. A camera is coupled to the gimbal mechanism for providing visual display of the one or more structures in the nuclear reactor. The camera is allowed to rotate about an axis using the gimbal mechanism. A wireless communication link allows the inspection robot to communicate wirelessly to an operator at a remote station. The operator issues commands to the inspection robot using the wireless communication link so as to perform various inspection tasks using the on-board control the gimbal mechanism, and the camera. The inspection robot communicates its findings with respect to the inspection tasks to the operator using the wireless communication link. According to another aspect of the invention, there is provided a method of performing inspection of a nuclear reactor using an inspection robot. The method includes controlling the operation of the inspection robot using an on-board control mechanism. The on-board control mechanism controls one or more sensors used to inspect one or more structures in the nuclear reactor as well as the movement requested by the inspection robot. Also, the method includes rotating the body of the inspection robot using a gimbal mechanism by shifting the center-of-mass so that gravity and buoyancy forces generate a moment to rotate the body in a desired direction. Moreover, the method includes providing visual display of the one or more structures in the nuclear reactor using a camera that is coupled to the gimbal mechanism. The camera is allowed to rotate about an axis using the gimbal mechanism. Furthermore, the method includes allowing the inspection robot to communicate wirelessly to an operator at a remote station using a wireless communication link. The operator issues commands to the inspection robot using the wireless communication link so as to perform various inspection tasks using the on-board control, the gimbal mechanism, and the camera. The inspection robot communicates its findings with respect to the inspection tasks to the operator using the wireless communication link. The invention provides a novel inspection robot used in inspecting a nuclear reactor. The invention addresses two technical challenges of the wireless inspection robot 12 that are 1) how to communicate reliably in underwater, and 2) how to assure that the robot can be retrieved in case of failure. The invention addresses these problems using specific wireless communications that can allow for underwater communication while allowing an inspection robot to determine if its internal components have failed thus allowing the inspection robot to use a horning procedure to head back to its original destination. This lessens the need to have humans exposed to the toxic environment of a nuclear reactor. FIG. 1 is a schematic diagram illustrating an overview of a typical inspection process 2 used in accordance with the invention. An inspection robot 12 is placed in the reactor 6 and is controlled wirelessly by a user at remote station 4. The inspection robot 12 can explore the reactor 6, such as rod structures 15, or it can enter the piping system 14. Moreover, the inspection robot 12 can explore the interior regions of a steam generator 10. The inspection robot 12 includes materials that can prevent water and hazardous materials from destroying its internal electronics as well as protecting against high temperatures. The inspection robot 12 must have a failsafe mechanism that causes it to float back to the surface in the event of any damage, loss of communication, or loss of power. The inspection robot 12 includes a hull, thrusters, battery, an on-board control, inspection sensors, and a wireless communication unit that can access the underwater internal structure of the nuclear reactor and associated equipment, and position and orient the inspection sensors to the various structures positioned in the reactor 6 based on wireless communications with the remote station 4. Moreover, the inspection robot 12 can also be used to inspect a steam generator that is connected to the nuclear reactor 12 thru the piping system 14. FIG. 2 is a schematic diagram illustrating a detailed depiction of the inspection robot 12 used in accordance with the invention. The inspection robot 12 is designed to have a smooth outer surface 21 to minimize drag and more importantly, to prevent snagging or tangling on the reactor structure and sensor probes placed within the pipe. The smooth outer surface 21 can include materials preventing water and hazardous materials from destroying its internal electronics as well as protecting against high temperatures. This means that the use of external propellers or control surfaces is highly undesirable. The inspection robot 12 is equipped with a hull 30, water jet thrusters 32, battery and on-board control 22, fail-safe mechanisms 24, inspection sensors 23, and a wireless communication link 34 that can access the underwater internal structure of the nuclear reactor 6 and associated equipment, and position and orient the inspection sensors 23 to the structures 15 internal the reactor 6 based on wireless communications with the remote station 4. A water intake system 28 is located at the front of the robot 12 that sucks water into an onboard pump. The pump then ejects the water at high speed from selected output ports. The inspection robot 12 moves and maneuvers by controlling which output ports are used. The robot is equipped with a video camera 26 and lights 36 for visual inspection of the structures 6 as well as for navigation of the inspection robot 12. Radio communication is used for the wireless communication between the inspection robot 12 and the remote station 4. However, optical communication, either laser or non-laser, can be used for the wireless communication between the inspection robot 12 and the remote station 4. Also, acoustic communication can be used for the wireless communication between the inspection robot 12 and the remote station 4 as well. In other embodiments of the invention, intermediate underwater robots can be used for relaying communication signals between the inspection robot 12 and the remote station 4. The intermediate robots 16 can be positioned in the piping system 4, as shown in FIG. 1. Moreover, radio communication, optical communication, and acoustical communication can be used for the wireless communication between the inspection robot 12 and the intermediate robots 16. In addition, radio communication, optical communication, and acoustical communication can be used for the wireless communication among the multiple intermediate robots 16 as well as between the intermediate robots 16 and the remote station 4. The inspection robot 12 has a fail-safe mechanism 24 to perform, facilitate, or enable the rescue of the inspection robot 12 in case of failure. The on-board control 22 is capable of detecting a failure of the inspection robot 12. The inspection robot 12 has a balloon that allows it to float to the water surface. Moreover, the inspection robot 12 can perform an emergency homing procedure to go back to the original start point using available resources. In addition, memory is provided to the inspection robot for recording its trajectory and can go back to the origin by back tracking the recorded trajectory. The inspection robot 12 includes a sensor for detecting an emergency signal from the remote station 4, and performs or triggers the emergency homing procedure. When failure in the wireless communication with the remote station 4 is detected, the inspection robot 12 performs or triggers the emergency homing procedure. An intermediate robot 16 can capture, tag, or rendezvous the failed inspection robot and takes it to the original start point. Also, the inspection robot 12 includes water jet thrusters 32 where each having a pump, solenoid valves, and a manifold being used for propulsion and maneuvering. The thrusters 32 are made from a single jet stream by branching it to a plurality of jet streams and controlling individually with solenoid valves. A gimbal mechanism is used for rotating the robot body by shifting the center-of-mass (CM) so that the gravity and buoyancy forces generate a moment to rotate the body in a desired direction. A two-axis Gimbal arrangement generates two orthogonal axes of body rotations by moving a mass in two directions. FIG. 3 is a schematic diagram illustrating the propulsion and maneuvering system 40 used in accordance with the invention having solenoid valves 44 and jet pump 42. To eliminate propellers, the inspection robot 12 has multi-axis water jet system for propulsion and multi-axis maneuvering. It includes a pump 42, solenoid valves 44, and a pipe manifold 48. The jet stream 48 created by the pump 42 branches out to multiple directions, each of which is controlled by a solenoid valve 44. By controlling the valve 44 openings the multi-axis jet streams 46 are accommodated to move the inspection robot 12 in a desired direction. This allows for sideway motion and yaw/pitch rotations in addition to forward motion and depth control. The solenoid valves are positioned on a smooth surface 43. The pipe manifold 48 is positioned in the interior region defining the smooth surface 43. FIG. 4 is a schematic diagram illustrating the gimbal mechanism 50 for two-directional orientation control used in accordance with the invention. The roll and pitch of the inspection robot 12 can be controlled more effectively by shifting the center-of-mass with a multi-axis gimbal mechanism 50. The gimbal mechanism 50 includes two geared motors 52 and a universal joint mechanism 56 with perpendicular axes of rotation. The two geared motors 52 include a roll gimbal motor 58 and a pitch gimbal motor 54. The roll gimbal motor 58 is fixed to the ROV body. The pitch gimbal motor 54 is free to rotate about the roll axis. The roll axis is defined by the outer sphere 60. The universal joint mechanism 56 can include a eccentric steel weight for providing the proper buoyancy. FIGS. 5A-5B are schematic diagrams illustrating a two-axis camera orientation control 66 using the gimbal mechanism 50 in accordance with the invention. A camera 71 is fixed to the body 72 of an inspection robot that can be rotated quickly and stably on a camera axis 76 with respect to the gimbal mechanism 50. The body 72 rotates in the opposite direction to the gimbal motion so that the direction of buoyancy aligns with that of gravity, as shown in FIG. 5A. As shown in FIG. 5B, the motion on the body 72 is produced by the thruster 70. This motion produces a buoyancy force 68 positioned on the vertical centerline 78. Also, the center of mass (CM) 74 and center of buoyancy (CB) 80 are positioned on the vertical centerline 78. When the motion occurs a resulting moment 69 is produced which produces a small deflection 72, as show in FIG. 5A. FIG. 6 is a schematic diagram illustrating the wireless communication architecture 90 used in accordance with the invention. The wireless communication architecture 90 includes an intermediate, signal-relaying robot 96 being used to relay data between the inspection robot 12 and the operator. In order to have a high-speed optical data link at this range (˜10-20 m), visible-light is used as the medium due to favorable signal attenuation characteristics in a water pool 92. The inspection robot 12 has a control system to maintain line of sight with a receiver 100. For communication between the two robots 12, 96, a short-range radio frequency (RF) data link 94 is used. While limited in range (˜2-7 m), this link 94 is much more tolerant to lack of line of sight and varying orientations of the inspection robot 12. The intermediate robot 96 can simply take the data from the RF link 94, and pass it via the optical link 106. In this way, a robust wireless communication system 66 is designed that allows the inspection robot 12 to inspect the interior regions of a nuclear reactor 92. In this case, the nuclear reactor 92 includes a size of approximately 4-5 m in length. Also, the intermediate robot 96 has dimension allowing it to travel in the piping system 104 of the reactor 92. The piping system 104 include a size approximately between 2 and 3 m in length. The invention provides a novel technique to inspect a nuclear reactor using an inspection robot that relies on wireless communication. The invention addresses two critical two challenges of the wireless inspection robot that are 1) how to communicate reliably in underwater, and 2) how to assure that the robot can be retrieved in case of failure. This invention addresses these two technical issues. In particular, the invention relies on various forms of wireless communication to assist an inspection robot in inspecting a nuclear reactor. The inspection robot includes logic to home back to its original location when it detects failure in its system components without having to use manpower to retrieve the inspection robot. The invention relies on wireless communications that is conceivable in water. The invention attempts to remove actual manpower in maneuvering and inspecting a nuclear reactor, which lessens the need of humans to be exposed to the harsh nuclear environment and toxins that is contained within a nuclear reactor. |
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044366914 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is the basis for an improved version of the S-1 Spheromak referred to above which improved version is described in great detail in a report of the Princeton University Plasma Physics Laboratory, "PPPL S-1 Spheromak Project Engineering Handbook," November 1980. The Spheromak Plasma Configuration The spheromak plasma configuration is characterized by magnetic field lines that are closed, as in a tokamak, and by a coil blanket topology that does not link the plasma--as in a mirror-type machine. A general description of spheromak plasma configurations including its stability and geometry plasma size and density and the prior methods of formation of a spheromak plasma are provided in S-1 Spheromak, Princeton University, Plasma Physics Laboratory, Aug. 24, 1979. In accordance with the inductive formation scheme of the present invention, an initial poloidal field is generated by a coil inside a toroidal ring-shaped shell (flux core). The initial poloidal field is weakened on the inner-major-radius side of this ring by superposition of a properly shaped external vertical field. The flux core also contains a toroidal field coil which is able to generate an interior toroidal flux and is, therefore, able to emit an equal and opposite toroidal flux on its exterior. In operation, when the toroidal field coil is energized, it induces a poloidal current in a sleeve-shaped plasma surrounding the flux core. The associated toroidal field distends the poloidal-field sleeve, stretching it in the direction towards the axis, where the poloidal field is weakest. Next, the current in the poloidal field coil is reversed to pinch off most or all of the distended plasma, producing a separated spheromak plasma configuration, and the electric currents inside the flux core can then be allowed to decay, while the spheromak configuration remains. Spheromak Construction A suitable spheromak construction for practicing the method of the present invention is shown in FIGS. 3a and 3b which illustrates the construction in a cutaway view. Referring to FIGS. 3a and 3b, a generally spheroidal vacuum vessel 1 having a major axis or axis of symmetry 10 houses a flux core 2 of toroidal shape and supported within the vessel by means of three flux core tubes 3. The flux core 2 has a major radius R.sub.maj and a minor radius R.sub.min as indicated in FIG. 3b. The plane of symmetry of the flux core 2 is perpendicular to the axis 10 and extends through the center C of the flux core. Three sets of equilibrium field (EF) coils 5 (EF-1, EF-2 and EF-3) are positioned exterior to the vacuum vessel 1 and radially outwardly of the flux core 2, spaced equidistantly above and below the flux core 2. An additional EF coil (EF-4) is positioned within the flux core. Flux Core The basic purpose of the flux core 2 is to house the poloidal flux coil (PC) 7 and the toroidal flux coil (TC) 8, and to protect both of these coils from the plasma. In the present exemplary embodiment the major radius of the flux core R.sub.maj is on the order of one meter, and the minor radius R.sub.min is approximately 19 centimeters. A top cutaway view and a cross-sectional view of the flux core 2 appear in FIGS. 4 and 5a, respectively, where the coils making up the PC and TC are illustrated. Referring to FIGS. 3a and 4, there are 10 radial arms including the three above mentioned substantially equally spaced radially extending coplenar mechanical supports 3 for the core 2 and seven radially extending lead support assemblies 4' containing electrical leads 4 for the PC, TC and interior EF coils. The PC coils consists of six turns housed in the flux core. Each turn has a cross sectional area of 0.0997 square inch. The six turns are suitably individually insulated water cooled copper cables connected in parallel outside the vessel. The parameters of the PC coil are summarized in Table 1 for convenience. TABLE 1 ______________________________________ POLOIDAL FIELD WINDING PARAMETERS ______________________________________ Total Turns 6 Max Current 83.3 kA/turn (500 kA total through 6 turns in parallel) Total NI 0.5 Mat ESW Capability 4.5 m sec Rep Rate 180 sec PC System Resistance 0.38 m.OMEGA. PC System Inductance 3.26 .mu.H Maximum I.sup.2 Rt 0.43 MJ 1/2 L I.sup.2 0.408 MJ Total Energy 0.838 MJ System GPM at .DELTA.p = 120 psi 3.6 Max Copper Temperature 51.2.degree. C. Conductor Type and Size 127,000 circular mil (0.0997 sq. in.) copper scalbe with an internal copper tube for water cooling; polyethylene insulation ______________________________________ The coil 8 that produces the toroidal flux is divided into six sections of 15 water-cooled, sheathed copper cable turns each, each section occupying 60.degree. of the major circumference of the flux core. Each turn has a cross section of 0.0997 square inches. Each section consists of an electrical lead, a 15 turn helical coil 90 and a return wire 92 which serves to cancel out the poloidal field effects of the current in the helical coil 90. The circuit of one of the six major sections is as follows: Current enters the corresponding lead 4, flows in the return wire 92 while traversing 60.degree. of the flux core major circumference, and terminates in a support. Current flows from the support into the helix 90 and back 15 turns in a left hand manner to the area of the lead stem where it exits from the coil, co-axially with the entering current lead. This results in 15 turns per section for six sections, thus giving 90 turns for the toroidal flux coils 8. TABLE 2 ______________________________________ TOROIDAL FIELD WINDING PARAMETERS ______________________________________ Major Radius 1 m Minor Radius 15 cm Total Turns 90, arranged in 6 groups of 15 connected in parallel Max Current 83.3 kA/turn; 500 kA, Total Total NI 7.5 Mat B.sub.T at Core Center (1 m) 1.4 Tesla ESW Capability 4.5 m sec Rep Rate 180 sec TC Coil System Resistance 0.8 m.OMEGA. TC Coil System Inductance 3.6 .mu.H Maximum I.sup.2 Rt 0.9 MJ 1/2 L I.sup.2 0.45 MJ Total Energy 1.35 MJ GPM for System at .DELTA.p = 120 psi 2.4 Max Copper Temperature 51.2.degree. C. Conductor Type and Size 127,000 circular mil (0.0997 sq. in.) copper cable with an internal copper tube for water cooling; polyethylene insultation ______________________________________ The TC, PC and EF-4 coils are mounted within a flux core conductive shell 11 broken in both the poloidal and toroidal directions to act as a passive stabilizer and to reduce toroidal field ripple. Shell 11 is suitably composed of an aluminum spinning. Completely surround the aluminum shell 11 is a thin Inconel liner 13. Liner 13 protects the core 2 from plasma sputtering and erosion, eliminates outgassing contamination from the organic materials contained in the core, and also serves to partially smooth an induced field during the initial breakdown state. Liner 13 is a major change from the original S-1 design described in U.S. Pat. No. 4,363,776, and was made possible by a doubling of the time scale of the pulse allowing the TC and PC fluxes to be expelled and the energy dissipated in the resistive Inconel liner to be acceptable. Manufacturing liner 13 using a ductile metal should greatly reduce the risk of fracture during assem liner 13 may be done by welding, simplifying the procedures in the original S-1 design. The TC and PC coils and the EF-4 are supported by a monolithic matrix of fiberglass and epoxy, which also acts as electrical insulation. The matrix may be made by several repetitive impregnating and curing steps, using either one mold with filler blocks or multiple molds, whichever is more cost effective. As previously noted, there are provided 10 electrical lead/mechanical support tubes affixed to the core 2. As is illustrated in FIG. 4, all of these tubes are coplanar. The three support tubes 3 are spaced equally apart on the major circumference of the flux core 2. Of the seven electrical lead assemblies 4', there are three electrical lead assemblies for the TC coils 8, three lead assemblies for the PC coils 7 and one lead assembly for the EF-4 coil. The electrical leads are water-cooled conductive tubes. The entire flux core is covered by the Inconel liner 13 which is in the present example is 0.010 inch thick. The TC and PC cables each have a net copper area of 0.0997 sq. in. This is sufficient to absorb the adiabatic heating, but clearly cannot support the large tensile load resulting from magnetic pressure within a coil winding. Thus, the cable must be well supported in such a manner that the load is primarily resisted by support structure rather than the cable. To accomplish this, the poloidal turns 7, toroidal turns 8 and the supply cables for both of these are laid into grooves machined into the core winding form, suitably G-10 epoxy-gloss laminate plates 12. As is illustrated in FIG. 5a, the toroidal windings 8 are supported against side loads in helical grooves machined into the surface of the core form, and then tightly over-wrapped with B-stage fiberglass armature banding tape 14 to resist the radial loads. Referring to FIGS. 5a and 5b, the core is assembled as follows in accordance with the exemplary embodiment: The core is made from a stack of G-10 rings 12 cut from plates which are machined to make the core form containing grooves that accept the PC, EF and TC windings. PC cables T2 and B2 are laid into their grooves in the core form plates which have been painted with a thixotropic epoxy with a long pot life to assure a zero clearance fit. The leads 4 are fed through aisles 15 in the core and potted in place. PC cables T1, T3, B1 and B3 are installed in a manner similar to those above, with enough cable on each of the six sectors to complete the TC windings. The EF-4 winding 6, which is a conventional water-cooled copper conductor, is prewound and grouted with epoxy into its cavity 17. The entire stack is then bolted together and cured. The toroidal winding cables are laid into grooves machined in the surface of the core form 12 and the leads fed through their access ports 15 in the core. Both the toroidal grooves and lead aisles 19 are first painted with thixotrophic epoxy to assure a zero clearance fit. Finally, cross-shaped lead supports (not shown in FIGS. 5a and 5b) are installed in order to isolate the leads from each other. Armature banding tape 14 is then wrapped over the torus to resist current produced forces within. The aluminum shell 11, having been insulated with Kapton tape 18, is then placed onto the core with thixotropic epoxy between it and the core to fill all voids. Additional armature banding tape 16 is then wrapped over the torus with modest tension and cured in layers to avoid wrinkling (which would have a detrimental effect on its load carrying ability). This tape layer resists the forces on the torus due to the current flowing in the shell segments. The Inconel liner 13, support tubes 3, and metallic covers for lead tubes 4' (not shown in FIGS. 5a and 5b) are then welded over the core and vacuum sealed. A urethane primer is applied to the inside of the liner 13 to increase the bond of the urethane compound which will fill the voids between the core 2 and liner 13. The entire assembly is placed in a vacuum enclosure and the annulus between the liner and core is potted with urethane 23. The potted assembly is cured and tested, and may then be installed into the vacuum vessel 1. Equilibrium Field Coil System As noted above, the equilibrium field system as seen in FIGS. 3a, 3b and 6 consists of two sets of three conventional water-cooled copper coils 5 located outside the vacuum vessel 1 and one set of coils 6 inside the flux core 2. This arrangement of coils is designed so as to minimize plasma loss to the flux core 2, i.e., so that the flux core surface coincides with a poloidal flux surface. These coils are powered in a series arrangement by a pair of generators. The equilibrium field coil system provides a vertical field with a moderate curvature that serves two functions; it provides an equilibrium by restraining the tendency of the toroidal plasma current to expand and it determines the shape of the plasma by varying the index "n" of the equilibrium field (.phi..sub.EF) (where .phi..sub.EF =Ar.sup.-n). In order to minimize plasma loss to the flux core, it is desirable that the surface of the flux core 2 coincide with a poloidal flux (constant .psi.) surface. Because the equilibrium field is pulsed on a long time scale the fields penetrate all conductors (including the vacuum vessel 1, Inconel liner 13 and aluminum shell 11 described above), and matching the core surface to a .psi. surface is a difficult constraint to satisfy. Using external coils only and at the same time providing the variable field index feature required for plasma shaping studies, it has been found that an excessive amount of poloidal flux (.DELTA..psi.) intercepts the flux core. A solution to this problem, which constitutes a part of the present invention, is to add equilibrium field turns to the inside of the flux core 2. The EF coil system is shown in relation to the total structure of the exemplary embodiment in FIG. 3a. The exemplary system may operate at field indices of -0.033, +0.060, +0.124 and +0.354. As previously mentioned, all of the EF coils are located outside of the vacuum vessel 1 except for the winding 6 located inside the core 2. The system is powered by large generators in the various index modes by making the appropriate bussing changes to engage or disengage from the circuit various combinations of coil turns within each of the equilibrium coils EF-1, EF-2, EF-3 and EF-4. The circuit arrangements which permit the various index modes to be realized in accordance with the present exemplary embodiments are schematically illustrated in FIGS. 7a and 7b, the coil specifications being given in Table 3. TABLE 3 __________________________________________________________________________ EQUILIBRIUM FIELD COIL DATA RESIS- MAX MEAN TANCE .DELTA.T GPM AT CU REP COPPER COIL NO. RADIUS COPPER m.OMEGA. PULSE .DELTA.P TEMP I.sub.p ESW RATE WT NO. TURNS IN./M. AREA IN.sup.2 (20.degree. C.) .degree.C. = 120 psi .degree.C. kA SEC SEC LBS (kA.sup.J __________________________________________________________________________ /in2) EF-1A 14 31.496/0.80 0.907 2.071 11.4 2.9 30.9 20 2 180 812 22 EF-1B 14 31.496/0.80 0.907 2.071 11.4 2.9 30.9 20 2 180 812 22 EF-2A 15 59.055/1.50 0.907 4.16 11.4 1.75 62.8 20 2 180 1627 22 EF-2B 15 59.055/1.50 0.907 4.16 11.4 1.75 62.8 20 2 180 1627 22 EF-3A 9 71.388/1.81 0.907 3.015 11.4 2.093 44.4 20 2 180 1181 22 EF-3B 7 70.669/1.795 0.907 2.66 11.4 2.25 39.6 20 2 180 1040 22 EF-3C 5 70.394/1.788 0.907 1.65 11.4 2.94 27.8 20 2 180 647 22 EF-4 1 35.040/0.89 0.844 0.22 57.3 3.15 65.9 40 2 180 74 47.4 __________________________________________________________________________ TOTAL SYSTEM WT: 15,640 lbs TOTAL COOLANT FLOW RATE: 39.5 GPM NOTE: Two of each coil type exists due to symmetry about the midplane of the device. The EF coils are made up of several individual, stacked double pancake windings. This simplifies manufacture and provides an easy method of varying the relative NI of the coils comprising the equilibrium field system. In the exemplary embodiment the conductor of each EF coil is extruded copper conductor 0.810".times.1.272" with a centrally located 0.360" diameter coolant hole. This conductor is stretched, reducing its area 2 percent, to raise its yield point to approximately 12 ksi and to straighten the coiled conductor. Eight layers of 0.00325" Mylar tape is applied as the primary electrical insultation, followed by four layers of Scotchply B-stage epoxy-glass tape, 0.010 thick to bond the turns together. Each entire EF coil is toroidally over-wrapped with 0.188" of additional Scotchply for mechanical reinforcement and protection against electrical faults to ground. The EF coils are press-cured in a fixture which provides pressure on all surfaces. Power Supplies Turning now to the energy system provided for the formation coils (TC and PC coils), FIG. 8 is a block diagram of the capacitive discharge power supply system. Each capacitor bank 20 (for the PC coils, the TC coils forward bias and the TC coils reverse bias) has its own dedicated charging supply whose output (up to 20 kV on the present example) is connected through high voltage disconnects 50. Capacitor bank voltage monitoring circuits 52 provide control and display signals. Output discharge and grounding switches 54 are also provided. The capacitor banks are connected to their loads through switch modules 56 (ignitrons), rigid bus work 58 and high voltage cables 46 and 48. FIG. 9a depicts an equivalent circuit for the power supply for the PC coils 7. The load consists of six parallel poloidal coils 7 embedded in the flux core 2. The capacitive discharge supply 30 consists of a 1800 uF, 20 kV capacitor bank 20 with its charge and discharge circuits. The switch module 32 connecting the capacitor bank to the PC coil load is made up of five forward and five reverse 25 kV, 300 kA (Size D) ignitrons in parallel. A crowbar switch 34 consisting of 5 ignitrons in parallel provides current free wheeling through the load. The PC current trace for operation of the exemplary embodiment is shown in FIG. 10b. The PC current is initiated about 75 mocroseconds before time zero. The PC current builds up to a peak value of about 450 kA at time zero, then rings through zero to a negative maximum of about 300 kA. At this point the crowbar ignitrons 34 are fired and the coil current decays with the L/R time constant of the circuit. Thus, the anti-parallel ignitrons 32 are provided for switching since the poloidal field current rings from a positive to a negative polarity and is then crowbarred. FIG. 9b depicts an equivalent circuit of the power supply for the TC coils. In the exemplary embodiment illustrated the power supply consists of two capacitor banks 20 (C.sub.1 and C.sub.2) with their separate charging and discharging circuits. Capacitor bank C.sub.1 provides 300 .mu.fd of capacitance made up of 20 cans of 60 .mu.fd each in a series parallel arrangement. The bank C.sub.1 has a 40 kilovolt capability because of possible fault requirements. Capacitor bank C.sub.2 contains 2040 .mu.fd of capacitance made up of 34 cans of 60 .mu.fd each in a parallel arrangement. For normal operation both banks are charged to 20 kv. In operation, capacitor bank C.sub.1 is switched across the load at about 150 .mu.sec before time zero. Two parallel ignitrons 36 provide the switching. At time zero, when the current from the first bank C.sub.1 crosses zero, the second bank C.sub.2 is fired through a ten tube series-parallel ignitron switch module 38. The current will rise to about 500 kA in 100 .mu.sec, at which point the crowbar ignitrons 40 are fired and the coil current decays with the L/R time constant of the circuit. FIG. 9c depicts the power supply for the EF coils in accordance with the present exemplary embodiment. Two large generators 60 with associated high-speed resistor breakers 62 and motor-operated safety disconnect switches 64 provides the EF coils with power. The two generators 60 are each capable of being pulsed to 22,300 amperes with an equivalent standard pulse with 5 seconds once every two minutes, and is operated in series at a total voltage of 1600 V. A bus and switch system connects the generators 60 to the outer EF coils 5 and inner EF coil 6. Referring again to FIG. 8, solid rigidly supported copper buswork interconnects the capacitors within each capacitor bank 20 and provides a termination for connection of the charging supply (one for each capacitor bank) and for connection of the bank output to its switch module 56. All buswork is mechanically braced for maximum possible fault currents, insulated for high voltage, and adequately sized for natural cooling during normal duty cycle operation. It is also configured for low self inductance. High voltage cable is provided from each charging supply to the capacitor bank 20 as well as from the output terminals of the switch module 56 to the TC and PC coils and also to grounding and disconnect switches. At the output of the switch modules 56 rigid bus to coaxial cable transition blocks 46 are provided, insulated for the high voltage and sized for the current required. In accordance with the exemplary embodiment the transmission line 58 from the switch modules 56 to the TC and PC coils consist of multiple parallel coaxial cables the number of which is selected for low self inductance. The PC and TC coil groups are each fed with a minimum of 18 parallel RG coaxial cables in three groups of six cables whose total parallel self inductance is a maximum of 0.25 microhenry with an AC resistance of approximately 2 milliohms. At the coil ends, these coaxial cables are terminated on coaxial to bus transition blocks 48, similar to the blocks 46 used at the switch modules. Vacuum System Referring now to FIGS. 3a and 11 the vacuum vessel 1 of the present exemplary embodiment is made up of three 1/2"-thick type-304 stainless steel segments. They include two dished heads (left side head 70 and right side head 72), with constant-radius dishes, and one central-rolled cylinder 74. The heads 70 are 150-cm-radius preformed weldments which are commercially available. The central-rolled segment 74, also 150 cm in radius, is bolted to the left head 70. The joint between the cylinder 74 and the right head 72 is flanged, allowing access from the left side of the machine. A dummy flange 76, welded at the right head cylinder weld line, assures symmetrical eddy current effects. The basic porting scheme consists of 20-cm and 40-cm ports 80, arranged alternately on 45.degree. radial lines from the machine center line. In total, there are sixteen 40-cm ports and sixteen 20-cm ports. Additional ports are provided for the vacuum pump, and for the toroidal core and poloidal core lead outs. Two large ports 82, 70-cm, at the two sides of the machine are arranged coaxially on the horizontal center line. Eight 20-cm ports 84 are also provided on the vertical midplane, equi-spaced about the equator of the cylinder 74. The main vacuum tank seal, at the parting flange, is of Viton O-ring design. External clamps spaced around the outside of the flange are used for seal compression. All ports are also of Viton O-ring design. The volume of the vacuum vessel 1 is approximately 9500 liters. The gas load for the vacuum pumping system (not shown in the drawings) is mostly outgassing of the materials used for construction of the vacuum vessel 1. In order to pump down the vessel 1.times.10.sup.-6 torr in approximately 29 minutes, two parallel mechanical pumps of high capacity may be used. The vacuum pumping system of the present exemplary embodiment includes two parallel pumping stacks each including a 1500 liter per second turbo molecular pump, a 200 liter per second blower, and a 30 liter per second mechanical pump. The pump system used is provided with a large enough diameter pump lines to achieve a net pumping speed of 1200 liters per second at the vacuum vessel. The system is capable of achieving a base pressure of 6.times.10.sup.-8 torr. For attaining lower pressures of approximately 2.times.10.sup.-8 torr, titanium getters may be employed. The Formation Process As indicated graphically in FIGS. 10a and 10b, the operating procedure used in the formation process includes pulsing up the vacuum poloidal field at a time when there is no current present in the toroidal field winding, and then initiating the plasma discharge by pulsing the toroidal coil current. Initially, the entire vacuum vessel 1 will be evacuated and then filled to a neutral pressure of about a few micron. The pulsing of the toroidal field circuit will ionize a plasma layer at the surface of the flux core 2, and will "unpinch" it away from the surface. In an optional mode, the toroidal field generating coil 8 is provided with an initial bias to produce an initial toroidal magnetic field before the step of pulsing that coil, so as to provide an ionized plasma just prior to the initiation of the main plasma discharge. As the discharge volume expands, neutral gas will be swept up by thermal motion, which is not negligible on the several microsecond time scale of the initial formation process. With this overview, the formation process will now be described in detail, with reference to a particular experiment run by the inventors. The volume between the flux core and the vacuum chamber is first filled with hydrogen gas at the density between 3.times.10.sup.13 and 10.sup.14 particles/cm.sup.3. FIGS. 10a and 10b show the computed currents in the circuits, flux core liner and plasma as a function of the time t. Before preionization, the EF and PC currents have been brought up slowly to their peak values. At t=0, when the plasma is preionized, the TC capacitor banks C.sub.1 and C.sub.2 are discharged initiating a negative current in the TC circuit. Simultaneously, the PC circuit is closed, causing the current to decrease by recharging the PC capacitors 20. The simultaneous increasing of the TC current and decreasing of the PC current leads to a balance at the surface of the flux core so that the resultant normal component of the velocity, V.sub.n =E.sub.P B.sub.T -E.sub.T B.sub.P, is approximately zero. At the times when the voltage drop across the capacitors corresponding to the TC and PC circuits reach zero, times t=100 .mu.sec and t=150 .mu.sec respectively, in the present example, the currents in the TC and PC circuits are crowbared and allowed to decay resistively. In response to the changing circuit currents, poloidal and toroidal currents are induced into the flux core liner and plasma as indicated in FIG. 10b. FIG. 12 shows the poloidal magnetic flux distribution at time t=0. Only the contours on the upper half plane are plotted since the device is symmetric about the midplane. The lower part of FIG. 12 shows the poloidal flux on the midplane plotted against the major radius R. A variation of the above described method would be to increase the relative strength of the TC current resulting in an uncompensated outward normal velocity. This additional toroidal flux would be trapped within the poloidal flux surfaces, inflating them and forcing them radially inward. FIGS. 13 through 16 show the distribution of the poloidal magnetic flux, the toroidal current, the toroidal magnetic field, and the poloidal current at time t=75 .mu.sec. Comparison of FIG. 12 with FIG. 13 shows that after 75 .mu.sec, the value of the poloidal flux at the flux core surface .psi. increases from .psi..sub.c =-0.080 to .psi..sub.c =-0.063. The increase of .psi..sub.c, through magnetic induction, has caused a local minimum to form between the symmetry axis 10 and the flux core 2. This local minimum is to become the magnetic axis of the spheromak plasma. FIG. 14 shows the toroidal current density in the plasma, J.sub.T at the time t=75 .mu.sec. At this time the plasma current is distributed around the flux core, but shows a preferential inward expansion toward the symmetry axis. This preferential inward expansion is dictated by the "external field" bias produced by the currents in the EF coils shown in FIGS. 3a and 3b. FIG. 15 shows the toroidal field function g=RB.sub.T at times t=75 .mu.sec, where B.sub.T is the magnitude of the toroidal magnetic field, and FIG. 14 shows vectors indicating the relative magnitude and direction of the associated plasma poloidal current J.sub.P. The poloidal current is induced into the plasma by the changing current in the TC circuit. The evolution of this current is governed by both resistive diffusion, and by the equilibrium equation, which dictates that the polodial current vectors lie in surfaces of constant poloidal flux. Since the poloidal flux surfaces are moving preferentially inward, the equilibrium constraint forces the toroidal field function contours to expand inward as well. FIGS. 17 through 20 show the fields and currents at time t=250 .mu.sec, when the spheromak configuration is fully formed. The magnetic axis is now located at R=0.53 m. From FIG. 17 it is seen that enough volt-seconds have been supplied by the PC circuit to raise the value of the poloidal flux on the flux core, .psi..sub.c, to the zero value, the same as that on the symmetry axis. All of the poloidal flux surfaces between the symmetry axis and the flux core have negative values of .psi., corresponding to closed magnetic surfaces that do not encircle the flux core. FIG. 18 shows the toroidal current density at time t=250 .mu.sec. Inward expansion has continued so that nearly all of the toroidal plasma current is now located in the confined region of closed magnetic field lines between the symmetry axis and the flux core. From FIG. 10(b) it is seen that the total toroidal current in the plasma is now about 500 kA, the same as the initial toroidal current in the PC circuit. This current has effectively been transferred from the flux core into the plasma by magnetic induction. FIG. 19 shows the toroidal magnetic field function g=RB.sub.T at time t=250 .mu.sec and FIG. 20 shows the associated poloidal current vectors. Essentially all of the toroidal flux has been "captured" in the closed magnetic field line region. From FIG. 20 it is apparent that in contrast to FIG. 16 the poloidal current paths encircle the magnetic axis but no longer encircle the flux core. Thus poloidal current, as well as toroidal current, has effectively been inductively transferred from the flux core into the final spheromak configuration. A schematic illustration of the spheromak formation process is given in FIGS. 22a-22d. FIG. 22a shows three poloidal flux surfaces .psi..sub.1 >.psi..sub.2 >.psi..sub.3 at an early stage in the formation. The induction of a poloidal current around the flux core and its subsequent radial diffusion cause toroidal flux to exist in the volume between surfaces .psi..sub.1 and .psi..sub.2, and between surfaces .psi..sub.2 and .psi..sub.3. The toroidal electric field set up by the decreasing PC current in the flux core causes the value of the poloidal flux .psi..sub.c on the flux core to increase. FIGS. 22(a) through (d) illustrate the geometry as .psi..sub.c =.psi..sub.3, .psi..sub.c =.psi..sub.2, and .psi..sub.c =.psi..sub.1, and .psi..sub.c >.psi..sub.1. Note that all of the toroidal flux in the initial configuration 22a has been captured in the final spheromak configuration 22d. The formation method of FIGS. 22a-22d is to be compared with the previously proposed formation method utilizing pinching coils, depicted in FIGS. 21a through 21d. In the pinching method, the value of the poloidal flux on the flux core, .psi..sub.c, is held fixed while pinching coils are activated to "pinch off" a piece of the plasma to form a spheromak configuration. This method has the disadvantage of requiring an additional set of coils and is intrinsically less efficient. Only a fraction of the poloidal and toroidal flux which exists in the initial configuration of FIG. 21a can end up in the final spheromak configuration of FIG. 21d since a sleeve containing a substantial proportion of the initial quantity of flux containing plasma remains encircling the flux core. In the present method, essentially all of the poloidal and toroidal flux present in FIG. 22a can be captured in the spheromak configuration of FIG. 22d. This invention has been described by way of illustration rather than limitation, and it is intended to cover in the appended claims all variations and modifications as fall within the true spirit and scope of the invention. |
051669625 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray mask for use in X-ray exposure and, more particularly, to an X-ray mask in which an X-ray transmitting thin film is improved. 2. Description of the Related Art Recently, as the degree of integration of semiconductor devices has been increased, the extent of micropatterning of a circuit pattern of LSI elements which constitute a semiconductor device has been increased. In order to form a very fine pattern on the order of so-called subhalfmicrons, high-resolution exposure transfer techniques are essential. As one of these techniques, there is proposed an exposure transfer technique using X-rays having a wavelength by far shorter than that of currently widely used ultraviolet rays. To put such an X-ray exposure transfer technique into practical use, a large number of technical problems must be solved. Of these problems, the formation of an X-ray mask is of most concern. FIG. 10 shows a representative sectional structure of an X-ray mask. The main portion of this X-ray mask is composed of a support frame 1, an X-ray transmitting thin film 2 serving as a mask substrate, and an X-ray absorber pattern 3. Of these parts, the X-ray transmitting thin film 2 is required to have a sufficient transmittance of X-rays used in exposure, a sufficient radiation resistance against intense X-rays used in exposure, and a sufficient transmittance of visible light (wavelength 633 nm) used in an alignment between a mask and a wafer. The film 2 is also required to have a sufficient mechanical strength and a small tensile stress so that a fine X-ray absorber pattern does not cause a displacement. In many cases, the X-ray transmitting thin film 2 is formed on a substrate, such as an Si wafer, which constitutes the support frame 1. For this reason, the step of forming the film on the substrate is an important step which determines the characteristics of the X-ray transmitting thin film 2. Note that unnecessary portions of the substrate are removed by etching. Conventionally, BN, Si, SiN, and SiC, for example, have been examined as the material of the X-ray transmitting thin film, and a vacuum vapor deposition method, a sputtering method, a CVD method, and the like have been studied as the formation method of the film. However, it is difficult to obtain a film which completely satisfies the above conditions. For example, the use of BN or SiN makes it difficult to form a film having a sufficient radiation resistance against intense X-rays used in exposure. Although Si is satisfactory in radiation resistance, a film having a high visible light transmittance is difficult to form by using this material. SiC is a substance which satisfies the above conditions comparatively well, but it has the following problem. That is, although SiC is a material originally having a high visible light transmittance, crystal defects are easily produced upon film formation using this material, and this makes it impossible to obtain a high visible light transmittance. In order to solve the above problems, the use of a stacked composite film consisting of two or more layers of different types of materials has been examined. In this method, however, it is necessary to use different source gases upon film formation performed by a CVD method. In addition, a technique of using different film formation methods for a single material has been studied. In this technique, for example, an amorphous film is formed by a plasma CVD or ECR-CVD method on a polycrystalline film formed by a thermal CVD method, and this composite film is used. However, this technique requires a plurality of different types of film formation apparatuses. As described above, it is difficult to obtain a sufficiently high visible light transmittance when SiC is used as the material of the X-ray transmitting thin film. In addition, the formation of a stacked composite film proposed as the X-ray transmitting thin film complicates the manufacturing steps and makes it difficult to easily improve the visible light transmittance. SUMMARY OF THE INVENTION The present invention has been made in consideration of the above situation and has as its object to provide an X-ray mask having a high visible light transmittance. It is another object of the present invention to provide a method of manufacturing an X-ray mask, which can form an X-ray transmitting thin film serving as a mask substrate by simple manufacturing steps and can improve a visible light transmittance. It is still another object of the present invention to provide an exposure method using the X-ray mask according to the present invention. The characteristic feature of the X-ray mask according to the present invention is that the overall visible light transmittance is improved by constituting an X-ray transmitting thin film serving as a mask substrate by a stacked film consisting of layers having different compositions. In addition, in order to form this stacked film, the film formation is performed under different film formation conditions in a CVD method. Suppose the film formation of SiC is performed by a CVD method under conditions in which the ratio of C atoms to Si atoms contained in source gases is changed. In this case, when the ratio is small, each crystal grain has high quality and the film has a high visible light transmittance. However, since unevenness in grain boundaries or on a film surface is enlarged, light is scattered on the surface of the film to cause the visible light transmittance to decrease. When the ratio is large, on the other hand, light is less scattered because unevenness in grain boundaries or on a film surface is small. However, since an inclusion which absorbs light is mixed in the film, the visible light transmittance decreases. For this reason, by stacking a plurality of layers having different ratios of C atoms to Si atoms, it is possible to form a good X-ray transmitting thin film having advantages of the respective layers. For example, both the major surfaces of an X-ray transmitting thin film are formed under a condition in which the ratio of C atoms to Si atoms is more (as compared with an average value of the entire thin film), whereas the central portion of the film is formed under a condition in which the ratio of C atoms to Si atoms is less. In this case, a good thin film having small undulations on its surface and containing a little inclusion which absorbs light can be obtained. In addition, according to the present invention, a desired X-ray transmitting thin film can be formed by properly selecting the flow rate of a source gas during film formation. Therefore, an X-ray transmitting thin film can be easily formed in a single reactor. Furthermore, since an X-ray transmitting thin film having a high visible light transmittance is realized, an alignment between a mask and a wafer can be performed with a high precision. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. |
055132278 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. FIGS. 2 to 5 show details of a first embodiment of the present invention. This embodiment features a basic combination of a modified GRAYLOC hub 100, a seal carrier 102, a retaining nut 104, a belleville washer 106, a loading ring 108 and a column assembly 110. The modified GRAYLOC hub 100 forms a pressure boundary at the top of the nozzle. It has a clearance fit with the column assembly 110 and includes a stepped bore the upper larger diameter portion of which is threaded to react to the loading of the retaining nut 104. It should be noted that with the present invention disassembly of the GRAYLOC flange is not required for removal of the reactor head. In this arrangement the column assembly 110 serves to allow the penetration of a plurality of ICIs (In-Core-Instruments) into the interior of the reactor core. The instant embodiment is such as to support six ICIs and provides guidance for the guide tube clusters which are associated with the ICIs. The ICI column assembly 110 includes six 1/2" SWAGELOC fittings 112 and bolts to the guide tube cluster. The SWAGELOC are not loosened unless the ICI are to be discarded and replaced with new units. The seal carrier 102 supports grafoil seals 102a and protects the same from damage during installation. A special T-handle tool is used to engage J-slots (see FIG. 4) which are formed in a vertical web of the seal carrier 102 during installation and removal. As shown, the seal carrier 102 is disposed in the lower portion of a stepped bore formed in the modified GRAYLOC hub 100. The retaining nut 104, which is threadedly received in the upper portion of the stepped bore of the GRAYLOC hub 100, is such as to react against the uplift of the column 110 and compress the grafoil seals 102a. The retaining nut 104 is formed with spanner holes in the upper surface thereof and does not require the application of large amounts of torque in order to thread the same into and out of place. The belleville washer 106 is provided to ensure that a load is maintained on the grafoil seals 102a under all thermal conditions and further prevents loosening of the load ring 108. As will be appreciated, load ring 108 is provided to apply a load to the grafoil seals 102a. In this embodiment it threads onto a threaded portion of the column assembly and is provided with six 5/8" bolts 108a which can be screwed down onto the upper surface of the belleville washer 106 in order to apply the required compressive force to the grafoil seals 102a. In this instance the ICI connectors 116 are staggered at three different elevations and are mounted on an integral bullet nose locking rod 118. During routine disassembly of the flange, there is no need to remove the connectors. FIG. 5 shows the nozzle covered with a bullet nose 120 such as during refueling when the reactor head is lifted. As will be noted, in this instance a nylon thread protector 122 is inserted into the upper section of the stepped bore to ensure that insertion of the lower open end of the bullet nose 120 does not damage the threads and reduce the integrity of the sealing effect which is provided thereby. FIG. 6A is a partially sectional view of a detector seal plug which forms part of the instant embodiment. FIG. 6B is an end view of the seal plug of FIG. 6A. As shown, this device includes a support tube 124 which is welded to a swaged detector 126 and includes a plurality of leads which are brazed to a header in the manner illustrated. As this element is not directly connected with the invention, no further disclosure will be given for brevity. FIGS. 9 through 13B, 15 and 16 show details of a second embodiment of the present invention. The second embodiment is shown in conjunction with a GRAYLOC flange assembly, such as that shown in FIG. 8, with like reference numerals used to refer to like elements in FIGS. 8 through 16. However, it should be understood that with minimal modifications the second embodiment could also be adapted for use with a bolted flange assembly, such as that shown in FIG. 7. The benefits of the quick locking mechanism of the present invention are substantially the same for either the bolted or the GRAYLOC flange assemblies. As shown in FIG. 9, the second embodiment includes a GRAYLOC hub 210' positioned over the opening of the closure head nozzle 211. The closure head nozzle 211 includes a GRAYLOC flange 212 which is clamped securely to the hub 210' by a GRAYLOC clamp 213. A metal GRAYLOC seal ring 214 is positioned between the GRAYLOC flange 212 and the hub 210'. The GRAYLOC clamp 213 includes a pair of large matching clamshell clamps secured together with four stud and nut sets inserted through holes 215. The GRAYLOC hub 210' has an open center geometry. A seal plug assembly 220 is received within the open center of the hub 210' and includes passages therethrough for receiving ICI guide tubes 221 of the ICI assemblies 216'. The seal plug assembly 220 fits on top and is secured to the guide tube cluster 222 which extends into the reactor vessel. In effect, the seal plug assembly extends the individual ICI guide tubes 221 up through one large permanent seal plug, rather than individual seal plugs for each guide tube, as in the prior art. At the top of the seal plug assembly, there is a group of SWAGELOC-type fittings 223 which restrain and form a seal with each ICI. These fittings 223 are disconnected only if the individual ICIs are scheduled for replacement. The SWAGELOC-type fittings 223 form fluid and radiation tight seals between the ICI tubes and the seal plug assembly 220 while enabling the ICI tubes to be a constant diameter throughout their full length. During normal outages, the fittings 223 are not disturbed, but rather, are left intact as shown in FIG. 10A. A bullet nose 250 (shown in FIG. 10B) is temporarily positioned over the ICI assemblies 216' to seal and protect the individual ICIs when the closure head (not shown) is removed from the pressure vessel. After the bullet nose 250 is sealingly secured to the seal plug assembly 220, the closure head (not shown) and the nozzle assembly 211 can be lifted from the pressure vessel and slid up over the top of the ICI assembly 216' and bullet nose 250 Thus, the entire ICI assembly 216' along with the seal plug 220, remains in place while the closure head (not shown) and nozzle 211 are removed from the pressure vessel. No individual seal plugs for the guide tubes 221 are necessary with the present invention because the ICI tubes all extend through the single seal plug 220 which remains in position during refueling. The bullet nose 250 protects the ICI assembly within a sealed chamber created by an O-ring fluid seal 251 between the bullet nose and the seal plug 220. The sealed chamber within the bullet nose is important to protect the ICIs from water and mechanical damage during refueling when the entire reactor is covered in water to reduce radiation exposure. A tapered top 252 of the bullet nose 250 facilitates positioning the closure head and nozzle 211 over the ICI assembly after refueling. A seal carrier assembly 224 (FIGS. 9, 11A and 11B) includes a seal carrier 225 and GRAFOIL seal rings 226. The GRAFOIL rings 226 fill and seal the annulus between the column assembly 220 and the GRAYLOC hub 210'. As shown in FIGS. 11A and 11B, the seal carrier 225 has an inverted T-shaped cross-section with a lower portion 225a and an upper vertical web portion 225b. The upper portion 225b of the seal carrier 225 is equipped with J-slots 225c which are engaged by a special installation/removal tool (not shown). The carrier 225 allows the seal rings 226 to be easily installed without damage. The carrier 225 also facilitates removal of the seal rings 226 during disassembly. An open-centered compression collar 227 (FIG. 9) is fitted about the seal plug assembly 220 above the seal carrier assembly 224. The compression collar 227 is secured in position by a threaded hold down nut 228. A special hydraulic loading tool 230 (shown in FIGS. 13A and 13B and discussed below) is used to drive the compression collar 227 into the GRAFOIL seal rings 226. While the loading tool is pressurized, the nut 228 is spun down hand tight to retain the compression of the GRAFOIL seal rings 226. There are virtually no torque requirements on the nut 228 since the nut 228 need only be hand tight before the loading tool is removed. FIGS. 12A and 12B show the top end components of the nozzle assembly of the second embodiment. FIGS. 13A and 13B show the same view of the nozzle assembly as shown in FIGS. 12A and 12B, respectively, with the special hydraulic loading tool 230 in an operating position for compressing the compression collar 227. The loading tool 230 includes a tool block 231 and three load arms 232. Six hydraulic pistons 233 are spaced about the circumference of the tool block 231, each piston 233 having a recess 234 in an upper surface thereof. Each of the loading arms 232 includes a pair of protrusions 235 received in respective recesses 234 of the pistons 233 when the tool is installed. Each of the loading arms also includes bottom flanges 236 at a lower end thereof for engaging a flange 237 of the GRAYLOC hub 210'. The loading tool 230 is powered by a source of hydraulic pressure (not shown) for actuating the hydraulic pistons 233. The pressure source is connected to the tool through a fluid port 238. To install the hydraulic loading tool 230, the tool block 231 is placed on the compression collar 227 of the nozzle assembly. Next, the three load arms 232 are inserted into the recesses 235 of the pistons, ensuring that the bottom flanges 236 of the load arms are located under the flange 237 of the GRAYLOC hub. Lastly, the fluid pressure source is connected to the fluid port 238 of the tool. Operation of the tool 230 only involves pressurizing the pistons 233 to a predetermined pressure. As the pistons 233 rise due to the pressure, the bottom flanges 236 of the load arms 232 engage the flange 237 of the GRAYLOC hub 210'. As the pressure in the pistons 233 is increased, the load is transmitted through the compression collar 227 into the seals 226 of the seal carrier 224. While the tool 230 is pressurized, the drive nut 228 is turned down by hand to retain the compression collar 227, which in turn retains the load on the seals 226. The tool 230 is then depressurized, the load arms 232 removed, and the tool block 231 removed. The initial installation of the quick locking mechanism of the present invention is relatively simple. The hubs 210' can be assembled to the closure head nozzles 211 when the head is in the storage area (i.e., off the critical path). As opposed to current plant procedures, once the GRAYLOC hub 210' is installed, the GRAYLOC clamps 213 and their corresponding large studs and nuts are not disassembled in subsequent outages. Similarly, the seal plug assemblies 220 are attached to the ICI guide tubes 221 and clusters 222 with fittings that remain connected during subsequent outages, unless the ICI is scheduled for replacement. The seal carrier assembly 224, compression collar 227, and hold down nut 228 can be easily assembled into proper position by sliding down over the ICI assemblies after the other components are attached as shown in FIG. 10A. FIG. 14 shows a portion of a conventional ICI guide tube cluster 130 disposed within a pressure vessel. The guide tube cluster includes a plurality of guide tubes 131 (e.g., six) held in a bundle by support plates 132 and 133 at upper and lower ends of the cluster, respectively. The cluster 130 is connected at its lower end to extensions 134 of the ICI guide tubes which continue on into the pressure vessel and are supported by a thimble support plate 135. FIGS. 15 and 16 show the ICI guide tube cluster 222 according to the second embodiment of the present invention. The cluster 222 includes a new column assembly 240 that bolts onto the existing guide tube cluster 130. The connection between the existing cluster 130 and the new column assembly 240, as shown in FIG. 16, includes a threaded member 241 connecting the two portions for relatively easy retrofitting to the existing configuration. The new guide tube cluster 222 includes a spring section 242 adjacent an upper end of the cluster to accommodate differential thermal growth between the reactor head and the internal components. The differential thermal growth often occurs because the reactor head is typically made of carbon steel while the internal components are typically made of stainless steel. The spring section 242 includes a compression spring 243 within the column assembly 240 between the seal plug assembly 220, which is connected directly to the column assembly 240, and a plate 244 secured within the column assembly 240. The preferred embodiment uses Stainless and Nitronic 60 as the material combination for mating threaded parts, such as the nut 228 and the hub 210' to minimize the possibility of galling. As the reactor primary system is pressurized, the load on the GRAFOIL seal rings 226 actually increases causing a slight further compression of the seal rings 226. Therefore, the design has a self-sealing tendency. Furthermore, since all of the components of the present invention are relatively lightweight and there are virtually no torque requirements during assembly, one person can easily perform the assembly/disassembly operations. Tables 1 through 4 provide a summary of the estimated time savings resulting from the use of the quick locking mechanism of the second embodiment of the present invention, as compared to the existing GRAYLOC flange design. The Tables use a typical nuclear power plant having only six flanges as an example. Since most power plants have either eight or ten flanges, the Tables present the most conservative time savings. In addition, a further benefit not shown in the Tables is that with the present invention it is possible for a single person to assemble and disassemble the flange assemblies. The existing flange design requires two or more people to perform the same job. Therefore, the radiation exposure time savings directly incurred by the time savings of the present invention may be multiplied by two or more. TABLE 1 __________________________________________________________________________ Assembly Operations - ICIs NOT Being Replaced OPERATION* EXISTING METHOD QUICKLOC __________________________________________________________________________ 1 Install GRAYLOC seal 6 .times. 5 min. = 30 min. 0 2 Install GRAYLOC clamps 6 .times. 10 min. = 60 min. 0 3 Install GRAYLOC bolts 6 .times. 4 .times. 5 min. = 120 min. 0 4 Install GRAFOIL ICI seals 28 .times. 5 min. = 140 min. 0 5 Install drive nuts 28 .times. 10 min. = 280 min. 0 6 Install Seal Carrier 0 6 .times. 1 min. = 6 min. 7 Install Compression Collar 0 6 .times. 1 min. = 6 min. 8 Install Hold Down Nut 0 6 .times. 1 min. = 6 min. 9 Compress Seals 0 6 .times. 2 min. = 12 min. 10 Make electrical connections 28 .times. 5 min. = 140 min. 28 .times. 5 min. = 140 min. TOTAL TIME REQUIRED 770 min. or 12.8 hrs. 170 min. or 2.8 hrs. TIME SAVED 10.0 hrs. __________________________________________________________________________ *All estimated installation times include the installation time and quality control verification time where applicable. TABLE 2 __________________________________________________________________________ Assembly operations - ICIs BEING Replaced OPERATION* EXISTING METHOD QUICKLOC __________________________________________________________________________ 1 Install GRAYLOC seal 6 .times. 5 min. = 30 min. 0 2 Install GRAYLOC clamps 6 .times. 10 min. = 60 min. 0 3 Install GRAYLOC bolts 6 .times. 4 .times. 5 min. = 120 min. 0 4 Install GRAFOIL ICI seals 28 .times. 5 min. = 140 min. 0 5 Install drive nuts 28 .times. 10 min. = 280 min. 0 6 Install Seal Carrier 0 6 .times. 1 min. = 6 min. 7 Install Compression Collar 0 6 .times. 1 min. = 6 min. 8 Install Hold Down Nut 0 6 .times. 1 min. = 6 min. 9 Compress Seals 0 6 .times. 2 min. = 12 min. 10 Make SWAGELOC ICI 0 28 .times. 2 min. = 56 min. Seals 11 Make electrical connections 28 .times. 5 min. = 140 min. 28 .times. 5 min. = 140 min. TOTAL TIME REQUIRED 770 min. or 12.8 hrs. 226 min. or 3.8 hrs. TIME SAVED 9.0 hrs. __________________________________________________________________________ *All estimated installation times include the installation time and quality control verification time where applicable. TABLE 3 __________________________________________________________________________ Disassembly Operations - ICIs NOT Being Replaced OPERATION EXISTING METHOD QUICKLOC __________________________________________________________________________ 1 Disconnect hose clamp 6 .times. 5 min. = 30 min. 0 2 Disconnect ICI Connectors 28 .times. 1 min. = 28 min. 28 .times. 1 min. = 28 min. 3 Remove drive nuts 28 .times. 2 min. = 56 min. 0 4 Remove GRAFOIL ICI 28 .times. 5 min. = 140 min. 0 seals 5 Remove GRAYLOC bolts 6 .times. 4 .times. 2 min. = 48 min. 0 6 Remove GRAYLOC clamps 6 .times. 10 min. = 60 min. 0 7 Remove Crayloc seal 6 .times. 1 min. = 6 min. 0 8 Compress seals 0 6 .times. 2 min. = 12 min. 9 Remove Hold Down Nut 0 6 .times. 1 min. = 6 min. 10 Remove Compression Collar 0 6 .times. 1 min. = 6 min. 11 Remove Seal Carrier 0 6 .times. 1 min. = 6 min. TOTAL TIME REQUIRED 368 min. or 6.1 hrs. 58 min. or 1.0 hrs. TIME SAVED 5.1 hrs. __________________________________________________________________________ TABLE 4 __________________________________________________________________________ Disassembly Operations - ICIs Being Replaced OPERATION EXISTING METHOD QUICKLOC __________________________________________________________________________ 1 Disconnect hose clamp 6 .times. 5 min. = 30 min. 6 .times. 5 min. = 30 min. 2 Disconnect ICI Connectors 28 .times. 1 min. = 28 min. 28 .times. 1 min. = 28 min. 3 Remove drive nuts 28 .times. 2 min. = 56 min. 0 4 Remove GRAFOIL ICI 28 .times. 5 min. = 140 min. 0 seals 5 Remove GRAYLOC bolts 6 .times. 4 .times. 2 min. = 48 min. 0 6 Remove GRAYLOC clamps 6 .times. 10 min. = 60 min. 0 7 Remove GRAYLOC seal 6 .times. 1 min. = 6 min. 0 8 Loosen SWAGELOC 0 28 .times. 1 min. = 28 min. fittings 9 Compress seals 0 6 .times. 2 min. = 12 min. 10 Remove Hold Down Nut 0 6 .times. 1 min. = 6 min. 11 Remove Compression Collar 0 6 .times. 1 min. = 6 min. 12 Remove Seal Carrier 0 6 .times. 1 min. = 6 min. TOTAL TIME REQUIRED 368 min. or 6.1 hrs. 116 min. or 1.9 hrs. TIME SAVED 4.2 hrs. __________________________________________________________________________ It will be appreciated that the present invention is not limited to the exact construction which has been described above and which is illustrated in the accompanying FIGS. 2 to 5, 9 to 13B, 15 and 16, and that various modifications and changes can be made without departing from the scope thereof. It is intended that the scope of the invention only be limited by the appended claims. |
047553464 | claims | 1. In a nuclear reactor comprising a vessel, a removable cover for said vessel, a core including fuel nuclear assemblies in said vessel, upper internal equipments situated between said core and said cover, a plurality of first clusters of control elements, each having a top head and movable vertically into and out of said core within and along a guide tube fixed rigidly to said upper internal equipments, a device for displacing and latching one of said first clusters comprising: (a) a vertical shaft vertically movable along its axis under the action of a fluid pressure difference across said shaft in a cylinder, (b) means for connecting said head of said first cluster to said shaft, having first resilient finger means carried by said shaft and notch means formed in said head for receiving said finger means and for resiliently securing and retaining said head on said shaft, (c) a high position head latching mechanism carried by the said fixed guide tube and having second resilient finger means arranged to resiliently engage cooperating means in said head for securing and retaining the head against gravity, and vertically movable bolt urged resiliently to a first position in which it positively prevents resilient deformation of said second resilient finger means and release thereof from said head, and (d) a mechanism for moving a second cluster vertically, cooperating with said bolt for positively moving said bolt into a second position in which it releases said second resilient finger means when the second cluster is moved above the highest position assumed during normal operation thereof. (a) a vertical control shaft for said internal cluster, (b) resilient blade means for connecting individually top heads of said sub-clusters to said shaft, (c) drive means of said shaft for moving said internal cluster between a low position in which the internal cluster rests on the assembly and a high position in which the internal cluster is outside the assembly, (d) a mechanism for latching the sub-clusters in the high position comprising a resilient finger for each sub-cluster, intended to fasten onto the head and retain said sub-clusters against gravity, said latching mechanism in the high position being supported by a guide tube of the internal cluster, and a mobile bolt urged resiliently to a position in which it prevents disengagement of the resilient fingers of said sub-clusters from said head, and (e) a mechanism for moving the external cluster vertically, cooperating with said bolt for forcibly moving said bolt upwardly into a position in which it releases said resilient fingers when the external cluster is moved above the highest position assumed during normal operation thereof. (a) a vertical control shaft for said internal cluster, (b) resilient blade means for connecting individually top heads of said sub-clusters to said shaft, (c) drive means of said shaft for moving said internal cluster between a low position in which the internal cluster rests on the assembly and a high position in which the internal cluster is outside the assembly, (d) a mechanism for latching the sub-clusters in the high position comprising a resilient finger for each sub-cluster, intended to fasten onto the head and retain said sub-clusters against gravity, and a mobile bolt urged resiliently to a position in which it prevents disengagement of the resilient fingers of said sub-clusters from said head, (e) a mechanism for moving the external cluster vertically, cooperating with said bolt for forcibly moving said bolt upwardly into a position in which it releases said resilient fingers when the external cluster is moved above the highest position assumed during normal operation thereof; and (f) means for detecting the position of the cluster, comprising a counter-weight movable axially between a low position which it occupies at rest and a high position into which it is pushed by the head or each head of the external cluster, and a sensor for detecting the axial position of the counter-weight, said sensor being placed on a passage sleeve through the vessel of the reactor and cooperating with a sliding thermal protection muff supported by the counter-weight. 2. A device according to claim 1, wherein the fixed guide tube and the end piece of the fuel assembly each comprises cluster guide slides, the slides being disposed so that the cluster engages one of the slides before it leaves another of said slides. 3. In a nuclear reactor comprising a vessel having a removable cover for said vessel, a core including fuel nuclear assemblies, upper internal equipments situated between said cover, at least one internal cluster of control elements movable vertically into and out of an assembly within and along a guide tube fixed rigidly to said upper equipment and placed above the assembly, said internal cluster comprising a plurality of sub-clusters each having a top head and also provided with an external cluster comprising at least one top head, movable coaxially with said first one and fulfilling a different function, said external cluster comprising at least one top head, a device for displacing and latching the internal cluster comprising: 4. A device acording to claim 2, wherein the vertical shaft for controlling the internal cluster projects upwardly into a sleeve through a tubular shaft supporting the external cluster therefore delimiting in this sleeve a chamber which is closed by said support shaft of the external cluster when this latter is in the high position, means being provided for reducing the pressure which prevails in the chamber below the pressure which prevails in the whole vessel of the reactor. 5. A device according to claim 2, wherein it comprises means for detecting the position of the cluster, comprising a counter-weight movable axially between a low position which it occupies at rest and a high position into which it is pushed by the head or each head of the external cluster and a sensor for detecting the axial position of the counter-weight. 6. In a nuclear reactor comprising a vessel having a removable cover for said vessel, a core including fuel nuclear assemblies, upper internal equipments situated between said cover, at least one internal cluster of control elements movable vertcially into and out of an assembly within and along a guide tube fixed rigidly to said upper equipment and placed above the assembly, said internal cluster comprising a plurality of subclusters each having a top head and also provided with an external cluster comprising at least one top head, movable coaxially with said first one and fulfilling a different function, said external cluster comprising at least one top head, a device for displacing and latching the internal cluster comprising: |
description | The present invention refers to a device for electron beam irradiation of at least one side of a web and a method of ventilating said device. Within the food packaging industry it has for a long time been used packages formed from a web of packaging material comprising different layers of paper or board, liquid barriers of for example polymers and gas barriers of for example thin films of aluminium. In the packaging machine the web is formed into a tube by overlappingly sealing the longitudinal edges of the web. The tube is continuously filled with a product and then transversally sealed and formed into cushions. The cushions are separated and formed into for example parallelepipedic containers. This technology of forming a tube from a web is well known per se and will not be described in detail. To extend the shelf-life of the products being packed it is prior known to. sterilise the web before the forming and filling operations. Depending on how long shelf-life is desired and whether the distribution and storage is made in chilled or ambient temperature, different levels of sterilization can be choosen. One way of sterilising a web is chemical sterilization using for example a bath of hydrogen peroxide. Another way is to irradiate the web by electrons emitted from an electron beam emitter. Such an emitter is disclosed in for example U.S. Pat. No. 5,194,742. There are amongst others two important things that have to be taken into consideration when using an electron beam emitter. The first is how to maintain a desired sterilization level inside the device. A device for web sterilization is formed with openings for the entrance and exit of the web. Unfortunately, bacteria and dirt particles may enter through the openings and also through interconnections between different portions of the device and the surrounding equipment. If these bacteria and dirt particles are left in the device they may recontaminate the web after it has been sterilised. The second consideration is how to safely discharge ozone (O3) from the device thereby minimising the risk of ozone leakage to the outside of the device. It is common knowledge that the presence of oxygen molecules (O2) in an electron irradiation device give rise to the formation of ozone during electron irradiation because of radical reactions. Therefore, an object of the invention has been to provide a device for electron beam irradiation in which both of the above mentioned considerations have been taken into account and solved. The present invention relates to a method of ventilating a device for electron beam irradiation of at least one side of a web. In accordance with a first aspect of the invention, the method comprises the steps of: providing a first chamber comprising a web inlet opening and a web outlet opening, providing a second chamber extending inside the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and an electron exit surface through which electrons are adapted to be emitted into the second chamber, passing the web through the second chamber, and creating a flow of a gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web by supplying said fluid into the web outlet opening of the first chamber and providing at least one outlet. By providing a flow of gaseous fluid through the device in a direction opposite the direction of travel of the web a desired level of sterilization can be maintained inside the device. Any bacteria or dirt particles entering the device at any point will be transported by the flow to that end of the device where the unsterilised web enters, and there it will be discharged from the device through the outlet. The risk of recontamination of the sterilised web before filling and sealing operations is thereby minimised. Further, ozone (O3) that is formed during irradiation with electrons can be effectively and reliably discharged from both the first and second chambers by the same flow of gaseous fluid. The risk of leakage of ozone to the outside of the device is thereby minimised. An additional advantage is that the flow of gaseous fluid is suitable for use during pre-sterilization of the device. Hydrogen peroxide can for example be supplied to the gaseous fluid and thereby the surfaces of both the first and second chambers are sterilised. In accordance with a second aspect of the invention, the method comprises the steps of: providing a first chamber comprising a web inlet opening and a web outlet opening, providing a second chamber extending inside the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and an electron exit surface through which electrons are adapted to be emitted into the second chamber, passing the web through the second chamber, providing fluid connection between the web outlet opening of the second chamber and the web outlet opening of the first chamber, preventing fluid connection between the first chamber and the web outlet opening of the first chamber, and creating a flow of a gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web by supplying said fluid into the first chamber and into the web outlet opening of the first chamber and providing at least one outlet. By providing a flow of gaseous fluid through the device in a direction opposite the direction of travel of the web a desired level of sterilization can be maintained inside the device and the ozone can be safely discharged without leakage to the outside of the device. Further, this design is advantageous if it is desired to have different pressures in the respective chambers since the chambers are supplied by at least one gaseous fluid supply each. Advantageously, the method comprises the step of providing fluid connection between the web inlet opening of the first chamber and both the first chamber and the web inlet opening of the second chamber. By providing this fluid connection, the gaseous fluid from the first chamber can be discharged from the second chamber, which makes it possible to provide only one outlet. In a preferred embodiment the method comprises the step of providing fluid connection between the web outlet opening of the first chamber and both the first chamber and the web outlet opening of the second chamber. In this way both chambers may be easily supplied by the same gaseous fluid supply. In an additional embodiment the web outlet opening of the second chamber is located at a distance from and preferably substantially in line with the web outlet opening of the first chamber. In this way it is not necessary to arrange web guides between the two chambers, and the gaseous fluid that enters through the outlet opening of the first chamber is easily supplied to both chambers. Preferably, the outlet is provided in vicinity of the web inlet opening of the second chamber. By providing the outlet in an end of the device opposite the web outlet opening any bacteria or dirt particles will be forced to the end of the device where the web has not yet been sterilised, thereby minimising the risk of recontamination once the web has been sterilised. Advantageously, the outlet is provided inside the second chamber in the vicinity of the web inlet opening. In this way the ozone is not likely to reach the first chamber, which further minimises the risk of leakage to the outside of the device. In a preferred embodiment, the outlet is provided in the vicinity of the web inlet opening of the first chamber. In this way the discharge can be made in a reliable way with minimised risk of recontamination of the sterilised web. Preferably, the method comprises the step of controlling the flow of gaseous fluid so that a first overpressure is created inside the first closed chamber, and a second overpressure is created inside the second chamber. By providing overpressure in the first and second chamber, the risk of having bacteria and dirt particles from outside the device entering the chambers is minimised. Thus, the inside of the device can be kept at a desired sterilization level. In an embodiment the overpressures are chosen so that the first overpressure and the second overpressure are the same. In this way undesired transport of for example ozone or dirt particles between the two chambers is prevented. In another embodiment the overpressures are chosen so that the first overpressure and the second overpressure are different. For example the first overpressure can be higher than the second overpressure. One reason for choosing such is to keep the ozone within the second chamber where it can be immediately discharged. One reason for choosing the second overpressure so that it is higher than the first overpressure could be to obtain a fast evacuation of ozone and eventual other volatile substances, that for example cause off-flavour, from the second chamber. The invention also comprises a device for electron beam irradiation of at least one side of a web. The device comprises a first chamber comprising a web inlet opening and a web outlet opening, a second chamber extending inside the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and being adapted to receive an electron beam emitter provided with an electron exit window through which electrons are adapted to be emitted into the second chamber, the web being adapted to pass the second chamber, and the web outlet opening of the first chamber being adapted to be in communication with a gaseous fluid supply and both chambers being in communication with an outlet, the supply and the outlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web. As explained before, a desired level of sterilization can be maintained inside the device. Further, ozone that is formed during irradiation with electrons can be effectively and reliably discharged from both the first and second chambers. The risk of leakage of ozone to the outside of the device is thereby minimised. The invention also comprises a device for electron beam irradiation of at least one side of a web, the device comprising a first chamber comprising a web inlet opening and a web outlet opening, a second chamber extending inside the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and being adapted to receive an electron beam emitter provided with an electron exit window through which electrons are adapted to be emitted into the second chamber, the web being adapted to pass the second chamber, a fluid connection is adapted to be provided between the web outlet opening of the second chamber and the web outlet opening of the first chamber, a fluid connection is adapted to be prevented between the first chamber and the web outlet opening of the first chamber, the web outlet opening of the first chamber being adapted to be in communication with a first gaseous fluid supply, the first chamber being adapted to be in communication with a second gaseous fluid supply, both chambers being in communication with an outlet, and the first and second supplies and the outlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web. The invention further comprises a device for electron beam irradiation of at least one side of a web, the device comprising a first chamber comprising a web inlet opening and a web outlet opening, a second chamber extending inside the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and an electron beam emitter provided with an electron exit window through which electrons are to be emitted into the second chamber, the web being adapted to pass the second chamber, and the web outlet opening of the first chamber is in communication with a gaseous fluid supply and both chambers are in communication with an outlet, the supply and the outlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web. Moreover, the invention also comprises a device for electron beam irradiation of at least one side of a web, the device comprising: a first chamber comprising a web inlet opening and a web outlet opening, a second chamber extending inside the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and an electron beam emitter provided with an electron exit window through which electrons are emitted into the second chamber, the web being adapted to pass the second chamber, a fluid connection is provided between the web outlet opening of the second chamber and the web outlet opening of the first chamber, the first chamber is prevented from being in fluid connection with the web outlet opening of the first chamber, the web outlet opening of the first chamber being in communication with a first gaseous fluid supply, the first chamber is in communication with a second gaseous fluid supply, both chambers being in communication with an outlet, and the first and second supplies and the outlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web. The device, shown in FIG. 1, comprises an inner housing 1 in which one or two emitters 2,3 are mounted. A central portion of the inner housing is adapted to receive the emitters. The inner housing 1 forms a tunnel and a packaging material web W is fed through the tunnel past the emitters 2,3. Further, the inner housing 1 is provided with an inlet portion 5 and an outlet portion 6 for the entrance and the exit of the web. The web inlet portion 5 is designed such that the inlet direction of the web W into the inlet portion 5 is angled in relation to the outlet direction of the web W out of the inlet portion 5. The outlet direction of the web W out of the inlet portion 5 is equal to the direction in which the web W passes the emitters 2,3. The angle between the inlet and the outlet direction of the web W in the inlet portion 5 is at least 90°. The inlet portion 5 is formed such that it is angled at at least two locations. In FIG. 2 is shown that the inlet portion 5 comprises three successive segments, an entrance segment 5a, a central segment 5b and an exit segment 5c. The central segment 5b forming a first angle α to the entrance segment 5a and the exit segment 5c forming a second angle β to the central segment 5b. Further, the relation between the tunnel widths, said angles α,β and the lengths of the segments 5a-c is such that an imagined straight line hitting the tunnel wall in the entrance segment 5a also hits the tunnel wall of at least the exit segment 5c, before exiting the exit segment 5c, and that an imagined straight line passing through the entrance segment 5a hits the tunnel wall of the central segment 5b such that it also hits the tunnel wall of at least the exit segment 5c, before exiting the exit segment 5c. In FIG. 3 and 4 are illustrated how the design can be obtained with help of paper, a ruler and a pen. In FIG. 3 a first worst case scenario is disclosed. A straight line is drawn beginning outside the entrace segment 5a and pointing substantially towards the outer corner between the entrance segment 5a and the central segment 5b. The line hits the tunnel wall in the entrance segment 5a and is drawn pointing substantially towards the inner corner between the central segment 5b and the exit segment 5c. If the relation between tunnel widths, angles α,β and segment lengths is to be considered good enough, the straight line will be forced to hit the tunnel wall of the exit segment 5c before exiting the exit segment 5c. In FIG. 4 a second worst case scenario is disclosed. A straight line is now drawn beginning outside the entrace segment 5a and pointing substantially towards the inner corner close to the exit of the entrance segment 5a, but is hitting the tunnel wall in the central segment 5b. The line is then drawn substantially towards the inner corner between the central segment 5b and the exit segment 5c. If the relation between tunnel widths, angles α,β and segment lengths is to be considered good enough, the straight line will be forced to hit the tunnel wall of the exit segment 5c before exiting the exit segment 5c. Thus, it is realised that if a certain angle is used, the parameters that can be modified are either the tunnel width or the length of the segment. A wide tunnel necessitates a long segment. If there is a need for a short segment, the tunnel width must be decreased. Another possibility is of course to change one or both of the angles. The change in the running direction of the web W is accomplished by providing the inlet portion 5 with at least one web guide. In the example the web guide is a first and a second roller 9, 10 mounted inside the inlet portion 5. In the disclosed design the web W runs substantially horizontal into the inlet portion 5 and substantially vertically upwards when it leaves the inlet portion 5 and enters the inner housing 1. To accomplish this change in direction the rollers 9, 10 being formed and mutually located in such a way that the first roller 9 angles the web W the second angle β and that the second roller 10 angles the web W the first angle α. Preferably, the rollers 9, 10 are journalled in support members. The support members can for example be bearings provided with an outer shielding or with a bearing housing designed following the same design criteria as the tunnel. The outlet portion 6 is similarly designed with an entrance segment 6a, a central segment 6b and an exit segment 6c. To change the running direction of the web W the outlet portion 6 comprises one or more rollers 11, 12. The inlet portion 5 and the outlet portion 6 are mounted and designed such that the web W runs in the same direction as it leaves the outlet portion 6 as it does as it enters the inlet portion 5. In the disclosed design the inlet portion 5 and the outlet portion 6 are identical and mounted to two opposite faces 1a, 1b of the inner housing 1 using the same flange on respective portion 5, 6 but turned 180° about an axis A extending along the centre line of the web W running through the inner housing 1. Thus, the respective entrance segment 5a, 6a of the inlet portion 5 and the outlet portion 6 are adjacent the central portion of the tunnel and that the respective exit segment 5c, 6c of the inlet portion 5 and the outlet portion 6 are directed away from each other. An outer housing 4 surrounds the inner housing 1 and the outer housing 4 is provided with openings forming an inlet 7 and an outlet 8 for the entrance and the exit of the web W. The emitters 2, 3 transmit an electron beam out through the exit windows 21, 31. One side of the web W is irradiated by the first emitter 2 and the other side is irradiated by the second emitter 3. For this purpose the second electron beam emitter 3 is positioned substantially opposite the first emitter 2 and the electron exit window 31 of the second emitter 3 is positioned substantially opposite the first electron exit window 21. Below only one emitter 2 will be described in more detail. In accordance with the disclosed design, shown in FIG. 5, the emitter 2 generally comprises a vacuum chamber 22 in which a filament 23 and a cage 24 is provided. The filament 23 is made of tungsten. When an electrical current is fed through the filament 23, the electrical resistance of the filament 23 causes the filament 23 to be heated to a temperature in the order of 2000° C. This heating causes the filament 23 to emit a cloud of electrons. A cage 24 provided with a number of openings surrounds the filament 23. The cage 24 serves as a Faraday cage and help to distribute the electrons in a controlled manner. The electrons are accelerated by a voltage between the cage 24 and the exit window 21. The emitters used are generally denoted low voltage electron beam emitters, which emitters normally have a voltage below 300 kV. In the disclosed design the accelerating voltage is in the order of 70-85 kV. This voltage results in a kinetic (motive) energy of 70-85 keV in respect of each electron. The electron exit window is substantially planar and provided substantially in parallell with the web. Further, the exit window 21 is made of a metallic foil and has a thickness in the order of 6 μm. A supporting net formed of aluminium supports the exit window 21. An emitter of this kind is described in more detail in U.S. Pat. No. 6,407,492B1. In U.S. Pat. No. 5,637,953 is another emitter disclosed. This emitter generally comprises a vacuum chamber with an exit window, wherein a filament add two focusing plates are provided within the vacuum chamber. In U.S. Pat. No. 4,910,435 is yet another emitter disclosed, wherein the electrons are emitted by secondary emittance from a material bombarded by ions. Reference is made to the above patents for a more detailed description of these different emitters. It is contemplated that these emitters and other emitters can be used in the described system. As long as the electrons are within the vacuum chamber, they travel along lines defined by the voltage supplied to the cage 24 and the window, but as soon as they exit the emitter through the emitter window they start to move in more or less irregular paths (scatter). The electrons are slowed down as they collide with amongst others air molecules, bacteria, the web and the walls of the housing. This decrease of the speed of the electrons, i.e. a loss in kinetic energy, gives rise to the emission of X-rays (roentgen rays) in all directions. The X-rays propagate along straight lines. When such an X-ray hits the inner wall of the housing, the X-ray enters a certain distance into the material and causes emittance of new X-rays in all directions from the point of entrance of the first X-ray. Every time an X-ray hits the wall of the housing and gives rise to a secondary X-ray, the energy is about 700-1000 times less, dependent upon the choice of material for the housing. Stainless steel has a reduction ratio of about 800, i.e. the energy of a secondary X-ray is reduced about 800 times in relation to the primary X-ray. Lead is a material often being considered when radiation is involved. Lead has a lower reduction ratio, but has on the other hand a higher resistance against transmission of the X-rays through the material. If the electrons are accelerated by a voltage of about 80 kV, they are each given a kinetic energy of about 80 keV. In order to secure that the X-rays of this energy level do not pass through the inner housing 1, the inner housing 1 is made of stainless steal having a thickness of 22 mm. This thickness is calculated for X-rays travelling perpendicular to the wall. An X-ray travelling inclined in relation to the wall will experience a longer distance in the wall to reach the same depth, i.e. the wall will appear thicker. The wall thickness is determined by the governmental regulations concerning amount of radiation outside the housing. Today the limiting value that the radiation must be less than is 0.1 μSv/h measured at a distance of 0.1 m form any accessible surface, i.e outside shielding. It should be noted that the choice of material and the dimensions are influenced by the regulations presently applicable and that new regulations might alter the choice of material or the dimensions. The energy of each electron (80 keV) and the number of electrons determine the total energy of the electron cloud. This total energy results in a total energy transfer to the surface to be sterilized. This radiation energy is measured in the unit Gray (Gy). In case of the electron emitter briefly described above (with a filament and Faraday cage) it is presently considered suitable to use a current of about 17 mA through the filament. This is however dependent upon the radiation level decided and the area of the surface to be sterilised. In the present example it is contemplated to sterilise a web with a width of 400 mm travelling with a speed of 35 m/s past the emitter. This will give a radiation energy in the order of 35 kGy on average. In another example the web width is still 400 mm, but the speed that the web is travelling with is increased to 100 m/s. To obtain the same radiation energy, 35 kGy, the current is increased to approximately 50 mA. In the following the gaseous fluid system of the device will be described. In this embodiment the fluid is air, but it can of course be any gaseous fluid suitable for the field of application in which the device is used. The air system 100 of the machine, shown in FIG. 6, comprises a compressor 101 and a water separator 102 from which pressurised air is obtained. This air is supplied to a heat exhanger 103 in which the air is pre-heated to about 100° C. From the heat exhanger 103, the air is fed to a superheater 104 in which the air is heated to a temperature within the range 330-450° C. At temperatures above 330° C. any bacteria in the air is killed. The killing rate is dependent upon the temperature and the time the bacteria are subjected to said temperature. The air from the superheater 104 is returned to the heat exhanger 103 for achieving the above-described pre-heating of the incoming air. After the second passage through the heat exchanger 103, the air has a temperature of about 90° C. The air is then fed to a change-over valve 106 having a first branch in fluid connection with the tower 105 of the filling machine and a second branch in fluid connection with a first chamber 107 formed by the outer housing 4. A small amount of the air supplied to the tower 105 will follow the web W out of the tower 105 through an outlet opening 108. In the tower 105 the web W is formed into a tube by overlappingly sealing the longitudinal edges of the web. The tube is continuously filled with a product via a product pipe 109 extending into the tube from the end where the web W has not yet been transformed into a tube. This technology of forming a tube from a web is well known per se and will not be described in detail. The outlet opening 108 is provided with a sealing ring (not shown) in order to have a controlled flow of air out of the outlet opening 108. This can also be achieved by forming the outlet opening 108 with a given clearance in respect of the tube being fed out through the opening 108. The tube is transversally sealed and formed into cushions, which are separated and formed into parallelepipedic containers. Again, this technology is well known per se and will not be described in detail. A significant portion of the air supplied to the tower 105 flows in the tower 105 in a direction opposite the direction of travel of the web W. The tower 105 is provided with a web inlet opening 110 acting as an air outlet opening 110. The air from the tower 105 is fed to a second chamber 111 formed of the inner housing 1. In the following the area marked with dashed lines in FIG. 6 will be described. The dashed lines represent two alternative embodiments of the air flow into the first and second chambers. In a first embodiment the lines are continuous and represents a closed communication directly between a web outlet opening 112 of the second chamber 111 and a web outlet opening 121, also denoted outlet 8, of the first chamber 107. In a second embodiment the lines are not present and represents an open communication between both the first and second chambers 107, 111 and the web outlet opening 121 of the first chamber 107. In the first embodiment there is provided a fluid connection between a web outlet opening 112 of the second chamber 111 and a web outlet opening 121 of the first chamber 107. Thus, the air is fed into the second chamber 111 via the web outlet opening 112 acting as an airflow inlet opening 112. The tower 105 acting as a first air supply. If the web outlet opening 112 of the second chamber 111 is located at a distance from and preferably substantially in line with the web outlet opening 121 of the first chamber 107, the fluid connection can for example comprise a pipe that connects the web outlet opening 112 of the second chamber 111 with the web outlet opening 121 of the first chamber 107. Alternatively, the web outlet opening 112 of the second chamber 111 extends to the web outlet opening 121 of the first chamber 107. A fluid connection between the first chamber 107 and the web outlet opening 121 of the first chamber 107 is thereby prevented. As been earlier described, the change-over valve 106 is acting as air supply 106 for the first chamber 107. In a second embodiment both the first chamber 107 and the second chamber 111 are in fluid connection with the web outlet opening 121 of the first chamber 107, thus both chambers 107, 111 being in connection with the air supply in the tower 105. In addition, the first chamber 107 is being in contact with valve 106 for additional supply of air. In both embodiments the air in the second chamber 111 flows in a direction opposite the direction of travel of the web W through the second chamber 111. After passage almost completely through the second chamber 111 the air is fed via a discharge outlet 113 for ultimate disposal of the air. Similarly, the air provided to the first chamber 107 flows in a direction opposite the direction of travel of the web W. The air from the first chamber 107 and the second chamber 111 is discharged via the outlet 113. Thus, both chambers 107, 111 being in contact with the outlet. A small amount of the air supplied to the first chamber 107 escapes via a web inlet opening 115, also denoted inlet 7. The amount escaping is dependent of the shape of the gap and the sealing used. This in turn depend amongst others upon if the web is supplied with pre-applied opening devices or not. The discharge outlet 113 is located close to the web inlet opening 114 of the second chamber 111. In FIG. 1, the outlet 113 is located inside the second chamber 111. For example the outlet 113 can be located in the vicinity of the web inlet opening 114 of the second chamber 111. The outlet 113 is discharging almost all the air from the second chamber 111 and most of the air from the first chamber 107. There is provided a fluid connection between the web inlet opening 115 of the first chamber 107 and both the first chamber 107 and the web inlet opening 114 of the second chamber 111. In an alternative embodiment shown in FIG. 7 the outlet 113 comprises two branches 113a, 113b in fluid connection with the second chamber 111. With reference to the figure, the first outlet branch 113a is located in the top of the chamber wall in the vicinity of the web inlet opening 114 of the second chamber 111, and the second outlet branch 113b is located in the bottom wall opposite the first. The flow of air in the system is controlled so that a first overpressure is created inside the first chamber 107. In the described embodiment the pressure is in the order of 30 mm H2O. Further, a second overpressure is created inside the second chamber 111. The overpressures can for example be choosen so that the first overpressure and the second overpressure are the same. Alternatively, the overpressures are choosen so that the first overpressure and the second overpressure are different. The first pressure can be higher than the second pressure and vice versa. One reason for choosing the first overpressure so that it is higher than the second overpressure is to keep ozone (O3), formed during irradiation, within the second chamber 111 where it can be immediately discharged through the outlet 113. Further, a lower second overpressure helps during pre-sterilization of the device at for example start-up of the machine. By having a lower pressure in the second chamber compared to the first chamber, a sufficient amount of the hydrogen peroxide used during the sterilization is forced inside the second chamber. The pre-sterilization will be explained in more detail below. One reason for choosing the second overpressure so that it is higher than the first overpressure could be to obtain a fast evacuation of ozone and eventual other volatile substances, that for example cause off-flavour, from the second chamber. Inside the inner housing 1, i.e. around the emitters 2,3, is provided a pressure that is preferably lower than the pressure inside the second chamber 111. One reason for choosing a pressure lower than the pressure inside the second chamber 111 is to minimise the risk of recontamination of the web W by contaminated air contained in the inner housing 1. Since no certain pressure is necessary for the emitters 2, 3 used in this particular embodiment, the pressure in the inner housing 1 can be atmospheric pressure. However, it should be understood that the inner housing 1 may be pressurised if necessitated by the emitters used. Outside the first chamber 107, the air system 100 is provided with a so-called zero point 116. The zero point 116 is a device making sure that if something fails in the system, any air needed to avoid a pressure below the atmospheric pressure will be fed into the system via the zero point 116. This way it is secured that the pressure inside the tower 105, the first chamber 107 and the second chamber 111 at least not will drop below the atmospheric pressure. The zero point 116 generally comprises a housing with an inlet 117 and an outlet 118 and an opening 119 being closed by a valve 120. Any pressure above the atmospheric pressure pushes the valve outwards sealingly closing of the opening 119. If the pressure inside the zero point 116 drops below the atmospheric pressure the valve 120 will not be pushed against the opening 119 (on the contrary it will be pushed inwards into the zero point 116 and air can be introduced into the system via the opening 119). During for example start-up of the machine, the air system 100 can be used for sterilizing the surfaces inside of tower 105 and the chambers 107,111 prior to entering the web W. The sterilization is made with hydrogen peroxide (H2O2). Sterilization using hydrogen peroxide is known per se, but will be briefly described in the following with regard to the air system 100. The tower 105 is in connection with a hydrogen peroxide supply, which is provided with aerosol nozzles. The nozzles feed hydrogen peroxide into the air as spray and the air supplied in the tower is heated to a temperature at which the hydrogen peroxide vapourises, normally a temperature in the order of 40-50° C. The hydrogen peroxide contained air flows through the tower and the chambers 107,111 in the arlier described direction and is discharged at the discharge outlet 113. Along he way the hydrogen peroxide condenses on the surfaces. The hydrogen peroxide is then removed from the surfaces by supplying air of a temperature at or above the hydrogen peroxide vapourisation temperature. In this embodiment a temperature in the order of 70-90° C. is used. By providing a temperture well above the vaporisation temperature the hydrogen peroxide is effectively and quickly removed from the surfaces. In accordance with the method for electron beam irradiation of a web W, the web W is provided to pass through the tunnel. The tunnel is being provided with a web inlet portion 5, a web outlet portion 6 and a central portion adapted to receive an electron beam emitter 2, 3 provided with an electron exit window 21, 31. Electrons are emitted into the tunnel from the emitter 2,3 through the electron exit window 21, 31, and any X-ray being formed by the electrons during irradiation of the web W is forced to hit the tunnel wall twice before exiting the tunnel. To accomplish at least two hits the tunnel is being formed angled at at least two locations in each of the inlet and outlet portions 5, 6. Further, the method comprises forming the inlet portion 5 so that it comprises a line of three sucsessive segments, an entrance segment 5a, a central segment 5b and an exit segment 5c. The central segment 5b is made so that it forms a first angle α to the entrance segment 5a. Furthermore, the exit segment 5c forms a second angle β to the central segment 5b. The outlet portion 6 is similarily designed. A relation between the tunnel widths, said angles α,β and the lengths of the segments 5a-c is formed so that an imagined straight line hitting the tunnel wall in the entrance segment 5a is also hitting the tunnel wall of at least the exit segment 5c, before exiting the exit segment 5c, and that an imagined straight line passing through the entrance segment 5a is hitting the tunnel wall of the central segment 5b such that it is also hitting the tunnel wall of at least the exit segment 5c, before exiting the exit segment 5c. It is known that during irradiation with electrons ozone (O3) is formed inside the device. Therefore, the invention also comprises a method of ventilating the device. The method comprises the step of providing a first chamber 107 comprising a web inlet opening 115 and a web outlet opening 121. The first chamber 107 being the outer housing 4. A second chamber 111, being the tunnel, is also provided and extends inside the first chamber 107. The second chamber 111 is formed comprising a web inlet opening 114 and a web outlet opening 112. Further, an electron exit window 21, 31 is provided through which electrons are adapted to be emitted into the second chamber 111. The web W is passing through the second chamber 111, and a flow of air through both the first and second chambers 107, 111 is created. The air flow flows in a direction opposite the direction of travel of the web W. The air is supplied into the web outlet opening 121 of the first chamber 107 and there is provided at least one outlet 113. In an alternative method fluid connection is being provided between the web outlet opening 121 of the second chamber 111 and the web outlet opening 112 of the first chamber 107. At the same time fluid connection between the first chamber 107 and the web outlet opening 121 of the first chamber 107 is prevented. A flow of air through both the first and second chambers 107, 111 in a direction opposite the direction of travel of the web W can then be created by supplying said air into the first chamber 107 and into the web outlet opening 121 of the first chamber 107 and providing at least one outlet 113. Air is supplied to the first chamber 107 through a valve 106 being in fluid connection with the first chamber 107. According to the method the web W is thus entering the device through the web inlet opening 115 of the first chamber 107 and enters the second chamber 111 at its web inlet opening 114. Both openings 115, 114 are located such that the web W is kept straight, substantially horizontal when passing them. Inside the inlet portion 5 the web W is angled the second angle β at the first roller 9 and angled the first angle α at the second roller 10. During travelling, the web W meets an airflow flowing in a direction opposite the web W. When the web W passes the central portion of the tunnel, now travelling in a vertical direction, it passes electron exit windows 21, 31 through which the web W is irradiated by emitters 2, 3. The electron exit windows 21, 31 are located on opposite sides of the tunnel thereby irradiating both sides of the web W. After the irradiation the web W enters into the outlet portion 6 in which it is angled twice like in the inlet portion 5. Finally, it is exiting the device through the web outlet opening 112 of the second chamber 111, and then through the web outlet opening 121 of the first chamber 107, thereby entering the tower 105. Although the present invention has been described with respect to a presently preferred embodiment, it is to be understood that various modifications and changes may be made without departing from the object and scope of the invention as defined in the appended claims. The described embodiment comprises two emitters 2,3, one for electron irradiation of one side of the web W and the other for electron irradiation of the other side of the web W. However, it is to be understood that the device does not need to comprise two emitters 2,3, but can comprise only one emitter. Further, it has been described that the two emitters 2,3 are located opposite each other. Alternatively they can be located at a distance from each other in the web direction. Moreover, it is also to be understood that the number of emitters can be more than two. It is for example possible to have several emitters side by side to handle wide webs. It is also possible to have two or more emitters located after each other along the direction of the web to form either subsequent sterilizing zones which together provide the decided radiation level, or as measure of selective radiation of a certain point, for example a closure device, that may need a higher radiation level. Further, it should be understood that the location of the outlet 113 can be modified. In the above-described emodiment the outlet 113 is located inside the second chamber 111. Alternatively the outlet 113 can for example be located in vicinity of the web inlet opening 114 of the second chamber 111 or in the vicinity of the web inlet opening 115 of the first chamber 107. It is also possible to locate the outlet 113 outside, near the inlet opening 115, of the first chamber 107. Moreover, in the above-described embodiment the outlet 113 is located inside the second chamber 111 and the first chamber 107 is in fluid connection with the second chamber 111. In an alternative embodiment the web inlet opening 114 of the second chamber 111 is in fluid connection with the web inlet opening 115 of the first chamber 107, while fluid connection between the first chamber 107, its web inlet opening 115 and the web inlet opening 114 of the second chamber 111 is prevented. The two chambers 107,111 will then be in communication with separate outlets. At least one outlet can be located in the first chamber 107 and at least one outlet can be located in the second chamber 111 or in fluid connection with the second chamber 111. Further, the air system described using hydrogen peroxide is preferably used in aseptic fields of application. In a corresponding air system in a packaging machine used for handling pasteurized products the air flows are similar, although the machine sterilization is usually made by using filtered air. Instead of the above described system, the system can then comprise a filter and a fan. To evacuate ozone from the chambers during operation, the system can be provided with a catalytic converter. Moreover, in the embodiment shown the web inlet opening 114 of the second chamber 111 is located at a distance from and preferably in line with the web inlet opening 115 of the first chamber 107. Alternatively, the second chamber 111 can extend all the way up to the web inlet opening 115 of the first chamber thereby preventing fluid connection between the first chamber 107 and the web inlet opening 115. The wall of the second chamber 111 is then instead provided with throughgoing openings, preferably slits, at a distance from the web inlet opening, but before the outlet 113. Fluid connection between the two chambers is thereby provided and the arrangement give rise to a so called injector effect making air flow from the first chamber through the slits into the second chamber where it can be evacuated through the outlet 113. A small amount of air is also sucked from outside the housings through the web inlet opening 115. |
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claims | 1. A hybrid indirect-drive/direct drive method for inertial confinement fusion utilizing indirect drive laser beams from a first direction and direct drive laser beams from a second direction, comprising the steps of:providing a deuterium-tritium gas fusion fuel,assembling a first indirect drive portion of a shell having a first thickness partially surrounding said deuterium-tritium gas fusion fuel,assembling a second direct drive portion of a shell having a second thickness greater than said first thickness of said first indirect drive portion of a shell partially surrounding said deuterium-tritium gas fusion fuel to complete said shell,assembling a hohlraum containing at least a portion of said deuterium-tritium gas fusion fuel and at least a portion of said first indirect drive portion of a shell in a position relative to the indirect drive laser beams,shock igniting said indirect drive portion of a shell and said deuterium-tritium gas fusion fuel using the indirect drive laser beams to produce X-rays that are directed to said indirect drive portion of a shell and said deuterium-tritium gas fusion fuel; andshock igniting said direct drive portion of a shell and said deuterium-tritium gas fusion fuel using the direct drive laser beams. 2. The hybrid indirect-drive/direct drive method for inertial confinement fusion of claim 1 further comprising the step of using a fill tube extending through said shell to inject said deuterium-tritium gas fusion fuel into said shell. |
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052805069 | summary | BACKGROUND OF THE INVENTION The present invention relates to a main steam isolation valve particularly of a boiling water reactor (BWR) plant for suppressing oscillation of a valve disk of the steam isolation valve. Generally, in a BWR plant, a reactor pressure vessel is directly connected to a steam turbine through a plurality of main steam pipes, and first and second main steam isolation valves are incorporated to each of the main steam pipes inside and outside of the reactor container. The reactor pressure vessel is isolated as occasion demands by closing these main steam isolation valves. The steam used in the steam turbine is condensed into condensate in a condenser and the condensate is then returned to the reactor pressure vessel. In a conventional main steam isolation valve, inlet and outlet end portions of a valve body are connected to each of the main steam pipes and a valve disk is accommodated in the valve body in an axially reciprocal manner. The valve disk is provided with a valve shaft which is inclined inwardly, in an installed state, by about 45.degree. with respect to the flow direction of the mainsteam thereby to reduce flow resistance. The valve shaft is connected at one end to a driving means to reciprocatingly move the valve disk thereby to open or close the fluid, i.e. steam, passage. The reciprocating motion of the valve disk is guided with a central guide rib and a bilateral pair of side guide ribs inwardly projecting at rear side portions of the valve body circumferentially apart from the central guide rib with a separation angle of about 120.degree. with each other. In such a structure, when the valve disk is rested on a valve seat, the valve disk is fully closed and the valve disk is upwardly lifted thereby to fully open a valve port. In the conventional structure of the main steam isolation valve, since the bottom portion of the valve disk is held, at its fully opened state, with substantially the half portion thereof being projected into the fluid passage, the projected bottom portion is exposed to the steam flow, thus being subjected to fluid pressure in the main steam flowing direction and a direction normal thereto. Because the fluid pressure is in proportion to two squares of the fluid velocity, the valve disk may be oscillated in case of high fluid velocity. When the valve disk is oscillated, the central guide rib is rubbed with the valve disk with each other, resulting in the wear thereof and hence causing the leakage of the steam even in the case of the fully closed state of the valve. Furthermore, since the steam flow is prevented by the paired side guide ribs and the valve disk, the pressure is locally increased at the upstream side of the steam flow, and since a force for pressing the valve disk against the side guide rib sides, friction force between the guide ribs and the valve disk is increased, thus the degree of wear therebetween being also increased, resulting in the increased possibility of causing the leakage of the steam. SUMMARY OF THE INVENTION An object of the present invention is to substantially eliminate the defects and drawbacks encountered in the prior art described above and to provide a steam isolation valve, particularly of a main steam isolation valve for a reactor power plant, capable of effectively suppressing oscillation of a valve disk of the isolation valve thereby to improve a reliance thereof during the valve disk opening and closing operations. This and other objects can be achieved according to the present invention by providing, in one aspect, a steam isolation valve comprising a valve box provided with inlet and outlet portions through which a steam flows and an end opening, a valve disk accommodated in the valve body to be reciprocatingly movable therein along an inner peripheral surface of the valve body for opening and closing the steam flow inlet portion, a driving mechanism secured to the valve body and operatively connected to the valve disk for reciprocatingly moving the valve disk body in the valve body, and a coupling member applied to the end opening of the valve body for holding the valve disk when the valve disk is shifted to a position fully opening the inlet portion. The open end of the valve disk has a tapered surface which is firmly engaged with a tapered surface of the coupling member. In another aspect of the present invention, there is provided a steam isolation valve comprising a valve body provided with inlet and outlet portions through which a steam flows and an end opening, a valve disk accommodated in the valve disk body to be reciprocatingly movable therein along an inner peripheral surface of the valve body for opening and closing the steam flow inlet portion, a driving mechanism secured to the valve body and operatively connected to the valve disk for reciprocatingly moving the valve disk body in the valve body, and a tubular wall member integrally formed with the valve body, the valve disk being accommodated in an inner hollow portion of the tubular wall member with a gap therebetween when the valve disk is shifted to a position fully opening the inlet portion. In a further aspect of the present invention, there is provide a steam isolation valve comprising a valve body provided with inlet and outlet portions through which a steam flows and an end opening, a valve disk accommodated in the valve body to be reciprocatingly movable therein along an inner peripheral surface of the valve body for opening and closing the steam flow inlet portion, a driving mechanism secured to the valve body and operatively connected to the valve disk for reciprocatingly moving the valve disk body in the valve box, and a tubular wall member integrally formed with the valve body, and a steam flow guide means disposed for the valve body for guiding the steam flow from the inlet portion of the valve body. The guide means comprises a central guide rib disposed at the inlet portion of the valve body and side guide ribs formed integrally with an inner peripheral surface of the valve body at portions circumferentially apart from the central guide rib. The central guide rib may be formed so as to have a various arrangement for changing the steam flow velocity on both the side of the central guide rib at the inlet portion of the valve body. According to the characters of the present invention described above, in one aspect, when the valve disk is fully opened, the coupling member is detachably engaged with the valve disk. Since the coupling member is secured to the valve body, the valve disk is firmly secured to the valve body through the coupling member when the valve disk fully closes the inlet portion of the valve body, thus the oscillation of the valve disk due to the steam flow being suppressed. Accordingly, the friction and, hence, the wearing between the valve disk and the associated members slidably engaged with the valve disk can be significantly reduced, resulting in the prevention of the steam from leaking and in the improved reliance of the steam isolation valve itself. In another aspect, when the valve disk is fully opened, the valve disk is accommodated in the tubular wall member formed integrally with the valve body, so that the direct striking of the steam flow against the valve disk can be prevented. Accordingly, the oscillation of the valve disk due to the steam flow can be suppressed. The friction and, hence, the wearing between the valve disk and the associated members slidably engaged with the valve disk can be significantly reduced, resulting in the prevention of the steam from leaking and in the improved reliance of the steam isolation valve itself. In a further aspect, since the steam flow sectional areas are made asymmetric around the valve disk by the specific location or arrangement of the guide rib, the flow velocities of the steams on both the sides of the guide rib differ from each other and, hence, there causes a difference between the static pressures of the steam flowing on both the sides of the guide rib. Accordingly, unidirectional force is always caused from the high static pressure side steam from to the low static pressure side steam flow, thus effectively suppressing the oscillation of the valve disk. Furthermore, substantially the same effects as described with respect to the above aspects can be also attained. |
description | This application is a divisional application of U.S. patent application Ser. No. 11/754,928, filed May 29, 2007, for Method and System for Controlled Fusion Reactions, claiming priority to U.S. Provisional Patent Application No. 60/809,453 entitled “Method & Apparatus for Controlled Fusion Reactions” filed May 30, 2006. The foregoing applications are hereby incorporated herein by reference in their entireties. The present invention relates to a system for producing electromagnetic radiation incorporating a drift tube modified to enable output of higher frequencies from a high power RF source incorporating the drift tube. Prior art Magnetically Insulated Linear Oscillators (MILOs) are high power RF sources, which have typical outputs between 300 MHz and 3.5 GHz. For various applications, it would be desirable to provide a high power RF source that can achieve even higher frequencies. The present invention relates to a system for producing electromagnetic radiation incorporating a drift tube which includes a hollow cylindrical conductive element having a grating surface formed on its inner surface, with the ends of the cylindrical conductive element being radiused to minimize electrical stress buildup. The interaction between a relativistic electron beam from an electron source passing through the inner space of the hollow element and the internal grating produces RF radiation by the Smith-Purcell Effect. The spacing, face angle and shape of the grating, and the energy of the electron beam, are determinants of the frequency of the RF radiation. The foregoing drift tube, having a grating on the inner surface of a cylindrical drift tube, can be used advantageously to increase the frequency output of such devices as a Magnetically Insulated Linear Oscillator (MILO) beyond the aforementioned range of 300 MHz to 3.5 GHz mentioned for a MILO. A list of drawing reference numbers, their associated parts and preferred materials for the parts can be found near the end of this description of the preferred embodiments. FIG. 1 shows a cross-section of a Stimulated X-ray Emitter (SXE) combined with a Magnetically Insulated Linear Oscillator (MILO) at the output (right-shown) end of the SXE. The Stimulated X-ray Emitters were first described by the inventor of this current invention in U.S. Pat. No. 4,723,263. The MILO is another well known, high power RF source, similar to the Vircator. The significant difference is that it can produce much higher frequencies than the Vircator. Structurally, the major difference is the incorporation of a drift tube 122 of FIG. 3A and use of a Traveling Wave Electron Gun (TWEG) instead of the planar cathode 90 and grid 92 of the Vircatron. There is a resonant cavity 98 and its dimensions in conjunction with the dimensions of the drift tube 122 (FIG. 3A) determine the output range. Conventional MILO devices have outputs between 300 MHz and 3.5 GHz. The inventor of the present invention has experimentally verified that by placing a grating surface on the inner face of the drift tube 122 (FIG. 3A), as shown in FIG. 3B, it is possible to generate RF at much higher frequencies than those available from a smooth bore drift tube 122. The source of this RF is due to the Smith-Purcell effect which describes the interaction of a relativistic electron beam with a grating surface 123. Outputs in the THz range are possible. The grating surface can be formed by many methods. The spacing, face angle and grating geometry all are determinants in the frequency achieved (FIG. 3B). It has been determined that the preferred embodiment of the drift tube grating is an internal thread as shown in FIGS. 3A and 3B. By altering the thread parameters, the output frequency is changed. The ends of the Drift Tube 125 are radiused to minimize formation of undesirable electric field perturbations inside the Resonant Cavity 98. The balance of the SXE-MILO driver is the same as the SXE-Vircator. In fact, the RF heads—Vircator and MILO—can be interchanged. As in the case of the SXE-Vircator, the TWEG of the MILO has a hollow center through which the x-rays pass. The electron output from the TWEG is compressed by the drift tube 122 and oscillates in the resonant cavity 98. The following list of drawing reference numbers has three columns. The first column includes drawing reference numbers; the second column specifies the parts associated with the reference numbers; and the third column mentions a preferred material (if applicable) for the parts. REFERENCE NUMBER LISTPREFERRED MATERIAL64AnodeRefractory Metal; Hi-Z66GridRefractory Metal68CathodeGraphite (PreferredEmbodiment)70Coaxial CapacitorDielectric/Metal Layers72Cathode FeedthroughCeramic & Metal74Grid FeedthroughCeramic & Metal78Radiation ShieldLead94Anode MeshRefractory Metal96Output WindowRF Transparent Low-ZCeramic98Resonant Circular CavityStainless Steel or Copper100Mounting FlangeStainless Steel102Cathode FeedthroughCeramic & Metal106Grid FeedthroughCeramic & Metal110Getter Pumpn/a112Getter Pump FeedthroughCeramic & Metal114MILO CathodeGraphite116MILO Cathode SupportRefractory Metal118MILO GridRefractory Metal120MILO Grid supportrefractory Metal122Drift TubeRefractory Metal123Grating SurfaceRefractory Metal124Drift Tube SupportCeramic125Radiused end of Drift TubeRefractory Material126Internal Anode InsulatorCeramic142Grid Output TerminalRefractory Metal The foregoing describes a drift tube where the inclusion of a grating surface on the inner surface of the tube generates higher frequencies of RF radiation. While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true scope and spirit of the invention. |
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abstract | Configurations of molten fuel salt reactors are described that utilize neutron-reflecting coolants or a combination of primary salt coolants and secondary neutron-reflecting coolants. Further configurations are described that circulate liquid neutron-reflecting material around an reactor core to control the neutronics of the reactor. Furthermore, configurations which use the circulating neutron-reflecting material to actively cool the containment vessel are also described. |
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abstract | An EUV source (82) that delivers a laser beam (94, 96) asymmetrical relative to first collection optics (88). The first collection optics (88) has an opening (90, 92) for the laser beam (94, 96) that is positioned so that the laser beam (94, 96) is directed towards the plasma off-axis relative to the collection optics (88). Thus, the strongest EUV radiation (98, 100) is not blocked by the target production hardware (84). |
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claims | 1. An x-ray optical apparatus for conditioning an x-ray beam, the apparatus comprising:a total reflection section comprising a material with an index of refraction less than unity at a selected wavelength of the x-ray beam, the material having a polished surface that receives and redirects the beam; anda multilayer section comprising alternating material layers that are spaced relative to each other such as to provide wavelength specific reflection at the selected wavelength of the x-ray beam and corresponding monochromating of the x-ray beam,wherein the total reflection section and the multilayer section are arranged relative to each other such that the x-ray beam encounters the polished surface of the total reflection section at an incidence angle low enough to provide total external reflection of the beam, and encounters the multilayer section at a Bragg angle that provides peak reflection of the selected wavelength, and wherein substantially all portions of the x-ray beam at the selected wavelength are redirected by both the total reflection section and the multilayer section along a predetermined path. 2. An x-ray optical apparatus according to claim 1 wherein the entire x-ray beam encounters one of the sections prior to the other. 3. An x-ray optical apparatus according to claim 2 wherein the sections are arranged in a Kirkpatrick-Baez configuration. 4. An x-ray optical apparatus according to claim 1 wherein part of the x-ray beam encounters the total reflection section prior to the multilayer section, and part of the x-ray beam encounters the multilayer section prior to the total reflection section. 5. An x-ray optical apparatus according to claim 1 wherein the optical apparatus focuses the x-ray beam. 6. An x-ray optical apparatus according to claim 1 wherein one of the sections is shaped like a side-by-side single bounce mirror, and one of the sections is shaped like a double side reflection mirror, and wherein the two sections are adjacent to each other such that the x-ray beam is reflected by each of the two sections. 7. An x-ray optical apparatus according to claim 6 wherein the relative positioning of the sections are changed in order to change a focus distance between the apparatus and a focus spot of the x-ray beam. 8. An x-ray optical apparatus according to claim 1 wherein each section has a surface with a cylindrical curvature, one of which is concave and one of which is convex, and wherein the two sections are adjacent to each other such that the x-ray beam is reflected by each of the two sections. 9. An x-ray optical apparatus according to claim 8 wherein the relative positioning of the sections are changed in order to change a focus distance between the apparatus and a focus spot of the x-ray beam. 10. An x-ray optical apparatus according to claim 1 wherein the sections are arranged in a double cross-coupled configuration in which the two sections are adjacent to each other along a primary propagation direction of the x-ray beam, and each of the sections comprises a side-by-side arrangement of reflective surfaces. 11. An x-ray optical apparatus according to claim 10 wherein the relative positioning of the sections are changed in order to change the focus distance between the apparatus and a focus spot of the x-ray beam. 12. An x-ray optical apparatus according to claim 1 wherein one of the sections encompasses the other section about an axis parallel to a primary propagation direction of the x-ray beam. 13. An x-ray optical apparatus according to claim 12 wherein the section that encompasses the other section has an inner surface with a radius, relative to the axis, that varies in a direction parallel to the axis. 14. An x-ray optical apparatus according to claim 12 wherein the section that is encompassed by the other section has an outer surface with a radius, relative to the axis, that varies in a direction parallel to the axis. 15. An x-ray optical apparatus according to claim 12 wherein the relative positioning of the sections are changed in order to change the focus distance between the apparatus and a focus spot of the x-ray beam. 16. A method of conditioning an x-ray beam, the method comprising directing the x-ray beam toward an x-ray optical apparatus having two sections, wherein a total reflection section of the apparatus comprises a material with an index of refraction less than unity at a selected wavelength of the x-ray beam, and the material has a polished surface that receives and redirects the beam, and wherein a multilayer section comprises alternating material layers that are spaced relative to each other such as to provide wavelength specific reflection at the selected wavelength of the x-ray beam and corresponding monochromating of the x-ray beam, and wherein the total reflection section and the multilayer section are arranged relative to each other such that the x-ray beam encounters the polished surface of the total reflection section at an incidence angle low enough to provide total external reflection of the beam, and encounters the multilayer section at a Bragg angle that provides peak reflection of the selected wavelength, and wherein substantially all of portions of the x-ray beam at the selected wavelength are redirected by both the total reflection section and the multilayer section along a predetermined path. 17. A method according to claim 16 wherein the entire x-ray beam is reflected by one of the sections prior to the other. 18. A method according to claim 16 wherein part of the x-ray beam encounters the total reflection section prior to the multilayer section, and part of the x-ray beam encounters the multilayer section prior to the total reflection section. 19. A method according to claim 16 further comprising focusing the x-ray beam with the optical apparatus. 20. A method according to claim 19 further comprising adjusting the focus length between the apparatus and a focus spot of the x-ray beam by adjusting the relative position of the two sections. |
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claims | 1. A radiation source, comprising:an electron gun,a pair of targets each locatable in the path of a beam produced by the electron gun, the targets having different emission characteristics, wherein a first target of the pair is an electron window that emits x-radiation used for the production of images, andan electron absorber insertable into and withdrawable from the path of the beam for removing electrons from the beam but allowing x-radiation to pass through. 2. A radiation source according to claim 1, wherein the electron window is of Nickel. 3. A radiation source according to claim 1, wherein a second target of the pair is of Copper, Tungsten, or a composite including Copper and Tungsten. 4. A radiation source according to claim 1, wherein the electron absorber comprises a material of a lower atomic number than the electron window. 5. A radiation source according to claim 1, wherein the electron absorber is of Graphite, Carbon, Beryllium or Aluminium. 6. A radiation source according to claim 1, wherein the electron gun is within a vacuum chamber, and at least one of the targets is located at a boundary of the vacuum chamber. 7. A radiation source according to claim 1 further comprising:a primary collimator located in the beam subsequent to the targets. 8. A radiation source according to claim 7, wherein the electron absorber is located in the primary collimator. 9. A radiation source according to claim 7, wherein there are a plurality of primary collimators interchangeably locatable in the path of the beam, at least one of which primary collimators contains the electron absorber. 10. A radiation source according claim 1, wherein the electron window is substantially transparent to the beam. 11. A radiation source according to claim 1 further comprising:at least one of a bow-tie filter and a diagnostic filter, such filter being selectably locatable in the path of the beam. 12. A radiation source according to claim 1 further comprising:at least one adjustable collimator extendable into the path of the beam thereby to delimit it, the adjustable collimator being sized to substantially attenuate a megavoltage x-ray beam. 13. A radiotherapy apparatus including a radiation source according to claim 1. 14. A radiotherapy apparatus according to claim 13, wherein the radiation source is rotatable around a horizontal axis that lies in the path of the beam. 15. A radiotherapy apparatus according to claim 14, wherein the horizontal axis is perpendicular to the beam. 16. A radiotherapy apparatus according to claim 13, further comprising a flat panel imaging device in the path of the beam. 17. A radiotherapy apparatus according to claim 16, wherein the flat panel imaging device includes a scintillator layer. 18. A radiotherapy apparatus according to claim 17, wherein the scintillator layer includes of at least one of Caesium Iodide, Gadolinium Oxisulphide and Cadmium Tungstate. 19. A radiotherapy apparatus according to claim 13, further comprising a patient support between the source and the flat panel imaging device. 20. A radiotherapy apparatus according to claim 13 further comprising:a control means programmed to obtain a plurality of two-dimensional images using x-radiation produced by the radiation source, anda reconstruction means adapted to reconstruct those images to form a three-dimensional CT dataset. |
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055240429 | claims | 1. An exit window for sealing an X-ray lithography beamline from an exposure chamber comprising: a frame for mounting the exit window, said frame having an opening; a thin material having a window section disposed within said opening of said frame, a peripheral section integral with said window section which extends within the frame, and a thickness; and said window section having a shape that is substantially concave along its width and substantially linear along its length and tapering to a flat surface at said peripheral section such that said thin material can withstand a pressure differential between said X-ray lithography beamline and said exposure chamber of at least 14.7 psi. a frame for mounting the exit window, said frame having an opening; and a thin material mounted within said opening, said thin material having a radius of curvature along predetermined portions of its length and widths converging to a flat surface along its edges and a thickness to withstand a pressure differential between said X-ray lithography beamline and said exposure chamber of at least 14.7 psi, wherein an X-ray beam emitted from the beamline and passed through the thin material has X-rays above and below a predetermined energy band substantially attenuated. positioning a stationary exit window having an opening that is approximately equal to the exposure field between said X-ray lithography beamline and said wafer, said opening having a thin material mounted therein, said thin material having a radius of curvative along predetermined portions of its length and width, converging to a flat surface along its edges and a thickness that can withstand a pressure differential of at least 14.7 psi; drawing a vacuum within said lithography beamline such that there is a pressure differential of at least 14.7 psi between the X-ray lithography beamline and an exposure chamber containing the wafer; scanning the X-ray beam between first and second positions such that the X-ray beam passes through the exit window and is incident on the wafer between first and second edges of the exposure field; attenuating X-rays emitted from the X-ray beam as passed through the exit window above and below a predetermined energy band. 2. The exit window of claim 1 wherein said opening of said frame has a rectangular shape having a length of 50 mm and a width of 25 mm. 3. The exit window of claim 2 wherein said peripheral section of said thin material has a length of 120 mm and a width of 42 mm. 4. The exit window of claim 1 wherein said thin material has a predetermined thickness to attenuate X-rays above and below a desired energy band. 5. The exit window of claim 1 wherein said thin material is formed of beryllium having a thickness of between 16 and 25 microns. 6. The exit window of claim 4 wherein said desired energy band is between 800 and 1800 eV. 7. The exit window of claim 4 wherein a radius of curvature of said window section is greater than two inches. 8. The exit window of claim 1 wherein the opening in said frame is equal to or larger than an exposure field on a wafer disposed in the exposure chamber to provide a stationary exit window. 9. The exit window of claim 1 wherein the opening in said frame is slightly larger than a cross-sectional area of an X-ray beam emitted from the X-ray beamline to allow the exit window to be stationary relative to the X-ray beam. 10. The exit window of claim 1 wherein said frame comprises first and second members each having said opening and an integral shoulder extending perpendicularly from one end thereof, said thin material being sandwiched between said first and second members. 11. The exit window of claim 10 wherein said thin material is fastened between said first and second frame members by two pins located at opposite ends of said shoulders of first and second frame members. 12. The exit window of claim 11 further including a seal means disposed within said first frame member completely surrounding said opening and abutting said thin material sandwiched between said first and second frame members. 13. An exit window for sealing an X-ray lithography beamline from an exposure chamber comprising: 14. The exit window of claim 13 wherein said thin material has a window section disposed within said opening of said frame and a peripheral section which is integral with said window section and extends within the frame. 15. The exit window of claim 14 wherein said opening of said frame has a rectangular shape having a length of 50 mm and a width of 25 mm. 16. The exit window of claim 15 wherein said peripheral section of said thin material has a length of 120 mm and a width of 42 mm. 17. The exit window of claim 13 wherein said thin material is formed of beryllium having a thickness of between 16 and 25 microns. 18. The exit window of claim 13 wherein the opening in said frame is equal to an exposure field on a wafer disposed in the exposure chamber to provide a stationary exit window. 19. A method of scanning an X-ray beam emitted from an X-ray lithography beamline onto an exposure field on a wafer comprising the steps of: |
abstract | A cost-effective method for repairing reflective optical elements for EUV lithography. These optical elements (60) have a substrate (61) and a coating (62) that reflects at a working wavelength in the range between 5 nm and 20 nm and is damaged as a result of formation of hydrogen bubbles. The method includes: localizing a damaged area (63, 64, 65, 66) in the coating (62) and covering the damaged area (63, 64, 65, 66) with one or more materials having low hydrogen permeability by applying a cover element to the damaged area. The cover element is formed of a surface structure, a convex or concave surface, or a coating corresponding to the coating of the reflective optical element, or a combination thereof. The method is particularly suitable for collector mirrors (70) for EUV lithography. After the repair, the optical elements have cover elements (71, 72, 73). |
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042636540 | abstract | A system for determining the normal operating value of at least one type of power plant data corresponding to the presently operating step of an operating plant first determines the present operation step of the plant, such as a nuclear power plant, by detecting at least one type of plant data, such as the reactor power, and then determines the normal value of at least one type of plant data, such as the main stream flow, the feedwater flow or the generator power in response to the presently determined operation step of the plant. |
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061920967 | claims | 1. A magnetostrictive wire control rod position detector assembly for detecting the position of a movable member within a cylindrical member, comprising: a ring-shaped magnet or ring-shaped magnets mounted on a non-magnetic portion of said movable member which is free to move in the longitudinal direction on the inside of said cylindrical member and is at least partly composed of a non-magnetic material; a plurality magnetostrictive wire detectors longitudinally mounted on the outer circumference of said cylindrical member, which is provided in a predetermined place with a receiver which detects torsional waves; and a pulsed current generator circuit which supplies a pulsed current from said receiver end of said magnetostrictive wire detector to the magnetostrictive wire of said magnetostrictive wire detector. said cylindrical member is the pressure housing of a control rod drive unit; said movable member is a drive shaft connected to the control rod of said control rod drive unit; and the position within a reactor core of said control rod which is connected to said drive shaft is detected along the entire length of a drive stroke from a fully withdrawn position to a fully inserted position by detecting the position of said drive shaft. said cylindrical member is the pressure housing of a control rod drive unit; said movable member is a drive shaft connected to the control rod of said control rod drive unit; and the position within a reactor core of said control rod which is connected to said drive shaft is detected along the entire length of a drive stroke from a fully withdrawn position to a fully inserted position by detecting the position of said drive shaft. 2. The magnetostrictive wire control rod position detector assembly according to claim 1, wherein a cylindrical support member is disposed so as to seal closed the outer circumference of said cylindrical member and said magnetostrictive wire detectors with a predetermined spacing. 3. The magnetostrictive wire control rod position detector assembly according to claim 2, wherein a protective member composed of the same non-magnetic material as said non-magnetic portion of said movable member is mounted so as to hermetically seal said magnets against said non-magnetic portion. 4. The magnetostrictive wire control rod position detector assembly according to claim 3, wherein: 5. The magnetostrictive wire control rod position detector assembly according to claim 4 wherein the construction comprises means for determining the time from the commencement of the descent of the control rod to any detected position of the control rod when the control rod is allowed to descend from the fully withdrawn position by measuring in advance a relationship between the times and distances from the fully withdrawn position. 6. The magnetostrictive wire control rod position detector assembly according to claim 1, wherein: 7. The magnetostrictive wire control rod position detector assembly according to claim 6, wherein the construction comprises means for determining the time from the commencement of the descent of the control rod to any detected position of the control rod when the control rod is allowed to descend from the fully withdrawn position by measuring in advance a relationship between the times and distances from the fully withdrawn position. 8. The magnetostrictive wire control rod position detector assembly according to claim 1, wherein a cylindrical support member is disposed so as to seal closed the outer circumference of said cylindrical member and said magnetostrictive wire detector with a predetermined spacing. 9. The magnetostrictive wire control rod position detector assembly according to claim 1, wherein a protective member composed of the same non-magnetic material as said non-magnetic portion of said movable member is mounted so as to hermetically seal said magnet or magnets against said non-magnetic portion. |
abstract | A process for immobilizing metallic sodium in glass form. The process comprises: (A) introducing in a dispersed state, into a reactor, an amount of a vitrified matrix precursor, metallic sodium and iron oxide (Fe2O3) sufficient to ensure oxidation of the metallic sodium; (B) producing a homogeneous mixture of these constituents; (C) heating the mixture to a temperature between 1000–1600° C. to form a molten homogeneous mixture in which the sodium introduced in (A) is converted to sodium oxide; and (D) recovering and cooling the molten mixture to obtain a vitrified matrix having a homogeneous composition, which matrix incorporates the sodium introduced in (A) as a constituent oxide. In a particular embodiment, the process may be used for the containment of metallic sodium containing radioactive elements. |
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claims | 1. A full-digital rod position measurement method, comprises:collecting output signals of rod position detectors by a universal signal processor, wherein the output signals comprise voltages of primary coils, currents of the primary coils, voltages of measurement coils, and voltages of auxiliary coils;determining a calculation interval, wherein determining the calculation interval comprises searching, by the universal signal processor, a starting point and an ending point of an avoidance interval that needs to be avoided due to interference of control rod motion in determining the avoidance interval according to the voltages of auxiliary coils,assigning the ending point of the avoidance interval to be a starting point of the calculation interval, and assigning a point located 400 milliseconds behind the ending point of the avoidance interval to be an ending point of the calculation interval,recording an avoidance interval between the starting point of the avoidance interval and the ending point of the avoidance interval, and recording a calculation interval between the ending point of the avoidance interval and the ending point of the calculation interval;for each group of a plurality of groups, calculating, by the universal signal processor, a respective average voltage of the auxiliary coils in the respective group in the calculation interval or a respective average current of the primary coils in the respective group in the calculation interval;for each group of the plurality of groups, calculating, by the universal signal processor, a respective average voltage of the measurement coils in the respective group in the calculation interval;for each group of the plurality of groups, calculating, by the universal signal processor, a respective voltage correction value of the measurement coils in the respective group, wherein the respective voltage correction value is calculated by dividing the respective average voltage of the measurement coils in the respective group by the respective average voltage of the auxiliary coils in the respective group, or dividing the respective average voltage of the measurement coils in the respective group by the respective average current of the primary coils in the respective group; andfor each group of the plurality of groups, comparing, by the universal signal processor, the respective voltage correction value of the measurement coils in the respective group with a preset threshold voltage to form a respective control rod position signal. 2. The full-digital rod position measurement method of claim 1, wherein determining the calculation interval further comprises assigning the calculation interval to be 400 milliseconds when the avoidance interval cannot be searched by the universal signal processor. 3. The full-digital rod position measurement method of claim 1, wherein calculating the respective average voltage of the auxiliary coils in the respective group in the calculation interval or the respective average current of the primary coils in the respective group in the calculation interval comprises using fast Fourier transform or average peak-to-peak value calculation. |
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description | Not Applicable. Computer systems and related technology affect many aspects of society. Indeed, the computer system's ability to process information has transformed the way we live and work. Computer systems now commonly perform a host of tasks (e.g., word processing, scheduling, accounting, etc.) that prior to the advent of the computer system were performed manually. More recently, computer systems have been coupled to one another and to other electronic devices to form both wired and wireless computer networks over which the computer systems and other electronic devices can transfer electronic data. Accordingly, the performance of many computing tasks are distributed across a number of different computer systems and/or a number of different computing environments. In some environments, distributed systems include a substantial number of client and server service and computer system components. Portions of the distributed system may from time to time experience operational errors leading to the need to perform diagnostic operations, such as, for example, tracing, profiling, and debugging. There is often undesirable overhead associated with diagnostic processes, such as, for example, additional processing, memory, or IO requirements, making it desirable to limit the scope and duration of diagnostic operations. Due to distributed system complexity, tasks required to enable diagnostics on demand, managing the diagnostic configuration of distributed systems, and collecting diagnostic results, it can be difficult and operationally expensive to use diagnostic processes within a distributed system. The present invention extends to methods, systems, and computer program products for remotely collecting and managing diagnostic information. In some embodiments, diagnostic information is provided from a service host to a remote diagnostic host. The remote diagnostic host is configured to provide a portion of broadcast diagnostic information that is of interest in diagnosing a condition at the service host. A remote diagnostic trace listener is installed as a local diagnostic trace listener within the service host. The remote diagnostic trace listener describes a diagnostic control endpoint that can be used to access and configure the remote diagnostic trance listener. The remote diagnostic trace listener includes a stub component. The stub component is configured to accept diagnostic information from the service end point and send the diagnostic information to the diagnostic host via the computer network. A connection request is received at the diagnostic control endpoint. The connection request is from an external component outside the service host and outside the diagnostic host. A diagnostic control application is boot strapped to the external component in response to the request. One or more diagnostic configuration commands are received through the diagnostic control application. The one or more diagnostic commands are for configuring the diagnostic host to collect and provide the portion of the broadcast diagnostic information. A diagnostic subscription endpoint is created to provide the portion of the broadcast diagnostic information to any external components outside of the service host and outside of the diagnostic host. An electronic address for the diagnostic subscription endpoint is returned to the external component. The portion of broadcast diagnostic information that is of interest in diagnosing a condition at the service host is provided to the external component. The remote diagnostic trace listener records the portion of broadcast diagnostic information to a diagnostic store in accordance with the one or more diagnostic configuration commands. A request for diagnostic information is received at the electronic address for the diagnostic subscription endpoint. The request has a return electronic address for the external component. The portion of broadcast diagnostic information is sent from the diagnostic store to the return electronic address. In other embodiments, the collection of broadcast diagnostic information is reconfigured during operation of the service host. A remote diagnostic trace listener collects a specified portion of broadcast diagnostic information in accordance with a first diagnostic filter. The specified portion of broadcast information is collected for storage in the diagnostic store while the service host is running. While the service host continues to run and without restarting the service host, the diagnostic trace listener and diagnostic store are reconfigured to collect a second different specified portion of broadcast diagnostic information that is to be collected for use in diagnosing a condition at the service host. Reconfiguration includes receiving one or more diagnostic configuration commands through the diagnostic control application. The one or more diagnostic configuration commands define the second different specified portion of broadcast diagnostic information that is to be collected. Reconfiguration includes selecting a second diagnostic filter to collect the second different specified portion of broadcast diagnostic information in accordance with the one or more diagnostic configuration commands. Reconfiguration includes reconfiguring the remote diagnostic trace listener to include the second diagnostic filter. Reconfiguration includes the remote diagnostic trace listener collecting the second different specific portion of broadcast diagnostic information in accordance with the second diagnostic filter. The second different portion of broadcast information is collected for storage in the diagnostic store. 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 or essential 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. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. The present invention extends to methods, systems, and computer program products for remotely collecting and managing diagnostic information. In some embodiments, diagnostic information is provided from a service host to a remote diagnostic host. The remote diagnostic host is configured to provide a portion of broadcast diagnostic information that is of interest in diagnosing a condition at the service host. A remote diagnostic trace listener is installed as a local diagnostic trace listener within the service host. The remote diagnostic trace listener describes a diagnostic control endpoint that can be used to access and configure the remote diagnostic trance listener. The remote diagnostic trace listener includes a stub component. The stub component is configured to accept diagnostic information from the service end point and send the diagnostic information to the diagnostic host via the computer network. A connection request is received at the diagnostic control endpoint. The connection request is from an external component outside the service host and outside the diagnostic host. A diagnostic control application is boot strapped to the external component in response to the request. One or more diagnostic configuration commands are received through the diagnostic control application. The one or more diagnostic commands are for configuring the diagnostic host to collect and provide the portion of the broadcast diagnostic information. A diagnostic subscription endpoint is created to provide the portion of the broadcast diagnostic information to any external components outside of the service host and outside of the diagnostic host. An electronic address for the diagnostic subscription endpoint is returned to the external component. The portion of broadcast diagnostic information that is of interest in diagnosing a condition at the service host is provided to the external component. The remote diagnostic trace listener records the portion of broadcast diagnostic information to a diagnostic store in accordance with the one or more diagnostic configuration commands. A request for diagnostic information is received at the electronic address for the diagnostic subscription endpoint. The request has a return electronic address for the external component. The portion of broadcast diagnostic information is sent from the diagnostic store to the return electronic address. In other embodiments, the collection of broadcast diagnostic information is reconfigured during operation of the service host. A remote diagnostic trace listener collects a specified portion of broadcast diagnostic information in accordance with a first diagnostic filter. The specified portion of broadcast information is collected for storage in the diagnostic store while the service host is running. While the service host continues to run and without restarting the service host, the diagnostic trace listener and diagnostic store are reconfigured to collect a second different specified portion of broadcast diagnostic information that is to be collected for use in diagnosing a condition at the service host. Reconfiguration includes receiving one or more diagnostic configuration commands through the diagnostic control application. The one or more diagnostic configuration commands define the second different specified portion of broadcast diagnostic information that is to be collected. Reconfiguration includes selecting a second diagnostic filter to collect the second different specified portion of broadcast diagnostic information in accordance with the one or more diagnostic configuration commands. Reconfiguration includes reconfiguring the remote diagnostic trace listener to include the second diagnostic filter. Reconfiguration includes the remote diagnostic trace listener collecting the second different specific portion of broadcast diagnostic information in accordance with the second diagnostic filter. The second different portion of broadcast information is collected for storage in the diagnostic store. Embodiments of the present invention may comprise or utilize a special purpose or general-purpose computer including computer hardware, such as, for example, one or more processors and system memory, as discussed in greater detail below. Embodiments within the scope of the present invention also include physical and other computer-readable media for carrying or storing computer-executable instructions and/or data structures. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer system. Computer-readable media that store computer-executable instructions are computer storage media (devices). Computer-readable media that carry computer-executable instructions are transmission media. Thus, by way of example, and not limitation, embodiments of the invention can comprise at least two distinctly different kinds of computer-readable media: computer storage media (devices) and transmission media. Computer storage media (devices) includes RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. A “network” is defined as one or more data links that enable the transport of electronic data between computer systems and/or modules and/or other electronic devices. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer properly views the connection as a transmission medium. Transmissions media can include a network and/or data links which can be used to carry or desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. Combinations of the above should also be included within the scope of computer-readable media. Further, upon reaching various computer system components, program code means in the form of computer-executable instructions or data structures can be transferred automatically from transmission media to computer storage media (devices) (or vice versa). For example, computer-executable instructions or data structures received over a network or data link can be buffered in RAM within a network interface module (e.g., a “NIC”), and then eventually transferred to computer system RAM and/or to less volatile computer storage media (devices) at a computer system. Thus, it should be understood that computer storage media (devices) can be included in computer system components that also (or even primarily) utilize transmission media. Computer-executable instructions comprise, for example, instructions and data which, when executed at a processor, cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. The computer executable instructions may be, for example, binaries, intermediate format instructions such as assembly language, or even source code. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the described features or acts described above. Rather, the described features and acts are disclosed as example forms of implementing the claims. Those skilled in the art will appreciate that the invention may be practiced in network computing environments with many types of computer system configurations, including, personal computers, desktop computers, laptop computers, message processors, hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, mobile telephones, PDAs, pagers, routers, switches, and the like. The invention may also be practiced in distributed system environments where local and remote computer systems, which are linked (either by hardwired data links, wireless data links, or by a combination of hardwired and wireless data links) through a network, both perform tasks. In a distributed system environment, program modules may be located in both local and remote memory storage devices. FIG. 1 illustrates an example computer architecture 100 that facilitates providing diagnostic information from a service host to a remote diagnostic host. Referring to FIG. 1, computer architecture 100 includes diagnostic host 101 and service host 121. Each of the depicted components is connected to one another over (or is part of) a network, such as, for example, a Local Area Network (“LAN”), a Wide Area Network (“WAN”), and even the Internet. Accordingly, each of the depicted computer systems as well as any other connected computer systems and their components, can create message related data and exchange message related data (e.g., Internet Protocol (“IP”) datagrams and other higher layer protocols that utilize IP datagrams, such as, Transmission Control Protocol (“TCP”), Hypertext Transfer Protocol (“HTTP”), Simple Mail Transfer Protocol (“SMTP”), etc.) over the network. Generally, a service may be one component within a distributed system. The service executes within a logical service host container that bounds what is considered a part of the service component. The service is configured to periodically collect interesting information and events about its operation as diagnostic traces. The service can broadcast the collected diagnostic traces to any local trace listeners that are configured as part of the definition of the service. However, the number of connected trace listeners is unimportant to the service and there may even be none. The service can expose one or more communication mediums as part of its normal operation to allow external parties to invoke service operations. As depicted, service host 121 includes service endpoint 122 and trace listeners 123, 124, etc. Service endpoint 122 can periodically broadcast diagnostic information and events about its operation within service host 121. Local trace listeners 123, 124, etc., are configured to listen for and collect diagnostic information and events from service host 121. Remote diagnostic trace listener 102 spans service host 121 and diagnostic host 101. Remote diagnostic trace listener 102 is installed as a local trace listener from the perspective of service endpoint 122. Thus, remote diagnostic trace listener 102 can listen for and collect diagnostic information and events from service host 121 similar to local trace listeners 123, 124, etc. Due to boundaries between the service host 121 and diagnostic host 101, remote diagnostic trace listener 102 can include stub 103 (a stub component) within the service host 121. Stub 103 is configured to remote diagnostic traces (e.g., in diagnostic information 141) from service endpoint 122 to diagnostic host 101. Use of stub 103 mitigates the likelihood of the diagnostic infrastructure of the service host producing spurious diagnostic traces describing the operation of diagnostic host 101 and remote diagnostic trace listener 102. Diagnostic host 101 includes diagnostic store 104, diagnostic security system 108, diagnostic control endpoint 107, diagnostic control application 106, diagnostic subscription endpoint 109, and diagnostic service 111. Generally, diagnostic store 104 is configured to store diagnostic traces collected by remote diagnostic trace listener 102. Diagnostic security system 108 authenticates and authorizes diagnostic user operations. Diagnostic control endpoint 107 can be contacted by a diagnostic user to obtain the diagnostic control application for service endpoint 122. Diagnostic control application 106 allows a remote diagnostic user to configure the operation of the remote diagnostic trace listener 102, diagnostic store 104, and diagnostic authentication system 108. Diagnostic subscription endpoint 109 can be contacted by a diagnostic user to retrieve diagnostic traces from diagnostic store 104. Diagnostic service 111 can be configured to take automated actions on behalf of a diagnostic user based on the contents of diagnostic store 104, such as, for example, when broadcast diagnostic information matches specified criteria. There can be one or more diagnostic subscription endpoints and diagnostic services based on the configuration performed by the diagnostic user. For example, diagnostic subscription endpoints and diagnostic services may be dynamically created and destroyed through user operation of the diagnostic control application. The components depicted in computer architecture 100 can interact to provide diagnostic traces to a diagnostic user. For example, diagnostic information can be provided to a diagnostic user that is debugging a distributed system that includes service host 121. Independently of the actions of a diagnostic user, service endpoint 122 can be identifying interesting information and events and broadcasting the interesting information and events to local trace listeners 123, 124, etc., Among the local trace listeners can be remote diagnostic trace listener 102 that is also recording a portion of broadcast information and events. The configuration of remote diagnostic trace listener 102 describes the properties of a diagnostic control endpoint 107, such as, for example, the address and connection settings of diagnostic control endpoint 107. Remote diagnostic trace listener 102 opens diagnostic control endpoint 107 to receive diagnostic control requests. The servicing of the diagnostic control endpoint 107 can be independent of the servicing of the service endpoint 122. For example, communication medium 131 and communication medium 133 can differ. It may be that communication medium 131 is User Datagram Protocol (“UDP”) and that communication medium 133 is HyperText Transfer Protocol (“HTTP”). In some embodiments, diagnostic control endpoint 107 is hosted by a lightweight web server that has been stripped of most functionality to increase its security, reliability, and performance. Separation between the service host and diagnostic host may also be beneficial if, for example, a diagnostic user needs to pause and debug service host 121 without wanting to disrupt diagnostic control. Upon suspecting a problem with the operation of the service endpoint 122, a diagnostic user can contact diagnostic control endpoint 107 and request access to diagnostic information for service 122. In response to the request, diagnostic control endpoint 107 can configure the collection of diagnostic information from service endpoint 122. Configuration can include installing remote diagnostic trace listener 102. FIG. 2 illustrates a flow chart of an example method 200 for providing diagnostic information from a service host to remote diagnostic host. Method 200 will be described with respect to the components and data of computer architecture 100. Method 200 includes an act of configuring the diagnostic host to provide a portion of the broadcast diagnostic information that is of interest in diagnosing a condition at the service host (act 201). For example, diagnostic control endpoint 107 can be configured to provide diagnostic information 142 (a portion of broadcast diagnostic information 141). Diagnostic information 142 can be of interest to a diagnostic condition (e.g., error or warning) occurring within service host 121. Configuring the diagnostic host includes an act of installing a remote diagnostic trace listener as a local diagnostic trace listener within the service host, the remote diagnostic trace listener describing a diagnostic control endpoint that can be used to access and configure the remote diagnostic trance listener, the remote trace listener including a stub component, the stub component configured to accept diagnostic information from the service end point and send the diagnostic information to the diagnostic host via the computer network (act 202). For example, diagnostic host 101 can install remote diagnostic trace listener 102 as depicted in computer architecture 100. Remote diagnostic trace listener 102 describes diagnostic control endpoint 107. Remote diagnostic trace listener 102 includes stub 103. Stub 103 is configured to accept diagnostic information from the service end point 122 and send the diagnostic information to diagnostic host 101 via a computer network Configuring the diagnostic host includes an act of receiving a connection request at the diagnostic control endpoint, the connection request from an external component outside the service host and outside the diagnostic host (act 203). For example, diagnostic control endpoint 107 can receive connection request 143 from a diagnostic user via communication medium 133. The connection request can originate from a computer system or communication component being used by the diagnostic user. Configuring the diagnostic host include an act of boot strapping a diagnostic control application to the external component in response to the request (act 204). For example, diagnostic control endpoint 107 can send control application information 144 back to the diagnostic user via communication medium 133. Control application information 144 can be information for boot strapping diagnostic control application 106. For example, control application information 144 can be actual application data or information for accessing actual application data. In some embodiments, diagnostic control application 106 is a downloaded separate application that the diagnostic user installs and runs. Alternately, diagnostic control application 106 can be a Web browser application, for example, using Java applets, Microsoft® Silverlight® controls, or HyperText Markup Language 5 (“HTML 5”), that is downloaded to be run in a Web browser of the diagnostic user. Diagnostic control application 106 can be preconfigured to point back to diagnostic host 101 (the diagnostic host from which it was generated). Configuring the diagnostic host include an act of receiving one or more diagnostic configuration commands through the diagnostic control application, the one or more diagnostic commands for configuring the diagnostic host to collect and provide the portion of the broadcast diagnostic information (act 205). For example, diagnostic control application 106 can receive diagnostic commands 146 from a diagnostic user via communication medium 132. Diagnostic commands 146 are for configuring diagnostic host 101 to collect and provide diagnostic information 142. Diagnostic control application 106 can derive configuration 151 for remote diagnostic trace listener 102 from diagnostic commands 146. Diagnostic control application 106 can configure remote diagnostic trace listener 102 in accordance with configuration 151. In general, diagnostic control application 106 enables the diagnostic user to configure and reconfigure remote diagnostic trace listener 102 and diagnostic store 104. Configuration and reconfiguration of diagnostic trace listener 102 and diagnostic store 104 can include one or more of: (1) changing filters to record specific categories of diagnostic traces, such as, for example, startup events or communication events, (2) changing filters to record specific severities of diagnostic traces, such as, for example, error events or warning events, (3) changing filters to collect specific information, such as, for example, the contents of messages, (4) creating subscriptions to retrieve at a later time recorded traces that match a set of criteria, (5) enabling services to take action when recorded traces match a set of criteria, such as, for example, a service to send a text message when an error trace is recorded, (6) setting retention policies on the diagnostic store such as, for example, the maximum quantity or length of time to keep diagnostic traces, and (7) changing user permissions to perform other diagnostic operations. Changing filters can be implemented by reconfiguring the service endpoint 122 to produce a different set of interesting information and events. Alternately, changing filters may be implemented by reconfiguring remote diagnostic trace listener 102 to alter which broadcasted debugging traces are recorded. Creating subscriptions and setting retention policies can be implemented by reconfiguring the diagnostic store. Diagnostic security system 108 can control permission to perform any of these operations or to view information about service host 121 and diagnostic configuration by authenticating and authorizing a requesting diagnostic user. In a more particular example, suppose a diagnostic user wants to be notified when an error event occurs in a Calculator subcomponent of a service component. The diagnostic user, through diagnostic control application 106, can change the filters to record diagnostic traces of error severity only. The diagnostic user also may create a subscription using a filter that matches the Calculator subcomponent. For example, diagnostic traces regarding the Calculator subcomponent may be identifiable by defining an eXstensible Markup Language Path Language (“XML Path Language” or “XPath”) expression “//Source[@component=‘Calculator’]” that searches for a Calculator component attribute in a Source element within each recorded diagnostic trace. Alternately, the diagnostic user may continue to collect diagnostic traces of many severities and add a filter to match diagnostic traces of error severity by adding that criteria to the criteria matching the subcomponent type. Configuring the diagnostic host includes an act of creating a diagnostic subscription endpoint to provide the portion of the broadcast diagnostic information to any external components outside of the service host and outside of the diagnostic host (act 206). For example, responsive to diagnostic commands 146, remote diagnostic trace listener 102 can start diagnostic subscription endpoint 109. Remote diagnostic trace listener 102 can assign electronic address 147 (a unique address) to diagnostic subscription endpoint 109. The unique address can be Uniform Resource Locator (“URL”). For example, referring back to the Calculator subcomponent example, diagnostic subscription endpoint 109 can be assigned the address: http://www.example.com:9000/?filter=%2F%2FSource%5B%40component%3D%E2%80%99Calculator%E2%80%99%5D&type=rss Configuring the diagnostic host includes an act of returning an electronic address for the diagnostic subscription endpoint to the external component (act 207). For example, diagnostic control application 106 can return electronic address 147 to the diagnostic user via communication medium 132. Method 200 includes an act of providing the portion of broadcast diagnostic information that is of interest in diagnosing a condition at the service host to the external component (act 208). For example, diagnostic subscription endpoint 109 can provide diagnostic information 142 to the diagnostic user. Providing the portion of broadcast diagnostic information that is of interest includes an act of the remote diagnostic trace listener recording the portion of broadcast diagnostic information to a diagnostic store in accordance with the one or more diagnostic configuration commands (act 209). For example, remote diagnostic trace listener 102 can record diagnostic information 142 to diagnostic store 104 in accordance with diagnostic commands 146. Remote diagnostic listener can receive diagnostic information 141 broadcast from service endpoint 122. One or more filters within remote diagnostic listener 102 can filter out diagnostic information 142 (a portion of diagnostic information of interest) from diagnostic information 141. Providing the portion of broadcast diagnostic information that is of interest includes an act of receiving a request for diagnostic information at the electronic address for the diagnostic subscription endpoint, the request having a return electronic address for the external component (act 210). For example, diagnostic subscription endpoint 109 can receive diagnostic request 148 from a diagnostic user via communication medium 134. Request 148 can be directed to electronic address 147 and can include a return address to diagnostic user. Providing the portion of broadcast diagnostic information that is of interest includes an act of sending the portion of broadcast diagnostic information from the diagnostic store to the return electronic address (act 211). For example, diagnostic subscription endpoint 109 can provide diagnostic information 142 back to the return address included in diagnostic request 148 via communication medium 134. Thus, by navigating to an assigned address a diagnostic user can retrieve diagnostic information that has been collected. For example, subsequent to configuration or reconfiguring using the diagnostic control application 106, a diagnostic user may input the assigned address into an Really Simple Syndication (“RSS”) reader application. The RSS reader application can periodically poll diagnostic subscription endpoint 109 to retrieve the latest diagnostic events and present them to a diagnostic user. Once the user has sufficient information to address a condition with (e.g., debug) a distributed system including service host 121, the diagnostic user may again access the diagnostic control application 106 to disable recording diagnostic traces and delete the subscription. Alternately, a subscription can be automatically deleted after a period of time as part of the retention policy of the remote diagnostic trace listener. In some embodiments, diagnostic host 101 listens for any requests coming to a specific base address. When a diagnostic user accesses an address that contains the base address as a prefix, diagnostic host 101 uses the resource access attempt to create a subscription without further input by the diagnostic user. For example, referring again to the Calculator subcomponent example, the string “% 2F % 2FSource % 5B % 40component % 3D % E2% 80% 99Calculator % E2% 80% 99% 5D” can be a URL encoded version of the previously described XPath expression “//Source[@component=‘Calculator’]”. A diagnostic user can navigate to the address in a Web browser without having previously created a subscription. Navigating to the address causes diagnostic host 101 to create a subscription with the filter defined by the XPath expression, similar to reconfiguration through diagnostic control application 106. Diagnostic security system 108 can perform authentication and authorization, such as, for example, by issuing an HTTP authentication request when accessing the resource address. In this way for example, a diagnostic user can bookmark a location that corresponds to an interesting diagnostic configuration and restore the diagnostic configuration at a later time for use with this or another instance of the distributed system. Embodiments of the invention include communicating with service host 121 and the various components of diagnostic host 101 using different communication mediums. For example, one or more communication mediums 131, 132, 133, 134, and 135 can be different from another. In other embodiments of the invention, the collection of diagnostic information from a service host is re-configured during operation of the service host. FIG. 3 illustrates an example computer architecture 300 that facilitates reconfiguring the collection of broadcast diagnostic information during operation of a service host. Referring to FIG. 3, computer architecture 300 includes diagnostic host 301 and service host 321. Each of the depicted components is connected to one another over (or is part of) a network, such as, for example, a Local Area Network (“LAN”), a Wide Area Network (“WAN”), and even the Internet. Accordingly, each of the depicted computer systems as well as any other connected computer systems and their components, can create message related data and exchange message related data (e.g., Internet Protocol (“IP”) datagrams and other higher layer protocols that utilize IP datagrams, such as, Transmission Control Protocol (“TCP”), Hypertext Transfer Protocol (“HTTP”), Simple Mail Transfer Protocol (“SMTP”), etc.) over the network. Within computer architecture 300, service endpoint 322 can be broadcasting diagnostic information to local trace listeners, including local trace listener 323, and to remote diagnostic trace listener 302. FIG. 4 illustrates a flow chart of an example method 400 for reconfiguring the collection of broadcast diagnostic information during operation of a service host. Method 400 will be described with respect to the components and data of computer architecture 300. Method 400 includes an act of the remote diagnostic trace listener collecting a specified portion of broadcast diagnostic information in accordance with a first diagnostic filter, the specified portion of broadcast information collected for storage in the diagnostic store while the service host is running (act 401). For example, remote diagnostic trace listener 302 can collect diagnostic information 342 in accordance with filter 361. That is, filter 361 can filter diagnostic information 342 from diagnostic information 341. Diagnostic information 342 can be collected for storage in diagnostic store 304 while service host 321 is running. Method 400 includes while service host continues to run and without restarting the service host, an act of reconfiguring the diagnostic trace listener and diagnostic store to collect a second different specified portion of broadcast diagnostic information that is to be collected for use in diagnosing a condition at the service host (act 402). For example, while service host 321 continues to run and without restarting service host 321, remote diagnostic trace listener 302 and diagnostic store 304 can be reconfigured to collect diagnostic information 343. Diagnostic information 343 can be collected for use in diagnostic a condition at service host 321. A retention policy can be set on diagnostic store 304 for diagnostic information 343. Reconfiguring the diagnostic trace listener and diagnostic store includes an act of receiving one or more diagnostic configuration commands through the diagnostic control application, the one or more diagnostic configuration commands defining the second different specified portion of broadcast diagnostic information that is to be collected (act 403). For example, diagnostic control application 306 can receive diagnostic commands 346. Diagnostic commands 346 can define configuration 351 for remote diagnostic trace listener 302. Configuration 351 can include an indication that diagnostic information 343 is to be collected from diagnostic information 341 Reconfiguring the diagnostic trace listener and diagnostic store includes an act of selecting a second diagnostic filter to collect the second different specified portion of broadcast diagnostic information in accordance with the one or more diagnostic configuration commands (act 404). For example, configuration 351 can indicate that filter 362 is to be selected to collect diagnostic information 343. Reconfiguring the diagnostic trace listener and diagnostic store includes an act of reconfiguring of the remote diagnostic trace listener to include the second diagnostic filter (act 405). For example, configuration 351 can be implemented at remote diagnostic trace listener 302. Implementing configuration 351 can include reconfiguring remote diagnostic trace listener 302 to include filter 362 (and either keep or remove filter 361). Alternately, configuration 352 can be issued to service endpoint 322 to cause service endpoint 322 to broadcast diagnostic information 343 directly. Reconfiguring the diagnostic trace listener and diagnostic store includes an act of the remote diagnostic trace listener collecting the second different specific portion of broadcast diagnostic information in accordance with the second diagnostic filter, the second different portion of broadcast information collected for storage in the diagnostic store (act 406). For example, diagnostic information 343 can be collected in accordance with filter 362. Diagnostic information 343 can be collected for storage in diagnostic store 304. A remote diagnostic user can connect to diagnostic subscription endpoint 309 to access diagnostic information 343. Filter 361 can remain active or be removed as part of reconfiguring the collection and storage of diagnostic information from service endpoint 322. Thus, configuration and reconfiguration of diagnostic trace listener 302 and diagnostic store 304 can include one or more of: (1) changing filters to record specific categories of diagnostic traces, such as, for example, startup events or communication events, (2) changing filters to record specific severities of diagnostic traces, such as, for example, error events or warning events, (3) changing filters to collect specific information, such as, for example, the contents of messages, (4) creating subscriptions to retrieve at a later time recorded traces that match a set of criteria, (5) enabling services to take action when recorded traces match a set of criteria, such as, for example, a service to send a text message when an error trace is recorded, (6) setting retention policies on the diagnostic store such as, for example, the maximum quantity or length of time to keep diagnostic traces, and (7) changing user permissions to perform other diagnostic operations, while service host 321 is running and without restarting service host 321. Accordingly, embodiments of the invention facilitate remote configuration, management, and collection of diagnostic results. A remote diagnostic system connects to the local diagnostics of the service or computer system in a non-invasive way to collect diagnostic information. Filter and subscription requests are used to guide the collection and retention of diagnostic information. A diagnostic user connects to the remote diagnostic system to dynamically change the filter and subscription requests as part of a diagnostic process. The collected diagnostic information can then be transmitted to interested system operators using either syndication subscriptions or push subscriptions. The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. |
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062890719 | description | DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail with reference to the drawings attached. Referring to FIG. 1, there is a schematic sectional view of a positron emitter-generating unit for generating a positron emitter (radioisotope) in a liquid target by irradiating a liquid target with a beam of charged particles. The positron emitter-generating unit 10 is composed of three blocks, an upper block 12 and an intermediate block 13 both having a through hole through the blocks 12 and 13 and a lower block 14 with a concave part 18. These three blocks are secured to one another by screws with the alignment of the through holes and the concave part 18 being made sure. In the intermediate block 13, the upper and lower openings of the through hole are sealed with a metal foil 15 (e.g., a titanium foil) and 16 (e.g., a silver foil), respectively, to form a space 17 for containing a liquid target (i.e., a liquid target container). O-rings 13a, 13b and 14a are provided seal between the blocks 12, 13 and 14. A charged particle beam 11 enters an opening 12a of the upper block 12 and passes through the metal foil 15 (e.g., a titanium foil) and applied to the liquid target in the container 17. The concave part 18 of the lower block 14 is provided with cooling water feed pipes 19a and 19b connected thereto, so that the target solution heated by the irradiation with the charged particle beam 11 is cooled down with the cooling water in the concave part 18 fed through the pipes 19a and 19b. To the container 17 are connected a liquid target feed pipe 23 shown in FIG. 1, a liquid target feed pipe (not shown) which is connected to the container 17 in a direction perpendicular to the plane of the sheet of FIG. 1, and a gas feed pipe (not shown) for introducing a N.sub.2 gas into the container 17. In the positron emitter-generating unit 10, a valve 23a is closed to store the liquid target in the container 17. In the container 17, the liquid target is irradiated with the charged particle beam 11, whereby a positron emitter is generated in the liquid target. In this embodiment, water containing H.sub.2.sup.18 O and 2 ppm of NaF is used as the liquid target, and H.sub.2.sup.18 O in the container 17 is irradiated with a proton beam (i.e., the charged particle beam 11) accelerated to an energy level of 16 MeV with an accelerator, thereby generating .sup.18 F through a .sup.18 O(p,n).sup.18 F reaction. The irradiation with the proton beam 11 is performed, for example, for 30 minutes. Thereafter, the valve 23a is opened, and N.sub.2 gas is introduced into the container 17 through the gas feed pipe, whereby the .sup.18 F-containing H.sub.2.sup.18 O in the container 17 is transferred into a container 30 placed in another room. The container 30 is formed of a copper block with a semispherical cavity 31 on the inner surface of which rhodium plating 32 is applied. Referring to FIG. 2, there is a partially sectional view illustrating the process of preparing a positron source by causing to bind the positron emitter .sup.18 F contained in the liquid target 35 in the container 30 onto an end surface of the carbon member. The container 30 contains a solution 35 containing both .sup.18 F and 2 ppm of NaF which has been subjected to irradiation with the proton beam. The upper end of the carbon member 40 is held to a stand 46 by a plastic-made insulating holder 45. The carbon member 40 and the container 30 are connected to a constant-voltage power supply 47 so that the carbon member 40 is located on an anode side and the container 30 is located on a cathode side. It is preferably for the carbon member 40 to pass an electric current in the state that the bottom surface of the carbon member 40 is contacted with the solution 35 with the smallest possible surface contact area so that .sup.18 F is mostly bound to the bottom surface of the carbon member 40 and is bound to the side surface of the carbon member 40 as small as possible. Therefore, for instance, the carbon member 40 is first located above the liquid surface of the solution 35 in the container 30 and then lifted down slowly toward the liquid surface of the solution 35. When the contact of the bottom surface of the carbon member 40 with the liquid surface of the solution 35 is confirmed by the detection of the flow of electricity from the constant-voltage power supply 47, the carbon member 40 is further lifted down (for example by 0.1 mm), and then held to the stand 46. Thus, the bottom surface of the carbon member 40 is ensured to contact with the solution 35 while maintaining the smallest possible contact area. When an electric current from the constant-voltage power supply is passed through the carbon member 40 contacting with the solution 35, .sup.18 F in the solution 35 is concentrated near the carbon member 40 (an anode) and bound onto the carbon member 40. Thus, a positron source with a .sup.18 F(positron emitter)-rich end surface can be prepared. Referring to FIGS. 3A and 3B, there are schematic views of embodiments of a positron source according to the present invention. FIG. 3A shows a positron source prepared by the process illustrated in FIG. 2. In the positron source of FIG. 3A, a positron emitter .sup.18 F is bound onto one end surface 41 of a fine cylindrical carbon member 40 in a high density. FIG. 3B shows an alternative embodiment of a positron source of the present invention, in which a fine cylindrical positron source 40a is applied with an insulating coating 42 at a part of the side surface near its one end. The application of the insulating coating 42 serves to prevent the bonding of the positron emitter .sup.18 F onto the side surface of the carbon member 40 even when the carbon member 40 is immersed in the solution 35 relatively deeply upon the passage of electric current in the process as shown in FIG. 2. Thus, the .sup.18 F binds onto the end surface 41a exclusively. In the positron source according to the present invention, a positron emitter .sup.18 F binds uniformly onto an end surface 41 or 41a of the carbon member 40 or 40a, respectively, without any carrier and the thickness of the positron emitter .sup.18 F bound onto the end surface is negligible. Therefore, the positron from the positron emitter .sup.18 F can be emitted from the small surface area of the carbon member 40 (which is almost a point source) efficiently without any influence of scattering or absorbance. Then, the binding efficiency of the positron emitter .sup.18 F onto the carbon member is examined. Water (1 ml) containing H.sub.2.sup.18 O (purity: 90%) and 2.mu.g of NaF is used as a liquid target. The liquid target is irradiated with a proton beam which is accelerated to an energy level of 16 MeV. After the irradiation, the liquid target is transferred to a semi-spherical container (void volume: 1 ml) of 8 mm in radius as shown in FIG. 2 and a carbon member 40 is set as shown in FIG. 2. The carbon member 40 used is a graphite rod which is prepared by working a high-purity graphite for spectrometry purpose into a cylindrical rod of 5 mm or 3 mm in diameter and 3 cm in length. The graphite rod is provided with a copper terminal on one end, and the other end is polished to give a smooth surface. The graphite rod is mounted to a plastic holder 45 and arranged so that the center of the end surface is aligned with the center of the container 30, and then connected to a constant-voltage power supply 47 to pass electric current. The voltage applied is varied from 70V to 180V in 10V intervals and the period of time for passing electric current is set at 5, 10 and 20 minutes. The intensity of the gamma ray of 0.511 MeV emitted from the graphite rod is measured with a semiconductor detector. As a control sample, the liquid target (1 ml) is irradiated with the proton beam, applied on an aluminum foil, dried, and then measured on the intensity of the gamma ray of 0.511 MeV emitted from the control sample in the, same manner. The measured value for the graphite rod is compared with that for the control sample to determine the binding efficiency relatively. Referring to FIG. 4, there is a graph illustrating the time course of the binding efficiency of .sup.18 F onto a 3 mm.phi. graphite rod at the electrodeposition voltage of 120V, in which the time for passing the electric current is plotted as abscissa and the binding efficiency as ordinate. As shown in FIG. 4, it is found that the binding efficiency of 50% or higher can be achieved by passing electric current for 20 minutes or 30 minutes. In the examination, graphite rods of 3 mm and 5 mm in diameter are used. However, other carbon materials having excellent conductivity and satisfactory material strength (e.g., glassy carbon) may also give the similar results. Although the diameters of the carbon member used in the tests is 3 mm and 5 mm, diameters of less than 3 mm (e.g., less than 1 mm) may also be employed. It will be obvious that the cross section of the carbon member is not particularly limited, such as a square, hexagonal or circular shape. Referring to FIG. 5, there is a sectional view of an embodiment of a slow positron beam-generating unit with the positron source according to the present invention. One end of a vacuum container 72 with a step 73 is double sealed with a reinforcing titanium foil 75 and a moderator 76, in the front of which a grid 77 is provided. The grid 77 is applied with a voltage of about -30V from a power supply 78. The moderator 76 is composed of a tungsten foil of about 10 .mu.m thick. A positron source 50 with a positron emitter .sup.18 F bonded onto its one end is engaged in the step 73 of the vacuum container 72 so that the positron source 50 is aligned in the right place against the moderator 76. The positron emitted from the positron emitter present at the end surface of the positron source 50 is ejected to the vacuum container 72 through the titanium foil 75. Then, the positron enters the moderator 76 to be slowed down. The slowed positron is then accelerated through the electric field generated by the grid 77 and transferred to a place where the positron beam is to be used as a slow positron beam 71 along the magnetic field generated by a coil 79. Referring to FIGS. 6 and 7, there are a schematic illustration of an embodiment of an automated system for supplying a positron source according to the present invention, and a connection diagram illustrating a general set-up for driving the system. The automated system for supplying a positron source comprises a rotary table 80 on which a plurality of containers 30a-30f are mounted, and a rotary member 90 to which the same numbers of carbon members 40a-40f as that of the containers are removably mounted. Each of the containers 30a-30f is manufactured by forming a semispherical cavity on a copper block and plating the inner surface of the cavity with rhodium. The rotary table 80 is capable of rotating in a 360-degree arc by the aid of a pulse motor 81. The rotary member 90 is capable of rotating in a 360-degree arc by the aid of a pulse motor 91. The rotary member 90 is also capable of up-and-down movement by the aid of a pulse motor 92. The pulse motors 81, 91 and 92 are driven by motor drivers 95, 96 and 97, respectively, that are controlled by a computer 106 through an interface 105. The constant-voltage power supply 100 is connected to the rotary plate 80 (negative side) and the rotary member 90 (positive side) through phospher bronze-made brushes 83 and 84, respectively. Between the power supply 100 and the rotary member 90 is provided a liquid surface-detection circuitry 101. The output of the liquid surface-detection circuitry 101 is input into the computer 106 through the interface 105. In the apparatus, there are determined Position A where the solution is supplied to the container and Position B where electric current is passed through the solution. At Position A, a solution containing a positron emitter .sup.18 F is supplied into a container 30a from a positron emitter-generating unit as shown in FIG. 1 through a liquid target feed pipe 23. After the supply of the .sup.l8 F-containing solution into the container 30a is completed, the pulse motor 81 is driven to rotate the rotary table 80, so that the container 30a moves to Position B which is positioned underneath the carbon member 40a mounted on the rotary member 90. Next, the pulse motor 92 is driven to move down the rotary member 90 slowly. Then, the carbon member 40a mounted on the rotary member 90 also moves down slowly toward the solution in the container 30a. When the carbon member 40a (at a positive potential) contacts with the liquid surface of the solution in the container 30a (at a negative potential), an electricity of about a few mA flows. The liquid surface-detection circuitry 101 detects the generated a micro-current by a photocoupler and sends it as a liquid surface-detection signal to the computer 106 through a ultra-compact relay. When the computer 106 receives the signal, it operates a driver 97 so that the carbon member 40a further moves down by about 0.1 mm. Thereafter, an electric current is passed through the liquid with the constant-voltage power supply 100 at 90V for 20 minutes to cause to bind the positron emitter .sup.18 F onto one end of the carbon member 40a. Thus, a positron source can be prepared. Once the positron source is prepared, the pulse motor 92 is driven to elevate the rotary member 90 upward, whereby the positron source (carbon member 40a) is also moved upward of the container 30a. The pulse motor 91 is also driven to move the carbon member 40a to the position opposed to the positron source-receiving section (step) 73 of the positron beam generating unit. Thereafter, the pulse motor 92 is driven to move the rotary member 90 upward by a predetermined distance, so that the carbon member 40a is attached to the positron source-receiving section (step) 73 of the positron beam generating unit. Using this sequence of operations, a slow positron beam 71 can be generated from the positron beam generating unit. The sequence of operations is performed automatically under computer control. The half-life of the positron emitter .sup.18 F is about 110 minutes. Therefore, the positron source (i.e., carbon member 40a) can generate a positron beam for about two hours. When the intensity of the positron beam 71 is decreased, a solution which contains a positron emitter .sup.18 F prepared as described above in the positron emitter-generating unit as shown in FIG. 1 is supplied to a next container 30b on the rotary table 80 through the liquid target feed pipe 23. Then, the positron emitter .sup.18 F in the container 30b is bound onto a carbon member 40b and supplied to the positron beam-generating unit 110. By these operations, for instance, a 20 minute passage of electric current at Position B and a subsequent two hour positron beam generation can be performed repeatedly. In this case, for instance, if the system is provided with six containers 30 and six carbon members 40, a continuous running for 12 hours becomes possible, and if the system is provided with 12 containers 30 and 12 carbon members 40, a continuous running for 24 hours becomes possible. The solution after the passage of electric current is recovered through a recovery pipe 109. As stated above, according to the present invention, a positron source capable of generating positrons of high intense efficiently from a small surface area which is almost a point source, can be prepared. Using the system of the present invention as described above, the positron source can be supplied to a positron beam-generating unit automatically. The invention has been described in detail with reference to various embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the invention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention. |
claims | 1. A radiation protection device comprising:a radiation attenuation component comprising a radiation attenuating material configured to provide varying radiation attenuation levels at different points across the radiation attenuating component,wherein the radiation attenuation component configured to be placed adjacent to and externally covering a body part that includes active bone marrow so as to reduce a radiation dose absorbed by the bone marrow in that body part,wherein the radiation attenuation component has a body part side and the sheets of radiation attenuating material are layered in increasing at least one of thickness and density orthogonal to the body part side to an external side, andwherein the varying radiation attenuation levels across the radiation attenuating component are substantially inversely related to radiation attenuation levels of tissue present between a given point of the radiation attenuating component and the active bone marrow. 2. The device of claim 1, wherein the body part that includes active bone marrow includes a bone selected from the group of bones consisting of: skull, sternum, ribs, vertebrae, humerus, pelvis and femur. 3. The device of claim 1, further comprising friction minimizing material provided between the layers. 4. The device of claim 3, wherein the friction minimizing material is selected from the group of materials consisting of Polytetrafluoroethylene (PTFE, Teflon), polyamide-imide (PAI), Nylon 6-6, Nylon 4-6, graphite, graphite powder, acetal homopolymer or carbon fiber, and a lubricant. 5. The device of claim 1, wherein the layers are interconnected so as to allow relative movement between the layers when subjected to bending. 6. The device of claim 1, wherein the radiation attenuating component is supported by a support structure. 7. The device of claim 6, wherein the support structure comprises a resilient material. 8. The device of claim 6, wherein the support structure is configured to prevent buckling of the radiation attenuation component when the radiation attenuation component is subjected to bending. 9. The device of claim 1, wherein the radiation attenuating component comprises one or more materials selected from the group of materials consisting of barium compounds, barium sulfate, barium chloride, tungsten compounds, tungsten carbide, tungsten oxide, tungsten, bismuth compounds, bismuth, lead, tantalum compounds, titanium, titanium compounds, diatrizoate meglumine, acetrizoate sodium, boron, boric acid, boron oxide, boron salts, other boron compounds, beryllium, beryllium compounds, bunamiodyl sodium, diatrizoate sodium, ethiodized oil, gold, lobenzamic acid, locarmic acid, locetamic acid, Iodipamide, Iodixanol, Iodized oil, Iodoalphionic acid, o-Iodohippurate sodium, Iodophthalein sodium, Iodopyracet, loglycamic acid, Iohexol, lomeglamic acid, Iopamidol, lopanoic acid, Iopentol, Iophendylate, lophenoxic acid, water, Iopromide, lopronic acid, lopydol, lopydone, lothalamic acid, Iotrolan, Ioversol, loxaglic acid, Ioxilan, Ipodate, meglumine acetrizoate, meglumine ditrizoate methiodal sodium, metrizamide, metrizoic acid, phenobutiodil, phentetiothalein sodium, platinum, propryliodone, silver, sodium Iodomethamate, sozoiodolic acid, thorium oxide, trypanoate sodium, uranium and depleted uranium. 10. The device of claim 1, wherein the radiation attenuating component is incorporated in a wearable item selected from the groups of items consisting of a helmet, a bifurcated garment and a belt. 11. The device of claim 1, further comprising a sealable opening for intraosseous injection of a substance into an underlying bone within the body part. 12. A method for protecting bone marrow of a subject from radiation, the method comprising:placing a radiation protection device that includes a radiation attenuation component comprising a radiation attenuating material providing varying radiation attenuation levels at different points across the radiation attenuating component, adjacent to and externally covering a body part that includes active bone marrow so as to reduce a radiation dose absorbed by the bone marrow in that body part,forming the radiation protection device to comprise a body part side and layering the sheets of radiation attenuating material in at least one of increasing thickness and density orthogonal to the body part side, andvarying radiation attenuation levels across the radiation attenuating component by substantially inversely relating to radiation attenuation levels of tissue present between a given point of the radiation attenuating component and the active bone marrow. 13. The method of claim 12, further comprising administering a substance to the subject for enhancing hematopoietic reconstitution or inducing proliferation of hematopoietic stem cells or progenitors. 14. The method of claim 13, wherein the substance is selected from the group of substances consisting of G-CSF, PEGylated G-CSF, GM-CSF, M-CSF (CSF-1), AMD3100, Filgrastim (Neupogen), Pegfilgrastim, Stem cell factor (c-kit ligand or Steel Factor), Interleukin 11, Interleukin 3, Interleukin 7, Interleukin 6, Interleukin 12, Interleukin 1, Interleukin 2, Interleukin 4, Interleukin 8, Interleukin 9 Interleukin 15, Erythropoietin (EPO), Epoetin alfa (Epogen), Darbepoetin alfa (Aranesp), Omontys (peginesatide), SDF-1, friend of GATA-1 (FOG-1), PTH and active PTH fragments or PTH/PTHrP receptor agonists, leukemia inhibitory factor (LIF), Platelet-derived growth factor (PDGF), Angiotensin-(1-7), Leridistimor, Flt3-ligand, thrombopoietin, Keratinocyte growth factor (KGF), TGF β, MPL receptor agonists, Promegapoietin-1 α (PMP-1 α), hyaluronic acid and K-7/D-6. 15. The method of claim 12, further comprising administering a substance to the subject for inhibiting apoptosis of hematopoietic stem cells or progenitors. 16. The method of claim 15, wherein the substance is selected from the group of substances consisting of G-CSF, PEGylated G-CSF, GM-CSF, M-CSF (CSF-1), AMD3100, Filgrastim (Neupogen), Pegfilgrastim, Stem cell factor (c-kit ligand or Steel Factor), Interleukin 11, Interleukin 3, Interleukin 7, Interleukin 6, Interleukin 12, Interleukin 1, Interleukin 2, Interleukin 4, Interleukin 8, Interleukin 9 Interleukin 15, Erythropoietin (EPO), Epoetin alfa (Epogen), Darbepoetin alfa (Aranesp), Omontys (peginesatide), SDF-1, friend of GATA-1 (FOG-1), PTH and active PTH fragments or PTH/PTHrP receptor agonists, leukemia inhibitory factor (LIF), Platelet-derived growth factor (PDGF), Angiotensin-(1-7), Leridistimor, Flt3-ligand, thrombopoietin, Keratinocyte growth factor (KGF), TGF β, MPL receptor agonists, Promegapoietin-1 α (PMP-1 α), hyaluronic acid and K-7/D-6, δ Tocotrienol (DT3), Angiotensin-(1-7), Inducers of nuclear factor-Kappa B, Flagellin, vitamin C, WR-2721 and WR-1065, CBLB502. 17. The method of claim 12, further comprising administering a substance to the subject to prevent hematopoietic stem cells or progenitors within the active bone marrow from leaving the protected active bone marrow and circulating. 18. The method of claim 17, wherein the substance is selected form the group of substances consisting of SDF-1 (CXCL12) or an analog, fusion protein, variant, functional derivative or fragment thereof having the activity of SDF-1 and/or an agent capable of inducing expression of said chemokine SDF-1, PDGF, Somatostatin, c-kit, Hepatocyte growth factor (HGF), anti MMP-9 (anti matrix metalloproteinase-9) antibody, neutrophil elastase (NE) inhibitor, Migrastatin or its analogues including but not limited to core macroketone and core macrolactam, TGF-β, IL-8 inhibitors, anti Gro βγ antibody, anti Gr1 antibody, anti LFA-1 antibody, anti Mac-1 (CD11b) antibody, cathapsin G inhibitors, anti SDF-1 blocking antibody, soluble CXCR4, soluble CCR2, MCP-1 (CCL2) and MCP-3 (CCL7) inhibitors, G-CSF inhibitors, GM-CSF inhibitors, soluble VLA-4, anti MMP-2 antibody CB2 agonists including but not limited to AM1241. 19. The method of claim 12, further comprising administering a substance to the subject to attract hematopoietic stem cells or progenitors into the protected active bone marrow. 20. The method of claim 19, wherein the substance is selected from the group of substances consisting of SDF-1 (CXCL12) or an analog, fusion protein, variant, functional derivative or fragment thereof having the activity of SDF-1 and/or an agent capable of inducing expression of said chemokine SDF-1, agonists or partial agonists of CXCR4 and/or CXCR7, CCR2 ligands including but not limited to MCP-1 (CCL2) and MCP-3 (CCL7), CB2 agonists including but not limited to AM1241, PDGF, Somatostatin, c-kit, Hepatocyte growth factor (HGF). 21. The method of claim 12, further comprising administering a substance to the subject before, during or after the exposure to ionizing radiation. 22. The device of claim 1, wherein a thickness or density of the radiation attenuating material at each point x,y,z, on the radiation attenuating component is varied so as to provide a required attenuation level AR that is determined by the formula AR (x, y, z)=AD/AT, AD is a radiation attenuation level needed to reduce the radiation dose absorbed in the active bone marrow contained within the body part that is covered by the point x,y,z, on the radiation attenuating component to a desired level, and AT is the tissue radiation attenuation level between the point x,y,z and the active bone marrow contained within the body part that is covered by the point x,y,z, on the radiation attenuating component. 23. The device of claim 1, wherein the radiation attenuating material comprises a gamma radiation attenuating component. 24. The device of claim 1, wherein the radiation attenuation component maintains the viability of at least 20% of the cells in 300 cm3 of active marrow. 25. The device of claim 1, wherein at least two of the sheets of radiation attenuating material vary in density. 26. The device of claim 1, wherein the sheets of radiation attenuating material are layered on top of each other in the orthogonal direction. 27. The method of claim 12, wherein a thickness or density of the radiation attenuating material at each point x,y,z, on the radiation attenuating component is varied so as to provide a required attenuation level AR that is determined by the formula AR (x, y, z)=AD/AT where AD is a radiation attenuation level needed to reduce the radiation dose absorbed in the active bone marrow contained within the body part that is covered by the point x,y,z, on the radiation attenuating component to a desired level, and AT is the tissue radiation attenuation level between the point x,y,z and the active bone marrow contained within the body part that is covered by the point x,y,z, on the radiation attenuating component. 28. The method of claim 12, wherein the radiation attenuating material comprises a gamma radiation attenuating component. 29. The method of claim 12, further comprising the step of maintaining the viability of at least 20% of the cells in 300 cm3 of active marrow. 30. The method of claim 12, wherein the forming step further comprising the step of varying the density of at least two of the sheets of radiation attenuating material. 31. The method of claim 12, wherein the forming step further comprises the step of layering the sheets of radiation attenuating material on top of each other in the orthogonal direction. 32. A radiation protection belt providing protection of active bone marrow from external ionizing radiation, comprising:a gamma radiation attenuating component configured to be placed adjacent to and externally cover at least one of the waist and the pelvis of a user so as to reduce a radiation dose absorbed in the active bone marrow in the pelvis, comprising radiation attenuating material of at least one of varying thickness and density to provide varying radiation levels across the gamma radiation attenuating component, such that the varying radiation attenuation level at each point on the radiation attenuating component is inversely related to radiation attenuation levels of tissue present between the point of the radiation attenuating component and the active bone marrow in the pelvis. 33. The belt of claim 32, wherein the gamma radiation attenuating component comprises layers of radiation attenuating material. 34. The belt of claim 32, wherein a portion of the active bone marrow being protected is in the iliac crest of the pelvis. 35. The device of claim 1, wherein the radiation attenuating component comprises sheets of radiation attenuating material configured in layers. 36. The method of claim 12, wherein the radiation attenuating component comprises sheets of radiation attenuating material configured in layers. |
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041705165 | abstract | In raising the power of a nuclear reactor, before the linear heat generating rate of nuclear fuel elements arranged in the core of the nuclear reactor reaches 240 W/cm, the power rise of the reactor is suspended at least once and the reactor power is held at the fixed level. The raise of the power of the nuclear reactor before the arrival of the linear heat generating rate at 240 W/cm is performed by pulling out control rods inserted into the core. When the linear heat generating rate exceeds 240 W/cm, the power of the nuclear reactor is gradually raised in such a way that the linear heat generating rate is increased in a proportion of below about 1.8 W/cm/hour by increasing the flow rate of a coolant supplied to the core. |
summary | ||
claims | 1. A scintillator based microscope image system comprising:a) a submicron source of high energy radiation;b) a substantially rigid first plate substantially transparent in at least one spectral range within a spectral range including visible and ultraviolet ranges;c) a second plate substantially transparent in at least one type of ionizing radiation;d) a single crystal scintillation crystal defining a peak scintillation wavelength in the form of a crystalline plate sandwiched between said first and said second plates, said scintillation crystal defining an illumination surface and a viewing surface;wherein the high-energy radiation from said source are directed through a target to illuminate said illumination surface to produce a scintillation image of said target within said scintillation crystal; ande) dual focus optical microscopic elements for producing a magnified view of said scintillation image produced by said scintillation and also a visible light image of a surface of said target; said dual focus optical microscopic elements comprising:1) a first set of optical elements focused on said illumination surface to obtain a shadow image of the target showing internal features of the target, and2) a second set of optical elements focused on a surface of said target to obtain a surface image of the target. 2. A microscope system as in claim 1 wherein with both illumination surface and viewing surface of said crystal being treated to reduce Fresnel reflections in said crystal at said peak scintillation wavelength to less than about 1.0 percent and to reduce surface roughness to less than about 100 angstroms. 3. A microscope as in claim 1 wherein said scintillation crystal is a single crystal CsI crystal. 4. A microscope system as in claim 3 wherein said CsI crystal is doped to produce a CsI (T1) crystal. 5. A microscope system as in claim 2 and further comprising optical grade adhesive located in spaces between said rigid first plate and said scintillation crystal wherein said scintillation crystal has a crystal index of refraction at said wavelength and said optical grade adhesive defines an adhesive index of refraction at said wavelength, said peak scintillation wavelength crystal index of refraction and said adhesive index of refraction being similar enough to reduce Fresnel reflections at said illumination surface to less than about 0.5%. 6. A microscope system as in claim 1 wherein said submicron high energy photon source is an x-ray source. 7. A microscope system as in claim 1 wherein said submicron high energy photon source is a high energy ultraviolet source. 8. A microscope system as in claim 1 wherein said submicron high energy photon source is a gamma ray source. 9. A microscope system as in claim 6 and further comprising a pinhole unit to provide a submicron high energy photon source. 10. A microscope system as in claim 9 wherein said pinhole is a funnel-type pinhole unit. 11. A microscope system as in claim 9 wherein x-rays are produced by alpha particles. 12. A microscope system as in claim 11 wherein said x-rays are produced by interaction of said alpha particles with a metal foil. 13. A microscope system as in claim 9 wherein said pinhole unit is an adjustable pinhole unit. 14. A microscope system as in claim 13 wherein said adjustable pin hole unit comprises two sets of two spaced apart plates each set defining a narrow crack with varying widths. 15. A method of making an image of at least a portion of a target utilizing a microscopic optical system and a scintillator comprising a single crystal scintillation crystal in the form of a plate, said scintillation crystal defining an illumination surface, said method comprising the steps of:a) illuminating from a submicron source said target with a beam of radiation having sufficient energy such that a portion of said beam is absorbed in said target and a portion passes through said target to define a shadow beam; a portion of said shadow beam passing through a reflector and being absorbed in said crystal to produce visible light scintillations in said crystal;b) focusing said microscopic optical system at or near said illumination surface to provide a magnified internal features view of said target; andc) providing a comparison visible light microscopic view of a surface of said target utilizing a set of visible light optical elements focused on a surface of said target. 16. A method as in claim 15 wherein said submicron high energy photon source is an x-ray source. 17. A method as in claim 15 wherein said submicron high energy photon source is a high energy ultraviolet source. 18. A method as in claim 15 wherein said submicron high energy photon source is a gamma ray source. 19. A method as in claim 15 and further comprising a pinhole unit to provide the submicron high energy photon source. 20. A method as in claim 19 wherein said pinhole is a funnel-type pinhole unit. |
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description | This application claims benefit to U.S. provisional application No. 62/314,702 filed on Mar. 29, 2016, the entire contents of which is incorporated by reference herein. The present disclosure relates to fission nuclear fuels. More specifically, the present disclosure describes a method to produce microencapsulated fuel forms with enhanced toughness in their ceramic coating layer and microencapsulated fuel forms made therein. In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art. There are many known types of nuclear fuel for both research and power producing nuclear reactors. The fuel can be of many types, including both fissionable (fissile) isotopes and fissile-producing (fertile) isotopes of Uranium, Plutonium, or Thorium, forming as example ceramic carbides, oxides, nitrides, or silicides. With the near complete dominance of current generation of light-water reactors (LWR's) for nuclear power production uranium dioxide (UO2) pellets have become the de facto standard nuclear fuel. The UO2 pellet is used in a pressured water reactor (PWR) and the boiling water reactor (BWR) configurations, being mass-produced through a ceramic processing route: once a powder of appropriate purity and fissile isotope enrichment is achieved it is pressed and then sintered in the presence of hydrogen and taken to final dimension by center-less grinding. Once the finished product is qualified it is placed inside a zirconium alloy tube and weld-sealed in an inert helium environment. This zirconium tube, during normal reactor operation, serves a number of functions including the plenum (barrier) for containment of the radiotoxic fission product gases. Another type of reactor is a high-temperature Gas-Cooled Reactor (HTGR). The HTGR reactors, whether in the prismatic or pebble-bed configuration, utilize a fuel specifically engineered as a primary barrier to fission product retention. This is achieved through engineering layers of carbon, graphite and silicon carbide (SiC) around a fissile-material-bearing (U, Pu, etc.) fuel kernel. In this design, the SiC coating layer specifically becomes a pressure vessel. Such a structure is known as a tristructure isotropic (TRISO) fuel. An example of a traditional TRISO fuel is illustrated by a schematic showing the layers in FIG. 1. Specifically, the traditional TRISO 10 of FIG. 1 includes a fissile fuel kernel 11, a buffer graphitic layer 12, an inner pyrolytic carbon layer 13, silicon carbide layer 14, and an outer pyrolytic carbon layer 15. The traditional TRISO 10 can be pressed into a host graphite matrix (not shown) and used in a small number of commercial power reactors. More recently, a fuel form has been developed whereby TRISO fuel, rather than being compacted within a graphite matrix, as is the case for HTGR, is compacted within a strong and impermeable fully dense SiC matrix. That fuel has been developed and previously described as a more robust fuel whereby the SiC layer of the microencapsulated “TRISO” fuel and the dense ceramic SiC matrix into which they are contained provide two barriers to fission product release in addition to any external cladding that may be present. A secondary barrier to fission product release significantly enhances the safety aspects of a nuclear fuel and reduces the related safety systems of modern LWR's, as well as benefiting gas-cooled reactors. The present disclosure provides a fabrication method for forming a TRISO particle with an enhanced toughness in the SiC coating layer of the TRISO particle. The coated fuel particle fabrication utilizes the fluidized bed coating furnace and precursor gases that are current in use for forming traditional TRISO particles. However, the deposition schedule is altered such that a single SiC coating layer is replaced with a multilayer pressure vessel including alternating layers of SiC and pyrolytic carbon (PyC or pyrocarbon). The multilayer pressure vessel including alternating layers of SiC and PyC enhances the toughness of the ceramic pressure vessel. Specifically, it was found that thin PyC layers between layers of SiC serve to deflect any cracks that develop in the structure. Although the multilayer structure could exhibit reduced strength compared with the single SiC layer, failure in these coated fuel structures is governed by probability of microcrack propagation. According, the multilayer has the effect of greatly enhancing the ability of the fuel to retain radionuclides compared to the single SiC layer. Additionally, the multilayer structure will exhibit higher tolerance for elastic strains and should delay the onset of any microcrack formation in the first place. One fuel particle including the multilayer structure includes: a fissile fuel kernel, a buffer graphitic carbon layer, an inner pyrolytic carbon layer, a multilayer pressure vessel, and an outer pyrolytic carbon layer. A method of forming a fuel particle described above includes: providing a fissile fuel kernel; coating a buffer graphitic layer on the fuel kernel; coating an inner layer of pyrolytic carbon onto the buffer graphitic layer; coating a multilayer pressure vessel onto the inner layer of pyrolytic carbon; coating an outer layer of pyrolytic carbon onto the multilayer pressure vessel. In a particular embodiment, the method comprises providing a fissile fuel kernel in a CVD furnace; depositing a buffer graphitic layer on the fuel kernel by decomposition of acetylene; depositing an inner layer of pyrolytic carbon onto the buffer graphitic layer by decomposition of a mixture of acetylene and propylene; depositing a multilayer pressure vessel onto the inner layer of pyrolytic carbon by alternatingly decomposing MTS and a mixture of acetylene/propylene during a continuous coating layer deposition process; and depositing an outer layer of pyrolytic carbon onto the multilayer pressure vessel by decomposition of a mixture of acetylene and propylene. All of the various coating layers can be deposited in a serial coating run without any interruption. The continuous deposition of different coatings can be achieved by adjusting the furnace temperature and switching between reactant gases once a coating step is complete. The deposition of thin SiC and PyC layers can also be reasonably achieved by employing a similar strategy. In an embodiment of the above fuel particle or the above method, the multilayer pressure vessel includes at least three layers in which a pyrolytic graphite layer is present between two layers of silicon carbide. In an embodiment according to any of the above fuel particles or the above methods, the multilayer pressure vessel includes at least one additional pair of pyrolytic graphite layer and silicon carbide layer between the pyrolytic graphite layer and one of the two layers of silicon carbide. In an embodiment, according to any of the above fuel particles or the above methods, the multilayer pressure vessel includes at least 2, at least 3, at least 4, or at least 5 pairs of pyrolytic graphite layer and silicon carbide layer. In each of the above mentioned embodiments, the pyrolytic graphite layer(s) and the silicon carbide layer(s) alternate throughout the multilayer pressure vessel. Accordingly, the pyrolytic graphite layers separate layers of silicon carbide. In an embodiment according to any of the above fuel particles or the above methods, the multilayer pressure vessel has a thickness from 20 to 50 μm, 25 to 45 μm, 30 to 40 μm, or about 35 μm. In an embodiment according to any of the above fuel particles or the above methods, the buffer carbon layer has a thickness from 50 to 300 μm, 70 to 200 μm, 80 to 150 μm, or about 100 μm. In an embodiment according to any of the above fuel particles or the above methods, the inner and outer layers of pyrolytic graphite each has a thickness from 10 to 100 μm, 20 to 50 μm, 30 to 40 μm, or about 40 μm. In an embodiment according to any of the above fuel particles or the above methods, each of the silicon carbide layers of the multilayer pressure vessel has a thickness from 200 nm to 10 μm, 200 nm to 5 μm, 300 nm to 2000 nm, or 400 nm to 1000 nm. In an embodiment according to any of the above fuel particles or the above methods, each of the pyrolytic graphite layers of the multilayer pressure vessel has a thickness from 20 nm to 1000 nm, 20 nm to 500 nm, 30 nm to 200 nm, or 40 nm to 100 nm. In an embodiment according to any of the above fuel particles or the above methods, a thickness of the silicon carbide layers of the multilayer pressure vessel is at least 2, 3, 4, 5, 6, 7, 10, 20, 50, 100, 200, or 500 times a thickness of the pyrolytic graphite layers of the multilayer pressure vessel. In an embodiment according to any of the above fuel particles or the above methods, the fuel kernel includes fissile and/or fertile materials (e.g., uranium, plutonium, thorium, etc.) in an oxide, carbide, or oxycarbide form. In a particular embodiment, the fuel kernel includes low enriched uranium (LEU) of any suitable enrichment level. In an embodiment according to any of the above fuel particles or the above methods, the fuel kernel includes transuranic elements extracted from a spent fuel of a light water reactor. In an embodiment according to any of the above fuel particles, the fuel kernel includes transuranic elements extracted from a nuclear weapon. In an embodiment according to any of the methods, each of the coating steps occurs in a fluidized chemical vapor deposition (CVD) furnace. In an embodiment according to any of the methods, each of the coating steps includes flowing reactant gases and optional carrier gases inside the furnace. The optional carrier gases can be selected from Ar, H, or mixtures thereof. The thickness, density, and microstructure of each of the coating layers can be controlled by controlling the particle batch size, gas flow rate and mixture, furnace temperature, and deposition time. In an embodiment according to the above method, the reactant gases include: acetylene (C2H2), the decomposition of which can form a porous buffer carbon layer; a mixture of acetylene and propylene (C3H6), the decomposition of which can form an inner pyrolytic carbon layer; and methyltrichlorosilane (CH3SiCl3) or MTS, the decomposition of which can form an isotropic layer of silicon carbide. The following detailed description can be read in connection with the accompanying drawings in which like numerals designate like elements. FIG. 2 is a schematic diagram illustrating a fuel particle according to an embodiment of the invention. In FIG. 2, fuel particle 20 includes a fissile fuel kernel 21, a buffer graphitic layer 22, an inner pyrolytic carbon layer 23, a multilayer pressure vessel 24, and an outer pyrolytic carbon layer 25. The multilayer pressure vessel 24 includes silicon carbides layers 241 and pyrolytic graphitic layers 242 as alternating coatings and appear as stripes in the cross-section of FIG. 2. The fuel particle 20 can be pressed into a host graphite matrix or an impermeable silicon carbide matrix (not shown) and used in a power reactor. In the embodiment shown in FIG. 2, the fuel particle 20 includes a fuel kernel 21 at its center. The fuel kernel may comprise fissile and/or fertile materials (e.g., uranium, plutonium, thorium, etc.) in an oxide, carbide, or oxycarbide form. In a particular embodiment, the fuel kernel 21 includes low enriched uranium (LEU) of any suitable enrichment level. When the fuel element is used for waste mitigation and/or disposal purposes, the fuel kernel 21 may alternatively or additionally include transuranics (TRU) and/or fission products extracted or otherwise reprocessed from spent fuels. For example, the fuel element may be used for destruction of transuranic waste generated from, for example, light water reactors or decommissioned nuclear weapons. For that purpose, the fuel element may include fuel kernels 21 formed of transuranic elements extracted from a spent fuel of a light water reactor and/or a core of a nuclear weapon. According to a particular embodiment, a fuel element formed in accordance with the described methods may be used as fuel for a light water reactor to destroy the transuranic waste while, at the same time, generating power from it. The carbon buffer layer 22 surrounds the fuel kernel 21 and serves as a reservoir for accommodating buildup of fission gases diffusing out of the fuel kernel 21 and any mechanical deformation that the fuel kernel 21 may undergo during the fuel cycle. The inner PyC layer 23 may be formed of relatively dense PyC and seals the carbon buffer layer 22. The multilayer pressure vessel 24 serves as a primary fission product barrier and a pressure vessel for the fuel kernel 21, retaining gaseous and metallic fission products therein. The multilayer pressure vessel 24 also provides overall structural integrity of the fuel particle 20. In some embodiments, the SiC in the multilayer pressure vessel 24 may be replaced or supplemented with zirconium carbide (ZrC) or any other suitable material having similar properties as those of SiC and/or ZrC. The outer PyC layer 25 protects the multilayer pressure vessel 24 from chemical attack during operation and acts as an additional diffusion boundary to the fission products. The outer PyC layer 25 may also serve as a substrate for bonding to a surrounding ceramic matrix. The configuration and/or composition of the fuel particle 20 are not limited to the embodiments described above. Instead, it should be understood that a fuel particle consistent with the present disclosure may include one or more additional layers, or omit one or more layers other than the multilayer pressure vessel, depending on the desired properties of the fuel particle. Although described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departure from the scope of the invention as defined in the appended claims. |
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052308600 | abstract | A nuclear reactor vessel cavity seal plate. An annular support plate is positioned over the cavity between the reactor vessel and the shield structure. The inner diameter of the support plate rests freely upon the reactor vessel flange to allow movement of the vessel thereunder during thermal expansion and contraction. A flexible annular seal positioned over the support plate has its inner diameter seal welded to the reactor vessel flange and its outer diameter seal welded to the shield structure. Matching ports in the support plate and seal provide access to nuclear instruments below the support plate. A mounting block around each port accepts a cover plate that seals the port. This provides a permanent seal plate that allows flooding of the cavity for refueling with it only being necessary to remove the cove plates for normal reactor operations. |
description | FIG. 1 is a functional block diagram for showing the ion implant system 100 of this invention. The deceleration optics described below can decelerate an ion beam from high energy, e.g. 5 keV, to energy as low as 0.2 keV, and at the same time disperse the decelerated ion beam in an angular-spread-out beam according to the ion particle energy range. The angular-spread-out characteristic of the ion beam provides a convenient method for selectively blocking out the beam in a certain energy range by employing a simple mechanical means known as a beam stop. Referring to FIG. 1, the ion beam implant system 100 includes an ion source associated with ion-beam formation electrodes 105, the mass analyzer magnet 125, post analysis deceleration electrodes 135, and target chamber 150 for implanting a target wafer 120 with an ion beam 110. Under normal operation (no ion beam deceleration), the ion beam 110, mass-filtered by the mass analyzer magnet 125, is transported through the decel electrodes 135 and reaches the wafer. In this situation, there is no voltage difference between the entrance electrode and exit electrode of the decel electrode assembly so that neither deceleration nor acceleration occurs for the ion beam. There is also no non-symmetric field applied in the region of the decel electrodes so that the ion beam is not steered away from the beamline symmetric axis. Under the operation of ion beam deceleration, after the ion beam 110 passes through the magnetic analyzer 125, a deceleration voltage 130 is applied to decelerate the ion beam 110 as shown in FIG. 1. When the ion beam 110 is a positively charged ion beam, a negative voltage 130 is applied. As the ion beam 110 travels through the ion beam system 100, some charged particles may be neutralized. The deceleration voltage will not decelerate the neutralized particles because they do not carry a net charge. The energy and direction of such particles are not affected by the electric field. After passing through the deceleration optics 135 the path of the neutral particles and the charged particles are therefore separated during deceleration and become two separate beams 110-1 and 110-2. The neutral particle beam 110-1 travels along a straight line while the charged ion beam 110-2 becomes spread out by employing a special deceleration optics as will be discussed below. The charged ion beam becomes an angularly spread-out beam and travels along a path with a slightly downward angle, e.g., a six-degree downward angle, to reach the target wafer 120. Note that the charged ion-beam is spread out over an angular range depending on the energy of the ion particles as will be discussed below. A beam stop 155 is employed on the path of the neutralized particle beam 110-1 to block the neutralized beam 110-1 from reaching the target wafer 120. The target wafer 120 is placed with a small slant angle, e.g., a six-degree angle relative to a vertical direction of the perpendicularly facing charged ion beam 110-2. By putting a beam stop 155 after the deceleration optics, but in the original beam path 110-1, the neutral particles are blocked and hence removed. By making the steering angle sufficiently large (at least 3 degrees) the problem of energy contamination associated with the neutral fraction in charged ion beams can be overcome. In this way, the problem of energy contamination in decel-mode operation can be resolved. Referring to FIG. 2, the angular spread of the ion beam generated by the deceleration optics provides a steering function that is specifically configured as an energy filter. For a given configuration of the deceleration optics, the individual ions in the beam will be deflected downward at a large (small) angle for ions having a relatively low (high) energy. Suppose that the steering angle is xcex8O for ions with initial energy EO decelerated to a final energy EF. The ion beam is typically composed of ions with a range of energies from EOxe2x88x92dE1 to EO+dE2, where dE1 and dE2 represent the lower and upper ion beam energy increment limits, respectively. Referring to FIG. 2, ions with energy much higher than EO will be deflected by a small deflection angle xcex8 less than less than xcex8O and thus will be blocked by the upper part of the beam stop as shown in FIG. 2. Ions with higher energy, but close to EO, will be partially blocked. Ions with energy smaller than EO will be blocked by the lower part of the beam stop although energy contamination is not as serious a problem for ions with energy much less than EO. The problems caused by energy contamination can be significantly resolved with a beam stop 155 as that shown in FIGS. 1 and 2. Even during high voltage glitch conditions, which may cause the original ion beam to have a large energy range, the implant profile will not be adversely affected by energy contamination. The opening of the beam stop also defines the targeted ion-beam direction when the deceleration optics decelerates and steers the ion beam through the opening to the target wafer. FIGS. 3 and 4 show the schematic diagrams of the deceleration optics 135 and the electrical voltage arrangement of the electrodes employed in the deceleration optics 135 of the present invention. The deceleration optics consists of three electrodes A, B, and C. The voltages of the ion source, the extraction suppression electrode, and the source terminal are shown in FIG. 3 as VS, VE, and VT, respectively, where VS and VT are referenced to ground while VE is referenced on the source terminal. Electrode A is at a potential VA and is equal to the ion source termination potential VT(VA=VT). The deceleration suppression electrode B is at a potential VB that is more negative than VA(VB less than VA). Electrode C is at a potential VC that is equal to the potential of the processed wafers, and is more positive than VA(VA less than VC). The original ion energy EO is equal to q(VSxe2x88x92VT)=q(VSxe2x88x92VA), and the decelerated ion energy EF is equal to q(VSxe2x88x92VA)xe2x88x92q(VCxe2x88x92VA)=q(VSxe2x88x92VC), where q is the charge of an ion in the beam and is usually positive. In most ion implanters, it is preferable for the processed wafers to be connected to ground (VC=0) or nearly so. In this configuration, the ion source power supply is floated or referenced on the source terminal potential which itself is floated or referenced on the ground potential. The resulting energies are, EO=q(VSxe2x88x92VT), EF=qVs, where, VC=0, VB less than 0, and in decel-mode, VT less than 0. Also, the extraction power supply, VE less than 0, is referenced on the source terminal and VB less than VA=VT less than 0 is referenced on the ground potential. Regardless of the configuration, VB is more negative than VA and VC(VB less than VA less than VC), so that Electrode B can suppress both the upstream and downstream electrons. Electrode B also provides focusing while the beam is being decelerated and steered. From the electrode cross-section diagram in FIG. 4, it can be seen that Electrode B and Electrode C can be displaced transversely off the centerline of electrode A. Both the electric field between Electrode A and B and the field between Electrode B and C steer the ion beam downward. Electrodes B and C are controlled by a manipulator and can move transversely to steer the ion beam with the correct angle so that the ion beam can reach the wafer position. The steering angle is a function of the original and final energies of the ion beam and the electric field distribution in the deceleration region. For different original and final energies of the ion beam, the parameters affecting the electric field distribution, including the suppression voltage VB and the transverse positions of Electrodes B and C, have to change to keep the steering angle unchanged so that the ion beam can reach the same wafer position. Because the suppression voltage VB is primarily used to focus the ion beam, its value is usually changed to give the proper focusing while the transverse positions of Electrodes B and C are changed to give the proper steering. The original beam is required to have small beam width for separating the decelerated and steered ion beam with the neutralized beam in a position not far from the deceleration region to significantly reduce energy contamination. Assume that the steering angle is xcex8O, the beam width is w for both the neutralized beam and decelerated ion beam, and the travel distance for completely separating the neutralized beam and the steered ion beam is L. The steering angle xcex8O should be maintained small, usually from three degrees to fifteen degrees, to minimize corresponding wafer position change and possible beam current loss. The travel distance L should be short to maximize beam current delivery to the wafer when space charge blow-up occurs for low energy and high current beam. Since the relation among these parameters is approximately w=L tanxcex8O, the beam width is required to be small, too. For instance, when xcex8O is equal to 6 degrees and L equal 30 cm, w will become 3.2 cm Considering that large beam cross section is required to minimize space charge blow-up for low energy and high current beam, the beam height should be large when the beam width is limited to be small. In other words, an ion beam with large aspect ratio (or large height-to-width ratio) is required in the deceleration and steering region for successfully separating the decelerated and steered ion beam from the neutralized beam, and transporting the production worthy low energy beam currents. An aspect ratio of 4 is considered to be the minimum requirement for separation of a low energy and high current ion beam from the corresponding neutralized beam. Since the beam width is usually larger than 2.5 cm, the beam height has to be at least 10 cm. After the neutralized beam is separated from the decelerated ion beam, a beam stop can be applied in the neutralized beam path to prevent the neutrals with higher energy from reaching the wafer and therefore minimize energy contamination. FIG. 5 shows a three-dimensional perspective view of the mechanical design of the deceleration electrode assembly. The apertures of the three electrodes are narrow and tall because they are designed to decelerate narrow and tall beams, or high aspect ratio beams as discussed above. Electrode B has a larger width than Electrode A and C to prevent ion beams from striking on Electrode B, generating large secondary electron emissions, and thereby overloading the suppression power supply. Another reason is to provide a better focusing field distribution. When the width of Electrode B is smaller than that of Electrode C, the transverse field components at the edge of Electrode C is high, which may inappropriate deflection of the beam. The deceleration optics of the present invention provides an apparatus to decelerate ion beams and at the same time steer these decelerated beams off the path of the original ion beams. In this way, the decelerated ion beam is steered in the target direction and the neutralized beam travels in the direction of the original ion beam. By blocking the neutralized beams with a beam stop, the energy contamination resulting from deceleration can be eliminated. The invention thus discloses an ion implantation apparatus, which includes a target chamber for containing a target for implantation and an ion source chamber includes an ion source for generating an ion beam. The ion source chamber further includes beam deceleration optics for decelerating the ion beam to produce a low energy ion beam. The deceleration optics further includes an ion beam steering means for generating an electrostatic field for separating neutralized particles by steering the charged particles to transmit in a targeted charged-particle direction that is slightly different from the neutral beam direction. The ion-beam deceleration optics further includes electrodes for generating a spread-out ion beam over an angular range along the beam line of the ion beam. The angular spread is determined by the energy of each ion in the ion beam and is used for more accurately controlling the energy of the ions for implantation and for blocking the neutralized particles and ions above a maximum implant energy from reaching the target for implantation. In a preferred embodiment, the ion-beam deceleration optics includes a first, second, and third electrode arranged along the direction of the ion beam for generating a filtering electric field wherein the second electrode is provided with a more negative voltage than the first electrode, and the third electrode is provided with a more positive voltage than the first electrode. In a preferred embodiment, the first electrode is provided with a voltage that is the same as the ion source terminal voltage and the third electrode is provided with a voltage that is the same as a wafer voltage. In another preferred embodiment, the third voltage is provided with a wafer voltage connected to a ground voltage. The ion-beam deceleration optics further includes a neutral beam blocking means for blocking the neutralized particles from reaching the target of implantation in the target chamber. The beam deceleration optics further includes a high energy beam blocking means for blocking ions of the ion beam having an energy higher than a maximum implant energy by placing the high energy beam blocking means at a pre-designated angular position along the beam line corresponding to an angular range for blocking ions of the ion beam having an energy higher than the maximum implant energy. The ion source generates a positively charged ion beam and the beam deceleration optics includes the electrodes for generating an energy filtering electric-field for decelerating and filtering the ion beam by producing a spreading-out ion beam over an angular range along the primary beam direction. The steered ion beam transmits in the targeted ion-beam direction having a small vertically deflected angle, e.g. six degrees, relative to a horizontal axis as shown in FIGS. 1 and 2. And, the target chamber containing the target for implantation leans at a small angle, e.g. six-degrees, relative to a vertical axis perpendicular to the horizontal axis whereby the target for implantation is perpendicular to the incident angle of the ion beam. In another preferred embodiment, the ion source chamber is provided with a vacuum in the range of 10xe2x88x925 torr and the ion beam may be decelerated to an energy level of 200 eV or less with a beam energy contamination of about 0.1%. In summary, an ion source apparatus for generating and directing an ion beam is disclosed in this invention. The ion source apparatus includes a beam deceleration optics used for decelerating the ion beam. The beam deceleration optics further includes a plurality of electrodes for generating an electric field used for spreading out the ion beam over an angular range according to energy of each ion of the ion beam for more accurately directing an ion beam with desired low energy to a target wafer. According to above descriptions, this invention further discloses a method for generating an implantation ion beam. The method includes the steps of (a) providing an ion source for generating an ion beam; (b) employing an analyzer magnet for steering the ion beam through a curved beam-trajectory to a targeted ion-beam direction; (c) applying the ion beam steering means for coordinating with the beam deceleration means for generating an electromagnetic field for separating a neutralized particle by steering a neutralized particle to transmit in a neutralized-particle direction slightly different from the targeted ion-beam direction; and (d)employing a beam deceleration optics for decelerating and filtering the ion beam for producing a spreading out beam over an angular range along a beam line of said ion beam according to an energy of ions of the ion beam and employing a high energy ion blocking means for blocking out ions having an energy higher than a maximum implant energy. Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention. |
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055442064 | claims | 1. Apparatus for inspecting a nuclear reactor comprising: a boom rotatably connected to a pivot point on a base; means for controllably rotating the boom with respect to said pivot point on said base; and a camera assembly affixed to said boom and being longitudinally slidable thereto such that the camera assembly may be slidably adjusted with respect to said boom. a boom rotatably connected to a base at a pivot point, said base being affixed atop a nuclear reactor, said boom having a caster at one end such that said boom can rotate with respect to said pivot point and said caster; means for selectively rotating and positioning said boom and said caster about said pivot point; a camera slidably mated with said boom between first and second positions on said boom; means for slidably moving said camera between said first and second positions along said boom; means for rotating said camera means in a first direction with respect to said boom; and means for rotating said camera means in a second direction with respect to said boom. a boom rotatably fixed about a pivot point on said reactor head, said boom having a caster at one end such that said boom can rotate 360.degree. with respect to said pivot point and said caster; means for rotating said boom about said caster; camera and light means slidably mated with said boom such that said camera and light means can move between first and second positions on said boom; and means for moving said camera and light means between said first and second positions on said boom. (a) affixing a camera to a boom member; (b) placing said boom member and camera on a rotational pivot point set on a position in said reactor and (c) selectively rotating said boom member such that said camera and boom member can be selectively positioned within said reactor; and (d) selectively rotating said camera and boom member can be selectively positioned within said reactor. 2. Apparatus of claim 1 further comprising means for adjusting said camera assembly in a vertical direction. 3. Apparatus of claim 1 further comprising means for adjusting said camera assembly in a horizontal direction. 4. Apparatus of claim 1 further comprising a light means lamp affixed to said camera assembly for illuminating said nuclear reactor. 5. Apparatus of claim 1 wherein said camera assembly is slidably adjustable by a drive screw situated longitudinally along the boom, which is in threaded connection with said camera assembly, such that when said drive screw is rotated in a first direction, the camera assembly slides in a first longitudinal direction along said boom, and when said screw is rotated in a second longitudinal direction, the camera assembly slides in the second direction with respect to said boom. 6. Apparatus of claim 1 further comprising a control module for controlling the rotation of the boom and the sliding of the camera assembly. 7. Apparatus for inspecting the reactor head of a nuclear reactor comprising: 8. Apparatus of claim 7 wherein said first direction is the horizontal direction. 9. Apparatus of claim 7 wherein said second direction is the vertical direction. 10. The apparatus of claim 7 further comprising light means connected to said camera for illuminating the area to be inspected by said camera. 11. Apparatus for inspecting the reactor head of a nuclear reactor comprising: 12. A method for inspecting a nuclear reactor comprising the following steps: |
description | This description refers to a patent application for a pair of modules composed of metal blocks filled with a metallic powder, in a configuration that will allow several units of these modules to be attached together and welded to form shielded walls for radiotherapy rooms, with high capacity of attenuation of radiation. The walls formed by these modules are easy and quick to assemble and do not show cracks, holes or fragmentation. The modules can also be used for repair or reinforcement of the radiotherapy area or room in a quick way and without the need of interdiction of the room for long periods of time both due to its capacity of shielding and due to the fact that its density is superior to that of the common concrete. As is well known to those who have technical knowledge on the subject, in order to implement a Radiotherapy Service, it is necessary to choose and acquire equipment and elaborate a shielding project, within the stipulated standards so that the service obtains the necessary registrations and authorizations to its operation. The Ministerial Order 1884/1994 of the Brazilian Ministry of Health determines that the service must comply with certain recommendations on protection of radiation and safety in radiotherapy, establishing the necessary requirements for the installation and operation of a radiotherapy service. In an architectural design of radiation shielding for protection of radiation, the most common materials for the fabrication of the walls of the site are the concrete of normal density or of high density, steel plates and/or lead liners, being the common concrete the cheapest material and the most simple to use, but it has a low density compared to others, thus requiring a thick wall for the shield. If there is a space restriction, the use of alternative materials is considered. In some situations, especially when renovating a room, or in buildings close to very busy areas where space is critical, it may be necessary to use steel plates or a combination of steel and concrete in order to maintain the minimum thickness of the shielding and maximize the use of the room size. Although concrete is the most suitable material, it is essential to take special care in the wall frame, joints, launching sequence, vibration and curing of the concrete to avoid cracks, holes or dilatations. Common concrete has the advantage of low cost and ease of construction, although concrete shields are quite thick. Concrete requires a metallic framing to increase resistance and molds for containment of fluid mass. High-density concrete can be used when there is a space limitation. However, its relatively high cost and the lack of appropriate attenuation curves contraindicate their regular use. Low carbon steel has appropriate shielding characteristics and, due to its strength, can also be used as a structural component. Steel plates can be used in addition to concrete when space is at the premium and also as a frame and shielding of doors and also as filling of recess in the walls. Lead is recommended as a shielding material for doors because although this material is denser than others, sheets or linings of lead are more expensive. Just as an example, a picture from the internet has been chosen as FIG. 1 in the accompanying drawings, representing a cross-sectional view of a room shielded with concrete for linear accelerator, illustrating the thickness required for the walls. Nowadays, this market has grown leaving a great gap between supply and need in the country. With increasing demand, radiotherapy equipment such as linear accelerator, perform treatments faster and on a larger scale. The problem here is that the shielding is not appropriate for the newer equipment and in a larger quantity. Usually, in an attempt to remedy such problems, adaptations are made with lead plates, iron or concrete, and in these cases, it is necessary to interdict the room during the period of the work to carry out the adjustments. In order to solve the above problems, the inventor has developed a pair of modules which consist of metal blocks filled with metal powder, preferably iron ore, in such a configuration to enable several units of these modules to be fitted together and welded, quickly and simply, for the formation of a wall, floor or ceiling with high radiation attenuation capacity and considerably less thickness when compared to concrete walls constructed for the same purpose. Thus, the walls formed by these modules are easy to construct, by the assembly, and do not have cracks, holes or fragmentation. This way, even when used for repair or strengthening of the radiotherapy area or room, the interdiction will not be necessary for long periods of time. The material with which the modules are manufactured guarantees its low cost. Thus, even when modules manufactured in a larger size are used, in order to increase the shielding capacity of the wall, there is a big cost reduction on the project, especially compared to steel plates and, especially lead, ensuring the same shielding capacity, taking into account the appropriate density ratios. According to the attached figures, the metallic modules and assembly system for the formation of shielded walls, floor and ceiling for rooms used for radiotherapy object of this invention, is constituted by a square block (1), parallelepiped, that is, two equal sides and a stretched body (2), longitudinally projecting and spacing the front face (3) of the rear face (4), which have small bevels on the edges (5). On one side of its body (2), the square block (1) has a second block welded to it (1a), of equal configuration but displaced vertically exactly at the midpoint of the face of the first block previously mentioned (1) and horizontally, in the same dimension of one of its sides. This pair of blocks (1 and 1a) joined together as previously described, form a structure that will be referred to, herein, as the base module (MB) which will work with a complementary module (MC) which is formed by a rectangular parallelepiped block (6) having a width and length identical to the width and lengths of the square blocks (1 or 1a), but with a height exactly equal to half the height of the square block (1 or 1a) and the front (6a) and rear faces (6b) are also bordered by small bevels (5). Blocks (1, 1a and 6) are high density and are formed by a metal casing (7) filled with metal powder (8), which may be iron ore, other derivative material or a blend, depending on the quality, and type of shielding to be achieved. Thus, the modules (MB and MC) will form shielded walls with radioprotection for the radiotherapy area or room, to avoid leakage of ionizing radiation. To do so, with the floor of the area preferably already installed and properly finished, several units of base modules (MB) and complementary modules (MC) are brought to the site, according to the construction project. After demarcating the wall area, a first base module (MB) is placed on the floor with the square block facing down (1), then receiving a complementary module (MC) shim, inserted under its second block (1a), supporting it and making it firm, filling the lower space left by its vertically offset configuration misplaced compared to the first square block (1). A new base module (MB) unit is then positioned behind the first one, matching and joining the rear faces (4) of the blocks (1 and 1a) with the front faces (3) of the blocks (1 and 1a) of the new unit, then a complementary module unit (MC) is being inserted underneath the second block (1a), supporting it. This action is repeated until the demarcated limit for the wall is reached, forming a pattern of unified modules (MB and MC) in a structure. That way, a new base module (MB) unit is placed on top of the first, in the same position, joining the upper faces of the block (1) and the displaced block (1a) of the first unit with the respective lower faces of the block (1) and displaced block (1a) of this new base module unit (MB), stacking them vertically. This action is then repeated with all other units already positioned, linearly and horizontally and, after being positioned, these new units receive the stacking of more units of a base module (MB), vertically, until a solid wall (P) is obtained. In this way, the first wall (P) is formed, a new base module unit (MB) is laid on the floor, perpendicular to the first one, where any of its blocks (1 or 1a) has its front face (3) or rear face (4) supported by the side face of the uneven block (1a) of the first base module (MB) of the wall (P) and its side face supported by the front face (3) of the block (1) of the latter. A complementary module unit (MC) is also inserted underneath the uneven block (1a) of the latter base module unit (MB) supporting it. Through the same process of stacking over the previous wall (P), this new perpendicular wall (P) is built and the same is done with the other walls (P), according to the project. Finally, on the upper part of the walls (P) a complementary module unit (MC) is positioned and fitted over each space left by the unevenness of the block (1) of the base module units (MB), leveling its surface and finishing, forming in each wall a monoblock consisting of several modules (MB and MC). During the described assembly, each module unit (MB or MC) can be welded to the previous unit, acting as a mooring weld, for the perfect fixation and unification of the wall (P), which may also be formed by more than one row of modules (MB and MC), that is, a double wall, triple wall or as many rows as required for the desired shielding capacity. Besides being used to construct the walls (P) of the area to be protected against radiation leakage, the modules (MB and MC) can only be used as reinforcement of existing walls, floor, and ceiling of concrete or other material, when necessary. For a person who has technical knowledge on the subject, it is clear that the walls (P) constituted by the modules (MB and MC) offer high capacity of shielding against radiation, since each block (1, 1a and 6), due to the construction method and the materials from which they are composed, can present density between 3.5 and 4 g cm-3 compared to 2.35 g cm-3 of the common concrete. Therefore, the required thickness of the walls (P) for the radiation insulation with the modules (MB and MC) will be considerably smaller than when constructed in common or dense concrete, while still maintaining a low cost for the project, very close to the use of concrete thanks to the low cost materials with which the modules (MB and MC) are manufactured. When required, the blocks (1, 1a and 6) of the modules (MB and MC) can be manufactured in larger scale, i.e., thicker, increasing the total density of the wall (P) and/or other shapes, different lengths or widths of each block (1, 1a and 6), however, maintaining its plug-in system and its module configuration (MB and MC). It is also clear that, unlike walls made of concrete, they will not have cracks and suffer from premature wear due to the weather, requiring frequent repairs or reinforcing. Finally, in addition to walls (P), the modules (MB and MC) presented here can be used for the construction of floors and ceilings, using the same pieces and the same system, but in horizontal assembly, achieving the same effect and shielding capability. |
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description | Pursuant to 35 U.S.C. § 119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2013-0052051, filed on May 8, 2013, the contents of which is incorporated by reference herein in its entirety. 1. Field of the Disclosure This specification relates to a cooling system of an emergency cooling tank with improved safety, which is capable of minimizing an increase in economical costs and maintaining a cooling function of the emergency cooling tank for a long term of time without refilling cooling water in the emergency cooling tank, by taking into account a characteristic of a quantity of heat transferred to the emergency cooling tank, as an ultimate heat sink, upon an occurrence of an accident of a nuclear reactor, and a nuclear power plant having the same. 2. Background of the Disclosure An emergency cooling tank is used as a heat sink, which removes heat of a nuclear reactor upon an occurrence of an accident, in various types of nuclear reactors including an integral nuclear reactor. The heat of the nuclear reactor is ultimately transferred to the emergency cooling tank via a passive residual heat removal system (heat within the nuclear reactor) or a passive containment (building) cooling system (heat emitted into a containment). Accordingly, cooling water within the emergency cooling tank is evaporated such that the heat is emitted to the air. A heat exchanger of the passive residual heat removal system is employing a water-cooling type (SMART nuclear reactor in Korea or AP1000 of Westinghouse Co. Ltd., in USA), an air-cooling type (SCOR in France), or a hybrid-cooling type (IMR in Japan) combining the water-cooling and the air-cooling. In general, the water-cooling type heat exchanger has an advantage in fabrication of a heat exchanger with a small scale by virtue of excellent cooling efficiency. However, cooling water within the emergency cooling tank, to which the heat is transferred from the heat exchanger upon an occurrence of an accident, is gradually evaporated to be run out. Accordingly, the cooling water in the emergency cooling tank has to periodically be refilled for long-term cooling exceeding a cooling water storage capacity. On the other hand, the air-cooling type heat exchanger does not have an emergency cooling tank, accordingly, there is no need to periodically refill the cooling water. However, the air-cooling type heat exchanger exhibits lower cooling efficiency than the water-cooling type. The heat transfer efficiency of transferring heat to the outside (to the air) through the wall surface of the tube is low. The efficiency of the air-cooling type heat exchanger depends on heat transfer efficiency of a wall surface of a tube with which air comes in contact. Consequently, an increase in a size (capacity) of the heat exchanger is required. Also, the hybrid-cooling type heat exchanger also exhibits a heat transfer performance which is decreased extremely lower than the water-cooling type at the time point of operating in an air-cooling manner. Thus, it requires for a greater size than the water-cooling type heat exchanger. In order to cool an inside of the heat exchanger of the passive residual heat removal system, a condensation heat exchanger of a steam condensation type with excellent heat transfer efficiency is employed. Since the heat exchanger of the passive residual heat removal system is generally operating under high temperature and high pressure environments, design pressure thereof may be extremely high and economic feasibility is drastically lowered when the heat exchanger has an increased size. The nuclear reactor does not always transfer constant heat upon an occurrence of an accident thereof. Unlike a typical boiler, the nuclear reactor generates residual heat from its core for a considerably long-term of time even after a shutdown of the core of the nuclear reactor. Accordingly, when the nuclear reactor is shut down due to an accident or the like, a large quantity of residual heat is emitted from the core at the beginning of the accident. As the time elapses, the emitted residual heat is drastically reduced. In turn, the heat transferred from the nuclear reactor into the emergency cooling tank is remarkably reduced according to the lapse of time after the occurrence of the accident. In the related art emergency cooling tank, the emergency cooling tank has a top open due to an accident characteristic of the nuclear reactor. When heat is transferred to the emergency cooling tank upon an occurrence of an accident, the cooling water within the emergency cooling tank, to which the heat is transferred, is increased in temperature and evaporated so as to be changed into a phase of steam. The steam is externally emitted through the open top of the emergency cooling tank. Consequently, a heat load is treated by evaporation heat. However, the related art structure had the problem that the cooling water within the emergency cooling tank is gradually reduced to be run out, due to a long-term operation of the emergency cooling tank. When the cooling water within the emergency cooling tank is depleted, the emergency cooling tank lost its function. Hence, unless it is refilled with cooling water in a periodic manner, there is a limitation in maintaining the function for a long term of time. Further, when the use of an electric power system for refilling the cooling water is stopped for an extended time upon an occurrence of an accident exceeding a design reference, the accident level might extend to a severe accident. Therefore, an aspect of the detailed description is to provide a cooling system of an emergency cooling tank, capable of maintaining a function of the emergency cooling tank for an extended time even when it is impossible to refill the emergency cooling tank due to an impossible use of an electric power system. Another aspect of the detailed description is to provide a nuclear power plant with improved safety, by constructing a cooling system, which operates under lower pressure of an atmospheric pressure level, together with an emergency cooling tank, so as to minimize an increase in economic costs by taking into account of a characteristic of a quantity of heat transferred to the emergency cooling tank upon an accident occurred in a nuclear reactor, and also maintain a cooling function of the emergency cooling tank for a long term of time even without refilling cooling water in the emergency cooling tank. To achieve these and other advantages and in accordance with the purpose of this specification, as embodied and broadly described herein, there is provided a cooling system of an emergency cooling tank, including an emergency cooling tank configured to store therein cooling water, which receives heat from a nuclear reactor or a containment when an accident occurs in the nuclear reactor, a heat exchanging device installed to be exposed to an outside of the emergency cooling tank to operate in air, and configured to externally emit heat by way of a heat exchange between a fluid within the emergency cooling tank and the air such that the operation of the emergency cooling tank is continued even without refilling the cooling water, and an opening and closing unit installed at an upper portion of the emergency cooling tank to be located higher than a water level of the cooling water, and configured to be open by a flow of fluid generated by an evaporation of the cooling water, the flow being formed due to a pressure difference from external air at pressure higher than a preset pressure, such that some of the fluid is externally emitted when a heat load exceeding a cooling capacity of the emergency cooling tank is transferred. In accordance with one exemplary embodiment disclosed herein, the heat exchanging device may include a duct installed on an upper portion of the emergency cooling tank and extending upwardly to provide an upward flow path to the fluid within the emergency cooling tank, and a heat exchanging portion configured to perform the heat exchange with air to cool or condense the fluid introduced through the duct. The heat exchanging portion may be connected to the emergency cooling tank to collect the fluid which has lost heat and flows down due to a density difference. The heat exchanging portion may have at least a part formed in a combined shape of a curved pipe and a straight pipe, or in a helical shape so as to ensure a sufficient heat-exchange area with the air. In accordance with another exemplary embodiment disclosed herein, the heat exchanging device may include a first heat exchanger installed in the emergency cooling tank to receive heat transferred from the fluid within the emergency cooling tank, and a second heat exchanger connected to the first heat exchanger by a connecting line to form a closed loop in which circulating fluid flows, and installed at the outside of the emergency cooling tank to emit heat, transferred from the first heat exchanger to the circulating fluid, to the air. Each of the first and second heat exchangers may include a tube configured to perform the heat exchange with the fluid within the emergency cooling tank or the air, and formed in a shape of bundle for sufficiently ensuring a heat-exchange area, and headers configured to distribute the circulating fluid into each tube at an inlet of the tube and join the distributed fluids at an outlet of the tube. The tube may have at least a part formed in a combined shape of a curved pipe and a straight pipe or in a helical shape so as to ensure a sufficient heat-exchange area with the air. The first heat exchanger may be installed at a position higher than a water level of the emergency cooling tank for the heat exchange with steam or air within the emergency cooling tank. The first heat exchanger may have at least a part sunk in the cooling water of the emergency cooling tank for the heat exchange with steam, air or the cooling water within the emergency cooling tank. The first heat exchanger may have at least a part inclined along a flowing direction of the circulating fluid for natural circulation of the circulating fluid to rise up due to a density change. The second heat exchanger may extend downward to be connected to the first heat exchanger such that the circulating fluid, condensed after transferring heat to air, circulates to the first heat exchanger. The emergency cooling tank cooling system may further include a pressurizer connected to the pipe to prevent overpressure of the heat exchanging device, and configured to accommodate fluid expanded or contracted by a temperature change. The pressurizer may contain refilling water therein to refill the circulating fluid circulating along the heat exchanging device. In accordance with another exemplary embodiment disclosed herein, the emergency cooling tank cooling system may further include an air circulating unit installed on the emergency cooling tank in a manner of covering at least part of the heat exchanging device, and configured to allow air introduced through a lower portion thereof to flow up therealong so as to increase a heat exchange rate of the heat exchanging device by natural convection. In accordance with another exemplary embodiment disclosed herein, the opening and closing unit may be implemented as a type of check valve or flap valve, which is passively open at pressure higher than a preset pressure formed by the fluid within the emergency cooling tank. In accordance with another exemplary embodiment disclosed herein, the opening and closing unit may prevent the emission of steam when a heat load transferred to the emergency cooling tank is reduced below the cooling capacity of the emergency cooling tank, and may be passively closed at pressure lower than a preset pressure to maintain a quantity of the cooling water of the emergency cooling tank. Also, to achieve those aspects and other advantages of the detailed description, there is provided a nuclear power plant having an emergency cooling tank cooling system. The nuclear power plant may include a passive containment cooling system configured to condense steam emitted from a nuclear reactor into a containment to prevent an increase in pressure of the containment when an accident occurs in the nuclear reactor, and an emergency cooling tank cooling system configured to receive sensible heat and residual heat of the nuclear reactor, transferred from the passive containment cooling system, and externally emit the received heat, wherein the emergency cooling tank cooling system may include an emergency cooling tank configured to store therein cooling water, which receives heat transferred from a nuclear reactor or a containment, when an accident occurs in the nuclear reactor, a heat exchanging device installed to be exposed to an outside of the emergency cooling tank to operate in air, and configured to externally emit heat by way of a heat exchange between fluid within the emergency cooling tank and the air such that the operation of the emergency cooling tank is continued even without refilling the cooling water, and an opening and closing unit installed at an upper portion of the emergency cooling tank to be located higher than a water level of the cooling water, and configured to be open by a flow of the fluid generated by an evaporation of the cooling water, the flow being formed due to a pressure difference from external air at pressure higher than a preset pressure, such that some of the steam is externally emitted when a heat load exceeding a cooling capacity of the emergency cooling tank is transferred. In accordance with one exemplary embodiment disclosed herein, a nuclear power plant may include a passive residual heat removal system configured to remove sensible heat and residual heat of a nuclear reactor by circulating cooling water when an accident occurs in the nuclear reactor, and an emergency cooling tank cooling system configured to receive sensible heat and residual heat of the nuclear reactor, transferred from the passive residual heat removal system, and externally emit the received heat, wherein the emergency cooling tank cooling system may include an emergency cooling tank configured to store therein cooling water, which receives heat transferred from a nuclear reactor or a containment, when an accident occurs in the nuclear reactor, a heat exchanging device installed to be exposed to an outside of the emergency cooling tank to operate in air, and configured to externally emit heat by way of a heat exchange between fluid within the emergency cooling tank and the air such that the operation of the emergency cooling tank is continued even without refilling the cooling water, and an opening and closing unit installed at an upper portion of the emergency cooling tank to be located higher than a water level of the cooling water, and configured to be open by a flow of the fluid generated by an evaporation of the cooling water, the flow being formed due to a pressure difference from external air at pressure higher than a preset pressure, such that some of the fluid is externally emitted when a heat load exceeding a cooling capacity of the emergency cooling tank is transferred. Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from the detailed description. Description will now be given in detail of the exemplary embodiments, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components will be provided with the same reference numbers, and description thereof will not be repeated. A singular representation may include a plural representation unless it represents a definitely different meaning from the context. FIG. 1 is a conceptual view of a cooling system 100 of an emergency cooling tank (or an emergency cooling tank cooling system) in accordance with one exemplary embodiment disclosed herein. An emergency cooling tank cooling system 100 may be configured to externally emit heat transferred from a nuclear reactor or a containment, and include an emergency cooling tank 110, a heat exchanging device (or a cooling device) 120 and an opening and closing unit 130. The emergency cooling tank 110 may be configured to store cooling water therein. A condensation heat exchanger 11 may be installed in the emergency cooling tank 110. When an accident happens in a nuclear reactor, the condensation heat exchanger 11 may transfer heat from the nuclear reactor or a containment into cooling water within the emergency cooling tank 110 through a passive residual heat removal system or a passive containment cooling system. The tank generally refers to a water pool or a water tank. When the accident happens in the nuclear reactor, residual heat is continuously generated from a core even after the core of the nuclear reactor is shut down. As a result, the passive residual heat removal system or the passive containment cooling system may continuously receive the heat from the nuclear reactor and transfer it to the cooling water within the emergency cooling tank 110 through the condensation heat exchanger 11. The emergency cooling tank 110 may serve as a heat sink which discharges the transferred heat to the air. The heat exchanging device 120 may discharge the heat transferred to the cooling water within the emergency cooling tank 110 to the air in a heat-exchanging manner with the air. The heat exchanging device 120 may be installed at an outside of the emergency cooling tank 110 so as to perform the heat exchange between the emergency cooling tank 110 and air. The related art emergency cooling tank does not employ an external device, such as the heat exchanging device 120. Thus, a heat load is treated (processed) using evaporation heat generated in response to an evaporation of the cooling water within the emergency cooling tank 110. However, when the cooling water is fully evaporated to be run out, the emergency cooling tank is unable to operate any more, which causes a limitation in long-term cooling. The heat exchanging device 120 may be installed at the emergency cooling tank 110 to address such problem so as to externally discharge the heat transferred to the cooling water within the emergency cooling tank 110 by way of the heat exchange between external air and the emergency cooling tank 110. The heat exchanging device 120 may ultimately prevent the cooling water shortage of the emergency cooling tank 110 by improving the heat exchanging method of the emergency cooling tank 110. The operation of the heat exchanging device 120 may prevent the exhaustion of the cooling water within the emergency cooling tank 110. This may allow the emergency cooling tank 110 to continuously maintain its heat-discharge function even without refill of the cooling water. The heat exchanging device 120 may be configured by employing a cooling method in a manner of allowing steam evaporated from the cooling water of the emergency cooling tank 110 to pass therethrough, and a cooling method by a heat exchange between a circulating fluid and the cooling water or the air in a manner of circulating the circulating fluid in a closed loop. The heat exchanging device 120 illustrated in FIG. 1 may employ the cooling method using the steam, and may include a duct 121 and a heat exchanging portion 122. The duct 121 may be installed on an upper portion of the emergency cooling tank 110, and extend upward to provide an upward flow path to steam which rises up in response to the transferred heat. The cooling water which has received the heat transferred from the condensation heat exchanger 11 may be evaporated to become steam. Steam of high temperature has a property to rise up due to a density difference. The duct 121 may communicate with the emergency cooling tank 110, and the steam may be introduced into the heat exchanging device 120 through the duct 121. An inlet of the duct 121 may have a greater cross-section than the flow line such that the steam can fully be introduced therein. The heat exchanging portion 122 may have one end connected to the duct 121 such that the steam passed through the duct 121 can be introduced. Headers 123 may be installed on an inlet and an outlet of the heat exchanging portion 122, respectively. While passing through the heat exchanging portion 122, the steam may lose heat due to the heat exchange with air so as to be cooled and condensed. The heat exchanging portion 122 may be connected to the emergency cooling tank 110 such that the fluid which has lost heat and flows down due to the density difference can be collected back into the emergency cooling tank 110. To correspond to the structure that the duct 121 provides the upward flow path to the heat-transferred steam, the heat exchanging portion 122 may provide a downward flow line to the fluid which falls with being condensed in response to the loss of heat. Cooling efficiency of the heat exchanging portion 122 may depend on a heat-exchange area between air and steam. The heat exchanging portion 122 may have at least part formed in a combined shape of a curved pipe and a straight pipe or in a helical shape, to ensure a sufficient heat-exchange area with air. As compared with the cooling efficiency of the heat exchanging portion 122 formed in the straight pipe and extending downward to be connected to the emergency cooling tank 110, the cooling efficiency of the heat exchanging portion 122 forming a complicated flow line may be improved by virtue of more chances for heat exchange with the air. Here, the helical pipe is difficult to be manufactured, so the shape of the heat exchanging portion 122 may be selectively applied. The fluid which is cooled and condensed through the heat exchanging portion 122 may be collected back into the emergency cooling tank 110. Accordingly, after a heat load transferred to the emergency cooling tank 110 is reduced below a cooling capacity of the emergency cooling tank 110, the quantity of cooling water of the emergency cooling tank 110 may be maintained at a constant level. The fluid, which is cooled while circulating along the duct 121 and the heat exchanging portion 122 and then collected back into the emergency cooling tank 110, uses a natural circulation according to a density difference. Therefore, the heat exchanging device 120 may operate even without another external device, such as a pump for heat exchange or the like. The opening and closing unit 130 may be installed at an upper portion of the emergency cooling tank 110 to be located higher than a water level of the cooling water. The opening and closing unit 130 may be open in a state over a preset pressure so as to emit part of the steam, generated responsive to the evaporation of the cooling water, to the outside of the emergency cooling tank 110, upon a transfer of a heat load exceeding a cooling capacity of the emergency cooling tank 110. The cooling capacity of the emergency cooling tank 110 may be decided based on a size of the tank, but in view of a design of a nuclear power plant, it may be impossible to unlimitedly increase the size of the emergency cooling tank 110. Therefore, an optimal size (capacity) of the emergency cooling tank 110 may be designed based on a construction condition of a nuclear power plant, economical efficiency, a quantity of power generated by a nuclear power plant, and the like. There may also be a limit to the cooling capacity of the emergency cooling tank 110. At the beginning of an accident of a nuclear reactor, at which a heat load transferred to the emergency cooling tank 110 exceeds the cooling capacity of the emergency cooling tank 110, an extremely large quantity of heat is emitted. Therefore, a considerably large heat exchanging device 120 is required in order to fully treat the heat load. This may, however, cause an excessive increase in equipment costs. The present disclosure is designed in consideration of the capacity of a latter part of the accident for which residual heat is extremely reduced. Thus, only the employment of the heat exchanging device 120 of the present disclosure cannot treat all thermal load generated at the beginning of the accident. Therefore, in the early stage of the accident, the steam evaporated from the cooling water may form high pressure within the emergency cooling tank 110, and the opening and closing unit 130 may be open by the flow of the fluid formed by the pressure difference. The steam generated in response to the evaporation of the cooling water may partially be emitted out of the emergency cooling tank 110 through the opening and closing unit 130, and partially introduced into the duct 121. Hence, in the early stage of the accident, the heat load, which exceeds the cooling capacity of the emergency cooling tank 110, may be treated by the steam emitted and the cooling by the heat exchanging device 120. The opening and closing unit 130 may be implemented as a check valve installed on a pipe connected to the emergency cooling tank 110, or a flap valve installed on an outer wall of the emergency cooling tank 110, or the like. The check valve and the flap valve may be open in response to the flow of the fluid of high pressure formed within the emergency cooling tank 110 toward the outside. As a time elapses, the heat load transferred to the emergency cooling tank 110 may gradually be reduced. When the heat load is reduced below the cooling capacity of the emergency cooling tank 110, the check valve or the flap valve may be passively closed below a preset pressure. When the heat load transferred to the emergency cooling tank 110 is below the cooling capacity of the emergency cooling tank 110, the heat load may fully be treated only by the heat exchanging device 120. As the opening and closing unit 130 is closed, the emission of the steam may be restricted and the heat load may be generated below the capacities of the emergency cooling tank 110 and the heat exchanging device 120. Therefore, the cooling water may all be collected such that the quantity of cooling water is maintained relatively constantly within the emergency cooling tank 110, and the shortage of the cooling water of the emergency cooling tank 110 may not occur. Even after the opening and closing unit 130 is closed, the heat exchanging device 120 may continuously operate to cool the steam so as to externally emit the heat transferred to the emergency cooling tank 110. In addition, the cooling water within the emergency cooling tank 110 may not be externally discharged any more, with merely circulating along the heat exchanging device 120. As a result, the emergency cooling tank 110 may semi-permanently play a role of the heat sink of the nuclear power plant. The condensation heat exchanger 11 of the passive residual heat removal system is designed with extremely high design pressure (SMART nuclear reactor: about 17 MPa). Hence, when it is increased in size for increasing the cooling capacity, extremely high fabricating costs are required. In addition, in view of the characteristic that a safety facility, such as the passive residual heat removal system, has to be conservatively designed, the size increase may bring about a drastic decrease of economical efficiency. The passive containment cooling system is also designed with higher pressure than atmospheric pressure, so it has the similar problem to the passive residual heat removal system. On the other hand, the cooling function of the emergency cooling tank 110 may be maintained for an extended time without refilling the cooling water. The emergency cooling tank cooling system 100 may also operate under low pressure of an atmospheric pressure level. This may result in remarkable improvement of safety of the nuclear power plant and minimization of an increase in equipment costs. The emergency cooling tank cooling system 100 may further include an air circulating unit 140 which circulates air in an air-cooling manner to cool the steam evaporated from the emergency cooling tank 110. The air circulating unit 140 may induce the heat exchange by natural convection of air. The air circulating unit 140 may be implemented as a cooling tower, a duct or a chimney. The air circulating unit 140 may be installed above the emergency cooling tank 110 to cover an outside of the heat exchanging device 120. Air may be introduced into a lower side of the air circulating unit 140 and heat-exchanged with fluid passing through the heat exchanging device 120, thereby absorbing heat. The heat-absorbed air may rise up to be emitted out of the upper side of the air circulating unit 140. Similar to the natural circulation of the heat exchanging device 120, the air circulating unit 140 may use a natural circulation principle based on a density difference of air passing through the air circulating unit 140. Hereinafter, a calculation of a capacity of the heat exchanging device 120 will be described. This capacity is merely illustrative, and may not be limited to this. As one example, four of the passive residual heat removal system applied to a system-integrated modular advanced reactor (SMART, a rated output: 330 MWt) according to the present disclosure may be installed. As main assumptions used for calculating the size of the heat exchanging device 120 applicable to the SMART, i) only a heat transfer (critical path) by natural convection at the outside of a tube of the heat exchanging device 120 is taken into account, and ii) a reference time of a capacity calculation is set after 72 hours. Besides to those, main input values for the size calculation of the heat exchanging device 120 are shown in the following Table 1. TABLE 1Shape of tubeAssumed as straight pipeNumber (NHX)4Diameter (d) of tube10~30 mmPitch (p) of tube2d mmAvailable height (L) of tube1 mHeat transfer coefficient of outer 5 W/m2Kwall of tube (Air) (hair)Tube temperature (THX)100° C.External air temperature (Tair) 40° C. Residual heat generated from a core after shutdown of a nuclear reactor may be obtained by Equation 1, when further considering 20% of margin in addition to ANS-73 decay heat curve.{dot over (Q)}decay=1.2{dot over (Q)}rated(58116.01+9769.69t)−1/4.0108 [Equation 1] Residual heat after 72 hours, as a time point that the heat exchanging device 120 proposed herein normally operates, may be about 0.54% of a normal output. A quantity of heat removal required for each heat exchanging device 120 may be obtained by the following Equation 2. Q . req = 0.0054 Q . rated N HX [ Equation 2 ] To maintain a water level of the emergency cooling tank 110 after 72 hours, a heat transfer rate by the natural convection at the outside of a tube should be greater than residual heat. This condition may be expressed by Equation 3.hairA(THX−Tair)≥{dot over (Q)}req [Equation 3] A heat transfer area A required for residual heat removal may be obtained by Equation 4. A = π dN tube L ≥ Q . req h air ( T HX - T air ) [ Equation 4 ] Therefore, a diameter and a number of a tube meeting the heat transfer area of Equation 4 may be obtained. Then, when those obtained tubes are arranged by considering their pitches, the results are represented as illustrated in Table 2. Table 2 shows the capacity of the heat exchanging device 120, which is calculated based on the residual heat of the SMART nuclear reactor after 72 hours. TABLE 2DivisionMarkUnitCase ACase BCase CCase DCase ENumber of heatNHXnumber44444exchangersNumber of tubes/eachNtubenumber16001600250036003600Diameter of tubedmm3020202010Pitch of tubePmm6040404020Height (length) ofLm45.53.52.55tubeTube temperatureTHX° C.200200200200200External airTair° C.4040404040temperatureHeat transferhairW/m2K55555coefficientQuantity of heatQreqMW0.450.450.450.450.45removal/eachEntire box size of tube of the heat exchanging device 120HeightHHXm6.67.35.75.16.4Horizontal/VerticalLHXm2.41.62.02.41.2 The heat exchanging device 120 does not have a valve or equipment which may cause an initial accident or a single failure, but the horizontal (or vertical) length of the heat exchanging device 120 may be increased by about 15% or a height thereof may be increased by about 33% upon conservatively considering the failures. This capacity calculation has been carried out under assumption that the tube is the straight pipe by taking convenience of maintenance and fabrication into account, but when a helical pipe is used or a pin is mounted on the tube of the heat exchanging device 200, the heat exchanging device 120 may further be reduced in capacity. FIG. 2 is a conceptual view of an emergency cooling tank cooling system 200 in accordance with another exemplary embodiment disclosed herein. The emergency cooling tank cooling system 200 may include an opening and closing unit 230 and an air circulating unit 240. A heat exchanging device 220 may employ a cooling method in a manner of a heat exchange between a circulating fluid and steam or air by circulating the circulating fluid within a closed loop. The heat exchanging device 220 may include a connecting line 221, a first heat exchanger 222a installed within an emergency cooling tank 210, and a second heat exchanger 222b installed outside the emergency cooling tank 210. A condensation heat exchanger 21 may be installed in the emergency cooling tank 210. The first heat exchanger 222a may be installed in the emergency cooling tank 210. Here, the first heat exchanger 222a may be disposed at a position higher than a water level of cooling water to carry out the heat exchange with steam or air within the emergency cooling tank 210. The circulating fluid flowing in the heat exchanging device 220 may receive heat transferred from the steam or air within the emergency cooling tank 210 while passing through the first heat exchanger 222a. The circulating fluid may increase in temperature due to receiving the transferred heat. The first heat exchanger 222a may have at least a part inclined along the flowing direction of the circulating fluid, as illustrated, so as to allow for natural circulation of the circulating fluid to rise up due to a reduced density, which results from the increased temperature. The second heat exchanger 222b may be installed at the outside of the emergency cooling tank 210 such that the circulating fluid receiving the transferred heat from the first heat exchanger 222a can be cooled by the heat exchange with air. The second heat exchanger 222b may be connected to the first heat exchanger 222a by the connecting line 221 to form a closed loop, such that the circulating fluid can circulate within the closed loop. The second heat exchanger 222b may be connected to the first heat exchanger 222a by extending downward such that the circulating fluid with the increased density due to the decreased temperature, which results from the heat transfer to the air, can be discharged into the first heat exchanger 222a. The circulating fluid flowing along the closed loop may circulate along the heat exchanging device 220 by natural convection. Each of the first heat exchanger 222a and the second heat exchanger 222b may include a tube 224 and headers 223. The tube 224 may be formed in a form of tube bundle to ensure a sufficient heat-exchange area. The headers 223 may be installed at an inlet and an outlet of the tube 224, respectively, to distribute the circulating fluid into the tube bundle or join the distributed circulating fluids. The emergency cooling tank cooling system 200 may further include a pressurizer 250, which is connected to a connecting line for preventing overpressure of the heat exchanging device 220. The pressurizer 250 may accommodate the circulating fluid expanded or contracted by heat. When the circulating fluid is introduced into the pressurizer 250 via the connecting line, internal pressure of the connecting line may be lowered, thereby preventing the overpressure of the heat exchanging device 220. The pressurizer 250 may be formed in a shape of a refilling tank for storing refilling water, and filled with the makeup water to supplement the circulating fluid circulating along the heat exchanging device 220. Upon long-term cooling of a nuclear reactor, some of the fluid flowing in the heat exchanging device 220 may be leaked. This may cause a failure of an entire function of the emergency cooling tank cooling system 200. To resolve such problem, the pressurizer 250 may be connected to the heat exchanging device 220 to supply the makeup water. Specifically, the pressurizer 250 has a property to maintain a pressure balance with the heat exchanging device 220. Accordingly, when the heat exchanging device 220 is over-pressurized, the pressurizer 250 may allow the circulating fluid to be introduced into the pressurizer 250 to passively lower the pressure of the heat exchanging device 220. Also, even when the heat exchanging device 220 suffers from the shortage of the circulating fluid, the pressurizer 250 may passively supply the makeup water filled therein into the heat exchanging device 220. FIG. 3 is a conceptual view of an emergency cooling tank cooling system 300 in accordance with another exemplary embodiment disclosed herein. The emergency cooling tank cooling system 300 may include an opening and closing unit 230, an air circulating unit 340, and a pressurizer 350 A heat exchanging device 320 may include a connecting line 321, a first heat exchanger 322a and a second heat exchanger 322b. Specifically, the first heat exchanger 322a may be configured in such a manner that at least part thereof is sunk in cooling water of an emergency cooling tank 310 so as to perform a heat exchange with the cooling water within the emergency cooling tank 310. Each of the first heat exchanger 322a and the second heat exchanger 322b may include a tube 324 and headers 323. A condensation heat exchanger 31 may be installed in the emergency cooling tank 310. When the first heat exchanger 322a is partially sunk in the cooling water, as illustrated, a circulating fluid passing through the first heat exchanger 322a may first perform a heat exchange with the cooling water of the emergency cooling tank 310. Then a direction that the circulating fluid flows may be turned to an upward way along a flow line such that the circulating fluid can rise up with performing the heat exchange with steam. The first heat exchanger 322a may also have at least a part inclined along the flowing direction of the circulating fluid, as illustrated, so as to allow natural circulation of the circulating fluid to rise up due to a reduced density, which results from an increased temperature. A case where the first heat exchanger 322a is sunk in the cooling water and a case where it is not sunk in the cooling water may exhibit a difference in cooling efficiency of the heat exchanging device. Also, an installation position of the first heat exchanger 322a is a design option which may be selectively used according to a required cooling efficiency. FIGS. 4A to 4C are conceptual views illustrating alternative embodiments of a tube of a heat exchanger. A tube may be formed in a simple shape of a straight pipe 424a, as illustrated in FIG. 4A, by taking its fabrication into account. However, it may be formed in such a manner that at least part is formed in a helical shape to ensure a sufficient heat-exchange area with air. The tube may also be formed in a shape of a helical tube 424b illustrated in FIG. 4B, or a combined shape 424c of a curved pipe and a straight pipe illustrated in FIG. 4C. A fluid passing through the helical tube 424b may expect a greater cooling effect than passing through the straight pipe 424a. A selection and a combination of the shape of the tube 424 may be selective depending on a required cooling efficiency. FIG. 5 is a conceptual view of a nuclear power plant 50 having a passive containment (building) cooling system 52 and an emergency cooling tank cooling system 500. A passive containment cooling system 52 is a safety system which cools and condenses steam emitted into a containment 54 to prevent an increase in pressure of the containment 54 upon an occurrence of an accident, such as a loss of coolant accident (LOCA) or steam line break (SLB) of a nuclear reactor 53. The passive containment cooling system 52 may include a cooling heat exchanger 52a installed in the containment 54 and connected to a condensation heat exchanger 51, a connection line 52b connecting the cooling heat exchanger 52a and the condensation heat exchanger 51, an isolation valve 52c, and a pressurizer (not illustrated). Due to an accident, such as the LOCA or SLB of the nuclear reactor 53, steam of high temperature and high pressure may be emitted into the containment 54, and the passive containment cooling system 52 may start to operate. A fluid may circulate between the cooling heat exchanger 52a and the condensation heat exchanger 51. The fluid may receive heat transferred from the cooling heat exchanger 52a and transfer the heat from the condensation heat exchanger 51 to an emergency cooling tank 510. The emergency cooling tank 510 with the transferred heat may discharge the heat to the air according to an operation mechanism of the emergency cooling tank cooling system 500 illustrated in FIGS. 1 to 4. The emergency cooling tank cooling system 500 may include a heat exchanging device 520 (further including a duct 521 and a heat exchanging portion 522) and an opening and closing unit 530. FIG. 6 is a conceptual view of a nuclear power plant 60 having a passive residual heat removal system 61 and an emergency cooling tank cooling system 600. Nuclear power plant 60 may include containment 64, feed water system 65, and turbine system 66. A passive residual heat removal system 61 is a safety system which circulates cooling water into a steam generator 63a within a nuclear reactor 63 when an accident happens in the nuclear reactor 63, so as to remove sensible heat of the nuclear reactor 63 and residual heat of a core. A lower end and an upper end of a condensation heat exchanger 61a may be connected to a water supply line 65a and a steam line 66a by connection lines 61b and 61c, respectively. Cooling water may transfer heat, which is transferred from the steam generator 63a through the water supply line 65a and the steam line 66a, from the condensation heat exchanger 61a, into an emergency cooling tank 610. The emergency cooling tank 610 with the transferred heat may discharge the heat to the air according to the operation mechanism of the emergency cooling tank cooling system 600 illustrated in FIGS. 1 to 4. The emergency cooling tank cooling system 600 may include a heat exchanging device 620 (further including a duct 621 and a heat exchanging portion 622) and an opening and closing unit 630. FIG. 7 is a conceptual view of a nuclear power plant 70 having a passive residual heat removal system 71, a passive containment (building) cooling system 72, and an emergency cooling tank cooling system 700. Heat of a nuclear reactor 73 and a containment 74 may be transferred from a passive residual heat removal system 71 and a passive containment cooling system 72 to an emergency cooling tank 710. The emergency cooling tank 710 may then operate as an integrated heat sink of the passive residual heat removal system 71 and the passive containment cooling system 72. The emergency cooling tank cooling system 700 proposed herein may be configured to allow for long-term cooling. As illustrated in FIG. 7, it may function as the integrated heat sink of the passive residual heat removal system 71 and the passive containment cooling system 72, which may facilitate for optimization of cooling capacity. The nuclear power plant 70 may further include a passive safety injection system 77 which injects cooling water into the nuclear reactor 73 to maintain a water level of the cooling water of the nuclear reactor 73, in addition to the passive residual heat removal system 71, the passive containment cooling system 72, and the emergency cooling tank cooling system 700. Condensed water by the operation of the passive containment cooling system 72 may be collected back into a water collecting tank 77a of the passive safety injection system 77 and then re-injected into a nuclear reactor 73. Accordingly, the cooling water may circulate along the nuclear reactor 73 and the passive safety injection system 77, which may allow for semi-permanently maintaining a water level of the nuclear reactor 73. Also, the passive residual heat removal system 71 and the passive containment cooling system 72 can semi-permanently discharge the heat of the nuclear reactor 73 and the containment 74 to the air through the emergency cooling tank cooling system 700. Therefore, when the nuclear power plant 70 includes the emergency cooling tank cooling system 700, the passive residual heat removal system 71, the passive containment cooling system 72, and the passive safety injection system 77, safety of the nuclear power plant 70 can be enhanced. The nuclear power plant 70 may further include a refueling pool 78 installed in the containment 74. Specifically, the refueling pool 78 illustrated in FIG. 7 may be configured in such a manner that the condensed water is introduced from the water collecting tank 77a of the passive safety injection system 77 through a water supply line 77b. The water supply line 77b may extend up to a preset height within the water collecting tank 77a, such that the condensed water exceeding the height of the water supply line 77b can be introduced into the water supply line 77b to flow into the refueling pool 78. Therefore, the condensed water collected in the water collecting tank 77a may be used partially for safe injection of the nuclear reactor 73 and partially for cooling a lower portion of the nuclear reactor 73 by use of the refueling pool 78. FIG. 8 is a conceptual view illustrating a normal operation state of the nuclear power plant 70 of FIG. 7. At a normal operation of the nuclear power plant 70, a feed water system 75 may supply water to a steam generator 73a through a feed water line 75a, and the steam generator 73a may convert the supplied water into steam of high temperature using heat supplied from a core. The steam of high temperature may then be transferred to a turbine system 76 through the steam line 76a such that the turbine system 76 can produce electricity. The emergency cooling tank cooling system 700, the passive residual heat removal system 71 (including connection lines 71b and connection lines 71c), the passive containment cooling system 72, the passive safety injection system 77, and the refueling pool 78 are all safety facilities for handling an occurrence of an accident in the nuclear power plant 70. Therefore, they may not operate in a normal operation state. FIG. 9 is a conceptual view illustrating operations of the passive containment cooling system 72 and the emergency cooling tank cooling system 700 prior to an operation of the passive residual heat removal system 71 upon an occurrence of a loss of coolant accident (LOCA) in the nuclear power plant 70 illustrated in FIG. 7. When the LOCA occurs in the nuclear reactor 73 due to a line break or the like, steam may be emitted into the containment 74 through a broken portion and accordingly internal pressure and internal temperature of the containment 74 may increase. The passive containment cooling system 72 may start to operate by a temperature difference from the steam emitted to the containment 74. Hence, even before the start of the operation of the passive residual heat removal system 71 or the passive safety injection system 77, the passive containment cooling system 72 may provide a function of preventing an increase in pressure and temperature of the containment 74. The heat, which is transferred to the emergency cooling tank 710 through the passive containment cooling system 72, may be emitted to the air through the emergency cooling tank cooling system 700. Specifically, in the early stage of an accident, a heat load exceeding a cooling capacity of the emergency cooling tank 710 is transferred to the emergency cooling tank 710. Accordingly, the emergency cooling tank 710 may treat the heat load by externally discharging some of steam, which is generated in response to the evaporation of the cooling water, through an opening and closing unit 730. FIG. 10 is a conceptual view illustrating operations of the passive safety injection system 77, the passive residual heat removal system 71, the passive containment cooling system 72 and the emergency cooling tank cooling system 700, in addition to FIG. 9. As a time elapses after an occurrence of the LOCA of the nuclear reactor 73, the pressure or temperature of the nuclear reactor 73 may start to gradually be lowered. When the pressure or temperature is dropped below a preset value, a related system may transfer an open signal to isolation valves of the passive residual heat removal system 71 and the passive safety injection system 77. In turn, the passive residual heat removal system 71 may continuously remove sensible heat of the nuclear reactor and residual heat of a core by circulating water to the steam generator 73a, and transfer the removed heat to the emergency cooling tank 710 through the condensation heat exchanger 71a. The passive safety injection system 77 may also inject the cooling water into the nuclear reactor 73 in response to its isolation valve being open by an activation signal. Here, the injected cooling water may be at least one of cooling water filled in several tanks of the passive safety injection system 77 and condensed water collected in the water collecting tank 77a. The heat, which has been transferred to the emergency cooling tank 710 responsive to the operations of the passive residual heat removal system 71 and the passive containment cooling system 72, may be emitted to the air through the emergency cooling tank cooling system 700. In a state where a heat load transferred to the emergency cooling tank 710 is still greater than the cooling capacity of the emergency cooling tank 700, the emergency cooling tank cooling system 700 may maintain an open state of the opening and closing unit 730, so as to emit the steam and treat the heat load by evaporation heat. FIG. 11 is a conceptual view illustrating long-term cooling of the passive safety injection system 77, the passive residual heat removal system 71, the passive containment cooling system 72 and the emergency cooling tank cooling system 700, in addition to FIG. 10. The passive residual heat removal system 71, the passive containment cooling system 72, and the passive safety injection system 77 may continue to operate. Specifically, the passive safety injection system 77 may maintain a water level of the nuclear reactor 73 for a long term of time by using the condensed water collected. At the time point that the heat load lower than the cooling capacity of the emergency cooling tank 710 is transferred to the emergency cooling tank 710, the opening and closing unit 730 may be closed and the emission of the steam may be stopped. Accordingly, from the time point that the opening and closing unit 730 is closed, the heat load may be treated only by the heat exchanging device 720 and a quantity of cooling water of the emergency cooling tank cooling system 700 may be maintained in a relatively uniform state. Heat exchanging device 720 may include a duct 721 and a heat exchanging portion 722. FIG. 12 is a graph illustrating a heat flow of an emergency cooling tank cooling system on the time basis. A horizontal axis of a graph denotes a time, and a vertical axis denotes a quantity of heat transferred. When a LOCA occurs due to a line break or the like, an operation signal of the passive residual heat removal system may be delayed or a time may be spent somewhat for thermal diffusion within the containment. As a result, an operation delay of the emergency cooling tank cooling system may be caused at the early beginning of an accident occurrence. When the passive containment cooling system starts to operate in response to the generation of the operation signal of the passive residual heat removal system or the thermal diffusion within the containment, the heat may be transferred to the emergency cooling tank and the emergency cooling tank cooling system may start to operate. The cooling water contained in the emergency cooling tank may absorb the heat so as to increase in temperature. However, until before the cooling water is changed into a phase of steam and then evaporated, a water level of the cooling water of the emergency cooling tank may be maintained. In the early stage of the accident, the heat which is transferred to the emergency cooling tank through the passive residual heat removal system or the passive containment cooling system may exceed the cooling capacity of the emergency cooling tank cooling system. When the heat load transferred to the emergency cooling tank exceeds the cooling capacity of the emergency cooling tank cooling system, the opening and closing unit may be open and steam may be externally emitted from the emergency cooling tank so as to discharge the heat load. The water level of the cooling water of the emergency cooling tank may be lowered as low as the steam being emitted. While emitting the steam, some of the condensed water may be collected again from the steam by the operation of the heat exchanging device. A quantity of the condensed water collected may theoretically correspond to the cooling capacity of the emergency cooling tank cooling system. When the quantity of heat transferred to the emergency cooling tank is decreased below the cooling capacity of the emergency cooling tank cooling system, the opening and closing unit may be closed and the steam collection by the cooling of the heat exchanging device may be continued. The water level of the cooling water of the emergency cooling tank may be maintained and accordingly, long-term cooling of the nuclear power plant may be allowed. The configurations and methods of the emergency cooling tank cooling system and the nuclear power plant having the same in the aforesaid embodiments may not be limitedly applied, but such embodiments may be configured by a selective combination of all or part of the embodiments so as to implement many variations. According to the present disclosure having the configurations, upon an occurrence of an accident, the cooling water filled in the emergency cooling tank may maintain its water level without being run out even by a long-term operation of the emergency cooling tank, thereby removing sensible heat and residual heat discharged from the nuclear reactor for an extended time. Also, the sensible heat and the residual heat discharged from the nuclear reactor can be removed for a long term of time using the emergency cooling tank, which is a system of an atmospheric pressure level, without increasing a capacity of the heat exchanger of the passive residual heat removal system or the passive containment cooling system, which is a system of high pressure. This may result in improvement of economical efficiency and safety. |
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claims | 1. A method for determining sample intervals for resource allocations in a dynamic computing system, the method comprising the steps of:collecting measured output data indicative of a performance of said dynamic computing system and of variable workloads of said dynamic computing system;determining whether to start interval tuning of the dynamic computing system by determining when the dynamic computing system is receiving a workload, wherein the dynamic computing system is not ready to start interval tuning when the dynamic computing system is not receiving the workload; andanalyzing the measured output data to determine a sample interval for the dynamic computing system, wherein analyzing comprises:separating the measured output data into a first group and a second group, wherein said first group has a smaller standard deviation within the first group relative to said second group;selecting the second group; anddetermining the sample interval based in part on a desired confidence range, wherein the desired confidence range is an accuracy of a desired maximum difference between a measured sample benefit reflected in said measured output data in said second , group and a statistically real mean benefit. 2. The method of claim 1, wherein said determining step whether to start interval tuning comprises:determining whether sufficient measured output data has been collected for interval tuning, prior to starting said analyzing. 3. The method of claim 2, wherein additional measured output data is collected when the collected measured output data is not sufficient. 4. The method of claim 1, wherein the measured output data is benefit indicative of system a response time of said dynamic computing system as a function of system resource allocations of said dynamic computing system. 5. The method of claim 1, wherein the measured output data is collected for a fixed number of intervals. 6. The method of claim 1, wherein resource re-allocation is halted during the collecting. 7. The method of claim 1, further comprising: determining if the dynamic computing system is attempting to perform interval tuning for a first time, when the dynamic computing system is receiving a workload. 8. The method of claim 7, further comprising: determining if the dynamic computing system has reached a steady state, when the dynamic computing system is attempting to perform interval tuning for first time. 9. The method of claim 7, further comprising: waiting for a next-scheduled tuning interval, when the dynamic computing system is not attempting to perform interval tuning for a first time. 10. The method of claim 8, wherein the dynamic computing system is ready for interval tuning only when the dynamic computing system has reached a steady state. 11. The method of claim 9, wherein the dynamic computing system is ready for interval tuning during a next-scheduled tuning interval. 12. The method of claim 7, wherein the dynamic computing system is presumed to be receiving a workload when at least one data point of the collected measured output data is not zero. 13. The method of claim 8, wherein the dynamic computing system has reached a steady state when data collected at a current state is representative of characteristics of the dynamic computing system. 14. The method of claim 2, wherein the dynamic computing system is ready for the analyzing when sufficient measured output data has been collected. 15. The method of claim 2, comprising: overriding a current resource allocation of the dynamic computing system, when sufficient measured output data has not been collected; setting a small sample interval; and collecting additional measured output data. 16. A non-transitory computer readable medium containing an executable program for determining sample intervals for resource allocations in a dynamic computing system, wherein the program performs the steps of:collecting measured output data indicative of a performance of said dynamic computing system and of variable workloads of said dynamic computing system;determining whether to start interval tuning of the dynamic computing system by determining when the dynamic computing system is receiving a workload, wherein the dynamic computing system is not ready to start interval tuning when the dynamic computing system is not receiving the workload; andanalyzing the measured output data to determine a sample interval for the dynamic computing system, wherein analyzing comprises:separating the measured output data into a first group and a second group, wherein said first group has a smaller standard deviation within the first group relative to said second group;selecting the second group; anddetermining the sample interval based in part on a desired confidence range, wherein the desired confidence range is an accuracy of a desired maximum difference between a measured sample benefit reflected in said measured output data in said second group and a statistically real mean benefit. 17. The non-transitory computer readable medium of claim 16, wherein said determining step whether to start interval tuning comprises:determining whether sufficient measured output data has been collected for interval tuning, prior to starting said analyzing. 18. The non-transitory computer readable medium of claim 16, wherein the measured output data is benefit indicative of a response time of said dynamic computing system as a function of resource allocations of said dynamic computing system. 19. The non-transitory computer readable medium of claim 16, wherein the measured output data is collected for a fixed number of intervals. 20. The non-transitory computer readable medium of claim 16, wherein resource re-allocation is halted during the collecting. 21. The non-transitory computer readable medium of claim 16, further comprising:determining if the dynamic computing system is attempting to perform interval tuning for a first time, when the dynamic computing system is receiving a workload. 22. The non-transitory computer readable medium of claim 21, further comprising:determining if the dynamic computing system has reached a steady state, when the dynamic computing system is attempting to perform interval tuning for a first time. 23. The non-transitory computer readable medium of claim 21, further comprising:waiting for a next-scheduled tuning interval, when the dynamic computing system is not attempting to perform interval tuning for a first time. 24. The non-transitory computer readable medium of claim 22, wherein the dynamic computing system is ready for interval tuning only when the dynamic computing system has reached a steady state. 25. The non-transitory computer readable medium of claim 23, wherein the dynamic computing system is ready for interval tuning during a next-scheduled tuning interval. 26. The non-transitory computer readable medium of claim 21, wherein the dynamic computing system is presumed to be receiving a workload when at least one data point of the collected measured output data is not zero. 27. The non-transitory computer readable medium of claim 22, wherein the dynamic computing system has reached a steady state when data collected at a current state is representative of characteristics of the dynamic computing system and suitable for use in interval tuning. 28. The non-transitory computer readable medium of claim 17, wherein the dynamic computing system is ready for the analyzing when sufficient measured output data has been collected. 29. The non-transitory computer readable medium of claim 17, comprising:overriding a current system resource allocation of the dynamic computing system, when sufficient measured output data has not been collected; setting a small sample interval; and collecting additional measured output data. 30. A method for providing an optimization service to a client for a data processing system receiving a variable workload, the method comprising steps of:collecting measured output data indicative of a performance of said data processing system and of variable workloads of said data processing system;determining whether to start interval tuning of the data processing system by determining when the data processing system is receiving a workload;determining if the data processing system is attempting to perform interval tuning for a first time, when the data processing system is receiving the workload; andanalyzing the measured output data to determine a sample interval for the data processing system, wherein analyzing comprises:separating the measured output data into a first group and a second group, wherein said first group has a smaller standard deviation within the first group relative to said second group;selecting the second group; and determining the sample interval based in part on a desired confidence range, wherein the desired confidence range is an accuracy of a desired maximum difference between a measured sample benefit reflected in said measured output data in said second group and a statistically real mean benefit. 31. The method of claim 30, wherein said determining step whether to start interval tuning comprises:determining whether sufficient measured output data has been collected for interval tuning, prior to the start of measured output data analysis starting said analyzing. 32. The method of claim 30, wherein the measured output data is benefit indicative of system a response time of said data processing system as a function of system resource allocations of said data processing system. 33. The method of claim 30, further comprising: determining if the data processing system has reached a steady state, when the data processing system is attempting to perform interval tuning for the first time. 34. The method of claim 30, further comprising: waiting for a next-scheduled tuning interval, when the data processing system is not attempting to perform interval tuning for the first time. 35. The method of claim 33, wherein the data processing system is ready for interval tuning only when the data processing system has reached a steady state. 36. The method of claim 33, wherein the data processing system has reached a steady state when data collected at a current state is representative of characteristics of the data processing system and suitable for use in interval tuning. 37. The method of claim 31, wherein the data processing system is ready for the analyzing when sufficient measured output data has been collected. 38. The method of claim 31, wherein the method further comprises the following steps if sufficient measured output data has not been collected further comprising:overriding a current resource allocation of the data processing system, when sufficient measured output data has not been collected; setting a small sample interval; and collecting additional measured output data. 39. A computing system, comprising:a processor configured to receive and process a variable workload, wherein the processor is further adapted to generate measured output data indicative of processing system processor indicative of a performance of said processor and of variable workloads of said processor;a plurality of resources available to the processor for processing the variable workload;a resource optimizer coupled to the processor and adapted for evaluating resource allocations in pre-defined intervals; andan interval tuner coupled to the processor and to the resource optimizer, the interval tuner being adapted for determining whether to start interval tuning of the computing system by determining when the computing system is receiving the variable workload, wherein the computing system is not ready to start interval tuning when the computing system is not receiving the variable workload, and wherein the interval tuner is further adapted for evaluating the measured output data in order to determine the pre-defined intervals in which the resource optimizer evaluates resource allocations by:separating the measured output data into a first group and a second group, wherein said first group has a smaller standard deviation within the first group relative to said second group;selecting the second group; anddetermining the pre-defined intervals based in part on a desired confidence range wherein the desired confidence range is an accuracy of a desired maximum difference between a measured sample benefit reflected in said measured output data in said second group and a statistically real mean benefit. |
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summary | ||
060884185 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention takes into account the interaction of oscillatory pressure disturbances arising at individual spargers during venting of high pressure steam into a suppression pool. The individual spargers are connected in series so that a time delay exists between first venting of noncondensable gas from successive spargers. This time delay can be adjusted so that the pressure disturbances from successive spargers are out of phase, partially or wholly canceling one other. This cancellation of oscillatory pressure disturbances minimizes dynamic loads on the walls of the suppression pool and on structures submerged in the suppression pool. The cancellation or mitigation of oscillatory pressure disturbances can be seen by examining the interaction of pressure disturbances arising at two or more spargers connected in series, each sparger venting noncondensable gas or steam into a pressure pool. In general, a periodic disturbance can be represented by a Fourier series expansion of sines and cosines. However, for simplicity, we consider periodic disturbances that at any time, t, have the form: EQU p.sub.i =A.sub.i sin(2.pi..function..sub.i t+.phi..sub.i), I where subscript i is a nonzero positive integer and identifies the sparger, and where p.sub.i, A.sub.i, .function..sub.i, and .phi..sub.i represent the pressure, amplitude, frequency (in Hz), and phase angle, respectively, of a pressure disturbance at the ith sparger for ##EQU4## First, consider two spargers in series having the same amplitude and frequency, but different phase angle. Without loss of generality, we can set the amplitude and frequency equal to 1 kPa (0.145 psi) and 1 Hz, respectively, in equation I. The total pressure p due to pressure disturbances from the two spargers is then given by expression: EQU p=p.sub.1 +p.sub.2 =sin(2.pi.t)+sin(2.pi.t+.phi..sub.2) II Substituting into equation II seven different values of the phase angle for the second sparger pressure disturbance ##EQU5## results in total disturbance pressure versus time curves shown in FIG. 1A-FIG. 1G, respectively. As can be seen in FIG. 1D, when the pressure disturbance from the second sparger is .pi. radians out of phase--i.e., there is a half cycle time delay in gas or steam venting from the downstream sparger--the pressure disturbance from the second sparger completely cancels the pressure disturbance from the first sparger after a half cycle time delay. However, when the second sparger discharges at the same time as the first sparger, as shown in FIG. 1A, or when the phase angle of the second sparger is 2 .pi. radians out of phase with the first sparger, as shown in FIG. 1G, the pressure disturbance from the downstream sparger adds to the first sparger pressure disturbance, resulting in a total disturbance amplitude of 2 kPa. Similarly, as can be seen in FIG. 1B and FIG. 1F, the second sparger pressure disturbance partially reinforces the first sparger disturbance when the downstream disturbance phase angle is, respectively, ##EQU6## radians out of phase with the first sparger. When the phase angle of the disturbance from the second sparger is ##EQU7## radians out of phase with the disturbance from the first sparger, as shown in FIG. 1C and FIG. 1E, respectively, the amplitude of the total pressure disturbance is the same as the disturbance from an individual sparger. That is, when ##EQU8## or more generally, when ##EQU9## the interaction of pressure disturbances from the first and second spargers results in a total disturbance pressure that is less than the pressure disturbances from each sparger individually. In equation IV, m is any integer greater than or equal to 0. Note however, even if .vertline..phi..sub.2 -.phi..sub.1 .vertline..apprxeq..pi.(1+2 m), complete cancellation will not occur, at least for purely harmonic disturbances represented by equation I, if .function..sub.1 and .function..sub.2 are not the same. Instead, the total pressure disturbance exhibits a beat frequency. This can be seen in FIG. 2A-FIG. 2D, which plot total disturbance pressure versus time for two pressure disturbances that are .pi. radians out of phase, but have disturbance frequencies .function..sub.1 =1.00 Hz and .function..sub.2 =0.95 Hz, 1.05 Hz, 1.10 Hz and 1.50 Hz, respectively. When the two frequencies are slightly different, as shown in FIG. 2A and FIG. 2B, a low frequency beat results; at larger differences, as shown in FIG. 2C and FIG. 2D, higher frequencies contribute to the beat. The results shown in FIG. 1A-FIG. IG can be extended to more than two sparcers connected in series. For example, FIG. 3A-FIG. 3F show plots of total disturbance pressure versus time for 1, 2, . . . , 6 spargers connected in series, respectively. Disturbances originating at each of the spargers have the same frequency (1 Hz) and pressure amplitude (1 kPa). Comparing FIG. 3B, 3D and 3F with FIG. 3C and 3E reveals that the pressure disturbance is completely nullified for N spargers in series, after an initial time delay, .tau., given by ##EQU10## when the number of spargers is even. When the number of spargers is odd, the total pressure disturbance is not completely canceled, but is equal to the pressure disturbance from a single sparger. Thus, one can minimize the overall pressure disturbance by adjusting the time delay between the start of gas or steam venting from two successive spargers so as to satisfy equation: ##EQU11## where .tau..sub.i is the time delay between the ith sparger and the preceding sparger, and .function..sub.i, is the frequency of the disturbance at the ith sparger. Generally, it is unnecessary to satisfy equation VI exactly since pressure disturbances from successive spargers can, for certain ranges of phase angles, interact to produce a total disturbance pressure that is less than the pressure disturbances from individual spargers. As can be seen from equation IV, such pressure mitigation occurs when the phase angles of disturbances from successive spargers are ##EQU12## out of phase. This phase difference can be expressed in terms of time delay between gas venting of successive spargers: ##EQU13## where .tau..sub.i and .function..sub.i have the same meaning as in equation VI, and where in is any integer greater than or equal to 0. FIG. 4 schematically illustrates a sparger train 10 of a pressure relief system for a nuclear power plant, which injects high pressure steam at different locations and times within a suppression pool 12. A pressure relief valve (not shown) vents high pressure steam into an exhaust line 14, which is connected to a header 16. The header 16 channels steam into a series of gas spargers 18. Because the spargers 18 are located at different points along the header 16, vented steam first enters the sparger 18 closest to the header-exhaust line connection 20, and then flows into successive spargers 18 located further downstream from the header-exhaust line connection 20. As shown in FIG. 4, spargers 18 typically comprise vertical pipes or downcomers 22 that are partially submerged in liquid coolant 24. Each of the spargers 18 shown in FIG. 4 have two sets of nozzles--a first set of nozzles 26 located near the surface 28 of the liquid coolant 24 in the downcomers 22 and consist of rectangular slots 30 surrounded by a concentric collar 32 that deflects gas flow from a radial direction to an axially downwards direction; and a second set of nozzles 34, located near the bottom 36 of the suppression pool 24, which consists of round holes 38 having diameters much less than the inner diameter of the sparger 18 pipes 22. In addition, the ends 40 of the downcomers 22 typically are at least partially open. The head 42 of each sparger 18 is the flow area defined by the second set of holes 34 and the open ends 40 of the downcomers 22. Generally, a sparger comprises one or more sets of nozzles, the sets of nozzles having the same or different geometry, and each set of nozzles located at different positions along the longitudinal axis of the sparger. Since the spargers 18 are indistinguishable in FIG. 4, the time delay, .tau..sub.i, between gas venting of successive spargers 18 depends on the separation distance 44 between the downcomers 22 of each sparger 18, and the fluid flow velocity in the header 16. When the header 16 initially contains gas, the time delay is related to the velocity of a shock wave in the header 16, which results from the abrupt opening of the pressure relief valve, as well as the velocity and pressure of the gas behind the shock wave. Instead of adjusting the separation distance 44 between downcomers 22, one may also adjust the length of downcomers 22 of successive spargers 18 to effect changes in the time delay, although this might also change the disturbance frequency. A time delay for equivalent spargers 18, like those shown in FIG. 4, is calculated in Example 1 below. In some instances, it will be impracticable to provide the requisite separation distance 44 between the spargers 18. For example, excessive header 16 length may result in unacceptable back pressure in the exhaust line 14 or may aggravate the pressure rise in the suppression pool 12 because of the increased volume of gas contained in the header 16. In such cases, the time delay between successive spargers 18 can be increased by filling the header 16 with liquid coolant 24; i.e., by submerging the header 16 below the surface 46 of the liquid coolant 24 within the suppression pool 12. However, the additional mass of liquid tends to increase the hydraulic resistance of the sparger train 10 and may cause an excessive back pressure at the pressure release valve. A time delay for a submerged header is calculated in Example 2 below. As noted when discussing FIG. 2A-FIG. 2D, it is generally best to maintain the same disturbance frequency at each of the spargers 18. One can typically alter the disturbance frequency by changing the sparger 18 characteristics. For example, the disturbance frequency from a particular sparger 18 can often be modified by manipulating its submergence depth within the suppression pool 12, or by changing the flow area of the sparger head 42. EXAMPLES The following examples are intended as illustrative and non-limiting, and represent specific embodiments of the present invention. EXAMPLE 1 Time Delay for a Gas Filled Header As discussed above, and with reference to FIG. 4, the time delay .tau..sub.i between gas venting of successive spargers 18 that are connected in series to a header 16 depends on the separation distance 44 between the downcomers 22 of each sparger 18, and the fluid velocity in the header 16. When the header 16 initially contains gas, the time delay is related to the velocity of a shock wave in the header 16, which results from the abrupt opening of the pressure relief valve. As the shock wave propagates through the stagnant gas (air) in the header 16, it induces gas motion behind the shock wave. Thus, immediately upstream of the shock wave, the air in the header 16 moves with velocity u, which one can determine from the pressure ratio across the shock wave and the speed of sound of the stagnant gas ahead of the shock wave: ##EQU14## In equation VIII, subscripts 1 and 2 refer to regions downstream and upstream of the shock wave, ##EQU15## represents the pressure ratio across the shock wave, .alpha..sub.1 is the speed of sound of the gas downstream of the shock wave, and .gamma. is the ratio of specific heats of the gas in the header 16, which for air at standard conditions is 1.4. The speed of sound in the stagnant gas region ahead of the shock wave can be calculated from the equation EQU a.sub.1 =.sqroot..gamma.RT, IX where R is the gas constant 0.287 kJ/kg.degree. K. (53.3 ft.multidot.lb/lb.sub.m .multidot..degree. R.) for air, and T is the temperature of the gas ahead of the shock wave. Note, limitations on the use of equation VII are described in John D. Anderson, Jr., Modern Compressible Flow 172-79 (1982), which is herein incorporated by reference. In an experimental investigation of a pressure relief system, saturated steam was vented into a water-filled suppression tank through a sparger similar to those shown in FIG. 4. In the study, ##EQU16## was about 5, and the temperature and pressure of the stagnant air ahead of the shock was about 311.degree. K. (560.degree. Rankine) and 101 kPa (14.7 psia), respectively. The speed of sound in the stagnant air ahead of the shock wave and the velocity of the gas behind the shock wave were calculated from equations IX and VIII, respectively, and were equal to 354 m/s (1160 ft/s) and 479 m/s (1570 ft/s). Since the measured fundamental frequency .function..sub.i of the pressure disturbances was about 10 Hz, one would expect, in view of equation VI, that a time delay of about 0.05 s between first venting of gas of successive spargers would minimize pressure disturbances. This would correspond in FIG. 4 to a separation distance 44 between the spargers 18 equal to about u.tau..sub.i =23.8 m (78 ft.) Because the gas within exhaust line 14, header 16 and downcomers 22 is compressed while the liquid coolant is purged from the spargers 18, the actual value of the time delay may be significantly longer than the calculated time delay, which would result in a decrease in the requisite separation distance 44 between the spargers 18. EXAMPLE 2 Time Delay for a Water-Filled Header As noted above, it may be desirable to increase the time delay between successive spargers 18 by filling the header 16 with liquid coolant 24. Again referring to FIG. 4, the time delay .tau..sub.i between gas venting of successive spargers 18 depends on the separation distance 44 between the downcomers 22 of each sparger 18, and the average velocity of the gas/liquid interface moving through the header 16. The velocity of the gas/liquid interface, in turn, depends on the flow rate of liquid coolant 24 (generally water) out of the spargers 18 through the two sets of nozzles 26, 42. During the line clearing process, the volumetric flow rate q of liquid coolant issuing from each of the spargers 18 into the suppression pool 12 can be approximated by analogizing the process to flow through an orifice. One can then calculate q using the equation: ##EQU17## where .rho. is the liquid coolant density; P.sub.s and p.sub.p are the average pressures within the sparger 18 and suppression pool 12 adjacent to the sparger nozzles 26, 42, respectively, during line clearing; S.sub.N and S.sub.D are the total flow areas normal to the sparger nozzles 26, 42 and downcomer 22, respectively; and C.sub.D is the discharge coefficient, which approaches 0.61 for high Reynolds number flow. See, for example, R. Byron Bird, Warren E. Stewart & Edwin N. Lightfoot, Transport Phenomenon 224-26 (1960), which is herein incorporated by reference. Data obtained in the experimental investigation described in Example 1 can be used to calculate the requisite separation distance 44 between spargers 18 of FIG. 4. In the experiments, the total area normal to flow in the downcomer and nozzles was, respectively, 0.02 m.sub.2 (0.216 ft.sup.2) and 0.0118 m.sup.2 (0.127 ft.sup.2), the collective area of holes, typically 100.sub.14 150, at the downcomer tip. The pressure in the sparger P.sub.s during flow was measured to be about 690 kPa (100 psia), and p.sub.p, which is the average hydrostatic pressure in the sparger head, was 203 kPa (29.4 psia). Substituting these data into equation X, and given that the density of the liquid coolant (water) is about 993 kg/rm.sup.3 (62 lbm/ft.sup.3), and that C.sub.D is 0.61, the volumetric flow rate from the sparger was equal to 0.279 m.sup.3 /s (9.84 ft.sup.3 /s). Thus, to calculate the separation distance 44 between the downcomers 22 of each sparger 18 shown in FIG. 4, we first note that the total volumetric flow rate Q of liquid coolant at the header-exhaust line connection 20 must equal the sum of the individual flow rates in the downcomers 22. If the volumetric flow rates in each of the downcomers 22 are about the same--which is a good approximation since the spargers 18 are identical and they each exhaust into the suppression pool 12 along the same horizontal grade line--the average velocity in the header, .nu..sub.H, is given by: ##EQU18## where A.sub.H is the cross sectional area in the header 16. Since the measured fundamental frequency .function..sub.i of the pressure disturbances from the experiments was about 10 Hz, equation VI predicts that a time delay of about 0.05 s between first venting of gas of successive spargers should minimize pressure disturbances. Given that the cross sectional area of the header is 0.0232.sup.m2 (0.25 ft.sup.2), equation XI yields .nu..sub.H =47.9 m/s (157 ft/s), which corresponds to a separation distance 44 between the spargers 18 equal to about .nu..sub.H .tau..sub.i =2.41 m (7.9 ft). It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reading the above description. Therefore, the scope of the invention should be determined, not with reference to the above description, but instead with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. |
050358405 | summary | BACKGROUND OF THE INVENTION EDTA (ethylene diamine tetraacetic acid) is used as a chelating agent for cleaning scale from steam generators used for pressurized water reactors. These steam generators accumulate great quantities of precipitated iron oxides that reduce the heat transfer coefficient and the efficiency of the steam generator. Periodically, it is necessary to clean the precipitated material from these steam generators. A 10-15% ammonium EDTA salt solution is typically injected into the steam generator. Since EDTA is a powerful chelating agent, it coordinates the iron and solubilizes it. In nuclear power plants, the shell side or secondary side of these steam generators is supposed to be the "clean" side. However, minor leaks in the tubes may occur allowing material from the primary side to leak low levels of radioactivity to the "clean" side, primarily in the form of radioisotopes of cesium cobalt and other metals. Acidifying the metal salt containing EDTA chelating solution produces a metal salt contaminated H.sub.4 EDTA. The cost of stabilization, transportation and disposal of these wastes are high, making volume reduction of the metal salt containing H.sub.4 EDTA precipitate a cost-effective alternative. INFORMATION DISCLOSURE STATEMENT The reduction of the volume of radioactive waste products resulting from steam generator cleaning has been the subject of various U.S. patents. However, none of the patents discloses or anticipates a process for eliminating radioactive salts from an EDTA acid precipitate. U.S. Pat. No. 3,669,631 to Bellbrook, et al. discloses a process for removing radioactive materials from ion-exchange resins. The ion-exchange resins are used to remove radioactive metal isotopes from a cleaning solution. The radioactive isotopes are recovered by dissolving the ion-exchange resins in an acid/catalyst mixture and thereafter recovering the radioactive isotopes from the solution. U.S. Pat. No. 3,791,981 to Calmon discloses a method for reducing the volume of radioactive contaminated ion-exchange resins prior to their disposal. The method consists of contacting the ion-exchange resins with an organic solvent to physically reduce the ion-exchange resin volume. U.S. Pat. No. 4,704,235 to Arvesen discloses a steam generator descaling method that is accomplished in a single step in the absence of EDTA. U.S. Pat. No. 4,705,573 to Wood et al. discloses a descaling process that does not use EDTA. The process comprises contacting a scale-containing surface with a specific reagent. No mention of subsequent reagent purification is made. An article by Robert W. Hay et al. entitled Reactions of Co-ordinated Ligands. Hydrolysis of Tetramethyl Ethylene-diaminetetra-acetate and its Copper (II) Complexes discloses methods of producing Me.sub.4 EDTA from H.sub.4 EDTA. SUMMARY OF THE INVENTION A principal object of this invention is to provide a process for removing metal contained in an H.sub.4 EDTA complex. The process results in a significant reduction in the volume of the unwanted metal containing H.sub.4 EDTA complex prior to disposal. Accordingly, in a broad embodiment the present invention is a process for removing metal contained in a metal contaminated H.sub.4 EDTA. The metal containing H.sub.4 EDTA complex undergoes esterification in the presence of an esterification reagent to produce an esterification mixture comprising a metal salt and a liquid EDTA ester. The metal salt is then separated from the esterification mixture. In a preferred embodiment, the invention is a process for removing radioactive metal salts contained in an H.sub.4 EDTA precipitate. The radioactive metal salt is removed by esterifying a radioactive metal salt containing H.sub.4 EDTA with an esterification reagent, in the presence of an organic solvent, at esterification conditions including a temperature of from about 0.degree. C. up to about the boiling point of the esterification reagent but no greater than 220.degree. C. for a period of time ranging from 15 minutes to about 24 hours or more to provide an esterification mixture comprising a solid radioactive metal salt, excess organic solvent and a liquid esterified EDTA. The liquid esterified EDTA is then recovered from the mixture. |
053923260 | summary | BACKGROUND OF THE INVENTION The present invention relates to a boiling water reactor provided with a core structure, incore structural machineries and a recirculation system of a reactor for realizing a reactor capable of improving maintenace workings and operability of the reactor and remarkably reducing labour, load or the like of workers or operators for periodical inspections of the reactor. A boiling water reactor is a reactor of the type in which slightly enriched uranium is used as a fuel, which is directly boiled in a core by utilizing water as a moderator or coolant and steam is then generated. A boiling water reactor power plant is generally composed of a reactor system and a turbine system. The reactor system comprises a reactor primary series system including a reactor body having a core fuel, an incore structure and a pressure vessel, a recirculation system, a control rod driving system and a main steam system and also comprises a reactor auxiliary system including an emergency core cooling system. In a known technology, there has been proposed an improved boiling water reactor in which an internal pump system is utilized for a coolant recirculation system instead of an incore jet pump system. Such a boiling water reactor is shown for example in FIG. 20. Referring to FIG. 20, a core 2 is disposed at a portion slightly lower from a central portion in the reactor pressure vessel 1. A plurality of control rod guide tubes 3 are arranged below the core 2, and the core 2 is composed of a shroud 4 having an upper opening closed by a shroud head 5. Stand pipes 7 of a centrifugal separator 6 stand from the shroud head 5 and six rectangular flat type driers 8 are mounted on the centrifugal separator 6. A control rod driving mechanism 9 for driving cross-blade type control rods under guidance of inner surfaces of the control rod guide tubes 3 is disposed at a lower portion of the reactor pressure vessel 1. A plurality of internal pumps 10 are mounted to a bottom portion of the reactor pressure vessel 1 at portions between an inside of the reactor pressure vessel 1 and an outside of the shroud 4. The core is composed of a plurality of fuel assemblies arranged in a lattice structure, and in each of fuel assemblies, fuel rods in 8-row.times.8-line arrangement are supported by upper and lower tie plates and spacers. An entire structure of the fuel assemblies is surrounded by a channel box. Each of the fuel rods is formed by baking a slightly enriched uranium in the shape of a pellet which is then charged into a fuel clad. The control rod has a cross shape and acts to control a chain reaction in a fission, and the control rod is charged or inserted into the lattice arrangement of the fuel assembly from the lower side of the reactor pressure vessel 1, and the insertion or withdrawal of the control rod from the fuel assembly is performed by means of the control rod driving mechanism 9 connected to the control rod. In the core 2, the lower portions of the fuel assemblies are supported by a core support plate 11, the upper portions thereof are supported by an upper grid plate 12, and the entire structure thereof is surrounded by the shroud 4. A main steam pipe 13 is connected to an upper side wall portion of the reactor pressure vessel 1, and the steam dried by the driers 8 is transferred to a turbine through the main steam pipe 13. A water supply pipe 14 is also connected to the side wall of the reactor pressure vessel 1 for supplying the coolant into the reactor pressure vessel 1, and the coolant fed thereinto is forcibly circulated by the internal pumps 10. The boiled two-phase, water and steam, flow from the core 2 is separated by the centrifugal separator 6 into water and steam and the water content in the separated steam is further removed by the driers 8. The reactor pressure vessel 1 is fixedly mounted on a pedestal 16 through a supporting skirt 15. The attaching or detaching operation of the contol rod driving mechanism 9 is carried out in the pedestal by means of a control rod handling machine 17. An upper end opening of the pressure vessel 1 is pressure-tightly closed by an upper cover 18 and the entire structure of the reactor pressure vessel 1 is accommodated in the reactor containment vessel 19. With the nuclear power plant including the boiling water reactor of the structure described above, at a time of maintenance operation for the periodical inspection of the power plant, operators or workers enter the lower portion of the reactor pressure vessel 1 for removing the internal pumps 10 and the control rod driving mechanism 9. Although the internal pumps 10 are removed by a removing apparatus, the operators must perform preliminary removing work before the operation of the removing apparatus. During such preliminary work removing, however, there is a fear that the water coolant will down to the workers from the reactor pressure vessel 1. Under this dangerous environment, the long time working in such place of relatively high possibility of exposure of radiation dose is not desired for the workers in their physical and mental conditions. These may be also referred to for the inspection working or exchanging working of the control rod driving mechanism 9 and incore neutron detectors. One object of the present invention is to completely eliminate such dangerous maintenance working under the reactor pressure vessel 1. In another point of view, it is necessary for the operator to pay his highest attention to a water level in the core during the running operation of the reactor. In an ordinary operation, the water level in the core is automatically maintained to a predetermined level by an automatic controlling, and the control of the water level can be usually done by monitoring a display on a control board in a central operation room. However, in a case of a turbine trip or in a case where the coolant in the core changes into steam and then flows out of the core by an operation of safety valve for a main steam escape after the closing of a main steam isolation valve, the water level in the core lowers downward, and at this moment, a water supply pump, which is driven in isolation by a steam turbine, is operated to thereby start the water supply, but if this starting of the water supply is delayed, the water level in the core further lowers and an emergency core water supply system starts to operate. The emergency core water supply system operates itself automatically under a preliminarily designed safety control mode of a safety system, but such operation gives feel of strain or pressure to the operaters. On the contrary, when the core water level rises during the operation of the reactor by any accident of, for example, a water level setter, water flows towards the turbine, which may result in damage to the turbine blades. As described, a transition phenomenon in which undesired water level change is caused gives mental strain to the operators, so that a second object of the present invention is to realize a boiling water reactor having a wide allowable range against the change of the core water level. SUMMARY OF THE INVENTION An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art and to provide a boiling water reactor having a structure capable of handling control rods from an upper side of a reactor pressure vessel for eliminating workings of operators at a portion below a reactor pressure vessel in a reactor building. Another object of the present invention is to provide a boiling water reactor having a reduced vertical height capable of realizing an installation on an instable place such as on a ship or a portion being liably suffered from an earthquake. These and other objects can be achieved according to the present invention by providing a boiling water reactor comprising, a reactor pressure vessel accommodated in a reactor containment vessel in a vertical fashion, a core disposed at a low portion in the reactor pressure vessel, the core being composed of a plurality of fuel assemblies arranged with spaces from each other, a plurality of control rods to be inserted from an upper side of the core into the spaces between the fuel assemblies and withdrawn therefrom upwardly, a shroud surrounding the fuel assemblies so as to define the core and having an upper end opening, a shroud head which closes the upper end opening of the shroud and through which the control rods are inserted or withdrawn, separator means standing upward from the shroud head to carry out Gas-water separation of steam Generated from the core, a fixing pedestal disposed above the separator means and provided with a steam flow hole through which steam separated by the separator means passes, a control rod driving mechanism mounted on the fixing pedestal and adapted to drive the control rods, a drier means arranged along an upper inner wall surface of the reactor pressure vessel and adapted to dry the steam passing through the steam flow hole of the fixing pedestal, and a jet pump means disposed in a space between an outer surface of the shroud and an inner wall surface of the reactor pressure vessel. In preferred embodiments, the drier means comprises a plurality of drier elements arranged annularly along the upper inner wall surface of the reactor pressure vessel, drain receiving vessels disposed at lower end portions of the drier elements and drain tubes extending downward from the drain receiving vessels. The drier element is composed of a metal plate formed with a number of punched holes. The control rod driving mechanism is provided with a drive means composed of electromagnetic coils or an electromagnetically driven motor. The separator means comprises a plurality of tube like cylindrical bodies standing upward from the shroud head, a plurality of cross-shaped control rod guide tubes to be inserted into a space between adjacent fuel assemblies and a support plate for supporting the cylindrical bodies in vertical attitude. Each of the control rods has a vertical length substantially equal to a vertical length of the core and a vertically moving length of a control rod driving shaft is substantially equal to the vertical length of the core. The jet pump means comprises a plurality of jet pumps arranged with equal spaces from each other and annularly along the inner wall surface of the reactor pressure vessel. The jet pump comprises first and second stage nozzles, first and second stage throats and a diffuser connected to the second stage throat. The jet pump means is driven by a plurality of jet pump driving pumps or a plurality of steam injectors. The jet pump means is operated so that a flow rate ratio of a driving water with respect to a driven water is at least more than 6. According to the present invention of the structures described above, since the control rod driving mechanism is disposed at a portion above the reactor core and the control rods are handled from the upper side of the core, any piping means or machineries for the control rod driving are not positioned below the core. Accordingly, the operators or workers can be made free from the working at a portion below the reactor pressure vessel and the entire vertical height of the reactor containment vessel, i.e. reactor building, can be reduced. Furthermore, the core is positioned at a lower portion in comparison with a conventional arrangement, so that a space in which relatively long separators or other means are arranged can be ensured above the core. The location of the long separator can ensure wide allowance with respect to a water level change in the reactor pressure vessel. Still furthermore, since the control rod driving mechanism is disposed at the upper portion of the reactor pressure vessel, so that the control rod driving mechanism and associated members or elements can be entirely taken out from the reactor pressure vessel at a periodical inspection time, thus enabling easy maintenance. |
abstract | One embodiment relates to a method of inspecting a substrate using electrons. Mirror-mode electron-beam imaging is performed on a region of the substrate at multiple voltage differences between an electron source and a substrate, and image data is stored corresponding to the multiple voltage differences. A calculation is made of a measure of variation of an imaged aspect of a feature in the region with respect to the voltage difference between the electron source and the substrate. Other embodiments and features are also disclosed. |
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claims | 1. A syringe containment apparatus for a syringe having a hypodermic needle comprising: a radiopharmaceutical pig including an upper portion removably securable to a lower portion, each portion having an inner surface defining an inner cavity and an outer surface surrounding the inner cavity and being made from a radiation-resistant material; and a puncture resistant tubular housing configured to fit within the inner cavity of the lower portion of the radiopharmaceutical pig, the housing having a cavity defined by a bottom closed end and a top open end, wherein the top open end of the housing is configured to receive the syringe. 2. The syringe containment apparatus as defined in claim 1 , wherein the top open end of the housing has a flange adapted to be held by the fingers of a person, the flange facilitating the insertion and removal of the housing from the radiopharmaceutical pig. claim 1 3. The syringe containment apparatus as defined in claim 1 , wherein the flange encircles the top open end of the housing. claim 1 4. The syringe containment apparatus as defined in claim 1 , further comprising a cap having a cavity, which is defined by a bottom open end and a top closed end, wherein the bottom open end of the cap is configured to attach to the top open end of the housing. claim 1 5. The syringe containment apparatus as defined in claim 4 , wherein the bottom open end of the cap is further configured to snap to the top open end of the housing. claim 4 6. The syringe containment apparatus as defined in claim 1 , wherein the inner surface of the lower portion of the radiopharmaceutical pig has a bottom section configured to support the housing in an upright position inside the inner cavity of the lower portion of the radiopharmaceutical pig. claim 1 7. The syringe containment apparatus as defined in claim 1 , further comprising a cap having a cavity, which is defined by a bottom open end and a top closed end. claim 1 8. The syringe containment apparatus as defined in claim 7 , wherein the bottom open end of the cap further comprises a snap and the top open end of the housing further comprises a notch, wherein the cap is secured to the housing by engaging the snap to the notch. claim 7 9. The syringe containment apparatus as defined in claim 1 , wherein the cavity of the housing is configured to hold a single syringe. claim 1 10. The syringe containment apparatus as defined in claim 1 , wherein the top open end of the housing further comprises a shoulder configured to support the syringe in the cavity of the housing. claim 1 |
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045267456 | summary | TECHNICAL FIELD The present invention relates to a fuel assembly with a lower lattice device or element and a plurality of fuel rods supported by said lattice device, a fuel box which surrounds all the fuel rods, and a base with a downwardly-facing inlet opening for reactor coolant, the fuel assembly having at least one vertical by-pass channel for a water flow along but being separated from the fuel rods. DISCUSSION OF PRIOR ART More particularly, the invention relates to a a fuel assembly which is constructed in such a way that it is capable of being used, with advantage, in a boiling water reactor which is originally intended for fuel assemblies having no water channel of the kind mentioned above, without it being necessary to introduce any considerable change of the other components of the reactor. A problem, which will then be encountered, is how to achieve a necessary by-pass flow through the central water channel(s) when the reactor power is being reduced by reducing the speed of the circulating pumps. With a fuel assembly according to the invention, an automatic adjustment of the water flow supplied to the above-mentioned vertical water channels takes place in such a manner that the magnitude of this flow is dependent on the magnitude of the power supplied to these water channels. DISCLOSURE OF THE INVENTION A fuel assembly according to the invention is intended to be arranged in a reactor core in a conventional manner, with four fuel assemblies in each core module, water gaps between adjacent assemblies, and a control rod of cruciform cross-section in each module. In addition to the flow flowing along the fuel rods and in contact therewith, the reactor core is traversed by a first by-pass flow, which is located at the above-mentioned gaps formed between the fuel assemblies, and by a second by-pass flow which is located at the above-mentioned vertical water channels. According to the invention, there is provided a fuel assembly having a vertical center line and comprising a lower lattice device and a plurality of vertical fuel rods supported by said lattice device, a fuel box which surrounds all the fuel rods, and a sleeve-like base with a downwardly-facing inlet opening for reactor coolant, the fuel assembly having at least one vertical water channel for a water flow flowing along the fuel rods and being separated therefrom, wherein the at least one vertical water channel is hydraulically connected at its lower end to at least one substantially radially extending channel opening out at the side surface of the fuel assembly, the wall of said base being provided with at least one through-hole, the at least one through-hole being positioned at a lower level than the outlet openings of said substantially radial channels and beng arranged in hydraulic connection with said inlet opening via a space surrounded by said base. |
description | This application is a § 371 U.S. National Phase application which claims priority from International Application Serial No. PCT/US2015/037080, filed Jun. 23, 2015, which published Dec. 30, 2015, as PCT Publication No. WO 2015/200257 Al. International Application Serial No. PCT/US2015/037080 claims the benefit of priority of U.S. Provisional Application Ser. No. 62/015,603, filed Jun. 23, 2014, entitled “An Additive Manufacturing Technology for the Fabrication and Characterization of Nuclear Reactor Fuel”, and from U.S. Patent Application Ser. No. 62/099,734, filed Jan. 5, 2015, entitled “An Additive Manufacturing Technology for the Fabrication and Characterization of Nuclear Reactor Fuel”, and from U.S. Patent Application Ser. No. 62/133,596, filed Mar. 16, 2015, entitled “An Additive Manufacturing Technology for the Fabrication and Characterization of Nuclear Reactor Fuel”, and from to U.S. Patent Application Ser. No. 62/153,715, filed Apr. 28, 2015, entitled “An Additive Manufacturing Technology for the Fabrication and Characterization of Nuclear Reactor Fuel”. Each of these applications is hereby incorporated herein by reference in its entirety. Nuclear energy continues to be an important source of energy for the United States and many countries around the world, as nuclear fuel can provide greater amounts of energy over long time periods without many of the problems associated with fossil fuel use, such as greenhouse gas emissions. The inherent risks in using and storing nuclear fuel sources, the need for ensuring safe operation of nuclear reactors, and the risks of nuclear fuel being misused to create weapons continue to drive innovation in developing safe and secure nuclear fuel technologies. Various shortcomings of the prior art are overcome, and additional advantages are provided through the provision, in one aspect, of a nuclear fuel structure which includes a plurality of fibers arranged in the nuclear fuel structure and a multilayer fuel region within at least one fiber of the plurality of fibers. The multilayer fuel region includes an inner layer region with a nuclear fuel material, an outer layer region encasing the nuclear fuel material. In another aspect, also provided is a method of facilitating fabricating a nuclear fuel structure, where the facilitating fabricating includes providing a plurality of fibers arranged in the nuclear fuel structure and forming a multilayer fuel region within at least one fiber of the plurality of fibers. The multilayer fuel region formed includes an inner layer region having a nuclear fuel material, and an outer layer region encasing the nuclear fuel material. Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. Aspects of the present invention and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting examples illustrated in the accompanying drawings. Descriptions of well-known materials, fabrication tools, processing techniques, etc., are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating aspects of the invention, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions, and/or arrangements, within the spirit and/or scope of the underlying inventive concepts will be apparent to those skilled in the art from this disclosure. Reference is made below to the drawings, which are not drawn to scale for ease of understanding, wherein the same reference numbers used throughout different figures designate the same or similar components. Nuclear energy production continues to be important in many countries to meet current and predicted future energy demands. Nuclear fuel materials, such as uranium and uranium-based compounds, have a much greater energy density than other energy sources such as fossil fuels, and may have energy densities over a million times greater than, for example, gasoline or coal fuels. Safe handling and storing of nuclear fuel materials within nuclear reactors, as well as prevention of nuclear reactor accidents and meltdowns, continue to be important issues in nuclear energy production, as several well-known nuclear reactor accidents illustrate, such as the Three Mile Island incident, the Chernobyl disaster, and the recent Fukushima Daiichi meltdown. FIG. 1 is a simplified schematic of an example nuclear reactor 100, as may be part of a nuclear power plant. The nuclear reactor 100 depicted in FIG. 1 includes a reactor vessel 105 encased inside a reactor shield 110, which may be made of concrete or other material capable of withstanding high temperatures, so that material within the reactor shield 110 may be contained in the event of an accident. Reactor vessel 105 includes a core 120 in which nuclear fuel rods 130 and control rods 140 are disposed. Reactor vessel 105 also holds a coolant material 150, such as water or heavy water, which may be drawn into reactor 105 through a coolant inlet 155. Fuel rods 130 include a nuclear fuel material, frequently uranium dioxide fuel capsules, encased in a metal alloy fuel rod casing or cladding, such as a zirconium alloy metal casing. (Many nuclear fuel rods make use of zirconium alloy cladding materials produced under the trademark name Zircaloy.) The nuclear fuel material is bombarded with neutrons that can initiate a fission reaction in the nuclear fuel; the reaction splits the nucleus of the nuclear fuel material, releasing heat energy and additional neutrons that subsequently continue the fission reaction. The heat energy heats the coolant 160, which may then be pumped out of reactor vessel 105 via coolant outlet 165; the heated coolant 160 may be used, for example, to generate steam to drive turbines that in turn generate electrical energy (not depicted in FIG. 1 for simplicity). Core 120 may be made of one or more moderator materials, such as graphite, capable of slowing neutrons down to speeds at which the neutrons are more likely to react with the nuclei of the nuclear fuel material. Coolant material 150 may also act as a moderator material to slow down high-speed neutrons bombarding fuel rods 130. Control rods 140 may be used to variably control a fission rate of the nuclear fuel material in fuel rods 130. Control rods 140 may be made of one or more materials capable of absorbing neutrons without undergoing a fission reaction, such as boron, silver, cadmium, and/or indium. As control rods 140 are pulled out partially or fully from the reactor vessel 105, more neutrons may successfully bombard and react with nuclear fuel material in fuel rods 130, increasing energy output; conversely, by inserting the rods further or fully into reactor vessel 105, more neutrons may be absorbed and the nuclear fission reactions slowed to reduce energy production. In some nuclear reactors, fully inserting control rods 140 may be used to fully stop fission reactions in fuel rods 130. FIGS. 2A and 2B illustrate an example of a nuclear fuel assembly 200, as may be deployed in a nuclear reactor. Generally, nuclear fuel rods 130 and control rods 140, as depicted in FIG. 1, are not deployed separately in a nuclear reactor, but are more often deployed in a nuclear fuel assembly such as nuclear fuel assembly 200. Nuclear fuel rods 210 may be arrayed together with control rods 220 interspersed among the nuclear fuel rods 210, and both nuclear fuel rods 210 and control rods 220 bound by one or more spacers 230. The entire nuclear fuel assembly 200 may be deployed within a nuclear reactor vessel, such as reactor vessel 105 of FIG. 1, so that the nuclear fuel assembly is surrounded by moderator materials, such as the core 120, and coolant 150 may flow around fuel rods 210 and control rods 220. The control rods 220 may be coupled with controls within or outside the reactor vessel so that the control rods 220 may be variably withdrawn or inserted further into nuclear fuel assembly 200, as illustrated by FIG. 2B. Referring to FIG. 1 again, it may be noted that coolant 150 may serve several purposes within nuclear reactor 100. Coolant 160, being heated by the heat generated from fission reactions, carries away heat from the fuel rods 130 and core 120, and the heat energy of coolant 160 may be converted to electrical energy. As well, coolant 150, 160 may act as a moderator to slow neutrons to speeds at which they are more likely to successfully react with nuclear fuel material. In a loss of coolant accident (LOCA), coolant levels may drop within the reactor vessel 105 so that heat energy is no longer adequately conveyed out of the reactor, allowing heat to build within the reactor and potentially damage fuel rods 130, including the casing material. Although a loss of coolant may also represent a loss of moderator material, and thus result in a slow-down of fission reactions in the nuclear fuel material, heat may still build rapidly in the reactor vessel as the radioactive nuclear fuel materials, as well as radioactive by-products of fission reactions, continue to radiate heat energy into the reactor. Both the Three Mile Island disaster and the Fukushima Daiichi disaster began as loss of coolant accidents, resulting in a meltdown and highly exothermic oxidation of the zirconium alloy cladding, producing vast amounts of hydrogen gas and resulting in further heat build-up and a subsequent core meltdown. Once the cladding of fuel rods has been breached or cracked in a meltdown, the radioactive nuclear fuel and its radioactive fission by-products may be exposed and mix with other gases produced by the meltdown, allowing the radioactive materials to escape into the surrounding environment. Incidents such as Three Mile Island have spurred research into alternative and safer fuel rod cladding materials that can replace zirconium alloy cladding and other cladding materials. Silicon carbide (SiC), for example, may be one such alternative cladding material. Although silicon carbide is a relatively brittle material, its brittleness may be mitigated by the use of silicon carbide fiber (SiCf) reinforced silicon carbide matrix (SiCm) Ceramic-Matrix Composite (CMC) structures. FIGS. 3A-3B illustrate one example embodiment of a reinforced SiCf—SiCm CMC structure. FIG. 3A depicts one embodiment of a structure 300 including a tube 310, such as a monolithic SiC tube, with a plurality of reinforcing ribbons 320 of SiC fibers or tows 340 braided or wound around tube 310. Reinforcing ribbons may include, for example, a plurality of SiC fibers or tows 340 as illustrated by the close-up view of portion 330 of one ribbon 320. Fibers or tows 340 may include a silicon-carbide compound, such as SiCf. FIG. 3A illustrates one example of a braiding or winding process and pattern of ribbons 320, with additional alternating strands not included in order to simplify the figure and better illustrate the exemplary pattern. Other patterns and processes of braiding or winding ribbons may also be possible. For example, ribbons 320 could also be braided inside tube 310 (not shown in FIG. 3A for clarity of illustration). FIG. 3B illustrates structure 300 with multiple layers of ribbons 320 encasing tube 310, and embedded an outer layer 360 covering the ribbons 320 and tube 310. The roles of 310 and 360 may be reversed, in which case 360 is an outer tube encasing the multiple layers of ribbon 320 and then covered with an inner layer 310. For clarity of presentation, the former architecture is assumed without loss of generality. Outer layer 360 may also include SiC, in which case structure 300 may be a SiCf—SiCm CMC structure. Outer layer 360 may be provided, for example, by a chemical vapor infiltration (CVI) process and/or a chemical vapor deposition (CVD) process. Close-up view 351 shows a view of a portion of the plurality of fibers 340 as seen looking radially into the structure 300, illustrating how fibers 340 may be ideally arranged in an ideal ‘cross-weave’ type pattern to provide reinforcement to structure 300 while providing open porosities to facilitate CVD or CVI. Close-up views 352 and 353 show a cross-sectional view of a cut-away portion of the plurality of fibers 340, illustrating one way in which fibers 340 may be ideally arranged to layer over tube 310. The exemplary structure 300 illustrated by FIG. 3B depicts eight layers of ribbons 320 layered over tube 310 for illustration purposes only; in practice, many more layers of ribbons 320 may be provided over tube 310 for structural reinforcement, or fewer layers of ribbons 320 may be needed. Alternatively, tube 310 and matrix 360 may be reversed to reflect a winding or braiding of ribbons 320 inside tube 310. Reinforced CMC structures, such as the exemplary structure 300 illustrated by FIGS. 3A-3B, may have a toughness comparable to metals, such as zirconium alloys, but with much greater tolerance for high temperatures. For example, beta-phase stoichiometric silicon carbide (β-SiC) CMCs retain their strength at a temperature of 1500° C. under irradiation. As well, β-SiC materials may exhibit low oxidation rates at high temperatures, and may have a relatively low reactivity with nuclear fuel compounds such as uranium dioxide (UO2). However, even reinforced CMC structures are not without drawbacks. For example, although SiC compounds had been identified as possible substitutes for zirconium alloy cladding when the Fukushima power plants were built, silicon carbide cladding fuel rods were still expensive to produce and use. Unlike metal alloys, which may be readily welded to seal fuel pellets within a metal alloy cladding, SiC materials do not readily fuse together, making it difficult to fully hermetically seal nuclear fuel pellets within a silicon carbide tube. As well, SiC CMC reinforced cladding is generally made relatively thick in order to overcome the inherent brittleness of pure silicon carbide; however, metal cladding of current fuel rods can be made relatively thin compared to SiC CMC cladding. Thus, in order for many SiC CMC clad fuel rods to be used as replacements for metal alloy clad fuel rods in current nuclear reactors, the SiC CMC cladding would have to be kept to a thickness similar to metal cladding, but at such thicknesses the cladding may not provide adequate structural reinforcement to the fuel rod. Tristructural-isotropic (TRISO) nuclear fuel may address some of these shortcomings. TRISO nuclear fuel encapsulates nuclear fuel in multiple spherical layers enclosed in a SiC sphere. The spherical design, however, provides a relatively low ratio of nuclear fuel volume fraction, requiring higher enrichments and more frequent replacement, thereby increasing the burden of storing spent nuclear fuel safely. As well, not every silicon carbide CMC may be suitable for use as cladding, but those CMCs that are suitable present challenges and drawbacks as well. For example, one of the few SiCf tow used to reinforce CMC materials currently being used to develop nuclear fuel rod structures is Hi-Nicalon Type-S(HNS), a commercially available β-SiCf compound that sufficiently approaches stoichiometry and that can withstand high doses of neutron bombardment during use in a nuclear reactor. However, HNS fibers typically do not form a well-ordered arrangement of continuous fibers as shown in the close-up views 351, 353 depicted in FIG. 3B. Instead, FINS fibers tend to twist and tangle, forming clumps of silicon carbide and leaving spaces or voids within the braided tow structure around tube 310. These problems occur regardless of the specific process used to form and deposit the HNS fibers, whether by chemical vapor infiltration (CVI) and/or chemical vapor deposition (CVD), polymer infiltration and pyrolysis (PIP), or melt infiltration processes. This tendency of HNS fibers to tangle and clump may also reduce the resulting CMC 300 fiber volume fraction in some portions of the braided fiber structure around tube 310, leaving those portions more susceptible to cracking. Formation of HNS reinforced CMC cladding by a melt infiltration process also tends to form pockets of silicon along portions of the HNS fibers; as silicon expands once it turns solid, the silicon pockets become weak points in the CMC that are highly susceptible to cracking. Thus, generally stated, disclosed herein is a nuclear fuel structure or cladding structure which includes a plurality of fibers arranged in the nuclear fuel structure and a multilayer fuel region within at least one fiber of the plurality of fibers. The multilayer fuel region includes an inner layer region with a nuclear fuel material, an outer layer region encasing the nuclear fuel material. As used herein, the term “fiber” can refer to any elongated structure along which discrete regions may be formed. This may include, but is not limited to, any CMC structure(s), filaments or filamentary structures, and other similar structures of the type disclosed herein. Filamentary structures may include, for example, structures that curl around a helix or branch out into multiple filaments or fibers. When used as cladding, the plurality of fibers may contain no fiber having a multilayer fuel structure. In any instance, the plurality of fibers may also contain elements intended to interact with nuclear reactions, for example material included as burnable poisons. In one embodiment, the plurality of fibers are arranged in the nuclear fuel structure to provide structural reinforcement to at least a portion of the nuclear fuel structure. The nuclear fuel structure may include an inner rod or tube structure, and the plurality of fibers may be wrapped around the inner rod or tube structure to facilitate providing structural reinforcement. As one or more of the plurality of fibers may also include a multilayer fuel region or regions within the one or more fibers, a CMC tube reinforced with a plurality of fibers may not only serve as stand-alone nuclear fuel but may also serve as cladding containing the additional nuclear fuel pellets. In another embodiment, the inner layer region having the nuclear fuel material may be a first inner region, and the structure may also include a second inner layer region below the first inner layer region. The second inner layer region may include a material selected to capture by-products, such as gaseous by-products, of nuclear fission reactions occurring in the nuclear fuel material. As exemplified in FIG. 11, the material of the second inner layer region 1102 may be, in one example, nanoporous carbon deposited upon a scaffold filament 1101. In yet another embodiment, the multilayer fuel region is one multilayer fuel region of a plurality of discrete multilayer fuel regions disposed along the at least one fiber. The plurality of discrete multilayer fuel regions may each have a respective inner layer region of nuclear fuel material and a respective outer layer region encasing the nuclear fuel material. The plurality of discrete multilayer fuel regions may be formed over a core filament along the length of the at least one fiber. In yet another embodiment, the fibers may include, in addition to or instead of a multilayer fuel region, an additional material layer selected to interact with nuclear fuel material in order to moderate or delay nuclear fission. In one example the additional material layer may include carbon as a moderator. In another example the additional material layer may include boron or gadolinium as a nuclear poison or burnable poison to delay nuclear fission. In another aspect, also disclosed herein is a method of facilitating fabricating a nuclear fuel structure, where the facilitating fabricating includes providing a plurality of fibers arranged in the nuclear fuel structure and forming a multilayer fuel region within at least one fiber of the plurality of fibers. The multilayer fuel region formed includes an inner layer region having a nuclear fuel material, and an outer layer region encasing the nuclear fuel material. In one example, forming at least one layer of the multilayer fuel region may be accomplished by a chemical vapor deposition (CVD) process. In another example, the method may also include providing an inner rod or tube structure of the nuclear fuel structure, and arranging the plurality of fibers to wrap around the inner rod or tube structure so that the plurality of fibers provide structural reinforcement to the nuclear fuel structure. FIG. 4A depicts one embodiment of a fiber 410 that includes a multilayer fuel region 420. A cutaway view 415 of multilayer fuel region 420 is provided to show clearly the multiple layers of multilayer fuel region 420. Multilayer fuel region 420 has an inner layer region 423 that includes nuclear fuel material, such as uranium or a uranium compound, and an outer layer region 424 that encases the nuclear fuel material of inner layer region 423. The nuclear fuel material of inner layer region 423 may be uranium dioxide (UO2), as uranium dioxide may be used frequently as a nuclear fuel in many nuclear fuel structures. However, because the inner layer region 423 is completely, hermetically sealed by outer layer region 424, uranium, plutonium or fissile material-containing compounds with a higher fissile material density than that of uranium dioxide may also be used, such as uranium mononitride (UN), uranium carbide (UC), and uranium silicide (U2Si3). Outer layer region 424 may include, for example, pyrolytic carbon (PyC), and/or may include silicon carbide. In the exemplary multilayer fuel region depicted in FIG. 4A, inner layer region 423 may be considered a first inner layer region 423 and multilayer fuel region 420 may include a second inner layer region 422 disposed below the first inner layer region 423. The second inner layer region may include a material, such as nanoporous carbon, selected to capture by-products of nuclear fission reactions, such as gaseous by-products, occurring in the nuclear fuel material of inner layer region 423. Outer layer region 424 may include, for example, pyrolytic carbon (PyC), and/or may include silicon carbide. Outer layer region 424 may, in one embodiment, be a first outer layer region 424, and multilayer fuel region 420 may include a second outer layer region. Second outer layer region may include a material that adds further functionality to fiber 410. For example, a second outer layer region may include a nuclear poison material, such as boron or gadolinium, that may delay activity of the nuclear fuel material of inner layer region 423. Second outer layer region, in another example, may include a material, such as carbon, that acts as a moderator of nuclear fission activity of the nuclear fuel material of inner layer region 423. In another example, second outer layer region may include an interphase layer for structural integration with a SiC matrix. Multilayer fuel region 420 may be formed over a core region 421. Core region 421 may be, for example, a silicon carbide filament along a length of fiber 410, over a portion of which the multiple layers of multilayer fuel region 420 are formed. Core region 421 generally may include any ceramic material, such as silicon carbide or hafnium carbide. Finally, an overcoat layer 425 may further encase the multiple layers of multilayer fuel region 420 and core region 421. Overcoat layer 425 may itself be a multilayer overcoat. Overcoat layer 425 may include a ceramic material, such as silicon carbide or hafnium carbide, and may include additional overcoat layers that further functionalize the fiber. For example, an additional layer may be a layer of pyrolytic carbon (PyC) applied as a CMC interphase layer. In another example, an additional layer may include boron nitride applied to serve both as an interphase layer and a burnable nuclear poison layer to inhibit nuclear fission reactions in nuclear fuel material 423. Multilayer fuel region 420 may be one multilayer fuel region of a plurality of discrete multilayer fuel regions 420 disposed along fiber 410, as illustrated in FIG. 4A. Each discrete multilayer fuel region 420 may have a respective inner layer region 423 made of the nuclear fuel material, and a respective outer layer region 424 encasing the nuclear fuel material. The plurality of discrete multilayer fuel regions may be disposed over core region 421 along the length of the at least one fiber 410. Overcoat layer 425 may encase the plurality of discrete multilayer fuel regions 420 and core filament 421, resulting in a completed fiber 410. Overcoat layer 425, as depicted in FIG. 4A, may have a substantially uniform thickness along the length of fiber 410. As illustrated by FIG. 4A, the plurality of discrete multilayer fuel regions 420 appear as “beads” disposed along fiber 410, as the plurality of discrete multilayer fuel regions have a greater thickness than regions of fiber 410 including core filament 421 and overcoat 425 without a multilayer fuel region. FIG. 4B is a close-up, cross-sectional view 455 of an alternative embodiment of a fiber 450 that includes a multilayer fuel region 460, in which the fiber 450 has a substantially uniform thickness, so that multilayer fuel region 460 appears to be embedded within fiber 450. In the alternative embodiment of FIG. 4B, first inner layer region 463, second inner layer region 462, outer layer region 464, and overcoat 465 may have varying thicknesses over a length of multilayer fuel region 460, with a thickness of a layer tapering at either end of multilayer fuel region 460. In one exemplary embodiment, core region 461 may be provided to have a variable thickness prior to providing the layers of multilayer fuel region 460. In another exemplary embodiment, core region 461 may have a substantially uniform thickness, and multilayer fuel region 460 may be formed over core region 461 and may initially have a beaded appearance as depicted in FIG. 4A, but overcoat layer 465 may be provided with a variable thickness over multilayer fuel region 460 and core region 461, resulting in fiber 450 having a substantially uniform thickness along a length of fiber 450. The exemplary embodiments of fibers 410 and 450, as depicted in FIGS. 4A and 4B, are only two possible embodiments of a fiber including a multilayer fuel region 420, 460, and including a plurality of discrete multilayer fuel regions 420, 460. Variations of the examples depicted, as well as alternative multilayer fuel region embodiments, may be possible and contemplated within the scope of the disclosure herein. For example, fibers such as fibers 410/450 may have other functionality added by either or both of coating or doping. Specifically, fibers may embed materials intended to either enhance or inhibit nuclear fission reactions, either temporarily or permanently. In one example, fibers can be coated or doped with materials intended to enhance nuclear reaction, which transmute into isotopes that are themselves fissionable. Examples of such isotopes are Thorium-232 and Uranium-238. In another example, fibers can be coated or doped with neutron-absorbing isotopes that inhibit nuclear reactions. Among such isotopes—known as “nuclear poisons”—are temporary inhibitors called “burnable poisons”, such as boron and gadolinium. Other elements are long-term inhibitors, such as hafnium. In one example, dopant may be added to a fiber or fibers during fabrication, and become part of a microstructure of the fiber, either as interstitial elements, substitution elements, or concentrated at grain boundaries. In yet another example, functional coatings can be coated locally over the entire length of a fiber. A coating can also be applied to the fibers in compound form, where the coating can serve to meet additional functional requirements. For example, boron can be added in the form of boron nitride, which can also serve as a lubricant interphase in a ceramic matrix composite. Boron can also be added as boron carbide. Similarly, hafnium can be coated as hafnium carbide and serve as a high-temperature environmental barrier. Without any loss of generality, any references herein to a fiber 410 and/or multilayer fuel region 420, as depicted in FIG. 4A, may also be considered to be applicable to a fiber 450 and/or multilayer fuel region 460, as depicted in FIG. 4B, and vice versa. FIG. 4C depicts a radial cross-section view through multilayer fuel region 460 of fiber 450 of FIG. 4B, illustrating exemplary thicknesses of the different layers of multilayer fuel region 460. A similar cross-section view and exemplary thicknesses may apply to multilayer fuel region 420 of FIG. 4A. Core region 461 may be a ceramic material filament, such as a silicon carbide filament, with a thickness 461a in a range of about 5 μm to about 10 μm measured radially from the center of core region 461 (resulting in core region 461 having a diameter ranging from about 10 μm to about 20 μm). First inner layer region 463, having the nuclear fuel material, may have a thickness 463a ranging from about 3 μm to about 30 μm or more. Second inner layer region 462, disposed between the nuclear fuel material 463 and the core region 461, may have a thickness 462a ranging from about 0.5 μm to about 1.5 μm or more. Outer layer region 424, encasing the nuclear fuel material of first inner layer region 463, may have a thickness 464a ranging from about 1 μm to about 2 μm. Overcoat layer 465 over multilayer fuel region 460 may have a thickness ranging from about 1 μm to about 2 μm or more, if desired. Overcoat layer 465 may have a similar thickness over portions of fiber 450 that do not have a multilayer fuel region (i.e., portions of the fiber 450 that include portions of core region 461 and overcoat layer 465 applied over core region 461), or may have a greater thickness over such portions of fiber 450. Multilayer fuel region 460 may thus have an overall thickness 460a ranging from about 10 μm to about 22 μm or more, depending on the thicknesses selected for the layers of multilayer fuel region 460, as measured radially from the center of core region 461 to the outer surface of overcoat layer 465. FIG. 4D may illustrate one embodiment of a portion of multiple fibers 410, for example multiple scaffold fibers 410 as illustrated, for example, in FIG. 10, and may also illustrate multiple fibers 410 including pluralities of discrete multilayer fuel regions 420, arrayed to form a ribbon or tow that may be wrapped around an inner rod structure of a nuclear fuel structure, as further discussed below and illustrated further in FIG. 5A. For clarity the fiber 410 and multilayer fuel region 420 illustrated in FIG. 4A is shown in FIG. 4D to illustrate clearly the plurality of discrete multilayer fuel regions 420 disposed along fibers 410, with the plurality of discrete multilayer fuel regions 420 separated by non-fuel portions 430 of fibers 410 that do not contain multilayer fuel regions, although it is to be understood that multiple fibers 450 as illustrated in FIG. 4B may similarly be arrayed in a similar ribbon or tow. In exemplary embodiments in which the plurality of discrete multilayer fuel regions 420 are disposed substantially uniformly over a length of fiber 410, any one of the plurality of discrete multilayer fuel regions 420 may, for example, be about 5 mm long, and any one non-fuel portion 430 may, for example, be about 5 mm long. The plurality of discrete multilayer fuel regions 420 may thus cover about half or 50% of an overall length of one fiber of the multiple fibers 410. The length dimensions provided are by way of example only, as the plurality of discrete multilayer fuel regions may be formed to have greater or smaller lengths, and may be separated by larger or smaller non-fuel portions 430 along fiber 410. For example, multilayer fuel regions 420 may be formed to a length of about 6.5 mm, and the non-fuel portions 430 separating the plurality of discrete multilayer fuel regions 420 may be about 3.5 mm in length. In this example, the plurality of discrete multilayer fuel regions 420 may cover about 65% or more of a length of fiber 410. FIG. 5A depicts one embodiment of a nuclear fuel structure 500 or cladding structure 500 with a plurality of fibers 410/450, such as in the examples of FIGS. 4A-4B, arranged within nuclear fuel structure 500 or cladding structure 500. Nuclear fuel structure 500 has an inner rod or tube structure 520 and an outer layer 560, similar to structure 300 of FIG. 3B, and the plurality of fibers 410/450 may be arranged to wrap around inner rod or tube structure 520 to facilitate providing structural support to nuclear fuel structure 500. Similar to structure 300 of FIG. 3B, the respective roles of tube 520 and outer layer 560 can be swapped, in which case the plurality of filaments 410/450 are wound inside an outer tube 560 and covered with an inner layer 520 to provide structural support to nuclear fuel structure 500. For clarity and simplicity, the former architecture of inner rod or tube 520 and outer layer 560 is assumed herein below without loss of generality. Hence, multiple fibers 410/450 of the plurality of fibers include pluralities of discrete multilayer fuel regions, similar to multilayer fuel regions 420/460 of FIGS. 4A-4D, as illustrated more clearly in close-up cross-sectional views 530 and 550 of a portion of the plurality of fibers 410/450. Thus, the plurality of fibers 410/450 arranged in nuclear fuel structure 500 or cladding structure 500 may provide both cladding for nuclear fuel pellets and/or provide the nuclear fuel material of nuclear fuel structure 500 and structural reinforcement, or cladding, for nuclear fuel structure 500. The close-up cross-sectional views 530 and 550 show one possible arrangement of segments of fibers without fuel regions alternating with segments of fibers that include multilayer fuel regions 460, as the fibers might appear if one were to cut longitudinally along the fibers wrapped around inner rod structure 520. It may be noted, however, that the alternating pattern depicted in FIG. 5A may not result everywhere in nuclear fuel structure 500, as fibers 410/450 need not be wrapped around inner rod structure 520 so as to produce such a symmetrical, alternating pattern of multilayer fuel regions 460 with non-fuel regions. In practice, a cross-sectional view 530, 550 of fibers 410/450 might have a random pattern of multilayer fuel regions 460 arrayed with non-fuel regions. The exemplary nuclear fuel structure 500 illustrated by FIG. 5A depicts eight layers of fibers 410/450 layered over inner rod or tube structure 520 for illustrative purposes only, and it may be understood that many more layers of fibers 410/450 including multilayer fuel regions may be provided to provide more nuclear fuel within nuclear fuel structure 500 and provide greater structural reinforcement to nuclear fuel structure 500. Referencing FIGS. 4A-4D and 5A again, fiber 410 or fiber 450 of FIGS. 4A-4B may provide a greater volume of nuclear fuel material for nuclear fuel structure 500 than a volume of nuclear fuel material possible for nuclear fuel rods in current use. The volume of nuclear fuel material that can be packed into nuclear fuel structure 500 may be a matter of volume fraction of the fiber 410/450 that is nuclear fuel, and a volume fraction of fiber 410/450 taken up by the composite (CMC) materials. These are respectively obtained from equations EQ. 1 and EQ. 2 below, where: uff and ff are respectively the fuel volume fraction of the fiber, and the fiber volume fraction of the composite, dc and f are respectively the fiber core and outer diameters, and d and D the nuclear fuel structure 500 inner and outer diameters, tn and tf are the respective thicknesses of the nanoporous carbon and fuel layers, δi and δo are the nuclear fuel structure's respective inner and outer layers of monolithic SiC thicknesses, n is the number of layers in the braid, c is the fraction of fiber length covered by fuel cells, and p is the pitch distance between adjacent filaments in a layer. u ff = 4 c ( d c + t n + t f ) f 2 t f ( EQ . 1 ) f f = n · π · ( d + δ i + δ o + n · f ) ( D 2 - d 2 ) p ( EQ . 2 ) For example, consider a fuel embedded in a 30 μm fiber, as shown in the example of FIG. 4C. If it is assumed that the fuel cells to cover 65% of the fiber's length, the volume fraction of the filament occupied by nuclear fuel is 33%. This is over 2.5 times the fuel packing density of TRISO. Similar to TRISO fuel, because the fuel is fully sealed in SiC, the fissile material content can be nearly doubled compared to UO2 by embedding UC, UN, U2Si3 or even U as nuclear fuel. Referring again to FIGS. 4A-4D and 5A, the issue of fiber packing density using the fibers described herein may be examined. Table 1 compares alternate designs for fiber volume fraction, and against TRISO for fuel volume fraction for various designs of tube inner diameter (‘ID’) and outer diameter (‘OD’). The analysis also assumes inner and outer monolithic SiC layer 500 μm thick sealing in the CMC tube, and an intra-layer pitch of 40 μm center to center between filaments. Although the embodiments described so far have assumed a tube configuration, alternative embodiments may include braiding over a monolithic SiC rod, which is what design No. 3 in Table 1 represents. Table 1 shows the superior fiber packing density afforded by the ribbon architecture introduced in FIGS. 3A-3B and 5A, comparing alternate embodiments or designs for fiber volume fraction and fuel volume fraction. Indeed, ceramic tow weaving or braiding seldom can produce fiber volume fractions reaching 30%, which is important for the structural strength and toughness of the CMC. The higher fiber volume fraction is achieved without exacerbating the “labyrinth effect” which typically prevents adequate infiltration by the matrix and results in unwanted voids in the CMC. The implementation suggested by the examples treated in would leave a well-controlled pore distribution of 10 μm between filaments, allowing for even diffusion of the matrix precursors throughout the volume of the CMC. More importantly for nuclear energy applications, the proposed approach allows fuel packing densities that are up to 3 times as much as TRISO spherical fuel, with the added benefit—assuming a tube—that heat could be convectively extracted from both the inner and outer surfaces, hence enhancing heat transfer. A final, but important remark, is that embodiments including tube designs, such as tube designs 1 and 3 in Table 1 below, could be made as drop-in replacements for Zircaloy fuel rods in light water reactors (LWR). TABLE 1Comparing alternate embodiments of a nuclear fuel structurefor fiber volume fraction and fuel volume fraction.IDODFiber volumeFuel volume#(in.)(in.)LayersfractionfractionReferenceTRISO 6.5%1¼½72 32%10.5%2½117849.5%16.3%3⅛½12546.3%15.25% Referring to FIGS. 5A-5E, through the use of a nuclear fuel structure such as nuclear fuel structure 500 it may be possible to achieve a fuel assembly design for which a fuel volume fraction exceeds an annulus minimum areal fuel load q of about 0.443576. Achieving such a fuel assembly design may be characterized as a paving problem, in which the paving problem may be parameterized as described below. For example, as depicted in part by FIG. 5B, it may be assumed that an integral fuel tube will be in a square pattern with a center-to-center distance m. The inner and outer diameters of the integral fuel tube are d and D respectively and the areal fuel loading in the tube cross-section is q. Further ρ and μ designate respectively: ρ = D m ( EQ . 3 ) µ = d D ( EQ . 4 ) The paving problem may be reduced to a single tile, with an areal fuel load given by EQ. 5 below:UVFt=(π/4)qρ2(1−μ2) (EQ. 5) EQ. 5 governs the design space of feasible solutions for a fuel assembly. Assuming the fuel assembly is paved with such tiles, then the tile's areal fuel load is the same as that of the FA. FIG. 5B depicts an example cross-section of a fuel assembly 501 including fuel rods 560. For the example 5×5 grid of distributed over a 214 mm×214 mm cross-section of fuel assembly 501, as depicted in FIG. 5B, a center-to-center distance 563 m=42.8 mm. As well, for the example fuel assembly 501, an inner to outer tube diameter ratio μ≈⅓, so that the tube's wall thickness is of the order of the inner diameter. As an illustrative example, we pick an annulus ID 562 and OD 561 respectively at 12.6 mm and 41.9 mm, i.e. ρ=0.978 and μ=0.3. The tables below show two sample design configurations that exceed the required annulus areal fuel load of q=0.443576. The designs differ only in their constitutive fibers and the corresponding monolithic layer. The fuel assembly areal fuel loads for these designs are 30.88% and 30.44% respectively. Both are greater than a benchmark areal fuel load of 30.36%. TABLE 2Comparing alternate design configurations of fuel assembly having annulus arreal fuel load q > 0.443576. As the share of fuel assembly cross-section functionally allocated to fuel is increased, the share of cross-section allocated to coolant flow may be reduced compared to other fuel assembly designs. The total convective perimeter may also be reduced to 4.28 m, a 45% reduction compared to other designs. This may require a two-fold improvement of convective heat transfer, which can be achieved with a flow increase, an increased operating temperature, or a combination thereof. Fortunately in this case, higher operating temperatures are not only permitted by the material, they are also desirable for thermal efficiency. It is also worth noting that with current fuel pellet-based design, conductive heat transfer is a limiting factor due to the poor thermal conductivity of UO2. Conductive heat transfer is no longer limiting in the case of CMC containing fuel in fibers as conductivity is increased by about two orders of magnitude by the SiC matrix and fibers. FIGS. 5C-5E depict cross-sectional views of alternative design variants of the fuel assembly depicted in FIG. 5B. The alternative designs depicted by FIGS. 5C-5E may have a similar fuel assembly areal content with different convective perimeters. Referring again to FIG. 5A, any of the described embodiments of nuclear fuel structure 500, as well as alternative embodiments, may provide several additional benefits in addition to those described above. In fuel rods currently in use, a structural breach in the cladding or casing may risk exposing a large amount of the nuclear fuel contained in the fuel rod, and potentially may expose all of the radioactive nuclear fuel to the surrounding environment. Because the nuclear fuel material of nuclear fuel structure 500 is embedded inside the plurality of fibers 410/450 in a plurality of discrete and separated multilayer fuel regions, rather than being deployed inside a tube, any breach in the structure of nuclear fuel structure 500 may only expose a small amount of the total nuclear fuel material, minimizing the amount of hazardous radioactive material that may escape into the surrounding environment in the event of an accident. As well, it may be extremely difficult and extremely dangerous for nuclear fuel material to be recovered from nuclear fuel structure 500 for misuse in making weapons, as the nuclear fuel material in inner layer regions 423 is embedded within carbon and silicon carbide materials and formed over carbon and silicon carbide layers as well. Finally, because nuclear fuel is embedded and sealed within the plurality of fibers before the fibers are wrapped around inner rod structure 420 of the nuclear fuel structure 500, there may be no need to provide a cap to seal nuclear fuel structure 500. This may eliminate problems with trying to fuse a silicon carbide sealing cap to ends of a silicon carbide fuel structure or cladding. As well, pure stoichiometric β-SiC fibers are capable of being resistant for long periods of time (>8 years) in close proximity to nuclear fuel. To date, the only SiC fibers to have achieved the required stoichiometry and purity have been deposited by CVD on a tungsten or carbon core filament. Such fibers, however, come only in large diameters (90 or 140 μm) that are unsuitable for the kind of braiding or weaving as disclosed herein, let alone the presence of a foreign core filament that would not necessarily survive the nuclear reactor environment. As discussed previously, a source of SiCf tows approaching stoichiometry and purity is HNS. There are two issues of critical import associated with HNS: Composition, and foreign sourcing. HNS fibers are produced by spinning a preceramic polymer, which must then be processed at great expense of money and energy to reduce impurity levels. These extreme levels of processing drive the cost of HNS to roughly $10,000/lb. yet only reduce oxygen contents down to 0.2-0.7%, which is barely acceptable for long-lived nuclear applications. The limitation on oxygen content is inherent to chemical processes that only achieve purity in the limit. It is therefore likely to recur with any preceramic polymer approach to SiC. The issue of foreign sourcing has also long been a frustration to the US government and industry. As disclosed herein, a CVD process is capable of producing a wide range of filament diameters (10-100 μm), without the requirement of a core filament. The nuclear fuel structures and processes for making such may include printing 3C-βSiC filaments that exhibit stoichiometry and purity in a single step, and that may not require foreign sourcing. Referring again to FIG. 5A, in one alternative embodiment the plurality of fibers 410/450 may also include multiple sensor fibers. The multiple sensor fibers may be arranged with the multiple fibers including the plurality of discrete multilayer fuel regions. Sensor fibers may include, for example, silicon carbide filaments coated with zirconium diboride (ZrB2), and may include, as another example, silicon carbide filaments coated with hafnium diboride (HfB2). In one embodiment, multiple zirconium diboride coated fibers may be braided with multiple hafnium diboride coated fibers, wherein each overlap or contact point between a zirconium diboride fiber and a hafnium diboride fiber provides a high temperature thermocouple. The resulting braid would form a square matrix of embedded thermal receptors capable of mapping temperature throughout the structure. In exemplary embodiments the boron of the zirconium diboride and hafnium diboride includes the 11B isotope to ensure that the fibers may be compatible with nuclear reactors. FIGS. 6A-6E depict one example of a part of a process for forming a nuclear fuel structure, such as nuclear fuel structure 500, including forming a multilayer fuel region within at least one fiber of a plurality of fibers. The process depicted in FIGS. 6A-6E may be described as forming a multilayer fuel region by spot-coating, or depositing a layer of material of a specified thickness over a given length of the at least one fiber. FIG. 6A depicts a portion of a fiber 600 including a core filament 610. Core filament 610 may be a core region, as described above, and may include a ceramic material such as silicon carbide or hafnium carbide. In the example depicted in FIG. 6A, core filament 610 may have a substantially uniform thickness. FIG. 6B depicts core filament 610 of FIG. 6A having a material layer 620 deposited over a portion of core filament 610, where material layer 620 includes a material selected to absorb gaseous by-products of nuclear fission reactions occurring in a nuclear fuel material. Material layer 620 may correspond to a second inner layer region 422 depicted in the example of FIG. 4A. In exemplary embodiments material layer 620 may include nanoporous carbon. A material layer 620 of nanoporous carbon may be provided, for example, by chlorine etching of a part of core filament 610. Alternatively, a material layer 620 of nanoporous carbon may be spot-coated onto core filament 610. FIG. 6C depicts fiber 600 of FIG. 6B with a nuclear fuel material 630 deposited over at least a part of a length of material layer 620. Nuclear fuel material may include one or more fissile materials such as uranium, plutonium and/or related compounds, for example uranium dioxide, uranium mononitride, uranium carbide, and/or uranium silicide. Nuclear fuel material 630 may be provided, for example, by an LCVD process using, for example, uranium hexafluoride (UF6) as a precursor for forming the nuclear fuel material layer. Alternatively, uranium hexafluoride (UF6) may be used as a precursor for LCVD along with appropriate precursors such as ammonia, methane or chorosilane for the formation of a UN, UC or U2Si3 layer 630. Nuclear fuel material 630 in FIG. 6C may correspond to a first inner layer region 423 of FIG. 4A. FIG. 6D depicts fiber 600 of FIG. 6C with an outer layer region 640 deposited over nuclear fuel material 630 and material layer 620 of FIG. 4C. In exemplary embodiments, outer layer region 640 encases nuclear fuel material 630 to seal the nuclear fuel within fiber 600. Outer layer region 640 may include, for example, pyrolytic carbon deposited by, in one instance, an LCVD process. Outer layer region 640 and inner layer region 630 including the nuclear fuel material, at least, form a multilayer fuel region of fiber 600. In one embodiment, outer layer region 640 may be a first outer layer region 640, and a second outer layer region may be included. Second outer layer region may be added to add further functionality to fiber 600. For example, a second outer layer region may include a nuclear poison material, such as boron or gadolinium, that may delay activity of the nuclear fuel material of inner layer region 630. Second outer layer region, in another example, may include a material, such as carbon, that acts as a moderator of nuclear fission activity of the nuclear fuel material 630. In another example, second outer layer region may include an interphase layer for structural integration with a SiC matrix. FIG. 6E depicts fiber 600 of FIG. 6D with an overcoat layer 650 deposited over fiber 600, covering both core filament 610 and the multilayer fuel region. Overcoat layer 650 may be provided, for example, by an LCVD process. In the example embodiment illustrated by FIG. 6E, overcoat layer 650 may have a substantially uniform thickness over fiber 600, resulting in the multilayer fuel region having a “beaded” appearance, as shown. In an alternative embodiment, overcoat layer may be formed to have a variable thickness over fiber 600, which may result in greater deposition of overcoat layer 650 over core filament 610 and lesser deposition of overcoat layer 650 over the multilayer fuel region. In such an alternative embodiment, the resulting fiber 600 may have a uniform appearance, as depicted in FIG. 7E. FIGS. 7A-7E depict an alternative embodiment of the process illustrated by FIGS. 6A-6E, in which core filament 710 of fiber 700, as shown in FIG. 7A, has a variable thickness over a length of fiber 700. For example, core filament 710 may have a smaller thickness over first portions 711 of core filament 710, and greater thickness 712 over second portions 712 of core filament 710. As illustrated in FIGS. 7B-7E, the layers of a multilayer fuel region may be formed over first portions 711 so that the multilayer fuel region, as finally formed, has a thickness substantially equal to the thickness of second portions 712. FIG. 7B depicts core filament 710 of FIG. 7A having a material layer 720 deposited over first portion 711 of core filament 710, where material layer 720 includes a material selected to absorb by-products of nuclear fission reactions occurring in a nuclear fuel material. Material layer 720 may correspond to second inner layer region 462 as depicted in the example of FIG. 4B. In exemplary embodiments material layer 720 may include nanoporous carbon. A material layer 720 of nanoporous carbon may be provided, for example, by chlorine etching of a part of core filament 710. Alternatively, a material layer 720 of nanoporous carbon may be provided by spot-coating. FIG. 7C depicts fiber 700 of FIG. 7B with a nuclear fuel material 730 deposited over material layer 720. Nuclear fuel material may include one or more fissile materials such as uranium, plutonium and/or related compounds, for example uranium dioxide, uranium mononitride, uranium carbide, and/or uranium silicide. Nuclear fuel material 730 may be provided, for example, by an LCVD process. Nuclear fuel material 630 may be provided by an LCVD process using, for example, uranium hexafluoride (UF6) as a precursor for forming the nuclear fuel material layer. Alternatively, uranium hexafluoride (UF6) may be used as a precursor for LCVD along with appropriate precursors such as ammonia, methane or chorosilane for the formation of a UN, UC or U2Si3 layer 730. Nuclear fuel material 730 of FIG. 7C may correspond to inner layer region 463 of FIG. 4B. FIG. 7D depicts fiber 700 of FIG. 7C with an outer layer region 740 deposited over nuclear fuel material 730 and material layer 720 of FIG. 7C. In exemplary embodiments, outer layer region 740 encases nuclear fuel material 730 to seal the nuclear fuel within fiber 700. Outer layer region may include, for example, pyrolytic carbon deposited by, in one instance, an LCVD process. Outer layer region 740 and inner layer region 730 including the nuclear fuel material, at least, form a multilayer fuel region of fiber 700. Multilayer fuel region of fiber 700 may now have a thickness substantially equal to the thickness of second portions 712 of core filament 710. In one embodiment, outer layer region 740 may be a first outer layer region 740, and a second outer layer region may be included. Second outer layer region may be added to add further functionality to fiber 700. For example, a second outer layer region may include a nuclear poison material, such as boron or gadolinium, that may delay activity of the nuclear fuel material of inner layer region 730. Second outer layer region, in another example, may include a material, such as carbon, that acts as a moderator of nuclear fission activity of the nuclear fuel material 730. In another example, second outer layer region may include an interphase layer for structural integration with a SiC matrix. FIG. 7E depicts fiber 700 of FIG. 7D with an overcoat layer 750 deposited over fiber 700, covering both core filament 710 and the multilayer fuel region. Overcoat layer 750 may be provided, for example, by an LCVD process. The resulting fiber 700 may have a substantially uniform thickness over a length of fiber 700 following provision of overcoat layer 750. Multilayer fuel region of fiber 700 may thus be embedded within fiber 700. The embodiments of the processes depicted in FIGS. 6A-6E and FIGS. 7A-7E may not only be applied to one fiber, but may be applied to multiple fibers arrayed together in a ribbon or tow-like structure, so that each layer of a multilayer fuel region for one fiber is also formed over the other multiple fibers, as shown in FIG. 8. Each step of layer formation may be carried out in a separate deposition tool, an example of which is depicted in FIG. 8, and the multiple fibers may be conveyed from one deposition tool to the next for the next layer to be deposited. As well, the deposition tool or tools may be controlled to automatically stop and start deposition of layers over the multiple fibers, thus allowing for a plurality of discrete multilayer fuel regions to be formed along the lengths of the multiple fibers while also automatically forming non-fuel regions of the fiber that separate the plurality of discrete multilayer fuel regions. FIG. 8 depicts one example of a deposition tool 800 that may be used to form a layer of a multilayer fuel region of at least one fiber, or respective layers of respective multilayer fuel regions for a plurality of fibers. Deposition tool 800 may, for example, be a laser chemical vapor deposition (LCVD) tool. Deposition tool 800 may convey multiple fibers 830 through a conveyer inlet 815 into a deposition chamber 830. Deposition chamber may contain one or more precursor gases that may facilitate forming a layer of a multilayer fuel region. A laser 820 may be provided, through a focusing lens or window 825, to be incident on multiple fibers 840 as the multiple fibers 840 are conveyed through the deposition chamber. As the laser 820 interacts with the multiple fibers 840 and precursor gases, the desired layer of a multilayer fuel region may be deposited over portions of the multiple fibers 845. In one example, the laser may be started and stopped at defined intervals as the multiple fibers pass through the deposition tool 800, thus controlling formation of multilayer fuel regions over portions of the multiple fibers 845 and leaving other portions unprocessed (i.e., non-fuel regions of the multiple fibers). The processed multiple fibers 845 may then be conveyed out of the deposition tool 800. The multiple fibers 845 may then be conveyed to another deposition tool, in which another layer of the discrete multilayer fuel regions will be formed, or may be finished and conveyed out of the tool entirely. The resulting multiple fibers may then be further arranged in a nuclear fuel structure, such as nuclear fuel structure 500, to be wrapped around an inner rod structure, as described herein. For clarity, FIG. 8 includes close-up views 810 and 815 of the multiple fibers 840, 845 as the multiple fibers undergo LCVD processing to deposit a layer of the multilayer fuel regions. FIG. 9 depicts one embodiment of a process 900 for forming a plurality of fibers arranged in a lattice 910. Magnified views 901 and 902 depict a filament lattice 910 including a plurality of filaments 920 undergoing treatment by a plurality of laser beams 930 in a LCVD process. Plurality of laser beams 930 induce a plasma 940 around a tip of the plurality of filaments 920, adding material to the plurality of filaments 920 to form the plurality of fibers. The plurality of fibers may, in turn, be the plurality of fibers depicted in any of FIGS. 3A-8, as described above. The LCVD process of FIG. 9 may, in one example, be controlled to form a plurality of fibers having a substantially uniform thickness. In another example, the LCVD process of FIG. 9 may be variably controlled to form a plurality of fibers having variable thickness along the lengths of the plurality of fibers. For example, the plurality of laser beams 930 may have an intensity that may be increased or decreased as the plurality of fibers are formed, resulting in corresponding increases or decreases in the amount of material added to the plurality of filaments 920 of filament lattice 900. Depicted in FIG. 9 is one exemplary method and apparatus for forming a plurality of fibers from (e.g., CVD) precursors, including a reactor adapted to grow a plurality of individual fibers; and a plurality of independently controllable lasers, each laser of the plurality of lasers growing a respective fiber of the plurality of fibers. The reactor and lasers may grow the fibers according to Laser Induced Chemical Vapor Deposition. The plurality of lasers in one embodiment comprises Quantum Well Intermixing (QWI) lasers. This technique is further discussed in PCT Publication WO2013180764 (A1) dated 2013 Dec. 5, entitled “HIGH STRENGTH CERAMIC FIBERS AND METHODS OF FABRICATION”, filed as PCT Application WO2013US22053 20130118; and the following three (3) previously filed U.S. Provisional Patent Applications: U.S. Provisional Application No. 61/588,733, filed Jan. 20, 2012, entitled “METHOD AND APPARATUS FOR LARGE SCALE MANUFACTURING OF HIGH STRENGTH CERAMIC FIBERS USING A PLURALITY OF CONTROLLABLE LASERS”; U.S. Provisional Application No. 61/588,765, filed Jan. 20, 2012, entitled “NON-BRIDGING IN-SITU BORON NITRIDE COATING OF SILICON CARBIDE FIBERS IN CERAMIC MATRIX COMPOSITE MATERIALS”; and U.S. Provisional Application No. 61/588,788, filed Jan. 20, 2012, entitled “NANOCOATING SYSTEMS FOR HIGH PERFORMANCE FIBERS FOR DIRECTING MICRO-CRACKS AND ENDOWING MATRIX COMPOSITES WITH AN IMMUNE RESPONSE TO MICRO-CRACKING AND OXIDATION”. Each of the above-noted PCT and provisional applications is hereby incorporated herein by reference in its entirety. FIG. 10 depicts an exemplary embodiment of the plurality of filaments of FIG. 9 in lattice 910 resulting from variation in the laser power of laser beams 930. The filament section 1001 produced at the highest level of laser power has the largest thickness. As laser power decreases smoothly over the section of filament 1002, ending with section 1003. As laser power increases back up, so does filament thickness until it maxes out in section 1004. Alternatively, the plurality of fibers may be formed by using “Digital Spinneret” (“DS”). This technology may also be known as a ‘Fiber Laser Printer.’ The DS technology induces the growth of parallel monofilaments by massive parallelization of Laser Induced Chemical Vapor Deposition (“LCVD”), similar to the technique depicted in FIG. 9, in which laser incidence occurs at a glancing angle to a substrate. One example embodiment of a SiCf ribbon 910 that may be produced by this method is shown in FIG. 10. The resulting filaments may be β-SiC 3C with grain size distribution varying from the fiber center outward. Grains at the edge of the fiber are equiaxed. The anisotropy of the laser printing process manifests itself at the fiber's center where grains are elongated along the fiber's axis, and present an aspect ratio of 2-3 or more, with a radial size of about 25 nm or more. The grain distribution may provide additional toughness. Any one or more of the nuclear fuel structures 500 disclosed herein may not only be appropriate for use in existing nuclear reactors, and may substitute directly for metal alloy cladding fuel rods, but may also be appropriate for use in nuclear thermal propulsion (NTP) applications. Nuclear thermal propulsion (NTP) has been a technical area of interest for the United States federal government and NASA since the late 1950's. Nuclear fuel structures 500 may offer several advantages for harnessing nuclear fission in a spacecraft engine, and may provide a nuclear fuel structure design equivalent to a hexagonal fuel element building block as developed by the Nuclear Engine for Rocket Vehicle Applications (NERVA) program. The following NERVA engineering parameters may be applied to determine a fuel-in-fiber system using a nuclear fuel structure such as nuclear fuel structure 500: a) uranium fuel density 600 mg/cc; b) hexagonal element leg length 0.753″; c) 19 nozzles equivalent to 19 channels found in hexagonal element. The resulting silicon carbide-silicon carbide (SiC—SiC) nozzle geometry would utilize a notional 2 millimeter (mm) inner diameter/4 mm outer diameter SiC monolithic tube mandrel and require 2 meters of fibber ribbon per inch of tube. The fiber volume fraction from this design would be 30%. With micro-encapsulated fuel cells covering 50% of the fiber's length, the fiber fuel content would be 13.4% and thus equivalent to the NERVA hexagonal fuel. The ribbon-wound mandrel structure would subsequently be infiltrated with a SiC matrix by either the chemical vapor infiltration or the polymer impregnation and pyrolosis process. In this manner, the SiCf—SiCm fuel-in-fiber composite nozzle structure would be fabricated. An interesting variation on the fuel layer composition would be to deposit thorium (232Th) as a fertile material for subsequent neutron activation and transmutation to a fissile uranium species (233U). There may be multiple advantages of using a nuclear fuel structure 500 for deployment in NTP. These may include the following: 1) Manufacturing ease—the LCVD additive manufacturing approach can produce a full fuel-in-fiber structure in-situ without the necessity of additional post-fabrication processing. There are multiple levels of economic savings possible via this method. An LCVD deposition system, as disclosed herein, is relatively straightforward, easily scalable, and is composed of significantly less expensive equipment than other CVD and additive manufacturing processes, thus reducing the capital outlay requirements to establish a high throughput manufacturing plant. The operational costs for running and maintaining such fiber production systems are similarly less expensive, including the outlays for raw materials and consumables. 2) Operational temperature range capability—the high purity materials deposited in the baseline fiber and overcoat layers, in particular the lack of oxygen and other detrimental contaminants in the structure, will be able to survive the 2600K operating temperature requirements for a NTP engine. 3) Favorable SiC thermal conductivity—the relatively high thermal conductivity of SiC enhances the ability to remove the heat generated by the fission process occurring in the fuel layers along the fiber length. SiC thermal conductivity values generally range in the 100-150 Watts/meter-K at room temperature, falling to 20-30 W/m-K at temperatures greater than 1500 C. The concept of a SiCf—SiCm composite nozzle with high heat transfer efficiency could find application in the NERVA NTP engine concept. Fuel-in-fiber wound SiC nozzles would be located in bored passages through the graphite (or other material) block in which H2 propellant travels through the tube inner diameter and is heated. 4) Capture of fission gas by-products—the nano-porous carbon layer adjacent to the deposited fuel layer in the fuel-in-fiber design may serve as a tortuous path medium that effectively traps the fission gas by-products, thus preventing these materials' release into the propellant stream. 5) Utilization of uranium nitride (UN) fuel—the overall integrated fuel package of a SiCf—SiCm nozzle would provide a barrier to exposure of a UN fuel layer to H2 propellant, thus minimizing the chemical attack and degradation of this fuel material. The advantages of UN fuel include higher uranium fuel density, significantly higher melting point (approaching 3000K at 1 atm) and enhanced thermal conductivity (approximately 20 W/m-K). 6) Safety enhancements—the issue of nuclear fuel safety is obviously a central concern for implementation of NTP technology that needs to be addressed to the satisfaction of government regulators and the general population. Three example safety considerations are: a. Accident/crash tolerance in which the integrity of the fuel encapsulation is maintained. The nuclear fuel structure 500 described herein would lead to enhanced protection because the fuel component is enclosed in a multitude of physically isolated micro-cells protected by outer coating layer(s) and embedded in a solid matrix. Should a fracture develop, only a minute fraction of the cells can be breached, hence greatly limiting the release of fissile material in case of a crash. b. From the NERVA program, a major issue arose as fissile material was ejected into the propellant stream during testing due to hydrogen gas etching of the graphite block with UO2 or UC2 particles. This chemical attack and material release would be mitigated due to the structure of the nozzle as well as having the nozzles embedded in a solid graphite matrix. c. For nozzles prepared with fertile nuclear material rather than fissile, the risks of diversion for WMDs is greatly diminished, and unused tubes will not represent a high-level nuclear waste. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises”, “has”, “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises”, “has”, “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of one or more aspects of the invention and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects of the invention for various embodiments with various modifications as are suited to the particular use contemplated. |
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048291919 | summary | BACKGROUND OF THE INVENTION This invention is a switchable radioactive neutron source device. It can provide a controllable ON or OFF generation of neutrons or a coded pulsed generation of neutrons by a sequence of switching. This neutron source device has various present and potential applications both in scientific research and in inspection and analysis techniques. Current neutron source devices are of two types: the standard radioiosotope source and the accelerator source. The standard radioisotope source employs a radioactive mixture of alpha emitter and target material which emits neutrons constantly. Therefore, it must be extensively shielded to protect operating personnel even when not in use. The accelerator neutron source requires bulky equipment, considerable electric power, and highly trained operating personnel, yet provides low reliability and maintainability. In applications involving inspection of a sample for content of fissile material, a standard neutron source is used for irradiation of a sample, after which a count is made of delayed neutrons from fissionable isotopes in the samples. Typically, an object to be analyzed is shuttled into the presence of the radioisotope source from a remote shielded area and back again. A potential application employing neutron irradiation is the detection of explosive materials attempted to be smuggled onto aircraft. High explosives tend to be rich in nitrogen, and so a possible detection scheme would have a suitcase on a conveyor belt passing through a neutron flux long enough for it to be tested for the presence of an unusual amount of nitrogen. Possible gamma ray detection techniques for this purpose include spectral analysis of prompt gamma rays from neutron capture or from inelastic neutron scattering or of decay gammas from neutron activation. Other potential applications include nondestructive testing and subcriticality monitoring. It is therefore an object of this invention to provide a reliable neutron source device that can be switched ON for use and OFF when not in use to eliminate costly shielding. It is a further object of this invention to provide a neutron source that is portable and easy to use. It is still a further object of this invention to provide a neutron source that can be pulsed at predetermined intervals for detection techniques that use time-coded sources. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. SUMMARY OF THE INVENTION This invention is an apparatus that provides a controllable source of neutrons by means of a series of disks, alternately containing alpha emitters and targets which are brought into alignment for generation of neutrons and brought out of alignment to cease generation of neutrons. This controllable feature provides improved ease of use for current applications and enables new applications relating to analysis and inspection of samples through neutron irradiation. |
claims | 1. An X-ray computed tomography apparatus, comprising: an X-ray generator configured to generate a first X-ray in a pre-scan mode and a second X-ray in an image scan mode; an X-ray detector configured to detect a first transmission X-ray exposed through a specimen to a first exposure width of the X-ray detector along a body axis of the specimen, resulting from the first X-ray at a first scanning position in the pre-scan mode and to detect a second transmission X-ray exposed through the specimen to a second exposure width of the X-ray detector along the body axis of the specimen, resulting from the second X-ray at a second scanning position in the image scan mode, the first exposure width being narrower than the second exposure width; a controller configured to control the first scanning position and the second scanning position; and a display configured to display a first image based on the first transmission X-ray detected by the X-ray detector and a second image based on the second transmission X-ray detected by the X-ray detector. 2. The apparatus according to claim 1 , further comprising a collimator, provided in between the X-ray generator and the X-ray detector, configured to collimate the first X-ray and the second X-ray, and wherein the controller is further configured to control the collimator to change a collimating width so that the fist transmission X-ray and the second transmission X-ray are exposed to the first exposure width and the second exposure width of the X-ray detector, respectively. claim 1 3. The apparatus according to claim 1 , wherein the controller is further configured to control the X-ray generator to change a generation angle along the body axis so that the first transmission X-ray and the second transmission X-ray are exposed to the first exposure width and the second exposure width of the X-ray detector, respectively. claim 1 4. The apparatus according to claim 1 , wherein, when a distance between the X-ray generator and the X-ray detector is variable, the first transmission X-ray is exposed to the first exposure width of the X-ray detector when the distance is a first distance and the second transmission X-ray is exposed to the second exposure width of the X-ray detector when the distance is a second distance longer than the first distance. claim 1 5. The apparatus according to claim 1 , wherein an intensity of the first X-ray is lower than an intensity of the second X-ray. claim 1 6. The apparatus according to claim 1 , wherein a number of slices in a single scan in the pre-scan mode is smaller than a number of slices in a single scan in the image scan mode. claim 1 7. The apparatus according to claim 1 , wherein the X-ray detector comprises a plurality of detecting elements along the body axis; and wherein each scanning slice in the pre-scan mode uses at least two of the plurality of detecting elements. claim 1 8. The apparatus according to claim 1 , wherein the X-ray detector comprises a plurality of detecting elements along the body axis; and wherein the first exposure width is over a first number of the plurality of detecting elements along the body axis and the second exposure width is over a second number of the plurality of detecting elements along the body axis, the first number being smaller than the second number. claim 1 9. The apparatus according to claim 8 , further comprising a data acquisition unit, comprising a plurality of data acquisition elements, configured to acquire data output from the X-ray detector; and a switch configured to switch a connection between the plurality of detecting elements and the plurality data acquisition elements, and wherein the connection is kept identical in between the pre-scan mode and the image scan mode. claim 8 10. The apparatus according to claim 1 , further comprising a data acquisition unit, comprising a plurality of data acquisition elements, configured to acquire data output from the X-ray detector, and wherein a predetermined number of the data acquisition elements are commonly used in both the pre-scan mode and the image scan mode. claim 1 11. The apparatus according to claim 10 , further comprising a reconstruction unit configured to reconstruct an image based on at least a portion of the data acquired by the data acquisition unit, and wherein a remaining portion of the data acquired by the data acquisition unit is not used for reconstruction by the reconstruction unit in the pre-scan mode. claim 10 12. The apparatus according to claim 1 , wherein the first scanning position is fixed along the body axis. claim 1 13. The apparatus according to claim 1 , wherein the second scanning position is movable along the body axis. claim 1 14. The apparatus according to claim 1 , wherein the second scanning position is achieved by moving at least the X-ray generator and the X-ray detector from the first scanning position relative to the body axis in response to an manual designation by an operator. claim 1 15. The apparatus according to claim 1 , wherein the second scanning position is achieved by moving at least the X-ray generator and the X-ray detector from the first scanning position relative to the body axis in response to that a CT number of the first image has reached a predetermined reference value. claim 1 16. The apparatus according to claim 1 , further comprising a calculator configured to calculate a CT number in a predetermined region of the first image, and wherein a scan in the pre-scan mode is automatically terminated when the specimen is injected with a contrast agent and the CT number calculated by the calculator has reached a predetermined reference value. claim 1 17. The apparatus according to claim 16 , wherein the controller is further configured to change the first scanning position to the second scanning position, responsive to termination of the scan in the pre-scan mode; and wherein a scan in the image scan mode is initiated at the second scanning position in a predetermined time after the termination of the scan in the pre-scan mode. claim 16 18. The apparatus according to claim 1 , wherein the display is further configured to display a CT number in a predetermined region of the first image in the pre-scan mode. claim 1 19. The apparatus according to claim 1 , wherein the X-ray detector comprises a plurality of detecting elements along the body axis; and wherein first data based on detection by one of the plurality of detecting elements under the first exposure width are stacked with second data based on detection by at least one other of the plurality of the detecting elements under the first exposure width in the pre-scan mode. claim 1 20. The apparatus according to claim 19 , further comprising a reconstruction unit configured to reconstruct an image based on third data resulting from the stack of the first data and the second data, and wherein the data stacking in the pre-scan mode is performed before the first data and the second data are supplied to the reconstruction unit. claim 19 21. The apparatus according to claim 1 , further comprising a data acquisition unit, comprising a plurality of data acquisition elements, configured to acquire data output from the X-ray detector, and wherein the X-ray detector comprises a plurality of detecting elements along the body axis; and wherein at least one of the detecting elements to be used, a slice thickness to be used in a single slice, and at least one of the data acquisition elements to be used are common between the pre-scan mode and the image scan mode. claim 1 22. The apparatus according to claim 1 , wherein a number of slices in a single scan in the pre-scan mode is smaller than a number of slices in a single scan in the image scan mode according to a difference between the first exposure width and the second exposure width. claim 1 23. The apparatus according to claim 1 , wherein the X-ray detector comprises a plurality of detecting elements along the body axis; and wherein a number of the detecting elements to be used in the pre-scan mode is smaller than another number of the detecting elements to be used in the image scan mode according to a difference between the first exposure width and the second exposure width. claim 1 24. The apparatus according to claim 1 , further comprising a data acquisition unit, comprising a plurality of data acquisition elements, configured to acquire data output from the X-ray detector, and wherein the X-ray detector comprises a plurality of detecting elements along the body axis; and wherein each of the plurality of data acquisition elements acquires the data output from one or more of the plurality of detecting elements. claim 1 25. The apparatus according to claim 1 , further comprising a data acquisition unit, comprising a plurality of data acquisition elements configured to acquire data output front the X-ray detector; and a reconstruction unit configured to reconstruct an image based on the data output acquired by the data acquisition unit; wherein the X-ray detector comprises a plurality of detecting elements along the body axis; and wherein information from one or more of the data acquisition elements not corresponding to detecting elements under the first exposure width is not used as the data output for reconstruction of the image by the reconstruction unit in the pre-scan mode. claim 1 26. The apparatus according to claim 1 , further comprising an input device configured to input information regarding determining an image scan condition for the image scan mode; and wherein the controller is further configured to determine the image scan condition for the image scan mode based on the information and also to automatically determine a pre-scan condition for the pre-scan mode based on the determined image scan condition. claim 1 27. The apparatus according to claim 26 , wherein, when a plurality of predetermined pre-scan conditions are prepared, each of which corresponding to each of a plurality of parts of the specimen, for the image scan condition, the controller determines one of the plurality of predetermined pre-scan conditions, as a determined pre-scan condition, which corresponds to one of the plurality of parts indicated in the determined image scan condition. claim 26 28. The apparatus according to claim 1 , further comprising a reconstruction unit configured to reconstruct an image based on data resulting from detection by the X-ray detector, and wherein the reconstruction unit performs reconstruction in a real time reconstruction manner in the pre-scan mode. claim 1 29. An X-ray computed tomography apparatus, comprising; an X-ray source configured to radiate an X-ray to a specimen; a collimator configured to vary a collimating width, along a body axis of the specimen, which determines an X-ray width exposed to the specimen; a detector, comprising a plurality of detecting elements along the body axis, configured to detect a transmission X-ray transmitted from the specimen; a data acquisition unit, comprising a plurality of data acquisition elements along the body axis, configured to acquire data output from the detector; is an implementing unit configured to implement a scan around the specimen with the X-ray source and the X-ray detector; a controller configured to control a scan mode to switch from a pre-scan to an image scan, and to control the collimator to make the collimating width wider in the image scan than in the pre-scan, the pre-scan being for monitoring a CT number in a predetermined region of interest of the specimen, the image scan being for scanning an examining region of the specimen; and a reconstruction unit configured to reconstruct a tomography of the specimen based on the data output acquired in the pre-scan, and also to reconstruct an image of the specimen based on projection data acquired in the image scan. 30. The apparatus according to claim 29 , further comprising a switch configured to switch a number of the data acquisition elements to be used; and wherein the controller is further configured to control the switch so that the number of the data acquisition elements to be used is identical in both the pre-scan and the image scan. claim 29 31. The apparatus according to claim 29 , further comprising: claim 29 a setting unit, when a plurality of slices are obtained in each single rotation of the scanning, configured to set a number of the slices and a slice width common to each of the slices, the slice width being defined as a number of the slices multiplied by a slice thickness common to the each of the slices; and a switch, provided in between the detector and the data acquisition unit, configured to switch a connection between the detecting elements and the data acquisition elements; and wherein the controller is further configured to control the switch so as to keep the connection identical in both the pre-scan and the image scan even when the setting unit sets one of the number of the slices and the slice width to be different in between the pre-scan and the image scan. 32. The apparatus according to claim 31 , wherein the controller is still further configured to control that the data output from at least a predetermined one of the detecting elements to at least one connected data acquisition element are not used in an image reconstruction by the reconstruction unit, the at least predetermined one of the detecting elements being not used in the pre-scan in accordance with the number of the slices and the slice width set by the setting unit. claim 31 33. The apparatus according to claim 29 , wherein, when a plurality of slices are obtained in each single rotation of the pre-scan and the image scan, the controller is also configured to set a slice thickness common to each of the slices and a condition using the data acquisition elements to be common in both the pre-scan and the image scan, and further configured to set a different number of the detecting elements to be used in between the pre-scan and the image scan. claim 29 34. A method of performing a scan in an X-ray computed tomography apparatus, comprising steps of; generating a first X-ray in a pre-scan mode; detecting with an X-ray detector a first transmission X-ray exposed through a specimen to a first exposure width of the X-ray detector along a body axis of the specimen, resulting from the first X-ray at a first scanning position in the pre-scan mode; displaying a first image based on the first transmission X-ray; generating a second X-ray in an image scan mode; detecting with the X-ray detector a second transmission X-ray exposed through the specimen to a second exposure width of the X-ray detector along the body axis of the specimen, resulting from the second X-ray at a second scanning position in the image scan mode, the second exposure width being wider than the first exposure width; displaying a second image based on the second transmission X-ray; and controlling the first scanning position and the second scanning position. 35. A computer program product on which is stored a computer program for performing a scan in an X-ray computed tomography apparatus, the computer program having instructions, which when executed, perform steps comprising: generating a first X-ray in a pre-scan mode; detecting with an X-ray detector a first transmission X-ray exposed through a specimen to a first exposure width of the X-ray detector along a body axis of the specimen, resulting from the first X-ray at a first scanning position in the pre-scan mode; generating a second X-ray in an image scan mode; displaying a first image based on the first transmission X-ray; detecting with the X-ray detector a second transmission X-ray exposed through the specimen to a second exposure width of the X-ray detector long the body axis of the specimen, resulting from the second X-ray at a second scanning position in the image scan mode, the second exposure width being wider than the first exposure width; displaying a second image based on the second transmission X-ray; and controlling the first scanning position and the second scanning position. |
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abstract | A process for encapsulating a radioactive object to render the object suitable for shipment and/or storage, and including the steps of preparing a plastic material, causing the plastic material to react with a foaming agent, generating a foaming plastic, encapsulating the radioactive object in the foaming plastic, and allowing the foaming plastic to solidify around the radioactive object to form an impervious coating. |
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claims | 1. A ventilated apparatus for transporting and/or storing radioactive materials comprising:an overpack body having an outer surface and an inner surface forming an internal cavity about a longitudinal axis;a base enclosing a bottom end of the cavity;a lid enclosing a top end of the cavity;a plurality of outlet ducts, each of the outlet ducts forming an air outlet passageway from a top portion of the cavity to an external atmosphere;a bottom portion of the overpack body formed by a plurality of curved segments, each of the curved segments extending circumferentially from a first end wall having a convex portion to a second end wall having a concave portion; andthe curved segments circumferentially surrounding the longitudinal axis and arranged in an intermeshing configuration such that for all adjacent curved segments: (1) the convex portion of the first end wall of one of the curved segments at least partially nests within the concave portion of the second end wall of an adjacent one of the curved segments; and (2) the convex portion of the first end wall of the one of the curved segments is spaced from the concave portion of the second end wall of the adjacent one of the curved segments, thereby forming an inlet duct forming an air inlet passageway 160 from the external atmosphere to a bottom portion of the cavity. 2. The ventilated apparatus according to claim 1 wherein each of the curved segments has a convex outer wall that forms a portion of the outer surface of the overpack body and a concave inner wall that forms a portion of the inner surface of the overpack body; and wherein the convex outer walls of the curved segments lie in a first reference cylinder and the concave inner walls of the curved segments lie in a second reference cylinder. 3. The ventilated apparatus according to claim 1 wherein, for each of the air inlet passageways, a line of sight does not exist from the cavity to the external atmosphere through the air inlet passageway. 4. The ventilated apparatus according to claim 1 wherein each of the air inlet passageways comprises a first radial section extending from the outer surface of the overpack body, a curved section extending from the first radial section, and a second radial section extending from the curved section to the inner surface of the overpack body. 5. The ventilated apparatus according to claim 1 wherein each of the curved segments is a singular uninterrupted member. 6. The apparatus according to claim 1 wherein the overpack body comprises an inner metal shell and an outer metal shell concentrically arranged so that a gap exists between the inner and outer shells, a concrete material provided in the gap. 7. The apparatus according to claim 6 further comprising a plurality of lower metal inter-shell connectors extending between the inner and outer metal shells, the lower metal inter-shell connectors defining the inlet ducts. 8. The apparatus according to claim 1 wherein each of the inlet ducts has a height and a width, and wherein a ratio of height to width is at least 10:1. 9. The apparatus according to claim 1 wherein the air outlet passageways of the outlet ducts are at least partially defined by an interface between the lid and the overpack body. 10. The apparatus according to claim 1 further comprising a hermetically sealed canister for containing radioactive materials positioned within the cavity so that a first reference plane that is perpendicular to the longitudinal axis of the overpack body intersects both the canister and the inlet ducts. 11. The apparatus of claim 10 further comprising a set of tubular shock absorbers coupled to the inner surface of the overpack body, the set of tubular shock absorbers positioned so that a second reference plane that is perpendicular to the longitudinal axis of the overpack body intersects both a lid of the canister and the set of tubular shock absorbers. 12. A ventilated apparatus for transporting and/or storing radioactive materials comprising:an overpack body having an outer surface and an inner surface forming an internal cavity about a longitudinal axis;a base enclosing a bottom end of the cavity;a lid enclosing a top end of the cavity;a plurality of outlet ducts, each of the outlet ducts forming an air outlet passageway from a top portion of the cavity to an external atmosphere;a bottom portion of the overpack body formed by a plurality of segments, each of the segments extending from a first end wall having a projection to a second end wall having a channel; andthe segments circumferentially surrounding the longitudinal axis and arranged in an intermeshing and spaced-apart configuration such that the projections of the first end walls of the segments project into the channels of the second end walls of adjacent ones of the segments, thereby forming an inlet duct between adjacent ones of the segments that includes an air inlet passageway from the external atmosphere to a bottom portion of the cavity through which a line of sight does not exist from the cavity to the external atmosphere. 13. The ventilated apparatus according to claim 12 wherein, for each of the segments, the channel and the projection extend along the entire height of the segment. 14. The ventilated apparatus according to claim 12 wherein, for each of the segments, the first end wall further comprises a first shoulder on a first side of the projection and a second shoulder on a second side of the projection opposite the first side. 15. The ventilated apparatus according to claim 12 wherein, for each of the segments, the second end wall comprises a first channel wall and a second channel wall that define the channel therebetween. 16. The ventilated apparatus according to claim 12 wherein each of the segments has a convex outer wall that forms a portion of the outer surface of the overpack body and a concave inner wall that forms a portion of the inner surface of the overpack body; and wherein the convex outer walls of the curved segments lie in a first reference cylinder and the concave inner walls of the curved segments lie in a second reference cylinder that is concentric to the first reference cylinder. |
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