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claims | 1. A system comprising:a transparent radiation shield comprising a container holding a transparent ammonium metatungstate solution, the transparent ammonium metatungstate solution having a density of greater than 1.5 grams/(cubic centimeter). 2. The system of claim 1, wherein:the transparent radiation shield is installed on mechanical or industrial equipment. 3. The system of claim 1, wherein:the transparent radiation shield is installed on medical equipment or facility. 4. The system of claim 1, wherein:the transparent radiation shield is wearable by a human. 5. A method comprising:placing an ammonium metatungstate solution with a density of approximately 2.35 grams/(cubic centimeter) in a container of a transparent radiation shield. 6. The method of claim 5, wherein:making the ammonium metatungstate solution by adding ammonium metatungstate powder in an amount greater than 1.5 grams per milliliter of water. 7. The method of claim 5, further comprising:making the ammonium metatungstate solution by adding an ammonium metatungstate powder in installments to a mixing vessel comprising water; andmixing the ammonium metatungstate powder with the water between installments. 8. The method of claim 5, further comprising:making the ammonium metatungstate solution by mixing the ammonium metatungstate solution in a mixing vessel for a predetermined time period. 9. The method of claim 5, further comprising:making the ammonium metatungstate solution by adjusting temperature in a mixing vessel. 10. The method of claim 5, further comprising:making the ammonium metatungstate solution by adjusting a rotational speed of a mixer in a mixing vessel. 11. The method of claim 5, further comprising:making the ammonium metatungstate solution by adjusting temperature in a mixing vessel to between 14° C. and 99° C. 12. The method of claim 5, further comprising:making the ammonium metatungstate solution by adjusting pH in a mixing vessel comprising ammonium metatungstate powder and water. 13. The method of claim 5, further comprising:making the ammonium metatungstate solution by adjusting pH in a mixing vessel comprising ammonium metatungstate powder and water to a level between 2.0 and 4.5. 14. The method of claim 5, further comprising:making the ammonium metatungstate solution by adding nitric acid to a mixing vessel comprising ammonium metatungstate powder and water. 15. The method of claim 5, further comprising:making the ammonium metatungstate solution by causing transfer of the ammonium metatungstate solution from a first container to a second container substantially without exposing the ammonium metatungstate solution to air. 16. A radiation shield comprising a container holding an ammonium metatungstate solution with a density of greater than 1.5 grams/(cubic centimeter), wherein the ammonium metatungstate solution is filtered to remove particles greater than 15 microns in size. 17. The radiation shield of claim 16, wherein:the ammonium metatungstate solution has a Raman spectra with peaks at approximately 884 cm−1, approximately 923 cm−1, and approximately 972 cm−1. 18. The radiation shield of claim 16, wherein:the ammonium metatungstate solution comprises greater than 30% tungsten by weight. 19. The radiation shield of claim 16, wherein:the ammonium metatungstate solution has a gamma ray mass attenuation coefficient of at least 0.06 (square centimeters)/gram. 20. The radiation shield of claim 16, wherein:the container is a polycarbonate container, which provides an effective barrier to penetration of any alpha particle, beta particle, gamma ray, bremsstrahlung, and other secondary radiation. |
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abstract | A hybrid nuclear reactor for producing a medical isotope includes an ion source for producing an ion beam from a gas, a target chamber including a target that interacts with the ion beam to produce neutrons, and an activation cell positioned proximate the target chamber and including a parent material that interacts with the neutrons to produce the medical isotope via a fission reaction. |
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description | The present invention generally discloses a micro-positioning motion transducer in the form of a flexure device. The flexure device includes a rigid frame or support structure securely carrying a flexure carriage assembly. The flexure carriage assembly includes a carriage having a plurality of structures which permit high precision translational movement in an X and a Y direction defining a substantially flat plane of movement. The structure precisely transmits forces at least partially applied in the X direction that are converted to translational movement of a translational section only in the X direction. The structure also transmits forces at least partially applied in the Y direction into translational movement of the translational section only in the Y direction. The structure essentially prevents any substantial movement of the translational section of the carriage in a Z direction perpendicular to the X-Y plane. The flexure carriage assembly includes a pair of piezoelectric assemblies that drive the translating section of the flexure carriage. One piezoelectric element drives the translating element in the X direction and the other piezoelectric element assembly drives the translating element in the Y direction. The piezoelectric assemblies are oriented substantially parallel to the Z axis, though they impart precision movement in the X-Y plane perpendicular to the Z axis. Referring now to the drawings, FIG. 1 illustrates generally a flexure device 20 having a frame or support structure 22 and a flexure carriage assembly 24 rigidly affixed to and supported by the frame. The carriage assembly 24 includes a carriage 25 and also includes a pair of piezoelectric assemblies 26 each having opposed distal end couplers 28 fixed to the frame 22. The piezoelectric assemblies 26 have a central coupler 30 fixed to a translating section 29 of the flexure carriage 25. In general, the frame or support structure 22 can be a separate frame element as is illustrated in FIG. 1 that is further attached to a suitable instrument or device. Alternatively, the frame 22 can be an integral portion of the instrument or device (not shown). The piezoelectric elements 26 are energized from a source of electric energy (also not shown) and, in accordance with known principles of such elements, the piezoelectric assemblies 26 move according to the applied energy. Since the elements have a central coupler 30 coupled to the translating section 29 of the flexure carriage 25, the translating section as described in detail below, moves in accordance with the motion of the piezoelectric assemblies 26. As described and shown herein, the movement of the piezoelectric assemblies 26 and the translating section 29 of the flexure carriage 25 is highly precise and has a relatively large range of motion. However, as discussed above, the typical and desirable range of motion for such a device is small in reality, for example, on the order of one xc3x85 to about a few hundred xcexc. FIG. 2A illustrates the flexure carriage assembly 24 in perspective view. FIG. 2B illustrates the carriage 25 in perspective view. FIGS. 3 and 4 illustrate two sides in plan view of the carriage 25 which have been arbitrarily selected for illustration. The carriage need not have a front, back and designated sides. However, for illustrative purposes, FIG. 3 illustrates a view arbitrarily shown as a back surface of the carriage 25, and FIG. 4 illustrates a side surface of the carriage which can be either side of the carriage when the carriage is rotated 90 degrees about a vertical axis relative to the views in FIGS. 3 and 4. Turning again to FIGS. 2-4, the flexure carriage 25 of the carriage assembly 24 is in the form of a rectangular three-dimensional structure. The carriage 25 is preferably made from a substantially rigid material such as stainless steel or the like wherein the material is not too brittle, soft or flexible so that it may perform the intended functions of the invention. The carriage 25 is comprised of a substantially symmetrical structure and is described herein including a top and bottom end as well as front, rear and side surfaces. However, these designations are arbitrarily selected and utilized only for simplicity of description. It will be obvious to one of ordinary skill in the art that the carriage as well as the flexure device 20 can be oriented in any manner and manipulated to any orientation without departing from the scope of the invention. With that in mind, FIG. 2A illustrates the flexure carriage assembly 24 and FIG. 2B illustrates the carriage 25. The carriage 25 includes four elongate vertical columns disposed parallel to one another and spaced equal distance from one another. Each of the elongate columns includes a first end, herein designated as a top end and a second end, herein designated as a bottom end. The four elongate columns are identified herein for simplicity as 32A, 32B, 32C and 32D. The respective top ends are identified as 34A, 34B, 34C and 34D. The respective bottom ends 36 are represented by 36A, 36B, 36C and 36D. Each of the elongate columns is essentially the same length and oriented so that each of the top ends terminate in the same plane relative to one another and each of the bottom ends terminate in the same plane relative to one another. Each of the top ends of the carriage 25 are interconnected to adjacent top ends of corresponding elongate columns by first cross members 38A-D. For example, the cross member 38A extends between the top ends 34A and 34B of the adjacent elongate columns 32A and 32B. Similarly, the cross member 38B extends between the top ends 34B and 34C, the cross member 38C extends between the top ends 34C and 34D, and the cross member 38D extends between the top ends 34D and 34A. The first cross members 38A-D combine to define an arbitrary top 39 of the carriage 25. Similarly, four second cross members 40A-D extend between the bottom ends 36A-D of the elongate columns 32A-D in an identical manner. The four second cross members 40A-D combine to define an arbitrary bottom 41 of the carriage 25. Each of the cross members 38A-D and 40A-D are arranged at right angles relative to one another when viewed from either the top 39 or the bottom 41 of the carriage 25. Thus, the combination of the cross members 38A-D and 40A-D along with the elongate columns 32A-D define a right angle three dimensional parallelogram. In the present embodiment, all of the cross members are of equal length so that the top 39 and bottom 41 are square. A symmetrical shape is preferred for the carriage but the overall cross section need not be a square shape in order to fall within the scope of the invention. The elongate columns 32A-D and the cross members 38A-D and 40A-D are each preferably integrally formed with one another and therefore, without more, would form a rigid frame structure. However, the carriage 25 of the flexure device 20 must allow for certain flexible movements as described below in detail. The flexible nature of the carriage 25 is provided by adding a plurality of flexures 50 to the structure of the carriage 25. The construction of one flexure 50 is now described in detail below. Subsequently, the placement of the flexures 50 on the carriage 25 is described along with the function and flexible nature of the carriage. In order to simplify the description of the carriage 25, a coordinate system is arbitrarily chosen and utilized in conjunction with the discussion herein. Referring to FIG. 2B, an X axis or X coordinate is defined along one axis perpendicular to the four elongate columns 32A-D and perpendicular to arbitrary side surfaces 52 and surface 54. A Y axis as illustrated in FIG. 2B is perpendicular to the X axis and also perpendicular to an opposed front 56 and back 58 of the carriage 25. The front and back 56 and 58, respectively, are perpendicular to the sides 52 and 54. A Z axis is also illustrated in FIG. 2B disposed parallel to and between to the four elongate columns 32A-D and perpendicular to the X-Y plane. The arbitrary back 58 is illustrated in FIG. 4 and the arbitrary side 52 is illustrated in FIG. 3. FIG. 5 illustrates the construction of one flexure 50 taken at the juncture between the elongate column 32C at its top end 34C and the cross member 38B. FIG. 6 illustrates the same flexure 50 viewed 90 degrees relative to the flexure shown in FIG. 5. Each flexure 50 includes an interior first material web 60 nearer the X and Y plane and an exterior second material web 62 nearer either the top 39 or bottom 41 of the carriage and essentially perpendicular relative to the first material web 60. Each material web is formed by creating a pair of opposed slots 64 perpendicularly or transversely into opposed surfaces of the appropriate elongate column 32. Thus, each material web 60 and 62 is a thin web or membrane of material between the slots 64 and extends the entire width of the appropriate elongate column 32 when viewed into one of the slots 64. Therefore, the view of the flexure 50 in FIG. 5 shows the interior material web 60 on an end view so that the thin-walled construction is visible. The exterior material web 62 is illustrated lengthwise. The same flexure 50 is illustrated in FIG. 6 where the interior material web 60 is lengthwise and the exterior material web 62 is in an end view. Each flexure 50 permits linear movement in the X direction and the Y direction but not in the Z direction. The web 60 will permit slight lateral movement of the elongate column 32C relative to the cross member 38B when a force is applied in the X direction. The web 62, because it is oriented lengthwise in the X direction and rigidly connected to both the cross member 38B and the elongate column 32C, prevents movement in the X direction. However, when viewed at a 90 degree angle as shown in FIG. 6, the web 62 permits movement in the Y direction upon an applied Y direction force. Each flexure 50 therefore permits movement in the X direction and the Y direction upon an applied force, respectively, in the X or the Y direction. Each flexure 50 also prevents any movement in the Z direction based on the rigid connections between each structural element connected to each flexure 50. The construction of each flexure 50 also enhances direct movement only in the direction of the applied force in that one web is oriented to permit movement only in one linear direction wherein the other web is oriented to permit movement in only one linear direction perpendicular to the linear direction of movement for the other web. Each web is also constructed to prevent any movement at that web other than in its intended direction of movement. Therefore, each flexure 50 provides a precise X or Y flexure according to the applied force and prevents any other movement and particularly prevents movement in the Z direction. As best illustrated in FIG. 2A, a flexure 50 is disposed at each top end 34A-D and each bottom end 36A-D between the respective elongate columns 32A-D and cross members 38A-D and 40A-D. Each flexure 50 disposed at the top ends 34 of the elongate columns 32 is oriented so that all interior webs 60 are oriented in the same direction relative to one another and all exterior webs 62 are oriented in the direction relative to one another. Each of the flexures 50 disposed at the bottom ends 36 of the elongate columns 32 is also oriented identically relative to one another. Each flexure 50 disposed at opposite ends of each of the elongate columns 32A-D are preferably oriented as mirror images of one another to provide symmetry in the construction of the carriage 25. For example, the flexures 50 on ends 34A and 36A of the elongate column 32A each have the exterior material webs 62 oriented parallel relative to one another and have the interior material webs 60 oriented parallel relative to one another. Each of the elongate columns 32A-D also has at least one, and preferably, a pair of flexures 50 disposed near the center defined by the X axis and Y axis noted in FIG. 2A with one flexure 50 being disposed on each side of the mid- line or X-Y plane. Again, each of these interior flexures 50 are disposed so that they are mirror images relative to one another. Therefore, the interior material webs 60 are oriented parallel relative to one another and the exterior material webs 62 are also oriented parallel relative to one another. Additionally, each of the flexures disposed near the mid-line 50 is oriented identically on each of the elongate columns 32A-D to provide uniform flexure. The translating section 29 is connected to each of the mid-line flexures 50 of the carriage. The translating section 29 is disposed corresponding to the X-Y plane of the carriage 25 so that the carriage is essentially symmetrical on either the top portion or the bottom portion of the carriage 25 relative to the translating section 29. A force F applied to a back surface 68 of the translating member in the X direction will cause all of the flexures 50 to flex at the appropriate material web to permit movement in the X direction as seen in phantom lines in FIG. 7. Because the carriage 25 is constructed symmetrically, any small movement in a Z direction of any particular flexure 50 on one side of the X-Y plane is negated by mirror image movement of the corresponding flexure on the other side of the X-Y plane. This mirror image movement also offsets emperical strain on the carriage during microactuator actuation. Thus, the translating section 29 moves in a very flat movement along the X-Y plane at the center axis of the carriage. A force applied to a side surface 70 of the translating section 29 in the Y direction causes each flexure 50 to bend slightly about the appropriate material web oriented to permit movement in the Y direction. Again, because of the symmetry of the structure, movement in the Y direction of the translating section 29 will be a very flat planar movement along the X-Y plane. Because of the construction of the flexures 50 and the carriage 25, any load applied along the Y axis is transmitted as movement only in the Y direction and yields no movement in the X or the Z direction. Loads applied in both the X direction and the Y direction simultaneously will move the translating section 29 in both the X direction and the Y direction but only for a distance according to the force vectors in each direction respectively. An X direction force produces no substantial movement in the Y direction, and a Y direction force produces no substantial movement in the X direction. Therefore, extremely accurate results are produced by utilizing the carriage assembly 24 of the invention. As illustrated in FIGS. 3 and 4, the carriage 25 includes a plurality of stiffening beams 80 spanning each adjacent pair of elongate columns 32A-D and running essentially parallel to the top and bottom cross members 38A-D and 40A-D. Each stiffening beam 80 is connected to an elongate column 32A-D at its opposite ends 82 and 84 by a material web 86. Each material web 86 is formed similar to any one of the material webs 60 or 62 described above in that a pair of opposed notches or slots 88 are cut into the carriage material adjacent to each of the ends 82 and 84 to form a thin web of material interconnecting the stiffening beams 80 to the elongate columns 32A-D. Each stiffening beam 80 essentially locks the adjacent elongate columns 32A-D laterally relative to one another so that if they move in either the X or the Y direction, they will move in tandem and not move closer to or further away from one another. However, the web 86 at each end of each stiffening beam permits the stiffening beams to pivot slightly relative to the respective one of the elongate columns 32A-D so that the carriage 25 can perform its intended flexure function by allowing the translating section 29 to move in the X-Y plane. As illustrated in FIGS. 3 and 4, the front 56, back 58, and sides 52 and 54 can include a stiffening beam 80 adjacent to each of the flexures 50 to provide lateral support to the carriage structure. As illustrated in FIGS. 1 and 2B, one side, such as the front 56, can be devoid of a stiffening beam to permit access to the interior of the carriage 25. Access may be necessary in order to activate or install or replace a sensor probe (not shown) or other apparatus attached to or carried by the translating section 29 of the flexure device. The number of stiffening beams 80 as well as the position or location of the stiffening beams can vary considerably without departing from the scope of the present invention. The addition and strength of the stiffening beams is determined by the particular application for which the flexure device 20 is intended. Some applications may require a stiffer carriage 25 while other applications may require a more flexible structure. As illustrated in FIGS. 1 and 2A, the back 58 and one side 52 are coupled to the piezoelectric assemblies 26. In the present embodiment, each piezoelectric assembly 26 has a pair of piezoelectric elements 90 extending symmetrically outward from a central block coupler 30 as illustrated in FIGS. 2A and 8. The coupler 30 is rigidly affixed to the back surface 68 of the translating section 29 for movement therewith. The coupler 30 includes a pair of symmetrically opposed flexures 50 essentially identical in construction to those described above for the carriage 25. Each of the flexures 50 is attached to one of the piezoelectric elements 90. Each piezoelectric element 90 is attached at their opposite distal ends to a corresponding end coupler 28, which is rigidly affixed to the frame or support structure 22 and retained thereby. Each of the end couplers 28 also includes a flexure 50 for coupling the piezoelectric elements 90 to the end couplers 28. Each piezoelectric element 90 is electrically connected to a power supply (not shown) wherein the power supply is utilized to energize each piezoelectric element and to move each element and hence the translating section 29. The flexures at each coupler 30 and 28 permit the piezoelectric elements 90 to drive the central coupler 30 and hence the translating section 29 as described above in either the X direction or the Y direction or both depending on how the piezoelectric assemblies 26 are energized. The piezoelectric elements 90 are intended to be identical in nature for each piezoelectric assembly 26 so that each piezoelectric element 90 of a particular assembly produces an equivalent movement. This insures that no out of balance force is applied to the translating section 29. Additionally, the movement produced by each piezoelectric assembly 26 is essentially only in the X or the Y direction because of the symmetrical construction of the piezoelectric assemblies 26 and because each end coupler 28 is rigidly affixed to the frame 22. Any movement which would otherwise be created in the Z direction at one end of the piezoelectric assembly is cancelled by an opposite and equal reaction at the other end of the assembly 26. As illustrated in FIG. 2A, the central couplers 30 of each piezoelectric assembly 26 are different in construction. However, the only difference is in the size of the rigid central portion of the couplers 30 affixed to the translating section 29. The size of this central portion of the central couplers is merely adapted to coincide or correspond to the size and shape of the particular surface 68 or 70 of the translating section 29 to which the coupler is attached. The shape and construction of the end couplers 28 as well as the central couplers 30 may vary considerably without departing from the scope and spirit of the invention. Additionally, the particular size, type and configuration of the piezoelectric elements may also vary considerably. The invention is not intended to be limited to any particular piezoelectric element construction. To summarize the invention, the structure of the flexure carriage 25 transmits an applied force in the X direction into an X direction movement of the translating section 29 without producing any movement in the Y direction or the Z direction. Similarly, an applied force in the Y direction produces movement of the translating section 29 only in the Y direction without producing any movement in the X direction or the Z direction. An applied force by both of the piezoelectric assemblies 26 produces corresponding movement in both the X and the Y direction wherein the movement in the X direction corresponds only to the applied X direction force and movement in the Y direction corresponds only to the applied Y direction force. The construction of the flexure device of the invention produces a highly accurate X-Y coordinate movement and produces such movement in a very flat X-Y plane virtually over a relatively large area while eliminating any significant movement of the translating section in the Z direction. Many modifications and changes to the invention as described may be made without departing from the spirit and scope of the invention. For example, the size, shape and construction of each of the elongate columns 32A-D, cross members 38A-D and 40A-D, flexures 50, material webs 60, 62, and 84, slots 64 and 86, and translating sections 29 may vary considerably without departing from the invention. The size, shape and construction as well as the materials utilized to produce the flexible carriage 25 may be selected and determined according to a particular application for which the device 20 is intended. The compact nature of the overall carriage assembly 24 including the piezoelectric elements 26 permits utilizing the invention in application environments smaller than previously possible. This is accomplished by the novel construction of the invention wherein the piezoelectric assemblies 26 are oriented in the Z direction relative to the X-Y plane of movement of the translating section produced by the piezoelectric assemblies. Other variations and modifications to the specifically described embodiments may be made without departing from the spirit and scope of the present invention. With that in mind, the invention is intended to be limited only by the scope of the appended claims. |
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claims | 1. A method for removing actinides in cationic form from an aqueous solution, said method comprising the steps of:reacting graphite with potassium permanganate in a mixture of sulfuric and phosphoric acids to form graphene oxide;contacting said solution with said graphene oxide to adsorb said actinides onto said graphene oxide from said solution. 2. The method of claim 1, wherein the contacting comprises mixing said graphene oxides with the solution. 3. The method of claim 1, wherein said actinides in cationic form are selected from the group consisting of Am, Pu, Np, and U. 4. The method of claim 1, further comprising a step of separating said graphene oxide having said actinides adsorbed thereon from the solution, wherein the separating step occurs after the adsorption step. 5. The method of claim 4, wherein the separating step is selected from the group consisting of centrifugation, ultra-centrifugation, filtration, ultra-filtration, precipitation, electrophoresis, reverse osmosis, sedimentation, incubation, treatment with acids, treatment with bases, treatment with chelating agents, and combinations thereof. 6. The method of claim 4, wherein the separating step comprises the addition of a polymer to the solution, wherein the polymer addition leads to a precipitation of said graphene oxide having said actinides adsorbed thereon from the solution. |
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abstract | A scanning type microscope that captures substance information of the surface of a specimen by the tip end of a nanotube probe needle fastened to a cantilever, in which an organic gas is decomposed by a focused ion beam in a focused ion beam apparatus, and the nanotube is bonded to the cantilever with a deposit of the decomposed component thus produced. With this probe, the quality of the nanotube probe needle can be improved by removing an unnecessary deposit adhering to the nanotube tip end portion using a ion beam, by cutting an unnecessary part of the nanotube in order to control length of the probe needle and by injecting ions into the tip end portion of the nanotube. |
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summary | ||
claims | 1. A two-directional device to replace a handling glove from an inside to an outside of a glove box and from the outside to the inside under confinement, said device being designed to replace a used glove by a new glove comprising a cuff connected in a sealed manner to a shoulder port mounted in a sealed manner on a wall of a confinement containment and connected in a sealed manner to a cuff sleeve, and a glove made of a flexible material connected in a sealed manner to a glove sleeve, wherein an outside of the glove sleeve comprises a determined number of snap-fitting studs located on flexible sectors, and wherein the cuff sleeve has a cylindrical internal surface without any obstacles and comprises a number of axial ramps on the cylindrical internal surface, equal to the number of snap-fitting studs, and configured to guide the snap-fitting studs into anchor cavities thereby locking the glove sleeve in the cuff sleeve, said glove sleeve and said cuff sleeve forming a fully sealed assembly called a cuff port once assembled. 2. The glove replacement device according to claim 1, wherein a static and dynamic seal during the replacement is composed of at least one seal, either injected or embedded in a sealed manner in a groove of the glove sleeve provided on a glove sleeve body/to provide a permanent seal between the cuff sleeve and the glove sleeve. 3. The glove replacement device according to claim 2, wherein the seal is made of elastomer on which surface ionisation has been done to improve its slip properties, facilitating placement of a new ring and ejection of an old ring. 4. The glove replacement device according to claim 1, further comprising stud retraction pins, wherein the snap-fitting studs and the stud retraction pins are provided with visual marks that facilitate correct positional alignment of the glove. 5. The glove replacement device according to claim 1, wherein visual marks are used to facilitate positioning during interchangeability actions consisting of a simple translation, so that no special tools are necessary for the interchangeability manipulation made by the operator. 6. The glove replacement device according to claim 1, further comprising a locking system composed of the snap-fitting studs being insertable into appropriate anchor cavities, these snap-fitting studs being unclipped by retraction pins that enter housings of the flexible sectors to retract towards the inside of the glove sleeve, this action resulting in unclipping of these snap-fitting studs. 7. The glove replacement device according to claim 1, wherein the glove sleeve is composed of a glove sleeve body comprising devices for guidance and locking of this glove sleeve body in a cuff sleeve body and wherein it comprises a glove assembly ring of the glove in the glove sleeve body, retention being obtained by the glove assembly ring in the glove sleeve body. 8. The glove replacement device according to claim 1, wherein the cuff sleeve is composed of a cuff sleeve body and a cuff assembly ring that pushes the cuff into contact with a stop of the cuff sleeve body, thus providing a seal of the cuff sleeve, the complete assembly being retained by assembling the parts making them indissociable. 9. A method of replacing a used glove by a new glove using a device according to claim 5, including the following steps:the new glove sleeve is placed on the used glove sleeve in position in a cuff sleeve body taking care to align a mark of the new sleeve with a mark of the cuff sleeve body,the new glove sleeve is pushed onto the used glove sleeve, andthe new glove sleeve and the used glove sleeve are pushed in a single piece into the cuff sleeve body, to the end of locking located on the cuff sleeve body, signalled by a “click”. 10. The method according to claim 9, applied to a glove box in positive pressure, wherein it begins with the following two phases:the used glove is rolled up towards an outside of the cuff, andthe new glove fitted with its sleeve is placed inside the confinement containment. 11. The method according to claim 9, applied to a glove box in positive pressure, wherein at the end of the process, the used glove sleeve is pushed clear into the inside of the cuff. 12. The method according to claim 9, applied to a glove box in negative pressure, wherein it begins with the following three phases:the cuff is rolled up towards an outside of a cell, andthe new glove is rolled up towards an inside of its own sleeve,the new glove fitted with its glove sleeve is placed outside the confinement containment. 13. The method according to claim 9, applied to a glove box in negative pressure, wherein at the end of the process, the used glove sleeve is pushed clear into the inside of the glove box. |
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059404620 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a coil gripping device or tool 2 which is constructed to rotate about its center and on the periphery of which an absorber finger or an absorber sheet 3 can be wound up in spiral form. The sheet 3 is formed of elongated components of control elements in which spent absorber material is gas-tightly enclosed. For this purpose, a fixing device 13 is disposed on the outer periphery of the coil gripping device 2. A start of the absorber finger or of the absorber sheet 3 can be secured on the periphery of the coil gripping device 2 with the fixing device 13. A compact coil having a spiral winding is produced from the elongated absorber finger or absorber sheet or component 3 by rotation about a winding spindle 14 and winding-up. The winding device has a bending roller 1 for pressing the absorber finger or the absorber sheet 3 against the outer periphery of the coil that is already wound up on to the coil gripping device 2. The result which this achieves is that the winding material fed to the coil makes firm contact with the outer periphery of the latter and as dense a winding as possible is produced. The winding spindle 14 of the coil gripping device 2 can be moved along an axis in the direction of arrows 4, that is to say perpendicularly to the longitudinal axis of the winding material (which is the absorber finger or absorber sheet), in order to compensate for the constant increase in the circumference of the coil produced during the winding-up. The winding material is advantageously moved in turn in its longitudinal direction in accordance with the winding speed. Once a predetermined, maximum circumference of the wound-up coil has been reached, an associated cutting tool 5 can separate the absorber finger or the absorber sheet 3 from the remaining coil. In this connection, advantageously only one mounting of the component on other parts of the control element is cut through in order to obtain the component as a gas-tight cladding of the absorber material. It is therefore also possible to determine the internal diameter which the coil should have for a given maximum circumference of the wound-up coil, i.e. the distance between the bending roller 1 and the winding spindle 14 at which the winding-up is started. FIG. 2 shows a section of a winding device according to FIG. 1, in which elements having the identical function are denoted by identical reference symbols to those in FIG. 1. The coil gripping device 2 is constructed with a suitable drive 4' so as to be rotatable about its winding spindle 14 and it has an associated support element 15 which fixes the coil produced on the coil gripping device 2 through the use of an associated winding coil 6 on the coil gripping device 2. The finished coil made of the absorber fingers or absorber sheets 3 can then be kept in the wound-up state by folding in lateral jaws of the winding coil 6 surrounding the coil with the aid of a folding element 16. However, according to the invention, the finished coil may also be kept in the wound-up state by a retention belt. In order to remove the coil, the coil gripping device 2 can be moved in the direction of arrows 7 along its winding spindle 14 in order to separate the coil gripping device 2 from the supporting element 15 and release the coil. The coil gripping device 2 can then perform a pivoting movement about a pivoting axis 8 and the retained coil can be pulled off the coil gripping device 2. FIG. 3 shows a plurality of coils 10 which have been produced by a winding device and which are retained by folding in the lateral jaws of winding coils on which the absorber fingers are wound up. The coils are stacked in the interior of a basket 9 having external dimensions which fit into a standard shielded container 17. A hollow center 12 of the coils is densely filled with compacted residual material 11 of control elements in order to enable an efficient space utilization of the shielded container 17. According to the invention, such a device can be disposed in a stationary or temporary manner in a water pond of a light-water-cooled nuclear reactor and can prepare elongated components originating from a spent control element of the nuclear reactor and containing gas-tightly enclosed absorber material, for storage in a storage container. According to FIGS. 1 and 2, in particular, such a device has the rotational drive 4' for the winding spindle 14, which is disposed next to the component and approximately perpendicularly to the longitudinal direction of the component (absorber finger or absorber sheet) and which is part of a gripping tool that, for example, supports the coil gripping device 2 and to which a free end of the originally elongated component can be attached. The component can be moved relative to the gripping tool in its longitudinal direction, while the pressing and bending roller 1 is disposed on its other side and situated opposite the winding spindle of the gripping tool. The distance between the pressing and bending roller 1 and the winding spindle is variable to suit the thickness of the winding being produced. In this way, coils are produced which are composed of an originally elongated component containing absorber material of a spent control element of a light-water-cooled nuclear reactor and which can be intermediately stored or finally stored in a space-saving manner in standard storage containers. In is therefore possible to avoid the escape of fairly large amounts of radioactive substances from the absorber material. |
abstract | Disclosed is a radioactive contaminant container including a wall that defines a containing space for containing radioactive contaminants and shields at least a portion of radiation irradiated from the radioactive contaminants, and the wall has an outer shape of a hexagonal cylinder or a substantially hexagonal cylinder. |
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048204781 | summary | 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 a unique control rod design in which the worth of the control rod can be changed approximately uniformly in the axial direction of the rod. 2. Description of the Prior Art In a typical nuclear reactor, the reactor core includes a large number of fuel assemblies each of which is composed of top and bottom nozzles with a plurality of elongated transversely spaced guide thimbles extending longitudinally between the nozzles and a plurality of transverse support grids axially spaced along and attached to the guide thimbles. Also, each fuel assembly is composed of a plurality of elongated fuel elements or rods transversely spaced apart from one another and from the guide thimbles and supported by the transverse grids between the top and bottom nozzles. The fuel rods each contain fissile material and are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A liquid coolant is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work. Since the rate of heat generation in the reactor core is proportional to the nuclear fission rate, and this, in turn, is determined by the neutron flux in the core, control of heat generation at reactor start-up, during its operation and at shutdown is achieved by varying the neutron flux. Generally, this is done by absorbing excess neutrons using control rods which contain neutron absorbing material. The guide thimbles, in addition to being structural elements of the fuel assembly, also provide channels for insertion of the neutron absorber control rods within the reactor core. The level of neutron flux and thus the heat output of the core is normally regulated by the movement of the control rods into and from the guide thimbles. One common arrangement utilizing control rods in association with a fuel assembly can be seen in U.S. Pat. No. 4,326,919 to Hill and assigned to the assignee of the present invention. This patent shows an array of control rods supported at their upper ends by a spider assembly, which in turn is connected to a control rod drive mechanism that vertically raises and lowers (referred to as a stepping action) the control rods into and out of the hollow guide thimbles of the fuel assembly. The typical construction of the control rod used in such an arrangement is in the form of an elongated metallic cladding tube having a neutron absorbing material disposed within the tube and with end plugs at opposite ends thereof for sealing the absorber material within the tube. Generally, the neutron absorbing material is in the form of a stack of closely packed ceramic or metallic pellets which only partially fill the tube, leaving a void space or axial gap between the top of the pellets and the upper end plug in defining a plenum chamber for receiving gases generated during the control operation. A coil spring is disposed within this plenum chamber and held in a state of compression between the upper end plug and the top pellet so as to maintain the stack of pellets in their closely packed arrangement during stepping of the control rod. Thus, control rods affect reactivity by changing direct neutron absorption. Control rods are used for fast reactivity control. A chemical shim such as boric acid dissolved in the coolant is used to control long term reactivity changes. More uniformly distributed throughout the core, the boron solution leads to a more uniform power distribution and fuel depletion than do control rods. The concentration of boron is normally decreased with core age to compensate for fuel depletion and fission product buildup. The buildup of fission products, such as Xenon-135, reduces reactivity by parasitically absorbing neutrons, thereby decreasing thermal utilization. The Xenon-135 (hereafter referred to as just "xenon") is removed by neutron absorption or by decay. Upon a reduction in core power (such as during load follow, which is a reduction in reactor power in response to a reduction in power demand), fewer thermal neutrons are available to remove the xenon and therefore the concentration of xenon in the core increases. This increase in xenon concentration which accompanies a reduction in core reactivity is usually compensated for by either decreasing the concentration of boron dissolved in the core coolant or by withdrawing the control rods from the core. However, both of these methods have drawbacks. Changing the boron concentration requires the processing of coolant (i.e., water) which is difficult and not desired by the utility, especially towards the end of core life (EOL). Removal of control rods means that the core's return to power capability is reduced and peaking factors are increased. The usual solution to this problem is to have several banks of reduced worth rods (i.e., grey rods) in the core at full power which are available for removal at reduced power to compensate for the xenon buildup. The drawback of this procedure is that moving these banks changes the axial offset and increases peaking factors. Also, because these reduced worth banks are in the core at power, shutdown margin can be affected. Consequently, a need exists for a different approach to xenon compensation, one which will effectively resolve the problem of xenon buildup during load follow, but which will not raise a host of new problems in the process. SUMMARY OF THE INVENTION The present invention provides a unique control rod configuration designed to satisfy the aforementioned needs. Underlying the present invention is the realization that since the xenon increase at reduced power will be fairly uniform across the core and, in particular, will be axially symmetric (if the axial offset is near zero and held constant at reduced power), the ideal xenon compensation solution will be uniform across the core and in particular will also be symmetric in the axial direction. (A change in the dissolved boron concentration, which is uniform across the core, would be a satisfactory solution, except for the problems associated with bleed and feed.) In other words, the solution should match the characteristics of the problem. The solution provided by the present invention does just that. It involves the full insertion into the core of a control rod whose worth can be changed uniformly in the axial direction during power operation. This is accomplished by a control rod composed of two cylindrical members, an inner one of solid cross-section and an outer one of annular cross-section so that the inner one fits inside the outer one. In the axial direction, each cylindrical member has successive regions which are alternately composed of a black poison (i.e., one that absorbs all neutrons) and no poison. When the two cylindrical members of the control rod are moved relative to each other, the worth of the rod will change by up to a factor of two depending on whether the poison regions of the two cylindrical members line up or not. The reason for this is that, when lined up, the black poison region of the outer cylindrical member will shield the poison region of the inner cylindrical member from neutrons which will reduce the worth of the overall rod. Because the poison and nonpoison regions uniformly alternate in the axial direction between the ends of the cylindrical members, when the position of one cylindrical member is axially adjusted relative to another cylindrical member (for example, as the inner cylindrical member is moved relative to the outer cylindrical member), the worth of the overall rod will change approximately uniformly in the axial direction. Also, since movement of the cylindrical member only a short distance is necessary to change the rod worth, there will be very little axial offset change when the rod worth changes and consequently little peaking factor increase. Thus, the use of this dual concentric cylindrical member control rod will be about as good as changing boron concentration for xenon transient compensation as far as peaking factors are concerned. It will be better than dissolved boron for speed of action especially near EOL. Accordingly, the present invention is directed to a control rod for use in a nuclear reactor core to provide xenon compensation. The control rod comprises: (a) an elongated inner cylindrical member; and (b) an elongated outer cylindrical member surrounding the inner member. Each of the members is composed of alternating poison and nonpoison regions. Also, one of the inner and outer members is axially movable relative to the other to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod. More particularly, the inner cylindrical member has a solid cross-sectional configuration, whereas the outer cylindrical member has an annular cross-sectional configuration and concentrically surrounds the inner member. The regions of each of the members extend axially and are alternately composed exclusively of respective black poison and nonpoison materials. Furthermore, each of the poison regions of the inner and outer members is of substantially the same axial height, while each of the nonpoison regions of the inner and outer members is of substantially the same axial height. Finally, one of the inner and outer members is axially movable relative to the other between one axially displaced position in which the poison regions of the members are disposed side-by-side and the nonpoison regions thereof are disposed side-by-side and another axially displaced position in which the poison regions of the members are disposed side-by-side with the nonpoison regions of the members so as to thereby change the overall worth of the rod in a substantially axially uniform manner. A fuel assembly guide thimble in which the control rod is placed has means for retaining the outer member in a stationary position therein, while the inner member is movable axially relative thereto to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod. Preferably, the retaining means is an annular stop fixed in the guide thimble and being sized to support a lower end of the outer member. The stop also has a central hole sized to allow passage of a lower end of the inner member therethrough. More particularly, the stop is a sleeve fixed in the guide thimble above a dashpot defined in the lower portion of the thimble. Also, the inner member has an outwardly projecting ledge defined on a lower end thereof upon which rests a lower end of the outer member for retaining the outer member about the inner member before the outer member rests on the guide thimble stop. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. |
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042141672 | claims | 1. In a device for protection of gonads in x-ray diagnosis comprising a retaining frame for fastening to the collimator of an x-ray diagnosis instrument by means of insert strips, said retaining frame having means for receiving a movable support strip of material that is permeable to x-rays and which supports a member of material that is impermeable to x-rays, the improvement comprising said retaining frame being provided with a plurality of insert strips for fastening said retaining frame to said collimator, said insert strips being disposed on the retaining frame so as to be movable with respect to each other so that the protective device can be fastened to different x-ray diagnosis instruments, wherein said plurality of insert strips includes a pair of parallel insert strips, wherein said pair of parallel insert strips are disposed on the retaining frame along a pair of parallel slots, said pair of insert strips being movable with respect to each other along said slots, wherein portions of said pair of parallel insert strips adjacent said retaining frame are provided with prismatic guide tips which engage in said slots, and wherein set screws are provided for securing said pair of parallel insert strips to said retaining frame, the shanks of said set screws projecting through said slots and engaging in threads provided in said pair of parallel insert strips. 2. The device for protection of gonads according to claim 1, wherein the means for receiving a movable support strip in said retaining frame includes two opposed retaining slots for receiving the movable strip and wherein two parallel retaining bridge members are provided on the retaining frame between said slots so that the support strip can be selectively inserted crosswise. 3. The device for protection of gonads according to claim 1, wherein said member is a plate having a configuration adapted to the female or male gonads to be protected. 4. A device for protection of gonads in x-ray diagnosis comprising a retaining frame for fastening to the collimator of an x-ray diagnosis instrument by means of insert strips, said retaining frame having means for receiving a movable support strip of material that is permeable to x-rays and which supports a member of material that is impermeable to x-rays, a plurality of insert strips for fastening said retaining frame to said collimator and means disposing said insert strips on said frame so that the relative position of said insert strips with respect to each other can be adjusted whereby the protective device can be fastened to different x-ray diagnosis instruments. 5. The device according to claim 4, wherein said plurality of insert strips includes a pair of parallel insert strips and said retaining frame includes a pair of parallel slots, said pair of insert strips being adjustably positioned with respect to each other along said slots by said means disposing the insert strips on the frame. 6. The device according to claim 5, wherein portions of said pair of parallel insert strips adjacent said retaining frame are provided with prismatric guide tips which engage in said slots. 7. The device according to claim 4, wherein the means for receiving a movable support strip in said retaining frame includes two opposed retaining slots for receiving the movable strip and wherein two parallel retaining bridge members are provided on the retaining frame between said slots so that the support strip can be selectively inserted crosswise. |
abstract | A gray control rod having a neutron absorber comprising terbium and dysprosium is provided. The neutron absorber comprises at least one first component and at least one second component, the reactivity worth of the first component increases as the service time of the neutron absorber increases, the reactivity worth of the second component decreases as the service time of the neutron absorber increases; the reactivity worth of the neutron absorber varying no more than 15% within the service time of the neutron absorber. By using the first component and the second component to form the neutron absorber, and adjusting the proportion of the respective components in the neutron absorber, the neutron absorber having a substantially planar reactivity worth loss characteristic can be obtained. The gray control rod and the assembly having required reactivity controlling ability can be obtained by increasing or decreasing the material dosage of the neutron absorber. |
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047078464 | claims | 1. A masking means for directing radiated energy to a specific area of a subject under observation or inspection comprising a first radiation shielding or filtering means having a vertically oriented elongated opening with a broader portion nearer its distal or lower end, said opening located medially along the horizontal, positioned immediately adjacent to and in front of the collimator of an X-ray radiation generating device within a space in a mount or support means defined by two sets of transverse tracks, a first set of tracks for removably positioning said first shielding or filtering means in said space and a second set of tracks transverse to said first set of tracks capable of removably securing and adjustably positioning a second shielding or filtering means adjustably secured to a substantially rectangular transparent plate, said transparent plate being juxtaposed in front of and against said first shielding or filtering means for retaining said first shielding or filtering means within its defined space and in juxtaposition to the collimator, said second shielding or filtering means being positioned to actively cooperate with said first shielding or filtering means for permitting only the X-ray radiation necessary to cause an image to appear on the X-ray film for the specific area to be observed or inspected to pass through to be filtered by said first and second shielding or filtering means and for blocking unecessary radiation from contacting the subject and causing excessive exposure to such radiation. 2. The masking means of claim 1 wherein said first radiation shielding or filtering means is substantially rectangular in configuration and comprised of a metallic radiopaque plate laminated between two similarly configured plates of translucent plastic. 3. The masking means of claim 1 wherein the broader portion of said elongated opening being in the lower one-fourth of said opening. 4. The masking means of claim 1 wherein the broader portion of said elongated opening being twice the width of the upper, narrower portion. 5. A full spine shielding means for directing radiated energy to a specific area of a subject under observation or inspection comprising a first radiation shielding or filtering means having a vertically oriented elongated opening with a broader portion nearer its distal or lower end, said opening located medially along the horizontal with said broader portion being in the lower one-fourth of said opening and twice the width of the upper, narrower portion, positioned immediately adjacent to and in front of the collimator of an X-ray radiation generating device within a space in a mount or support means defined by two sets of transverse tracks, a first set of tracks for removably positioning said first shielding or filtering means in said space and a second set of tracks transverse to said first set of tracks capable of removably securing and adustably positioning a second shielding or filtering means adjustably secured to a substantially rectangular transparent plate, said transparent plate being juxtaposed in front of and against said first shielding or filtering means for retaining said first shielding or filtering means within its defined space and in juxtaposition to the collimator, said second shielding or filtering means being positioned to actively cooperate with said first shielding or filtering means for permitting only the X-ray radiation necessary to cause an image to appear on the X-ray film for the specific area to be observed or inspected to pass through or be filtered by said first and second shielding or filtering means and for blocking unecessary radiation from contacting the subject and causing excessive exposure to such radiation. 6. The full spine shielding means of claim 5 wherein said first radiation shielding or filtering means is substantially rectangular in configuration and comprised of a metallic radiopaque plate laminated between two similarly configured plates of translucent plastic. 7. A masking means for directing radiated energy from an X-ray radiation generating source to a specific area of a subject under observation or inspection including a means for attaching a support means to a front portion of a collimator of an X-ray radiation generating machine, said support means having first and second sets of transverse tracks, said second set of tracks capable of removably securing and adjustably positioning a radiation shielding or filtering means adjustably secured to a substantially rectangular transparent plate within said second set of tracks, the improvement comprising another radiation shielding or filtering means having a vertically oriented elongated opening with a broader portion nearer its distal or lower end, said opening being located medially along the horizontal, removably interposed in juxtaposition between the collimator of the X-ray radiation generating machine and said transparent plate within a space defined by said first set of tracks of said support means and being retained in said juxtaposition within said support means by said transparent plate, said another radiation shielding or filtering means being positioned to actively cooperate with said radiation shielding or filtering means for permitting only the X-ray radiation necessary to cause an image to appear on the X-ray film for the specific area to be observed or inspected to pass through or be filtered by said shielding or filtering means and for blocking unnecessary radiation from contacting the subject and causing excessive exposure to such radiation. 8. The masking means of claim 7 wherein said another radiation shielding or filtering means is substantially rectangular in configuration and comprised of a metallic radiopaque plate laminated between two similarly configured plates of translucent plastic. 9. The masking means of claim 7 wherein the broader portion of said elongated opening being in the lower one-fourth of said opening. 10. The masking means of claim 7 wherein the broader portion of said elongated opening being twice the width of the upper, narrower portion. |
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039765415 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, the core of a nuclear reactor 10 is cooled by a coolant which is circulated to steam generator 12 and which is returned to the reactor 10 by primary coolant pump 14. The primary coolant is circulated through heat exchange tubes 16 in steam generator 12 in out-of-contact heat exchange relationship with a secondary coolant that circulates around the outside of heat exchange tubes 16. By means of this heat exchange, secondary coolant is converted from water into steam and the steam is then delivered via steam conduit 20 to turbine 22. After the steam has passed through the turbine it is condensed in main condenser 24 to its liquid state. In the condenser 24 the noncondensible fractions in the coolant are separated from the condensate and ejected from the main condenser's hot well through the condenser vacuum system 28 or through a system commonly referred to as the air ejection vent. Next, the condensate is circulated by condensate pumps 26 through a full flow condensate demineralizer system 38, which is a commercially available and well understood system. Upstream of the fullflow condensate demineralizers 38 is a flow regulation valve 36 and a bypass line 34 which straddles the condensate demineralizers 38 and which is in turn regulated by bypass valve 32. Downstream of the condensate demineralizers 38 and downstream of the re-entrance of the bypass line 34 is a chemical injection means 46. At this position volatile chemicals, such as ammonia and hydrazine, are injected into the feedwater flow stream. After the addition of the appropriate chemicals, the condensate or feedwater passes through a low pressure feedwater heater system 48, main feed pump 54 and high pressure feedwater heater system 56, before being delivered back to the steam generators 12. In order for the full flow condensate demineralizers 38 to operate continuously on the full flow of the feedwater delivered to steam generators 12, provision must be made for continuously regenerating the resin of the condensate demineralizers 38. Thus, external regeneration system 40 with incoming lines 42 and outgoing lines 44 is included as indicated in FIG. 1. Conduits 42 and 44 withdraw the spent resin from the condensate demineralizer and return regenerated resin after it has been regenerated by the external regeneration system 40. It has been found that even the condensate demineralization of the full flow of the feedwater delivered to the steam generators, the steam generators still have a tendency to concentrate impurities in the feedwater that either pass through the condensate demineralizers or result from corrosion in the secondary feedwater chain 58 upstream of the steam generator. As a result, it has been found that in order to eliminate concentration of these impurities a continuous blowdown of the steam generator secondary side should be maintained. This invention discloses a continuous blowdown of a pair of steam generators, the blowdown amounting to 1 percent of the steaming rate of both steam generators. The blowdown lines from the two steam generators 12 are indicated by piping 60. During normal operation, the blowdown which is siphoned off by piping 60 is cooled by blowdown heat exchanger 64 and then passed through lines 82 and 86 back to a point which is upstream of the full flow condensate demineralizers 38 but downstream of the condensate pump 26. In this manner, the impurities which are concentrated by the steam generators 12 are drawn off from the steam generators and continuously subjected to the condensate demineralizers 38, thereby reducing or eliminating the impurity concentration which tends to occur in the steam generator. The system and mode of operation described above are sufficient for cleaning the secondary coolant and minimizing contamination buildup in the steam generators during normal operation of the nuclear steam supply system, but are insufficient to cope with the abnormal operation of one or more failed steam generator tubes which allow the leakage of radioactive primary coolant into the normally nonradioactive secondary coolant. The inherent defect of the above described system during such abnormal operation is that the full flow condensate demineralizer resin bed becomes contaminated with radioactive contaminants. Ordinarily the resin regeneration system 40 is not equipped to handle radioactive wastes. Inclusion of a resin regeneration system which could handle radioactive wastes would be extremely expensive and would lie unused during the greater part of the life of the plant. An alternative solution to this radioactivity problem would be to dispose of the resin as it becomes radioactive. This, however, is an unattractive solution inasmuch as the resin beds involved are very expensive and the volume of radioactive waste resin required to be disposed of would be large. It is a particularly novel aspect of this invention that provision is made to avoid the contamination of the condensate demineralizer resin. This is accomplished by bypass line 34 and bypass valve 32 in combination with flow control valve 36. Radiation monitors are located on the air ejection system 28 in order to monitor the carryover of any radioactivity from the steam generator and on the blowdown line 60 in order to detect any radioactivity which is passed through the blowdown line. Upon detection of radioactivity in excess of a predetermined allowable level by blowdown line monitor 62 or air ejection vent monitor 30, a signal is sent by electrical conductor 66 or by electrical conductor 67 to the actuation means of bypass valve 32 and flow control valve 36. These valves 32 and 36 are quick acting valves so that valve 36 shuts and valve 32 opens in relatively short order and the contaminated fluid is passed around the full flow condensate demineralizers. In this manner, the resin bed of the condensate polisher is protected from being radioactive. It should be noted that one might expect the radiation monitor 62 to receive an indication of a primary to secondary leak in advance of radiation monitor 30 if a leak in heat exchange tubes 16 were to occur relatively low on one of the heat exchange tubes 16. The opposite would be the case, i.e., radiation monitor 30 could be expected to receive an indication of radioactivity before radiation monitor 62, if the leak between the primary and secondary systems through tubes 16 were to occur in a relatively high position on one of the tubes 16. A further aspect of this invention is the auxiliary ion exchanger system, generally indicated by 91, which includes a multiplicity of blowdown ion exchangers 88 and 90 having throw-away resin beds. Throw-away resin beds enable the secondary system to be cleaned of its radioactivity component in a relatively simple and inexpensive manner by allowing the radioactive fluid to pass only to the auxiliary ion exchangers, and not through the full flow condensate demineralizers 38. This avoids the radioactive contamination of the full flow condensate demineralizers while also assuring that serious impurity concentration in steam generator is avoided. As a result, the nuclear steam supply system can remain in operation, without jeopardizing the steam generators and a mandatory and inconvenient shutdown can be avoided. Therefore, this invention increases the flexibility of the nuclear steam supply system operator's response to a steam generator tube failure and thereby increases plant availability. The auxiliary ion exchanger system 91 consists of auxiliary blowdown heat exchanger 70, bypass valve 74, temperature detector 78, valve 80 and a plurality of blowdown ion exchangers 88 and 90. Upon receipt of a signal from the radiation monitors, the appropriate actuating devices open valve 74 and close valve 72. This action diverts the blowdown flow from its normal path leading to the full flow condensate polisher 38 to the auxiliary ion exchange system 91. It should be noted that the actuation devices of valves 72 and 74 are slow acting so that the transfer of the blowdown coolant is not made abruptly to ensure that the auxiliary blowdown heat exchanger is protected against severe thermal shock. The radioactive blowdown is passed through the auxiliary blowdown heat exchanger 70 where it is cooled to a temperature which is compatible with the temperature requirements of the blowdown ion exchangers 88 and 90. Temperature detector 78 monitors the temperature of the blowdown exiting from the heat exchanger 70 and operates bypass valve 80 via electrical conductor 79. Prior to the blowdown coolant attaining a sufficiently low temperature, the bypass valve 80 passes the coolant through conduit 76 and spur conduit 84 to conduit 82 and 86 and to the bypass line 34. As a result, the radioactive fluid passes around the full flow condensate demineralizers 38. When the blowdown coolant has attained a sufficiently low temperature, the temperature detector 78 sends an activation signal to bypass valve 80 and the flow is diverted through the blowdown ion exchangers 88 and/or 90. The blowdown ion exchangers 88, 90 pass the radioactive coolant through a throw-away resin bed to perform radioactive contaminant removal. Subsequent to this cleaning action the coolant is returned through conduit 92 back to the secondary feedwater train 58. It should be noted here that blowdown ion exchangers 88 and 90 are state of the art pieces of equipment, and are sized to individually take the full flow of the blowdown, so that the full blowdown flow can be passed through one of the ion exchangers while the resin bed in the other ion exchanger is being replaced. In this manner and due to the present invention the nuclear reactor steam supply system is allowed to continue operation even though a steam generator heat exchange tube has failed. In this way the radioactive contamination of the secondary coolant is tolerated without the necessity of an immediate forced outage. Thus, the plant operating personnel can continue to operate the plant without further jepardizing the steam generator and can wait until a scheduled plant shutdown to repair or plug the steam generator heat exchange tubes. This represents additional plant flexibility and can amount to a substantial savings by avoiding excessive forced plant shutdowns. |
description | The following relates to the nuclear power generation arts, nuclear reaction control arts, control rod operation arts, and related arts. In known nuclear power plants, a nuclear reactor core comprises a fissile material having size and composition selected to support a desired nuclear fission chain reaction. To moderate the reaction, a neutron absorbing medium may be provided, such as light water (H2O) in the case of light water reactors, or heavy water (D2O) in the case of heavy water reactors. It is further known to control or stop the reaction by inserting “control rods” comprising a neutron-absorbing material into aligned passages within the reactor core. When inserted, the control rods absorb neutrons so as to slow or stop the chain reaction. The control rods are operated by control rod drive mechanisms (CRDMs). In so-called “gray” control rods, the insertion of the control rods is continuously adjustable so as to provide continuously adjustable reaction rate control. In so-called “shutdown” control rods, the insertion is either fully in or fully out. During normal operation the shutdown rods are fully retracted from the reactor core; during a SCRAM, the shutdown rods are rapidly fully inserted so as to rapidly stop the chain reaction. Control rods can also be designed to perform both gray rod and shutdown rod functions. In some such dual function control rods, the control rod is configured to be detachable from the CRDM in the event of a SCRAM, such that the detached control rod falls into the reactor core under the influence of gravity. In some systems, such as naval systems, a hydraulic pressure or other positive force (other than gravity) is also provided to drive the detached control rod into the core. To complete the control system, a control rod/CRDM coupling is provided. A known coupling includes a connecting rod having a lower end at which the control rod is secured. The upper portion of the connecting rod operatively connects with the CRDM. A known CRDM providing gray rod functionality comprises a motor driving a lead screw that is integral with or rigidly connected with the connecting rod, such that operation of the motor can drive the lead screw and the integral or rigidly connected connecting rod up or down in a continuous fashion. A known CRDM providing shutdown functionality is configured to actively hold the control rod in the lifted position (that is, lifted out of the reactor core); in a SCRAM, the active lifting force is removed and the control rod and the integral or connected connecting rod fall together toward the reactor core (with the control rod actually entering into the reactor core). A known CRDM providing dual gray/shutdown functionality includes a motor/lead screw arrangement, and the connection between the motor and the lead screw is designed to release the lead screw during SCRAM. For example, the motor may be connected with the lead screw via a separable ball nut that is actively clamped to the lead screw during normal (gray) operation, and separates in the event of a SCRAM so that the control rod, the connecting rod, and the lead screw SCRAM together (that is, fall together toward the reactor core). Related application Ser. No. 12/722,662 titled “Control Rod Drive Mechanism For Nuclear Reactor” filed Mar. 12, 2010 and related application Ser. No. 12/722,696 titled “Control Rod Drive Mechanism For Nuclear Reactor” filed Mar. 12, 2010 are both incorporated herein by reference in their entireties. These applications disclose configurations in which the connection between the motor and the lead screw is not releasable, but rather a separate latch is provided between the lead screw and the connecting rod in order to effectuate SCRAM. In these alternative configurations the lead screw does not SCRAM, but rather only the unlatched connecting rod and control rod SCRAM together toward the reactor core while the lead screw remains engaged with the motor. The CRDM is a complex device, and is typically driven electrically and/or hydraulically. In the case of shutdown or dual gray/shutdown rods, the control rod system including the CRDM may also be classified as a safety related component—this status imposes strict reliability requirements on at least the shutdown functionality of the CRDM. To reduce cost and overall system complexity, it is known to couple a single CRDM with a plurality of control rods via an additional coupling element known as a “spider”. In such a case all the control rods coupled with a single CRDM unit move together. In practice a number of CRDM units are provided, each of which is coupled with a plurality of control rods, so as to provide some redundancy. The spider extends laterally away from the lower end of the connecting rod to provide a large “surface area” for attachment of multiple control rods. The spider typically comprises metal tubes or arms extending outward from a central attachment point at which the spider attaches with the connecting rod. In some spiders, additional supporting cross-members may be provided between the radially extending tubes. The diameters (or more generally, sizes) of the metal tubes or arms comprising the spider are kept as low as practicable in order to minimize hydraulic resistance of the spider during SCRAM and to enable the control rod support structure to contact and cam against all control rods during raising or lowering of the control rods. The coupling comprising the connecting rod and the spider is a relatively lightweight structure that minimizes material cost and weight-loading on the complex CRDM. For various reasons such as strength and robustness, low cost, manufacturability, and compatibility with the reactor vessel environment, both the connecting rod and the spider are usually stainless steel elements. In one aspect of the disclosure, an apparatus comprises: at least one control rod comprising a neutron absorbing material; a control rod drive mechanism (CRDM) unit; and a control rod/CRDM coupling connecting the control rod and the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod; wherein the control rod/CRDM coupling has an average density greater than the density of stainless steel at room temperature. In another aspect of the disclosure, an apparatus comprises a connecting rod of a control rod assembly of a nuclear reactor. The connecting rod includes a hollow or partially hollow connecting rod tube comprising a first material having a first density at room temperature, and a filler disposed in the hollow or partially hollow connecting rod tube, the filler comprising a second material having a second density at room temperature that is greater than the first density. In another aspect of the disclosure, an apparatus comprises a nuclear reactor pressure vessel, and a control rod assembly including at least one movable control rod comprising a neutron absorbing material, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM. The coupling includes at least a connecting rod comprising a hollow or partially hollow connecting rod tube comprising a first material having a first density at room temperature, and a filler disposed in the hollow or partially hollow connecting rod tube, the filler comprising a second material having a second density at room temperature that is greater than the first density. In another aspect of the disclosure, an apparatus comprises a nuclear reactor pressure vessel, and a control rod assembly including at least one movable control rod comprising a neutron absorbing material, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM. The coupling includes a first portion comprising a first material having a first density at room temperature, and a second portion comprising a second material having a second density at room temperature that is greater than the first density. Disclosed herein is a paradigm shift in control rod/CRDM coupling assemblies. In existing control rod/CRDM coupling assemblies, the control rod is terminated by a lightweight, “spidery” spider having a minimal weight and surface area oriented broadside to the SCRAM direction. The spider is configured to provide a large “effective” area for attachment of control rods, but a small “actual” area contributing to hydraulic resistance during SCRAM. Both the spider and the connecting rod are stainless steel components so as to provide benefits such as strength and robustness, low cost, manufacturability, and compatibility with the reactor vessel environment. Disclosed herein are control rod/CRDM coupling assemblies that include one or both of the following aspects: (i) replacement of the conventional lightweight spider with a terminal weighting element, and/or (ii) replacement of a substantial portion of the stainless steel of the control rod/CRDM coupling assembly with a denser material such as tungsten (optionally in a powdered or granulated form), molybdenum, tantalum, or so forth. The disclosed control rod/CRDM coupling assemblies are substantially heavier than conventional connecting rod/spider assemblies, which advantageously enhances the speed and reliability of gravitationally-induced SCRAM. In the case of control rod/CRDM coupling assemblies employing the disclosed terminal weighting element, the increased weight provided by the terminal weighting element as compared with a conventional lightweight spider enables the terminal weighting element to optionally have a larger actual surface area broadside to the SCRAM direction (for example, in order to provide the additional weight) as compared with the conventional spider. With reference to FIG. 1, a relevant portion of an illustrative nuclear reactor pressure vessel 10 includes a core former 12 located proximate to a bottom of the pressure vessel 10. The core former 12 includes or contains a reactive core (not shown) containing or including radioactive material such as, by way of illustrative example, enriched uranium oxide (that is, UO2 processed to have an elevated 235U/238U ratio). A control rod drive mechanism (CRDM) unit 14 is diagrammatically illustrated. The illustrative CRDM 14 is an internal CRDM that is disposed within the pressure vessel 10; alternatively, an external CRDM may be employed. FIG. 1 shows the single illustrated CRDM unit 14 as an illustrative example; however, more generally there are typically multiple CRDM units each coupled with a different plurality of control rods (although these additional CRDM units are not shown in FIG. 1, the pressure vessel 10 is drawn showing the space for such additional CRDM units). Below the CRDM unit 14 is a control rod guide frame 16, which in the perspective view of FIG. 1 blocks from view the control rod/CRDM coupling assembly (not shown in FIG. 1). Extending below the guide frame 16 are a plurality of control rods 18. FIG. 1 shows the control rods 18 in their fully inserted position in which the control rods 18 are maximally inserted into the core former 12. In the fully inserted position, the terminal weighting element (or, in alternative embodiments, the spider) is located at a lower location 20 within the control rod guide frame 16 (and, again, hence not visible in FIG. 1). In the illustrative embodiment of FIG. 1, the CRDM unit 14 and the control rod guide frame 16 are spaced apart by a standoff 22 comprising a hollow tube having opposite ends coupled with the CRDM unit 14 and the guide frame 16, respectively, and through which the connecting rod (not shown in FIG. 1) passes. FIG. 1 shows only a lower portion of the illustrative pressure vessel 10. In an operating nuclear reactor, an open upper end 24 of the illustration is connected with one or more upper pressure vessel portions that together with the illustrated lower portion of the pressure vessel 10 form an enclosed pressure volume containing the reactor core (indicated by the illustrated core former 12), the control rods 18, the guide frame 16, and the internal CRDM unit 14. In an alternative embodiment, the CRDM unit is external, located above the reactor pressure vessel. In such embodiments, the external CRDM is connected with the control rods by a control rod/CRDM coupling assembly in which the connecting rod extends through a portal in the upper portion of the pressure vessel. With reference to FIG. 2, the control assembly including the CRDM unit 14, the control rod guide frame 16, the intervening standoff 22, and the control rods 18 is illustrated isolated from the reactor pressure vessel. Again, the control rod/CRDM coupling assembly is hidden by the control rod guide frame 16 and the standoff 22 in the view of FIG. 2. With reference to FIG. 3, the control rod guide frame 16 and the standoff 22 is again illustrated, but with the CRDM unit removed so as to reveal an upper end of a connecting rod 30 extending upwardly above the standoff 22. If the CRDM unit has gray rod functionality, then this illustrated upper end of the connecting rod 30 engages with the CRDM unit to enable the CRDM unit to raise or lower the connecting rod 30 and, hence, the attached control rods 18 (not shown in FIG. 3). If the CRDM unit has shutdown rod functionality, then this illustrated upper end is detachable from the CRDM unit during SCRAM. In each of FIGS. 1-4, a SCRAM direction S is indicated, which is the downward direction of acceleration of the falling control rods in the event of a SCRAM. With reference to FIG. 4, the control rods 18 and the connecting rod 30 are shown without any of the occluding components (e.g., without the guide frame, standoff, or CRDM unit). In the view of FIG. 4 an illustrative terminal weighting element 32 is visible, which provides connection of the plurality of control rods 18 with the lower end of the connecting rod 30. It will be noticed that, unlike a conventional spider, the terminal weighting element 32 has substantial elongation along the SCRAM direction S. The illustrated terminal weighting element 32 has the advantage of providing enhanced weight which facilitates rapid SCRAM; however, it is also contemplated to replace the illustrated terminal weighting element 32 with a conventional “spidery” spider. With reference to FIGS. 5 and 6, a perspective view and a side-sectional perspective view, respectively, of the terminal weighting element 32 is shown. The terminal weighting element 32 includes a substantially hollow casing 40 having upper and lower ends that are sealed off by upper and lower casing cover plates 42, 44. Four upper casing cover plates 42 are illustrated in FIG. 5 and two of the upper casing cover plates 42 are shown in the side-sectional persective view of FIG. 6. The tilt of the perspective view of FIG. 5 occludes the lower cover plates from view, but two of the lower cover plates 44 are visible “on-edge” in the side-sectional view of FIG. 6. The illustrative terminal weighting element 32 includes four lower casing cover plates 44 arranged analogously to the four upper casing cover plates 42 illustrated in FIG. 5. Further visualization of the illustrative terminal weighting element 32 is provided by FIG. 7, which shows a top view of the hollow casing 40 with the cover plates omitted. As seen in FIG. 7, the hollow casing 40 is cylindrical having a cylinder axis parallel with the SCRAM direction S and a uniform cross-section transverse to the cylinder axis. That cross-section is complex, and defines a central passage 50 and four cavities 52 spaced radially at 90° intervals around the central passage 50. The cross-section of the hollow casing 40 also defines twenty-four small passages 54 (that is, small compared with the central passage 50), of which only some of the twenty-four small passages 54 are expressly labeled in FIG. 7. Comparison of FIG. 7 with FIGS. 5 and 6 show that the passages 50, 54 each pass completely through the casing 50 and are not covered by the upper or lower cover plates 42, 44. Considering first the twenty-four small passages 54, these provide structures for securing the plurality of control rods 18. In some embodiments, each of the twenty-four of the small passages 54 retain a control rod, such that the plurality of control rods 18 consists of precisely twenty-four control rods. In other embodiments, one or more of the twenty-four small passages 54 may be empty or may be used for another purpose, such as being used as a conduit for in-core instrumentation wiring, in which case the plurality of control rods 18 consists of fewer than twenty-four control rods. It is to be further appreciated that the terminal weighting element 32 is merely an illustrative example, and that the terminal weighting element may have other cross-sectional configurations that provide for different numbers of control rods, e.g. more or fewer than twenty-four. The four cavities 52 spaced radially at 90° intervals around the central passage 50 are next considered. The substantially hollow casing 40 and the upper and lower cover plates 42, 44 are suitably made of stainless steel, although other materials are also contemplated. The upper and lower cover plates 42, 44 seal the four cavities 52. As shown in the side-sectional view of FIG. 6, the four cavities 52 are filled with a filler 56 comprising a heavy material, where the term “heavy material” denotes a material that has a higher density than the stainless steel (or other material) that forms the hollow casing 40. For example, the filler 56 may comprise a heavy material such as tungsten (optionally in a powdered or granulated form), depleted uranium, molybdenum, or tantalum, by way of some illustrative examples. By way of illustrative example, stainless steel has a density of about 7.5-8.1 grams/cubic centimeter, while tungsten has a density of about 19.2 grams/cubic centimeter and tantalum has a density of about 16.6 grams per cubic centimeter. In some preferred embodiments, the heavy material comprising the filler 56 has a density that is at least twice the density of the material comprising the casing 40. In some preferred embodiments in which the casing 40 comprises stainless steel, the heavy material comprising the filler 56 preferably has a density that is at least 16.2 grams per cubic centimeter. (All quantitative densities specified herein are for room temperature.) In some embodiments, the filler 56 does not contribute to the structural strength or rigidity of the terminal weighting element 32. Accordingly, heavy material comprising the filler 56 can be selected without consideration of its mechanical properties. For the same reason, the filler 56 can be in the form of solid inserts sized and shaped to fit into the cavities 52, or the filler 56 can be a powder, granulation, or other constitution. The cover plates 42, 44 seal the cavities 52, and so it is also contemplated for the heavy material comprising the filler 56 to be a material that is not compatible with the primary coolant flowing in the pressure vessel 10. Alternatively, if the heavy material comprising the filler 56 is a material that is compatible with the primary coolant flowing in the pressure vessel 10, then it is contemplated to omit the upper cover plates 42, in which case the cavities 52 are not sealed. Indeed, if the filler 56 is a solid material securely held inside the cavities 52, then it is contemplated to omit both the upper cover plates 42 and the lower cover plates 44. With continuing reference to FIGS. 5-7 and with further reference to FIG. 8, the terminal weighting element 32 passes through the control rod guide frame 16 as the control rods 18 are raised or lowered by action of the CRDM unit 14. The cylindrical configuration with constant cross-section over the length of the terminal weighting element 32 along the SCRAM direction S simplifies this design aspect. Moreover, the control rod guide frame 16 should cam against each control rod 18 to provide the desired control rod guidance. Toward this end, the cross-section of the terminal weighting element 32 is designed with recesses 58 (some of which are labeled in FIG. 7). As shown in FIG. 8, into these recesses 58 fit mating extensions 60 of the control rod guide frame 16. A gap G also indicated in FIG. 8 provides a small tolerance between the outer surface of the terminal weighting element 32 and the proximate surface of the control rod guide frame 16. The twenty-four partial circular openings of the guide frame 16 which encompass the twenty-four small passages 54 of the terminal weighting element 32 are sized to cam against the control rods 18. For completeness, FIG. 8 also shows the connecting rod 30 disposed inside the central passage 50 of the terminal weighting element 32. FIGS. 5-7 show that providing space for the four cavities 52 substantially increases the actual cross-sectional area of the terminal weighting element 32 (that is, the area arranged broadside to the SCRAM direction S), as compared with the actual cross-sectional area that could be achieved without these four cavities 52. In some embodiments, the “fill factor” for the cross-section oriented broadside to the SCRAM direction S (including the area encompassed by the cover plates 42, 44) is at least 50%, and FIG. 7 demonstrates that the fill factor is substantially greater than 50% for the illustrative terminal weighting element. Thus, the design of the terminal weighting element 32 is distinct from the “spidery” design of a typical spider, which is optimized to minimize the actual surface area broadside to the SCRAM direction S and generally has a fill factor of substantially less than 50% in order to reduce hydraulic resistance. In general, the SCRAM force achieved by the weight of the terminal weighting element 32 more than offsets the increased hydraulic resistance of the greater actual broadside surface area imposed by the four cavities 52. Additional weight to overcome the hydraulic resistance and enhance SCRAM speed is obtained by elongating the terminal weighting element 32 in the SCRAM direction S. Said another way, a ratio of a length of the terminal weighting element 32 in the SCRAM direction S versus the largest dimension oriented broadside to the SCRAM direction S is optionally equal to or greater than one, and is more preferably equal to or greater than 1.2. The illustrative terminal weighting element 32 is not a generally planar element as per a typical spider, but rather is a volumetric component that provides substantial terminal weight to the lower end of the connecting rod 30. The illustrative terminal weighting element 32 has a substantial advantage in that it places the filler 56 comprising heavy material between the radioactive core (contained in or supported by the core former 12 located proximate to the bottom of the pressure vessel 10 as shown in FIG. 1) and the CRDM unit 14. The heavy material comprising the filler 56 is a dense material which can generally be expected to be highly absorbing for radiation generated by the reactor core. High radiation absorption is a property of heavy materials such as tungsten, depleted uranium, molybdenum, or tantalum, by way of illustrative example. Thus, the filler 56 comprising heavy material provides radiation shielding that protects the expensive and (in some embodiments and to various extent) radiation-sensitive CRDM unit 14. The elongation of the terminal weighting element 32 in the SCRAM direction S has additional benefits that are independent of providing weight. The elongation in the SCRAM direction S provides a longer length over which each control rod 18 can be secured to the terminal weighting element 32, and similarly provides a longer length over which the connecting rod 30 can be secured to the terminal weighting element 32. This provides a better mechanical couplings, and also provides enhanced stabilizing torque to prevent the control rods 18 from tilting. In general, the elongation of the terminal weighting element 32 in the SCRAM direction S provides a more rigid mechanical structure that reduces the likelihood of problematic (or even catastrophic) deformation of the connecting rod/terminal weighting element/control rods assembly. Another advantage of the elongation of the terminal weighting element 32 in the SCRAM direction S is that it optionally allows for streamlining the terminal weighting element 32 in the SCRAM direction S. This variation is not illustrated; however, it is contemplated to modify the configuration of FIG. 5 (by way of illustrative example) to have a narrower lower cross-section and a broader upper cross section, with a conical surface of increasing diameter running from the narrower lower cross-section to the broader upper cross section. The small passages 54 for securing the control rods would remain oriented precisely parallel with the SCRAM direction S (and, hence, would be shorter for control rods located at the outermost positions). Such streamlining represents a trade-off between hydraulic resistance (reduced by the streamlining) and weight reduction caused by the streamlining. Instead of the mentioned optional streamlining, the cross-section of the terminal weighting element can be otherwise configured to reduce hydraulic resistance. For example, the cross-section can include additional passages (not shown) analogous to the small passages 54, but which are not filled with control rods or anything else, and instead provide fluid flow paths to reduce the hydraulic resistance of the terminal weighting element during a SCRAM. The illustrative terminal weighting element 32 provides a desired weight by a combination of the filler 56 comprising a heavy material (which increases the average density of the terminal weighting element 32 to a value greater than the average density of stainless steel) and the elongation of the terminal weighting element 32 (which increases the total volume of the terminal weighting element 32). The total mass (equivalent to weight) is given by the product of the volume and the average density. To achieve a desired weight, various design trade-offs can be made amongst: (1) the size or amount or volume of the filler 56; (2) the density of the heavy material comprising the filler 56; and (3) the elongation of the terminal weighting element 32. In some embodiments, it is contemplated to achieve the desired weight by using a filler comprising a heavy material without elongating the terminal weighting element. In such embodiments, the terminal weighting element 32 may optionally have a conventional substantially planar and “spidery” spider configuration, in which the tubes or other connecting elements of the spider are partially or wholly hollow to define cavities containing the filler comprising a heavy material. Such a terminal weighting element can be thought of as a “heavy spider”. In other embodiments, it is contemplated to omit the filler material entirely, and instead to rely entirely upon elongation to provide the desired weight. For example, the illustrated terminal weighting element 32 can be modified by omitting the four cavities 52 and the filler 56. In this configuration the casing 40 can be replaced by a single solid stainless steel element having the same outer perimeter as the casing 40, with the top and bottom of the single solid stainless steel element defining (or perhaps better stated, replacing) the upper and lower casing cover plates 42, 44. Such embodiments omitting the filler comprising heavy material are suitably employed if the elongated terminal weighting element 32 made entirely of stainless steel provides sufficient weight. Such embodiments are also suitably employed if the weight of the terminal element is not a consideration, but other benefits of the elongated terminal element are desired, such as providing a longer length for secure connection with the control rods and/or the connecting rod 30, or providing an elongated geometry in the SCRAM direction S which is amenable to streamlining. Various embodiments of the disclosed terminal weighting elements use a stainless steel casing that does not compromise the primary function of providing a suitable structure for coupling the control rods to the lower end of the connecting rod. At the same time, the stainless steel casing leaves sufficient void or cavity volume to allow a filler comprising a heavy material to be inserted. Although stainless steel is referenced as a preferred material for the casing, it is to be understood that other materials having desired structural characteristics and reactor pressure vessel compatibility can also be used. The filler comprising heavy material is suitably tungsten, depleted uranium, or another suitably dense material. Various embodiments of the disclosed terminal weighting elements also have elongation in the SCRAM direction S. This elongated design is readily configured to fit into the control rod guide frame without any redesign (e.g., widening) of the guide frame, and hence does not impact the space envelope of the overall control rod assembly. The elongation is an adjustable design parameter, and can be set larger or smaller to provide the desired weight. Increasing the elongation generally increases the control rod assembly height, and this may impose an upper limit on the elongation for a particular reactor design. (This may be at least partially compensated by reducing the connecting rod length, but the connecting rod has a minimum length imposed by the desired maximum travel). Another advantage of the disclosed terminal weighting element is that it can provide adjustable weight. For example, in some embodiments different CRDM units may be located at different heights, or may support control rods of different masses, such that the different translating assemblies associated with the different CRDM units are not identical. If it is deemed beneficial for all translating assemblies associated with the various CRDM units to have the same weight, then different amounts of the filler comprising heavy material can be included in the cavities 52 of different terminal weighting elements 32 in order to equalize the weights of the translating assemblies. In some cases this might result in some cavities 52 being only partially filled with the filler 56. Optionally, the unfilled space of the cavities 52 can be filled with a light weight filler material such as a stainless steel slug (not shown) or can contain a compressed loading spring (not shown) to prevent the filler 56 comprising heavy material from moving about within the cavities 52. The weight of the light weight filler or loading spring is suitably taken into account in selecting the amount of filler 56 of heavy material to achieve a desired overall weight. Equalizing weights of the various translating assemblies can be useful, by way of example, to allow the use of a common plunger or other kinetic energy absorbing element in each translating assembly. The kinetic energy absorbing element (not shown in FIGS. 5-8) is designed to provide a “soft stop” to a translating assembly undergoing SCRAM when the control rods reach the point of full (i.e., maximal) insertion. The casing 40 of the illustrative terminal weighting element 32 acts as the structural part providing mechanical support. All loads associated with the coupling between the connecting rod 30 and the control rods 18 are transferred into the casing 40 which serves as the attachment location for each control rod. With reference to FIGS. 9, 10, and 11, various attachment configurations can be used for securing the connecting rod 30 in the attachment passage 50 of the casing 40 of the terminal weighting element 32. In an illustrative example of one such attachment configuration, the central passage 50 of the casing 40 houses a J-Lock female attachment assembly 70, which is suitably coaxially disposed inside the central passage 50 of the casing 40. FIG. 9 illustrates a side sectional view of the J-Lock female attachment assembly 70, while FIG. 10 shows a side view of the connected assembly and FIG. 11 shows a side sectional view of the connected assembly. With particular reference to FIG. 9, the illustrative J-Lock female attachment assembly 70 includes a hub 72 which in the illustrative embodiment comprises a round cylinder coaxially welded or otherwise secured in the central passage 50 of the casing 40. Alternatively, the hub may be integral with or defined by an inside surface of the central passage 50. The hub 72 serves as an interface between the casing 40 and the J-Lock female attachment components, which include three J-Lock pins 74 (two of which visible in the sectional view of FIG. 9) disposed inside of the hub 72. These pins 74 provide the connection points for a J-Lock male attachment assembly 80 (see FIG. 11) disposed at the lower end of the connecting rod 30. A J-Lock plunger 76 and a J-Lock spring 84 keeps the J-Lock male attachment assembly 80 of the connecting rod 30 in place once it has been engaged with the terminal weighting element 32. (Locked arrangement shown in FIG. 11). The illustrative J-Lock female attachment assembly 70 further includes a lower plunger 82, an inner spring 78, and a spring washer 86 which cooperate to absorb the impact of the lower translating assembly (that is, the translating combination of the control rods 18, the terminal weighting element 32, the connecting rod 30, and optionally a lead screw (not shown)) during a SCRAM. The illustrative J-Lock connection between the lower end of the connecting rod 30 and the terminal weighting element 32 is an example. More generally, substantially any type of connection, including another type of detachable connection or a permanently welded connection or an integral arrangement, is contemplated. The J-Lock arrangement has the advantage of enabling the connecting rod 30 to be detached from the terminal weighting element 32 (and, hence, from the control rods 18) by a simple “push-and-twist” operation. This allows the connecting rod 30 to be moved separately from the remainder of the translating assembly (that is, the terminal weighting element 32 and the attached control rods 18) during refueling of the nuclear reactor. The casing 40 of the terminal weighting element 32 can be manufactured using various techniques. In some embodiments manufacturing employing Electrical Discharge Machining (EDM) is contemplated. The EDM method operates on a solid block of stainless steel which is then cut to define the spider casing 40. Advantageously, EDM is fast and precise. Other contemplated methods include casting techniques or extrusion, both of which are fast and have low material cost. The translating assembly comprising the control rods 18, terminal weighting element 32, connecting rod 30, and optionally a lead screw (not illustrated) is advantageously heavy in order to facilitate rapid and reliable SCRAM of the translating assembly toward the reactor core in the event of an emergency reactor shutdown. Toward this end, the terminal weighting element 32 is configured to be heavy. One way disclosed herein to achieve this is by increasing the average density of the terminal weighting element 32 to a value greater than that of stainless steel (or, more generally, increasing its average density to a value greater than that of the material comprising the casing 40) by the addition of the filler 56 comprising heavy material (where “heavy” denotes a density greater than that of the stainless steel or other material comprising the casing 40). Another way disclosed herein to achieve this is by elongating the terminal weighting element 32 in the SCRAM direction S. The illustrative terminal weighting element 32 employs both enhanced average density via filler 56 and elongation in the SCRAM direction S. With reference to FIGS. 10 and 11, additional weight for the translating assembly is additionally or alternatively obtained by enhancing the density of the connecting rod 30. Toward this end, the illustrative connecting rod 30 includes a hollow (or partially hollow) connecting rod tube 90 which (as seen in the sectional view of FIG. 11) contains a filler 92 comprising heavy material. Thus, the connecting rod tube 90 serves the structural purpose analogous to the casing 40 of the terminal weighting element 32, while the filler 92 comprising heavy material serves a weighting (or average density-enhancing) purpose analogous to the filler 56 of the terminal weighting element 32. The hollow connecting rod tube 90 can be manufactured using various techniques, such as EDM (although longer tube lengths may be problematic for this approach), casting, extrusion, milling, or so forth. In one suitable embodiment, the filler 92 comprising heavy material is in the form of tungsten slugs each having a diameter substantially coinciding with an inner diameter of the connecting rod tube 90 and being stacked in the connecting rod tube 90, with the number of stacked tungsten slugs being selected to achieve the desired weight. If the number of tungsten slugs is insufficient to fill the interior volume of the connecting rod tube 90 and it is desired to avoid movement of these slugs, then optionally the filler 92 is prevented from shifting by a suitable biasing arrangement or by filling the remaining space within the interior volume of the connecting rod tube 90 with a light weight material such as stainless steel slugs. In the illustrative example of FIG. 11, a biasing arrangement is employed, in which the interior volume of the connecting rod tube 90 is sealed off by upper and lower welded plugs 94, 96, and a compressed spring 98 takes up any slack along the SCRAM direction S that may be introduced by incomplete filling of the interior volume of the connecting rod tube 90 by the filler 92. Instead of tungsten, the heavy material comprising the filler may be depleted uranium, molybdenum, tantalum, or so forth, by way of some other illustrative examples. The filler 92 may comprise one or more solid slugs or rods, a powder, a granulation, or so forth. In the context of the connecting rod 30, the term “heavy material” refers to a material having a density that is greater than the density of the stainless steel or other material comprising the connecting rod tube 90. By way of illustrative example, stainless steel has a density of about 7.5-8.1 grams/cubic centimeter, while tungsten has a density of about 19.2 grams/cubic centimeter and tantalum has a density of about 16.6 grams per cubic centimeter. In some preferred embodiments, the heavy material comprising the filler 92 has a density that is at least twice the density of the material comprising the hollow connecting rod tube 90. In some preferred embodiments in which the hollow connecting rod tube 90 comprises stainless steel, the heavy material comprising the filler 92 preferably has a density that is at least 16.2 grams per cubic centimeter. (All quantitative densities specified herein are for room temperature.) With continuing reference to FIGS. 10 and 11, the illustrative connecting rod 30 has an upper end that includes an annular groove 100 for securing with a latch of the CRDM unit 14 (latch not shown), and a magnet 102 for use in conjunction with a control rod position sensor (not shown). A suitable embodiment of the CRDM unit 14 including a motor/lead screw arrangement for continuous (gray rod) adjustment and a separate latch for detaching the connecting rod 30 from the CRDM unit 14 (with the lead screw remaining operatively connected with the motor) is described in related application Ser. No. 12/722,662 titled “Control Rod Drive Mechanism For Nuclear Reactor” filed Mar. 12, 2010 and related application Ser. No. 12/722,696 titled “Control Rod Drive Mechanism For Nuclear Reactor” filed Mar. 12, 2010, both of which are both incorporated herein by reference in their entireties. Alternatively, in other embodiments a lead screw (not shown) is secured with or integral with the connecting rod tube 90, and the lead screw SCRAMs together with the connecting rod/terminal weighting element (or spider)/control rod (in other words, the lead screw forms part of the translating assembly during SCRAM). In some such alternative embodiments, the motor is suitably coupled with the lead screw by a separable ball nut that separates to release the lead screw and initiate SCRAM. The illustrative connecting rod 30 includes eight components. The weight of the connecting rod 30 assembly is increased by using the hollow connecting rod tube 90. This may be only partially hollow—for example, only a lower portion may be hollow. Located inside the hollow connecting rod tube 90 is the filler 92 comprising heavy material. In some embodiments, the filler 92 comprises several smaller rods or slugs of tungsten. The number of tungsten rods or slugs inside the hollow connecting rod tube 90 is selected to achieve a desired weight. If different translating assemblies are employed with different CDRM units, the number of tungsten rods or slugs inside each of the hollow connecting rod tubes 90 may be different, and selected so as to ensure that each connecting rod of the several CDRM units has the same weight. This is advantagous since it follows that all of the CRDM units can be designed to lift a single weight independent of factors such as connecting rod length, control rod composition, or so forth. As already noted, such weight “tuning” can also be achieved by adjusting the filler 56 in the terminal weighting element 32. If both fillers 56, 92 are employed, then the combined weight of the fillers 56, 92 can be tuned by adjusting the amount and/or density of either one, or both, of the fillers 56, 92. If the amount of weight tuning is expected to be small, then in some such embodiments the fillers 56, 92 may be solid elements of standard size/weight, and the total weight may then be trimmed by adding additional filler comprising heavy material in the form of a powder, granulation, small slug or slugs, or so forth. If the interior volume of the hollow connecting rod tube 90 is only partially filled by the filler 92, then stainless steel rods or some other light weight filler (not shown) may be inserted into the remaining interior volume to fill complete the filling. Additionally or alternatively, the spring 98 or another mechanical biasing arrangement may be employed. It is contemplated to have the filler 92 arranged “loosely” in the rod tube 90; however, such an arrangement may complicate absorption of kinetic energy at the termination of a SCRAM drop. The filler 92 generally has a lower coefficient of thermal expansion than the stainless steel (or other material) of the hollow connecting rod tube 90. The connecting rod 30 is assembled at room temperature, and then heated to its operating temperature. For a connecting rod having a length of, e.g. 250 centimeters or greater, the thermal expansion will result in the rod tube 90 increasing by an amount of order a few centimeters or more. The lower coefficient of thermal expansion of the filler 92 results in a substantially lower length increase of the filler 92. The spring 98 suitably compensates for this effect. Additionally, if the spring 98 is located below the filler 92 (as shown in FIG. 11), then it can assist in dissipating the kinetic energy of the filler 92 at the termination of the SCRAM drop. As shown in the illustrative embodiment depicted in FIG. 11, the hollow connecting rod tube 90 may be less than the total length of the connecting rod 30. In the illustrated case, the connecting rod 30 includes additional length below the rod tube 90 corresponding to the J-Lock male attachment assembly 80, and also includes additional length above the rod tube 90 corresponding to an upper tube that includes the latch groove 100 and houses the position indicator magnet 102. The upper and lower welded plugs 94, 96 are optionally provided to seal off the interior volume of the hollow connecting rod tube 90. These plugs 94, 96 are attached to the upper and lower ends, respectively of the hollow connecting rod tube 90 so as to seal the filler 92 and the optional spring 98 inside. In the illustrative embodiment, the outer ends of the plugs 94, 96 are configured to facilitate connection of the upper connecting rod and the J-lock male attachment assembly 80, respectively. The connecting rod 30 also has a substantial advantage in that it places the filler 92 comprising heavy material between the radioactive core (contained in or supported by the core former 12 located proximate to the bottom of the pressure vessel 10 as shown in FIG. 1) and the CRDM unit 14. The heavy material comprising the filler 92 is a dense material which can generally be expected to be highly absorbing for radiation generated by the reactor core. High radiation absorption is a property of heavy materials such as tungsten, depleted uranium, molybdenum, or tantalum, by way of illustrative example. Thus, the filler 92 comprising heavy material provides radiation shielding that protects the expensive and (in some embodiments and to various extent) radiation-sensitive CRDM unit 14. If both fillers 56, 92 are used, then both fillers contribute to this advantageous CRDM shielding effect. The illustrative control rod/CRDM coupling includes a combination of (1) the terminal weighting element 32 including elongation and the filler 56, and (2) the connecting rod 30 including the filler 92. In other control rod/CRDM coupling embodiments it is contemplated to include a combination of the terminal weighting element 32 including elongation and the filler 56 but coupled with a conventional solid stainless steel connecting rod (without the filler 92). In other control rod/CRDM coupling embodiments it is contemplated to include a combination of a terminal element (which may or may not be a weighting element) including elongation but without the filler 56, coupled either with (i) the connecting rod 30 including the filler 92 or (ii) a conventional solid stainless steel connecting rod (without the filler 92). In other control rod/CRDM coupling embodiments it is contemplated to include a combination of a terminal weighting element without elongation (for example, having a “spidery” topology similar to a conventional spider) but which includes the filler 56 disposed in hollow regions of the tubes or other members of the terminal weighting element, coupled either with (i) the connecting rod 30 including the filler 92 or (ii) a conventional solid stainless steel connecting rod (without the filler 92). In other control rod/CRDM coupling embodiments it is contemplated to include a combination of (I) a conventional spider without elongation and without the filler 56 and (II) the connecting rod 30 including the filler 92. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. |
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043494536 | abstract | The method of processing alkaline solutions containing radioactive iodine consists in dissolving irradiated fuels in a nitric acid solution. The vapors constituted essentially by nitrogen oxides, iodine and water formed during dissolution are passed into a condenser and then into a first absorption column in which the recombined nitric acid is formed. The recombined acid is returned to the dissolver while the gases discharged from the first absorption column are passed into a second absorption column in counterflow to an alkaline solution which is loaded with iodine and with nitrous ions. The alkaline solution discharged from the second absorption column is passed into a reaction vessel containing a mixture of nitric acid and sulphamic acid which destroys the nitrous products and releases the iodine. |
abstract | A method and system for maintaining an item of equipment supports the provision of predictive maintenance in a manner which eliminates or reduces downtime of the equipment. The method includes tracking performance data on the equipment or a particular component of the equipment. At least one required maintenance activity is predicted based upon the performance data with respect to a defined performance standard. Performance of the required maintenance activity is scheduled at a defined respective time based upon the prediction. |
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claims | 1. A method for delivering therapeutic radiation to a target volume of a subject, wherein the target volume is located at a predetermined depth, the predetermined depth being measured from an irradiated portion of a surface of the skin of the subject, the method comprising:selecting a species of light ions for forming an array of minibeams directed at the target volume based on the predetermined depth;selecting a predetermined energy of the species of light ions for confining the therapeutic radiation within the target volume such that the Bragg peak corresponding to the predetermined energy of the species is at a distal side of the target volume;delivering the therapeutic radiation to the target volume, including:forming the array of minibeams directed at the target volume, the minibeams comprising the species of light ions at the predetermined energy, andirradiating a portion of the surface of the skin with the array, the array comprising parallel, spatially distinct minibeams at the surface of the skin in an amount and spatially arranged and sized to maintain a tissue-sparing effect from the surface of the skin to a proximal edge of the target volume and to merge into a solid beam at the proximal edge of the target volume, wherein the species of light ions is selected such that the minibeams broaden and merge into the solid beam at the proximal edge of the target volume to deliver a therapeutic dose of radiation to at least a portion of the target volume; andwherein forming the array further includes selecting a gap between adjacent minibeams in the array to maintain the solid beam at the predetermined energy of the species of light ions at the proximal edge. 2. The method of claim 1, wherein the step of delivering the therapeutic dose further includes spreading the Bragg-peak of the light ions forming the minibeams by stepwise lowering the predetermined energy of the light ions across a range of energies to produce a uniform dose distribution throughout the target volume, and wherein the step of selecting the gap includes selecting the gap for which the solid beam is maintained at the proximal edge for each of the energies across the range of energies. 3. The method of claim 2, wherein the energies of the light ions forming the minibeams are between about 10 MeV and 1000 MeV per nucleon. 4. The method of claim 1, wherein the light ions forming the minibeams are protons. 5. The method of claim 1, wherein the array of minibeams is a two-dimensional array of pencil minibeams. 6. The method of claim 5, further comprising shaping a cross-section of the two-dimensional array to substantially match a cross-sectional shape of the target volume. 7. The method of claim 1, wherein the species of light ions forming the minibeams are selected from the group consisting of deuterons and ions of helium, lithium, beryllium, and boron. 8. The method of claim 1, further comprising providing a light ion source and a collimator downstream of the light ion source for forming the array of minibeams on the surface, wherein the gap between the adjacent beams is adjusted by adjusting a spacing of slits in the collimator. 9. The method of claim 8, wherein the collimator is spaced apart from the surface of the skin. 10. The method of claim 1, wherein a width of each of the minibeams at the surface is between 0.1 mm and 0.6 mm. 11. The method of claim 10, wherein the width is about 0.3 mm. 12. The method of claim 1, wherein a cross-sectional profile of the minibeams is one of a circular, square, rectangular, elliptical, and polygonal shape. 13. The method of claim 1, wherein the gap between the minibeams is between about 0.1 mm and about 3.0 mm. 14. The method of claim 1, wherein the gap between the minibeams is between about 0.1 mm and about 1.0 mm. 15. The method of claim 1, wherein the array of minibeams is a one-dimensional array of planar minibeams. 16. The method of claim 1, further comprising additionally performing the steps of selecting a species of light ions, selecting a predetermined energy, and delivering the therapeutic radiation from a second direction, a second portion of the surface of the skin being irradiated from the second direction, the predetermined depth of the target volume being measured from the second portion of the skin. 17. The method of claim 16, wherein the step of delivering the therapeutic dose from the second direction further includes spreading the Bragg-peak of the selected light ions forming the minibeams on the second portion of the skin by stepwise lowering the predetermined energy across a range of energies to produce a uniform dose distribution throughout the target volume, and wherein the gap between adjacent minibeams of an array irradiating the second portion is selected to maintain a solid beam at a proximal edge relative to the second direction for each of the energies across the range of energies. 18. A method for delivering therapeutic light ion radiation to a target volume of a subject, wherein the target volume is located at a predetermined depth, the predetermined depth being measured from an irradiated portion of the skin of the subject, the method comprising:irradiating a portion of a surface of the skin with an array of light ion minibeams comprising parallel, spatially distinct minibeams at the surface in an amount and spatially arranged and sized to maintain a tissue-sparing effect from the surface of the skin to a proximal side of the target volume, and to merge into a solid beam at the proximal side of the target volume; andwherein a gap between adjacent parallel, spatially distinct minibeams at the surface and a species of light ions forming the minibeams are selected based on a depth of the target volume from the surface. 19. The method of claim 18, wherein a species of light ions forming the light ion minibeams is selected from the group consisting of protons, deuterons, and ions of helium, lithium, beryllium, and boron. 20. The method of claim 19, the method further comprising spreading the Bragg-peak of the species of light ions forming the minibeams by stepwise adjusting the predetermined energy of the light ions across a range of energies to produce a uniform dose distribution throughout the target volume, and wherein the species of light ions and the gap are selected so that the minibeams broaden and merge into the solid beam at the proximal side for each of the energies across the range of energies. |
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054835615 | abstract | A reactor core inspection apparatus is disclosed which comprises a hollow tube containing a distally located radial opening, and having an ultrasonic transducer located therein. The tube is connected by a hollow cable to a calibrated degree wheel which allows rotation of the tube once lowered through the top of a partially raised upper internals assembly of a reactor. The transducer is connected to a detector which senses whether one of the fuel assemblies contained within the core has become entangled with the internals assembly prior to full removal of the assembly. If a hangup is detected, the assembly can be lowered in an attempt to disentangle the fuel assembly, to avoid damage. |
summary | ||
abstract | New compounds which meet general formula (I): |
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claims | 1. A method of improving a core inlet enthalpy for a core of a nuclear reactor, comprising:directing a downward flow of water to an inlet of the core of the nuclear reactor; andinterrupting the downward flow of the water within a downcomer region of a reactor pressure vessel of the nuclear reactor with a plurality of first trip structures and a plurality of second trip structures, the downcomer region being an annular space defined by the reactor pressure vessel and a chimney within the reactor pressure vessel, the plurality of first trip structures disposed on an exterior surface of the chimney and spaced apart from an inner surface of the reactor pressure vessel, the plurality of second trip structures disposed on the inner surface of the reactor pressure vessel and spaced apart from the exterior surface of the chimney, the plurality of second trip structures arranged in a staggered manner relative to the plurality of first trip structures so as to alter the downward flow of the water to an undulating flow of the water that enhances axial and radial mixing to thereby improve the core inlet enthalpy for the core of the nuclear reactor. 2. The method of claim 1, wherein the interrupting includes disrupting the downward flow of the water with a planar surface of the plurality of first trip structures. 3. The method of claim 2, wherein the planar surface is perpendicular to the exterior surface of the chimney. 4. The method of claim 1, wherein the interrupting includes disrupting the downward flow of the water with a curved surface of the plurality of first trip structures. 5. The method of claim 1, wherein the plurality of first trip structures protrude a first length into the annular space, the first length being about 1% to 15% of a distance between the exterior surface of the chimney and the reactor pressure vessel. 6. The method of claim 1, wherein the interrupting includes directing the downward flow of the water away from the exterior surface of the chimney and toward the reactor pressure vessel. 7. The method of claim 1, wherein the interrupting includes increasing thermal uniformity such that a temperature of the water at a bottom of the downcomer region varies by no more than 5 degrees Celsius at a given point in time. 8. The method of claim 1, wherein the downcomer region spans at least 7 meters. 9. The method of claim 1, wherein the plurality of first trip structures protrude to different extents into the downcomer region. 10. The method of claim 1, wherein the directing includes guiding the downward flow such that the water is fed to the inlet of the core of the nuclear reactor. 11. The method of claim 1, wherein the interrupting occurs upstream from the inlet of the core of the nuclear reactor. |
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049816403 | claims | 1. A cell for receiving and dismantling a nuclear fuel assembly comprising a bundle of fuel rods retained at the nodal points of a regular lattice by a skeleton formed of a lower end piece and an upper end piece connected together by tie rods and of a plurality of grids spaced apart along the tie rods, said cell comprising: a vertical structure having an internal cross-section sized to receive a fuel assembly; a plurality of gripping mechanisms each for retaining a respective one of the grids and lower end piece of said fuel assembly; and a comb mechanism for holding the fuel rods of the fuel assembly at their normal spacing in the regular lattice, said comb mechanism comprising at least two sets of combs, the combs of each of said sets being movable with respect to the structure between a first position in which they are outside a fuel assembly located within the structure and a second position in which fingers of the combs are engaged between the rods, above one of said grids which is uppermost after removal of an upper portion of said skeleton, wherein the combs of each set are carried by and guided on a frame securely connected to said structure, and are operatively connected to jack means arranged for moving them toward and away from each other between said first and second position in a direction transverse to the movement of the combs of the other of said sets, and wherein one of said gripping mechanisms comprises a plurality of jaws mounted on the structure and connected to additional jack means for moving the jaws simultaneously away from each other to a position with respect to the structure in which they release said uppermost grid and toward each other into a predetermined position with respect to the structure in which the jaws grip and clamp all sides of said uppermost grid and center said uppermost grid with respect to said structure. a vertical structure having an internal cross-section sized to receive a fuel assembly; a plurality of gripping mechanisms each for retaining one of the grids and lower end piece of said fuel assembly; and a comb mechanism for holding the fuel rods of the fuel assembly at their normal spacing in the regular square lattice, said comb mechanism comprising two sets of combs, the combs of each of said sets being movable with respect to the structure orthogonally to the combs of the other set between a first position in which they are outside a fuel assembly located within the structure and a second position in which fingers of the combs are engaged between the rods, above one of said grids which is uppermost after removal of an upper section of said skeleton, wherein the combs of each set are carried by and guided on a frame securely connected to said structure, and are operatively connected to jack means arranged for moving them toward and away from each other rectilinearly between said first and second position in a direction transverse to the rectilinear movement of the combs of the other of said sets, and wherein one of said gripping mechanisms comprises a plurality of jaws pivotally mounted on the structure and connected to additional jack means for moving the jaws simultaneously between a position with respect to the structure in which they release the uppermost grid and a predetermined position with respect to the structure in which the jaws grip all sides of said uppermost grid, said jaws of said gripping mechanism having projections for engaging an upper edge of said uppermost grid between mutually adjacent ones of said fuel rods and preventing upward movement thereof. a vertical structure having an internal cross-section sized to receive a fuel assembly; a plurality of gripping mechanisms each for retaining a respective one of the grids and lower end piece of said fuel assembly; and a comb mechanism for holding the fuel rods of the fuel assembly at their normal spacing in the regular lattice, said comb mechanism comprising at least two sets of combs, the combs of each of said sets being movable with respect to the structure between a first position in which they are outside a fuel assembly located within the structure and a second position in which fingers of the combs are engaged between the rods, above one of said grids which is uppermost after removal of an upper portion of said skeleton, wherein the combs of each set are carried by and guided on a frame securely connected to said structure, and are operatively connected to jack means arranged for moving them toward and away from each other between said first and second position in a direction transverse to the movement of the combs of the other of said sets, wherein one of said gripping mechanisms comprises a plurality of jaws pivotally mounted on the structure and connected to additional jack means for moving the jaws simultaneously between a position with respect to the structure in which they release said uppermost grid and a predetermined position with respect to the structure in which the jaws grip all sides of said uppermost grid, and wherein the gripping mechanisms further comprise at least one mechanism for retaining a grid other than the uppermost grid, having a single set of two additional jaws pivotally mounted on the structure and connected to individual control jacks for simultaneously moving the additional jaws of said gripping mechanism between a position in which the jaws engage one side of the grid and a position in which they release said one side, said additional jaws having projections located for retaining said other grid by insertion between adjacent rods and engagement of an upper edge of the grid, whereby they retain said other grid. 2. A cell for receiving and dismantling a nuclear fuel assembly having a square cross-section comprising a bundle of fuel rods retained at the nodal points of a regular square lattice by a skeleton formed of a lower end piece and an upper end piece connected together by tie rods and of a plurality of grids spaced apart along the tie rods, said cell comprising: 3. Cell according to claim 1, wherein the jaws of the gripping mechanisms are controlled by two opposed jacks via a same plate connected to said jacks and surrounding said structure. 4. Cell according to claim 2, further comprising means for retaining and centering the lower end piece of said fuel assembly in said structure, said means having centering studs carried by a bottom part of the structure and a single additional set of two jaws arranged to clamp two opposed faces of the lower end piece, said jaws being operatively connected to a jack for movemet thereof between a position in which the jaws clamp the lower end piece and a position in which the jaws release the lower end piece. 5. Cell according to claim 4, wherein the jaws of said means for retaining and centering the lower end piece and the jaws of the grid holding mechanisms act on alternate sets of two opposed faces along the fuel assembly, 6. Cell according to claim 1, wherein each of the jaws is guided in its movements by pins fixed to the structure and retained in elongate holes in the jaws and the jaws are actuated by jacks via hinged connections. 7. Cell according to claim 1, wherein said combs are each carried by a slide formed on the frame and have respective drive jacks and each comb carries lateral racks meshing with pinions carried by a common shaft so as to cause smooth and even movement of the comb. 8. Cell according to claim 1, having a height proportioned to that of the fuel assembly to be received so that the upper end piece and the grid of the assembly which is closest to the upper end piece are above the structure whereby the tie rods can be cut below the uppermost grid and a sub-assembly to be removed formed by the upper end piece, the said grid closest to the upper end piece and upper sections of the tie rods above the cut. 9. A cell for receiving and dismantling a nuclear fuel assembly comprising a bundle of fuel rods retained at the nodal points of a regular lattice by a skeleton formed of a lower end piece and an upper end piece connected together by tie rods and of a plurality of grids spaced apart along the tie rods, said cell comprising: |
description | The present invention relates to a fastening and loosening device that rotates and fastens a nut with causing tension to act on a stud bolt when a cover is attached to an upper portion of a reactor vessel, or rotates and loosen the nut with causing tension to act on the stud bolt when the cover fixed to the upper portion of the reactor vessel is removed, for example. For example, a pressurized water reactor (PWR) uses light water as a reactor coolant and a neutron moderator, fills a reactor core with not-boiled, high-temperature and high-pressure water, sends the high-temperature and high-pressure water to a steam generator to generate steam by heat exchange, and sends the steam to a turbine generator to generate power. A reactor vessel used for such a pressurized water reactor is constructed of a reactor vessel main body and a reactor vessel cover mounted on the reactor vessel main body so that a reactor-internal structure can be inserted in the reactor vessel, and the reactor vessel cover is openable/closable with respect to the reactor vessel main body. Further, when the reactor vessel cover is mounted on the reactor vessel main body in a freely attachable/detachable manner, a stud bolt is caused to penetrate an outer peripheral flange of the reactor vessel cover and is screwed in and embedded in an upper outer peripheral flange of the reactor vessel main body, and a nut is screwed with the stud bolt with tension acting on the stud bolt, so that fastening is performed. Such a fastening and loosening device is disclosed in Patent Literature 1 described below. A device disclosed in Patent Literature 1 performs work using a bolt tensioner. Patent Literature 1: Japanese Patent Application Laid-open No. 10-227888 When a nut is rotated with respect to a stud bolt using the above-described fastening and loosening device and a reactor vessel cover is removed from a reactor vessel main body, a plurality of stud bolts and nuts is provided along each outer peripheral flange of the reactor vessel main body and the reactor vessel cover. Therefore, the work is performed with the device being moved along the direction. In this case, before performing the fastening and loosening work, it is necessary to position the bolt tensioner into proper positions with respect to the stud bolts and nuts, and for example, the fastening and loosening device is caused to be freely movable along an arrangement direction of the stud bolts and nuts by a guide device. By the way, the reactor vessel differs in size depending on a position where a reactor is disposed, power generation capacity of a plant, and the like. An outer diameter of each outer peripheral flange of the reactor vessel main body and the reactor vessel cover, an outer diameter and the number of the stud bolts and nuts, and the like differ. Therefore, since the guide device that guides the fastening and loosening device differs in shape and size depending on the size of the reactor vessel, it is necessary to prepare the fastening and loosening device for each reactor vessel, and there is a problem of rising a cost of facilities. The present invention solves the above-described problem, and an object of the present invention is to provide a fastening and loosening device enables proper fastening and loosening of a nut with respect to a stud bolt regardless of the size and shape of a member to be fastened. According to an aspect of the present invention, a fastening and loosening device having a plurality of stud bolts screwed in an object to be fastened and arranged and nuts respectively screwed with the stud bolts, and rotating the nut with causing tension to act on the stud bolt in a shaft center direction away from the object to be fastened to perform fastening or loosening, includes: a device main body having an upper portion movably supported along an arrangement direction of the stud bolts; a bolt tensioner supported by the device main body and being freely movable along the shaft center direction of the stud bolts; a guide device provided in a lower portion of the device main body and having right and left guide members contactable with an outer periphery of the nut from both right and left sides of a moving direction of the device main body; and a guide position adjustment device capable of moving at least one of the right and left guide members in a horizontal direction intersecting with the moving direction of the device main body. Therefore, the right and left guide members can guide the device main body by contacting with the outer periphery of the nut from both the right and left sides of the device main body, and the guide member is moved in the horizontal direction intersecting with the moving direction of the device main body by the guide position adjustment device, so that the guide position of the guide member with respect to the nut can be adjusted. Therefore, the guide member can properly guide the device main body regardless of the size and shape of the member to be fastened, and as a result, the fastening and loosening of the nut with respect to the stud bolt can be properly performed. In the fastening and loosening device, the arrangement direction of the stud bolts is a circumferential direction along an outer periphery of the object to be fastened, and the guide device allows the guide member positioned at an inner side of the circumferential direction to be movable by the guide position adjustment device. Therefore, the guide member positioned at the inner side of the circumferential direction is moved by the guide position adjustment device, so that the guide position of the guide member with respect to the nut is adjusted, and position adjustment of the guide member can be easily performed with a simple configuration. The fastening and loosening device, further includes a positioning device having a positioning member inserted between adjacent nuts from an outside of the circumferential direction. Therefore, the positioning member is inserted between the nuts from the other side of the guide member by the positioning device, whereby proper positioning of the device main body can be performed. The fastening and loosening device, further includes an insertion position adjustment device capable of adjusting an insertion position of the positioning member. Therefore, since the position where the positioning member is inserted can be adjusted by the insertion position adjustment device, the positioning member can properly position the device main body regardless of the size and shape of the member to be fastened. As a result, the fastening and loosening of the nut with respect to the stud bolt can be properly performed. In the fastening and loosening device, the guide position adjustment device includes a support shaft supporting one end portion of the guide member in a freely rotatable manner, and an eccentric mechanism allowing the other end portion of the guide member to be movable. Therefore, by simply actuating the eccentric mechanism, the guide position of the guide member can be easily changed, and the device can be simplified. In the fastening and loosening device, the guide device is constructed of the right and left guide members fixed to a lower portion of a box body with a predetermined interval, and the guide position adjustment device is capable of horizontally swinging the box body. Therefore, the box body is swung by the guide position adjustment device to adjust the position of the guide member, whereby versatility can be improved by sufficiently securing a position adjustment margin. In the fastening and loosening device, the guide devices are provided before and behind the bolt tensioner in the moving direction of the device main body, and the guide member is contactable with the outer peripheries of two or more of the nuts. Therefore, the movement of the device main body is guided before and behind the bolt tensioner by the guide devices, whereby the device can be stably moved and guided. According to a fastening and loosening device of the present invention, a guide device having right and left guide members contactable with an outer periphery of a nut from both the right and left sides of a moving direction of a device main body, and a guide position adjustment device capable of moving at least one of the guide members in a horizontal direction intersecting with the moving direction of the device main body are provided. Therefore, fastening and loosening of a nut with respect to a stud bolt can be properly performed regardless of the size and shape of a member to be fastened. Hereinafter, preferred embodiments of a fastening and loosening device according to the present invention will be described in detail with reference to the appended drawings. Note that the present invention is not limited by these embodiments and includes configuration made by combining the embodiments where there is a plurality of embodiments. FIG. 1 is a perspective view illustrating a whole configuration of a fastening and loosening device according to the first embodiment of the present invention, FIG. 2 is a plan view illustrating the whole configuration of the fastening and loosening device of the first embodiment, FIG. 3 is a perspective view illustrating the fastening and loosening device of the first embodiment, FIG. 4 is a front view illustrating the fastening and loosening device of the first embodiment, FIG. 5 is a side view illustrating the fastening and loosening device of the first embodiment, FIG. 6 is a cross sectional view illustrating a bolt tensioner, FIGS. 7-1 to 7-5 are schematic views illustrating actuations of the bolt tensioner, FIG. 8 is a plan view illustrating a guide device in the fastening and loosening device of the first embodiment, FIG. 9 is a plan view illustrating a guide position adjustment device and an insertion position adjustment device, FIG. 10 is a plane view of an actuation of the guide position adjustment device and the insertion position adjustment device, FIG. 11 is a schematic configuration diagram of a nuclear power plant, and FIG. 12 is a longitudinal sectional view illustrating a pressurized water reactor. A reactor of the first embodiment is a pressurized water reactor (PWR) that uses light water as a reactor coolant and a neutron moderator, fills the entire reactor core with not-boiled, high-temperature and high-pressure water, sends the high-temperature and high-pressure water to a steam generator to generate steam by heat exchange, and sends the steam to a turbine generator to generate power. In a nuclear power plant that has the pressurized water reactor of the first embodiment, as illustrated in FIG. 11, a pressurized water reactor 12 and a steam generator 13 are housed in a containment 11, the pressurized water reactor 12 and the steam generator 13 are coupled with each other via cooling water pipes 14 and 15, the cooling water pipe 14 is provided with a pressurizer 16, and the cooling water pipe 15 is provided with a cooling water pump 15a. In this case, light water is used as a moderator and primary cooling water (a coolant), and a primary cooling system maintains a high-pressure condition of about 150 to 160 atmospheres with the pressurizer 16 in order to suppress boiling of the primary cooling water in a reactor core part. Therefore, the light water as the primary cooling water is heated by low-enriched uranium or MOX as fuel (nuclear fuel) in the pressurized water reactor 12, and the high-temperature primary cooling water is sent to the steam generator 13 through the cooling water pipe 14 with predetermined high pressure maintained by the pressurizer 16. In this steam generator 13, heat exchange is performed between the high-pressure and high-temperature primary cooling water and secondary cooling water, and the cooled primary cooling water is returned to the pressurized water reactor 12 through the cooling water pipe 15. The steam generator 13 is coupled with a steam turbine 17 via a cooling water pipe 18, and the steam turbine 17 has a high-pressure turbine 19 and a low-pressure turbine 20, and is connected with a generator 21. Further, a moisture separator/heater 22 is provided between the high-pressure turbine 19 and the low-pressure turbine 20, a cooling water branch pipe 23 branched from the cooling water pipe 18 is coupled with the moisture separator/heater 22, the high-pressure turbine 19 and the moisture separator/heater 22 are coupled with each other by a low-temperature reheat pipe 24, and the moisture separator/heater 22 and the low-pressure turbine 20 are coupled with each other by a high-temperature reheat pipe 25. Further, the low-pressure turbine 20 of the steam turbine 17 has a condenser 26, and a water intake pipe 27 and a drain pipe 28 that supplies/discharges cooling water (for example, seawater) is coupled with the condenser 26. This water intake pipe 27 has a circulating water pump 29, and the other end of the circulating water pump is disposed in the sea together with the drain pipe 28. The condenser 26 is coupled with a deaerator 31 via a cooling water pipe 30, and the cooling water pipe 30 is provided with a condenser pump 32 and a low-pressure feedwater heater 33. The deaerator 31 is coupled with the steam generator 13 via a cooling water pipe 34, and the cooling water pipe 34 is provided with a feed pump 35 and a high-pressure feedwater heater 36. Therefore, steam generated by heat exchange with the high-pressure and high-temperature primary cooling water in the steam generator 13 is sent to the steam turbine 17 through the cooling water pipe 18 (from the high-pressure turbine 19 to the low-pressure turbine 20), and the steam turbine 17 is driven by this steam and generate power is performed by the generator 21. At this time, after the steam from the steam generator 13 drives the high-pressure turbine 19, moisture included in the steam is removed in the moisture separator/heater 22 and the steam is heated. Then, the steam drives the low-pressure turbine 20. The steam that has driven the steam turbine 17 is then cooled in the condenser 26 using seawater and becomes condensed water, and is heated in the low-pressure feedwater heater 33 by low-pressure steam extracted from the low-pressure turbine 20, for example. Then, after impurities such as dissolved oxygen and non-condensable gas (ammonia gas) are removed in the deaerator 31, the steam is heated in the high-pressure feedwater heater 36 by high-pressure steam extracted from the high-pressure turbine 19, for example, and is then returned to the steam generator 13. In the pressurized water reactor 12 constructed in this way and applied to a nuclear power plant, as illustrated in FIG. 12, a reactor vessel 41 is constructed of a reactor vessel main body 42 and a reactor vessel cover 43 mounted on the reactor vessel main body 42 so that an reactor-internal structure can be inserted inside the reactor vessel 41, and the reactor vessel cover 43 is openable/closable with respect to the reactor vessel main body 42. The reactor vessel main body 42 has a cylindrical shape with an upper portion open and a lower portion blockaded in a spherically-shaped manner, and has an inlet nozzle 44 and an outlet nozzle 45 that supplies/discharges the light water (coolant) as the primary cooling water formed on the upper portion. In the reactor vessel main body 42, a core barrel 46 having a cylindrical shape is disposed below the inlet nozzle 44 and the outlet nozzle 45 with a predetermined gap with an inner surface of the reactor vessel main body 42, an upper core plate 47 having a disk shape and in which a plurality of flow holes (not illustrated) is formed is coupled with an upper portion of the core barrel 46, and, similarly, a lower core support plate 48 having a disk shape and in which a plurality of flow holes (not illustrated) is formed is coupled with a lower portion of the core barrel 46. Further, an upper core support 49 having a disk shape and positioned above the core barrel 46 is fixed in the reactor vessel main body 42, the upper core plate 47, that is, the core barrel 46 is hung and supported from the upper core support 49 via a plurality of reactor core support rods 50. Meanwhile, the lower core support plate 48, that is, the core barrel 46 is positioned and held to an inner surface of the reactor vessel main body 42 by a plurality of radial suppose keys 52. A reactor core 53 is formed of the core barrel 46, the upper core plate 47, and the lower core support plate 48, and a plurality of fuel assemblies 54 is disposed in the reactor core 53. The fuel assembly 54 is constructed of a plurality of fuel rods (not illustrated) bundled by a support lattice in a lattice-like manner, and an upper nozzle is fixed to an upper end portion and a lower nozzle is fixed to a lower end portion. Further, the plurality of control rods 55 serves as a control rod cluster 56 by upper end portions thereof being put together, and is insertable into the fuel assembly 54. A plurality of control rod cluster guide tubes 57 penetrates the upper core support 49 and is supported by the upper core support 49, and has lower end portions extended to the control rod cluster 56 of the fuel assembly 54. A magnetic-jack control rod driving mechanism 58 is provided on an upper portion of the reactor vessel cover 43 that constitutes the reactor vessel 41, and is housed in a housing 59 that constitutes an integral part with the reactor vessel cover 43. Upper end portions of the plurality of control rod cluster guide tubes 57 are extended to the control rod driving mechanism 58. Control rod cluster drive shafts 60 extended from the control rod driving mechanism 58 pass through the control rod cluster guide tubes 57 and are extended to the fuel assembly 54, and are capable of holding the control rod cluster 56. Further, a plurality of reactor-internal instrumentation guide tubes (not illustrated) penetrates the upper core support 49 and is supported by the upper core support 49, has lower end portions extended to the fuel assembly 54, and has sensors insertable therein, which is capable of measuring a neutron flux. The control rod driving mechanism 58 is vertically extended and is coupled to the control rod cluster 56, and upwardly and downwardly moves, by a magnetic jack, the control rod cluster drive shaft 60 that has a plurality of circumferential grooves arranged on a surface with equal pitches in a longitudinal direction, so that an output of the reactor is controlled. Therefore, the control rod cluster drive shaft 60 is moved by the control rod driving mechanism 58 and the control rod 55 is inserted to the fuel assembly 54, so that nuclear fission in the reactor core 53 is controlled. The light water filled in the reactor vessel 41 is heated by generated thermal energy, and the high-temperature light water is discharged from the outlet nozzle 45 and is sent to the steam generator 13, as described above. That is, the neutrons are irradiated by uranium or plutonium as fuel that constitutes the fuel assembly 54 subjected to the nuclear fission, and the light water as a moderator and the primary cooling water lowers kinetic energy of the irradiated fast neutrons and causes them to be thermal neutrons, so that the new nuclear fission is facilitated and the generated heat is taken and cooled. Further, the number of neutrons generated in the reactor core 53 is adjusted by insertion of the control rod 55 to the fuel assembly 54, and when the reactor is subjected to emergency stop, the control rod 55 is rapidly inserted to the reactor core 53. Further, an upper plenum 61 that communicates into the outlet nozzle 45 is formed above the reactor core 53 and a lower plenum 62 is formed below the reactor core 53 in the reactor vessel 41. Further, a downcomer portion 63 that communicates into the inlet nozzle 44 and the lower plenum 62 is formed between the reactor vessel 41 and the core barrel 46. Therefore, the light water flows into the reactor vessel main body 42 from the four inlet nozzles 44, flows downward in the downcomer portion 63 and reaches the lower plenum 62, is guided upward by a spherically-shaped inner surface of the lower plenum 62 and goes upward, passes through the lower core support plate 48, and then flows into the reactor core 53. The light water flowing into the reactor core 53 cools the fuel assembly 54 by absorbing the thermal energy generated from the fuel assembly 54 that constitutes the reactor core 53 while the light water is subjected to high temperature, passes through the upper core plate 47, goes upward to the upper plenum 61, and passes through the outlet nozzle 45 and is discharged. Such a reactor vessel 41 is constructed of the reactor vessel main body 42 and the reactor vessel cover 43, as described above, and the reactor vessel cover 43 is mounted on an upper portion of the reactor vessel main body 42 in a freely attachable/detachable manner by a plurality of stud bolts 65 and a plurality of nuts 66. In this case, the stud bolt 65 includes, as illustrated in FIG. 7-1 in detail, a lower screw portion 65a, a penetration portion 65b, an upper screw portion 65c, and a parallel groove portion 65d. In a state where the stud bolt 65 having the upper screw portion 65c screwed with the nut 66 has the penetration portion 65b that penetrates a mounting hole 43a formed in the reactor vessel cover 43, and has the lower screw portion 65a screwed in a screw hole 42a formed in the reactor vessel main body 42, the nut 66 is screwed with tension acting on the stud bolt 65 in a shaft center direction (here, upward) away from the reactor vessel main body 42, whereby fastening and loosening can be performed, and the reactor vessel cover 43 can be attached to/detached from the reactor vessel main body 42. Here, a member to be fastened of the present invention is the reactor vessel main body 42 and the reactor vessel cover 43. Further, the fastening and loosening device of the first embodiment enables the reactor vessel cover 43 to be attached to/detached from the reactor vessel main body 42 using the plurality of stud bolts 65 and nuts 66. Hereinafter, the fastening and loosening device of the first embodiment will be described in detail. In the first embodiment, as illustrated in FIGS. 1 and 2, a support disk 59a of the housing 59 is supported by a building 11a that constitutes the containment 11 (see FIG. 11) by a plurality of support rods 71. The support disk 59a has a guide rail 72 fixed to an outer peripheral portion, and four conveyance devices (electric trolley hoist) 73 are supported by the guide rail 72 in a freely movable manner. Each of the four conveyance devices 73 has a lift device 74, and the fastening and loosening device 76 is hung from and supported by the conveyance device 73 via a hanging cable 75 and is ascendable/descendable. In this case, the four conveyance devices 73 and fastening and loosening devices 76 have an almost equal configuration and are disposed at even intervals (90-degree intervals) in a circumferential direction. A conveyance control device 77 is connected with a tension control device 78, and is connected with a power supply unit 79 and an air pressure source 80. Further, the conveyance control device 77 is coupled with each of the conveyance devices 73 and the fastening and loosening devices 76 by a power supply cable 81, and is coupled with each of the fastening and loosening device 76 by an air-pressure hose 82. The fastening and loosening device 76 has, as described above, the plurality of stud bolts 65 screwed in and arranged in the outer peripheral portions of the reactor vessel main body 42 and the reactor vessel cover 43, has the nuts 66 respectively screwed with the plurality of stud bolts 65, and rotates the nuts 66 with causing tension to act on the stud bolts 65 in the shaft center direction away from the reactor vessel main body 42, so that the fastening and loosening is performed. That is, the fastening and loosening device 76 is constructed of a device main body 101, a bolt tensioner 102, two guide devices 103, two positioning devices 104, a guide position adjustment device 105, and an insertion position adjustment device 106, as illustrated in FIGS. 3 to 5. A hanging hook 111 is hangable from/supportable to the hanging cable 75 of the lift device 74 in the conveyance device 73, and a support plate 113 is supported by a plurality of hanging rods 112. The device main body 101 is constructed of the hanging hook 111, the hanging rods 112, the support plate 113, and the like. Therefore, the device main body 101 is, by an upper portion thereof being supported by the conveyance device 73, supported along an arrangement direction of the stud bolts 65 (in a circumference direction of the reactor vessel main body 42 and the reactor vessel cover 43) in a freely movable manner. The bolt tensioner 102 is supported such that an upper portion thereof penetrates a center portion of the support plate 113, and an oil tank 114, a hydraulic pump unit 115, and a pressure gauge 116 are disposed on the bolt tensioner 102. Therefore, since the bolt tensioner 102 is mounted to the device main body 101, the bolt tensioner 102 is freely movable along the shaft center direction of the stud bolts 65 by an actuation of the lift device 74. In the bolt tensioner 102, as illustrated in FIG. 6, a housing 201 with a cylindrical shape has an upper portion inserted and fixed to the support plate 113 and has a tip portion capable of coming into contact with an upper surface of the reactor vessel cover 43. A puller bar 202 has a cylindrical shape with a smaller diameter than the housing 201 and is housed in a center portion of the housing 201. The puller bar 202 is fit into an inner peripheral surface of the housing 201 via a piston (not illustrated) in a freely movable manner, and is movable along the shaft center direction (vertical direction) by oil pressure supplied/discharged by the hydraulic pump unit 115. Further, the puller bar 202 has a parallel groove portion 202a formed in a lower end portion. A puller bar socket 203 has a cylindrical shape divided in quarters in a circumferential direction, and is disposed between the housing 201, and a lower end portion of the puller bar 202 and the stud bolt 65. The puller bar socket 203 has an upper end portion supported by a lower portion of the puller bar 202 via a collar 204, and each of the quartered members is freely movable in the circumferential direction and is outwardly energized and supported. Further, the puller bar socket 203 has an upper engagement groove portion 203a formed on an upper inner peripheral surface, the upper engagement groove portion 203a being engaged with the parallel groove portion 202a of the puller bar 202, and has a lower engagement portion 203b formed on a lower inner peripheral surface, the lower engagement portion 203b being engaged with the parallel groove portion 65d of the stud bolt 65. Also, the puller bar socket 203 has an uneven portion 203c formed on an outer peripheral surface. Further, a locking ring 205 has a cylindrical shape and is disposed between the housing 201 and the puller bar socket 203. The locking ring 205 has an uneven portion 205a formed in an inner peripheral surface, the uneven portion 205a being capable of fitting into the uneven portion 203c of the puller bar socket 203. Further, the locking ring 205 is ascendable/descendable by a plurality of air cylinders 206 mounted on an inner peripheral surface of the housing 201. Therefore, when the locking ring 205 is at an ascended position, as illustrated in the left side of FIG. 6, the puller bar socket 203 is moved outward in a radial direction, and the uneven portion 205a is fit into the uneven portion 203c of the puller bar socket 203. The engagement groove portions 203a and 203b are not engaged with the parallel groove portion 202a of the puller bar 202 and the parallel groove portion 65d of the stud bolt 65. Meanwhile, when the locking ring 205 is at a descended position, as illustrated in the right side of FIG. 6, the uneven portion 205a presses the uneven portion 203c of the puller bar socket 203, and the puller bar socket 203 is moved inward in the radial direction. The engagement groove portions 203a and 203b are engaged with the parallel groove portion 202a of the puller bar 202 and the parallel groove portion 65d of the stud bolt 65. The housing 201 has a nut socket 207 supported by a lower end inner peripheral portion thereof in a freely rotatable manner, and has a driven gear 208 fixed to an outer peripheral portion. The nut socket 207 is, with respect to the nut 66, freely relatively movable in a shaft center direction while being freely integrally rotatable in a circumferential direction. Further, the housing 201 has a nut rotating device 209 mounted to a lower end outer peripheral portion, the nut rotating device 209 rotating the nut socket 207. The nut rotating device 209 is constructed of a case 210 fixed to the housing 201, an electric servo motor 211, a drive gear 212, and three intermediate gears 213. Therefore, when the drive gear 212 is forwardly rotated by the electric servo motor 211, rotational driving force is transmitted to the driven gear 208 via each of the intermediate gears 213, rotates the nut socket 207, and rotates and fastens the nut 66. Meanwhile, when the drive gear 212 is backwardly rotated by the electric servo motor 211, the rotational driving force is transmitted to the driven gear 208 via each of the intermediate gears 213, rotates the nut socket 207, and rotates and loosens the nut 66. Therefore, first, as illustrated in FIG. 7-1, the fastening and loosening device 76 is moved by the conveyance device 73, and is stopped at a predetermined position, that is, stopped at a position of the bolt tensioner 102, the stud bolt 65, and the nut 66. Next, as illustrated in FIG. 7-2, the fastening and loosening device 76 is descended by the lift device 74 to cause the bolt tensioner 102 to be engaged with the stud bolt 65 and the nut 66. Then, as illustrated in FIG. 7-3, the puller bar socket 203 is moved inward in a radial direction to chuck the parallel groove portion 65d of the stud bolt 65. Under this condition, as illustrated in FIG. 7-4, the puller bar 202 is ascended by actuation of the hydraulic pump unit 115 to cause tension to act on the stud bolt 65 in the shaft center direction (upward) away from the reactor vessel main body 42. Then, as illustrated in FIG. 7-5, the nut socket 207 is rotated by actuation of the nut rotating device 209, so that the nut 66 is rotated, and fastening or loosening can be performed. Further, the fastening and loosening device 76 is, as illustrated in FIGS. 3 to 5, provided with the guide devices 103 before and behind the bolt tensioner 102 in the moving direction of the device main body 101. The before and behind guide devices 103 have a symmetrical shape with respect to a center line of the bolt tensioner 102, and have an almost equal configuration. That is, main bodies of before and behind cylinders 121 are fixed to the support plate 113, and tip portions of piston rods 121a that extend downward are respectively coupled with box bodies 122 that have an inverted U-shape cross section. Note that a most extended position of the piston rod 121a of the cylinder 121 is controlled. The box body 122 has, as illustrated in FIG. 8 in detail, an inner guide member 123 and an outer guide member 124 mounted on both the right and left sides of the moving direction of the device main body 101. The guide members 123 and 124 have guide pieces 125 and 126 respectively fixed to sides facing each other, and the guide pieces 125 and 126 have a curved shape along the arrangement direction (a circumferential direction) of the stud bolts 65. In this case, each of the guide pieces 125 and 126 is contactable with outer peripheries of two (or three or more) adjacent nuts 66. Further, the guide members 123 and 124 have guide rollers 127 and guide rollers 128 mounted to a front side end portion and a back side end portion, respectively, the guide rollers 127 and the guide rollers 128 having rotating shaft centers along a vertical direction, respectively. In this case, the box bodies 122, the guide members 123 and 124, the guide pieces 125 and 126, the guide rollers 127 and 128, and the like constitute the guide devices 103. Further, the cylinder 121 functions as a damper by being filled with oil, and even if the bolt tensioner 102 is ascended together with the device main body 101, the device main body 101 and the guide device 103 relatively moves by extension/retraction of the piston rod 121a. Further, the two guide devices 103 have box bodies 122 coupled with each other by two upper and lower coupling members 129 at an outside of the circumferential direction, and predetermined rigidity is secured. Therefore, the guide pieces 125 and 126 and the guide rollers 127 and 128 of the guide members 123 and 124 can guide a lower portion of the device main body 101 by contacting the outer periphery of each of the nuts 66 screwed with the stud bolts 65 from both the right and left sides of the moving direction of the device main body 101. Further, the fastening and loosening device 76 is, as illustrated in FIGS. 3 and 5, provided with the positioning devices 104 together with the guide devices 103 before and behind the bolt tensioner 102 in the moving direction of the device main body 101. The before and behind positioning devices 104 are mounted on the guide devices 103, and have a symmetrical shape with respect to a center line of the bolt tensioner 102, and have an almost equal configuration. That is, a box-type case 131 is fixed to a side portion (an outside of the circumferential direction of the reactor vessel cover 43) of the box body 122 of the guide device 103, and an air cylinder 132 is mounted in the case 131. The air cylinder 132 has a piston rod 132a (see FIG. 8) extendable/retractable toward an inner side of the circumferential direction of the reactor vessel cover 43, and has a positioning member 133 mounted to a tip portion between the adjacent nuts 66, the positioning member being inserted from an outside of the circumferential direction. Further, the case 131 has a wheel 134 mounted on a lower portion at a box body 122 side, and a load of the guide device 103 and the positioning device 104 is supported by the wheel 134. The case 131 is rollable on an upper surface of the reactor vessel cover 43. In this case, the case 131, the air cylinder 132, the positioning member 133, and the like constitute the positioning device 104. Therefore, when the air cylinder 132 is actuated to extend the piston rod 132a at a predetermined position, the positioning member 133 is inserted between the adjacent nuts 66, whereby the device main body 101 can be positioned to a predetermined position with respect to the moving direction thereof. Note that an extended amount detection device 141 that detects extended amounts of the stud bolt 65 before and after the work by the fastening and loosening device is provided in the box body 122 of a front-side guide device 103, and whether the tension has been properly caused to act on the bolt tensioner 102 and fastening has been performed is detected based on a detection result of the extended amount detection device 141. Further, a nut detection sensor (optical sensor) 142 that detects the nut 66 is provided in the box body 122 of the front-side guide device 103, and a rotary encoder 143 that detects the number of rotation of the wheel 134 is provided in the case 131 of the positioning device 104. A position where the device main body 101 is moved, that is, a position where the bolt tensioner 102 is moved is detected based on a detection result of the nut detection sensor 142 and the rotary encoder 143. Further, in the first embodiment, as illustrated in FIGS. 9 and 10, the guide device 103 is provided with the guide position adjustment device 105 capable of moving the inner guide member 123 in a horizontal direction intersecting with the moving direction of the device main body 101, that is, in an inward and outward direction nearly perpendicular to the circumferential direction. Further, at the positioning device 104, the insertion position adjustment device 106 is provided, which is capable of adjusting a position where the positioning members 133 (133a and 133b) is inserted. Typically, a differs in size depending on a position where the reactor vessel is disposed, a power generation capacity of a plant, and the like, and outer diameters of the reactor vessel main body 42 and the reactor vessel cover 43, outer diameters and the number of the stud bolts 65 and the nuts 66, and the like differ. Therefore, it is necessary to adjust positions of the guide device 103 and the positioning device 104 according to the outer diameters and an arranged condition of the stud bolts 65 and the nuts 66. At the guide position adjustment device 105, the inner guide member 123 is supported by a support shaft 152 in a freely horizontally movable manner to the mounting bracket 151, one end portion of which (bolt tensioner 102 side) is fixed to the box body 122 and the other end portion of which is swingably supported by an eccentric mechanism 153 provided in the box body 122. At the eccentric mechanism 153, the mounting bracket 154 is provided with a rotating body 155 fixed to the box body 122, and the rotating body 155 is supported by a rotation shaft 156 fixed to the mounting bracket 154 in a freely rotatable manner. Further, in the rotating body 155, an eccentric body 157 that the rotation shaft 156 penetrates is formed, and a base end portion of the support arm 158 is engaged with an outer peripheral portion of the eccentric body 157, and a tip portion of the support arm 158 is coupled with the other end portion of the inner guide member 123 by a coupling shaft 159. Further, the rotating body 155 has an operating handle 160 mounted thereon, the box body 122 is provided with stoppers 161a and 161b of the operating handle 160 and the mounting bracket 154 is provided with lock pins 162a and 162b of the operating handle 160 in a freely attachable/detachable manner. Therefore, in a case where the arranged position of the stud bolt 65 and the nut 66 illustrated in FIG. 9 and the arranged condition of the stud bolt 65 and the nut 66 illustrated in FIG. 10 differ, it is necessary to adjust positions of the inner guide members 123 by the guide position adjustment devices 105 according to respective arranged conditions. That is, when the operating handle 160 is rotated in a clockwise direction by 180 degrees from the condition illustrated in FIG. 9, the integrated eccentric body 157 is rotated similarly, and as illustrated in FIG. 10, the inner guide member 123 can be moved to an outside of the circumferential direction via the support arm 158 by the eccentricity of the eccentric body 157. Also, when the operating handle 160 is rotated in the counter-clockwise direction by 180 degrees from the condition illustrated in FIG. 10, the inner guide member 123 can be, in a similar manner to the above, moved to an inside of the circumferential direction via the support arm 158 by the eccentricity of the eccentric body 157. Further, at the insertion position adjustment device 106, as illustrated in FIGS. 9 and 10, the air cylinder 132 has the positioning member 133 mounted on a tip portion of the piston rod 132a, and the positioning member 133 is exchangeable according to the arranged positions of the stud bolt 65 and the nut 66. The two positioning members 133a and 133b have support plates 171a and 171b freely attachable to/detachable from a tip portion of the piston rod 132a by coupling pins 172a and 172b. The support plates 171a and 171b have two positioning rollers 173a and 173b supported by a tip portion side in a freely rotatable manner, and contactable with an outer peripheral surface of an adjacent nut 66. In this case, the two positioning members 133a and 133b differ in the positions where the positioning rollers 173a and 173b are mounted with respect to the support plates 171a and 171b. The positions where the positioning rollers 173a and 173b are mounted are set according to the condition of arrangement of the stud bolts 65 and the nuts 66. Here, an actuation of the above-described fastening and loosening device of the first embodiment will be described. In the fastening and loosening device of the first embodiment, as illustrated in FIGS. 1 and 2, when the reactor vessel cover 43 is removed from the reactor vessel main body 42, first, the fastening and loosening devices 76 are hung from and supported by the four conveyance devices 73 via the lift devices 74, and the fastening and loosening device 76 is descended by the lift devices 74, so that the fastening and loosening device 76 is set up with respect to the stud bolts 65 and the nuts 66 fastened to the reactor vessel main body 42 and the reactor vessel cover 43. Then, the bolt tensioner 102 is ascended together with the device main body 101, and the bolt tensioner 102 is arranged above the stud bolts 65 and the nuts 66. In this case, the before and behind guide devices 103 are engaged with the arranged nuts 66. Under this condition, the conveyance device 73 is actuated, and the fastening and loosening device 76 is moved along the arrangement direction of the stud bolts 65 and the nuts 66. Then, when the bolt tensioner 102 is moved to a position where the bolt tensioner 102 vertically faces the stud bolts 65 and the nuts 66, the actuation of the conveyance device 73 is stopped, and positioning of the bolt tensioner 102 is performed by an actuation of the positioning device 104. That is, the bolt tensioner 102 is merely hung from the conveyance device 73 together with the device main body 101, and a gap is provided between the guide device 103 and the nut 66 for the movement of the guide device 103. Therefore, accurate positioning between the bolt tensioner 102, and the stud bolt 65 and the nut 66 is difficult. Therefore, when the positioning device 104 is actuated, and the positioning member 133 is inserted between the adjacent nuts 66 from outside, and the positioning device 104 (positioning member 133) and the guide device 103 (inner guide member 123) sandwiches the nuts 66, so that the accurate positioning of the bolt tensioner 102 becomes possible. When the accurate positioning between the bolt tensioner 102, and the stud bolts 65 and the nuts 66 is completed, under this condition, the nut 66 is loosened by actuation of the bolt tensioner 102. That is, the nut 66 is backwardly rotated and loosened with tension acting on the stud bolt 65 in the shaft center direction away from the reactor vessel main body 42. When loosening of one nut 66 is completed, the bolt tensioner 102 is ascended by the lift device 74 together with the device main body 101, and the bolt tensioner 102 is upwardly away from the stud bolts 65 and the nuts 66. At this time, the cylinder 121 is extended due to the weights of the guide device 103, the positioning device 104, and the like, so that the before and behind guide devices 103 and the positioning device 104 are engaged with the arranged nuts 66. Under this condition, as described above, when the fastening and loosening device 76 is moved along the arrangement direction of the stud bolts 65 and the nuts 66 by the conveyance device 73, the guide device 103 and the positioning device 104 are rolled on an upper surface of the reactor vessel cover 43 by the wheel 134. Then, when the bolt tensioner 102 is moved to a position where the bolt tensioner 102 vertically faces the stud bolts 65 and the nuts 66, the actuation of the conveyance device 73 is stopped. The plurality of nuts 66 is loosened one by one by repetition of works similar to the above description. Note that the four fastening and loosening devices 76 are disposed at even intervals in the circumferential direction, and the fastening and loosening devices 76 are actuated in synchronization with each other, whereby the nuts 66 can be loosened without action of an offset load on the stud bolts 65 and the nuts 66 fastened to the reactor vessel main body 42 and the reactor vessel cover 43. Then, when the loosening work of all nuts is completed, the four conveyance devices 73 are stopped, the lift devices 74 are actuated and all of the fastening and loosening devices 76 are hung, and all of the fastening and loosening devices 76 are removed using a crane device (not illustrated). Then, after the stud bolts 65 are rotated and removed using a rotating device (not illustrated), the reactor vessel cover 43 is removed from the reactor vessel main body 42 by a crane device. Meanwhile, when the reactor vessel cover 43 is mounted on the reactor vessel main body 42, the process is similar to the above-described actuation. However, the rotation direction of the nuts 66 in the bolt tensioner 102 is opposite. Further, when the fastening and loosening device of the first embodiment is applied to another reactor vessel 41, since the arrangements of the stud bolts 65 and the nuts 66 differ, the position of the inner guide member 123 is adjusted by the guide position adjustment device 105 and the positioning members 133a and 133b are exchanged by the insertion position adjustment device 106, in advance. Therefore, even if the arrangements of the stud bolts 65 and the nuts 66 differ, one guide device 103 and a positioning device 104 can be used by using the guide position adjustment device 105 and the insertion position adjustment device 106. In this way, the fastening and loosening device of the first embodiment is provided with the device main body 101, an upper portion of which is supported along the arrangement direction of the stud bolts 65 by the conveyance device 73 in a freely movable manner, the bolt tensioner 102 freely ascendable/descendable with respect to the stud bolts 65 by the lift device 74 together with the device main body 101, the guide device 103 having the right and left guide members 123 and 124 coupled with the device main body 101 via the cylinder 121 in a freely relatively movable manner and contactable with the outer periphery of the nut 66 from both the right and left sides of the moving direction of the device main body 101, and the guide position adjustment device 105 capable of moving the inner guide member 123 in the horizontal direction intersecting with the moving direction of the device main body 101. Therefore, the right and left guide members 123 and 124 can guide the device main body 101 by contacting with the outer periphery of the nut 66 from the both sides of the device main body 101, and the inner guide member 123 is moved in the horizontal direction intersecting with the moving direction of the device main body 101 by the guide position adjustment device 105, whereby the guide position of the inner guide member 123 to the nut 66 is adjusted. Therefore, the inner guide member 123 can properly guide the device main body 101 regardless of the size and shape of the stud bolt 65 and the nut 66. As a result, fastening and loosening of the nut 66 with respect to the stud bolt 65 can be properly performed. Further, in the fastening and loosening device of the first embodiment, since the arrangement direction of the stud bolts 65 is the circumferential direction along the outer peripheral portion of the reactor vessel main body 42 and the reactor vessel cover 43, the inner guide member 123 in the guide device 103 can be moved by the guide position adjustment device 105. Therefore, the inner guide member 123 is moved by the guide position adjustment device 105, whereby the guide position of the inner guide member 123 with respect to the nut 66 is adjusted, and the position adjustment of the inner guide member 123 can be easily performed with a simple configuration. Further, the guide position adjustment device 105 can be disposed at an inner guide member 123 side, and therefore, an outward protrusion can be eliminated and complication of the device can be prevented. Also, the fastening and loosening device of the first embodiment is provided with the positioning device 104 having the positioning member 133 inserted between the adjacent nuts 66 from an outside of the circumferential direction. Therefore, the positioning member 133 is inserted between the nuts 66 by the positioning device 104 from an opposite side of the inner guide member 123, so that the nut 66 is sandwiched by the inner guide member 123 and the positioning member 133, and the proper positioning of the device main body 101 can be performed. Further, the fastening and loosening device of the first embodiment is provided with the insertion position adjustment device 106 capable of adjusting the insertion position of the positioning member 133. Therefore, the insertion position adjustment device 106 can adjust the insertion position by exchanging the positioning members 133a and 133b. Therefore, the positioning members 133a and 133b can properly position the device main body 101 regardless of the size and shape of the stud bolts 65 and the nuts 66. As a result, fastening and loosening of the nuts 66 with respect to the stud bolts 65 can be properly performed. Also, the fastening and loosening device of the first embodiment is, as the guide position adjustment device 105, provided with the support shaft 152 that supports one end portion of the inner guide member 123 in a freely rotatable manner and the eccentric mechanism 153 that allows the other end portion of the inner guide member 123 to be movable. Therefore, the guide position of the inner guide member 123 can be easily changed only by simply actuating the eccentric mechanism 153, and the device can be simplified. Further, the fastening and loosening device of the first embodiment is provided with the guide devices 103 before and behind the bolt tensioner 102 in the moving direction of the device main body 101, and the outer and inner guide members 123 and 124 are contactable with the outer peripheries of the two or more nuts 66. Therefore, the movement of the device main body 101 is guided before and behind the bolt tensioner 102 by the guide devices 103, whereby the device can be stably moved and guided. Note that, in the above-described first embodiment, the guide device 103 has been constructed of the box body 122, the guide members 123 and 124, the guide pieces 125 and 126, the guide rollers 127 and 128, and the like. However, the configuration is not limited to the above-described configuration. For example, the guide device 103 may be simply constructed of the guide members 123 and 124 only, or of the guide pieces 125 and 126 only. Alternatively, the guide device 103 may be constructed of a plurality of guide rollers. Further, in the first embodiment, only one end portion of the inner guide member 123 has been moved in the guide position adjustment device 105. However, the eccentric mechanism 153 may be provided in the other end portion of the inner guide member 123 so that the guide member as a whole may be caused to be movable. Further, not only the inner guide member 123 but also the outer guide member 124 may be provided with a guide position adjustment device and may be caused to be movable. The guide position adjustment device 105 is not limited to the eccentric mechanism 153. The guide member may be caused to be movable with a long hole and may be fixed at a predetermined position by a lock pin. Further, a rack and pinion mechanism, a boll screw mechanism, or the like may be applied to the motor. Further, in the above-described first embodiment, the positioning device 104 has been constructed of the case 131, the air cylinder 132, the positioning member 133, and the like. However, the configuration is not limited to the above-described configuration. For example, a hydraulic cylinder, an electric motor, or the like may be used in place of the air cylinder 132. Further, the positioning members 133 (133a and 133b) have been constructed of the support plates 171a and 171b, the positioning rollers 173a and 173b, and the like. However, the configuration is not limited to the above-described configuration. For example, the number of the positioning rollers 173a and 173b is not limited to two, but may be one, or three or more. An insertion member having a tapered tip portion may be employed in place of the positioning rollers 173a and 173b. Further, in the first embodiment, the insertion position adjustment device 106 has been constructed of two exchangeable positioning members 133 (133a and 133b). However, the configuration is not limited to the above-described configuration. For example, three or more exchangeable positioning members may be provided, a positioning member that is freely horizontally swingable within a predetermined angle may be mounted on the tip portion of the piston rod 132a of the air cylinder 132, or, the position where the air cylinder 132 is mounted may be movable or swingable along the moving direction of the device main body 101. FIG. 13 is a schematic view illustrating a guide position adjustment device in a fastening and loosening device according to a second embodiment of the present invention, and FIG. 14 is a plan view illustrating the guide position adjustment device of the second embodiment. Note that members having similar functions to the above-described embodiment will be denoted with the same reference signs and detailed description is omitted. In a fastening and loosening device of the second embodiment, as illustrated in FIG. 13 and FIG. 14, a guide position adjustment device 181 allows a box body 122 of a guide device 103 to be horizontally swingable. That is, the guide position adjustment device 181 includes a movement adjustment base plate 182, two guide plates 183, an adjustment mechanism 184, and an eccentric mechanism 185. The movement adjustment base plate 182 has two guide plates 183 placed on an upper surface portion, and the guide device 103 is placeable on each of the guide plates 183. The adjustment mechanism 184 is housed inside the movement adjustment base plate 182, and the guide plate 183 can be horizontally rotated around a virtual shaft center O by rotation of a handle 184a. Note that a specific configuration of the adjustment mechanism 184 can be a typical one, and for example, may be one that horizontally rotates the guide plate 183 by rotating a worm wheel that meshes with a worm. The eccentric mechanism 185 has an eccentric body 185a to which a tip portion of a piston rod 121a of a cylinder 121 is fit and an outer peripheral portion of which is fit to the box body 122. Note that the eccentric mechanism 185 has an almost equal configuration to the eccentric mechanism 153 of the first embodiment. Therefore, the guide device 103 is ascended by a crane device (not illustrated) via a device main body 101 (see FIG. 3), and the guide device 103 is mounted on each of the guide plates 183 on the movement adjustment base plate 182. Then, with respect to the box body 122 of the guide device 103, after the piston rod 121a of the cylinder 121 is removed, the guide device 103 is rotated together with the guide plate 183 by rotation of the handle 184a, and a position of the guide plate 183 is adjusted. When the position adjustment work of the guide device 103 is completed, a position where the cylinder 121 and the box body 122 are coupled is adjusted by rotation of the eccentric body 185a of the eccentric mechanism 185, and the piston rod 121a of the cylinder 121 is attached to the box body 122 of the guide device 103. Note that, although the two guide devices 103 are coupled by a coupling member 129, the coupling member 129 may be removed before the position adjustment work of the guide device 103 and another coupling member may be attached after the work. In this way, the fastening and loosening device of the second embodiment allows the box body 122 of the guide device 103 to be horizontally swingable by the guide position adjustment device 181. Therefore, the guide device 103 as a whole is swung via the box body 122 by the guide position adjustment device 181 to adjust the position of the guide member. Versatility can be improved by sufficiently securing a position adjustment margin. Note that, in the above-described second embodiment, the guide device 103 has been horizontally rotated around the virtual shaft center O at an outside of the guide device 103. However, the configuration is not limited to the above-described configuration. For example, the guide device 103 may be horizontally rotated around a position where the piston rod 121a of the cylinder 121 is mounted with respect to the box body 122 of the guide device 103, and in this case, the eccentric mechanism 185 becomes unnecessary and the structure can be simplified. Alternatively, the guide position adjustment device may be simply constructed only of the eccentric mechanism 185. Further, in the above-described embodiments, description has been given in which the fastening and loosening device of the present invention is applied to a reactor vessel 41. However, the member to be fastened is not limited to the above-described member, and any member is applicable as long as the plurality of stud bolts and nuts is arranged along a predetermined direction. 11 Containment 12 Pressurized water reactor 13 Steam generator 17 Steam turbine 21 Generator 41 Reactor vessel 42 Reactor vessel main body (member to be fastened) 43 Reactor vessel cover (member to be fastened) 46 Core barrel 53 Reactor core 54 Fuel assembly 55 Control rod 58 Control rod driving mechanism 59 Housing 65 Stud bolt 66 Nut 73 Conveyance device 74 Lift device 76 Fastening and loosening device 101 Device main body 102 Bolt tensioner 103 Guide device 104 Positioning device 105 and 181 Guide position adjustment device 106 Insertion position adjustment device 123 Inner guide member 124 Outer guide member 125 and 126 Guide piece 127 and 128 Guide roller 132 Air cylinder 133, 133a, and 133b Positioning member 153 Eccentric mechanism |
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description | The present disclosure pertains to production of technetium-99m and molybdenum-99 from molybdenum-100 using particle accelerators exemplified by cyclotrons. In particular, the present disclosure pertains to target systems for irradiating molybdenum with charged particles to produce technetium and molybdenum radioisotopes. Technetium-99m (Tc-99m) is a widely used radioisotope for nuclear medical diagnostics. It emits gamma rays of 140 keV and decays with a half-life of approximately six hours. Common diagnostic procedures involve labeling a suitable tracer molecule with Tc-99m, injecting the radiopharmaceutical into the patient's body and imaging with radiological equipment. Currently, Tc-99m is supplied in the form of molybdenum-99/technetium-99m generators. The parent isotope molybdenum-99 (Mo-99) is produced in nuclear reactors. Mo-99 has a half-life of 66 hours which enables its global distribution to medical facilities. The Mo-99/Tc-99m generator uses column chromatography to separate Tc-99m from Mo-99. Mo-99 is loaded onto acidic alumina columns in the form of molybdate, MoO42−. As the Mo-99 decays it forms pertechnetate, TcO4−, which can be eluted selectively from the generator column with saline as sodium pertechnetate. The solution containing sodium pertechnetate is then typically added to a radiochemical ‘kit’ to form an organ-specific radiopharmaceutical. Several nuclear reactors producing the world's supply of Mo-99 are close to the end of their lifetimes. Some of the main facilities, such as the reactors at Chalk River Laboratories in Ontario, Canada, and the Petten nuclear reactor in the Netherlands, had substantial shut-down periods which caused a world-wide shortage of Mo-99 for medical applications. Significant concerns remain regarding reliable long-term supply of Mo-99. Small quantities of radioisotopes can be produced for research purposes only, by using beams of accelerated particles generated by accelerators, to interact with Mo-100 targets wherein they cause nuclear transformations resulting in the conversion of Mo-100 to Mo-99. However, the scalability of such systems is limited by numerous problems. For example, the absorption of accelerated particles by the target material results in the concurrent generation of thermal energy, which needs to be dissipated to avoid damage to the target system and to the system components. Some small-scale systems, water cooling may be used to remove the heat loads from the targets, and therefore, constructing the target assemblies wherein the target material is housed, from materials having high thermal conductivities may be used to maximize heat dissipation during bombardment with accelerated particles. Silver and copper may be used for fabrication of the small-scale target assemblies. However, both silver and copper are annealed at temperatures as low as 100° C. if exposed to elevated temperatures for extended periods. Furthermore, these compounds are rapidly and completely annealed at temperatures above 500° C. Such annealing renders the target assemblies and the targets housed therein unable to withstand the mechanical stresses of the water cooling. Additionally, the target material itself may be deformed by thermal stresses during bombardment with accelerated particles. The exemplary embodiments of the present disclosure pertain to a target system for the production of technetium and molybdenum radioisotopes from molybdenum metal, for example Tc-99m and Mo-99 from molybdenum-100 (Mo-100) by irradiation with particles from an accelerator, such as a cyclotron. Some exemplary embodiments of the present disclosure relate to target assemblies comprising a target holder for housing therein a Mo-100 target for bombardment with accelerated particles, and a bombardment target engaged with the target holder. Some exemplary embodiments relate to methods for assembling and preparing the target assemblies for bombardment with accelerated particles. The preparation of metallic molybdenum targets generally needs to be carried out under inert atmosphere if the process requires elevated temperature, as molybdenum reacts rapidly with oxygen if heated to greater than 400° C. Instead of an inert atmosphere, a reducing gas mixture exemplified by hydrogen in argon, may be applied to protect the molybdenum from oxidation and to reduce any molybdenum oxide contained in the target material to molybdenum metal. The joining of refractory metals such as molybdenum to other materials typically involves intricate multi-step processes. Soldering or brazing of such metals usually requires extensive pre-treatment of the surfaces to be joined (degreasing, sanding, chemical etching, pre-coating with suitable metals) and the application of aggressive, sometimes toxic flux materials. Any soldering or brazing of Mo-100 can only be accomplished under exclusion of oxygen. An exemplary embodiment of the present disclosure relates to processes for manufacturing a target system consisting of a metallic Mo-100 body that is furnace brazed to a backing material of high thermal conductivity and high mechanical strength. The processes may generally comprise the steps of: 1. Pressing a quantity of molybdenum powder using a mechanical device to form a pressed Mo-100 plate having a desired thickness and size. 2. Sintering the pressed Mo-100 plate in an inert or reducing atmosphere for about 2 to about 20 hours at a temperature from a range of about 1300° C. to about 2100° C. 3. Brazing the sintered plate in a furnace at a temperature from a range of about 500° C. to about 1000° C. in a vacuum, or alternatively in an inert or in a reducing atmosphere, onto a backing made of a dispersion strengthened copper composite material exemplified by GLIDCOP® metal matrix composite alloys (GLIDCOP is a registered trademark of North American Hoganas High Alloys LLC, Hollsopple, Pa., USA), using a brazing filler suitable for producing a bond of high mechanical strength, high thermal conductivity and high ductility between the sintered Mo-100 plate and the backing material. The exemplary embodiments disclosed herein are described in reference to the manufacture of a solid molybdenum target for the production of Tc-99m by irradiation of a molybdenum target with 16.5 MeV protons, up to, for example, 130 μA beam current in a small medical cyclotron such as the cyclotron exemplified by the GE PETTRACE® (PETTRACE is a registered trademark of the General Electric Company Corp., Schenectady, N.Y., USA). A suitable target assembly for use with the PETTRACE® cyclotron may comprise an exemplary target holder having an outer diameter of about 30 mm and a thickness of about 1.3 mm. The exemplary target holder is provided with a recess that has a diameter of about 20 mm and a depth of about 0.7 mm. A sintered Mo-100 disc having a diameter of about 18.5 mm to about 19.5 mm and a thickness of about 0.6 mm is housed within the recess of the exemplary target holder, and is securely engaged to the target holder by braising. The first step of an exemplary method for producing the exemplary target assembly housing a sintered Mo-100 target relates to production of a Mo-100 target disc. A selected quantity of commercial Mo-100 powder is transferred into a cylindrical disc form using a cylindrical tool and die set. A pressure is then applied with a hydraulic press to the cylindrical tool and die set containing therein the Mo-100 powder, thereby pressing the Mo-100 powder into a compacted disc. The compacted Mo-100 disc is removed from the die and transferred to a ceramic vessel for further processing. For example, 20-mm diameter compacted Mo-100 discs can be prepared with a hardened steel cylindrical tool and die set comprising (1) a base with a recess for receiving and positioning a 20-mm diameter spacer pellet, said base configured for receiving and demountably engaging a cylindrical sleeve with an inner bore having a 20-mm diameter, (2) the cylindrical sleeve, and (3) at least two 20-mm diameter spacer pellets. A suitable cylindrical tool and die set is exemplified by a 20-mm diameter ID dry pressing die set from Access International (Livingston, N.J., USA). A small amount of a Vaseline lubricant is spread on the upper, lower, and side surfaces of the two spacer pellets. One of the spacer pellets is placed into the recess of the base, and then the cylindrical sleeve is slipped over the spacer pellet and then engaged with the base. A suitable amount of pre-weighed enriched Mo-100 powder is then poured into the cavity within the cylindrical sleeve and tamped into place. A suitable amount of Mo-100 powder for preparing a 20-mm diameter Mo-100 disc is about 1.6 g. Also suitable are amounts from a range of 0.3 g to 3.0 g, for example, 0.3 g, 0.5 g, 0.75 g, 1.0 g, 1.25 g, 1.5 g, 1.75 g, 2.0 g, 2.25 g, 2.5 g, 2.75 g, 3 g. The second spacer pellet is then inserted into the cavity within the cylindrical sleeve until it is resting on the top of the Mo-100 powder. A piston, which may be provided with the tool and die set, is then inserted into the cavity of the sleeve to engage the top of the second spacer pellet, and then hand pressure is applied to the piston to sandwich the Mo-100 powder between the two spacer pellets. The assembled cylindrical tool and die set is then transferred into a pellet press, or a hydraulic press, or a mechanical press, or the like. A suitable pellet press is exemplified by 40-ton laboratory pellet press with built-in hydraulic pump available from Access International. After the assembled cylindrical tool and die set is installed into the pellet press, a selected pressure is applied to the tool and die set for about 30 sec. A suitable pressure is about 30,000 lbs. Also suitable are pressures from the range of 2,000 lbs to 100,000 lbs, for example 2,000 lbs, 5,000 lbs, 10,000 lbs, 15,000 lbs, 20,000 lbs, 25,000 lbs, 30,000 lbs, 35,000 lbs, 40,000 lbs, 45,000 lbs, 50,000 lbs, 65,000 lbs, 60,000 lbs, 65,000 lbs, 70,000 lbs, 75,000 lbs, 80,000 lbs, 85,000 lbs, 90,000 lbs, 95,000 lbs, 100,000 lbs. After the pressure is released, the cylindrical tool and die set is removed from the pellet press, the tool and die set is disassembled and the pressed Mo-100 disc is removed into a container. The second step of the exemplary method relates to sintering of the pressed Mo-100 discs in a furnace under a hydrogen/argon atmosphere (e.g. a 2%/98% mixture) at a temperature of about 1700° C. for 5 h. For example, the pressed Mo-100 discs produced in step one of the exemplary process, can be placed into alumina boats having a flat bottom face. An alumina piece is placed, as a weight, on top of each pressed Mo-100 disc in an alumina boat which is then placed into a furnace after which, a flow of a 2%/98% hydrogen/argon gas mixture is started at a pressure of about 2 PSI and a flow rate of about 2 L/min. The temperature is then ramped up from ambient temperature, for example 22° C., to 1,300° C. at a rate of 5° C./min. Then, the temperature is ramped up from 1,300° C. to 1,700° C. at a rate of 2° C./min. The furnace is then held at 1,700° C. for 5 h after which, it is cooled from 1,700° C. to 1,300° C. at a rate of 2° C./min, and then to ambient temperature at a rate of 5° C. The cooled sintered Mo-100 discs are then assessed for suitability for bombardment with accelerated particles. Only those sintered Mo-100 discs that are flat and do not show any evidence of cracks are selected for the third step of the exemplary method. The third step of the exemplary method relates to preparation of an exemplary target assembly. A target holder 20 (FIGS. 1, 2) is fabricated from a dispersion strengthened copper composite backing exemplified by GLIDCOP® AL-15 having a recess large enough to fit the sintered plate. A suitable size for a target holder (for example, item 20 in FIGS. 1, 2) for the PETTRACE® cyclotron is an outer diameter of 30 mm with a thickness of about 1.3 mm, and has a recess with a diameter of about 20 mm and a depth of about 0.7 mm. The recess of target holder is roughened for example, with a very fine emery paper or steel wool after which, the target holder is washed in a cleaning solution, dried, then placed into methanol and sonicated for about 5 min, then dried. A piece of a suitable brazing material 30 having a diameter of about 12 mm, is then placed into the recess of the target holder 20. Suitable brazing materials are silver-copper-phosphorus brazing fillers exemplified by SIL-FOS® (SIL-FOS is a registered trademark of Handy & Harman Corp., White Plains, N.Y., USA). Next, a sintered Mo-100 disc is placed on top of the brazing material after which, a weight 50 (FIG. 3) exemplified by a tantalum pellet is placed on top of the sintered Mo-100 disc to prevent the stacked components from moving during the brazing process. The target assembly is heated in a brazing furnace under an argon/hydrogen atmosphere (e.g. 98%:2%) to approximately 750° C. and kept at this temperature for 1 h, and then cooled to room temperature. It should be noted that selection of an appropriate brazing filler metal is of particular importance for the successful joining of sintered Mo-100 discs to GLIDCOP® backing materials. For example, a SIL-FOS® product sold in the USA under the trade name Mattiphos (Johnson Matthey Ltd., Brampton, ON, CA) comprises a group of silver-copper-phosphorus materials of the approximate composition Ag 2-18%, Cu 75-92%, P 5-7.25%, which are mainly used for brazing copper and certain copper alloys. SIL-FOS® is commercially available as rod, strip, wire or foil. SIL-FOS® melts in the range of about 644° C. to about 800° C. and has a flow point of approximately 700° C. Joints brazed with SIL-FOS® are very ductile. If applied to pure copper, the phosphorus enables a self-fluxing capability. Brass, bronze and other copper alloys require a separate flux, but GLIDCOP® can be brazed with SIL-FOS® only, thus eliminating the need for a cleaning procedure after the brazing. Although SIL-FOS® type brazing fillers were initially developed for copper to copper brazing, it was found that they also bond to some refractory metals such as molybdenum. The molybdenum body to be brazed with GLIDCOP® may be present as a foil, plate, pellet, pressed, sintered or any other self-supporting structure. The process described above yields an exemplary Mo-100 target system 10 (FIGS. 4, 5, 6) for the irradiation of Mo-100 with high power particle beams, such as protons from a cyclotron. The exemplary Mo-100 target system 10 comprises (i) a backing material 20 comprising a dispersion-strengthened copper composite, (ii) a self-supporting sintered Mo-100 target material 40, and (iii) a brazed material 30 interposed between and engaging the backing material 20 and the Mo-100 target material 40. The selection of a dispersion strengthened copper composite as backing material provides several advantages over other materials with high thermal conductivity The brazing process described above reliably joins a sintered molybdenum plate to a GLIDCOP® backing. SIL-FOS® affords a uniform, mechanically solid but ductile interface between the two components of the assembly. This ductility of the brazing joint plays a major role in regards to its durability under irradiation conditions. During bombardment with high energy protons the incident beam is primarily absorbed in the molybdenum, which causes a substantial temperature rise in the molybdenum plate. The thermal expansion coefficients of molybdenum (4.8 μm/m·K) and GLIDCOP® (16.6 μm/m·K) are remarkably different. Thermal stress effects between the beam heated molybdenum and the cooled GLIDCOP® backing are mitigated by the ductile SIL-FOS® interface layer, thus contributing to the mechanical stability of the assembly without compromising the adhesion of the molybdenum plate to the backing. While the exemplary embodiments disclosed herein have been specified in reference to their use with a PETTRACE® cyclotron, those skilled in these arts will understand that the dimensions of the target holders and the pressed Mo-100 discs disclosed herein can be modified to produce target holders and pressed Mo-100 discs suitable for use with other apparatus that generate accelerated particles. |
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045004498 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method for solidifying radioactive residues from liquid waste of pressurized-water reactors which are also called concentrates and usually comprise boron in the form of borates. 2. Description of the Prior Art It is known to solidify such concentrates by embedding them in binders by means of a mixing device. Worm dryers such as shown in German Published Prosecuted Application No. 22 40 119 are used, among others, as a mixing device. Bitumen is used particularly as the binder. However, the binder may also include plastics, for instance, polyethylene, as well as concrete or the like. The residues to be embedded, which are usually concentrated by evaporation but are still liquid, are frequently accumulated over an extended period of time before they are present in an amount worthwhile for embedding. For this purpose, shielded containers are provided which, because of the radioactivity, are practically inaccessible. In this connection no disturbances must occur to the concentrate, for instance, through crystallization of boron compounds in the concentrate. Further difficulties in embedding the mentioned radioactive residues can result from the fact that the residues crystallize in being embedded. Extremely hard crystals can be produced in this connection so that, at a minimum, heavy abrasion results in the mixer used for the embedment with a greater danger of the hard crystalline solids blocking the mixing device. The water vapor and volatility of boron compounds can furthermore lead to incrustation at steam-carrying internals of the mixing apparatus under certain conditions. A further aggravating disadvantage of conventional embedment methods is that the end products have only low leaching resistance. SUMMARY OF THE INVENTION It is an object of the invention to provide an improved method of conditioning liquid concentrates of boron-containing radioactive residues to be solidified by embedment in a binder such that storage and embedment can be carried cut in an optimum manner, optimum meaning, among other things, that the amount of residue relative to the amount of binder is maximized. With the foregoing and other objects in view there is provided in accordance with the invention a method for solidifying radioactive liquid concentrate residues from liquid wastes of pressurized-water reactors containing boron in the form of borates by embedding the residues in a binder by mixing in a mixing device, the improvement comprising prior to said embedding in a binder, adding sodium hydroxide to the waste concentrate to obtain a mole ratio of sodium to boron of about 0.25 or 0.7 with a respective corresponding pH value in the range of 7.3 to 8.0 or 9.8 to 10.2 and mixing the waste concentrate to which sodium hydroxide has been added with a binder to embed the waste concentrate in the binder. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method for solidifying boron-containing radioactive residues, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. |
abstract | A hazardous material storage system includes a drillhole extending into the Earth and including an entry at least proximate a terranean surface. The drillhole includes a substantially vertical portion, a curved portion, and a horizontal portion that includes a hazardous waste repository formed within a first portion of the horizontal portion of the drillhole, the hazardous waste repository vertically isolated, by a rock formation, from a subterranean zone that includes mobile water, and a safety runway formed within a second portion of the horizontal portion exclusive of the hazardous waste repository and adjacent the curved portion, the safety runway defined by a particular length. |
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claims | 1. A computer tomography apparatus comprising: an X-ray source for applying a cone-like X-ray beam to a target object to be examined; a two-dimensional X-ray detector being disposed on an X-ray optical axis of the X-ray source so as to be opposed to the X-ray source, for obtaining X-ray fluoroscopic data of the target object; a turn table disposed between the X-ray source and the two-dimensional X-ray detector, said turn table having the target object mounted thereon and being operable to rotate the target object around an axis orthogonal to the X-ray optical axis; a data processing section for reconstructing a plurality of tomograms of the target object cut on a plane orthogonal to a rotation axis of the turn table; a number-of-imaging-times setting section for setting a number of imaging times; and a move mechanism for moving the turn table in a rotation axis direction of the turn table by an effective view field of the two-dimensional X-ray detector each time an imaging is executed until the number of imaging times reaches the set number of imaging times. 2. The computer tomography apparatus as claimed in claim 1 , further comprising: claim 1 a direction setting section for setting a direction when the turn table is moved in the rotation axis direction, wherein the move mechanism moves the turn table in the direction set by the direction setting section. 3. The computer tomography apparatus as claimed in claim 1 , wherein the data processing section concatenates the plurality of tomograms reconstructed to obtain three-dimensional data of the target object. claim 1 4. A computer tomography method using a computer tomography apparatus including an X-ray source, a turn table, and a two-dimensional X-ray detector, the method comprising: setting a number of imaging times and an effective view field of the X-ray detector; applying a cone-like X-ray beam to a target object to be examined mounted on the turn table while rotating the target object around an axis orthogonal to an X-ray optical axis; collecting X-ray fluoroscopic data of the target object and reconstructing a tomogram of the target object cut on a plane orthogonal to a rotation axis of the turn table; moving the turn table in a rotation axis direction of the turn table by the effective view field of the two-dimensional X-ray detector if the number of imaging times does not reach the set number of imaging times and repeating the collecting step. 5. The computer tomography method as claimed in claim 4 , further comprising: claim 4 setting a direction when the turn table is moved in the rotation axis direction of the turntable. 6. The computer tomography method as claimed in claim 4 , further comprising: claim 4 concatenating a plurality of tomograms reconstructed to obtain three-dimensional data of the target object. |
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abstract | Embodiments provide a system and apparatus for visual inspection of a nuclear vessel. The system includes a submersible remotely operated vehicle (SROV) system that is movable to an area within a nuclear vessel. The SROV system includes a maneuverable inspection camera assembly for visual inspection of nuclear vessel components, where the inspection camera assembly is maneuverable in relation to the SROV system. The system also includes a control system located in an area remote from the area within the nuclear vessel. The control system is configured to control the movement of the SROV system and the maneuvering of the inspection camera assembly. |
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051241161 | claims | 1. A method for keying exterior grid cells in a nuclear fuel assembly having grid assemblies formed form interleaved grid strips with the grid assemblies forming interior and exterior grid cells, comprising: a. inserting a grid key having a T-shaped first end and a main body portion bent at approximately a 45 degree angle into the window of the exterior grid strip of the exterior grid cell such that the top of the T-shaped first end is inside the window and parallel to the longitudinal axis of the grid assembly; b. rotating the main body portion of the grid key approximately 90 degrees such that the top of the T-shaped first end is perpendicular to the longitudinal axis of the grid assembly and behind the exterior grid strip; c. pulling the main body portion away from the exterior grid strip in a vertical rotating motion to move it approximately 90 degrees to a vertical position whereby the top of the T-shaped first end pulls the exterior grid strip away from the center of its cell defined by the grid assembly. |
040452875 | abstract | A fuel assembly includes a bundle of vertical fuel rods. Some of the rods are tying rods provided with extended upper end plugs, and the rest of the rods are spring-furnished ones, the spring forces balancing the tying forces exerted by the tying rods between a top plate and a bottom plate. The top plate is grid-like and provided with attachment holes for the upper end plugs. The lower end plugs of the tying rods are screwed in threaded holes in the bottom plate. Each of the upper end plugs of the tying rods has a portion located above the top plate and provided with a nut. Rotation of the nut is limited by at least one downwardly directed projection on the nut, the end surface of which lies below the upper edge of the top plate. The maximally allowable length of this projection is less than the maximum shortening of the springs that can be carried out by exerting a downwardly directed force on the top plate. With such a projection length the projections can clear the side and the nut can be rotated and removed. |
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054815754 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cross section of a reactor vessel 1 associated with a boiling-water reactor. The reactor core 2 contains fuel in the form of fuel assemblies between and through which cooling water is pumped. A plurality of vertical neutron detector tubes are arranged evenly distributed over the core. The figure shows a cross section of a neutron detector tube 3. The neutron detector tube is hollow and includes four equidistantly distributed, fixedly mounted neutron flux detectors 4A, 4B, 4C, 4D, so-called LPRM detectors. All the LPRM detectors in the core are distributed at four levels, 80%, 60%, 40% and 20% of the height of the core. The levels are designated A, B, C, D in FIG. 1. The core comprises about 80-150 LPRM detectors, depending on the reactor type. The LPKM detectors form a regular lattice in the core. FIG. 2 shows part of the core in FIG. 1 in a horizontal section through level D. Fuel assemblies 5 with a substantially square cross section are arranged vertically in the core at a certain distance from each other. This forms a check pattern of vertically extending gaps between the fuel assemblies. The section includes 36 fuel assemblies. The total number of fuel assemblies in a whole cross section amounts to several hundred. The reactor core comprises a plurality of control rods 6, placed parallel to the fuel assemblies in the vertically extending gaps. In the vertically extending gaps, also LPIM detectors 4D.sub.1 -4D.sub.9 are arranged. FIG. 3 shows in a block diagram one embodiment of a device for detecting instability in the core. In practice, it has proved that core oscillations primarily arise in the lower part of the core. In a preferred embodiment, oscillations are detected only in the LPRM detectors at the two lowermost levels (C, D) in the core. All the detectors at the two lowermost levels are divided into four detector groups 8a, 8b, 8c, 8d. Detectors mounted in the same neutron detector tube belong to the same detector group. The detectors in one detector group are chosen so that as large parts of the core as possible are represented in each group. Each detector group is associated with a group of oscillation detectors 9a, 9b, 9c, 9d. Each LPRM detector in the detector group is connected to an oscillation detector in the corresponding group of oscillation detectors. The oscillation detector detects oscillations in the output signal from the LPRM detector. An oscillation detector has two output signals (K, R), one triggering alarm for a remaining oscillation (K), and the other triggering alarm for an intermittent oscillation (R). If a detector is, or is suspected to be, defective, the alarm signals from the corresponding oscillation detector are blocked manually. The output signals from one group of oscillation detectors are combined into an alarm unit 10a, 10b, 10c, 10d. The output signals from all the alarm units La, Lb, Lc, Ld are transmitted to a reactor protection system 11 for further processing. As an example, FIG. 3 shows how the output signal Sa from the LPRM detector 4D.sub.1 is processed. Sa is input signal to the oscillation detector 12a, which detects whether the input signal Sa oscillates, and if it oscillates it is determined whether it is a remaining or an intermittent oscillation. The output signals Ka and Ra from the oscillation detector are forwarded to the alarm unit 10a but can also constitute information to the operator. The alarm unit determines whether the reactor protection system 11 is to be alarmed. Alarm to the reactor protection system is given via the alarm signal LA. In a corresponding way, the output signals from the other LPRM detectors are processed. The alarm unit alarms the reactor protection system if an optional alarm criterion is fulfilled. A suitable alarm criterion may, for example, be that at least two of the LPRM detectors in the detector group oscillate, whether the detector oscillates because of an intermittent or a remaining core oscillation is of no importance for fulfilling the alarm criterion. The reactor protection system automatically initiates a partial reactor scram or a full scram if an optional reactor scram criterion is fulfilled. A suitable reactor scram criterion is that at least two of the alarm units give alarm. What kind of oscillation (intermittent or remaining) has given rise to an alarm can be conveyed as information to a reactor operator. It may, for example, also be of interest to the reactor operator to see which individual detectors alarm. FIG. 4a shows an example of a remaining oscillation in the output signal from an LPRM detector. TAV is the time-average value of the detector signal. Instability arose suddenly because of a temporary event, for example a cooling pump that stopped. The output signal oscillates around its time-average value with an approximately constant maximum and minimum amplitude. The period of a remaining oscillation is designated T. The frequency of the oscillations in case of an instability varies between different reactors and is normally known for an individual reactor. The frequency of the oscillation is due to the coolant's time of transportation through the fuel channel, that is, the time it takes for a "density wave" to transport through the core. In this example, the reactor oscillates with a frequency of about 0.5 Hz in case of an instability, which means that the period T is about two seconds. An oscillation has been detected when the output signal from the LPRM detector fulfills one oscillation criterion. The oscillation criterion means that the output signal of the detector during one oscillation interval of a predetermined duration, at least once exceeds an upper limit, which consists of the sum of the time-average value TAV an upper limit value .DELTA.G1 (TAV+G1), and at least once is lower than a lower limit, which consists of the difference between the time-average value TAV and a lower limit value .DELTA.G2 (TAV-.DELTA.G2). A remaining oscillation is an oscillation for which the oscillation criterion is fulfilled for a long period of time. To fulfill the oscillation criterion, the detector output signal must at least once exceed the upper limit and at least once be below the lower limit. If the output signal only exceeds the upper limit, or if it is only lower than the lower limit, this may be a sign of a power increase or a power decrease, which is now allowed to release an alarm. Short randomly occurring oscillations may sometimes arise without this being a sign of a core instability. This type of oscillation is not allowed to give rise to alarm. An alarm may only be released when the detector signal continuously oscillates around its own average value, or when the oscillations recur at regular intervals, so-called intermittent oscillations. FIG. 4b shows an example of the appearance of an intermittent oscillation. The intermittent oscillation consists of a remaining oscillation with the period T, the amplitude of which varies periodically. The period of the intermittent oscillation, that is, the time between two amplitude maximums, is designated Trot and is greater than or equal to the period of the remaining oscillation T. For an intermittent oscillation, the oscillation criterion is only fulfilled during part of the period T.sub.rot. For the remainder of the period, the oscillations are too small to fulfill the oscillation criterion. FIG. 5 shows in more detail the oscillation detector 12a in FIG. 3. The output signal Sa of the LPRM detector is filtered hard in a filter 13, the output signal TAV of which corresponds to the time-average value of the output signal Sa. To remove unnecessarily high noise signals from the output signal Sa, it is slightly filtered in a filter 14. In a comparison device 15, the noise-reduced signal is compared with its own time-average value TAV. If the noise-reduced signal exceeds the upper limit (TAV+.DELTA.G1), a pulse P is generated on the positive output of the comparison device, and if the noise-reduced signal is lower than the lower limit (TAV-.DELTA.G2), a pulse N is generated on the negative output of the comparison device. These two pulses are each extended in a pulse extender 16a, 16b by an extension time T2 corresponding to the oscillation interval. A pulse extender functions in such a way that if a signal at its input is low, the output of the pulse extender is not reset until after the set extension time. If a new pulse should enter the input before the extension time has expired, the output will not be reset. The extended pulses are combined in an AND circuit 17. The output signal from the AND circuit, called the oscillation signal SS, indicates that the oscillation criterion is fulfilled. The oscillation signal must not be reset only because the comparison device has failed to observe that the signal exceeded the upper limit, or that the signal was below the lower limit. Therefore, the oscillation interval should cover a good two periods of the oscillation sought. In this example, it is suitable to set the oscillation interval at five seconds, which covers 2.5 periods. In a delay circuit 18, all brief alarms are filtered away, for example alarms caused by intermittent oscillations. The delay interval T3 constitutes a limit value for the shortest time that an oscillation can proceed to be considered a remaining oscillation. The output signal Ka from the delay circuit 18 is an alarm signal for remaining oscillations Ka. In this example, the delay interval is 30 seconds. The output signal Ka from the delay circuit 18 only releases alarm for remaining oscillations, that is, oscillations which last more than 30 seconds. An intermittent oscillation may have a frequency f.sub.rot in the interval from zero up to the frequency of the remaining oscillation (0 Hz<f.sub.rot <0.5 Hz). For identification of the intermittent oscillations down to a chosen lowest frequency, the oscillation signal SS, which shows whether the oscillation criterion is fulfilled, is connected to a pulse extender 19 which extends the oscillation signal during an alarm interval T1, corresponding to the period of the lowest frequency chosen. The oscillation signal FSS thus extended remains in case of periodically recurring oscillations with frequencies above the lowest frequency chosen. To be certain that it is a question of a recurring oscillation, the alarm in a delay circuit 20 is delayed for a delay time T4, corresponding to a specified number n of alarm intervals (T4=n * T1). A suitable number of alarm intervals is five, which provides the delay time T4=5 * T1. An alarm is only released if the extended oscillation signal FSS is high during the whole delay time T4. The alarm signal LR from the delay circuit 20 alarms both for remaining and intermittent oscillations. To block away alarms for remaining oscillations, the alarm signal LR is connected to one of the inputs of an AND circuit 21, and the alarm signal for remaining oscillations Ka is connected to the other input thereof, which is an inverted input. The output signal Ra from the AND circuit 21 is a pure alarm signal for intermittent oscillations. The alarm signals Ka and Ra are transmitted to the alarm unit, provided that the LPRM detector is not defective. If the detector is, or is suspected to be, faulty in any way, the alarm signals Ka and Ra will be blocked. One advantage of the invention is that also local oscillations can be detected. This is possible because the oscillations are detected directly in the output signal for each individual neutron detector, and not in a combination of output signals from a plurality of detectors. Another advantage of the invention is that oscillations with a constant amplitude can be detected, since there is no demand for a growing amplitude of the oscillation. In the foregoing, an embodiment of the invention comprising separate units has been described. The scope of the invention comprises different embodiments, which may consist of more or less integrated, possibly program-controlled embodiments. In this embodiment, all the LPRM detectors from the two lowermost levels in the core are utilized for detecting an instability, but, of course, an optional number of detectors from all the levels can be utilized. |
051867648 | description | DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIGS. 1 to 3 these show a furnace suitable for nitriding the surfaces of thin apertured steel plates. The furnace comprises a central chamber 20 mounted within a furnace structure indicated generally at 21. The furnace has an outer housing 22 of refractory and heat-insulating material and a lining 23. Between the housing 21 and the lining 23 are heating elements, two of which are shown at 24. A pipe 25 is connected to the lining 23 and passes through the housing 22 and allows the introduction of gaseous treating medium into the interior of the lining. There is a space 26 between the lining 23 and the exterior of the chamber 20. The furnace structure carries a door 27 which fits into the left-hand end of the lining 23 to close the furnace. The door may be opened by moving it to the left in FIG. 1 and then lifting it by means not shown. A lower wall 28 of the furnace structure is pivoted at 29 so that it may move to the dotted line position shown at 28a which then places a duct 30 in communication with the interior of the lining 23. The duct 30 is connected to an evacuation fan 31 which enables gas to be drawn out of the furnace. The chamber 20 is defined by bottom and top walls 32 and 33, side walls 34 and end walls 35 and 36. The end wall 35 has a central aperture 37 in which is mounted a circulating fan 38 which is arranged to draw gas from the chamber 20 and discharge it into the space 26 between the chamber 20 and the lining 23. The fan is driven by an electric motor 39. The end wall 36 of the chamber has an aperture 40 which is partially closed by the furnace door 27 which thus forms part of the left-hand end wall of the chamber. The clearance 41 between the aperture and the door 27 communicates with the space 26 and the interior of the chamber. Each of the walls 32 to 34 is provided with three baffles. Thus the bottom wall 32 is provided with baffles 42, 43 and 44. The baffles are inclined to the right in the drawings towards the wall 35 and it will be seen that the baffles extend further from the wall 32 the nearer they are to the wall 35. Thus the baffle 44 extends further from the wall 32 than does the baffle 43 and the latter extends further from the wall 32 than does the baffle 42. The top wall 33 has three baffles 45, 46 and 47 and each of the side walls 34 has three baffles 48, 49 and 50. As will be seen from the drawings all the baffles are inclined to the right towards the wall 35 and they are all arranged as described with reference to the baffles 42 to 44 i.e. the baffles nearer the wall 35 extend further from the wall to which they are attached than do the baffles further from the wall 35. The bottom wall 32 of the chamber supports a roller conveyor 51 on which is received a fixture 52, described below, on which plates are mounted for treatment in the chamber. The fixture can be moved into and out of the chamber 20 when the door 27 is open. Referring now to FIGS. 4 to 11 the fixture 52 comprises a base 53, FIGS. 5 and 6, comprising opposed sides 54 in the form of square tubes which are held in spaced apart relation by six cross-pieces 55. Each side 54 of the base supports ten vertical columns 56, each column on one side of the base being aligned with a column on the other side of the base. Referring to FIG. 7 the base of each column 56 comprises a cylindrical tube 57 welded in aligned apertures in the upper and lower walls 58 and 59 of a side 54 to project upwardly from the side. A cylindrical re-enforcing bar 60 is received in the lower part of the tube while the upper part thereof forms a socket 61. Each column 56 is built up on a tube 57 with a number of components such as 62 and spacers shown in FIGS. 8 and 9 respectively. Each component 62 comprises a cylindrical tube 63 of the same diameter as the tube 57 and a cylindrical spigot 64 dimensioned to fit into the socket 61 in the tube 57 and a similar socket 65 in the tube 63 of another component 62. The tube 63 and spigot 64 are welded together at 66. Thus a column 56 is built on a tube 57 by inserting the spigot 64 of a component 62 into the socket 61 and then inserting the spigot 64 of another component 62 into the socket 65 of the component already in place on the column and so on. FIG. 10 shows a support bar 67 which fits between two aligned columns of the fixture, one on each side 54 of the base 53. The support bar has a central section 68 of Vee-section with opposed sides 69. Formed in each of the opposed sides 69 is a series of Vee-shaped notches 70, the notches in one side 69 being aligned with the notches in the other side 69. At each end the support bar has an apertured end fitting 71 of angle section with its flanges vertical and horizontal. The vertical flanges 72 are welded to the ends of the central section 68 and the horizontal flanges 73 are provided with apertures 74. The apertures 74 are of such size as to fit over the tubes 57 and 63 with a small clearance. As will be described below, the apertures 74 of the support bars are threaded over the tubes 57 and 63 and are held in vertical spaced relation by tubular spacers 75 shown in FIG. 9 which slide over the tubes 57 and 63. FIG. 11 shows a tie bar 76 for the fixture. The tie bar is of angle section having horizontal and vertical flanges 77 and 78. The flange 77 is apertured at 79 to receive the tubes 63 of the components 62 and so that it may be supported by spacers 75. The apertures 79 are spaced to receive the upper ends of the columns 56. The vertical flange is cut away at 80 to give clearance to the vertical flanges 72 of the support bars 67 as shown in FIG. 6. FIG. 4 is a section through the whole fixture assembled and carrying a multiplicity of apertured plates 81, the edges of the apertures being received in the notches 70 of the support bars 67. Each plate is received in one aligned pair of notches in a support bar and this holds the plates in fixed positions in spaced-apart relation. The fixture 52 is built up and filled with plates as follows. Starting with the base 53 with the attached tubes 57, one aligned pair of columns is built up at a time. Thus the spigots 64 of components 62 are inserted in the sockets 61 of the tubes 57 and short spacers 82, similar to the spacers 75 but shorter, are put on the tubes 57. A support bar 67 is then filled with plates 81 and the apertures 74 on the ends thereof threaded over the tubes 63 to rest on the tops of the spacers 82. Spacers 75 are then threaded over the tubes 63 of the lowermost components 62. Then another pair of components 62 has its spigots inserted in the sockets 65 of the lowermost pair of components 62. Then another support bar with its plates 81 is threaded over the tubes 63 of the uppermost components 62 and the sequence is continued until there are five support bars on each column as shown in FIGS. 4 and 6. The remaining columns on the base are built up in the same way. When all the columns have been built up a tie bar 76 is slipped over the upper ends of the columns on each side of the fixture to give a rigid assembly. The fixture 52 with its plates is then placed in the chamber 20 so that the support bars 67 extend parallel to the end walls 35 and 36 of the chamber as shown diagramatically in FIG. 2 so that the faces of the plates are parallel to the side walls 34 of the chamber and, as will be described, parallel to the general direction of gas flow through the chamber. Preferably the plates 81 are made of non-alloyed steel or fine grained structural steel containing niobium and vanadium or titanium and range from 0.4 to about 5 mm in thickness. When the fixture 52 with its plates has been inserted in the chamber 20, the door 27 is shut. The lower wall 28 of the furnace is pivoted down and air is evacuated from the interior of the furnace by the pump 31. An inert atmosphere e.g. nitrogen is introduced into the furnace through the pipe 25 and the lower wall 28 closed. The furnace is then heated by the heaters 24 to a temperature between 600 and 700 degrees C. The inert gas is then evacuated by the pump 30 and a gaseous medium capable of nitriding the surfaces of the plates is introduced as described in said above mentioned U.S. Pat. No. 4,793,871. During the heating of the furnace the inert atmosphere is circulated by the fan 38. Thus the inert gas is drawn by the fan 38 from the interior of the chamber and discharged to the space 26 from which it again enters the left-hand end of the chamber. The baffles 42 to 50 respectively direct the flowing gas inwardly towards the centre of the chamber and thus into the spaces between the rows of plates 81 on the support bars 67. This gives a substantially uniform flow of gas over all the plates and thus even heating of the plates. The gas flow is shown by the arrows in FIGS. 2 and 3. When the nitrogen-containing gas is introduced into the chamber to treat the plates, this also is circulated by the fan 38 and deflected by the baffles to give a substantially uniform flow of reactive gas over the surfaces of the plates and thus ensure a uniform coating of nitride on the plates. The provision of the baffles in the furnace ensures an even flow of gas over the surfaces of the plates both to heat and to treat them and the support of the plates in the fixture as described enables a large number of plates to be treated at one time and exposed to a uniform gas flow due to the baffles. |
046613137 | abstract | A cost-effective configuration of a metal liner for a reinforced concrete pressure vessel is disclosed wherein only stud shear connectors and cooling tubes of the liner cooling system are used to anchor the liner and the passages provided in the liner and the wall of the vessel. In the areas of the introduction of forces, stud connectors of different stud rigidities are used. In the anchoring of loads which is again effected by stud connectors only, further transmission is obtained by means of reinforcing rods. |
060884177 | claims | 1. An apparatus for detecting and locating leaks in a nuclear plant, comprising: a collection line permeable to a substance to be detected; a pump communicating with said collection line; a sensor communicating with said collection line for sensing the substance, said sensor not suited to detecting radioactivity of the substance; a detector communicating with said collection line for detecting radioactivity of the substance; and a suction pump associated with said detector. 2. The apparatus according to claim 1, wherein said collection line is disposed in the vicinity of a pipeline of a nuclear plant. 3. The apparatus according to claim 1, including a branch line branching off said collection line upstream of said sensor and communicating with said detector. 4. The apparatus according to claim 1, including a supply container in which said detector is disposed. 5. The apparatus according to claim 1, including a valve disposed upstream of said collection line. 6. The apparatus according to claim 1, including check valves disposed at spaced-apart openings formed in said collection line, said check valves opening if a predetermined pressure fails to be exceeded. 7. The apparatus according to claim 1, wherein said sensor determines a concentration of substances. |
claims | 1. A pressurized water nuclear reactor, comprising:a core comprising a containment shield surrounding a reactor vessel having fuel assemblies that contain control rods and fuel rods filled with fuel pellets, and a steam generator thermally coupled to said reactor vessel via a primary flow loop;a secondary flow loop comprising said steam generator, a turbine, a condenser, and a pump for circulating a water-based heat transfer fluid in said secondary flow loop, wherein said heat transfer fluid comprises a plurality of nanoparticles comprising at least one carbon allotrope or related carbon material dispersed therein. 2. The pressurized water nuclear reactor of claim 1, wherein said at least one carbon allotrope or related carbon material comprises diamond nanoparticles. 3. The pressurized water nuclear reactor of claim 2, wherein said diamond nanoparticles are primarily colloidal. 4. The pressurized water nuclear reactor of claim 2, wherein said diamond nanoparticles have a mean size that is in a range from 0.5 nm to 200 nanometers. 5. The pressurized water nuclear reactor of claim 4, wherein said mean size is in a range from 1 nm to 100 nm. 6. The pressurized water nuclear reactor of claim 4, wherein said mean size of said plurality of nanoparticles is in a range from 40 nm to 100 nm. 7. The pressurized water nuclear reactor of claim 1, wherein said at least one carbon allotrope or related carbon material comprises fullerenes. 8. The pressurized water nuclear reactor of claim 1, wherein said at least one carbon allotrope or related carbon material comprises carbon nanotubes. 9. The pressurized water nuclear reactor of claim 1, wherein a concentration of said plurality of nanoparticles in said heat transfer fluid is in a range from 0.0001 to 10 volume percent of said heat transfer fluid. 10. The pressurized water nuclear reactor of claim 9, wherein said concentration of said plurality of nanoparticles in said heat transfer fluid is in a range from 0.1 to 3 volume percent of said heat transfer fluid. |
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description | The present invention relates to an apparatus for extracting multiple laser Compton scattering photon beams using a laser Compton scattering reaction. The invention has been published in NURER2016 on 18 Sep. 2016. A laser Compton scattering (LCS) reaction is a reaction in which a low energy laser light is emitted to accelerated high energy electrons to cause inverse Compton scattering, thereby generating LCS photons of a specific energy region. The high energy LCS photons generated after the reaction may be used in various fields such as nuclear transmutation, physical experiments, and the like. In particular, nuclear waste disposal corresponds to a backend of a nuclear fuel cycle and is a most challenging task. Radioactive waste contains various toxic and dangerous fissile materials. Many of these materials have short half-lives to quickly decay into stable nuclei, but some of the materials have very long half-lives. Such long-living fission products (LLFPs) are so mobile that special handling thereof is required. A common choice for inhibiting mobility of the LLFPs is disposal in geological repositories, but designing geological repositories that may store LLFPs for millions of years may not be a viable option. Meanwhile, another alternative may be a transmutation of the LLFPs into short-lived or stable nuclides. Possible approaches for transmutation of toxic radionuclides are neutron capture reactions using (n, y) reaction. However, such a process has problems, namely, fairly large neutron flux (1015-1016 n/cm2sec) is required and, according to transmutation from one nuclide to another, a neutron capture cross section is sharply changed. Another method is to use high-intensity gamma rays for photonuclear reactions using (y,n) transmutation. The (y,n) transmutation is governed by a giant dipole resonance (GDR) cross section. The GDR is a dominant excitation mechanism, in which a collective bulk oscillation of nuclei against all protons occurs. The GDR cross section is a function of a, slowly changing, mass number and does not sharply change according to transmutation from one radionuclide to another. Such high intensity gamma rays for the excitation may be produced by other methods, and the most suitable method is using LCS technology. An LCS phenomenon is that low energy (energy of approximately several eV) photons are scattered by an electron beam of the predetermined energy to produce very high energy gamma rays. FIG. 1 is a view conceptually illustrating the LCS phenomenon. LCS gamma rays are quasi-monochromatic light with considerable energy and are energy-tunable. The gamma rays generated by such characteristics may overlap an energy range (10-20 MeV) of the GDR cross section of the LLFPs. Of the various LLFPs, only a few are of major concern in terms of radioactive waste management, and when considering toxicity levels, half-life, effects on the repositories, and annual inventories as references, iodine and cesium have considerably significant problems in spent fuel handling. [Table 1] shows isotopic composition of radionuclides that require transmutation in spent nuclear fuel of a typical light water reactor (LWR). TABLE 1ElementIsotopeIsotopic Composition (wt %)Iodine127I22.98129I77.02Cesium133Cs76.41134Cs0.292135Cs16.83137Cs6.47 In general, because the GDR cross section does not show a significant change from one isotope to another, (y,n) reaction-based nuclear transmutation is required for isotope separation. Thus, some short-lived or stable isotopes may be transmuted into long-lived radionuclides with a considerable significant probability that the (y,n) reaction will proceed. [Table 2] shows a half-life of each of the radionuclides to be transmuted and of each of the products after (y,n) reaction. TABLE 2RadionuclideProduct after (γ, n) reaction127I(stable)126I(12.93 d)129I(T1/2 = 15.7 × 106 y)128I(24.99 m)133Cs(stable)132Cs(6.48 d)134Cs(T1/2 = 2.07 y)133Cs(stable)135Cs(T1/2 = 2.3 × 106 y)134Cs(T1/2 = 2.07 y)137Cs(T1/2 = 30 y)136Cs(T1/2 = 13.16 d) When only the (y,n) reaction is considered from [Table 2], and iodine and cesium do not require any isotope separation. After being transmuted, each product becomes stable or short-lived, and some of the stable isotopes are transmuted also to radionuclides, which have very short-lived nuclides, thereby being able to be managed within the current waste management category. Other considerations for this kind of transmutation may include higher order photonuclear reactions such as (y,2n), (y,3n), (y,xn), and the like, but threshold energy for higher order reactions other than (y,2n) reaction is very high. However, it was confirmed that the (y,2n) reaction has a considerably smaller cross section compared with the (y,n) reaction, and hence the (y,n) reaction may be maximized while minimizing (y,2n) reaction by optimizing the LCS spectrum. U.S. Patent Application Publication No. 2012-0002783 (published on Jan. 5, 2012) Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus capable of extracting multiple LCS gamma rays to efficiently induce a nuclear transmutation by a photonuclear reaction to a target such as nuclear waste and the like. In order to accomplish the above objective, the present invention provides an apparatus for extracting multiple laser Compton scattering photon beams: the apparatus including: a linear accelerator for accelerating an electron beam; and an LCS gamma ray generation module including an LCS gamma ray generator for irradiating a target with an LCS gamma ray generated by emitting laser light to an electron beam released from the linear accelerator and a bending magnet for adjusting a direction of the electron beam passed through the LCS gamma ray generator, wherein the at least two LCS gamma ray generation modules are sequentially arranged to form a closed loop together with the linear accelerator. The at least two LCS gamma ray generation modules may be arranged to irradiate a same target with the LCS gamma rays. The LCS gamma ray generation modules may generate the LCS gamma rays of different energy from each other, thereby allowing photonuclear reactions to occur for targets of nuclides different from each other. Bending angle θ of the electron beam of the bending magnet may be 0<θ≤90°. As described above, an apparatus for extracting multiple laser Compton scattering photon beams according to the present invention includes a linear accelerator and a plurality of LCS gamma ray generation modules. Each of the LCS gamma ray generation modules generates an LCS gamma ray, generated by Compton scattering due to an electron and laser light emitted to the electron, and includes a bending magnet adjusting a direction of the electron beam by which the LCS gamma ray has been extracted. In addition, at least two LCS gamma ray generation modules are sequentially arranged to form a closed loop together with the linear accelerator. Accordingly, a probability of inducing a specific nuclear transmutation using one linear accelerator can be increased, or induction of nuclear transmutation for various nuclides can be collectively carried out. Specific structures or functional descriptions presented in the embodiments of the present invention are illustrated only for the purpose of describing the embodiments according to the concept of the present invention, and the embodiments according to the concept of the present invention may be implemented in various forms. In addition, the present invention should not be construed as limited to the embodiments described herein, but should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope thereof. Hereinafter, with reference to the accompanying drawings will be provided description in detail with respect to the present invention. With reference to FIG. 2, an apparatus for extracting multiple laser Compton scattering photon beams according to an embodiment of the present invention includes a linear accelerator 110 for accelerating an electron beam, and a plurality of LCS gamma ray generation modules 210 generate LCS gamma rays and to adjust a direction of the electron beam. The linear accelerator 110 is for accelerating electrons and may be provided with an injector 111 at an inlet side for injecting electrons into a microwave cavity in which the electrons are accelerated or decelerated. In addition, the linear accelerator 110 may use as an energy recovery LINAC (ERL) constituting a closed loop with a plurality of the LCS gamma ray generation modules 210 and may be provided with a beam dump 112 capable of absorbing the electron beam by being installed at an outlet side thereof. Such a linear accelerator 110, in which acceleration of the electron beam is made, has a configuration the same as in the related art for the acceleration and focusing of the electron beam, and therefore description thereof will be omitted. In addition, a beamline having a vacuum state is provided between the linear accelerator 110 and each of the LCS gamma ray generation modules 210, thereby transporting the electron beam. At this time, it should be appreciated that equipment or instrumentation, which is a well-known supplementary installation used for a particle accelerator to focus or diagnose the electron beam, may be added in the beamline. The LCS gamma ray generation module 210 includes an LCS gamma ray generator 211 irradiating a target with the LCS gamma ray generated by emitting laser light to an electron beam released from the linear accelerator 110 and a bending magnet 212 adjusting a direction of the electron beam passed through the LCS gamma ray generator 211. The LCS gamma ray generator 211 may include a mirror 4 allowing the laser light 2 generated by a laser light source 1 to be emitted in the direction of the electron beam 3, wherein the mirror 4 may use a multilayer structure mirror that reflects only the laser light 2 of a predetermined wavelength band and is transparent to the LCS gamma rays. Such an LCS gamma ray generator 211 may be a separate chamber provided in the beamline in which the electron beam 3 is transported. The LCS gamma ray generator 211 generates LCS gamma rays having a solid angle by elastic scattering between the accelerated electron beam 3 and the laser light 2, and nuclear waste, which is a long-living fission products (LLFPs), is irradiated with the LCS gamma rays, thereby causing a nuclear transmutation reaction to proceed. The bending magnet 212 is for changing a path of the electron beam 3 and may be provided by an electromagnet or a superconducting magnet capable of generating a uniform magnetic field. A plurality of the LCS gamma ray generation modules 210, each configured as described above, is configured such that at least two are sequentially arranged to form a closed loop together with the linear accelerator 110. In the present exemplary embodiment, eight units of nuclear waste, which is the LLFPs, and ten LCS gamma ray generation modules are illustrated, but the number and layout thereof may be variously modified. Nuclear waste, which is the LLFPs, is irradiated with the LCS gamma rays generated in each of the LCS gamma ray generation modules 210 to cause a nuclear transmutation reaction to proceed, and one unit of nuclear waste, which is the LLFPs, may be arranged corresponding to one LCS gamma ray generation module 210 but is not limited hereto. For example, in the present embodiment, the fourth nuclear waste may be irradiated with the LCS gamma rays by three LCS gamma ray generation modules 210A, 210B, and 210C to increase the nuclear transmutation reaction efficiency. Each of the LCS gamma ray generation modules 210 is emitted by the laser light 2 having different energy, thereby generating various LCS gamma rays using a single linear accelerator 110 as a whole. Here, the various LCS gamma rays may be determined depending on a nuclide of the nuclear waste, which is the LLFPs, to be disposed of. The electron beam 3 generated by the linear accelerator 110 has a cycle of generating the LCS gamma rays, in the plurality of LCS gamma ray generation modules 210 sequentially arranged, and of entering into the electron accelerator 110 again. In addition, depending on a target (nuclear waste), the arrangement of the LCS gamma generation module 210 may be configured in various ways. On the other hand, when taking a look at loss of the electron beam 3 generated in each of the LCS gamma ray generation modules 210, theoretically, a collision probability of the accelerated electron beam 3 and laser light 2 in the LCS reaction is only 0.0016%, so 99.9984% of the electrons in each LCS gamma ray generation module do not respond to the laser light 2. In addition, scattered electrons also maintain 99.1% of energy thereof compared to before being scattered. Therefore, the electron beam 3 passed through the LCS gamma ray generation module 210 has sufficient energy to cause an additional LCS reaction in a LCS gamma ray generation module of a next stage. In addition, an energy loss ΔE of the electron beam 3, the energy loss being able to be generated in the bending magnet 212 of the LCS gamma ray generation module 210, may be calculated using [Equation 1] below. X E X t ( GeV / s ) = c ( m / s ) C γ ( m / GeV 3 ) 2 π E 4 ( GeV 4 ) ρ 2 ( m 2 ) [ Equation 1 ] Here, E is the energy of the electron beam 3, c is a speed of light, and Cy is a constant. Meanwhile, ρ is a bending radius and is represented by following [Equation 2]. ρ ( m ) = lengthofmagnet ( m ) Bendingangle ( rad ) l θ [ Equation 2 ] From [Equation 1] and [Equation 2], it may be seen that the larger the bending angle in the bending magnet 212, the greater the energy loss. Therefore, in order to reduce the energy loss, the bending angle may be configured to be small. For example, the energy loss that may be generated when the bending angle is a right angle (90°) is no greater than 0.4%. Accordingly, the bending angle θ of the electron beam 3 of the bending magnet 212 may be determined between 0<θ≤90°. FIG. 3 is a diagram schematically illustrating an apparatus for extracting multiple laser Compton scattering photon beams according to another embodiment of the present invention, wherein the bending magnet 212 of each of the LCS gamma ray generation modules 210 has a bending angle θ of the electron beam 3 of a right angle (90°). In the present embodiment, it is shown that five units of nuclear waste (#2, #4, #8, #11, and #14) are irradiated with the LCS gamma ray by two gamma ray generation modules. As described above, the present invention may minimize the energy loss of the electron beam 3 by determining the bending angle of the electron beam 3 in the bending magnet 212 of each of the LCS gamma ray generation modules. In addition, by appropriately configuring the LCS gamma ray generation modules according to the number or nuclide of the target, it may increase a probability of inducing a specific nuclear transmutation using one linear accelerator or may collectively carry out induction of nuclear transmutation for various nuclides. The present invention described above is not limited to the above-described embodiments and the accompanying drawings. In addition, it will be apparent to those skilled in the art that various substitutions, modifications, and changes may be made without departing from the technical spirit of the present invention. 110 Linear accelerator 210 LCS gamma ray generation module 211 LCS gamma ray generator 212 Bending magnet |
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055324959 | description | DETAILED DESCRIPTION OF THE INVENTION The following discussion will begin with a description of the system utilized to produce the ion beams. This system has two major subsystems, the pulsed power source and the ion diode. The discussion will then continue with descriptions of a number of examples of ion beam treatments to various materials. The present invention provides an ion beam generator capable of high average power and repetitive operation over an extended number of operating cycles for treating large surface areas of materials at commercially attractive costs. In particular, the ion beam generator of the present invention can produce high average power (1 kW-4 MW) pulsed ion beams at 0.1-2.5 MeV energies and pulse durations or lengths of from about 10 nanoseconds (ns)-2 microseconds (.mu.s) or longer as necessary for the particular application. The ion beam generator can directly deposit energy in the top 50 micrometers (.mu.m) of the surface of a material. The depth of treatment can be controlled by varying the ion energy and species as well as the pulse length. FIG. 1 schematically illustrates irradiating a material with ion beams in accordance with the principles of the present invention. Although this process can be used to implant ions to the extent that the chemical composition of the implanted region is altered, normally the process will be utilized to deposit energy into the top surface of the material and will not significantly change the atomic composition of the material. As such the process will either heat or ablate the near surface using typically 3.times.10.sup.13 ions/cm.sup.2 per pulse. Such a dose will represent only approximately 10.sup.-5 -10.sup.-3 atomic percent of the sample density. Deposition of ion beam energy 11 in a thin near surface layer 13 causes melting of the layer with relatively small energies (typically 1-10 J/cm.sup.2) and allows rapid cooling of the melted layer by thermal diffusion into the underlying substrate 17 as depicted in FIG. 1. FIG. 2 is a graph which represents the effects whereby, when high energy ions come to rest in a material, the energy is deposited preferentially near the end of the range of penetration into the material. FIG. 2 is a graph showing the so-called Bragg peak for a 0.9 MeV proton beam, plotting electron volts per Angstrom as a function of depth in microns. At higher energy intensities (.gtoreq.10-20 J/cm.sup.2), this process can cause rapid ablation of the substrate. This in turn can be used to deposit a polycrystalline or nanocrystailine layer onto another substrate or to redeposit such a layer on the original substrate. This is shown schematically in FIGS. 5A and 5B which depict rapid ablation and redeposition onto the same material specimen and rapid ablation from one material surface with deposition onto a second material surface, respectively. FIG. 5A shows a production process with the material 54 moving from left to right as indicated by the arrow 55. Ions 50 from the ion beam source 25 ablate the material 54 to form particles 52 which rise above the material 54 and then redeposit back onto the material 54. In FIG. 5B the high energy ions 50 from the ion beam source 25 ablate the first material 60 creating ablated particles 52 which then fall onto the second material 62 which is moving in the direction of the arrow 55. Of course, either ablation process could also be conducted on stationary materials. These higher intensity pulses can also be used to induce shock hardening of much deeper regions of the irradiated substrate. The relatively small energy densities needed for treatment together with the high instantaneous powers available using the present invention allow large surface areas (50 to more than 1000 cm.sup.2) to be treated with a single ion beam pulse, greatly reducing or eliminating the portions of the treated material which are subject to edge effects at the transition between treated and untreated areas. The relatively short ion beam pulse lengths, preferably .congruent.200 ns for use with metals, developed by the ion beam generator limit the depth of thermal diffusion, thus allowing the treated/melted region to be localized to a selected depth. Typical cooling rates of the present invention (10.sup.8 -10.sup.10 K/sec) are sufficient to cause amorphous layer formation in some materials, fine grain structures in some materials, the production of non-equilibrium microstructures (nano-crystalline and metastable phases), and the formation of new alloys by rapid quenching and/or liquid phase mixing of layers of different materials. Such rapid thermal quenching (>10.sup.8 K/sec) can significantly improve smoothness, corrosion, wear and hardness properties of the treated near surface layer. The ion beam generator of the present invention is composed of two major components: a high energy, pulsed power system (shown in FIG. 3) and an ion beam source 25 (shown in FIG. 4), both capable of high repetition rates and both having extended operating lives. The Pulsed Power Source The first of these components is a compact, electrically efficient, repetitively pulsed, magnetically switched, pulsed power system capable of 10.sup.9 pulse operating cycles aof the type described by H. C. Harjes, et al, Pro 8th IEEE Int. Pulsed Power Conference (1991), and D. L. Johnson et al., "Results of Initial Testing of the Four Stage RHEPP Accelator" pp. 437-440 and C. Harjes et al., "Characterization of the RHEPP 1 .mu.s Magnetic Pulse Compression Module", pp. 787-790, both reprinted in the Digest of Technical Papers of the Ninth IEEE International Pulsed Power Conference, June, 1993, all of which is incorporated by reference herein. These references in conjunction with the discussion herein below place fabrication of such a pulsed power source within the skill of the art. A block diagram of a power system produced according to the teachings of the present application is shown in FIG. 3. From the prime power input, several stages of magnetic pulse compression and voltage addition are used to deliver a pulsed power signal of up to 2.5 MV, 60 ns FWHM, 2.9 kJ pulses at a rate of 120 Hz to an ion beam source for this particular system. The power system converts AC power from the local power grid into a form that can be used by an ion beam source 25. Referring to FIG. 3, in one embodiment of the invention, the power system comprises a motor 5 which drives an alternator 10. The alternator 10 delivers a signal to a pulse compression system 15 which has two subsystems, a 1 .mu.s pulse compressor 12 and a pulse forming line 14. The pulse compression system 15 provides pulses to a linear inductive voltage adder (LIVA) 20 which delivers the pulses to the ion beam source 25. The alternator 10 according to one embodiment is a 600 kW, 120 Hz alternator. In the unipolar mode, it provides 210 A rms at a voltage of 3200 V rms with a power factor of 0.88 to the magnetic switch pulse compressor system 15. The alternator is driven by a motor connected to the local 480V power grid. The particular alternator used herein was designed by Westinghouse Corporation and fabricated at the Sandia National Laboratories in Albuquerque, N.M. It is described in detail in a paper by R. M. Caifo et al., "Design and Test of a Continuous Duty Pulsed AC Generator" in the Proceedings of the 8th IEEE Pulsed Power Conference, pp. 715-718, June, 1991, San Diego, Calif. This reference is incorporated herein in its entirety. This particular power system was selected and built because of its relative ease in adaptability to a variety of loads. Other power sources may be used and may indeed be better optimized to this particular use. For example, a power supply of the type available for Magna-Amp, Inc. comprising a series of step-up transformers connected to the local power grid feeding through a suitably-sized rectifier could be used. The present system however has been built and performs reasonably well. In one embodiment, the pulse compression system 15 is separated into two subsystems, one of which is a common magnetic pulse compressor 12 composed of a plurality of stages of magnetic switches (i.e., saturable reactors) the operation of which is well known to those skilled in the art. This subsystem is shown in more detail in FIG. 3A. The basic operation of each of the stages is to compress the time width (transfer time) of and to increase the amplitude of the voltage pulse received from the preceeding stage. Since these are very low loss switches, relatively little of the power is wasted as heat, and the energy in each pulse decreases relatively little as it moves from stage to stage. The specific subsystem used herein is described in detail by H. C. Harjes, et al., "Characterization of the RHEPP 1 .mu.s Magnetic Pulse Compression Module", 9th IEEE International Pulsed Power Conference, pp. 787-790, Albuquerque, N.M., June, 1993. This paper is incorporated by reference herein in its entirety. These stages as developed for this system are quite large. In the interest of conserving space, it would be possible to replace the first few stages with appropriately designed silicon control rectifiers (SCR's) to accomplish the same pulse compression result. These stages 12 convert the output of the alternator 10 into a 1 .mu.s wide LC charge waveform which is then delivered to a second subsystem 14 comprising a pulse forming line (PFL) element set up in a voltage doubling Blumlein configuration. The PFL is a triaxial water insulated line that converts the input LC charge waveform to a flat-top trapezoidal pulse with a design 15 ns rise/fall time and a 60 ns FWHM. The construction and operation of this element is described in detail by D. L. Johnson et al. "Results of Initial Testing of the Four Stage RHEPP Accelerator", 9th IEEE International Pulsed Power Conference, pp. 437-440, Albuquerque, N.M., June, 1993. This paper is also incorporated by reference in its entirety. A cross sectional view of the PFL is shown in FIG. 3B. The pulse compression system 15 can provide unipolar, 250 kV, 15 ns rise time, 60 ns full width half maximum (FWHM), 4 kJ pulses, at a rate of 120 Hz, to the linear inductive voltage adder (LIVA) (20). In a preferred embodiment, the pulse compression system 15 should desirably have an efficiency >80% and be composed of high reliability components with very long lifetimes (.about.10.sup.9 -10.sup.10 pulses). Magnetic switches are preferably used in all of the pulse compression stages, MS1-MS5, because they can handle very high peak powers (i.e., high voltages and currents), and because they are basically solid state devices with a long service life. The five compression stages used in this embodiment as well as the PFL 14 are shown in FIG. 3A. The power is supplied to the pulse compression system 15 from the alternator 10 and is passed through the magnetic switches, MS1-MS5, to the PFL 14. The PFL is connected to the linear induction voltage adder (LIVA) 20 described below. The second and third magnetic switches, MS2 and MS3, are separated by a step-up transformer T1 as shown. Switch MS6 is an inversion switch for the PFL. The pulse forming line (PFL) element 14 is shown in schematically in FIG. 3A and in cross section in FIG. 3B. MS6 in FIG. 3A corresponds to the inversion switch 302 shown in FIG. 3B located on the input side of the tri-axial section 314 of the PFL. Output switches 304 and charging cores 306 are also shown. The regions 310 are filled with deionized water as the dielectric. The interior region 308 is filled with air and oil coiling lines, not shown, for the output switches 304. The output of the PFL is fed in parallel to each of the individual LIVA stages 20, with the positive component flowing through conductors 316 and the shell 318 of the PFL serving as ground. The positive conductors 316 are connected to each of the LIVA stages. The LIVA (20) is preferably liquid dielectric insulated. It is connected to the output of the PFL and can be configured in different numbers of stages to achieve the desired voltage for delivery to the ion beam source. The LIVA 20 can deliver nominal 2.5 MV, 2.9 kJ, pulses at a rate of 120 Hz to the ion beam source 25 when configured with 10 stages of 250 kV each. For most of the ion beam treatments, the LIVA was configured with four stages of 250 kV each, such that the LIVA delivered a total of 1.0 MV to the ion beam source. However, this voltage can be increased or decreased by changing the number of stages in the LIVA to match the particular material processing need. The nominal output pulse of the LIVA 20 is the same as that provided to it by the PFL, namely, trapezoidal with 15 ns rise and fall times and 60 ns FWHM. FIG. 3C shows a cross section of the four stage LIVA. The four stages, 320, 322, 324, and 326, are stacked as shown and fed the positive pulses from the PFL via the cables 321, 323, 325, and 327. The stages are separated by gaps 330 and surrounded by transformer oil for cooling. The output from each of the LIVA stages adds to deliver a single total pulse to the ion beam source shown here schematically as 25 which is located within a vacuum chamber 332, shown in partial view. As with the PFL, the outside shell of the LIVA is connected to ground. The power system P (FIG. 3) as described, can operate continuously at a pulse repetition rate of 120 Hz delivering up to 2.5 kJ of energy per pulse in 60 ns pulses. The specific power system described here can deliver pulsed power signals of about 20-1000 ns duration with ion beam energies of 0.25-2.5 MeV. The power system can operate at 50% electrical efficiency from the wall plug to energy delivered to a matched load. The power system P uses low loss pulse compression stages incorporating, for example, low loss magnetic material and solid state components, to convert AC power to short, high voltage pulses. The ability to produce voltages from 250 kV to several MV by stacking voltage using a plurality of inductive adders incorporating low loss magnetic material is a principle feature when high voltages are needed, although it is also possible to use a single stage pulse supply, eliminating the need for the adder. The power system can operate at relatively low impedances (<100.OMEGA.) which also sets it apart from many other repetitive, power supply technologies, such as transformer-based systems. This feature allows high treatment rates and the treatment of large areas (5 to more than 1000 cm.sup.2) with a single pulse so as to reduce edge effects occurring at the transition between treated and untreated areas. The Ion Diode The second component of the present invention is an ion beam source 25 (shown in FIG. 4). The ion beam source is capable of operating repetitively and efficiently to utilize the pulsed power signal from the power system efficiently to turn gas phase molecules into a high energy pulsed ion beam. A precursor of the ion beam source is an ion diode described generally by J. B. Greenly et al, "Plasma Anode Ion Diode Research at Cornell: Repetitive Pulse and 0.1 TW Single Pulse Experiments", Proceedings of 8th Intl. Conf. on High Power Particle Beams (1990) all of which is incorporated by reference herein. Although this reference ion diode differs significantly from the ion diode utilized in the present system, the background discussion in this reference is of interest. An ion beam source 25, according to the principles of the present invention, is shown in FIG. 4. The ion beam source 25 is preferably a magnetically-confined anode plasma (MAP) source. FIG. 4 is a partially cross-sectional view of one symmetric side of the ion beam or MAP source 25. The ion beam or MAP source 25 produces an annular ion beam K which can be brought to a broad focus symmetric about the axis X--X 400 shown. In the cathode electrode assembly 30 slow (1 ms rise time) magnetic field coils 414 produce magnetic flux S (as shown in FIG. 4A) which provides the magnetic insulation of the accelerating gap between the cathodes 412 and the anodes 410. The anode electrodes 410 also act as magnetic flux shapers. The slow coils 414 are cooled by adjacent water lines, not shown, incorporated into the structure supporting the cathodes 412 and the slow coils 414. The main portion of the MAP structure shown in this Figure is about 18 cm high and wide. The ion beam or MAP source 25 operates in the following fashion: a fast gas valve assembly 404 located in the anode assembly 35 produces a rapid (200 ms) gas puff which is delivered through a supersonic nozzle 406 to produce a highly localized volume of gas directly in front of the surface of a fast driving coil 408 located in an insulating structure 420. After pre-ionizing the gas with a 1 ms induced electric field, the fast driving coil 408 is fully energized, inducing a loop voltage of 20 kV on the gas volume, driving a breakdown to full ionization, and moving the resulting plasma toward the flux filled shaping anode electrodes 410 in about 1.5 ms, to form a thin magnetically-confined plasma layer. The pre-ionization step is a departure from the earlier MAP reference which showed a separate conductor located on the face of a surface corresponding to the insulating structure 420 herein. Since this conductor was exposed to the plasma, it broke down frequently. One of the inventors herein discovered that the separate pre-ionizing structure was unnecessary. The gas can be effectively pre-ionized by placing a small ringing capacitor in parallel with the fast coil. The field oscillations produced by this ringing circuit pre-ionize the gas in front of the anode fast coil. We have also discovered that, prior to provision of the main pulse to the fast coil, it is beneficial to have the ability to adjust the configuration of the magnetic field in the gap between the fast coil and the anode to adjust the initial position of plasma formation in the puffed gas pulse prior to the pre-ionization step. This is accomplished by the provision of a slow bias capacitor and a protection circuit both being installed in parallel with the fast coil and isolated therefrom by a controllable switch. A slow bias field is thus created prior to pre-ionization of the gas by the fast coil. After pre-ionization the fast coil is then fully energized as described above to completely breakdown the gas into the plasma. After this pulse the field collapses back into the fast coil which is connected to a resistive load which is in turn connected to a heat sink, not shown. In this manner heat build up in the fast coil is avoided. The fast coils 408 have been redesigned from the reference fast coils in several ways as well as the heat sinking mentioned above. The gap between the fast coil and the anode electrodes 410 has been reduced with the result that the amount of necessary magnetic energy has been decreased by over 50%. The lower energy requirement permits repetitive use at higher frequencies and reduces the complexity of the feed system voltages for the fast coils. The design of the new flux-shaping anode electrode assembly has also contributed to these beneficial results. The pulsed power signal from the power system is then applied to the anode assembly 35, accelerating ions from the plasma to form an ion beam K. The slow (S) and fast (F) magnetic flux structures, at the time of ion beam extraction, are shown in FIG. 4A. The definite separation between the flux from the fast coil from the flux from the slow coil is shown therein. This is accomplished by the flux-shaping effects of the anodes 410 and also by the absence of a slow coil located in the insulating structure 420 as was taught in the earlier MAP reference paper. The slow coils in the present system are located only in the cathode area of the MAP. This anode flux shaping in conjunction with the location of slow coils in the cathode assembly is different from that shown in the MAP reference paper and permits the high repetition rate, sustained operation of the MAP diode disclosed herein. This design allows the B=0 point (the separatrix) to be positioned near the anode surface, resulting in an extracted ion beam with minimal rotation. This minimal rotation is necessary for effective delivery of the beam to the material to be treated. FIG. 4B is a detailed view of the gas valve assembly 404 and the passage 425 which conducts the gas from the valve 404 to the area in front of the fast coil 408. The passage 425 has been carefully designed to deposit the gas in the localized area of the fast coil with a minimum of blow-by past this region. The gas valve flapper 426 is operated by a small magnetic coil 428 which opens and closes the flapper 426 upon actuation from the MAP control system. The flapper valve is pivoted on the bottom end 427 of the flapper. The coil 428 is mounted in a high thermal conductivity ceramic support structure 429 which is in turn heat sinked to other structure, not shown. This heat sinking is necessary for the sustained operating capability of the MAP. The gas is delivered to the valve from a plenum 431 behind the base of the flapper. The vacuum in the nozzle 406 rapidly draws the gas into the MAP once the flapper 426 is opened. The function of the nozzle is to produce a directed flow of gas only in the direction of flow and not transverse to it. Such transverse flow would direct gas into the gap between the anode and the cathode which would produce detrimental arcing and other effects. The reduction of the fast coil-anode gap discussed above makes the design of the nozzle very important to the successful operation of the MAP. Fortunately, gas flow design tools are available and were used to develop a nozzle with improved gas flow (higher mach number) and minimal boundary effects. This improved nozzle has an enlarged opening into the gap between the fast coil and the near edge of the anode which tapers from 9 to 15 mm instead of the straight walled 6 mm conduit in the reference MAP. The operating pressure of the gas in the puff valve has been increased from the range of 5-25 psig to the range of 35-40 psig. Experiments have confirmed much improved MAP operation as a result of this new design. The ion diode of this invention is distinguished from prior art ion diodes in several ways. Due to its low gas load per pulse, the vacuum recovery within the MAP allows sustained operation up to and above 100 Hz. As discussed above, the magnetic geometry is fundamentally different from previous ion diodes. Prior diodes produced rotating beams that were intended for applications in which the ion beam propogates in a strong axial magnetic field after being generated in the diode. The present system requires that the ion beam be extracted from the diode to propogate in field-free space a minimum distance of 20-30 cm to a material surface. The magnetic configurations of previous ion diodes are incapable of this type of operation because those ion beams were forced by the geometries of those diodes to cross net magnetic flux and thus rotate. Such beams would rapidly disperse and be useless for the present purposes. By moving the slow coils (the diode insulating magnetic field coils) to the cathode side of the diode gap eliminated the magnetic field crossing for the beam but required a total redesign of the magnetic system for the anode plasma source. The modifications to the fast coil discussed above result in an energy requirement that is 5-10 times less than previous configurations. The modifications include: the elimination of a slow coil on the anode side of the diode and its associated feeds, better control over the magnetic field shaping and contact of the anode plasma to the anode electrode structure through use of the partially field-penetrable electrodes, the elimination of the separate pre-ionizer coil from the prior ion diodes, the circuit associated with the fast coil to provide "bias" current to adjust the magnetic field to place the anode plasma surface on the correct flux surface to eliminate beam rotation and allow optimal propagation and focusing of the beam, and the redesign of the gas nozzle to better localize the gas puff which enables the fast coil to be located close to the diode gap which in turn reduces the energy requirements and complexity of the fast coil driver. The plasma can be formed using a variety of gas phase molecules. The system can use any gas (including hydrogen, helium, oxygen, nitrogen fluorine, neon, chlorine and argon) or vaporizable liquid or metal (including lithium, beryllium, boron, carbon, sodium, magnesium, aluminum, silicon, phosphorous, sulfur, and potassium) to produce a pure source of ions without consuming or damaging any component other than the gas supplied to the source. The ion beam K propagates 20-30 cm in vacuum (.about.10.sup.-3) to a broad focal area (up to 1000 cm.sup.2) at the target plane, not shown, where material samples are placed for treatment and can thermally alter areas from 5 cm.sup.2 to over 1000 cm.sup.2. The ion beam or MAP source 25 is capable of operating at repetitive pulse rates of 100 Hz continuously with long component lifetimes >10.sup.6. The ion beam or MAP source 25, according to the principles of the present invention, draws ions from a plasma anode rather than a solid dielectric surface flashover anode used in present single pulse ion beam sources. Use of a flashover anode typically introduces a variety of contaminants to the surface of the material, often with detrimental results. One of the significant advantages of the using the improved MAP source disclosed herein is that one has precise control over the components in the ion beam by controlling the composition of the gas source. The present invention combines the pulsed power supply P and the MAP ion source 25 to obtain a system for repetitively generating pulsed high voltage ion beams in a manner that allows the use of this technology for the efficient treatment of surfaces in commercial applications. In particular, the ion voltage is in the range 0.1-2.5 MeV per ion, the energy per pulse is as large as 2.5 kJ, and the ion source impedance is significantly less than 100.OMEGA., allowing the pulse width to be as small as 30 ns. These numbers are characteristic of the present embodiment, and may be superseded by design changes obvious to worker in the art. The detailed description of the new class of ion beam generators having been completed, attention now turns to the many applications made possible and practical in an industrial sense by said generators. There are three broad classes of surface effects upon which the aforementioned applications depend. These are: a) Surface Smoothing; b) Evaporation and Ablation from a Surface, and; c) Generation and Quenching of Non-Equilibrium Surface Structure. Other types of effects exist, and are not intended to be removed from the scope of the claims, but the effects listed above illustrate the enormous breadth of the present invention. Surface Smoothing has a sphere of influence far wider than the innocuous name would suggest. Every surface has an energy (or surface tension) raising the energy of the atoms which make up the surface above the energy they would have if located in the bulk of the material. Accordingly, given the opportunity any surface structure which increases the surface area (thereby increasing the number of surface atoms) will adjust by moving material around to reduce the total surface area. As described in the Background section, Surface Smoothing is driven by the surface tension of the molten surface following surface heating by the ion beam, but before sufficient heat has conducted into the body of the material to allow the near-surface regions to resolidify. During this time, the surface morphology will become less jagged and smoother, the improvement limited primarily by the duration of surface melting. Another effect which can add to the smoothing of the surfaces of fine-grain sintered materials, such as ceramics or materials resulting from powder metallurgy, via ion beam surface melting. In these cases, when proper process parameters are used, a glass or alloy surface may be formed, thereby eliminating the grain structure from the surface in favor of a smooth glassy surface. Note further that the glass or alloy need not be equilibrium forms of the material, as the rapid quenching will preserve many forms of molecular solid solutions which do not exist in the relevant equilibrium phase diagram. The process conditions for Surface Smoothing are not onerous, so long as the near-surface region of the material does melt to some depth. In contrast to some of the techniques to be described later, Surface Smoothing can often be carried out in a number of smaller ion pulses, each one melting the surface, thereby allowing said surface to become a little smoother. Having described how to smooth a surface using ion beam surface heating, the range of applications of Surface Smoothing must be described. Again, these examples are simply for illustration, and there is no intent to limit the present invention to a scope inferior to that of the attached claims. The simple process of smoothing a surface, e.g., to remove surface defects resulting from etching or machining, is straightforward. Example 1 describes the removal of etching defects on a copper surface using the Surface Smoothing process. The surface initially consisted of canyons and mountains some 3-5 .mu.m in height having sharp edges and points. Following Surface Smoothing, the surface exhibited surface roughness only on a size scale of less than 0.5 .mu.m. Example 2 describes the polishing of machining marks from a machinable titanium alloy. The marks were originally some 5 .mu.m, the remnants of a precision machining operation. The process of Surface Smoothing reduced the surface roughness to less than 0.1 .mu.m, again removing the sharp, abrupt initial features and leaving only a gently rolling surface. This polishing of machining marks will also be useful in polishing of diamond-turned optics, allowing such polishing to be executed without danger of changing the carefully controlled surface generated by the machining process, thus greatly reducing the cost of such optical elements. Another application will be in the treatment of machine tool surfaces, so that a minimum of machine marks may be made in the first place. Example 3 describes the smoothing of an Al.sub.2 O.sub.3 ceramic surface by conversion of the surface to a glassy layer. Such a process should be useful on a wide range of ceramics and other materials having a pronounced grainy structure. There are certain materials, such as most stainless steels, which do not form glassy layers. They can, however, be melted to form a solid layer of metal in these circumstances, said layer of metal having a very-fine-grained structure. Surface Smoothing makes two primary alterations in surface morphology; it reduced the average surface roughness and it reduces the surface area of the body treated. Both of these effects have clear applications. The phenomenon of adhesion between two materials is not well-understood. However, it is clear that the more surface area upon which two materials meet, the more adhesive force will exist between them. In fact, the function of many adhesives is not only to stick to the surfaces of both bodies being glued together, but also to maximize the area of contact by flowing into small grooves and crevasses before hardening. The increase in surface area which occurs in this process is enormous, and also increases with time, explaining why fast-curing epoxies are generally not as strong as their slower-curing cousins. If one produces a surface which is (approximately) maximally smooth using Surface Smoothing, the result will be a surface which will experience minimal adhesive forces to another body in contact. In other words, Surface Smoothing is another approach to non-stick surfaces. Note that a non-stick surface need not be a low-friction surface, as the one refers to the force required to start the body into motion and the other to the force needed to keep it in motion once moving. Another general result of the Surface Smoothing process, resulting directly from reduction in surface roughness, is reduction of wear between two elements in contact and in relative motion. As discusses in the Background section, the amount of material lost in a given time to adhesive wear should be a linear function of the surface roughness of the two elements. Although that estimate is oversimplified, it is clear that less wear will result from the mechanical interaction of two surfaces after Surface Smoothing has been performed, beyond any surface hardening which might also have taken place. Related to the above is the fact that a smooth surface can increase the working toughness of a material, although the actual micro-properties of that material are not altered. The materials used for mechanical applications are rarely, if ever, completely homogeneous. Among other defects, incipient surface cracks provide sites for failure of the element under stress. If the surface of such a body is essentially smoothed, all incipient cracks are located below the surface, and thus have two closed ends rather than one. Such cracks are nearly twice as resistant to growth as is a crack which intersects the surface. Thus, a smooth surface gives a tougher part. Corrosion resistance can also be increased through the use of Surface Smoothing. Increased surface area, cracks, and other defects associated with rough surfaces increase the rate of corrosive processes, including in particular pitting, stress corrosion, and attack by microbiological organisms. A number of processes exist which directly attack the chemistry of corrosion, such as formation of a layer of corrosion-resistant surface alloy, but all such techniques work better if the surface is also smooth and relatively free of cracks. This is the role of Surface Smoothing in preventing corrosion. Several examples have been investigated, which will be discussed in the section on Non-Equilibrium Surface Structures. An application of Surface Smoothing closely related to the above is that of passivation or protection of welds against corrosion. Exposed welds, particularly between dissimilar materials, offer fertile ground for corrosive processes. The reason is at least two-fold. Generally, the region of the weld is rather heterogeneous in composition and structure. Any corrosive process is thus likely to act with different rates in different regions, resulting in a surface of increasing micro-roughness as corrosion continues. Also, the initial surface of a weld is usually very rough, having many flaws and cracks on a small size scale. The effect of Surface Smoothing following the welding process thus acts to ameliorate both effects, resulting in a more corrosion-resistant weld. A final illustration of the use of Surface Smoothing is in application to amorphous magnetic materials. When a thin layer of a magnetic material is considered, the surface roughness can have a significant effect of magnetic properties, including coercive field and dc hysteresis losses. An example of great industrial significance is METGLAS.TM., a class of magnetic alloys produced by shooting a jet of the molten alloy at a spinning metal wheel which cools the alloy into a ribbon quickly enough that the resulting structure is amorphous. One negative aspect of this means of production is that the side of the ribbon opposite the wheel has a very rough surface. This roughness also limits the thickness of material that can be commercially produced, limiting the high frequency range of METGLAS.TM. applications. Surface cracking of the METGLAS.TM. ribbon also limits the thickness of material that can be produced commercially, increasing the cost of METGLAS.TM. cores for power distribution and related applications. As a result, although the potential of METGLAS.TM. in power handling devices is enormous, it has not yet realized that potential. Surface Smoothing is a technique capable of smoothing and even forming METGLAS.TM., with the hoped-for improvement in magnetic properties, as described in Example 4. The technique of Surface Smoothing can, of course, be applied to any amorphous or fine-grained material, with beam kinetic energy and ion species tailored to obtain the proper cooling rate. Due to the extremely rapid quench rate, Surface Smoothing can also be used to produce or modify new magnetic materials not accessible using existing techniques. A related technique can be applied to thin layers of amorphous or nanocrystailine material, given only that these layers are deposited on a substrate having high thermal conductivity (roughly speaking, metals and ceramics rather than polymers and insulators). The physics behind the design of a smoothing treatment is the same as above, except that the heat from the ion pulse is conducted into the substrate instead of into the bulk of a thick sample. Examples of such processes include smoothing e.g., plasma spray deposited films, filling in pinhole defects in the amorphous film, and precisely controlling the grain size of fine-grain films by melting and recrystallization. Having described a number of applications for the process of Surface Smoothing as made possible by the present invention, attention is now focused on Evaporation and Ablation from a Surface (EAS for short). One of the most important applications of EAS is the simple task of cleaning surfaces. Simple, that is, except that one wants to consistently clean a surface to an environmentally-limited amount of contamination, without the use of EPA- of OSHA-regulated solvents, preferably immediately before using the clean surface (e.g., in welding, flux-free soldering, vacuum deposition, and the like). If cleaning is also extended to the removal of, for example, oxide layers from a metal surface, it becomes clear that cleaning can be an essential and difficult part of the manufacturing process. The process of EAS has many uses in this domain. A conventional form of cleaning is degreasing parts prior to some assembly step, such as welding, soldering, gluing, etc. As will be shown in Example 5 below, a 100 nm thick layer of conventional lubricating oil is easily removed from a stainless steel surface using a single pulse of about 1-2 J/cm.sup.2, a very small dosage for the present class of ion beam generators. Note that no attempt is made to restrict the beam to the contaminant layer alone, as an extremely low beam energy would be required, owing to the low density and small thickness of the contaminant. Rather, the ion species and the energy of the beam is adjusted to superheat a thin layer of the metal surface, which then vaporizes the hydrocarbon contaminant before the bulk of the steel can cool the surface. A further extension of cleaning a surface is the rapid and thorough sterilization of surfaces subjected to appropriate EAS treatment. Such techniques are likely to have impact in the manufacture of pre-sterilized medical implements. The technique described above is quite general, and may be used on any form of contamination that has a significantly lower boiling point than the substrate material. In fact, in cases where a natural passivating layer, e.g., a surface oxide, must be removed before soldering, for example, can take place, and the relative characteristics of the bulk material and the surface passivating layer are as outlined above, the passivating layer can be removed by superheating the underlying metal. In most cases, however, the materials encountered in both natural and artificial surface layers have higher vaporization points than do the materials they protect. In such cases, the EAS technique can still be used to remove the surface layer provided only that loss of a few microns of the underlying material is acceptable. This is accomplished by ablating the surface layers of the underlying material, taking along the unwanted overlayer. The total energy required for ablation is generally quite high (>10 J/cm.sup.2), and should be restricted to as thin a layer of material as is reasonable (perhaps 0.5-1.0 .mu.m). These numbers, like all specific numbers appearing in the specification, depend to some extent on the ion species used and the type of bulk material being processed. Note particularly the difference caused by attempting to treat a polymer substrate, whose thermal conductivity is perhaps 1000-10000 times smaller than that of a metal alloy. The ablation temperature will be about the same, and the energy contained in a given layer is perhaps 10-20% that of an equivalent metal layer, owing to the lower density of the polymer. As a result, the characteristic time to remove energy from a heated surface layer will be on the order of 10 times that for a typical metal. In addition, the range of ions in the polymer is much greater for a given beam kinetic energy than in normal structural metals. The net effect is that a much greater thickness (say, .times. times the distance in the metal, for example) will be heated by a beam of given kinetic energy. As the characteristic time depends quadratically on this thickness and inversely on the thermal conductivity, the characteristic time in polymer heating will be .about.(10.sup.2 -10.sup.3).times..sup.2 longer than that in a metal. Extremely rapid quenching thus cannot be produced on a polymer surface by the techniques of the present invention. The time required for heating, however, is limited only by the maximum peak power of the ion beam generator. The EAS techniques therefore apply to polymers, whereas most of the Surface Smoothing and Non-Equilibrium processes do not. If an patterned ion-absorbing mask or compound is used to prevent the ion pulse from affecting certain areas of the element being treated, a surface having a pattern of varying surface properties can be generated. Such a pattern can range from removing an oxide layer in certain areas to obtain patterned etching of a surface by chemical action to direct etching of ablated patterns in large scale solar cells to manufacture of patterned printed circuit boards. The EAS process offers the advantage of limiting the use of solvents and powerful acids in such procedures. When a higher level of pulse power (>>10J/cm.sup.2), is deposited in a thin surface layer (.about..mu.m in thickness), violent ablation occurs. The expanding gases accelerate the evaporated layer outward from the body of the material at extreme velocity, generating as a result of momentum conservation a strong pressure wave in the material. As most materials exhibit a nonlinear stress-strain relationship, the pressure wave rapidly sharpens into a shock wave. As this shock wave propagates inward through the material, it generates dislocations, twinning planes, and complex systems of these structural defects, thereby dissipating its power and eventually (within perhaps 100 .mu.m or more) ceases to exist as a cohesive entity. This damaged region, however, has undergone a phenomenon known as shock-hardening, an extreme form of work-hardening. Even though the direct heating action of the ion beam may be limited to the first few .mu.m, the shock hardening effect penetrates much deeper, offering a surface treatment which cannot be directly obtained using the present invention. EAS uses the pulsed ion beam generators of the present invention to rapidly vaporize material from the surface of a body. This vaporized material can be used as a source material for vapor deposition processes, having the advantage that chemical compositions will not be changed by segmentation effects due to the phase diagram of the alloy system or chemical reactions with a resistive heating element, as is often used in vapor phase deposition. In addition, the vapor deposition will take place in a very short period of time (<1 .mu.s). As a result the heat of adsorption will rapidly conduct away into the bulk of the substrate, and one will again obtain a rapidly quenched material, given only that the substrate has large thermal conductivity. The large surface area that the ion beam generators of the present invention can vaporize makes this approach available to large-scale manufacturing efforts. Another effect associated with EAS used in this mode has been observed. A layer of material a few .mu.m thick is vaporized within the period of a few tens of nanoseconds. This converts a metal layer having a given density into a plasma which initially has very nearly the same density, as it has not yet had time to expand away from the bulk of the material. The energy distribution of this layer follows a Boltzmann distribution, meaning that a significant percentage of the vaporized material has kinetic temperatures significantly less than the average temperature of the plasma. Because of this, and because the plasma is so close to a relatively cool conducting surface, a small amount of the vaporized material redeposits on the surface from which it came. In doing so, that surface acquires a structure which is extremely rough on a nanoscale, particularly having numerous protuberances much smaller than a .mu.m in size, possessing unique properties. EAS processes can be used for many other manufacturing purposes, and presentation of these examples is not intended to limit the scope of the invention beyond the limitations outlined in the attached claims. The final major class of processes made practical for large-scale manufacturing by the new category of pulsed ion beam generators made possible by the current invention is the production of non-equilibrium surface structures (NESS for short). The name is a bit misleading, as some near-equilibrium applications also come under this title, but the general concept is that one heats a surface having an initial structure rapidly to some depth with a pulsed ion beam, the heat is rapidly lost to conduction into the material, and the result is a product surface having a structure with different properties than those of the initial structure. As the structure of many of the product surfaces is non-equilibrium, that term is used herein to describe the whole family of processes. A good example of the production and retention of high-temperature structures is offered by Example 6, in which an NESS-type process is applied to the surface of a tool steel component. (Such a process is not limited to the hardening of steel.) The hardness of the surface roughly tripled, but the important point is how this increase in hardness came about. X-ray and electron microscope analysis of the untreated surface shows the simple co-ferrite phase with a significant density of cementite precipitates. However, the treated surface showed the presence of small crystallites of austenite, the possible presence of martensite, and no carbide precipitates. This is significant in that austenite is stable only at high temperatures, and that the equilibrium structure at room temperature is a mixture of ferrite and cementite (Fe.sub.3 C precipitates). At high temperature, the carbon dissolves into the matrix, producing austenite in the process. The NESS process has thus quenched a high-temperature phase structure so that it exists at room temperature. Conventionally hardened tool steels are composed either of a very fine grain pearlite or of tempered martensite. The structure obtained from the NESS treatment differs from these, thus providing another surface microstructure useful for hardening steel alloys. Other precipitates than carbon, of course, can be dissolved and retained in a non-equilibrium solid solution using the NESS technique, and other materials than steel can be successfully treated. Another approach toward hardening the surface of steel (or other alloys) is to add elements, usually carbon and/or nitrogen, which encourages the formation of high-hardness carbides and nitrides in the near-surface region. The NESS process offers an alternate approach to the usual process of addition, which involves long periods of diffusion in hot environments. For carburization, it is possible to start by depositing a glassy layer of carbon on the surface to be treated (this deposition may use an EAS process, but need not). The layer of carbon and a suitable thickness of the underlying metal would then be melted by the pulse of an ion beam, whereupon the carbon would dissolve into the steel. Further heat treatment may be necessary to obtain optimal surface conditions, depending on the starting alloys. A similar technique which may work for nitriding would require deposition of a layer of a high-temperature nitride, such as titanium or vanadium nitride. (The titanium or vanadium also improve the properties of the resulting steel. However, this hardening process is not limited to these two elements, but may use any nitride which can withstand the high process temperatures without volatilizing.) The remainder of the process is carried out as for carbon above, save that further thermal treatment are generally not useful in nitridization. Other elements can be introduced into the surface layers of a compatible body using this type of NESS technique. The beneficial effects of Surface Smoothing on corrosion resistance was discussed earlier. Additional phenomena more closely related to the NESS processes are also of value in holding back corrosion. This is illustrated in Example 7, in which a stainless steel surface is treated with a mixed carbon-hydrogen ion beam pulse from an early device utilizing a flashover ion source. Although this technology is primitive compared to that offered by the current invention, in particular not allowing industrial scale-up, it did prove adequate to demonstrate the increase of corrosion resistance. When 304 stainless steel is annealed at high temperatures as described in the Example, chromium-depleted regions form near the grain boundaries of the metal. The chromium precipitates out in large chromium carbide particles in the interiors of the grains. The chromium-depleted regions are intrinsically more susceptible to corrosion, and the chromium carbide particles present intergranular surfaces which are also particularly susceptible to corrosion. As a result, 304 stainless steel, when subjected to the described heat treatment, becomes extremely susceptible to corrosion, primarily preferential grain boundary corrosion. When the heat-treated surface is subjected to a 0.3 MeV, .about.300 ns pulse of mixed ions with a total energy of 2-3 J/cm.sup.2, the rapid melting and recrystalization removed the chromium-depleted grain boundaries and caused the chromium carbide particles to redissolve in the metal. This treatment was observed to increase corrosion resistance essentially back to the pre-heat treatment level. Similar work aimed at studies of pitting susceptibility of 316L and 316F stainless steels has also been undertaken with similar results. Aluminum alloys have also been subjected to NESS processes to increase their corrosion resistance. Again, the pulsed ion beam used was a mix of carbon and hydrogen ions accelerated to 0.7 MeV. The pulses were .about.100 ns wide, and the total energy of each pulse was .about.2-3 J/cm.sup.2. Exposure testing for the alloys used was conducted in a saturated salt fog environment. The alloys treated have included 2024-T3, 6061-T6, and 7075-T6. In all cases the NESS treatment increased the corrosion resistance of the samples. This should be true for all structural aluminum alloys. Another approach to increasing corrosion resistance through NESS treatment can be illustrated best by considering a carbon steel (i.e., low chromium content). Such steels are extremely susceptible to corrosion, rusting in moist air, disintegrating over time in saline environments, and failing even more quickly in more hostile conditions. The addition of chromium to such steels produces stainless steels, which do not share this extreme sensitivity to environment. However, stainless steel is expensive, especially considering that the mechanical properties of stainless steels are suboptimal, and that the property of being "stainless" need only exist at the surface of the element. NESS treatment can help to solve this problem by mixing a surface-deposited layer of chromium with the near-surface regions of the steel element. The result will be an element having the superior mechanical properties of carbon steel combined with an outer layer of stainless steel perhaps 5-20 .mu.m thick (depending on conditions) which is both smooth and uniform, thus providing excellent corrosion resistance. This sort of technique is extendible to many metal alloy systems, including welds, the scope of which are well-known to practitioners in the metallurgical arts. The Examples referred to above will now be described in detail. These Examples are not intended to limit the scope of the claims appended in any manner, but rather to illustrate their application in specific instances. EXAMPLE 1 A sample of nominally pure Cu was etched in 1 molar nitric acid for one minute. Scanning electron microscopy (SEM) analysis of the resulting surface showed a roughened surface with hillocks and "sharp" features approximately 3-5 .mu.m in height. These samples were treated using a single pulse of an ion beam generated using a RHEPP prototype power source and a flashover ion source. (In a flashover ion source an electrical discharge volatilizes the surface of a polymer, resulting in the generation of mixed carbon and hydrogen ions.) The beam kinetic energy was 1.0 MeV, the pulse width was approximately 60 ns, and the total pulse energy density at the treated surface was .about.3J/cm.sup.2. Post-treatment SEM analysis revealed a smoother surface with more gradual changes in surface configuration and an average surface roughness of .about.0.5 .mu.m. In this example the Cu surface was molten for .about.500 ns. The driving force of surface tension during this period was clearly sufficient to produce nearly complete removal of the original surface morphology. EXAMPLE 2 A piece of Ti-6Al-4V alloy (a common machinable titanium alloy) was machined using conventional precision machining techniques, leaving a nominally fiat surface with machining marks producing a surface roughness of .about.5 .mu.m. This surface was treated by exposure to four pulses, each pulse having a beam kinetic energy of .about.3.0-0.4 MeV, a duration of .about.400 ns, and a total pulse energy density of .about.7 J/cm.sup.2. SEM analysis of the treated surface revealed surface roughness had been reduced to .about.0.1 .mu.m. The time the metal surface was liquid was again some 250-500 ns, suggesting that the effect of multiple pulses in the smoothing process is additive, i.e., that more pulses give a smoother surface. EXAMPLE 3 One side of an alumina (Al.sub.2 O.sub.3 ceramic) sample was polished using submicron abrasive grit suspensions. Following characterization of the surface with an SEM, the polished surface was subjected to a single ion pulse having a beam kinetic energy of .about.1.0 MeV, a beam duration of .about.60 ns, and a total pulse energy density of .about.10 J/cm.sup.2. Post-treatment analysis showed evidence for melting and resolidification resulting in reduction of surface porosity. There remained, however, some microcracking on a 0.1 .mu.m size scale. It is considered likely that further treatment would yield a uniformly smooth surface. EXAMPLE 4 Because of its unique magnetic properties, various amorphous magnetic alloys known by the registered trademark (Allied-Signal, Inc.) METGLAS.TM. are desirable in high frequency applications, including pulsed power supplies and control. These materials are made by spraying the molten alloy on a cooled rotating wheel, thereby quenching the material at .about.10.sup.6 .degree.K/sec and forming an amorphous ribbon having thicknesses in the range of 15-50 .mu.m. Due to hydrodynamic instabilities during the cooling process, one side of such ribbons has significant ripples in thickness having a period similar to the thickness of the ribbon. This non-uniformity is important for two reasons. First, the magnetic properties at high frequencies are a function of the thickness of the ribbon; hence the variation in thickness limits the performance of devices constructed of non-uniform ribbon. Second, the size scale of the surface roughness is sufficient that when the ribbon is formed into a coil, or similar structure, the layer of insulation between alternate layers of ribbon must be very thick to prevent formation of short-circuits. The thick insulation reduced the density of magnetic material in a given construct, lowering performance and increasing the physical dimensions of the ultimate device. An experiment was performed to discover if Surface Smoothing with ion beam pulses could even out the non-uniformities of a METGLAS.TM. surface while retaining the unique magnetic properties which result from the amorphous structure. METGLAS.TM. 2605CO material was chosen for the test, as it is perhaps most widely used in commercial applications at this time. The nominal composition of METGLAS.TM. 2605CO is Fe.sub.66 Co.sub.18 B.sub.15 Si.sub.1, and it is produced using the wheel-quenching technique described above. A sample was selected, and subjected to a single 2 J/cm.sup.2 pulse of mixed carbon and hydrogen ions from a flashover source. The beam kinetic energy was .about.0.6 MeV, and the pulse width was .about.60 ns. The resulting surface was virtually fiat. A second concern, of course, was that the nanostructure which helps to give METGLAS.TM. 2605CO its unique properties might be damaged by remelting and quenching at a rate different than encountered in the original manufacture. Tests have shown that the amorphous structure of the original METGLAS.TM. is unchanged by the ion pulse treatment. EXAMPLE 5 A 0.1 .mu.m layer of machining fluid (a hydrocarbon mixture) was applied to the surface of a sample of 304 stainless steel. The surface was examined using x-ray photo-emission spectroscopy (XPS) to verify the thickness of the hydrocarbon layer. The sample was then exposed to three ion pulses, each having a total energy density of 2-3 J/cm.sup.2, a beam kinetic energy of 0.5-0.75 MeV, and a pulse duration of .about.50 ns. Following treatment, XPS was again performed, and showed only that amount of hydrocarbon expected from atmospheric contamination (about a monolayer). The surface cleaning was thus totally successful. EXAMPLE 6 A sample of 0-1 tool steel was subjected to ion pulses to determine if the surface could be hardened thereby. The sample was subjected to a single pulse having a beam kinetic energy of .about.1 MeV, a duration of .about.40 ns, and a surface energy density of .about.5 J/cm.sup.2. On recovery, the top few microns of the sample showed only fine grains on the order of 20 nm in size, compared to the initial material which had grain size on the order of 1 .mu.m in size. The initial material had a significant density of iron carbide precipitates, whereas the surface layers did not, having apparently redissolved the carbon into the iron matrix. Hardness testing on the samples was done using microindentation techniques. A Knoop indentor tip was pressed into the samples with a 25 gram load, producing indentations about 5 .mu.m in thickness. A direct reduction of this data showed that the untreated surface had a Knoop hardness of 330, while the treated surface has a Knoop hardness of 900, roughly three times higher. Further, indentation hardness tests are influenced by the hardness of the material out to a distance of perhaps 10 time the size of the indentations. Since the treated layer is only .about.7 .mu.m thick, this means that it is actually much harder than the indentation testing revealed. .theta.-2.theta. x-ray diffraction measurements were taken of the treated and untreated surfaces. The untreated surface shows only a sharp peak corresponding to large ferrite grains (the Fe.sub.3 C precipitates would not diffract at the angles examined). The treated surface, however, showed three interesting differences from the untreated surface. First, austenite peaks appeared, showing that high-temperature species had been successfully recovered in the rapid quench. Second, the diffraction peaks were all quite broad, in agreement with the observation that the grain size in the treated material was very small. Finally, the ferrite peak in the treated sample is asymmetric, suggesting the existence of lattice strains consistent with the presence of martensite. It is likely that all of these effects combine to increase the hardness of the surface of the treated sample. EXAMPLE 7 Four flat samples of 304 stainless steel were prepared to determine if ion beam pulses could eliminate preferential grain boundary corrosion due to heat treatment. All samples were held at 1100.degree. C. for 24 hours, and then quenched in cold water. Two of the samples were sensitized to corrosive action by heating them at 600.degree. C. for 100 hours, followed by cooling in air. This second anneal produces precipitation of chromium carbide particles, formed through depletion of the grain boundaries of the metal of their chromium, a well-known problem in the application of stainless steels having too much carbon. All samples were polished to a mirror finish. Two of the samples, one from each group of annealing conditions, were subjected to four pulses each having a surface energy density of .about.3 J/cm.sup.2, a beam kinetic energy of .about.0.3 MeV, and a duration of .about.300 ns. Each pulse was a combination of carbon and hydrogen ions, the ions source using flashover technology. The degree of sensitization was determined using potentiokinetic reactivation in a 0.5M H.sub.2 SO.sub.4 plus 0.01M KSCN solution held at 30.degree. C. The charge per unit area Q/A required for reactivation is a measure of the susceptibility of the surface to the corrosive effects of this solution. The sample exposed only to the 1100 .degree. C. anneal had a Q/A value of 0.018 Coulombs/cm.sup.2. The sample having the same heat treatment but also exposed to the ion beam pulses had a Q/A value of 0.057 and 0.084 Coulombs/cm.sup.2 (on separate measurements), suggesting that the beam treated surface was somewhat more susceptible to corrosion. The more important results, however, are on the samples which had undergone both annealing cycles. The sample which only received both annealing cycles had a Q/A value of 0.825 and 0.817 Coulombs/cm.sup.2 (again two measurements were made), an enormous increase from the value of 0.018 for the sample which only received the high-temperature anneal. This huge difference in corrosive sensitivity explains why temperatures in the 600.degree. C. range are avoided in application of most stainless steels. However, when such a sample is treated with the above described ion beam pulse schedule, the Q/A value dropped to 0.027 and 0.028 Coulombs/cm.sup.2, a value nearly as low as the original material. One example of why this result is important lies in the problem of welding stainless steel for applications in which corrosive environments are to be encountered. In welding there will clearly be a zone of material which will slowly cool from a temperature in the sensitization range (roughly 400.degree.-800.degree. C.). This zone will be somewhat sensitized to corrosion, although not to the extreme of the experimental sample described above. Unless the entire assembly can be subjected to high-temperature annealing when complete, most stainless steels will not be practical choices for corrosive environments. When stainless steels must be welded now, a steel is chosen having so little carbon that the grain boundary sensitization process cannot occur, thus solving the corrosion problem. However, low-carbon steels are generally soft and weak by comparison to other possibilities, so this choice is a compromise. The ion beam pulse surface modification technology described herein will reduce the number of design compromises required, in this problem and in many others. The capacity of the present invention for producing high energy, high average power pulsed ion beams results in a new, low cost, compact surface treatment technology capable of high volume commercial applications and new treatment techniques not possible with existing systems. Having thus described the present invention with the aid of specific examples, those skilled in the art will appreciate that other similar combinations of the capabilities of this technology are also possible without departing from the scope of the claims attached herewith. |
summary | ||
059360070 | description | EXAMPLES To prepare test specimens, an additive-free, unstabilised polycarbonate with an average molecular weight of about 30,000 (Mw by GPC), solution viscosity: .eta.=1.293, was compounded at 300.degree. C. on a twin screw extruder with the stated amount of stabiliser and then granulated. Colour test platelets (thickness 4 mm) were then made from this granular material by injection moulding. The yellowness index of these platelets is determined before irradiation (Hunter Lab. equipment), then the specimens are irradiated (dose: 5 Mrad; Co bomb), stored for 10 days in the dark and the YI determined again. YI.sub.diff, used for assessment, is determined from the difference between the two measurements, before and after irradiation. a) Comparison test ______________________________________ Conc. Compound (wt. %) YI.sub.initial YI.sub.irrad YI.sub.diff ______________________________________ Polycarbonate.sub.reextr -- 6.31 48.88 42.57 -- 6.27 48.07 41.80 Polypropylene glycol 0.75 4.58 29.24 24.66 0.75 4.70 30.07 25.37 Distearyl sulphide 0.50 10.47 25.93 15.46 0.50 10.16 25.70 15.54 ______________________________________ b) According to the invention (Irradiation dose: 5 Mrad) ______________________________________ Conc. Compound (wt. %) YI.sub.initial YI.sub.irrad YI.sub.diff ______________________________________ Example 1: Compound A 0.5 3.6 9.9 6.3 Compound B 0.5 5.3 13.1 7.8 Compound C 0.5 7.6 19.5 11.9 Compound D 0.5 6.5 12.0 5.5 ______________________________________ All the examples also contained 0.75 wt. % of polypropylene glycol M.Wt. about 2000. Compound A: phenyl--SO.sub.2 --CH.sub.2 --SO.sub.2 --phenyl PA1 Compound B: phenyl--CO--CH.sub.2 --SO.sub.2 --phenyl PA1 Compound C: dibenzylsulphone PA1 Compound D: ##STR6## According to the invention (Irradiation dose: 3 Mrad) PA1 Compound B: phenyl--CO--CH.sub.2 --SO.sub.2 --phenyl PA1 Compound D: ##STR7## ______________________________________ Conc. Compound (wt. %) YI.sub.initial YI.sub.irrad YI.sub.diff ______________________________________ Example 2 Compound B 0.5 5.3 11.4 6.1 Compound D 0.5 6.5 10.3 3.8 ______________________________________ All the examples also contained 0.75 wt. % of polypropylene glycol M.Wt. about 2000. |
055568980 | description | The following examples are intended to be illustrative only: EXAMPLES Two multi-layer laminates were prepared using KYNAR 460 sheet, KYNAR 461 (a powder form of KYNAR 460 vinylidene fluoride homopolymer) and gadolinium oxide powder. The first such laminate (of one quarter inch thickness) was made by heat pressing, between 0.06 inch thick sheets of KYNAR 460, an eighth inch thick powder mix of 95% KYNAR 461 and 5% gadolinium oxide. The second laminate (of one half inch thickness) was made by heat pressing, between 0.09 inch thick sheets of KYNAR 460, a 0.3 inch thick powder mix of 85% KYNAR 461 and 15% gadolinium oxide. Both laminates were exposed to neutron and gamma radiation in the 60 KEV (60,000 electron volt) range and found to give acceptable shielding, in each case providing a shielding at least about 80% as effective as a comparable lead-based laminate but without the other problems associated with lead usage. |
claims | 1. A system for installing or removing a component of a nuclear reactor, comprising:a riser apparatus, the riser apparatus having a lift assembly structured to hold and support the component and a first drive assembly coupled to the lift assembly and structured to selectively move the lift assembly and the component along a length of the riser apparatus; anda transition cart movable along an under vessel area of the nuclear reactor in a first direction and having a pivot mechanism, wherein the riser apparatus is moveable along the under vessel area separate from and relative to the transition cart along the first direction and is selectively engageable with and disengageable from the pivot mechanism, and wherein the pivot mechanism is structured to selectively rotate the riser apparatus from a horizontal position to a vertical position when the riser apparatus is engaged with the pivot mechanism. 2. The system according to claim 1, wherein the riser apparatus includes a second drive assembly structured to selectively move the riser apparatus relative to the transition cart in a direction parallel to a longitudinal axis of the riser apparatus. 3. The system according to claim 2, wherein the riser apparatus includes a riser trolley selectively engageable with the pivot mechanism, wherein the second drive assembly includes a lead screw, a motor operatively coupled to the lead screw for rotating the lead screw, and a coupling device coupled to the lead screw and the riser trolley, wherein rotation of the lead screw by the motor causes the riser apparatus to move relative to the transition cart in the direction parallel to the longitudinal axis of the riser apparatus. 4. The system according to claim 3, wherein the riser apparatus includes a first rail assembly and a second rail assembly, and wherein the riser trolley includes a first one or more wheels and a second one or more wheels, wherein the first rail assembly moves relative to the first one or more wheels and the second rail assembly moves relative to the second one or more wheels when the riser apparatus is caused to move relative to the transition cart. 5. The system according to claim 4, wherein the pivot mechanism includes a transition drive assembly operatively coupled to a first pivot arm and a second pivot arm, wherein the riser trolley includes a first flange structured to engage and be securely held by the first pivot arm and a second flange structured to engage and be securely held by the second pivot arm, and wherein the transition drive assembly is structured to selectively rotate the first and second pivot arms. 6. The system according to claim 1, wherein the pivot mechanism includes a transition drive assembly operatively coupled to one or more pivot arms, wherein the one or more pivot arms are structured to engage one or more portions of the riser apparatus, and wherein the transition drive assembly is structured to selectively rotate the one or more pivot arms. 7. The system according to claim 1, wherein the first drive assembly includes a lead screw, a first motor operatively coupled to the lead screw for rotating the lead screw, and a coupling device coupled to the lead screw and the lift assembly, wherein rotation of the lead screw by the first motor causes the coupling device to move along the lead screw and the lift assembly to move along the length of the riser apparatus. 8. The system according to claim 7, wherein the riser apparatus includes a first rail assembly and a second rail assembly, and wherein the lift assembly includes a first one or more wheels structured to move along the first rail assembly and a second one or more wheels structured to move along the second rail assembly. 9. The system according to claim 8, wherein the lift assembly includes a one or more supports structured to receive and hold a portion of the component. 10. The system according to claim 1, wherein the under vessel area includes a rail system having first top rail and a second top rail, wherein the transition cart includes a first one or more wheels structured to move along the first top rail and a second one or more wheels structured to move along the second top rail. 11. The system according to claim 10, wherein the rail system includes a first bottom rail and a second bottom rail, wherein the riser apparatus includes a third one or more wheels structured to move along the first bottom rail and a second one or more wheels structured to move along the second bottom rail. 12. The system according to claim 11, further comprising a guide cart movable along the first and second bottom rails for moving the riser apparatus along the first and second bottom rails. 13. The system according to claim 12, wherein the guide cart includes a support area structured to engage and hold a portion of the component when the component is held by the riser apparatus. 14. The system according to claim 13, wherein the guide cart includes a hitch for coupling the guide cart to a cable of a winch system structured to move the guide cart along the first and second bottom rails. 15. The system according to claim 1, further comprising an extension column having a first end structured to be held and supported by the lift assembly and a second end structured to hold and support the component, wherein the riser apparatus is structured to selectively move and lift the extension column and the component when the component is held by the extension column. 16. The system according to claim 15, wherein the second end includes a plurality of support members, each support member being structured to hold a bolt used to secure the component in place in the nuclear reactor. 17. The system according to claim 1, wherein the component is a CRDM. 18. The system according to claim 1, wherein the riser apparatus includes a selectively pivotable transfer bar for supporting the component when the component is disengaged from the lift assembly and the lift assembly is lowered. 19. The system according to claim 1, wherein the first drive assembly includes a lead screw, a motor operatively coupled to a first end of the lead screw for rotating the lead screw, a nut housing coupled to the lead screw, a first pulley coupled to the nut housing, and a cable coupled to the first pulley and the lift assembly, wherein rotation of the lead screw by the motor causes the nut housing to move along the lead screw and the lift assembly to move along the length of the riser apparatus. 20. The system according to claim 19, wherein the riser apparatus includes first and second rails, wherein the lift assembly is moveably coupled to the first and second rails, and wherein rotation of the lead screw by the motor causes the nut housing to move along the lead screw and the lift assembly to move along the first and second rails. 21. The system according to claim 20, wherein the cable has a first end attached to the lift assembly and a second end attached to a dead end location at second end of the lead screw opposite the first end, wherein at least one second pulley is provided adjacent the first end of the lead screw and at least one third pulley is provided at the dead end location, and wherein the cable passes from the lift assembly, through the at least one second pulley, then through the at least one third pulley, and then through the first pulley to the dead end location. 22. An apparatus for raising and lowering a component of a nuclear reactor, comprising:a lift assembly structured to hold and support the component; anda drive assembly coupled to the lift assembly and structured to selectively move the lift assembly and the component along a length of the apparatus, wherein the drive assembly includes a lead screw, a motor operatively coupled to a first end of the lead screw for rotating the lead screw, a nut housing coupled to the lead screw, a first pulley coupled to the nut housing, and a cable coupled to the first pulley and having a terminal end attached to the lift assembly, wherein rotation of the lead screw by the motor causes the nut housing and the first pulley to together move along the lead screw and the lift assembly to move along the length of the riser apparatus. 23. The apparatus according to claim 22, wherein the apparatus includes first and second rails, wherein the lift assembly is moveably coupled to the first and second rails, and wherein rotation of the lead screw by the motor causes the nut housing to move along the lead screw and the lift assembly to move along the first and second rails. 24. The apparatus according to claim 23, wherein the cable has a second end attached to a dead end location at a second end of the lead screw opposite the first end, wherein at least one second pulley is provided adjacent the first end of the lead screw and at least one third pulley is provided at the dead end location, and wherein the cable passes from the lift assembly, through the at least one second pulley, then through the at least one third pulley, and then through the first pulley to the dead end location. 25. The apparatus according to claim 23, wherein an amount of movement of the cable is double an amount of movement of the nut housing along the lead screw. |
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046702130 | summary | CROSS REFERENCE TO RELATED APPLICATION Reference is hereby made to the following copending application dealing with related subject matter and assigned to the assignee of the present invention: "Reconstitutable Nuclear Reactor Fuel Assembly With Unitary Removable Top Nozzle Subassembly" by John M. Shallenberger, assigned U.S. Ser. No. 673,681 and filed Nov. 20, 1984, a continuation-in-part of copending U.S. patent application Ser. No. 457,790, filed Jan. 13, 1983. 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 a top nozzle incorporating improvements which eliminate relative sliding engagement between the upper support plate of the reactor core and the hold-down structure of the top nozzle while providing removable mounting of the top nozzle as a unitary subassembly on the guide thimbles of a reconstitutable fuel assembly as well as desired alignment of the fuel assembly with the upper core support plate. 2. Description of the Prior Art Conventional designs of fuel assemblies include a multiplicity of fuel rods held in an organized array by grids spaced along the fuel assembly length. The grids are attached to a plurality of control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the control rod guide thimbles which extend above and below the opposite ends of the fuel rods. At the top end of the fuel assembly, the guide thimbles are attached in openings provided in the top nozzle. Conventional fuel assemblies also have employed a fuel assembly hold-down device to prevent the force of the upward coolant flow from lifting a fuel assembly into damaging contact with the upper core support plate of the reactor, while allowing for changes in fuel assembly length due to core induced thermal expansion and the like. Such hold-down devices have included the use of springs surrounding the guide thimbles, such as seen in U.S. Pat. Nos. 3,770,583 and 3,814,667 to Klumb et al and U.S. Pat. No. 4,269,661 to Kmonk et al. Due to occasional failure of some fuel rods during normal reactor operation and in view of the high costs associated with replacing fuel assemblies containing failed fuel rods, the trend is currently toward making fuel assemblies reconstitutable in order to minimize operating and maintenance expenses. Conventional reconstitutable fuel assemblies incorporate design features arranged to permit the removal and replacement of individual failed fuel rods. Reconstitution has been made possible by providing a fuel assembly with a removable top nozzle. The top nozzle is mechanically fastened usually by a threaded arrangement to the upper end of each control rod guide thimble, and the top nozzle can be removed remotely from an irradiated fuel assembly while it is still submerged in a neutron-absorbing liquid. Once removal and replacement of the failed fuel rods have been carried out on the irradiated fuel assembly submerged at a work station and after the top nozzle has been remounted on the guide thimbles of the fuel assembly, the reconstituted assembly can then be reinserted into the reactor core and used until the end of its usefuel life. One type of such reconstitutable fuel assembly can be seen in the aforementioned Klumb et al patents. The fuel assembly of Klumb et al includes a top nozzle which incorporates a hold-down plate and also coil springs coaxially disposed about upwardly extending alignment posts. The alignment posts extend through an upper end plate, spaced below the hold-down plate, and are joined thereto and to the upper ends of the guide thimbles with fastener nuts located on the underside of the upper plate. The upper hold-down plate is slidably mounted on the alignment posts and the coil springs are interposed, in compression, between the hold-down plate and the end plate. A radially enlarged shoulder on the upper end of each of the alignment posts retains the hold-down plate on the posts. However, the Klumb et al reconstitutable fuel assembly involves a top nozzle arrangement which is difficult to remove and reattach both due to the location of the fasteners and because removal appears to cause the hold-down device of the top nozzle to come apart, requiring added steps and apparatus to prevent this or to later reassembly the hold-down device. The reconstitutable fuel assembly described and illustrated in the patent application cross-referenced above includes design improvements which overcome the aforementioned problems and shortcomings of the Klumb et al top nozzle design. Particularly, the top nozzle of the cross-referenced application is adapted to be removed and then replaced as a unitary subassembly on the guide thimbles. Notwithstanding these improvements, several additional problems are inherent in the Klumb et al design. Only recognized recently, these problems are not addressed in the Kmonk et al patent nor in the improved top nozzle design of the cross-referenced application and so likewise are present in them. These problems arise from the impingement of coolant cross-flow from adjacent fuel assemblies on the hold-down springs of a given fuel assembly and the relative sliding engagement allowed between the upper ends of the alignment posts (or guide tube extensions) and the upper core support plate at the region of the holes defined therein which receive the upper ends of the alignment posts. With regard to the first problem, cross-flow from adjacent fuel assemblies occurs because of the radial flow maldistribution across pressurized water reactor cores which is caused by core inlet flow maldistribution and by temperature differences across the core. Thus, there is a radial pressure gradient at the fuel assembly outlet which induces cross-flow above the fuel rods of the assembly. The hold-down springs in the Klumb et al type top nozzle are exposed to the cross-flow which has led to spring failure due to fatigue caused by flow induced vibration. With regard to the second problem, relative motion occurs between the upper ends of the alignment posts and the upper core support plate because fuel assembly alignment with the upper core plate is accomplished by projecting the guide thimble mounted posts into the holes in the core plate and such alignment must accommodate axially-directed differential growth of the fuel assembly due to differential thermal expansion and irradiation growth. Core plate vibration also produces relative motion between the core plate hole and the thimble alignment post. Such relative motion accompanied by contact between the upper ends of the alignment posts and the hole region of the core plate results in wear of the core plate. Small amplitude vibration, even at low frequencies, can lead to appreciable wear when considered over long periods of time. Since the core plate has a forty year life, wear at the hole region therein can lead to expensive core plate rework to resize the holes. Consequently, a need exists for a fresh approach to reconstitutable fuel assembly top nozzle design with the objective of eliminating the aforementioned problems of core plate wear and hold-down spring fatigue while retaining the capability of removal and reattachment of the top nozzle without the possibility of its hold-down device coming apart. SUMMARY OF THE INVENTION The present invention provides an improved top nozzle construction designed to satisfy the aforementioned needs. Specifically, the top nozzle of the present invention includes improved structures which eliminate relative moving contact or sliding engagement between the upper support plate of the reactor core and the hold-down structure of the top nozzle while providing removable mounting of the top nozzle as a unitary subassembly on the guide thimbles of a reconstitutable fuel assembly as well as desired alignment of the fuel assembly with the upper core support plate. Relative motion between the upper core plate and the alignment sleeves of the top nozzle still takes place but without damaging contact with one another. Consequently, there is no wear on the upper core plate. Any wear which might occur takes place between readily replaceable parts of the top nozzle. Deleterious affects on the hold-down springs of coolant cross-flow between fuel assemblies is substantially eliminated in the preferred form of the present invention by the incorporation of an enclosure wall about the perimeter of the top nozzle which protects the springs from flow induced vibration. Accordingly, the present invention is directed to an improved top nozzle on a fuel assembly for aligning the fuel assembly with an upper core plate of a nuclear reactor core. The fuel assembly has a plurality of guide thimbles with respective upper end portions and the upper core plate has a lower side and a plurality of holes defined therein which open at its lower side. The improved top nozzle comprises: (a) lower means being stationarily supported on the upper end portions of the guide thimbles; (b) upper means having a plurality of passageways defined therethrough in a pattern which matches that of the guide thimbles and being adapted to abut the lower side of the upper core plate; (c) a plurality of upstanding means having respective central bores defined therethrough, each of the upstanding means being disposed above the upper means and attached thereto such that its central bore is aligned with a respective one of the passageways of the upper means, with each upstanding means also being of a cross-sectional size adapted to interfit within one of the holes in the upper core plate when the upper means abuts the lower side of the upper core plate; (d) a plurality of elongated tubular members having lower and upper ends and being releasably connected at their respective lower ends to the upper end portions of the guide thimbles and inserted at their respective upper ends into the passageways of the upper means for slidable movement within the passageways of the upper means and the corresponding aligned bores of the upstanding means; (e) a plurality of yieldable members disposed between the lower and upper means and supporting the upper means in a spaced relation above the lower means at a stationary position in which the upper means abuts the upper core plate with the upstanding means interfitted within the holes of the upper core plate; and (f) means interconnecting the spaced lower and upper means so as to accommodate movement of the lower means toward and away from the upper means upon axial movement of the guide thimbles of the fuel assembly toward and away from the upper core plate, the interconnecting means also being effective to limit movement of the lower means away from the upper means to maintain the yieldable members in a state of compression therebetween. Therefore, concurrently as alignment of the fuel assembly with the upper core plate is achieved through abutting of the upper means with the upper core plate and interfitting of the upstanding means within the upper core plate holes, axial movement of the fuel assembly relative to the upper core plate is accommodated through movement of the lower means and the plurality of tubular members relative to the upper means. No wear is incurred by the upper core plate since there is no relative sliding engagement of the upper means, the plurality of upstanding means nor the plurality of tubular members of the improved top nozzle with the upper core plate. More particularly, the lower means includes a lower adapter plate with a plurality of openings defined therethrough in a pattern which matches that of the guide thimbles such that the upper end portions of the guide thimbles are received therethrough and extend above the adapter plate. The elongated tubular members are releasably connected at their respective lower ends to the upper end portions of the guide thimbles extending above the lower adapter plate. Specifically, each of the lower ends of the respective tubular members is internally threaded for releasable threaded connection to an externally threaded section on each of the upper end portions of the respective guide thimbles. Furthermore, each of the tubular members has a lower portion of a cross-sectional size greater than an upper portion thereof and greater than the size of the passageway in the upper means such that the tubular member remains captured between the upper means and lower means when released from its connection with the respective one guide thimble. Still further, the upper means is a hold-down plate composed of an array of hubs and ligaments extending between and interconnecting the hubs, with each of the hubs having one of the passageways defined therethrough. The interconnecting means includes at least one lug connected to each of at least several of the hubs and extending downwardly therefrom. Alternatively, the lug can be connected to each of at least several of the ligaments and extend downwardly therefrom. Finally, each upstanding means is a boss disposed above and connected to each of at least several of the hubs of the upper hold-down plate with the bore of the boss aligned with the passageway of the hub. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described in illustrative embodiment of the invention. |
claims | 1. A method for determining parallelism of an ion beam in an ion implanter system for implanting into a work piece, the method comprising the steps of:determining a first test position of the ion beam while not exposing the ion beam to an acceleration/deceleration electrical field;determining a second test position of the ion beam while exposing the ion beam to the acceleration/deceleration electrical field; anddetermining the parallelism of the ion beam based on the first test position and the second test position. 2. The method of claim 1, wherein the first and second test position determining steps each include obtaining a profile and a position of the ion beam within an acceleration/deceleration column of the ion implanter system. 3. The method of claim 2, wherein the obtaining steps include using a traveling Faraday cup system. 4. The method of claim 1, wherein the parallelism determining step includes:determining a lateral shift between the first test position and the second test position; anddetermining the parallelism of the ion beam based on the lateral shift. 5. The method of claim 1, further comprising the step of adjusting the ion implanter system based on a result of the parallelism determining step. 6. The method of claim 5, wherein the adjusting step includes adjusting at least one of the following: an angle of the work piece and an optical component of the ion implanter system. 7. The method of claim 1, wherein the first and second test position determining steps are repeated for a plurality of scanning positions of the ion beam, and the parallelism determining step includes determining the parallelism based on each of the first and second test positions. 8. A system for determining a parallelism of an ion beam in an ion implanter system for implanting into a work piece, the method comprising the steps of:a position determinator for determining a first test position of the ion beam while not exposing the ion beam to an acceleration/deceleration electrical field and a second test position of the ion beam while exposing the ion beam to the acceleration/deceleration electrical field; anda parallelism determinator for determining the parallelism of the ion beam based on the first test position and the second test position. 9. The system of claim 8, wherein the position determinator communicates with an ion beam profiler that obtains a profile of the ion beam within an acceleration/deceleration column of the ion implanter system. 10. The system of claim 8, wherein the parallelism determinator includes:a lateral shift determinator for determining a lateral shift between the first test position and the second test position; anda parallelism calculator for calculating the parallelism of the ion beam based on the lateral shift. 11. The system of claim 8, further comprising an adjuster for adjusting the ion implanter system based on a result of the parallelism determinator. 12. The system of claim 11, wherein the adjuster adjusts at least one of the following: an angle of the work piece and an optical component of the ion implanter system. 13. The system of claim 8, wherein the position determinator determines the first and second test position for a plurality of scanning positions of the ion beam, and the parallelism determinator determines the parallelism based on each of the first and second test positions. 14. A computer program product for determining a parallelism of an ion beam in an ion implanter system for implanting into a work piece, the computer program product comprising:a computer usable medium having computer usable program code embodied therein, the computer usable medium including:program code configured to determine a first test position of the ion beam while not exposing the ion beam to an acceleration/deceleration electrical field;program code configured to determine a second test position of the ion beam while exposing the ion beam to the acceleration/deceleration electrical field; andprogram code configured to determine the parallelism of the ion beam based on the first test position and the second test position. 15. The program product of claim 14, wherein the first and second test position determining codes each use a profile of the ion beam after an acceleration/deceleration column of the ion implanter system. 16. The program product of claim 14, wherein the parallelism determining code includes:program code configured to determine a lateral shift between the first test position and the second test position; andprogram code configured to determine the parallelism of the ion beam based on the lateral shift. 17. The program product of claim 14, further comprising program code configured to adjust the ion implanter system based on a result of the parallelism determining code. 18. The program product of claim 17, wherein the adjusting code includes program code for adjusting at least one of the following: an angle of the work piece and an optical component of the ion implanter system. 19. The program product of claim 14, wherein the first and second test position determining codes repeat the first and second test position determining for a plurality of scanning positions of the ion beam, and the parallelism determining code includes program code configured to determine the parallelism based on each of the first and second test positions. 20. An ion implanter system for implanting an ion beam into a work piece, the ion implanter system comprising:an ion beam generator; anda system for determining a parallelism of the ion beam in the ion implanter system including:a position determinator for determining a first test position of the ion beam while not exposing the ion beam to an acceleration/deceleration electrical field and determining a second test position of the ion beam while exposing the ion beam to the acceleration/deceleration electrical field; anda parallelism determinator for determining the parallelism of the ion beam based on the first test position and the second test position. 21. The ion implanter system of claim 20, wherein the position determinator communicates with an ion beam profiler that obtains a profile of the ion beam after an acceleration/deceleration column of the ion implanter system. 22. The ion implanter system of claim 20, wherein the parallelism determinator includes:a lateral shift determinator for determining a lateral shift between the first test position and the second test position; anda parallelism calculator for calculating the parallelism of the ion beam based on the lateral shift. 23. The ion implanter system of claim 20, further comprising an adjuster for adjusting the ion implanter based on the parallelism, wherein the adjuster adjusts at least one of the following: an angle of the work piece and an optical component of the ion implanter system. 24. The ion implanter system of claim 20, wherein the position determinator determines the first and second test positions for a plurality of scanning positions of the ion beam, and the parallelism determinator determines the parallelism based on each of the first and second test positions. |
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047028793 | summary | BACKGROUND OF THE INVENTION The present invention relates to an improved pressurized water nuclear reactor having an integral means for in-core spraying of a liquid coolant in case of a loss of coolant event, and a passive safety system incorporating an improved reactor vessel. The nuclear power industry has been making efforts to provide for more safe operation of nuclear reactors. While some efforts have taken the form of adding more "active" safety features and then performing probability analyses to show that risks are very small, a portion of the public has remained unconvinced. In such active systems of the prior art, a large number of components such as pumps and fans which may be electrically powered, and optionally diesel powered in the event of electric failure, are provided. Thus, in a pipe break, termed a loss of coolant accident, water is provided to the primary circuit and then the reactor vessel by pumps. Additionally, motor-driven fans as well as pump-operated spray devices, are used to remove containment heat. The reactor decay heat and heat from containment is also transferred into an emergency cooling water system. These safety systems are all required to be redundant in order that failure of a component will not render the safety system ineffective. Thus, the active approach to nuclear plant safety results in plant designs of highly complex and costly design. The need thus exists for a nuclear reactor, of the pressurized water reactor type, which is convincingly safe to one and all without significant increase in costs, which are already high. The most likely approach is thus a system which is of a "passive" nature, i.e. which requires little or no operator action but rather uses gravity or stored energy to perform its functions. It is an object of the present invention to provide a pressurized water nuclear reactor which has a large volume of relatively cold supplementary pressurized water integral within the reactor vessel, which supplementary water is sprayed into the core of the reactor upon occurrence of a loss of coolant accident in the primary coolant circuit, without need for pumps or other active components. It is another object of the present invention to provide a passive safety system incorporating the reactor of the present invention. SUMMARY OF THE INVENTION A pressurized water nuclear reactor having a passive system for in-core spraying of liquid coolant uses an accumulated supply of liquid coolant, a portion of which flashes to form steam upon depressurization of the reactor, to force coolant into the core region of the reactor. The reactor has a substantially cylindrical flow liner that has an open top, a cylindrical wall section, and a bottom wall, with said cylindrical wall section forming therein a lower reactor internals chamber. A cylindrical barrel is disposed in the flow liner spaced from the bottom thereof, to form an annular chamber thereabout and a riser chamber therein, which riser chamber contains the lower reactor internals including the fuel assemblies and control rod assemblies. The flow liner is contained within a pressure vessel that has a removable top, an intermediate cylindrical wall section and a lower wall section, the lower wall section thereof spaced from the flow liner, to form a second annular chamber. The intermediate cylindrical wall section of the pressure vessel has inlet and outlet nozzles that communicate with a cooled coolant return port and a hot coolant discharge port in the flow liner. The hot primary coolant discharge nozzles, and cooled primary inlet nozzles to the annular chamber, are connected to a steam generator, with means provided to circulate the primary coolant therethrough. A supply of supplementary liquid coolant is provided in the second annular chamber. Insulating means are provided to maintain a major portion of the supplementary liquid coolant at a first elevated temperature and a localized minor portion of the supplementary liquid coolant at a second, higher, elevated temperature. Means are provided to effect communication between the second annular chamber and the riser chamber in the cylindrical flow liner and provide for spraying of supplementary liquid coolant into the core in the riser chamber. The communicating means preferably comprise axially aligned openings in the bottom wall of the flow riser and the barrel bottom support plate with tubular elements connecting said openings and elongated tubular elements having spaced apertures therealong disposed within the core assembly. Upon depressurization of the interior of the substantially cylindrical flow liner and concomitantly the second annular chamber, the higher elevated temperature localized portion of the supplementary coolant flashes to a vapor and the increase in volume, so produced, forces the supplementary liquid coolant into the core region in the riser chamber. Means for injecting and removing coolant chemistry control solution, such as a borated water solution, are provided on the pressure resistant vessel, and a pool of liquid is provided about the pressure resistant vessel to further cool the supplementary liquid coolant. The passive safety system incorporates the reactor with means for circulating water solely by natural convection, from the hot leg to the cold leg of the primary coolant system, including a heat exchange means and a means for introducing stored coolant, under superatmospheric pressure, into the substantially cylindrical vessel. |
description | As global demand for energy grows, greenhouse gas emissions into the earth's atmosphere also increase. This growth in greenhouse gas emissions disrupts the balance of the Earth's ecosystem and affects all life. Greenhouse gases, particularly carbon dioxide (CO2), undesirably absorb and emit radiation within the atmosphere, causing a “greenhouse effect.” Attention to curb greenhouse gases has focused on CO2 emissions due to the ever-increasing combustion processes emitting CO2 as a waste product into the environment. Lawmakers, worldwide, have also focused their efforts in cutting CO2 emissions by pushing carbon neutrality, legislating the development of new technologies and changing tax, penalty, and incentive programs to cut down on CO2 emissions and develop new carbon neutral integrative processes. The increase in CO2 emissions has led to the development of Carbon Capture, Utilization and Storage (CCUS). CCUS is a set of technologies that is used to capture carbon dioxide emissions at the source, thus preventing the CO2 from entering the atmosphere. The CO2 emissions are transported away and may be either stored deep underground or turned into useful products. Capturing CO2 has been used to help improve the quality of natural gas. As the field continues to innovate, CO2 may be removed and sequestered indefinitely. Moreover, it may also be turned into a marketable industrial commercial product, thus adding value to an otherwise harmful waste stream. Accordingly, there exists a need for innovations in carbon (dioxide) capture and storage capabilities. This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. In one aspect, embodiments disclosed herein relate to a system for a carbon neutral cycle of gas production. The system may include a molten salt reactor configured to generate zero carbon dioxide (CO2) emissions electricity. A desalination unit may be provided and configured to receive the zero-CO2 emissions electricity from the molten salt reactor and produce a desalinated water. An electrolysis unit may also be provided and configured to be powered by the zero-CO2 emissions electricity generated by the molten salt reactor and generate hydrogen (H2) and oxygen (O2) from the desalinated water. The system may also include an oxy-combustion unit configured to receive and combust a hydrocarbon fuel with the O2 from the electrolysis unit to produce electricity and CO2. The system may also provide a CO2 capture system adapted to capture the CO2 produced by the oxy-combustion unit and a catalytic hydrogenation unit configured to receive and convert H2 from the electrolysis unit and CO2 from the CO2 capture system to produce the hydrocarbon fuel. In another aspect, embodiments disclosed herein relate to a method for a carbon neutral cycle of a natural gas production. The method may include generating electricity with a molten salt reactor configured to generate zero carbon dioxide (CO2) emissions. The method may also include powering a desalination unit with the electricity from the molten salt reactor, producing desalinated water (H2O) with the desalination unit. The method may include producing hydrogen (H2) and oxygen (O2) from the desalinated water (H2O) with an electrolysis unit and introducing the H2 produced by the electrolysis unit to a catalytic hydrogenation unit. The method may include reacting captured CO2 and the H2 generated from the desalination unit by catalytic hydrogenation in a catalytic hydrogenation unit, wherein the reaction produces a hydrocarbon fuel. The method may also include introducing the hydrocarbon fuel into an oxy-combustion unit and producing CO2 in the oxy-combustion unit by reacting the hydrocarbon fuel with the O2 from the electrolysis unit. The method may also include capturing CO2 from the oxy-combustion unit and introducing the captured CO2 to the catalytic hydrogenation unit. Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. Embodiments of the present disclosure relate to the fields of CO2 utilization and value creation. Embodiments of the present disclosure relate to systems and methods of using green (clean) electrical energy with zero CO2 emissions generated by a molten salt reactor (MSR) to convert CO2 into commercial products for a carbon neutral life cycle. The capture and conversion of CO2 is useful across industrial and commercial applications, such as the production of methane (CH4) and methanol (CH3OH). Carbon capture and storage is a central part of efforts to achieve net zero CO2 and other greenhouse gas emissions, while also ensuring the world can continue to innovate and thrive. Capturing carbon has been used to help improve the quality of natural gas, but has fallen short of turning CO2 into a marketable industrial and commercial product while also achieving carbon neutrality. Embodiments of the present disclosure relate to CO2 utilization and value creation. CO2 may be captured and converted into useful industrial products. The driving energy of the CO2 conversion is clean electricity generated with zero CO2 emission operation, such as molten salt reactor operations. FIG. 1 shows an embodiment of the overall CO2 utilization and value creation process 100 of the current disclosure. In the embodiment shown in FIG. 1, CO2 may be captured from a natural gas production process 101, such as a natural gas production plant gas sweetening process, and enter line 112. It will be understood by those skilled in the art that CO2 may be captured from other sources, including cement factories, biomass power plants, oil refineries, and other heavy industrial sources, particularly those that burn fossil fuels. The captured CO2 may be fed into a catalytic hydrogenation unit 103 through line 102. In the catalytic hydrogenation unit 103, hydrogen (H2) may enter in through line 104, wherein it may react with the CO2 from line 102 to produce a hydrocarbon fuel, such as CH4. The H2 may be produced from an electrolysis unit 105 connected to the catalytic hydrogenation unit 103 via line 104. The CH4 may flow through line 106 and into the natural gas grid 107. Although the embodiment shown in FIG. 1 shows the production of CH4, it will be understood by those skilled in the art with the benefit of the current disclosure that other hydrocarbon fuels, such as CH3OH, may be produced in embodiments of the present disclosure. As shown in FIG. 1, some embodiments may have an oxy-combustion unit 108 fluidly connected to the catalytic hydrogenation unit 103 and the natural gas grid 107 via line 106 and line 109. CH4 may be injected into the oxy-combustion unit through line 109 wherein it may react with oxygen (O2) from line 110 to produce a CO2 stream in line 111. The O2 may be produced in the electrolysis unit 105 connected to the oxy-combustion unit 108 via line 110. The CO2 produced by the oxy-combustion unit 108 and flowing through line 111 may be captured and combined with the CO2 from the natural gas production process 101 flowing though line 112. The combined captured CO2 may be stored in a CO2 storage unit 113 until the CO2 is fed into the catalytic hydrogenation unit 103 via line 102. It will be understood by those skilled in the art that the captured CO2 from the natural gas production process 101 and the CO2 from the oxy-combustion unit 108 may not be stored in the same storage unit. It will also be understood by those in the art that the captured CO2 from the natural gas production process 101 and the captured CO2 from the oxy-combustion unit 108 may be directly connected to the catalytic hydrogenation unit 103, either separately/independently of each other or through a combined line wherein both captured CO2 streams (line 111 and line 112) fluidly connect in a single line 102 to the catalytic hydrogenation unit 103 (not shown in the FIG. 1 embodiment). In embodiments of the present disclosure, the combined captured CO2 (as shown stored in CO2 storage unit 113), the CO2 in line 102, the catalytic hydrogenation unit 103, the CH4 in line 106, the natural gas grid 107, the CH4 flowing in line 109, the oxy-combustion unit 108, and the CO2 in line 111, or any combination thereof, may form a carbon neutral natural gas cycle. In embodiments of the present disclosure, the driving energy of the overall CO2 utilization and value creation process 100 may be electricity generated by a molten salt reactor 114. As shown in FIG. 1, a molten salt reactor 114 may generate electricity. The molten salt reactor 114 may generate clean/green electricity, wherein the molten salt reactor 114 does not release CO2 into the atmosphere. Oxy-combustion unit 108 may also be used to produce electricity, used within the carbon-neutral natural gas cycle (113→103→107→108→113) and/or exported; energy from the oxy-combustion unit 108 may also or additionally be used for other processes requiring radiant or convective heat or transformation into work, such as via a turbine. In embodiments of the present disclosure, the electricity generated from the molten salt reactor 114 may be used to desalinate seawater. The electricity may flow from the molten salt reactor 114 through line 115 to provide power to the desalination of seawater in desalination unit 116. The high salinity water, brine, and/or salts produced from the desalination unit 116 may be used in an enhanced oil recovery unit 117. The desalination unit 116 may be incorporated into the enhanced oil recovery unit 117, wherein the high salinity water, brine, and/or salts may be injected into oil-bearing reservoirs to maintain the reservoir pressure and improve secondary hydrocarbon recovery. The water (H2O) product stream from the desalination unit 116 may flow through line 118 to an electrolysis process. As shown in FIG. 1, the H2O from the desalination unit 116 may flow through line 118 to an electrolysis unit 105. In the electrolysis unit 105, the H2O may be decomposed into O2 and H2 in an electrolysis reaction. The electrolysis reaction may also be powered by the electricity generated in the molten salt reactor 114. The electrolysis of H2O in the electrolysis unit 105 may produce an O2 stream in line 110 and a H2 stream in line 104. The O2 stream in line 110 may be connected to the oxy-combustion unit 108 via line 110 wherein it may provide O2 for the oxy-combustion reaction. The H2 stream may be connected to the catalytic hydrogenation unit 103 via line 104 wherein it may provide H2 for the catalytic reaction with CO2 to form a methane product. The H2 produced in the electrolysis of H2O may also be connected via line 119 to be used in other industrial applications 120, such as refinery applications, fuel cells, and hydrogenation. In one aspect, embodiments disclosed herein relate to CO2 captured from industrial operations. An example of a source for captured CO2 is a conventional natural gas plant. Natural gas with carbon capture uses post-combustion capture methods. CO2 is a product of burning natural gas. Post-combustion capture of CO2 is a conventionally available integrated operation of natural gas combined cycle plants. Methods of CO2 separation/removal from a natural gas emission may include membrane-based systems and filter systems. The high cost of efficiency penalties associated with carbon capture and storage, as well as methane leakage from natural gas extraction and distribution limit the benefit of carbon capture and storage on reducing greenhouse gases. Some embodiments of the present disclosure may use the captured CO2 of a natural gas production plant in a subsequent, downstream, value-added process to ensure the CO2 is not released into the atmosphere. In some embodiments of the present disclosure, conventional natural gas plants capture CO2 in a gas sweetening process. Gas sweetening is the process of removing hydrogen sulfides, carbon dioxide, and mercaptans from natural gas to make it suitable for transport and sale. It is desirable to sweeten natural gas because H2S and CO2 have a corrosive effect on gas pipelines. The CO2 is removed, captured from the pipeline and either stored in facilities or used in processes that use CO2, and not released into the atmosphere as greenhouse gases. In embodiments of the present disclosure, captured CO2 may be used in a catalytic hydrogenation process. Catalytic hydrogenation of the present disclosure produces methane or methanol from CO2 (from a captured CO2 stream) and H2 (e.g., from an electrolysis process). Catalytic hydrogenation may be used to convert CO2 and H2 into a usable hydrocarbon-based fuel, including methane (CH4) and methanol (CH3OH). The conversion of CO2 into methane or methanol is the prime target reactions in catalytic hydrogenations of the present disclosure, as shown below: CO2+4H2CH4+2H2O ΔH298 K=−165.0 kJ mol−1 CO2+3H2CH3OH+H2O ΔH298 k=−49.4 kj mol−1 To catalyze the reaction between CO2 and H2, surface sites that bind and activate CO2 need to co-exist and cooperate with sites for dissociation of H2. Activation of CO2 by heterogeneous catalysis is often carried out using conventional reducible oxides, including ceria, zirconia, or titania, while metals are conventionally used to dissociate H2. It is desirable to use a catalyst that can efficiently and effectively suppress the formation of by-products in favor of the formation of methane or methanol. Hydrogenation of CO2 to methane is thermodynamically favorable over other CO2 conversion reactions. Different transition metals, such as Ru, Rh, Ni, and Pd have been known to be highly selective and active for the methane formation by CO2 hydrogenation, particularly at low temperatures. The supported Ni catalysts conventionally have the highest selectivity to form methane. Catalytic hydrogenation of CO2 with H2 to produce CH4 and CH3OH has a wide range of applications, including the production of syngas and the formation of compressed natural gas. It is a key pathway for CO2 recycling and it can offer a solution for renewable H2 storage and transportation. In parallel, the CO2 hydrogenation reactions to produce CH4 and/or CH3OH are considered to be useful in reclaiming oxygen (O2) within a closed cycle. Catalytic hydrogenation of CO2 to produce CH4 and/or CH3OH requires substantial amounts of H2. In embodiments of the present disclosure, the CO2 capture and catalytic hydrogenation unit may be oversized, thus producing a surplus of CH4 and/or CH3OH. This oversized unit may improve the unit operations and efficiency of scale. A portion of the CH4 or CH3OH product stream from an oversized unit may be fed to a downstream process. For example, in embodiments of the present disclosure, CO2 may be catalytically hydrogenated into CH3OH, wherein the CH3OH is injected into the natural gas grid. The CH3OH produced by catalytic hydrogenation may also be injected/fed into an oxy-combustion process to produce electricity. CH3OH, as produced by embodiments of the present invention, may be used as a feedstock for chemicals, such as ethylene or propylene through a methanol to olefin process. H2 may be produced by a number of processes, but industrially is preferentially produced using non-renewable feedstocks. Hydrogen production is also generally considered an expensive undertaking, particularly with methods such as steam methane reforming. Steam methane reforming is one of the most commonly used commercialized methods of producing hydrogen. Steam methane reforming produces hydrogen (syngas) by reaction of hydrocarbons with water. The reaction is often conducted under high pressure mixture of steam and methane in the presence of a nickel catalyst. In some steam methane reforming processes, a desulfurized hydrocarbon feedstock (e.g., natural gas) is preheated, mixed with steam and passed over a catalyst to produce carbon monoxide, carbon dioxide, and hydrogen, wherein the hydrogen is subsequently separated. Steam methane reforming accounts for the majority of the worlds produced hydrogen, but is not considered a clean/green resource due to its production of greenhouse gases. Thus, it is desirable to decrease CO2 emissions wherein the H2 necessary for the catalytic hydrogenation is sourced from a clean, renewable resource. An example of a clean resource that produces hydrogen is water electrolysis powered by green energy. Water electrolysis is considered an effective alternative to steam methane reforming for the production of H2. In embodiments of the present disclosure, electrolysis of H2O produces the H2 used in the catalytic hydrogenation process. The hydrogen production process in the present disclosure may be connected to an energy source, such as a molten salt reactor, to power the electrolysis reaction. A molten salt reactor (MSR) is a nuclear fission reactor that uses molten fluoride salts as a primary coolant at low pressure, wherein fissile and fertile fuel may be dissolved in the salt instead of fuel rods. FIG. 2 shows a schematic of an exemplary MSR system 200. As shown in FIG. 2, fuel is dissolved within a fluoride salt mixture, producing either uranium fluoride or thorium fluoride inside a reactor tank 210 and circulated around a reactor core unit 202 via circulation motors 201. The reactor core unit 202 may include a graphite reactor core defining an internal space that houses one or more fuel wedges 216. The fuel salt flows through line 203 to a heat exchanger 204 where it is used to heat solar salt that enters the primary heat exchanger 204 through line 205. The heated solar salt exits the primary heat exchanger 204 through line 206 wherein it enters a steam generator 207. The heat from the solar salt is used to heat water entering the steam generator 207 through line 208. The water is heated under high pressure in the steam generator 207 and exits through line 209 as steam. The cooled solar salt is pumped via salt circulating pump 211 back to heat exchanger 204. The steam from line 209 drives turbine 212 by operations understood by those skilled in the art. The turbine rotates a shaft 215 connected to a generator 213. The generator 213, in turn, converts the mechanical energy to electrical energy based on mechanisms understood by those skilled in the art. The arrangement and operation of MSRs vary according to design specifications. For example, the use of molten salt as fuel and as coolant are independent design choices. The original circulating-fuel-salt MSR and the more recent static-fuel-salt stable salt reactor use salt as fuel and salt as coolant; a dual fluid reactor uses salt as fuel but metal as coolant; and the fluoride salt-cooled high temperature reactor has solid fuel but salt as coolant. Although MSRs operate on the same basic principle as other nuclear power reactors (controlled fission to produce steam that powers electricity-generating turbines), MSRs offer advantages over conventional nuclear power plants. As in all low-pressure reactor designs, MSRs achieve passive decay heat removal. In some designs, the fuel and the coolant may be the same fluid, so a loss of coolant removes the reactor's fuel, similar to how loss of coolant also removes the moderator in light water reactions. Unlike steam in alternative reactors, the fluoride salts of MSRs dissolve poorly in water and do not form burnable hydrogen. Also, molten salts are not damaged by the core's neutron bombardment, unlike steel and solid uranium oxide in other reactors. Some reactors, such as a boiling water reactor (BWR), utilize high pressure radioactive steam that may leak the radioactive steam and cooling water, requiring expensive containment systems, piping, and safety equipment. MSRs advantageously utilize low pressure with a lower risk of leakage. However, most MSR designs require fluid with radioactive fission product in direct contact with pumps and heat exchangers. Other advantages of MSRs include cheaper closed nuclear fuel cycles because they can operate with slow neutrons. If fully implemented, reactors that close the nuclear fuel cycle may reduce environmental impacts. For example, chemical separation may turn long-lived actinides back into reactor fuel. The MSR fuel's liquid phase might be pyroprocessed to separate fission products (nuclear ashes) from actinide fuels. The discharged wastes generally have shorter half-lives. This reduces the need for geologic containment to 300 years rather than the tens of thousands of years as needed by a light-water reactor's spent nuclear fuel. It also permits the use of alternate nuclear fuels, such as thorium. It is also notable that fuel rod fabrication is not required in MSRs, as they are replaced with fuel salt synthesis. Some MSR designs are compatible with the fast neutron spectrum, which can pyroprocess problematic transuranic elements like Pu240, Pu241 and up (reactor grade plutonium) from traditional light-water nuclear reactors. An MSR can react to load changes in less than 60 seconds (unlike “traditional” solid-fuel nuclear power plants that suffer from xenon poisoning). Molten salt reactors can run at high temperatures, yielding high thermal efficiency. This reduces size, expense, and environmental impacts. MSRs can offer a high “specific power,” that is high power at a low mass. A possibly good neutron economy makes the MSR attractive for the neutron poor thorium fuel cycle. A notable advantage of the MSR as a source of energy in embodiments of the present disclosure is that the energy produced by MSR may be considered a green energy, in that it may not produce CO2 emissions. This green energy may be utilized in embodiments of the present disclosure to power desalination of seawater to create H2O, wherein the H2O is ultimately used to produce the H2 for the catalytic hydrogenation process described above. Embodiments of the present disclosure may include a desalination process, wherein H2O may be produced by desalination of seawater (water with dissolved salt and other minerals). Desalination refers to the removal of salts and other minerals from a target substance, like seawater. In desalination, salt water (seawater) is fed into a container. Feed sources may include brackish, seawater, wells, rivers, streams, wastewater, and industrial feed and process waters. Desalination processes may use membrane separation techniques. Salt water may pass through a semipermeable membrane. The membrane filters the salt and minerals from the salt water, producing H2O (fresh water). Membrane separation requires a high driving force, including applied pressure, vapor pressure, electric potential, and concentration to overcome natural osmotic pressures and effectively force water through a target membrane. As such, desalination is an energy intensive process. It is conventionally powered by fossil fuel processes, thereby contributing the CO2 emissions. Reverse osmosis (RO) and nanofiltration (NF) are the leading pressure driven membrane processes. Membrane configurations include spiral wound, hollow fiber, and sheet with spiral being the most widely used. Contemporary membranes are primarily polymeric materials with cellulose acetate still used to a much lesser degree. Electrodialysis (ED), electrodialysis reversal (EDR), forward osmosis (RO), and membrane distillation (MD) are also membrane processes used in desalination. Embodiments of the present disclosure may power the desalination process with the energy generated by a molten salt reactor. As described above, the energy from the MSR in embodiments of the present disclosure may be generated without producing CO2 emissions. By using the energy created by a MSR with zero/negligible CO2 emissions as the driving force for the desalination of seawater instead of conventional methods that burn fossil fuels, less CO2 is released into the atmosphere. Embodiments of the present disclosure may use the concentrated salt water, brine, and/or salts produced by the desalination in an enhanced oil recovery (EOR) process. The desalination partially or fully removes H2O from seawater, producing pure water (H2O) and either high salinity water, brine, or salts, depending on the extent of the H2O removal. EOR may use the high salinity water (or add the salts to water to create high salinity water) in water flooding techniques. Water flooding may be used as a secondary method to improve oil recovery. Oil pressures decline during oil production, leading to a reduction in oil productivity. EOR methods, such as water flooding, inject high-salinity water into target reservoir zones to maintain, support, or increase the reservoir pressure and oil productivity. The high salinity water and salts produced by the desalination of embodiments of the present disclosure may be used in these EOR. Embodiments of the present disclosure may use the high salinity, brine, or salts for other industrial applications, such as cooling water for power generation, aquaculture, and for a variety of other uses in the oil and gas industry, such as drilling and hydraulic fracturing. Embodiments of the present disclosure may use the H2O produced in the desalination process to produce H2 and O2 streams via electrolysis. The H2 produced may be used in the catalytic hydrogenation process and the O2 may be used in an oxy-combustion process. Electrolysis (i.e., water-splitting) of H2O produces H2 and O2 from renewable resources by using electricity to split water molecules. Electrolysis may occur in a vessel called an electrolyzer. The electrolyzer may be configured to house an anode and a cathode. The anode and cathode may be connected to power source. H2 will form at the cathode and O2 will form on the anode. In some embodiments, the anode and cathode may be separated by an electrolyte. The efficiency of the electrolysis process may be increased through the addition of an electrolyte, as well as the use of an electrocatalyst. Electrolyzers may function in different ways depending on the type of electrolyte material used in the process. Examples of different electrolyzers include polymer electrolyte membrane electrolyzers, alkaline electrolyzers, and solid oxide electrolyzers. The electrolysis process may be scaled depending on production facility requirements. H2 produced via electrolysis may result in zero greenhouse gas emissions, depending on the source of the electricity used. The source of the required electricity, the electricity cost and efficiency, as well as emissions resulting from electricity generation must be considered when evaluating the benefits and economic viability of hydrogen production via electrolysis. In embodiments of the present invention, the electricity from the MSR may drive the electrolysis process, resulting in zero/negligible CO2 emissions when producing the hydrogen and oxygen. In embodiments of the present disclosure, the hydrogen produced via electrolysis may be used in the catalytic hydrogenation process with CO2 to produce CH4 and CH3OH. CH4 and CH3OH are considered valuable industrial products and fuels. Other applications for the H2 produced in the electrolysis reaction may include refinery hydrogenation operations and other hydrogen economy applications, such as fuel cell powered devices (e.g., cars). O2 is also a product of electrolysis. In embodiments of the present disclosure, the O2 produced by the electrolysis process is fed into an oxy-combustion process. In the oxy-combustion process, a fossil fuel, such as CH4, is burned in the presence of O2 instead of air to produce CO2, H2O (water vapor), and electricity. O2 increases combustion efficiency and the concentration of CO2 in flue gasses, thereby improving CO2 capture. The H2O may be condensed through cooling and the CO2 stream may be captured. The increased CO2 concentration in flue gas may enable the capture of CO2 with a reduced NOx (nitrogen oxides) emission due to the purity of the O2 feed from the O2 produced by the electrolysis process. In the oxy-combustion process of embodiments of the present disclosure, CH4 is fed to the oxy-combustion process and reacted with O2 to create CO2. The oxy-combustion reaction in embodiments of the present disclosure is shown below:CH4+2O2→CO2+2H2O The source of CH4 may include the CH4 produced in the catalytic hydrogenation unit, CH4 from a natural gas grid, and a combination of both the CH4 produced in the catalytic hydrogenation unit and natural gas grid. In embodiments of the present disclosure, CH3OH, and not CH4, may be produced in the catalytic hydrogenation unit and fed into the oxy-combustion unit to produce electricity. In the embodiments that produce CH3OH, the O2 from the electrolysis unit reacts with the CH3OH in the oxy-combustion unit to produce CO2, H2O (water vapor), and electricity. The oxy-combustion reaction of the methanol reaction with O2 is shown below:2CH3OH+3O2→2CO2+4H2O In embodiments of the present disclosure, the CO2 from the oxy-combustion reaction may be captured. The captured CO2 from the oxy-combustion reaction may be stored with the CO2 captured from the natural gas plant. The combined captured CO2 streams may thereby be fed to the catalytic hydrogenation process, wherein it is reacted with the H2 to create CH4 or CH3OH. It will be appreciated by those skilled in the art and the benefit of the present disclosure that the production of CH4 or CH3OH using embodiments of the present disclosure may be a design choice and depend on the industrial application utilizing embodiments of the present disclosure. Embodiments of the overall CO2 utilization and value creation process of the current disclosure may capture and process CO2 using clean energy to reduce CO2 emissions in industrial operations. In embodiments of the current disclosure, CO2 captured from industrial processes, such as natural gas sweetening processes, may be combined with CO2 produced by an oxy-combustion reaction to produce CO2 for a catalytic hydrogenation process. The catalytic hydrogenation process may produce either CH4 or CH3OH by reacting the CO2 with H2. The CH4 or CH3OH may be fed into a natural gas grid and is in fluid communication with the oxy-combustion process, wherein the CH4 or CH3OH may react with O2 to produce the CO2 that combines with the CO2 captured from an industrial process. The cycle comprising the CO2 streams (both captured CO2 and CO2 produced by the oxy-combustion process), the catalytic hydrogenation, the natural gas grid, and the oxy-combustion process is exemplary of a carbon neutral natural gas cycle according to embodiments of the current disclosure. According to embodiments of the current disclosure, the driving energy for the CO2 utilization and value creation process may be energy produced by a MSR. The energy produced by a MSR may be used in a desalination process to produce H2O. The H2O produced in the desalination process may produce H2 and O2 through electrolysis of the H2O. The O2 from the electrolysis process may be used in the oxy-combustion process of the carbon neutral natural gas cycle. The H2 from the electrolysis may be used in the catalytic hydrogenation of the carbon neutral natural gas cycle, as well as other industrial applications. Embodiments of the present disclosure may provide an option of using clean electrical energy produced, for example, by a molten salt reactor (nuclear) with zero CO2 emission, to convert CO2 into commercial products for a carbon neutral life cycle use of natural gas. Green (clean) electricity/energy, as defined herein, means energy produced with minimum environmental impact. It is representative of energy resources and technologies that provide the highest environmental benefit, while minimizing environment harm. The U.S. market defines green power/electricity as electricity produced from solar, wind, geothermal, biogas, eligible biomass, and low-impact small hydroelectric sources. It may be synonymous with other terms, such as renewable energy, clean energy, and green energy. Embodiments of the present disclosure may decrease the CO2 emissions into the atmosphere by a system and process powered by clean/green energy. The driving energy of embodiments of the present disclosure may be green/clean energy generated by a molten salt reactor. The molten salt reactor may have negligible to no measurable CO2 emissions. The O2 in the oxy-combustion process according to embodiments of the present disclosure and the hydrocarbon fuel produces CO2 that may otherwise be released into the atmosphere. The CO2 produced by the oxy-combustion reaction may be combined with CO2 from natural gas production, wherein it is captured and reacted with H2 to produce product streams, such as CH4, CH3OH, or other chemicals (e.g., ethylene and propylene). The water produced in the desalination process may be used for a variety of applications. The desalination process of the present disclosure, powered by the green/clean energy generated by a molten salt reactor, may produce pure H2O that may be used for human consumption and industrial applications. Embodiments of the present disclosure may provide a carbon neutral cycle for the world's future circular carbon economy. Some embodiments of the present disclosure form a carbon neutral gas cycle of natural gas production, CO2 capture, CO2 utilization, CO2 value creation, and CO2 transportation, all powered with clean/green energy generated from a zero CO2 emission molten salt reactor. Examples of CO2 value creation in embodiments of the present disclosure include the production of methane, methanol, methanol, hydrogen, and oxygen. The production of methane and methanol require extensive amounts of hydrogen. According to embodiments of the present disclosure, the hydrogen may be produced by electrolysis of water, the electrolysis process powered by the zero CO2 emission MSR. Embodiments of the present disclosure decrease CO2 emissions in the production of methane and methanol by producing the hydrogen necessary to produce methane and methanol using clean resources. These clean resources may be desalination and electrolysis powered by a source with zero CO2 emissions, such as a molten salt reactor. Embodiments of the present disclosure may reduce emission of NOx, by integrating an oxy-combustion process for natural gas power plants, as described above. Embodiments of the present disclosure may increase potable water production, improve refinery operations, improve hydrogen economic activities with the use of green energy, and increase oil recovery by supporting EOR operations with high-salinity fluids. Excess methane or methanol produced in the carbon neutral natural gas cycle may be exported or converted into other useful products. Similarly, excess hydrogen and oxygen not used in the carbon neutral natural gas cycle may be exported for other industrial or commercial uses. Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function. |
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043938990 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 2 and 3, the plugging apparatus of this invention comprises four plugs 11 which water-tightly plug four corresponding main steam pipes 1 opening from a reactor pressure vessel 9, a plug support ring 12 for withstanding counter pressure of compressed air applied to the insie of the steam pipes 1 at the time of inspection or maintenance of safety valves in the steam pipes so as not to push out the plugs from the pipes into the reactor pressure vessel 9, and a beam assembly comprising two beams 13 for simultaneously operating the plugs 11 and the ring 12. Each plug 11 has substantially the same construction as that of the conventional plugging apparatus shown in FIG. 1 and the plug 11 is provided with a bracket 14 (FIGS. 3 and 4) at its base end for remotely handling the plug 11. The plug support ring 12 is concentric with the reactor pressure vessel 9 and has an outer diameter smaller than the inner diameter of the vessel 9. The ring 12 is constructed to be splittable circumferentially into four parts as shown in FIGS. 3 through 5 and movable vertically in the reactor pressure vessel 9 through guides 15 engaging vertical guide rods 16. The guides 15 are mounted on the outer peripheral surface of the ring 12 and the vertical guide rods 16 are mounted on the inner surface of the pressure vessel 9. As shown in FIGS. 6 and 7, support members 17 are secured on the outer surface of the plug support ring 12 to engage with corresponding brackets 18 mounted on the inner wall of the reactor pressure vessel 9 to support in position the plug support ring 12. The other support members 19 are disposed on the lower side of the ring 12 so as to support the plugs 11 at predetermined positions in the inlet openings of the steam pipes 1 after insertion of the plugs so that the plugs 11 are not blown out from the steam pipes into the reactor pressure vessel 9 due to the counter pressure caused by air pressure applied to the inside of the steam pipes 1. Each of the support members 19 can be moved in a radial direction of the ring 12 by the operation of a hydraulic piston-cylinder assembly 20 attached to the lower surface of the ring 12. The inserted plug 11 is supported by the plug support ring 12 by pushing forwardly a rod 21 which is driven by a hydraulic piston cylinder assembly 22 attached to the ring 12 (FIG. 2). Two beams 13 are crossed and connected together at their central portions to form an X-shaped unitary beam assembly vertically movable in the reactor pressure vessel 9. Support plates 23 and 33 are welded to the beams 13 as shown in FIG. 3 and the plates 23 and 33 are provided with four eyebolts 23A and 33A at predetermined positions as shown in FIG. 3 to which are secured wire ropes operated by a crane disposed at a ceiling of a reactor container vessel, not shown. Thus, the beam assembly is operated by the crane. The beams 13 are detachably connected to the plug support ring 12 through rods 24 (FIG. 2) which are driven by hydraulic piston-cylinder assemblies 25 attached to the lower surfaces of the beams 13. Each support plate 33 is provided with a guide member 35 which engages a corresponding guide member 34 secured to the plug support ring 12 for vertically guiding the beam assembly when it is vertically moved in the reactor pressure vessel 9 after it is separated from the ring 12. The beams 13 and the support plates 23 and 33 are made of shaped steel generally H-shaped in cross section. Bogies 26 for conveying the plugs 11 along the beams 13 are mounted on the respective front end portions of the beams to be movable thereon by the operation of hydraulic piston-cylinder assemblies 27 attached to the beams 13 and wheels 28 are attached to the bogies 26 for smoothly moving them along the beams 13. Guides 29 are secured to the beams for guiding the plugs 11 in accordance with the movement of the bogies 26 and the plugs 11 are detachably connected to the bogies by engaging the brackets 14 of the plugs with connecting members 30 provided at both sides of the bogies 29. The hydraulic piston-cylinder assemblies 20, 22, 25 and 27 attached to the plug support ring 12 and the beam assembly 13 are driven by an operating device disposed on a fuel rod exchanging platform of the nuclear reactor, not shown. The plugging apparatus according to this invention operates as follows: The plugging apparatus preassembled as an integral body on the floor of the reactor container is lifted by the crane located on the ceiling of the reactor container and moved to a position directly above the reactor pressure vessel 9. The plugging apparatus is then gradually lowered to a position as shown in FIG. 2 or FIG. 3 to be immersed in water filled in the pressure vessel 9. During this operation, the guides 15 of the plug support ring 12 are guided along the guide rods 16 mounted on the inner wall of the reactor pressure vessel 9 so as to direct the plugs 11 on the beams 13 towards the corresponding inlet openings of the steam pipes 1 to be plugged. By further lowering the plugging apparatus, the support members 17 of the plug support ring 12 are contacted to and firmly engaged with the support brackets 18 so that the positions of the plugs 11 would align with the inlet openings of the steam pipes 1 and the entire weight of the apparatus is then borne by the brackets 18. Then the hydraulic piston-cylinder assemblies 27 mounted on the beams 13 are operated thereby to simultaneously slide four plugs 11 along the beams and push them into the corresponding inlet openings of the steam pipes 1. After insertion of the plugs 11, the steam pipes 11 are plugged by substantially the same manner, by applying compressed air, described in connection with the conventional plugging apparatus shown in FIG. 1. The plug support ring 12 and the beam assembly are then moved upwardly along the guide rods 16 so that the ring 12 takes a position slightly above the inlet openings of the steam pipes and the hydraulic piston-cylinder assemblies 20 are thereafter operated to push the support members 19 towards the brackets 18. The ring 12 is then lowered together with the beam assembly to rest the support members 19 on the brackets 18. Each of the hydraulic piston-cylinder assemblies 22 operates to push forwardly the rod 21 to firmly engage the plug 11 with the plug support ring 12 thereby preventing the plug from rushing out from the steam pipe due to the counter pressure prevailing in the steam pipe. When it is desired to separate the beams from the plug support ring, four hydraulic piston-cylinder assemblies 25 are operated to withdraw the rods 24 from the ring 12 and the beams 13 are easily lifted through guide members 34 and 35 on the floor as shown in FIG. 5, and in a case where it is desired to inspect or maintain a jet pump, not shown, located at the lower portion in the pressure vessel to agitate the reactor water, can be separated from the plugs 11 and removed so as not to disturb the inspection of the jet pump. According to this invention, four plugs are simultaneously handled as one plugging apparatus to plug corresponding four steam pipes, which largely reduces working time for workers. Even when counter pressure caused by air pressure applied in the steam pipe is added to the plug inserted into the steam pipe, the plug does not rush out into a reactor pressure vessel because the plug is firmly supported by a plug support ring. Moreover, since the plug support ring is constructed to be concentric with the reactor pressure vessel and to have a hollow central portion, the ring does not disturb the operation for changing fuel rods, for example, and since the plug support ring is also constructed to be detachable from a beam assembly, only the ring can be easily removed at a time when a jet pump is to be inspected. In addition, the beam assembly, the plug support ring, and the plugs can be operated and controlled by an operator on a platform disposed at the upper portion of a reactor container vessel, so that irradiation dose for operators can be greatly reduced. In the foregoing, although a preferred embodiment of this invention is described which is applied to a steam pipe of a reactor pressure vessel, it is of course possible to apply the present invention to plug a cylindrical hole of any other apparatus. |
claims | 1. An adjusting device for adjusting imaging parameters of an X-ray apparatus, comprising:a user interface adapted to, with the aid of a preliminary image, allow a user to specify an image region of interest and a visibility criterion desired for this image region; anda data processing device arranged to carry out the following steps:a) calculation of adjusted imaging parameters of the X-ray apparatus, by use of which the visibility criterion is achieved for the given image region of interest; andb) control of the X-ray apparatus on the basis of the calculated, adjusted imaging parameters,wherein the visibility criterion is the contrast-to-noise ratio of the image region of interest. 2. A device as claimed in claim 1, wherein the data processing device is arranged to determine, in a preliminary image, the current value of the visibility criterion for a predetermined image region of interest. 3. A device as claimed in claim 1, wherein the imaging parameters influence the dose per exposure, the intensity and/or the quality of the X-ray radiation generated with the X-ray apparatus. 4. A device as claimed in claim 3, wherein the imaging parameters include the tube current, the tube voltage, the pulse length and/or the setting values of filter elements. 5. A device as claimed in claim 1, wherein, in a preliminary image, on the basis of at least one pixel predefined via the user interface, the data processing device is arranged to segment an image region of interest. 6. A device as claimed in claim 1, wherein the data processing device is arranged to take account of the influence of image processing procedures, in particular noise filtration, when adjusted imaging parameters are calculated. 7. A device as claimed in claim 1, wherein the device includes a control module for feedback control of imaging parameters of the X-ray apparatus during an X-ray image. 8. An adjusting device for adjusting imaging parameters of an X-ray apparatus comprising:a user interface adapted to, with the aid of a preliminary image, allow a user to specify an image region of interest and a visibility criterion desired for an image region; anda data processing device arranged to carry out the following steps:a) calculation of adjusted imaging parameters of the X-ray apparatus, by use of which the predetermined visibility criterion is achieved for the given image region of interest; andb) control of the X-ray apparatus on the basis of the calculated, adjusted imaging parameters,wherein the device includes a dectector for detecting changes in the imaging geometry and that the data processing device is arranged to adjust the calculated imaging parameters in the case of a change in the imaging geometry such that the predetermined visibility criterion is still achieved, andwherein the visibility criterion is a contrast-to-noise ratio of the image region of interest. 9. A device as claimed in claim 8, wherein the data processing device is arranged to determine, in a preliminary image, the current value of the visibility criterion for a predetermined image region of interest. 10. A device as claimed in claim 8, wherein the imaging parameters influence the dose per exposure, the intensity and/or the quality of the X-ray radiation generated with the X-ray apparatus. 11. A device as claimed in claim 10, wherein the imaging parameters include the tube current, the tube voltage, the pulse length and/or the setting values of filter elements. 12. A device as claimed in claim 8, wherein the device includes a control module for feedback control of imaging parameters of the X-ray apparatus during an X-ray image. 13. A device as claimed in claim 8, wherein, in a preliminary image, on the basis of at least one pixel predefined via the user interface, the data processing device is arranged to segment an image region of interest. 14. X-ray apparatus having an adjusting device according to claim 8. 15. A device as claimed in claim 8, wherein the data processing device is arranged to determine, in a preliminary image, the current value of the visibility criterion for a predetermined image region of interest. 16. A device as claimed in claim 8, wherein the imaging parameters influence the dose per exposure, the intensity and/or the quality of the X-ray radiation generated with the X-ray apparatus. 17. A method for adjusting imaging parameters of an X-ray apparatus, comprising the following steps:a) generation of a preliminary image with starting values for the imaging parameters;b) interactive stipulation of an image region of interest and of a visibility criterion desired for this image region;c) calculation of adjusted imaging parameters for the X-ray apparatus, during the use of which the predetermined visibility criterion is achieved for the predetermined image region;d) control of the X-ray apparatus based on the calculated, adjusted imaging parameters. 18. X-ray apparatus having an adjusting device according to claim 1. |
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description | The invention relates to a device for generating terahertz (THz) radiation comprising a short pulse laser with mode locking to which a pump beam is supplied, and a semiconductor component including a resonator mirror, which semiconductor component simultaneously is designed for deriving the THz radiation on the basis of impacting laser pulses. Furthermore, the invention relates to a semiconductor component including a resonator mirror to be used in a laser, which resonator mirror is adapted to enable mode-locked operation of the laser, wherein the semiconductor component simultaneously is designed to generate terahertz (THz) radiation on the basis of impacting laser pulses. Electromagnetic radiation in the terahertz range (1011 Hertz to 1013 Hertz), i.e. in the form of continuous waves just as in the form of pulses, would be usable with great advantage e.g. in spectroscopy, but also in other fields, e.g. in future computers. Various proposals have already been made for the generation of such a terahertz radiation, as e.g. in Sarukura et al., “All-Solid State, THz Radiation Source Using a Saturable Bragg Reflector in a Femtosecond Mode-Locked Laser”, Jpn. J. Appl. Phys., Vol. 36, Part 2, No. 5A, 1 May 1997, pp. L560–L562. In this article, the use of a mode-locked laser for generating short laser pulses in connection with a semiconductor mirror, a saturable Bragg reflector (SBR element), has been described which comprises a quantum well for generating terahertz radiation. The SBR element is installed within the resonator of a mode-locked laser, wherein the impact angle of the laser beam approximately corresponds to the so-called Brewster angle. In this manner, outcoupling of the terahertz radiation is possible. What is disadvantageous, however, is that each laser pulse impacts twice on the SBR element during its roundtrip in the resonator, whereby the terahertz radiation is radiated in four different directions. Thus, an efficient bundling and use of the generated radiation is not possible, and only extremely low outputs of the terahertz radiation—in the range of nW—are achieved. In a further article by Sarukura et al., “THz-radiation Generation from an Intracavity Saturable Bragg Reflector in a Magnetic Field”, Jpn. J. Appl. Phys. Vol. 37, No. 2A, 1 Feb. 1998, pp. L125–L126, a somewhat modified arrangement of a SBR element in connection with a short pulse laser with mode locking is disclosed, wherein the SBR element is used as an end mirror of the laser resonator. There, the SBR element is mounted in the field of a permanent magnet, wherein the magnetic field controls the radiation pattern of the main lobes of the terahertz radiation to thus prevent capture of the radiation within the substrate of the SBR element. With this arrangement of the SBR element as a resonator end mirror, an increase of the output of the terahertz radiation up to a value of 0.8 μW was, in fact, obtained, yet a higher output would still be desirable for practical applications, apart from the fact that the provision of a magnetic field is complex in practice. A similar arrangement with an InAs(indium arsenide) mirror in a magnetic field is disclosed in Liu et al., “Efficient Terahertz Radiation Generation from Bulk InAs Mirror as an Intracavity Terahertz Radiation Emitter”, Jpn. J. Appl. Phys. Vol. 39, Part 2, No. 4B, 15 Apr. 2000, pp. L366–L367. There, the impacting angle of the laser beam on the InAs mirror is very large, in the range of 85°. This mirror again is arranged within the laser resonator, resulting in the already previously mentioned disadvantage that each laser pulse meets the mirror twice and that thus the terahertz radiation is generated in four directions. When carrying out experiments, the average output of the terahertz radiation achieved was in the range of 5 nW, with an average laser resonator output of 4.5 W. A further disadvantage is that with the InAs mirror a separate component is additionally introduced in the laser resonator. Besides, the arrangement of an SBR element in a magnetic field is also known from the earlier article by Liu et al., “THz Radiation from Intracavity Saturable Bragg Reflector in Magnetic Field with Self-Started Mode-Locking by Strained Saturable Bragg Reflector”, Jpn. J. Appl. Phys., Vol. 38, Part 2, No. 11B, 15 Nov. 1999, pp. L1333–L1335. Furthermore, a mode-locked laser with an SBR element is described in Liu et al., “High Average Power Mode Locked Ti:Sapphire Laser with Intracavity Continuous-Wave Amplifier and Strained Saturable Bragg Reflector”, Jpn. J. Appl. Phys., Vol. 38, Part 2, No. 10A, 1 Oct. 1999, pp. L1109–L1111. From EP 606 776 A, furthermore a device for delivering terahertz radiation is known in which an superimposed arrangement of two electrodes on a substrate is provided, between which an LT-GaAs material shall be provided. With the occurrence of laser pulses, the terahertz radiation is generated in the plane of the substrate, resulting in technological disadvantages and a low robustness. Another manner of generating terahertz radiation by using an antenna with a large aperture is described in Fattinger et al., “Terahertz beams”, Appl. Phys. Lett. Vol. 54, No. 6, 6 Feb. 1989, pp. 490–492. Here, the generation of the terahertz radiation is based on a transient photocurrent obtained by optically generated charge carriers which move in an electric field between two electrodes. The semiconductor material used for the emitter typically has a high resistance, with the useful life of the charge carriers being very short. A corresponding arrangement is also described in U.S. Pat. No. 5,729,017 A. It is also known to use compounds such as GaAs (gallium arsenide) compounds, AlGaAs (aluminum-gallium-arsenide) compounds, LT-GaAs compounds and LT-AlGaAs compounds (LT—low temperature) for the semiconductor material in which the charge carriers are produced, cf. also Mitrofanov et al., “Thin terahertz detectors and emitters based on low temperature grown GaAs on sapphire”, Conference on Lasers and Electro-Optics (CLEO 2000). Technical Digest. Postconference Edition. TOPS Vol. 39; IEEE Cat. No. 00CH37088. Opt. Soc. America, Salem, Mass., USA; May 2000; pp. 528–529. The aforementioned low temperature semiconductor materials are applied at low temperatures in the order of 200° C. to 500° C., and they are characterized by short recombination times of the photo charge carriers. In particular, here it is also known that in case of LT-GaAs material with the light-induced transient terahertz radiation a recombination time of the charge carriers of a few ps or below 1 ps is attainable. Departing from the known investigations, it is now an object of the invention to provide a device and a semiconductor component, respectively, with which the generation of terahertz radiation by using a mode-locked short pulse laser is efficiently enabled, wherein also the output of the terahertz radiation shall be substantially higher than in the known arrangements and, preferably, shall also be controllable. In particular, for the terahertz radiation outputs in the range of mW shall be rendered possible. The arrangement according to the invention and of the initially defined type is characterized in that the resonator mirror, preferably a resonator end mirror, is provided with a semiconductor layer which is partially permeable for the laser radiation of the short pulse laser, the absorption edge of the semiconductor layer being below the energy of the laser radiation of the short pulse laser, and electrodes connectable to a bias voltage source being mounted thereon in a manner known per se so as to generate the THz radiation in the electric field and radiate it. Correspondingly, the inventive semiconductor component of the initially defined type is characterized in that on the resonator mirror, preferably on a resonator end mirror, a semiconductor layer partially permeable for the laser radiation is provided, the absorption edge of the semiconductor layer being below the energy of the laser radiation and electrodes connectable to a bias voltage source being mounted thereon in a manner known per se so as to generate the THz radiation in the electric field and radiate it. Thus, the concept of the invention is generally based on combining the semiconductor resonator mirror of the short pulse laser with a semiconductor layer with electrodes which also serve as antennas for the THz radiation, and to generate the desired terahertz radiation in this semiconductor layer on the resonator mirror by means of the laser beam. In doing so, the output of the terahertz radiation can be adjusted or even modulated simply by means of the applied voltage, i.e. the applied electric field. In mote detail, the intensity-rich laser pulse generates movable charge carriers in the semiconductor material applied on the semiconductor resonator mirror; what is important in this context is, of course, that the energy of the laser beam be high enough so as to produce the charge carriers, i.e. the energy of the laser radiation lies above the absorption edge (that is that energy level starting from which electrons are lifted into the conduction band) of the semiconductor material, which therefore has to be chosen accordingly—depending on the type of laser used, which can be done without any problems on the basis of available semiconductor material data. Due to the electric field applied, the thus generated electrons and the holes are brought out of their resting position, and depending on their charge, they will be accelerated in opposite directions. The resultant polarisation leads to a return force, whereby plasma oscillation is obtained. This results in a transient photocurrent which generates the desired terahertz radiation which, for instance, is radiated through the resonator mirror. By means of the applied voltage, the amount of the acceleration of the charge carriers and, consequently, the intensity, or the output power, respectively, of the terahertz radiation can be controlled, or adjusted, respectively. For producing the terahertz radiation, the intensity-rich optic pulses of the short pulse laser are efficiently used, similar as in the suggestions made by Sarukura et al., as explained before, yet a principle of generating the terahertz radiation different therefrom is employed, with the separate semiconductor layer on the resonator mirror, and with the generation of the movable charge carriers in this semiconductor material by means of the laser pulses, similar as described as such e.g. in the aforementioned U.S. Pat. No. 5,729,017 A. Naturally, the semiconductor layer applied on the resonator mirror shall allow the laser radiation substantially to penetrate to the resonator mirror, wherein, however, a part of the energy of the laser radiation is used in the semiconductor layer for generating the charge carriers. On the other hand, the material of the resonator mirror, if the terahertz radiation is delivered throught the latter, must be chosen such that it will be substantially permeable for the terahertz radiation generated. Preferably, the resonator mirror is an end mirror, and in particular, it is formed by a saturable Bragg reflector (SBR element in short) known per se. To avoid undesired saturation effects, it is advantageous if the semiconductor layer is made of a semiconductor material with short recombination time for free electrons. The material of the semiconductor layer suitably is chosen in adaptation to the material of the resonator mirror, it being suitable if the semiconductor layer is a gallium-arsenide (GaAs) layer, in particular a low temperature gallium-arsenide (LT-GaAs) layer. On the other hand, it may also be advantageously provided that the semiconductor layer is an aluminum-gallium-arsenide (AlGaAS) layer, in particular a low temperature aluminum-gallium-arsenide (LT-AlGaAs) layer. Such semiconductor materials can be grown on a Bragg reflector which in turn is made up of layers of aluminum-gallium-arsenide (Al-GaAs)/Aluminum-arsenide (AlAs), these layers being epitaxially applied on a gallium-arsenide (GaAs) substrate. Advantageously, molecular beam epitaxy may be employed for applying the layers. In order to bundle the generated terahertz radiation, it may furthermore be suitable if a dielectric lens, e.g. of silicon (Si), gallium-arsenide (GaAs) or the like, is mounted as a beam control element for the emitted THz radiation on the side of the resonator mirror that faces away from the electrodes. In particular, the electrodes are designed strip-shaped and arranged in parallel to each other, having a width of from 5 μm to a few 10 μm, wherein the distance between the electrodes may be from 30 μm up to a few mm. Typically, the distance between the electrodes is larger than the diameter of the laser beam, at least the dimensions should be chosen such that the intensity center of “gravity” of the beam cross-section of the laser beam is located between the electrodes. The electrodes may me made e.g. of metal, such as gold, aluminum, chromium, platinum-gold-layer systems or titanium-gold-layer systems, yet it is also possible to form the electrodes of a doped semiconductor material, with the semiconductor material electrodes in turn being connected by metallic contacts. With such electrodes or antenna elements for generating the terahertz radiation and the aforementioned dimensions and distances, respectively, bias voltages in the order of 150 volts and more, practically even up to 400 volts, may be applied so as to generate the electric field. The limit is given by the breakdown voltage in the semiconductor material. Preferably, the bias voltage source is adapted to deliver variable bias voltages for adjusting the intensity of the THz radiation and/or for modulating the THz radiation. In FIG. 1, a short pulse laser 1 is schematically illustrated, in which, e.g., the per se known Kerr-lens mode locking principle is used for generating the short pulse. According to FIG. 1, the short pulse laser 1 includes a laser resonator 2 to which a pump beam 3, e.g. an argon laser beam, is supplied. For the sake of simplicity, the pump laser (Argon laser, e.g.) itself has been omitted and belongs to the art. After having passed a lens L1 and a dichroic mirror M2, the pump beam 3 excites a laser crystal 4, a titanium:sapphire solid laser crystal (commonly termed Ti:S in short in the literature and also in the following) in the instant example. The dichroic mirror M2 is permeable for the pump beam 3, yet highly reflective for the Ti:S laser beam. This laser beam, the resonator beam, impacts on a laser mirror M1 and is reflected by the latter to a laser mirror M3 which also serves for outcoupling. This laser mirror M3 again reflects the laser beam back to mirror M1, and from there the laser beam is reflected to laser mirror M2, passing through the laser crystal 4 a second time. From there, the laser beam then is reflected to a resonator end mirror M4 with a saturable Bragg reflector 5, termed SBR element in short hereinafter, whereby a per se common X-folded laser resonator 2 is formed. Via the outcoupling mirror M3, the laser beam is coupled out, with possible compensation means being provided, a compensation platelet 6 as well as a mirror in thin film technique not further shown providing for a dispersion compensation as well as taking care that no undesired reflections will occur in the direction of the laser resonator 2. The laser beam obtained in the manner described in the laser resonator 2 is denoted by 7 in FIG. 1. The laser crystal 4 is a plane-parallel body which is optically non-linear and forms a Kerr element which has a greater effective optical thickness for higher field strengths of the laser beam 7, yet a slighter effective thickness if the field strength, or intensity, respectively, of the laser beam 7 is lower. This per se known Kerr effect is then used for self-focussing of the laser beam 7, i.e. the laser crystal 4 forms a focussing lens for the laser beam 7. In the exemplary embodiment illustrated, the saturable Bragg reflector 5 is used for mode-locking in per se conventional manner. The mirrors M1, M2 are made in per se known thin film technique, i.e. they are each designed with many layers which fulfill their function when reflecting the ultra-short laser pulse which has a large spectral bandwidth. The different wave length components of the laser beam enter to different depths into the layers of the respective mirror before being reflected. By this, the different wave length components are delayed on the respective mirror for different amounts of time; the short-wave components will be reflected rather outwardly, the long-wave components, however, will be reflected deeper within the mirror. This means that the long-wave components will be temporally delayed relative to the short-wave components. In this manner, a dispersion compensation is attained insofar as pulses of a particularly short time range (preferably in the range of 10 femtoseconds and below) have a wide frequency spectrum; this is due to the fact that the different frequency components of the laser beam in the laser crystal 4 “see” a different refraction index, i.e. the optical thickness of the laser crystal 4 is differently large for the various frequency components, and the different frequency components therefore will be differently delayed when passing through the laser crystal 4. This effect is counteracted by the above-mentioned dispersion compensation at the thin film laser mirrors M1, M2. As described above, this is a conventional set-up of a short pulse laser with mode-locking, and a detailed description of the same therefore is not required. What is essential for the sought generation of terahertz radiation 14 is that the resonator mirror M4 is equipped with additional means in a special way, as will be explained in more detail with reference to FIGS. 2 and 3. In detail, the resonator mirror M4 comprises a semiconductor layer 8 as a semiconductor component on the SBR element 5 proper (cf. also FIG. 2 in addition to FIG. 1), which semiconductor layer 8 consists of a semiconductor material with a short recombination time for free electrons. On this semiconductor layer 8, two substantially strip-shaped, parallel-extending electrodes 9, 10 are applied which are connected with terminals 11 and 12, respectively (cf. FIG. 3) for applying a voltage U to the electrodes 9, 10. The distance between the strip-shaped electrodes 9, 10 is denoted by D in FIG. 3 and is chosen such that the impacting laser beam 7 with its beam cross-section 7′ (cf. also FIG. 3) comes to lie substantially between the electrodes 9, 10 during operation—at least the intensity centre of gravity of the beam cross-section 7′ of the laser beam 7 should lie between the electrodes 9, 10 so as to avoid unnecessary losses. This distance D may, e.g., be from 30 μm up to a few mm. The strip-shaped electrodes 9, 10, in turn may have a width B of e.g. from 5 μm up to a few 10 μm. The SBR element 5 as mirror and saturable absorber is assembled in usual manner from a plurality of dielectric layers which, however, are not further illustrated in the drawing and which are applied to a substrate likewise not further visible in detail. The substrate may be made of a conventional material which is substantially permeable for electromagnetic radiation in the THz range, in particular 1011 Hz to 1013 Hz, and it serves as a carrier for the Bragg reflector. A conventional gallium-arsenide(GaAs) substrate with high resistance is used, e.g., which carries layers of aluminum-gallium-arsenide, or aluminum-arsenide, respectively, which are epitaxially grown on the gallium-arsenide substrate. Of course, however, also other combinations of semiconductor materials and dielectric materials are possible to build up the Bragg reflector, and also other conventional production methods (thin film techniques) may be used. The semiconductor layer 8 forms a saturable absorber, and it consists, e.g. in the case of a Bragg reflector with aluminum-gallium-arsenide, or aluminum-arsenide layers, of a gallium-arsenide applied at low temperature, a so-called LT (low temperature) GaAs layer, which, e.g., is applied by molecular beam epitaxy (MBE) and has a saturable absorption at a wave length of, e.g., approximately 800 nm and a recombination time in the order of picoseconds. Another possible way is to use LT-AlGaAs for the semiconductor layer 8, if shorter laser wavelengths are used. The thickness of the semiconductor layer 8 is chosen with a view to the sought pulse energy, which is absorbed, wherein the function of the Bragg reflector 5 should not be deteriorated. In one concrete exemplary embodiment, an LT-GaAs layer having a thickness of 326 nm was grown as semiconductor layer 8 at 220° C. on an AlGaAs/AlAs Bragg reflector structure with a GaAs quantum well. Then the semiconductor layer 8 was heat-treated in a manner known per se at 660° C. for 10 min, and subsequently electrodes 9, 10 of titanium-gold were applied to the upper side of the semiconductor layer 8. Alternatively, metal electrodes 9, 10 of aluminum, chromium, platinum-gold etc. could be used; the choice of the metal for the electrodes 9, 10 is not critical. The width B of the electrodes was 10 μm, and the distance D between the electrodes was 50 μm. As a bias voltage U, a direct voltage of 150 volts was applied to the thus obtained THz emitter. For bundling the THz radiation 14 generated and to be delivered, a collimator-beam control element in the form of a dielectric lens 13 can be applied to the rear side or outer side of the resonator mirror M4 located opposite the electrodes 9, 10 and illustrated in dot-and-dash lines in FIG. 2 (i.e. at the rear side of the substrate of the SBR element 5), this dielectric lens 13 bundling the THz radiation 14 in the desired direction. As the material for this beam control element 13, high-resistance silicon, semiinsulating gallium-arsenide or sapphire may, e.g., be used. Such a dielectric lens 13 was also present in the previously described practical exemplary embodiment. In the case of the previously described practical exemplary embodiment, the resonator mirror M4 thus formed was attached as end mirror in the laser resonator 2 of the short pulse laser with mode-locking, and the electrodes 9, 10 were connected to an external voltage supply unit not further illustrated in FIGS. 2 and 3, respectively, for applying the bias voltage U. Due to the saturable absorber (GaAs quantum well) in the laser resonator 2, a mode-locking was achieved independently of the bias voltage at electrodes 9, 10. Without a bias voltage U at the electrodes 9, 10, no measurable THz radiation could be detected, however, when applying the bias voltage U to the semiconductor layer 8 via the electrodes 9, 10, there resulted a THz radiation, the intensity of which increased with the bias voltage. In FIG. 4, the resultant, substantially linear correlation between the pulse amplitude of the THz radiation (in μV) and the applied bias voltage (in V) is visible. The average radiation output was measured with a calibrated silicon bolometer, wherein with the present simple test embodiment, already a value of 1.5 μW was obtained at an average resonator output of 900 mW. The typical shape of the transient THz signal which is generated in this manner in the resonator mirror M4, i.e. semiconductor component, is illustrated in FIG. 5. As can be seen, there is substantially one single narrow pulse, which means that a broadband signal is achieved. For this desired occurrence of a single pulse (instead of several decaying pulses), the short recombination time of the charge carriers in the semiconductor material is co-responsible, and this is particularly achieved in case of a low temperature application of the semiconductor layer 8. The waveshape of the THz pulse illustrated in FIG. 5 (the amplitude is shown in arbitrary units) was registered by means of an electrooptical detector. In the frequency range there results a corresponding amplitude course (again with the amplitude in arbitrary units) as shown in FIG. 6. The frequency spectrum has a maximum at approximately 0.5 THz and extends to up to approximately 2.5 THz. This THz radiation is voltage-controlled by means of the bias voltage U at the emitter electrodes 9, 10, wherein also a modulation with frequencies of up to 50 kHz (cf. the following explanations relating to FIG. 7) was tested. The generated THz radiation 14 is indicated by an arrow and by dashed lines in FIG. 2 and by an arrow in FIG. 1. Instead of metallic electrodes, also electrodes 9, 10 of highly doped semiconductor material, such as, e.g., gallium-arsenide layers, are conceivable for generating the THz radiation 14. Such an embodiment will be advantageous if the beam cross-section 7′ of the laser beam 7 has a larger diameter than the distance between the electrodes 9, 10, and reflections on the metallic electrodes 9, 10 would impair the laser activity. The electrodes 9, 10 then will be made e.g. in an etching process (wet etching or dry chemical etching), and externally of the impacting region of this laser beam 7, metallic contacts 9′, 10′ may be applied to the electrodes 9, 10 of semiconductor material, as schematically illustrated in FIG. 7 at a modified resonator end mirror M4. The width of the strip-shaped electrodes 9, 10 may, as mentioned, quite generally be e.g. from 5 μm up to several 10 μm so as to keep low the entire resistance. The distance between the electrodes 9, 10 may be from 10 μm or several 10 μm up to several mm. Here, the limit will be determined by the desired breakdown voltage, on the one hand, and by the beam cross-section 7′ of the laser beam 7 on the THz emitter, on the other hand. Mostly, the distance between the electrodes 9, 10 will be larger than the diameter of the laser beam 7. Besides, in FIG. 7 again the embodiment of the resonator end mirror M4 with the SBR element 5 and the semiconductor layer 8 is visible. Furthermore, it is illustrated in FIG. 7 that the one electrode 10 is connected to ground 15 via the metallic contact 10′, whereas the other electrode 9, via its metallic contact 9′, is connected to a signal source 16 with variable frequency, with a high voltage amplifier 17 interposed. In this manner, the THz radiation generated (14 in FIGS. 1 and 2) can be controlled in its intensity according to the frequency of the bias voltage U. Of course, circuits 18 known for frequency variation and not further visible in FIG. 7 can be used in connection with the signal source, i.e. bias voltage source 16. |
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abstract | The wafer scanning device causes a wafer to scan in a vacuum area and includes a holder 10 to hold a wafer, a ball screw 20 to move the holder 10 to scan, a motor 50 to drive the ball screw 20 and an integrally formed support frame 60. While the holder 10 and the ball screw 20 are installed in the vacuum area, a transmission mechanism offset from the line of travel of the ball screw 20 and the motor 50 are installed in the atmosphere. Thus the wafer scanning device improves responsiveness with respect to the scanning speed control, enhances the uniformity of the scanning speed, has the motor or the like arranged properly and achieves the tilt of a wafer in a most preferable manner. |
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summary | ||
abstract | A glitch duration threshold is determined based on an allowable dose uniformity, a number of passes of a workpiece through an ion beam, a translation velocity, and a beam size. A beam dropout checking routine repeatedly measures beam current during implantation. A beam dropout counter is reset each time beam current is sufficient. On a first observation of beam dropout, a counter is incremented and a position of the workpiece is recorded. On each succeeding measurement, the counter is incremented if beam dropout continues, or reset if beam is sufficient. Thus, the counter indicates a length of each dropout in a unit associated with the measurement interval. The implant routine stops only when the counter exceeds the glitch duration threshold and a repair routine is performed, comprising recalculating the glitch duration threshold based on one fewer translations of the workpiece through the beam, and performing the implant routine starting at the stored position. |
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description | This application claims the benefit of the following U.S. provisional patent applications: Provisional Patent Application No. 60/430,005, filed Dec. 2, 2002; Provisional Patent Application No. 60/449,236, filed Feb. 20, 2003; and a Provisional Patent Application No. 60/479,756, filed Jun. 18, 2003. This application is a continuation-in-part of U.S. patent application Ser. No. 10/289,209, filed Nov. 7, 2002 now U.S. Pat. No. 6,841,787, and published as U.S. Patent Application Publication 2003/0122091. All of these related applications are assigned to the assignee of the present patent application, and their disclosures are incorporated herein by reference. The present invention relates generally to methods and systems for writing a master image onto a substrate, and specifically to direct writing of lithographic patterns onto wafers, masks, reticles and other substrates used in production of microelectronic devices. In semiconductor device production, circuit patterns are commonly written onto semiconductor substrates by lithographic processes. In image-projection lithography, radiation is projected through a master mask or reticle onto a photoresist layer on the substrate in order to create the circuit patterns. In direct-write systems, on the other hand, the circuit pattern is written onto the substrate by directly modulating a beam of light or electrons, which is then incident on the photoresist layer. Masks and reticles may also be produced by this sort of direct-write process. One method known in the art for direct writing of circuit patterns is to scan a focused laser beam or electron beam over the surface of the substrate in a pattern of multiple, parallel lines, known as a raster. Each line consists of a single row of pixels in the master image that is to be written on the substrate. At each pixel location, the beam intensity is controlled to give the desired pixel exposure. A direct-writing photolithography system of this sort is described, for example, in U.S. Pat. No. 5,635,976, whose disclosure is incorporated herein by reference. Alternatively, it is possible to write an entire frame of pixels on the substrate simultaneously, using a spatial light modulator (SLM) to create the desired pattern. For example, U.S. Pat. No. 5,691,541, whose disclosure is incorporated herein by reference, describes a lithography system in which a programmable array of binary light valves or switches is programmed to replicate a portion of the circuit pattern each time an illuminating light source is flashed. The substrate is mounted on a scanning stage. The stage motion and the pattern of the programmable array are synchronized with the illumination system so that each flash accurately positions the image of the pattern on the substrate. In this manner, the entire image is built up of multiple flashes. In one embodiment, the light pattern projected by the programmable array is incident not on the substrate, but rather on an electron-emitting photocathode. The light pattern causes the photocathode to emit electrons, generating a corresponding electron image that is focused onto the substrate by electron optics. By using electrons rather than photons to create the final image, it is possible to achieve higher resolution. Another approach to electron beam shaping is described in U.S. Pat. No. 6,014,200, whose disclosure is also incorporated herein by reference. This patent describes an electron beam lithography system that uses multi-aperture arrays to shape an electron beam. The electron beam is divided up into multiple beamlets. Deflection logic is then used to blank selected beamlets in order to create selected beam patterns. The unblanked beamlets are directed onto a surface to be exposed. A moving objective lens (MOL) may be used in scanning the beam over the surface. Other systems for direct-light lithography based on spatial light modulators are described in U.S. Pat. No. 6,285,488, U.S. Pat. No. 6,312,134, U.S. Pat. No. 6,399,261, U.S. Pat. No. 6,493,867 and U.S. Patent Application Publication 2002/0024714, whose disclosures are incorporated herein by reference, as well as in the above-mentioned U.S. Patent Application Publication 2003/0122091. In some of these systems, the SLM is operated to project gray-scale images onto the substrate, with multiple gray levels, rather than binary images as in the system described in U.S. Pat. No. 5,691,541. For example, U.S. Patent Application Publication 2002/0024714 describes apparatus for creating a pattern on a workpiece, wherein the modulating elements of the SLM can be set by drive signals to more than two different states, thus giving intermediate exposure values of the light incident on the workpiece. U.S. Pat. No. 6,285,488 describes a method for creating a large pattern on a workpiece by stitching together partial images created by different light pulses. The partial images are made to overlap one another, and are projected with reduced light intensity in the overlap region in order to reduce the visibility of the edges between the partial images. Embodiments of the present invention provide improved methods and systems for writing a master image onto a substrate, combining the advantages of raster scanning and frame projection. In these embodiments, the master image is divided into a matrix of frames, each comprising an array of pixels defining a respective frame image that is derived from the master image. An electron beam is scanned in a raster pattern over the substrate, so as to traverse the positions of the frames in the matrix. Electron optics focus the beam onto the substrate so that in each frame position along the scan, the beam covers the area of a single frame on the substrate. At each frame position, the beam is shaped in accordance with the corresponding frame image at that position. In this manner, the beam writes all the pixels in each frame at the appropriate intensity levels (also referred to as pixel values), while writing multiple pixels in each frame at the same time. Typically, all the pixels in the frame that have the same pixel value are written onto the substrate substantially simultaneously, and all the pixels in the frame are written by the beam simultaneously or within a short period of time, before the beam is scanned to the next frame position in the raster. This approach has the advantages of high resolution and high accuracy in reproducing the features of the master image on the substrate, along with high throughput thanks to the raster frame scanning scheme. In some embodiments of the present invention, the electron beam is shaped by projecting a light pattern corresponding to each frame image onto a photocathode, which then emits electrons in a spatial pattern proportional to the incident light intensity. In other embodiments, an array of miniature electron beam blankers is operated to modulate the electron beam directly. In some embodiments of the present invention, the master image corresponds to an integrated circuit production mask, and the systems and methods described herein are used in direct writing of the circuit patterns in the mask onto semiconductor wafers. In other embodiments, these systems and methods may be used in creating masks and reticles for use in projection lithography, as well as in patterning flat panel displays and other types of electronic circuits, and in other applications in which high-resolution master images must be written onto a substrate with high accuracy. There is therefore provided, in accordance with an embodiment of the present invention, a method for writing a master image on a substrate, including: dividing the master image into a matrix of frames, each frame including an array of pixels defining a respective frame image in a respective frame position within the master image; scanning an electron beam in a raster pattern over the substrate; and shaping the electron beam responsively to the respective frame image of each of the frames as the electron beam is scanned over the respective frame position on the substrate, so that in each frame, the electron beam simultaneously writes a multiplicity of the pixels onto the substrate. Typically, each of the pixels has a respective pixel value, and shaping the electron beam includes writing all the pixels having the same pixel value in the respective frame image substantially simultaneously, and possibly writing all the pixels substantially simultaneously. Additionally or alternatively, shaping the electron beam includes writing all the pixels in each frame within a short period of time, before scanning the electron beam to a successive frame in the raster pattern. Further additionally or alternatively, shaping the electron beam includes focusing the electron beam onto the substrate so that at each position in the scan, the focused electron beam covers an area of a single frame. In a disclosed embodiment, scanning the electron beam includes mechanically scanning the substrate along a primary scan direction, and electrically scanning the electron beam in a secondary scan direction, transverse to the primary scan direction. Typically, mechanically scanning the substrate includes moving the substrate in the primary scan direction substantially continuously, and electrically scanning the electron beam includes electrically shifting the electron beam in the primary scan direction so as to compensate for motion of the substrate. Additionally or alternatively, electrically scanning the electron beam includes scanning the electron beam in the secondary scan direction in steps corresponding to the frames in a row of the matrix. Alternatively, mechanically scanning the substrate may include stepping the substrate to the desired locations, thus eliminating the need for electrical compensation of the electron beam. In some embodiments, shaping the electron beam includes dividing the electron beam into multiple beamlets, and selectively blocking the beamlets responsively to the respective frame image of each of the frames. Typically, each of the pixels has a respective pixel value, and selectively blocking the beamlets includes controlling a duration of blocking each of the beamlets responsively to the respective pixel value. Additionally or alternatively, selectively blocking the beamlets includes selectively deflecting the beamlets so that the deflected beamlets do not impinge on the substrate. Selectively deflecting the beamlets may include directing each of the beamlets through a respective aperture among a plurality of apertures in a multi-blanker array, and applying a deflecting field in the respective aperture. In a disclosed embodiment, the multi-blanker array includes a semiconductor substrate, through which the apertures are etched, having electrodes formed thereon for applying the deflecting field. Typically, scanning the electron beam includes applying a controlled deflection to the beamlets that are not blocked. Additionally or alternatively, shaping the electron beam further includes focusing the beamlets so as to demagnify the frame image formed by the beamlets that impinge on the substrate. In a disclosed embodiment, focusing the beamlets includes forming the frame image on the substrate with a pixel size approximately in the range of 25 to 35 nm. In other embodiments, shaping the electron beam includes modulating a beam of optical radiation responsively to the respective frame image of each of the frames, and converting the modulated beam of optical radiation into the shaped electron beam. Typically, converting the modulated beam of optical radiation includes directing the modulated beam of optical radiation to impinge on a photocathode, so that the photocathode emits electrons responsively to the optical radiation, and shaping the electron beam further includes accelerating the electrons emitted by the photocathode toward the substrate. Scanning the electron beam typically includes applying a controlled deflection to the accelerated electrons. Additionally or alternatively, directing the modulated beam of optical radiation includes focusing the modulated beam of optical radiation so as to form a demagnified image on the photocathode, and accelerating the electrons includes focusing the electrons that impinge on the substrate so as to further demagnify the demagnified image. In a disclosed embodiment, modulating the beam of optical radiation includes creating an optical image having a first pixel size, and focusing the electrons that impinge on the substrate includes forming an electron image having a second pixel size that is less than about 1/100 of the first pixel size. Typically, the second pixel size is less than about 1/400 of the first pixel size, and focusing the electrons that impinge on the substrate includes forming an electron image having a pixel size approximately in the range of 25 to 35 nm. In disclosed embodiments, modulating the beam of optical radiation includes directing the beam of optical radiation to impinge on spatial light modulator (SLM) including at least one array of micromirrors, and controlling respective states (or orientations) of the micromirrors responsively to the respective frame image. Typically, each of the micromirrors corresponds to a pixel in the respective frame image and has an “on” position and an “off” position, and controlling the respective states includes setting a respective time during which each of the micromirrors is to be in the “on” position responsively to the corresponding pixel in the respective frame image. Setting the respective time may include controlling a length of time during which each of the micromirrors is to be in the “on” position responsively to a gray-scale pixel value of the corresponding pixel. Alternatively, directing the beam of optical radiation includes varying an intensity of the beam of optical radiation so that the intensity has different values in a plurality of different time slots, and setting the respective time includes selecting the time slots during which each of the micromirrors is to be in the “on” position responsively to a gray-scale pixel value of the corresponding pixel. In another embodiment, the at least one array of micromirrors includes a plurality of arrays of micromirrors, which are aligned in mutual registration such that each of the micromirrors in each of the arrays corresponds to a pixel in the respective frame image and has an “on” position and an “off” position, and directing the beam of optical radiation includes directing at least a portion of the beam of optical radiation to impinge on each of the plurality of the arrays so that the arrays of micromirrors create respective partial frame images having respective sets of intensity levels, and combining the partial frame images to produce the frame image. Typically, directing at least the portion of the beam of optical radiation includes directing at least the portion of the beam to impinge on the arrays in succession, so that the partial frame images are created sequentially and not simultaneously. In a disclosed embodiment, the substrate includes a semiconductor wafer, and the master image includes a circuit pattern, and scanning and shaping the electron beam includes writing the circuit pattern on the wafer. There is also provided, in accordance with an embodiment of the present invention, a method for writing a master image on a substrate, including: dividing the master image into a matrix of frames, each frame including an overlap region in which the frame overlaps one or more other frames adjacent thereto in the matrix; identifying a feature of the master image in the overlap region between first and second frames in the matrix; and writing the matrix of frames onto the substrate, while applying an overlap writing procedure to the identified feature. Typically, applying the overlap writing procedure includes, if the feature does not extend outside the overlap region into either of the first and second frames, writing the feature in one of the first and second frames but not in the other of the first and second frames. Additionally or alternatively, applying the overlap writing procedure includes, if the feature extends outside the overlap region into the first frame but not into the second frame, writing the feature in the first frame using a first writing procedure, and if the feature extends outside the overlap region into both the first and second frames, writing the feature in both the first and second frames using a second writing procedure, different from the first writing procedure. In a disclosed embodiment, writing the feature in the first frame using the first writing procedure includes writing the feature in the first frame but not in the second frame, and writing the feature in both the first and second frames using the second writing procedure includes blending a portion of the feature in the overlap region. Typically, blending the portion of the feature includes writing the portion of the feature with reduced intensity at some pixels in each of the first and second frames, so as to avoid discontinuity in the feature due to imperfect registration between the first and second frames. There is additionally provided, in accordance with an embodiment of the present invention, a method for writing a frame image on a substrate, including: directing a beam of radiation to impinge on the substrate; shaping the beam responsively to a known reference pattern, so as to generate a reference image; comparing the reference image to the reference pattern so as to map a distortion of the pattern; modifying a frame pattern so as to correct for the mapped distortion; and shaping the beam responsively to the modified frame pattern so as to write the frame image on the substrate, thereby reducing the distortion in the frame image. Typically, mapping the distortion includes mapping a displacement of one or more pixels in the reference image. Additionally or alternatively, mapping the distortion includes computing an inverse transformation to the distortion, and wherein modifying the frame pattern includes applying the inverse transformation to the frame pattern. Comparing the reference image to the reference pattern may further include detecting a deviation in the image comprising at least one of an image displacement, an image rotation and an intensity deviation of one or more pixels in the reference image, wherein modifying the frame pattern includes correcting for the deviation. Typically, the beam of radiation includes an electron beam. There is further provided, in accordance with an embodiment of the present invention, a method for generating an electron beam, including: enclosing a photocathode in an enclosure, which includes a window and a membrane; irradiating the photocathode through the window with modulated optical radiation so as to cause the photocathode, responsively to the modulated optical radiation, to generate a modulated beam of electrons; and directing the electrons so that the modulated beam exits the enclosure through the membrane. Typically, enclosing the photocathode in the enclosure includes evacuating the enclosure so as to reduce a partial pressure of oxygen in the enclosure to less than about 10−7 torr. In a disclosed embodiment, the membrane has a thickness less than 1 μm, and possibly less than 100 nm. In a further embodiment, irradiating the photocathode includes irradiating a portion of the photocathode, causing the electrons to exit the enclosure through an area of the membrane, and directing the modulated optical radiation so as to vary the portion of the photocathode that is irradiated, so that the area of the membrane through which the electrons exit the enclosure varies accordingly. There is moreover provided, in accordance with an embodiment of the present invention, apparatus for writing a master image on a substrate, including: a controller, which is adapted to divide the master image into a matrix of frames, each frame including an array of pixels defining a respective frame image in a respective frame position within the master image; a translation device, which is adapted to cause an electron beam to scan over the substrate in a primary scan direction; electron optics, which are adapted to scan the electron beam in a secondary scan direction, transverse to the primary scan direction, so that the electron beam is scanned in a raster pattern over the substrate; and an electron beam generator, which is adapted to generate and shape the electron beam responsively to the respective frame image of each of the frames as the electron beam is scanned over the respective frame position on the substrate, so that in each frame, the electron beam simultaneously writes a multiplicity of the pixels onto the substrate. In a disclosed embodiment, the translation device includes a translation stage, which is adapted to translate the substrate along the primary scan direction. In some embodiments, the electron beam generator includes a multi-lens array, which is adapted to divide the electron beam into multiple beamlets, and a multi-beam blanker, which is aligned to selectively block the beamlets responsively to the respective frame image of each of the frames. In one embodiment, the multi-beam blanker includes a plurality of apertures, which are aligned so that each of the beamlets passes through a respective aperture among the plurality of apertures, and electrodes, which are respectively associated with each of the apertures, and are coupled to apply a deflecting field in the respective aperture. The multi-blanker array may include a semiconductor substrate, through which the apertures are etched, and on which the electrodes are formed in proximity to the respective apertures. In another embodiment, the electron beam generator includes an optics module, which is adapted to modulate a beam of optical radiation responsively to the respective frame image of each of the frames, and a photocathode, on which the modulated beam of optical radiation is incident, and which is adapted to emit electrons responsively to the optical radiation, so as to generate and shape the electron beam. Typically, the optics module includes an optical objective, which is adapted to focus the modulated beam of optical radiation so as to form a demagnified image on the cathode, and the electron optics include an electron objective, which is adapted to focus the electrons that impinge on the substrate so as to further demagnify the demagnified image. Additionally or alternatively, the optics module includes a spatial light modulator (SLM) including at least one array of micromirrors, on which the beam of optical radiation is incident, and the controller is coupled to cause the SLM to modulate the beam of optical radiation by controlling respective orientations of the micromirrors responsively to the respective frame image. There is furthermore provided, in accordance with an embodiment of the present invention, apparatus for writing a master image on a substrate, including: a radiation source, which is adapted to write a matrix of frames onto a substrate; and a controller, which is adapted to divide the master image into the matrix of frames to be written by the radiation source, each frame including an overlap region in which the frame overlaps one or more other frames adjacent thereto in the matrix, wherein the controller is adapted to identify a feature of the master image in the overlap region between first and second frames in the matrix, and to cause the radiation source to write the matrix of frames onto the substrate while applying an overlap writing procedure to the identified feature. There is also provided, in accordance with an embodiment of the present invention, apparatus for writing a frame image on a substrate, including: a radiation source, which is adapted to direct a beam of radiation to impinge on the substrate; and a controller, which is coupled to cause the radiation source to shape the beam responsively to a known reference pattern, so as to generate a reference image, and which is adapted to compare the reference image to the reference pattern so as to map a distortion of the pattern, and which is further adapted to modify a frame pattern so as to correct for the mapped distortion, and to cause the radiation source to shape the beam responsively to the modified frame pattern so as to write the frame image on the substrate, thereby reducing the distortion in the frame image. There is additionally provided, in accordance with an embodiment of the present invention, apparatus for generating an electron beam, including: an evacuable enclosure, which includes an optical window adapted for passage of modulated optical radiation therethrough and a membrane adapted for passage of an electron beam therethrough; a photocathode, which is arranged in the enclosure so that the modulated optical radiation impinges on the photocathode, and which is adapted, responsively to the modulated optical radiation, to generate a modulated beam of electrons; and electron optics, associated with the enclosure, which are configured to direct the modulated beam of electrons through the membrane. The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: FIG. 1 is a schematic, partly pictorial illustration of a system 20 for direct-write lithography on a semiconductor wafer 22, in accordance with an embodiment of the present invention. A master image, which typically contains image features corresponding to a layer of circuit elements to be formed on wafer 22, is divided up into a matrix of frames 32 by a controller 28. Each frame 32 contains a frame image, which is a small subset of the master image. An electron beam (e-beam) generator 24 generates an electron beam, which is scanned over wafer 22 in a raster pattern by electron optics 26, operating in conjunction with a translation device, such as a translation stage 30 on which wafer 22 is mounted. Optics 26 focus the electron beam to a size on wafer 22 that is equal to the size of a single frame. As the electron beam is scanned over the position of each of the frames in the raster pattern, e-beam generator 24 spatially shapes the beam so as to write the appropriate frame image in each position. Typically, the frame images are defined as gray-scale images, and the e-beam is modulated so as to write each pixel at the proper gray-scale intensity level. Controller 28 monitors and controls the operation of e-beam generator 24, electron optics 26 and stage 30, as described hereinbelow. FIG. 2 is a schematic top view of wafer 22, showing details of the raster pattern of frames 32, in accordance with an embodiment of the present invention. Here it is assumed that stage 30 scans wafer 22 in the primary scan direction, identified here as the X-direction, as indicated by an arrow 44 in FIG. 2. Meanwhile, electron optics 26 scan the electron beam across the wafer in the Y-direction, i.e., the secondary scan direction, transverse to the primary scan direction, as indicated by an arrow 40. The Y-direction scanning covers an area 42 that is approximately N frames wide. Frames 32 are labeled in FIG. 2 according to their sequential scan order. In other words, e-beam generator 24, electron optics 26 and stage 30 are timed so that the appropriate frame image is incident on wafer 22 in the scan position of each frame 32, and so that the scan covers a complete row of N frames in the Y-direction in the time it takes stage 30 to advance by a single frame in the X-direction. After the electron beam writes frame N, optics 26 return the beam to write frame N+1 at the beginning of the next row, and so forth. Typically, each frame 32 includes about 1000×1000 pixels, with a pixel pitch on wafer 22 between about 25 and 35 nm. Thus, each frame has a height 46 and a width 48 that are between about 25 and 35 μm, while N is typically between about 20 and 30. Based on these exemplary figures, it can be seen that a complete raster frame scan over wafer 22 in the X-direction covers a stripe whose width (in the Y-direction) is between 0.5 and 1 mm. Multiple parallel stripes may be scanned in this manner in order to cover the entire wafer surface. Furthermore, e-beam generator 24 and optics 26 may be controlled to scan over and write each frame multiple times, in order to ensure that the entire master image is accurately written on the wafer. Note that the above figures regarding frame size, pixel size and scan width are given here only by way of example. Pixel sizes, frame sizes and scan widths both greater than and less than these values may be used instead, depending on application requirements and system capabilities. The frame images to be written onto wafer 22 are typically defined prior to beginning the scan of the wafer in system 20, by dividing up the master image into a matrix of frames 32 of the appropriate size. Controller 28 loads each frame image into e-beam generator 24 at the appropriate point in the scan. In order to avoid discontinuities in features written on wafer 22 due to imperfect registration between different frames, the frames are preferably defined so that each frame overlaps with its neighbors. Typically, an overlap region 50 between adjacent frames of 1000×1000 pixels is about 10% of the frame width, for example, 128 pixels wide. The frame images are adjusted to ensure that features that fall inside overlap region 50 are written properly on wafer 22, as described hereinbelow with reference to FIGS. 4A and 4B. Alternatively, non-overlapping frames may be used. FIGS. 3A and 3B are schematic plots of electrical signals 54 and 56, which are used in controlling deflection of the electron beam by optics 26, in accordance with an embodiment of the present invention. Signal 54, which controls the Y-direction scan, comprises a sequence of N steps, separated in time by the frame period of e-beam generator 24, which is typically about 100 μs. Alternatively, longer or shorter frame periods may be used. After the Nth step, signal 54 retraces to the opposite end of the Y-direction scan to begin scanning the next row. Alternatively, signal 54 may be modified so that the next row may be scanned in the opposite direction. Typically, stage 30 scans wafer 22 continuously in the X-direction. Alternatively, the X-direction scan may be accomplished by another translation device, which scans electron optics 26 or the electron beam itself in the X-direction while wafer 22 is stationary. To compensate for the X-direction motion of wafer 22 over the duration of each row scan in the Y-direction, signal 56 is applied to optics 26 in order to deflect the beam continuously in the X-direction. In other words, during each row scan, as stage 30 advances, optics 26 progressively deflect the beam in the opposite direction by the appropriate amount so that all the frames in the row are aligned at the same X-coordinates, and image blur due to the X-direction motion of the wafer is avoided. Alternatively, the continuous mechanical scanning in the X direction may be replaced by stepping the stage to its desired location, thus eliminating the need for electrical compensation of the electron beam angle. Preferably, stage 30 provides position feedback to controller 28 of both X- and Y-deviations, by means of interferometric position measurements, for example. Based on this feedback, the controller determines the precise amount by which the electron beam must be deflected, and adjusts signals 54 and 56 accordingly. Alternatively or additionally, other methods known in the art may be used for carrying out the X- and Y-direction scanning. For example, U.S. Pat. No. 6,262,429, whose disclosure is incorporated herein by reference, describes a scanning electron beam system that includes means for retrograde scanning, which may be applied in scanning the electron beam in system 20. FIG. 4A is a schematic, enlarged view of overlap region 50 between two frames 60 and 62 in a master image to be written on a substrate. Overlap region 50 is bounded by a right edge 64 of frame 60 and a left edge 66 of frame 62. For the sake of simplicity, FIGS. 4A–4C and the following discussion refer to overlapping of frames at the horizontal (X) direction. The methods described below for treating overlap regions between frames may be applied, mutatis mutandis, to frame overlap in the vertical (Y) direction, as well as to regions in which four frames overlap at the corners of the frames. Three types of image features are shown in FIG. 4A: An extended feature 68, which crosses overlap region 50 and extends beyond the overlap region into both of frames 60 and 62; A partially-extended feature 70, which continues from overlap region 50 into frame 62, but does not extend beyond the overlap region into frame 60; and A confined feature 72, which is completely contained within overlap region 50. In generating the frame images to be used by e-beam generator 24, controller 28 (or an image pre-processor, not shown in the figures) treats each of these feature types differently. FIG. 4B is a schematic, enlarged view of portions of the frame images of frames 60 and 62, based on the feature type classifications described above, in accordance with an embodiment of the present invention. Extended feature 68 is reproduced in both of frames 60 and 62, using a first writing procedure to deal with the overlap. This writing procedure is applied in such a way that portion 74 of the extended feature that is located in overlap region 50 is blended, however, in order to minimize the possible effect of misregistration between the frames. Typically, the intensity of the pixels in portion 74 in each of the frames is reduced, so that the sum of the intensities at each pixel is equal to the total intensity of the original feature 68 in the master image. FIG. 4C is a schematic plot of the intensity of the electron beam that is used to write features 68, 70 and 72 in frames 60 and 62, in accordance with an embodiment of the present invention. The beam intensity used to write frame 60 is shown by solid lines in this figure, while that used to write frame 62 is shown by dashed lines. In this example, the intensity of portion 74 in frame 60 decreases gradually from left to right, while the intensity in frame 62 decreases gradually from right to left in frame 62. Alternatively, the intensity reduction method described in the above-mentioned U.S. Pat. No. 6,285,488 may be used for this purpose. FIG. 4D is a schematic, enlarged view of overlap region 50 between frames 60 and 62 as written on wafer 22 following application of the blending procedure described above, in accordance with an embodiment of the present invention. In the example shown here, frame 60 is displaced vertically relative to frame 62 when the frames are written on wafer 22, as may occur due to any system misalignment. In this case, the portion of feature 68 in overlap region 50 (as a result of the blending shown in FIG. 4B) has the form of a diagonal connecting the mutually-offset horizontal portions of the feature outside the overlap region. This sort of diagonal connection will have minimal or no effect on the integrated circuit of which it forms a part. If blending were not used, there would be a sharp step in feature 68 between frames 60 and 62, which could affect circuit performance. Partially-extended feature 70, on the other hand, is reproduced only in frame 62. In this case, a second writing procedure is used, in which feature 70 is reproduced in frame 62 at full intensity, as illustrated in FIGS. 4B and 4C. There is no need to blend this feature, since it will be accurately reproduced regardless of any misregistration between frames 60 and 62. Similarly, there is no need to blend confined feature 72. Therefore, feature 72 is reproduced only in frame 60 (or it may alternatively be reproduced only in frame 62). Assignment of feature 72 to one of the frames is arbitrary, and any suitable assignment rule may be used for dealing with contained features of this sort. The selective blending illustrated by FIGS. 4B–4D, in which only features extending beyond the overlap region into both adjacent frames are blended, is useful in ensuring that partially-extended and confined features are not blended unnecessarily, and are therefore reproduced on wafer 22 with maximal fidelity. Alternatively, other blending methods may be applied in overlap region 50. For example, feature 72 may be printed in both frames 60 and 62 at half intensity in each, so as to average the system errors. Further alternatively, a feature-independent blending method, such as “always blend” or “never blend,” may be applied. Note that the definition of overlap regions 50 and blending of features in the overlap regions may take place either before or after rasterization of the frame images, as described below with reference to FIG. 6. FIG. 5 is a flow chart that schematically illustrates a method for generating frame images to be written by e-beam generator 24 so as to compensate for distortions introduced by the e-beam generator and by electron optics 26, in accordance with an embodiment of the present invention. This method is typically used to correct for distortions of low spatial frequency (relative to the pixel density), such as barrel and pincushion distortion. For this purpose, the distortions are first mapped, by inputting a known, reference image pattern to e-beam generator 24, at a reference input step 80. The e-beam generator modulates the electron beam in accordance with the reference image pattern, and optics 26 focus the modulated beam onto a reference sample, at a pattern creation step 82. For example, the reference pattern may comprise a set of well-defined, straight edges or other regular geometrical elements, and the reference sample may comprise a substrate with an overlying layer of photoresist, which is then etched to form the pattern on the substrate. Alternatively, other reference patterns may be used, and the reference sample may comprise any other suitable medium or device that is capable of recording the intensity of a microscopic electron beam pattern. For example, an electron sensor, such as an e-beam sensitive camera, may be used to directly record the e-beam image of the reference pattern in real time at step 82. The reference pattern that is formed on the test sample (or captured by a recording device) in this manner is compared to the original reference image in order to map the distortion of the image, at a mapping step 84. The comparison may be carried out, for example, by capturing an image of the pattern on the test sample, using an optical or electron microscope, for example. Based on this mapping, the displacement (offset) of each pixel in the input reference image is determined, relative to the position of the pixel in the captured image of the reference pattern formed by the electron beam, at a matrix computation step 86. The matrix represents, in effect, the inverse of the image distortion, indicating the amount by which each pixel in the captured image must be shifted in the X- and Y-directions in order to recover the original, undistorted image. To reduce the computational load, the shifts may be computed for blocks of pixels, rather than individual pixels. Before printing the frame images on wafer 22, the gray-scale values of the pixels are resampled using the offset matrix, at a resampling step 88. This step has the effect of moving each pixel by the appropriate displacement amount, but in the opposite direction to the actual, measured displacement, in order to “pre-distort” the individual frame images. In this manner, the distortion of e-beam generator 24 and optics 26 is corrected in the actual frame images that are written on wafer 22. In other words, the inverse transformation to the actual distortion is applied to the frames. Resampling the pixel values at step 88 may cause edges in the pre-distorted frame image to blur, since after resampling the edge may contain more than a single gray pixel (between the black and white pixel values on either side of the edge). In order to eliminate this sort of blur, a sharpening filter is typically applied to the resampled image at step 88. The sharpening filter runs over the resampled pixel values on the edges in the frame image and recalculates their values so that a section line through any given edge contains no more than a single gray pixel. Note, however, that the pixels in the electron beam itself are typically Gaussian in shape. Therefore, a simple linear adjustment of the gray-scale values at the edges will actually have a non-linear effect on the displacement of the edge in the image written on wafer 22. The magnitude of this non-linear effect may be determined in advance and stored in a lookup table, which is then used in applying a final correction to the value of each pixel along each of the edges in the frame image based on the distance of the pixel from the actual edge. In addition to the method of FIG. 5, further calibration procedures are typically used to correct for other distortions and non-uniformities in system 20. For example, image displacement and rotation introduced by optics 26 may be measured and corrected by realignment of the optics. Deviations in image intensity due to non-uniformities in e-beam generation and/or focusing, as well as deviation in the intensities of individual pixels (which may arise from defects in the modulator used in shaping the electron beam in e-beam generator 24) may be measured and corrected using a look-up table. Other means of correction will be apparent to those skilled in the art. Alternatively, such calibration procedures and the resulting corrections may be incorporated in the method of FIG. 5. Although the embodiments of FIGS. 4A, 4B and 5 are described here with reference to system 20, and the use of an electron beam to write lithographic patterns on wafer 22, the principles of these embodiments may similarly be applied to writing high-resolution images on a substrate using other systems and other types of radiation sources. FIG. 6 is a block diagram showing functional elements of system 20, in accordance with an embodiment of the present invention. In this embodiment, system 20 comprises an optics module 100 and an electron optics (E/O) column module 102, which operate in concert to modulate the successive frame images onto the electron beam. Module 100 generates the frame images in the form of optical images, using a spatial light modulator (SLM) 112, as described below. These optical images are focused onto a photocathode unit 104, which generates the electron beam with spatially-modulated intensity, in proportion to the intensity of the incident light, as determined by the SLM. Typically, SLM 112 generates gray-scale images with resolution of 6–8 bits/pixel, in order to enhance the resolution of the image features in the master image that are written on wafer 22. The resolution enhancement of a gray-scale image with n gray levels, relative to a binary image with the same pixel size, can be as great as 1/n. Exemplary gray-scale SLM implementations for this purpose are described below with reference to FIGS. 8 and 9. Controller 28 generates input signals to control SLM 112 so as to create the desired frame images. For this purpose, a data path preprocessor 106 divides the master image to be written on wafer 22 into a matrix of frame images, as illustrated in FIG. 2. Preprocessor 106 also performs any required blending or separation of features in overlap regions 50 between frames, as shown in FIG. 4B, and corrects for image distortions, typically using the method of FIG. 5. The preprocessor may also adjust parameters of the frame images to compensate for artifacts of the lithography process, such as electron beam fogging, proximity effects due to back-scattered electrons (which may occur on the wafer particularly in densely-patterned areas of the image) and etch loading. Typically, the gray levels of pixels in these areas are modified to offset the undesired electron beam effects. In addition, the preprocessor may perform “data healing,” i.e., resolving and correcting for overlaps of the shapes to be written on the wafer, as is known in the art. A rasterizer 108 converts each frame image into a string of data values, each corresponding to the gray-scale intensity of a successive pixel of SLM 112, arranged in row- and column-order. The definition of the frames to be written on wafer 22 and blending in the overlap regions of the frames may alternatively take place after this rasterization step. In this case, the master image is rasterized once, on a global basis, followed by dividing the rasterized image into frame images with appropriate blending and other corrections. An optical module interface 110 then converts the data values into control input signals to SLM 112. The type of signals required depends on the type of SLM that is used, as described further hereinbelow. Typically, interface 110 comprises an array of memory buffers, which are written by rasterizer 108 and then read out to SLM 112 using a double-buffering technique. Given a frame rate of 10 kHz (i.e., 10,000 frames per second written on wafer 22), with 1000×1000 pixels per frame, the optical module interface must be capable of processing 10 Gpixels/sec, typically at 8 bits/pixel. Possible implementations of optics module 100 are described in greater detail with reference to FIGS. 8 and 9. Briefly, illumination optics 114 generate a spatially-uniform beam of light, which illuminates SLM 112. Typically, the illumination optics comprise a laser, with suitable beam conditioning and scanning optics, as described below. SLM 112 is controlled to create a variable intensity pattern across the illuminating beam. The spatially-modulated beam from the SLM is imaged by collection optics 116 into an objective 118, which demagnifies and focuses the beam onto the photocathode in unit 104. Each frame image is actually demagnified twice: once by objective 118, and then again by electron optics 26. Total demagnification of at least 100× is desirable. Assuming SLM 112 has a pixel pitch of 13 μm (typical of commercially-available SLM devices based on micro-mirror arrays), a total demagnification of about 400–500× is required in order to reach the target pixel size of 25–35 nm on wafer 22. To achieve this desired total demagnification, objective 118 typically demagnifies the image of the SLM by about 25×. Assuming illumination optics 114 output a laser beam in the blue or green spectral range, this demagnification reduces the pixel size on the photocathode to approximately the diffraction limit minimum. FIG. 7 is a schematic, sectional view of E/O column module 102, in accordance with an embodiment of the present invention. The spatially-modulated light beam from SLM 112 is focused by objective 118, as noted above, through a window 120 onto a photocathode 122. Typically, photocathode 122 has fast temporal response (>1 MHz), high uniformity, and high photoyield (>20 μA/mW of optical power), with the possibility of operating at high current density (>0.1 A/cm2) and optical power density that may be in excess of 10 W/cm2. A bi-alkali or multi-alkali photocathode may be capable of meeting these requirements. Alternatively, the specifications of photocathode 122 may be relaxed, at the expense of reduced throughput of system 20. In order to maximize the lifetime of photocathode 122, it is advantageous to exclude heavy molecules, such as oxygen and water vapor, from the area of the photocathode during operation. It is desirable that the partial pressures of such molecules be on the order of 10−7 to 10−9 torr, or even lower. Although the lithography chamber (not shown) in which wafer 22 is irradiated by the electron beam is itself evacuated, it is not generally possible to pump the heavy molecules out of the chamber down to the desired partial pressure in a reasonable amount of time. Therefore, photocathode 122 is preferably contained in a separate enclosure 123, which is closed off on one side by window 120 and on the other side by a thin protective membrane 126. This arrangement allows enclosure 123 to be pumped out independently of the rest of the chamber. Another advantage of keeping photocathode 122 inside enclosure 123 is that material that vaporizes off the photocathode during operation remains contained inside the enclosure. Consequently, some of this vaporized material redeposits on the photocathode, thus slowing the degradation of the photocathode due to material loss. Membrane 126 is made as thin as is feasible in order to minimize interference with the electrons emitted from photocathode 122. The membrane is preferably less than 1 μm thick, and is most preferably 100 nm thick or less. The membrane must be made of a material with sufficient mechanical rigidity to prevent fracture and shifting of position even at this very low thickness. It should also have high thermal conductivity and electrical conductivity, in order to prevent thermal effects and charging of the membrane by the electron beam. Suitable materials for these purposes include silicon, silicon nitrides, silicon carbide and diamond-like carbon (DLC). Even under the desired high-vacuum conditions, photocathode 122 and membrane 126 will still be subject to degradation over time, due to the high electron flux levels to which they are exposed. On the other hand, the size of the area on the photocathode that is activated by the beam from optics module 100 is relatively small—typically on the order of 0.5×0.5 mm—as is the area of membrane 126 through which the electron beam passes. In order to extend the lifetime of the photocathode and membrane, the photocathode may be made considerably larger, with a diameter of several millimeters or more. The optics module may be periodically shifted relative to the photocathode (typically once in several hundred hours of operation), or the optics may be readjusted, so as to activate different areas of the photocathode. Shifting the active area of the photocathode also shifts the area of membrane 126 through which the electron beam passes. The electron optics in module 102 are designed to focus the spatially-modulated electron beam generated by photocathode 122 onto wafer 22 with high accuracy and with demagnification of about 15×, so that the pixel size of 400–500 nm at the photocathode is reduced to a pixel size of 25–35 nm on the wafer. Alternatively, as noted above, greater or lesser levels of demagnification may be used. At the same time, the electron optics accelerate the electrons, typically to an energy of about 50 keV at impact on wafer 22, as well as scanning the electron beam in the X- and Y-directions, as described above with reference to FIG. 2. (The 50 keV electron energy is suitable for writing on photoresist materials known in the art. Alternatively, a retarding lens may be added in optics 26 in order to reduce the electron impact energy if desired.) To maintain accurate reproduction of the electron image from photocathode 122 onto wafer 22 over the entire scan, the electron optics are preferably telecentric, with total aberrations no greater than about 3 nm, and depth of focus >1 μm in order to accommodate possible height deviations in the wafer surface plane. The first element in the electron optics column in module 102 is an illumination lens 124, surrounding enclosure 123, which images the electron distribution at photocathode 122 onto the plane of membrane 126 with unit magnification. Lens 124 generates a homogeneous magnetic field along the electron trajectory and an electrostatic field to accelerate the electrons. An electrostatic field lens 128, typically operating at a potential of 50 kV, accelerates the electrons. The field lens is useful in reducing chromatic aberrations and Coulomb interaction. A collimator 134 focuses the accelerated electron beam through an aperture 136, which eliminates off-axis rays. A beam deflector 135 deflects the beam along the primary and secondary scan directions (X- and Y-axes) as described above with reference to FIGS. 2, 3A and 3B. The beam is then focused and demagnified onto wafer 22 by an objective 138. Various designs of the beam deflector and objective may be used for these purposes, including doublet and moving objective lens designs, as are known in the art. To meet the requirements of high beam stability and large depth of focus, as specified above, objective 138 typically has a small numerical aperture, which may be on the order of several mrad. FIG. 8 is a schematic side view of optics module 100, in accordance with an embodiment of the present invention. In this embodiment, SLM 112 comprises an array of micromirrors, such as a Digital Micromirror Device (DMD) produced by Texas Instruments DLP Products (Plano, Tex.). The SLM is controlled by controller 28 so as to generate the succession of gray-scale frame images at high speed, as described briefly hereinbelow. Further details and variations on these spatial modulation methods and associated devices are described in the above-mentioned U.S. Patent Application Publication 2003/0122091. Alternatively, SLM 112 may be controlled to create binary images. Further alternatively, other types of spatial light modulators and other control techniques, as are known in the art, may be used in generating the gray-scale image, as long as the devices and techniques are capable of operating at sufficient speed to meet the throughput requirements of system 20. Either reflective modulators (such as the above-mentioned DMD) or transmissive modulators (such as LCD-based devices) may be used. The modulator elements in the array may be operated using binary control, as described below, or they may alternatively be controlled in an analog mode (gray-level based). Analog or high-speed binary control (such as the PWM technique described below) may be used to write all the pixels in each frame on wafer 22 simultaneously. Alternatively, the pixels in each frame may be written in groups, wherein typically all pixels having the same intensity value are written simultaneously, as described hereinbelow. A beam source, typically a laser 140, generates a beam of optical radiation, which may be pulsed or continuous wave (CW). The term “optical radiation,” as used in the present patent application and in the claims, includes all wavelengths in the visible, ultraviolet and infrared ranges. Typically, a solid-state laser operating in the wavelength range between about 400 and 550 nm, with average output power between about 0.2 and 3 W, will provide adequate optical power on photocathode 122, depending on the required pixel size, speed and other system requirements. Alternatively, an ultraviolet laser may be used for enhanced optical resolution. An intensity converter (IC) 142 converts the Gaussian beam intensity profile that is typically output by laser 140 into a flat-top profile. An acousto-optic modulator (AO) 144 is used to block the laser beam while SLM 112 is in the process of being loaded with new data, so that the laser beam strikes the SLM only after the micromirrors have settled in their proper orientations to create the current frame image. A beam expander (BE) 146 expands the beam to cover the active area of the SLM. SLM 112 comprises an array of micromirrors, each of which has two stable orientations (or states): an “on” position in which it reflects the laser radiation toward the desired target (i.e., photocathode 122), and an “off” position in which it reflects the radiation away from the target. The SLM is controlled via interface 110 so that each pixel in the frame image reflected from the SLM has the desired gray level, typically with eight-bit resolution. One method for achieving this result is pulse-width modulation (PWM) of the signal applied to each micromirror. The amount of time in each frame during which the micromirror is in the “on” position is proportional to the length of the pulse. To meet the frame rate objective defined above (10,000 frames/sec), however, with eight-bit gray scale resolution, requires that the shortest control pulse applied to the micromirrors be approximately 0.4 μs long. Currently-available SLM devices are not capable of such high modulation speed. Alternatively, SLM 112 may be controlled in this manner (or using other methods) to produce a smaller number of gray levels. As another alternative, the intensity of the laser beam may be controlled, using AO modulator 144, for example, so as to emit a number of different intensity levels during each frame. For example, each frame may be divided into eight time slots, during which the laser intensity on SLM 112 is successively set to 1/128, 1/64, . . . , ¼, ½ and full power. Each micromirror is then controlled to be in the “on” position during the appropriate time slot(s) in order to give the desired total gray-scale intensity. This scheme requires that the minimum-length control pulses to the micromirrors be no more than 12.5 μs long. This method, as well, may alternatively be used to produce a smaller or larger number of gray levels. A pulsed laser, synchronized with the SLM control signals, may be used advantageously in this configuration. FIG. 9 is a schematic side view of optics module 100, in accordance with another embodiment of the present invention. This embodiment is directed to reducing still further the speed requirements involved in controlling SLM 112, which are stringent in comparison to the capabilities of currently-available SLM devices. Therefore, in the embodiment of FIG. 9, SLM 112 is effectively built up from an array of eight binary micromirror devices 150, labeled DMD1 through DMD8, which may operate at substantially slower speeds than the SLM used in the embodiment of FIG. 8. Alternatively, a larger or smaller number of binary spatial modulation devices may be used. Devices 150 are aligned in mutual registration, so that a given pixel in the frame images created by SLM 112 corresponds to the same micromirror in all of the devices. The beam from laser 140 is split into eight beams of equal intensities by a 1:N splitter 152. Alternatively, a larger or smaller number of beams may be used, and the individual beam intensities may be different. Each beam is switched on and off by its own AO modulator 144 and is then directed toward a respective micromirror device 150. (Intensity converter 142 and beam expander 146 are omitted here for the sake of simplicity.) The optical paths of all the beams are arranged to have equal lengths. The modulated beams reflected from DMD1 through DMD7 are recombined by an array of 50/50 beamsplitters 154. This arrangement has the effect of attenuating the intensity output of DMD7 by a factor of two, DMD6 by a factor of four, and so forth up to DMD1, which is reduced by a factor of 128. Thus, each of the devices creates a partial frame image, having a different (binary) set of intensity levels. The beams reflected from DMD1 through DMD7 are set to a first polarization, while that from DMD8 has the opposite polarization. Therefore, the combined beam from DMD1 through DMD7 may be merged with the unattenuated output of DMD8 without further loss using a polarization beamsplitter 156. The combination of the partial frame images creates the complete, gray-scale frame image on photocathode 122. FIG. 10 is a timing diagram that schematically illustrates electrical signals applied to micromirror devices 150, in accordance with an embodiment of the present invention. The gray-scale intensity of each pixel in the frame image on photocathode 122 is controlled by setting the corresponding micromirrors in the appropriate devices 150 to the “on” position, in order to give the desired combination of intensities. For example, an intensity of 96 at a given pixel (on a scale of 0 to 255) in a certain frame would be generated by setting the corresponding micromirrors in DMD 6 and DMD 7 to the “on” position for that frame. The mirrors are set to the desired positions during a setting period 160, and AO modulators 144 then turn on the laser beam to the micromirror devices during an exposure period 162. Note that in this scheme, the micromirrors need be set only once per frame, i.e., once in TFRAME≅100 μs. Typically, the length of time required to set the mirrors to their new positions for the next frame, TS, is considerably shorter than TFRAME. The remainder of the frame period may be used to load the data for the next frame image into devices 150, during the loading time TL. Combining the beams from the eight DMD channels in the modulator configuration of FIG. 9 may cause undesired intensity variations on photocathode 122 due to interference between the coherent beams. In the embodiment illustrated in FIG. 10, these coherence effects are avoided by time multiplexing of the laser beam, by means of pulses 164 applied to AO modulators 144. In other words, during exposure period 162, the laser beams strike each of devices 150 in succession, so that no more than one channel is active at any given point of time. This temporal offset between the beams prevents interference, but reduces the effective laser power on the photocathode by a factor of eight. Alternatively, a scanner may be used to switch the laser beam among the DMD channels, so that each channel gets the full laser intensity. Further alternatively, other means, as are known in the art, may be used to reduce the coherence of the laser beams optically, so that all eight channels can operate simultaneously without interference effects. In other embodiments (not shown in the figures), the optical beam may be modulated using a multi-level modulator, as described, for example, in the above-mentioned U.S. Pat. No. 6,399,261. The modulator described in this patent performs multi-level modulation, driven by analog signals. The modulator is susceptible to manufacturing inaccuracies and temperature variations. It is therefore calibrated using an empirical calibration procedure, wherein a series of test patterns are images and analyzed. Micronic Laser Systems AB (Taby, Sweden) has recently presented a prototype of a 1 Mega-pixel analog spatial light modulator. In yet another embodiment, multiple modulators can be used as described in a U.S patent application entitled, “A Printer and a Method for Recording a Multi-Level Image,” filed Jul. 7, 2003, whose disclosure is incorporated herein by reference. Alternatively, light modulation methods described in other publications cited in the Background of the Invention may be used. Reference is now made to FIGS. 11A and 11B, which schematically illustrate an electron beam module 180 for generating a spatially-modulated electron beam, in accordance with an alternative embodiment of the present invention. In this embodiment, e-beam generator 24 creates and modulates the electron beam electronically, rather than by means of optical modulation as in the preceding embodiment. FIG. 11A is a sectional illustration of the e-generator and electron optics in module 180, while FIG. 11B is an equivalent optical diagram. An electron beam source 182 comprises a cathode 184, which generates a high-intensity electron flux, typically on the order of 1–2 mA/steradian. Cathode 184 may comprise, for example, a thermal field emission (TFE) tip of ZrO/W (zirconium oxide coated with tungsten). Electrons emitted from cathode 184 are accelerated by an electrostatic lens 188, typically through a potential difference of about 30 kV. An illumination lens 186 generates a homogeneous magnetic field along the electron trajectory, in order to irradiate a multi-lens array (MLA) 190 with a slightly-divergent electron beam. MLA 190 comprises multiple electron lenses, which divide the electron beam into multiple beamlets, one per aperture. Typically, MLA 190 comprises about 100×100 apertures, although larger or smaller arrays may similarly be used. An electrostatic field lens 192 accelerates the beamlets following MLA 190 and focuses the beamlets onto a multi-beam blanker 194. Typically, to accelerate the electrons from cathode 184 through blanker 194, the cathode is held at about −50 kV, while lens 188 is held at −20 kV, and blanker 194 is held in a mount 196 at ground potential, i.e., at the potential of wafer 22. Blanker 194 comprises an array of apertures, each controlled by an electronic shutter element or beam deflector. Each aperture in blanker 194 is aligned to receive the beamlet generated by a corresponding aperture in MLA 190. Typically, the shutter elements are spaced about 100 μm apart and have clear apertures of about 8–10 μm. Miniature electron optics associated with each aperture control the passage of the respective beamlet through the aperture. When a given shutter is open, the beamlet passes through the aperture and continues along the optical path to impinge on wafer 22, as described below. When the shutter is closed, a deflecting field is typically generated in the aperture, which deflects the beamlet away from the open optical path. The length of time for which a particular shutter element is open during the exposure of a given frame controls the number of electrons that flow through the corresponding aperture, and thus determines the gray level of the corresponding pixel in that frame. The electron optics in each aperture, and hence the shutter exposure times, are controlled by PWM signals from controller 28. Alternatively, the shutter elements may simply be set either open or shut, to create a binary electron image. Various implementations of blanker 194 may be used in module 180. For example, the blanker may be fabricated as a monolithic microelectronic device on a silicon wafer, as shown below in FIGS. 12A and 12B. Alternatively, blanker 194 may be implemented as a micro-electro-mechanical system (MEMS) device coupled to a control chip (or to several control chips, in order to support the desired data rate of 10 Gpixels/sec). Another possible implementation may be based on the system described in the above-mentioned U.S. Pat. No. 6,014,200. A collimator 198 focuses the electron beamlets, following modulation by blanker 194, through an aperture 200. The aperture blocks beamlets that have been deflected by “closed” shutter elements, as shown in FIG. 11B. A beam deflector deflects the beamlets as a group in the primary and secondary scan directions, in substantially the same manner as deflector 135, described above. An objective 202 focuses and demagnifies the beamlets to form a reduced electron image on wafer 22, with pixel size typically in the range of 25–35 nm. As in the case of optics 26 shown in FIG. 7, the focusing optics are preferably telecentric. FIG. 12A is a schematic top view of blanker 194, in accordance with an embodiment of the present invention. In this embodiment, blanker 194 comprises a silicon chip with apertures 210 passing through the chip, and deflection electrodes associated with each aperture, as shown in FIG. 12B below. Typically, the blanker comprises about 100×100 apertures, spaced about 100 μm apart, as described above. Thus, in this case, the frame images written by system 20 are 100×100 pixels in size (rather than 1000×1000 as in the examples described above). Alternatively, both larger and smaller blanker arrays, with either larger or smaller aperture spacing, may be used. Blanker 194 is contained in a vacuum chamber 212 (which also contains the other electron optics and wafer 22). Notwithstanding the smaller frame image size, blanker 194 is still capable of operating at a rate of 10 Gpixels/sec, as in the embodiments described above. To meet this speed requirement, four data transceivers 214 may be used, for example, to input control signals to blanker 194, with each transceiver operating at a rate of 2.5 Gpixels/sec. Control and status lines to and from the blanker chip may operate at lower speed. FIG. 12B is a schematic, sectional view showing a detail of blanker 194, in accordance with an embodiment of the present invention. Apertures 210 are etched through a silicon substrate 220, which is thinned to a thickness of about 100 μm. Metal electrodes 226 and 228 are deposited above a layer 230 of SiO2 on substrate 220. Electrode 226 receives control signals via conductors 232 passing through oxide layer 230, while electrodes 228 are grounded. A ground plane 234 is formed over the upper oxide layer to shield the electronics on the blanker chip. As can be seen in the figure, a pair of electrodes 226 and 228 bounds each aperture 210. When the control signal carried by conductor 232 to electrode 226 is low (ground), the electron beamlet passes through aperture 210 without deflection. On the other hand, when the control signal is high, an electrostatic potential is created between electrodes 226 and 228, which deflects the beamlet passing through the aperture 210. Aperture 200 blocks the deflected beamlet, which is thus effectively blanked and does not reach wafer 22. As noted above, the length of time for which a given beamlet is deflected during a given frame determines the gray level of the pixel written by that beamlet in the frame. Although system 20 is described above in the context of creating lithographic patterns on semiconductor wafer 22, the principles of the present invention may similarly be applied in writing high-resolution images on substrates of other sorts. For example, the methods and devices described above may be used, mutatis mutandis, in creating masks and reticles for use in projection lithography, and in patterning flat panel displays and other types of electronic circuits. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Although the steps in the method claims in this application may be recited in a certain order, variations on this step ordering are also considered to be within the scope of the present invention. |
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description | The present disclosure relates to a safety system shutdown including a passive electrical component that senses a system parameter and becomes tripped if a predetermined set point is reached so that a signal is sent to take an action in the system. The passive electrical component makes use of the principles of Ampere's Law. This section provides background information related to the present disclosure which is not necessarily prior art. Modern nuclear reactors use a variety of digital systems for both control and safety, referred to as a Distributed Control and Information System (DCIS). These systems must be redundant, diverse, fault tolerant, and have extensive self-diagnosis while the system is in operation. Meanwhile, the nuclear digital industry is concerned with common cause software failure. Even more damaging is a cyberattack to, or through, the system safety systems. In the digital industry, the desire to increase computational power while decreasing component size results in a very small digital device with embedded software. It is very difficult to convince a regulatory body that these systems cannot have a common cause failure. Even more damaging operations can occur when this compact digital system is subjected to a cyberattack. These extreme unknown conditions of a nuclear power plant safety system lead to the cause for redundancy, independence, and determinacy, all of which contribute to significant added cost. FIG. 3 schematically shows a conventional distributed control and information system (DCIS) 200 with both a safety portion 202 and non-safety portion 204 that are interfaced by a control panel 203. The present disclosure is directed to the safety portion 202 of the DCIS 200 which is shown in FIG. 3. The safety portion 202 of the DCIS 200 includes four independently designed divisions 202A-202D which each receive measured system signals that are collected and sent from a remote multiplexer unit RMU 205 which provides output to the digital trip module DTM 206 which each provide outputs to the trip logic units TLU 208 which each provide an output signal to the output logic unit OLU 210. The conventional safety portions 202 use a voting logic of at least two out of four of the different divisions 202A-202d receiving like signals in order to determine a fault (i.e. pressures and temperatures are not compared against each other). It becomes more difficult for the nuclear power plant control system designer, purchaser, installer, and operator to establish and trace the essential safety signals to ensure the system is performing as designed. A device and method is needed on a scale that humans can vary “signal flow” or trace the flow of electrons/data so that the system is immune from cyber-attack. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. The present disclosure provides electro-technical devices that, coupled to control systems, can provide passive system safety shutdown using Ampere's Law. These devices will solve the issue of common cause software failure or cyber security attacks that are inherent limitations of digital safety systems. The Ampere's law contactor provides an electro-technical device that can be set up in multiple configurations to protect a nuclear power plant, or another sensitive infrastructure. The electro-technical devices of the present disclosure can be produced in part using metallic and plastic 3-D printing machines that can be utilized to ensure consistent manufacture of the electro-technical device for which the manufacturing data can be captured and stored for utilization in confirming the device's consistent operational characteristics. The devices use a simple pass/fail or go/no-go check to convey to an electrical safety system to change state to safe shutdown. The printed device is placed into the safety system to perform three basic tasks: senses a system parameter (e.g. temperature, flow, pressure, power or rate of change), if the predetermined set point is reached—result in a “tripped” state, and lastly, if the safety system logic is met-send a signal or activate a device to take an action in the system, such as shutdown. The device also eliminates failures due to software or digital cyber-attacks. An electro-technical device includes a circuit including a coil connected to a voltage source for receiving a predetermined current therefrom and connected to an output device. The circuit includes a breakable junction and a photodiode for receiving a light signal from a fiber optic cable. The photodiode receives a light signal from a sensor. A permanent magnet includes a pole end opposing a common pole end of the coil, wherein when the coil receives an increased current from the photodiode, the coil creates a magnetic flux that repels against the common pole of the permanent magnet in order to cause the breakable junction to break and disrupt a connection between the voltage source and the output device. Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. FIG. 1 is an illustration of photodiode 404 to illustrate how the curl of the magnetic fields can be used to detect a time changing electric flux density. As shown in FIG. 1, an optical signal 402 is being picked up by the photodiode 404 which is an electromagnetic wave that is composed of electric and magnetic fields that oscillate perpendicularly to the direction of the light wave. The photons from the signal are absorbed into the semiconducting materials of the photodiode 404, which results in a generated current. The amount of current generated is proportional to the amount of light entering the photodiode 404. Ampere's law describes that the magnetic field around an electric current is proportional to the electric current providing the source for the field. Additionally it also describes that a variation in an electric field over time can generate a magnetic field. The current flowing within the photodiode 404 after photon absorption follows this law. The current, and subsequent magnetic field, can be measured and then communicated throughout the entire system. As shown in FIG. 2, the Ampere's law logic contactor 410 is utilized in a nuclear safety system to produce a logic device without software when a system trip condition exists. As shown in FIG. 2, the Ampere's law logic contactor 410 includes a pair of circuits 412, 414 each including a respective input connector 416, 418 which are each provided with input signals 420, 422. The input connectors 416, 418 are connected to respective coils 424, 426 which are each connected to respective system solenoids 428, 430 via a breakable/disconnectable junction 432, 434. A pair of photo diodes 404A, 404B are connected to the pair of circuits 412, 414 to provide additional current to the circuits 412, 414. The coil 424 is arranged so that a magnetic field generated by current flow has a north pole at a downstream side of the coil 424 relative to the current flow direction while the coil 426 is arranged so that a magnetic field generated by current flow has a south pole at a upstream side of the coil 426 relative to the current flow direction. A permanent magnet 436 is provided with a north pole “N” opposing the north pole side of the coil 424 and a south pole “S” of the permanent magnet 436 opposing the south pole side of the coil 426. The photodiodes 404A, 404B are each provided with photo-optic signals from fiber optic lines 438, 440 that provide signals representative of a sensor 442, 444 that senses one of temperature, pressure, flow or another parameter which is relevant to a system safety factor for indicating a need for a shutdown. The photodiodes 404A, 404B convert the optical signal “O” from the fiber optic lines 438, 440 into a current density J that provides more current into the coils 424,426. The coils 424, 426 are in balance with the permanent magnet 436 such that there is a balance force at the breakable junctions 432, 434. As illustrated in FIG. 2, the right portion of the breakable junctions 432, 434 are anchored and the left portion of the junctions are attached to movable coils 424, 426. When an optical trip signal from sensors 442, 444 is received due to the light wave O and is converted by the photodiodes 404A, 404B into an electrical current J this causes a divergence change in the magnetic field H of the coils 424, 426. This imbalance causes the coils 424, 426 and the magnetic field of the permanent magnet 436 to oppose each other resulting in a separation at one or both of the breakable junctions 432, 434. This stops current flow to the solenoid connections 428,430 resulting in a safety system action. The amount of current generated is proportional to the amount of light O hitting the photodiodes 404A, 404B which is proportional to the divergence in the magnetic field and the imbalance to the permanent magnetic field 436. Accordingly, the Ampere's law contactor 410 can be utilized in a nuclear safety system as previously described and can replace the DTM, TLU and OLU previously described in FIGS. 3 and 4. During steady-state, operation of the Ampere's Law contactor receives input from the photodiodes 404A, 404B. If the photon level exceeds the device baseline, the safety system response is actuated. The breakable junctions 432, 434 of the device respond as a once-in-a-lifetime component activation, such as a fuse. The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. |
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claims | 1. An X-ray detector for phase contrast imaging, the X-ray detector comprising:a scintillation device comprising a wafer substrate having a plurality of grooves spaced apart from each other, wherein each groove of the plurality of grooves extends to a depth along a first direction from a first side of the scintillation device into the wafer substrate, each groove of the plurality of grooves being at least partially filled with a scintillation material; anda photodetector comprising a plurality of photosensitive pixels optically coupled to the scintillation device;wherein a primary axis is substantially parallel to a surface normal vector of the scintillation device;wherein first directions of at least a part of the plurality of grooves are different from the primary axis, such that at least a part of the plurality of grooves is tilted with respect to the primary axis; andwherein an angle between a first direction of a groove arranged in a center region of the scintillation device and the primary axis is smaller than an angle between a first direction of a groove arranged in an outer region of the scintillation device and the primary axis. 2. The X-ray detector according to claim 1, wherein grooves of the plurality of grooves arranged in an outer region are more tilted with respect to the primary axis than grooves of the plurality of grooves arranged in a center region. 3. The X-ray detector according to claim 1, wherein at least one groove of the plurality of grooves has a first direction parallel to the primary axis; and wherein the at least one groove of the plurality of grooves is arranged in a center region of the scintillation device. 4. The X-ray detector according to claim 1, wherein an angle between a first direction of a groove of the plurality of grooves and the primary axis increases with an increasing distance of the groove of the plurality of grooves from a center region to an outer region of the scintillation device. 5. The X-ray detector according claim 1, wherein each groove of the plurality of grooves is completely filled with a scintillation material. 6. The X-ray detector according to claim 1, wherein each groove of the plurality of grooves is divided into a plurality of sections along a longitudinal extension direction. 7. The X-ray detector according to claim 1, wherein at least a part of the plurality of grooves has at least one of the following shapes: a rectangular shape, a trapezoidal shape, a tubular shape, a cylindrical shape, a conical shape, and an asymmetric shape. 8. The X-ray detector according to claim 1, wherein the detector comprises a flat detector. 9. The X-ray detector according to claim 1, wherein the wafer substrate comprises silicone; and/or wherein the scintillation material comprises at least one of CsI, NaI, CsI(Tl), CsI(Na), CsI(pure), CsF, KI(Tl), LiI(Eu) and gadolinium oxysulfide. 10. The X-ray detector according to claim 1, wherein each groove of the plurality of grooves has a depth of about 0.5 mm to 5 mm; and/or wherein each groove of the plurality of grooves has a width of about 1 μm to 200 μm. 11. The X-ray detector according to claim 1, wherein each groove of the plurality of grooves has a length along a longitudinal extension direction that corresponds to a length of a photosensitive pixel of the plurality of photosensitive pixels. 12. A phase contrast imaging system, comprising:an X-ray source for emitting a beam of X-rays centered around an optical axis;an X-ray detector comprising:a scintillation device comprising a wafer substrate having a plurality of grooves spaced apart from each other, wherein each groove of the plurality of grooves extends to a depth along a first direction from a first side of the scintillation device into the wafer substrate, each groove of the plurality of grooves being at least partially filled with a scintillation material; anda photodetector comprising a plurality of photosensitive pixels optically coupled to the scintillation device, wherein a primary axis of the X-ray detector is substantially parallel to a surface normal vector of the scintillation device, wherein the first direction of at least a part of the plurality of grooves is different from the primary axis, such that at least a part of the plurality of grooves is tilted with respect to the primary axis, and wherein an angle between the first direction of a groove of the plurality of grooves arranged in a center region of the scintillation device and the primary axis is smaller than an angle between the first direction of a groove of the plurality of grooves arranged in an outer region of the scintillation device and the primary axis; andat least one grating arranged between the X-ray source and the X-ray detector, wherein the primary axis of the X-ray detector is substantially parallel to the optical axis. 13. The phase contrast imaging system according to claim 12, wherein the X-ray detector is arranged such that the first direction of each groove of the plurality of grooves is oriented towards a focal spot of the X-ray source. 14. A method of fabricating an X-ray detector, the method comprising:forming a plurality of grooves into a wafer substrate of a scintillation device, such that the plurality of grooves are spaced apart from each other and such that each groove of the plurality of grooves extends to a depth along a first direction from a surface of the wafer substrate into the wafer substrate;at least partially filling each groove of the plurality of grooves with a scintillation material; andarranging the wafer substrate with the at least partially filled plurality of grooves on a photodetector;wherein the X-ray detector comprises a primary axis parallel to a surface normal vector of the wafer substrate;wherein the first direction of at least a part of the plurality of grooves is different from the primary axis, such that at least a part of the plurality of grooves is tilted with respect to the primary axis, andwherein an angle between the first direction of a groove of the plurality of grooves arranged in a center region of the scintillation device and the primary axis is smaller than an angle between the first direction of a groove of the plurality of grooves arranged in an outer region of the scintillation device and the primary axis. |
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046648739 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. 1, a large-area hot cell 2 contains several racks disposed along mutually-adjacent walls 6 and 8. These racks 4 are provided with an indexed structure and contain the process components (not shown) which are to be maintained by the system according to the invention. The mutually-adjacent rows of racks conjointly define a canyon-like transport passageway 10 along which a manipulator assembly 12 can be moved are accommodated. The manipulator assembly 12 is connected to an elongated supporting member in the form of a transverse beam 14 of an overhead bridge crane which can be moved along rails 13 and 15 disposed in respective sidewalls 6 and 8. A vertical guide column or mast 16 is coupled to the beam 14 and has a roller assembly 18 at its lower end for engaging the floor of the hot cell. The mast 16 is rotatable about its longitudinal axis and a support 20 is mounted thereon. The support is mounted so as to be movable up and down the mast 16. The support carries a telescopically-extendable arm 22 mounted thereon asymmetrically with respect to the column. At the end of the telescopically-extendable arm 22, a manipulator, tools or other remotely-controlled manipulating device is provided. In the schematic representation of FIG. 2, the manipulator is shown as a master slave device 24 with two slave arms 25. At the lower end, the mast 16 carries a tool table 26. A remotely-controlled overhead bridge crane 28 is arranged above the bridge crane of beam 14 and multipulator assembly 12. The bridge crane 28 is disposed just beneath the ceiling wall 27 of the hot cell. The bridge crane 28 is guided by and can be moved along rails 17 and 19 mounted in respective walls 6 and 8. The rails 13, 15 and 17, 19 constitute elevated track means for guiding the respective overhead bridge cranes 11 and 28 in the hot cell and in the direction of the longitudinal axis thereof. The bridge crane 28 includes a trolley 32 movable along the beam 30. The trolley 32 includes hoist means comprising an engaging device in the form of a crane hook 36 at the end of a hoist 34. The crane hook 36 is movable in the vertical direction and with aid of the hoist means of trolley 32. The crane hook 36 can be also moved in the horizontal direction by moving the trolley 32 along the beam 30. The cooperative relationship between the overhead bridge crane 28 and the manipulator carrier apparatus, made up of the bridge crane 14 and manipulator assembly 12, will now be described with reference to FIG. 3 for the situation where they both operate at the same work location 40. At the work location 40, the crane hook 36 lifts a component (not shown) of the process equipment. For this purpose, it is necessary that the crane hook 36 be lowered to the work location 40. A maintenance function is to be performed at the same location 40 with the remotely-controlled apparatus 24 (FIG. 2) on the extendible arm 22 of the manipulator assembly 12. The extendible arm 22 must be brought to the work location in the same vertical plane as the crane hook 36. Because of the asymmetrical arrangement of the extendible arm 22 with respect to the vertical mast 16, the longitudinal vertical axis of the mast 16 lies outside of the vertical working plane so that the crane hook clears the beam 14 of the bridge crane 11. Accordingly, the crane hook 36 is movable in the vertical direction and can pass unobstructed to the work location 40 in the same working plane in which extendible arm 22 is disposed. FIG. 4 discloses another embodiment of the system according to the invention for performing remotely-controlled manual-like maintenance and/or component replacement operations on process equipment contained in racks of a hot cell. FIG. 4 is a section view perpendicular to the longitudinal axis of the hot cell 50. The process equipment is accommodated in racks 52 arranged in two rows along respective vertical walls 54 and 56 of the hot cell. A first overhead bridge crane 58 is arranged just under the ceiling wall 60 of the hot cell 50 and includes a trolley 62 movable along the horizontal beam 64 of the bridge crane 58. The trolley 62 includes hoist assembly 66 for lowering and raising a device such as a hook 68 for engaging and moving a component of the process equipment in a first vertical plane transverse to the longitudinal axis of the hot cell. End sections 70 and 72 are attached to beam 64 and contain the wheels for engaging respective rails 74 and 76 extending along the length of the hot cell. An overhead bridge crane 80 is disposed beneath the first overhead bridge crane 58. The bridge crane includes end sections 82 and 84 attached to beam 86 thereof. The end sections 82 and 84 contain wheels for engaging respective rails 88 and 90. The sets of rails (74, 76) and (88, 90) define elevated track means for guiding the first and second bridge cranes in the hot cell in respective horizontal planes and in the direction of the longitudinal axis of the hot cell. Both overhead bridge cranes are arranged so that they pass over the canyon-like passageway 92 and the respective rows of racks 52 of process equipment. A manipulator assembly 93 includes a mast 94 connected to the elongated beam 86 and extends downwardly into the canyon-like passageway 92 from the beam. The beam 86 and the mast 94 conjointly define a second vertical plane transverse to the longitudinal axis of the hot cell. Manipulator means for performing manual-like operations on the process equipment is provided in the form of a telescopically-extendible arm 96 mounted asymmetrically on the mast 94 so as to be on one side thereof and in a third vertical plane also transverse to the longitudinal axis of the hot cell. When it is desired to perform a maintenance and/or replacement operation at a predetermined location of the process equipment, the first overhead bridge crane 58 is moved along the rails (74, 76) to bring the above-mentioned first vertical plane into coincidence with the third vertical plane so as to permit movement of the hook 68 by the assembly 66 in the third vertical plane clear of the transverse elongated beam 86 of the second overhead bridge crane 80. In this way, the extendible arm 96 and the hook 68 can be brought simultaneously to the predetermined work location at the purpose equipment. The extendible arm 96 is mounted on a support 116 which is mounted so as to be movable up and down the mast 94. Still referring to FIG. 4, it is noted that in this embodiment the lower end of the mast 94 is clear of the floor 98 of the hot cell by a distance indicated by a reference numeral 100. This clearance permits two separate trolleys 102 and 104 to pass beneath the mast 94 in the direction of the longitudinal axis of the hot cell. The trolleys 102 and 104 are useful for bringing tools such as impact wrenches for the manipulator means to utilize in its maintenance work on the process equipment. Other uses for the trolleys 102 and 104 include bringing replacement parts into the hot cell and bringing them to a location where they are convenient to the racks 52 where an exchange of components is to be made. The trolleys 102 and 104 are guided by rails embedded in the concrete floor 98. FIG. 5 is a side elevation view and shows the first overhead bridge crane 58 displaced from the second overhead bridge crane 80 and the manipulator assembly 93 associated therewith. The second overhead bridge crane 80 is equipped with a trolley 106 and a hoist assembly 108. The hoist assembly 108 of the trolley 106 includes a horizontal boom 126 which can be moved in the direction of its longitudinal axis through a predetermined stroke which can be 1.5 meters, for example. The two opposite ends of the boom are provided with block and tackle means 110. This hoist assembly can be used, for example, for small loads up to 500 kilograms on each block and tackle means. The hoist assembly 66 of the first overhead bridge crane 58 is also equipped with a horizontal boom and respective block and tackle means at respective ends of the boom. The first overhead bridge crane 58 and its hoist assembly 66 are used for moving heavier equipment weighing 20 tons on each of its two block and tackle means 112. Reference numeral 114 indicates a telescopic assembly for accommodating a video camera and/or a lamp for illuminating the work location. FIG. 6 shows the different movements which the components of the system according to the invention can be made to perform. The first overhead bridge crane 58 can be moved in the direction of the longitudinal axis of the hot cell as shown by arrow 118. The trolley 62 is movable in the direction of arrow 120 along the beam 64 of the bridge crane 58. The block and tackle means 68 can be moved upwardly and downwardly by suitable motors. The second overhead bridge crane 80 can likewise be moved in the direction of the longitudinal axis of the hot cell as shown by arrow 122. The movement of the trolley 106 and hoist assembly 108 mounted on the second overhead bridge crane 80 is indicated by arrow 124 and corresponds to that of the trolley and hoist assembly on the first overhead bridge crane 58. The boom 126 of the hoist assembly 108 can move along its longitudinal axis in a direction parallel to the longitudinal axis of the hot cell as shown by arrow 128. Arrow 130 indicates that the mast 94 can be moved in the direction of the beam 86 from one side of the hot cell to the other and the support 116 and manipulator means can be moved in the vertical direction up and down the mast as indicated by arrow 132. The extendible arm 96 of the manipulator means can rotate through 360.degree. in a vertical plane as indicated by arrow 134 and the arm 96 is telescopically extendible as indicated by arrow 135. Also, the mast 94 can be rotated about its longitudinal axis as indicated by arrow 136. On the floor of the hot cell, the trolley 102 can move along rails 138 and 140 embedded in the concrete in the direction indicated by arrow 142. The trolley 104 (FIG. 4) travels on embedded rails 144 and 146. Monitoring and/or illumination is provided by a telescopic arrangement indicated generally by reference numeral 114. A video camera can, for example, be mounted in the housing 148 and this housing can be raised and lowered with telescopic means in the direction shown by arrow 150. From FIG. 6, it becomes manifest that the first and second bridge cranes in combination with the equipment mounted thereon enable the block and tackle means of the hoist assemblies 66 and 108 and the manipulator means to reach virtually any point within the hot cell to perform maintenance operations on the process equipment. A still further advantage of the asymmetrical arrangement of extendible arm 96 on the mast 94 is that the arm 96 and the manipulator 24,25 (FIG. 2) at the outer end thereof can be utilized to perform "self" maintenance work on the bridge crane 80 and the equipment associated therewith. Because the extendible arm 96 is mounted asymmetrically on the mast 94, it can be extended upwardly in a vertical plane so that it clears the elongated beam 86. Thus, by moving the support 116 up the mast to the predetermined elevation and by rotating the arm 96 in the direction of vector 134 to a position where it can be extended upwardly, maintenance work could, for example, be performed on the trolley 106 and/or the hoist assembly 108 associated therewith. In this connection, it is noted that because the mast 94 can be rotated about its longitudinal axis in the direction of vector 136, the extendible arm 96 can reach upwardly from either the left-hand or the right-hand side of the beam 86. The perspective view of FIG. 7 shows a shielded control housing 152 for operating personnel and a control panel 154. The cables 156 and 158 connect the control panel 154 to the first and second overhead bridge cranes 58 and 80, respectively. The cable 156 is connected to bridge crane 58 via a cable-retracting drum 160 and carries all of the operating leads for the equipment associated with the first overhead bridge crane 58 such as the drive motors for moving the bridge crane along the rails 74 and 76; the drive motors for the trolley 62 for moving the trolley 62 along the beam 64; and, the drive motors for the hoist assembly 66 for raising and lowering the block and tackle means 68. The cable segment 166 conducts the electrical energy from end section 70 to the trolley 62 and collapses and expands in an accordian-like manner as the trolley 62 moves back and forth along beam 64. The second cable 158 is connected to bridge crane 80 via a cable-retracting drum 162 and carries all the leads for supplying electrical energy to the motors for driving the second bridge crane along the rails 88 and 90. This cable also includes the leads for delivering energy for the motors for operating the trolley 106 and the hoist assembly 108 associated therewith. In addition, the cable 158 carries energy via a slip-ring coupler 164 to the motor for turning the mast 94 about its longitudinal axis and conducts electrical energy via coupler 164 down to the manipulator means for energizing the motor which enables the support 116 to move up and down the mast 94 as well as for energizing the motor of the extendible arm 96 for rotating the same as indicated by arrow 134 (FIG. 6). The electrical energy for telescoping the arm 96 and the manipulator 24 (FIG. 2) at the end thereof is also supplied through the coupler 164. Cable segment 168 functions with respect to trolley 106 in the same manner as cable 166 for trolley 62. Cable segment 170 likewise folds and expands and conducts electrical energy to the telescopic arrangement 114. Referring now to FIG. 8, there is shown an elevation view of the mast 94 and the drive motors associated therewith. The drive motor 172 acts via a pinion 174 on a spur gear 176 to rotate the mast 94 about its longitudinal axis; whereas, the motor 178 drives a pinion that engages a linear gear 180 on the beam 86 for moving the mast 94 therealong. The linear gear 180 is a bar containing teeth formed in one face thereof for meshing with the pinion. The motor 182 is mounted on the support 116 and drives a pinion that engages a linear gear 184 fixedly secured to the mast 94 for moving the support 116 and manipulator means up and down the mast. The motor 186 rotates the arm 96 through 360.degree. in a vertical plane. FIG. 9 is an elevation view which shows the drive motors for the second overhead bridge crane 80. The drive motor 188 drives the wheels 190 and moves the overhead bridge crane 80 along the rails 88 and 90. It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. |
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abstract | Passive reactivity control technologies that enable reactivity control of a nuclear thermal propulsion (NTP) system with little to no active mechanical movement of circumferential control drums. By minimizing or eliminating the need for mechanical movement of the circumferential control drums during an NTP burn, the reactivity control technologies simplify controlling an NTP reactor and increase the overall performance of the NTP system. The reactivity control technologies mitigate and counteract the effects of xenon, the dominant fission product contributing to reactivity transients. Examples of reactivity control technologies include, employing burnable neutron poisons, tuning hydrogen pressure, adjusting wait time between burn cycles or merging burn cycles, and enhancement of temperature feedback mechanisms. The reactivity control technologies are applicable to low-enriched uranium NTP systems, including graphite composite fueled and tungsten ceramic and metal matrix (CERMET), or any moderated NTP system, such as highly-enriched uranium graphite composite NTP systems. |
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054950627 | claims | 1. A method of decontaminating soil containing nuclear waste, which comprises the steps of: (a) mixing a liquid ammonia with a soil contaminated with nuclear waste in a closed vessel to form an ammonia-nuclear waste-containing soil dispersion or slurry; (b) allowing soil particles to selectively precipitate from the dispersion or slurry of step (a) to form a lower solid phase of soil particulates while forming an upper liquid-solid phase comprising soil fines dispersed in said liquid ammonia, the soil particulates of said lower phase having greater bulk density relative to the soil fines of said upper liquid-solid phase; (c) separating said upper liquid-solid phase from said lower solid phase of soil particulates, the lower solid phase being sufficiently free of said nuclear waste, and (d) separating the ammonia from the soil fines containing the nuclear waste material for disposal or further treatment of said fines. (a) mixing a liquid ammonia with a soil contaminated with nuclear waste in a closed vessel to form an ammonia-nuclear waste-containing soil dispersion or slurry; (b) treating the dispersion or slurry of step (a) with solvated electrons by contacting with a reactive metal; (c) allowing soil particles to selectively precipitate from the dispersion or slurry of step (b) to form a lower solid phase of soil particulates while forming an upper liquid-solid phase comprising soil fines dispersed in said liquid ammonia, the soil particulates of said lower phase having a greater bulk density relative to the soil fines of said upper phase; (d) separating said upper liquid-solid phase from said lower solid phase of soil particulates, the lower solid phase being sufficiently free of said nuclear waste, and (e) separating the ammonia from the soil fines containing the nuclear waste material for disposal or further treatment of said fines. 2. The method of claim 1 including the step of recovering and recycling the ammonia from step (d). 3. The method of claim 1 wherein the liquid ammonia of step (a) is anhydrous liquid ammonia or an ammonia-containing solution. 4. The method of claim 3 wherein the nuclear waste comprises at least one radionuclide, and the soil comprises at least one member selected from the group consisting of clay, disintegrated rock and organic matter. 5. The method of claim 3 wherein the nuclear waste contaminated soil comprises mainly sand. 6. The method of claim 4 wherein the soil of step (a) comprises a radionuclide selected from the group consisting of uranium, plutonium and mixtures thereof. 7. The method of claim 5 wherein the sand comprises a radionuclide selected from the group consisting of uranium, plutonium and mixtures thereof. 8. The method of claim 1 including the step of separating the ammonia from the soil fines of step (d) by distillation means. 9. A method of decontaminating soil containing nuclear waste, which comprises the steps of: 10. The method of claim 9 including the step of recovering and recycling the ammonia from step (e). 11. The method of claim 9 wherein the liquid ammonia is anhydrous liquid ammonia and the reactive metal is a member selected from the group consisting of alkali metal and alkaline earth metal. 12. The method of claim 11 wherein step (b) is performed by circulating at least a portion of the ammonia-containing slurry through a by-pass containing the reactive metal where it dissolves and the slurry is recirculated to the closed vessel for treating the balance of the slurry with solvated electrons. 13. The method of claim 11 wherein the liquid ammonia of step (a) is anhydrous liquid ammonia or an ammonia-containing solution. 14. The method of claim 13 wherein the nuclear waste comprises at least one radionuclide, and the soil comprises at least one member selected from the group consisting of clay, disintegrated rock and organic matter. 15. The method of claim 13 wherein the nuclear waste contaminated soil comprises mainly sand. 16. The method of claim 14 wherein the soil of step (a) comprises a radionuclide selected from the group consisting of uranium, plutonium and mixtures thereof. 17. The method of claim 15 wherein the sand of step (a) comprises a radionuclide selected from the group consisting of uranium, plutonium and mixtures thereof. 18. The method of claim 9 including the step of separating the ammonia from the soil fines of step (e) by distillation means. |
claims | 1. An X-ray apparatus comprising:an X-ray source for emitting X-ray radiation; anda beam chopping apparatus coupled to said X-ray source, wherein said beam chopping apparatus is adapted to rotate, receive said X-ray radiation and form a moving beam spot having a variance in frequency, wherein said variance in frequency decreases as said beam chopping apparatus is rotated faster. 2. The X-ray apparatus of claim 1 wherein said beam chopping apparatus comprises a hollow cylinder having at least one helical aperture. 3. The X-ray apparatus of claim 1 wherein said beam chopping apparatus comprises a hollow cylinder having at least two helical apertures. 4. The X-ray apparatus of claim 3 wherein said beam has a linear scan velocity and wherein said linear scan velocity is varied by modifying a pitch and roll of at least one of said helical apertures. 5. The X-ray apparatus of claim 3 wherein said beam has a linear scan velocity and wherein said linear scan velocity is kept constant by modifying a pitch and roll of at least one of said helical apertures. 6. The X-ray apparatus of claim 3 wherein said beam has a spot size and wherein said spot size is varied by modifying an aperture width of at least one of said helical apertures. 7. The X-ray apparatus of claim 3 wherein said beam has a spot size and wherein said spot size is kept constant by modifying an aperture width of at least one of said helical apertures. 8. The X-ray apparatus of claim 2 further comprising a motor for rotating said cylinder. 9. The X-ray apparatus of claim 8 further comprising a controller for dynamically modifying a rotation speed of said cylinder to achieve a predetermined scan velocity. 10. The X-ray apparatus of claim 9 wherein said rotation speed is equal to or less than 80,000 rpm. 11. The X-ray apparatus of claim 8 wherein said beam has a scan velocity and a spot size and wherein scan velocity and spot size can be modified without varying a speed of said motor. 12. The X-ray apparatus of claim 1 wherein said beam chopping apparatus comprises a hollow cylinder having at least two helical apertures, each having a length and an aperture width along said length and wherein said aperture width narrows along length. 13. The X-ray apparatus of claim 1 wherein said beam chopping apparatus comprises a hollow cylinder having at least two helical apertures, each having a length and an aperture width along said length and wherein said aperture width increases along length. 14. An X-ray apparatus comprising:an X-ray source for emitting X-ray radiation; anda beam chopping apparatus coupled to said X-ray source, wherein said beam chopping apparatus rotates and comprises a hollow cylinder with a first end and a second end defining a length of said cylinder and at least one helical aperture extending substantially along said length, wherein said cylinder is adapted to receive said X-ray radiation and emit said X-ray radiation, having a variance in frequency, through said helical aperture and wherein said variance in frequency decreases as said beam chopping apparatus is rotated faster. 15. The X-ray apparatus of claim 14 wherein said X-ray radiation passes through the helical aperture to produce a beam spot projection pattern, wherein said beam spot projection pattern comprises a beam spot moving vertically with a substantially constant velocity in a plane perpendicular to a plane of the X-ray source. 16. The X-ray apparatus of claim 15 wherein said beam spot projection pattern comprises a beam spot moving vertically with a substantially constant velocity in a plane parallel to a plane of the beam chopping apparatus. 17. The X-ray apparatus of claim 16 wherein said beam spot provides substantially equal illumination of a target object. 18. The X-ray apparatus of claim 14 wherein said beam spot is trapezoidal. 19. The X-ray apparatus of claim 14 wherein said helical aperture has a width that is more narrow at the second end relative to said first end. |
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description | The present invention relates generally to methods and structures for identifying minerals using charged particle beam systems and energy dispersive spectroscopy systems. Mineral analysis systems, such as the Qemscan and MLA available from FEI Company, Hillsboro, Oreg., have been used for many years to analyze mineral samples. To determine the type and relative quantity of minerals present in a mine, a sample in the form of small granules, is fixed in epoxy in a mold and the mold is placed in a vacuum chamber. An electron beam is directed toward a sample and, in a process called “energy dispersive x-ray spectroscopy” or “EDS,” the energies of x-rays coming from the sample in response to the electron beam are measured and plotted in a histogram to form a spectrum. The measured spectrum can be compared to the known spectra of various elements to determine which elements and minerals are present. Mineral analysis systems, such as the QEMSCAN® (Quantitative Evaluation of Minerals by Scanning electron microscopy) and MLA (Mineral Liberation Analyzer) from FEI Company, the assignee of the present invention, have been used for many years to determine minerals present in mines in order to determine the presence of valuable minerals. Such systems direct an electron beam toward the sample and measure the energy of x-rays coming from the material in response to the electron beam. One such process is called “energy dispersive x-ray analysis” or “EDS,” which can be used for elemental analysis or chemical characterization of a sample. Backscattered electron (BSE) detectors are also used for mineral analysis in conjunction with electron beam columns. The intensity of the BSE signal is a function of the average atomic number of the material under the electron beam, and this relationship can be used to develop a useful mineral identification method. EDS systems rely on the emission of X-rays from a sample to perform elemental analysis. Each element has a unique atomic structure, which allows x-rays that are characteristic of an element's atomic structure to be uniquely identified from one another. To stimulate the emission of x-rays from a sample, a beam of charged particles is focused onto the sample, which causes electrons from inner shells to be ejected. Electrons from outer shells seek to fill this electron void, and the difference in energy between the higher energy shell and the lower energy shell is released as an x-ray, which can be detected by an EDS detector. QEMSCAN® comprises a SEM, multiple EDS detectors, and software for controlling automated data acquisition. This technology identifies and quantifies elements within an acquired spectrum and then matches this data against a list of mineral definitions with fixed elemental ranges. The size of the ranges depends directly on the number of x-rays in the spectrum and cannot be applied to higher quality spectra without creating a new mineral definition. Thus, it is not possible to define a universal database for an arbitrary number of X-ray counts. Furthermore, the match is not given as a probability value, it is given as either true or false, and it picks the first match it finds even if a better match might be present elsewhere in the mineral database. MLA technology also combines a SEM, multiple EDS detectors, and automated quantitative mineralogy software. MLA computes a probability match between a measured mineral spectrum and a reference mineral spectrum. This method works reasonably, but the numerical value obtained tends to be dominated by the size of the largest peak in the x-ray spectrum. The acquisition time of a suitable BSE signal is typically on the order of microseconds per pixel. However, EDS systems are usually slower and have a longer acquisition time, typically on the order of several seconds per pixel to uniquely discriminate the spectrum from all other mineral spectra. As a result, the time required to collect an x-ray spectrum to uniquely identify a mineral reduces the number of pixels that can be measured substantially. EDS systems are also typically insensitive to light atoms. Because of the advantages of both EDS detectors and BSE detectors, it is sometimes useful to use both BSE and x-ray spectra to accurately identify minerals, which requires more time and becomes a difficult problem to solve with a commercially viable approach. A mineral classification system must be capable of comparing each unknown measured spectrum to a library of known mineral spectrums, and then making a selection based on which known mineral is most similar to the measured spectrum. Typically, to find the most similar spectrum requires the use of a metric that represents the degree of similarity between the measured data and the known material. Currently, there are various ways to compare two spectrums directly, either by calculating a distance metric or a similarity metric. An example of a method of comparison used in the prior art is to take the sum of the differences between the two spectrums as a distance. The Mineral Liberation Analyzer manufactured by FEI Company, Inc., the assignee of the present invention, uses a chi-squared statistical test to compare the value at each energy channel of the measured spectrum to the value at the corresponding channel of the known mineral spectrum. These prior art approaches are based around comparing the spectrums on a channel by channel basis. The problem of using a comparison on a channel by channel basis is that there is no guarantee that all required peaks in the mineral spectrum are present in the measured spectrum. It is possible that a measured spectrum appears to be similar to a mineral yet it is missing an element that is required by the definition of that mineral, or has an additional element not found in that definition of a mineral. In the XBSE_STD measurement mode of the MLA, each data point is compared against a mineral list. If the data point is not similar to any mineral, then a new mineral entry is created and a high quality EDS spectrum is immediately measured from the sample. However, there are several significant limitations of this approach. First, the user is presented with hundreds of unknown data points and there is no way to distinguish which ones occur most frequently and which ones are outliers. Second, the analysis cannot be performed offline as it requires access to the SEM to collect the high quality data during measurement. Finally, only the raw data is presented to the user and there is no analytical tool to give elemental composition. Thus, there is a need for an improved mineral identification method. An objection of the invention is to improve the identification of minerals in a sample. The present invention facilitates the determination of the mineral content represented of an SEM-EDS dataset, including initially unknown data points. SEM-EDS data points are collected and compared to a set of known data points. Any data point that is not sufficiently similar to the known data point is classified as unknown and clustered with like unknown data points. After all data points are analyzed, any clusters of unknown data points with a sufficient number of data points are further analyzed to determine their characteristics. Embodiments of the invention differentiate unknown data points that are simply outliers, from data points that represent a genuine mineral that is occurring in the sample. The clustering analysis can be performed offline, online, or in real time, and re-processed anytime. The results presented to the operator are typically elemental compositions, average atomic number, or other characteristics that are measured by the analysis. The raw EDS and BSE spectrums may also be presented, as well as the raw data of any other tests done. The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. Embodiments of the present invention are directed to a method and apparatus for efficiently and easily classifying data points. A “data point” is a group of data, such as an EDS spectrum and/or backscattered electron (“BSE”) value. A data point typically corresponds to a mineral. Characteristics of data points corresponding to known minerals are compared to the characteristics of the measured data points. If the characteristics are identical or very similar, the data point is labeled as a known or similar data point. However, if the characteristics of the data point are not similar to the characteristics of the known data points, the data point is labeled as an unknown or dis-similar data point. Any unknown or dis-similar data points will enter into the clustering analysis. Basic Scanning Technology A beam is directed toward a sample surface and emissions generated from the surface by the beam impact are detected. The primary beam can comprise, for example, electrons, ions, photons (e.g., a laser beam or x-rays), or atoms. The beam is typically focused to a point on the sample and the point is scanned across the sample. Particles (used herein to include photons and scattered primary particles) that are emitted, backscattered, or transmitted through the sample in response to the primary beam are detected. Different emissions from the sample, such as x-rays, backscattered electrons, secondary electrons, Auger electrons, transmitted electrons, or photons, are detected in various analysis modalities. The invention is not limited to any particular analytical technique. The different modalities may provide different information about properties of the sample, such as contour information, compositional information, topographical information, or chemical state information. For example, backscattered electron data may be acquired at the same time as x-ray data, with the x-rays being placed at the correct location in the backscattered electron image to produce a spectrum cube. In some embodiments, the different analysis modalities include detecting emissions generated by different beams at different times. In some embodiments, an electron beam is directed toward a sample and scanned across regions having different characteristics, such as different mineral compositions. A first detector may provide information about contour, topography, or atomic number, for example, by detecting backscattered electrons, while a second detector may provide information about composition, for example, by detecting characteristic x-rays. Clustering Cluster analysis, or clustering, is the task of assigning a set of objects into groups, also called clusters, so that the objects in the same cluster are more similar to each other than to those in other clusters. Cluster analysis groups objects based on the information found in the data describing the objects or their relationships. The goal is that the objects in a group will be similar to one other and different from the objects in other groups. The greater the similarity within a group, and the greater the difference between groups, the “better” or more distinct the clustering. Cluster analysis itself is not one specific algorithm, but is an general approach to assigning minerals identifications. It can be achieved by various algorithms that differ significantly in their notion of what constitutes a cluster and how to efficiently find them. Clustering can therefore be formulated as a multi-objective optimization problem. The appropriate clustering algorithm and parameter settings, including values such as the distance function to use, a density threshold or the number of expected clusters, depend on the individual data set and intended use of the results. Cluster analysis is typically an iterative process of knowledge discovery or interactive multi-objective optimization that involves trial and error. It will often be necessary to modify preprocessing and parameters until the result achieves the desired properties. Any standard clustering technique, such as Agglomerative, Single-Pass or K-Means, may be used for the analysis of the present invention. For example, one possible distance metric takes the sum of the differences between the EDS Spectrum channel values. As shown in FIG. 1, the first step in the process is to classify every data point in the SEM-EDS data set, 100, as a known or unknown, 105. A data point is “known” if its spectrum matches the known spectrum of a mineral within a predetermined limit. For example, one measurement of how well spectra match is the Cosine Similarity metric analysis as given in Equation 1. similarity = cos ( θ ) = A · B A B = ∑ i = 1 n A i × B i ∑ i = 1 n ( A i ) 2 × ∑ i = 1 n ( B i ) 2 Equation ( 1 ) Where “i” represents each measurement parameter, such as each normalized energy channel height, average atomic number from back-scattered electron analysis, or other measurement parameter, and the values of data point each spectrum are summed over all the energy channels and other measurements. In some embodiments, a spectrum is considered a match to a reference spectrum when the similarity metric of the two is greater than 90%. After excluding known data points, all unknown data points are compared to the clusters of unknown data points, 110. If the unknown data point's characteristics are similar to another cluster, that is, the similarity metric is greater than a pre-determined amount, the unknown data point is placed in that cluster, 115. If the unknown data point is not similar to other clusters, a new cluster is created, 120. The average value of every cluster for each energy channel is recalculated after the addition of each new data point to further refine the cluster's characteristics and differentiate each cluster from the others, 125. The results of the clustering analysis will be several clusters, with each cluster containing least one “unknown” data point. As shown in FIG. 2., once the SEM-EDS data set is reduced to known data points and clusters of unknown data points, the clusters are sorted by the number of data points in the clusters, 200. This list can be reduced to only those clusters that matched a significant number of data points, 205, for example the top 20 clusters, although analysis of all or fewer clusters is possible. As used herein matching means unknown data points are clustered or grouped together when the characteristics of each data point are identical or similar to the characteristics of the other data points in the cluster or group. In one embodiment, the characteristics of each data point in a group should be within at least three percent of the average value of the all data points in the group. The matching criteria can be tightened if more precise measurements are needed. Once all clusters have been sorted, it is determined whether or not there are any clusters remaining, 210. If there are no clusters remaining after removal of those with few data points, the remaining clusters are outliers, 215, and the process is complete. However, if there are clusters remaining, it means that there is a mineral in the sample that has not been identified. The remaining clusters then undergo quantitative EDS analysis to give the elemental composition of the unknown minerals, 220, and a BSE analysis to determine the average atomic number of the minerals, 225. The average EDS spectrum and BSE value is calculated from each cluster, by averaging all the data points within a cluster. This gives a high quality EDS spectrum that can be further analyzed to give accurate elemental composition and atomic numbers based on BSE data. Once all data is analyzed and placed in the appropriate cluster, the analyzed cluster data is presented to the operator, 230, who may make use of the data to expand the list of mineral definitions to minimize the unknown data points, 235, eliminate clusters with minimal data points, 205, and/or determine that all “unknown” data points are outliers and can be ignored, 215. If desired the operator can instruct the analysis to be repeated so as to rerun the sample with and updated known data point list which will produce fewer unknown data points. The following example shows an analysis of 10 different samples having spectra show in FIGS. 3a-3j. The spectra of the ten samples are being compared to spectra of known minerals in a mineral list. In this example, the mineral list has only two minerals, quartz and pyrite, having spectra as shown in FIGS. 4a and 4b. Each of the spectra of a sample represents a data point. In this example, the data point does not include back scattered electron data. After obtaining the spectra corresponding to the ten points, each data point is analyzed for its similarities with known spectra, for example, by using a cosine comparison on multiple energy channels. Table 1 shows the results of the comparison, and the classification shows how the result of the analysis. In this example the known data points are Quartz and Pyrite. TABLE 1Sample Data and Cluster AnalysisSimilarity WithSimilarity WithSimilarity withSimilarity withNumberQuartzPyriteUnknown_lUnknown_2Classification199.2% 4.3%——Identified as quartz23.73%54.19%——New cluster added‘Unknown_1’33.04%98.18%——Identified as Pyrite45.77%43.08%8.63%New Cluster added‘Unknown_2’54.54%47.81%95.37%10.43%Matches cluster‘Unknown_1’698.96% 4.7%4.16%7.22%Identified as Quartz76.45%44.89%10.72%91.70%Matches cluster‘Unknown_2’88.96%43.72%11.03%92.81%Matches cluster‘Unknown_2’96.02%43.03%11.67%92.42%Matches cluster‘Unknown_2’109.04%43.93%11.45%93.16%Matches cluster‘Unknown_2’ In this example, a spectrum is considered a match when the similarity between samples is greater than ninety percent (90%). As seen in Table 1, samples 1 and 6 have a 99.2% match and 98.96% match respectively with the known values of Quartz, thus the software will designate those samples as Quartz. Sample 2 does not match with either Quartz or Pyrite to a degree of greater than 90%, so it is classified as an unknown sample and place in unknown cluster one. Sample 3 has a match of 98.18% with the known value of Pyrite, thus the software will classify this sample as Pyrite. Sample 4 does not match any of the known samples, and does not match closely with the first unknown sample, sample 3, so it is classified as a second unknown sample and placed in unknown cluster two. Sample 5 has a greater than 90% match to Sample 2 and is placed in unknown cluster one. Samples 7-10 have a greater than 90% match to sample 4, therefore these samples are placed in unknown cluster two. At this point the operator can evaluate the samples in unknown clusters one and two to determine if further analysis is needed, additional known data sets should be added to the software, or if the unknown clusters are simply outlier data points that can be ignored. Thus it can be seen that the current method can quickly and easily cluster unknown samples for more efficient handling. FIG. 5 is an example of a scanning electron beam system 500 with an x-ray detector 540 suitable for analyzing samples prepared according to the present invention. A scanning electron microscope 541, along with power supply and control unit 545, is provided with system 500. An electron beam 532 is emitted from a cathode 553 by applying voltage between cathode 553 and an anode 554. Electron beam 532 is focused to a fine spot by means of a condensing lens 556 and an objective lens 558. Electron beam 532 is scanned two-dimensionally on the specimen by means of a deflection coil 560. Operation of condensing lens 556, objective lens 558, and deflection coil 560 is controlled by power supply and control unit 545. A system controller 533 controls the operations of the various parts of scanning electron beam system 500. The vacuum chamber 510 is evacuated with ion pump 568 and mechanical pumping system 569 under the control of vacuum controller 534. Electron beam 532 can be focused onto sample 502, which is on movable X-Y stage 504 within lower vacuum chamber 510. When the electrons in the electron beam strike sample 502, the sample gives off x-rays whose energy correlated to the elements in the sample. X-rays (not shown) have energy inherent to the elemental composition of the sample are produced in the vicinity of the electron beam incident region. Emitted x-rays are collected by x-ray detector 540, preferably an energy dispersive detector of the silicon drift detector type, although other types of detectors could be employed, which generates a signal having an amplitude proportional to the energy of the detected x-ray. Output from detector 540 is amplified and sorted by the processor 520, which counts and sorts the total number of X-rays detected during a specified period of time, at a selected energy and energy resolution, and a channel width (energy range) of preferably between 10-20 eV per channel. Processor 520 can comprise a computer processor; operator interface means (such as a keyboard or computer mouse); program memory 522 for storing data and executable instructions; interface means for data input and output, executable software instructions embodied in executable computer program code; and display 544 for displaying the results of a multivariate spectral analysis by way of video circuit 542. Processor 520 can be a part of a standard laboratory personal computer, and is typically coupled to at least some form of computer-readable media. Computer-readable media, which include both volatile and nonvolatile media, removable and non-removable media, may be any available medium that can be accessed by processor 520. By way of example and not limitation, computer-readable media comprise computer storage media and communication media. Computer storage media include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. For example, computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by processor 520. Program memory 522 can include computer storage media in the form of removable and/or non-removable, volatile and/or nonvolatile memory and can provide storage of computer-readable instructions, data structures, program modules and other data. Generally, the processor 520 is programmed by means of instructions stored at different times in the various computer-readable storage media of the computer. Programs and operating systems are typically distributed, for example, on floppy disks or CD-ROMs. From there, they are installed or loaded into the secondary memory of a computer. At execution, they are loaded at least partially into the computer's primary electronic memory. The invention described herein includes these and other various types of computer-readable storage media when such media contain instructions or programs for implementing the steps described below in conjunction with a microprocessor or other data processor. The invention also includes the computer itself when programmed according to the methods and techniques described herein. An x-ray spectrum obtained as described above can be stored in a portion of memory 522, such as the measured spectra memory portion 523. Data template memory portion 524 stores data templates, such as definitions of known spectra of elements or, in some embodiments, known diffraction patterns of materials. A weighing factor memory 525 stores weighing factors. While the embodiment shown includes a scanning electron microscope, related embodiment could use a transmission electron microscope or a scanning transmission electron microscope to generate x-rays from the sample. An x-ray fluorescence system could also be used to generate x-rays from the sample. Other embodiments may detect other characteristic radiation, such as gamma rays, from a sample. Further, whenever the terms “automatic,” “automated,” or similar terms are used herein, those terms will be understood to include manual initiation of the automatic or automated process or step. Whenever a scan or image is being processed automatically using computer processing, it should be understood that the raw image data can be processed without ever generating an actual viewable image. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” It should be recognized that embodiments of the present invention can be implemented via computer hardware or software, or a combination of both. The methods can be implemented in computer programs using standard programming techniques—including a computer-readable storage medium configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner—according to the methods and figures described in this specification. Each program may be implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the programs can be implemented in assembly or machine language, if desired. In any case, the language can be a compiled or interpreted language. Moreover, the program can run on dedicated integrated circuits programmed for that purpose. Further, methodologies may be implemented in any type of computing platform, including but not limited to, personal computers, mini-computers, main-frames, workstations, networked or distributed computing environments, computer platforms separate, integral to, or in communication with charged particle tools or other imaging devices, sensors, and the like. Aspects of the present invention may be implemented in machine readable code stored as memory on a storage medium or device, whether removable or integral to the computing platform, such as a hard disc, optical read and/or write storage mediums, RAM, ROM, and the like, so that it is readable by a programmable computer, for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Moreover, machine-readable code, or portions thereof, may be transmitted over a wired or wireless network. The invention described herein includes these and other various types of computer-readable storage media when such media contain instructions or programs for implementing the steps described above in conjunction with a microprocessor or other data processor. The invention also includes the computer itself when programmed according to the methods and techniques described herein. Computer programs can be applied to input data to perform the functions described herein and thereby transform the input data to generate output data. The output information is applied to one or more output devices such as aberration correctors or to a display monitor. In preferred embodiments of the present invention, the transformed data represents physical and tangible objects, including producing a particular visual depiction of the physical and tangible objects on a display. Preferred embodiments of the present invention may make use of a particle beam apparatus, energy beam apparatus, or apparatus using a physical probe tip in order to image a sample. Such beams or physical probes used to image a sample inherently interact with the sample resulting in some degree of physical transformation. Further, throughout the present specification, discussions utilizing terms such as “calculating,” “determining,” “measuring,” “generating,” “detecting,” “forming,” “resetting,” “reading,” “subtracting,” “detecting,” “comparing,” “acquiring,” “mapping,” “recording,” “transforming,” “changing,” or the like, also refer to the action and processes of a computer system, a sensor, or similar electronic device, that manipulates and transforms data represented as physical quantities within the computer system into other data similarly represented as physical quantities within the computer system or other information storage, transmission or display devices. The invention has broad applicability and can provide many benefits as described and shown in the examples above. The embodiments will vary greatly depending upon the specific application, and not every embodiment will provide all of the benefits and meet all of the objectives that are achievable by the invention. Particle beam systems suitable for carrying out some embodiments of the present invention are commercially available, for example, from FEI Company, the assignee of the present application. To the extent that any term is not specially defined in this specification, the intent is that the term is to be given its plain and ordinary meaning. The accompanying drawings are intended to aid in understanding the present invention and, unless otherwise indicated, are not drawn to scale. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. |
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058870415 | summary | BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a system for a nuclear power plant and, more particularly, to a system for identifying nuclear power plant components such as, for example, nuclear fuel assemblies. The invention also relates to a method for identifying nuclear power plant components. Background Information In a typical nuclear reactor, the reactor core includes a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include top and bottom nozzles, a plurality of elongated transversely spaced guide thimbles extending longitudinally between and connected at opposite ends to the nozzles, and a plurality of transverse support grids axially spaced along the guide thimbles. Each fuel assembly also includes a multiplicity of elongated fuel elements or rods. The fuel rods are transversely spaced apart from one another and from the guide thimbles. The transverse grids support the fuel rods between the top and bottom nozzles. The fuel rods each contain fissile material in the form of a plurality of generally cylindrical nuclear fuel pellets maintained in a row or stack thereof in the rod. The fuel rods are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and, thus, the release of a large amount of energy in the form of heat. A typical nuclear reactor core contains about 100 to 200 nuclear fuel assemblies which are typically about 13 feet tall with a square cross-section having 8.5 inch sides. The fuel assemblies are vertically positioned in an array within the reactor core and are subject to both twisting and leaning motions away from their intended positions in the array. The top nozzle of each of the fuel assemblies has two locator holes on the top thereof. These locator holes must be properly aligned with corresponding locator pins of a reactor vessel head. The reactor vessel head, which normally rests on top of the reactor core, is typically made of 8 inch sheet steel and weighs about 10 to 15 tons. Therefore, it is critical that the fuel assemblies are suitably inline for correctly engaging the corresponding locator pins of the reactor vessel head before "dropping the head". During a refueling process, nuclear fuel assemblies are added to the reactor core and previously existing assemblies are either removed or repositioned. The correct positioning of the appropriate assembly is crucial in terms of reactor efficiency and safety. After the assemblies are placed in their planned positions, a video camera is swept over the entire core a plurality of times to verify the identity of each assembly and its correct placement relative to adjacent assemblies. The operator views the video output on a screen, reads a fuel assembly identifier or identification number engraved on a spring clamp of each assembly, and compares the identification number to a core map plan for verification. During this process, the operator dwells on each individual assembly until its identifier can be read. Light adjustments are made, if necessary, and unreadable identifiers are noted. In other camera sweeps, the camera is focused on the gaps between adjacent assemblies. The operator examines the video output and measures the distances between known points on adjacent assemblies to indirectly determine gap distances. At least three camera passes over the core are typical. The operator also compares the measured gaps to predetermined gap allowances for verification. It is known to manually use a measuring device, such as a ruler, on a video monitor in order to measure the distance or gap between nuclear fuel assemblies. However, such manual technique is laborious, subject to human error, and subject to cumulative errors as the various gaps are measured between all of the adjacent pairs of the fuel assemblies in the reactor core. Accordingly, there is room for improvement in determining the gap between an adjacent pair of fuel assemblies. It is also known to manually compare the identifier values and gap measurements with planned values for verification. Those values which cannot be determined with the video output are manually checked in the reactor core. Human mistakes may take much time to correct and require another verification before acceptance. Various difficulties are associated with the fuel assembly identity and gap alignment verification processes. Phenomena, such as poor lighting, the presence of shadows, and dark deposits, may make identifier values very difficult to read. Also, such phenomena may hide or distort key image features used for making gap measurements. In cases of uncertainty, the operator must physically go to the core and make a manual check, thereby being exposed to unwanted radiation. The current fuel assembly identity and gap verification processes together take approximately four to six hours to complete and is subject to human error. There is a need, therefore, for a method and apparatus which will significantly reduce verification time while increasing accuracy. SUMMARY OF THE INVENTION The invention is directed to an automated system for identifying at least one of a plurality of nuclear power plant components. The automated system includes camera means for inputting a first image of at least one of the nuclear power plant components and providing an input signal therefrom; digitization means for generating a second, digitized image of the nuclear power plant components from the input signal; means for locating the component identifier of the nuclear power plant components from pixel elements of the digitized image; and determining means at least for determining the component identifier including: plural recognizer means having an output providing an intermediate recognition of the component identifier, and means for combining the outputs of the plural recognizer means to recognize the component identifier. The outputs of the plural recognizer means may include an intermediate identifier and a corresponding confidence value. The means for combining the outputs may include means for determining unique ones of the intermediate identifiers, means for summing the confidence values corresponding to each unique intermediate identifier to provide a summed confidence value therefor, and means for recognizing the component identifier as the unique intermediate identifier having the largest summed confidence value. |
063200910 | claims | 1. A process for immobilizing actinide oxides in a ceramic form comprising pyrochlore, brannerite and rutile, which comprises the steps of: milling said actinide oxides into powder form to achieve powder particle size less than 50 microns; blending ceramic precursors with said powder, said ceramic precursors comprising neutron absorbers, oxides of titanium and hydroxides of calcium, wherein said blending is accomplished via wet ball milling or an attritor mill; pouring said blend into a die; cold pressing said blend at a pressure in the range of 1,000-20,000 psi; and sintering said pressed blend at a temperature range of 1200-1500 deg C. for 1-8 hours in an atmosphere selected from the group consisting of air, reducing atmosphere and inert atmosphere to form a ceramic material. said milling and blending steps are accomplished using a high-speed attritor mill. granulating said blend prior to said pouring step to facilitate transfer of the blend into said die. adding binder and lubricant materials to said blend during said granulating step. adding a binder material to said blend and applying a lubricant material to said die during said granulating step. said lubricant material is ten wt % oleic acid added to acetone. heating said cold pressed material to a temperature between 100 and 300 deg C. and holding at said temperature for one-half to three hours to thoroughly dry said ceramic and decompose said binder and lubricant materials, prior to said sintering step. heating said cold pressed material to a temperature between 100 and 300 deg C. and holding at said temperature for one-half to three hours to thoroughly dry said ceramic and decompose said binder and lubricant materials, prior to said sintering step. said halides are selected from the group consisting of fluorides, chlorides, bromides and iodides; said alkalis are selected from the group consisting of lithium, sodium, potassium, rubidium and cesium; and said alkaline earths are selected from the group consisting of magnesium, calcium, strontium and barium. calcining said actinide oxides, prior to said blending step, at a temperature greater than 750 deg C., in an air or inert atmosphere. calcining said ceramic precursors, prior to blending with said actinide oxides, in an air atmosphere at a temperature ranging from 700 to 800.degree. C. for about one hour. placing said ceramic in a can; placing said can in a canister; pouring high level waste glass into said canister around said can. wet mixing said neutron absorbers, titanium oxides and calcium hydroxides; drying said wet mixture; size reducing said dried mixture; and calcining said size reduced mixture. milling said oxides using a high-speed attritor mill into powder form to achieve nominal powder particle size of than 20 microns; calcining ceramic precursors at a temperature of about 750 deg C., in an air atmosphere for about one hour, said ceramic precursors comprising TiO.sub.2 (anatase), Ca(OH).sub.2 and neutron absorber materials HfO.sub.2 and Gd.sub.2 O.sub.3 ; blending said calcined ceramic precursors with said milled oxides powder using a high-speed attritor mill to a degree such that uniform blending on a scale of less than 20 microns is achieved; granulating said blend with addition of binder and lubricant materials, pouring said blend into a die and cold pressing said blend at 2000 psi, heating said cold pressed blend to binder burnout temperature of 100 to 300 deg C. and holding at said temperature for one-half to two hours in an air atmosphere; sintering said heated blend to 1350 deg C. and holding at said temperature for 4 hours in an air atmosphere; and cooling said ceramic to room temperature. oxidizing said actinides; milling said actinide oxides into powder form to achieve nominal powder particle size less than 20 microns; blending ceramic precursors with said powder, said ceramic precursors comprising neutron absorbers and oxides or hydroxides of titanium and calcium, wherein said blending is accomplished via wet ball milling or an attritor mill; pouring said blend into a die; cold pressing said blend at a pressure in the range of 1,000-20,000 psi; and sintering said pressed blend at a temperature range of 1200-1500 deg C. for 1-8 hours in an atmosphere selected from the group consisting of air, reducing atmosphere and inert atmosphere to form a ceramic material. hydriding said actinides to a fine powder; nitriding said hydride powder; oxidizing said nitride powder; calcining said oxides; and removing any halide impurities present after said calcining step. 2. The process according to claim 1 wherein said actinide oxides are selected from the group consisting of uranium, plutonium, thorium, americium and neptunium. 3. The process according to claim 2 wherein the quantity of actinide oxide is no greater than 36 wt %. 4. The process according to claim 2 wherein said actinide oxides are uranium oxide and plutonium oxide. 5. The process according to claim 4 wherein the ratio of uranium oxide to plutonium oxide is 2:1. 6. The process according to claim 5 wherein the quantities of plutonium oxide and uranium oxide are 12 wt % and 24 wt % respectively. 7. The process according to claim 4 wherein said plutonium oxide has a nominal particle size less than 2 millimeters. 8. The process according to claim 1 wherein said actinide oxide is milled to a powder particle size of nominally 20 microns. 9. The process according to claim 1 wherein said neutron absorber material is at least one material selected from the group consisting of hafnium, gadolinium and samarium. 10. The process according to claim 9 wherein said neutron absorber materials are HfO.sub.2 and Gd.sub.2 O.sub.3, in the amounts of 10.6 wt % HfO.sub.2 and 8 wt % Gd.sub.2 O.sub.3, and the ratios of Gd.sub.2 O.sub.3 to PuO.sub.2 and HfO.sub.2 to PuO.sub.2 are each equal or greater than unity. 11. The process according to claim 1 wherein said oxide of titanium is TiO.sub.2 (anatase) and said hydroxide of calcium is Ca(OH).sub.2. 12. The process according to claim 1 wherein said cold pressing step occurs at about 2000 psi. 13. The process according to claim 1 wherein said sintering step occurs at about 1350 deg C. with temperature held for four hours. 14. The process according to claim 1 wherein; 15. The process according to claim 14 wherein said attritor mill is operated at approximately 950 rpm for a 1-gallon attritor mill and wherein the equivalent rpm is used for larger attritor mills by having tip speeds matched. 16. The process according to claim 14 wherein said attritor mill is operated for five minutes. 17. The process according to claim 14 further comprising adding a sufficient amount of dispersant to said attritor mill to maintain powder flowability and reduce holdup of the mill, said amount being in the range of a half of a percent to three weight percent. 18. The process according to claim 17 wherein said dispersant is selected from the group consisting of ethylene bis-stearamide, polyolefin, stearic acid, citric acid and monoisopropanol-amine. 19. The process according to claim 18 wherein said dispersant is a half a percent of ethylene bis-stearamide or three weight percent polyolefin. 20. The process according to claim 14 wherein said attritor mill utilizes a milling media with size ranging from two to five millimeters, and said media is selected from the group consisting of zirconia, aluminum oxide, depleted uranium, stainless steel, and ceramic. 21. The process according to claim 20 wherein said media is 5 mm spherical yttria stabilized zirconia. 22. The process according to claim 1 further comprising: 23. The process according to claim 22 further comprising: 24. The process according to claim 23 wherein said binder material is a mixture of hydroxy-propyl methylcellulose, polyethylene glycol and water. 25. The process according to claim 24 wherein the proportions of said mixture are 0.5 to 2 wt % hydroxy-propyl methylcellulose, 0.5 to 5 wt % polyethylene glycol, and 0.5 to 10 wt % water. 26. The process according to claim 23 wherein said lubricant material is polyolefin or ethylene bis-stearamide. 27. The process according to claim 22 further comprising: 28. The process according to claim 27 wherein: 29. The process according to claim 23 further comprising: 30. The process according to claim 27 further comprising: 31. The process according to claim 1 further comprising addition of sintering aids materials during said blending step to facilitate the sintering process. 32. The process according to claim 31 wherein said sintering aids materials are selected from the group consisting of B.sub.2 O.sub.3, Al.sub.2 O.sub.3, SiO.sub.2, and alkalis and alkaline earth oxides, halides, sulfates, and hydroxides; 33. The process according to claim 32 wherein said sintering aids are in quantities ranging from 0.1 to 5 wt %. 34. The process according to claim 1 wherein said atmosphere is air. 35. The process according to claim 1 wherein said reducing atmosphere is a mixture of 5% CO and 95% CO.sub.2. 36. The process according to claim 1 wherein said inert atmosphere comprises at least one gas selected from the group consisting of helium, neon, argon, krypton and xenon. 37. The process according to claim 36 wherein said gas is argon. 38. The process according to claim 1 further comprising: 39. The process according to claim 38 wherein said calcination occurs for about one hour at a temperature of 950 deg C. 40. The process according to claim 1 further comprising: 41. The process according to claim 40 wherein said calcination occurs for about one hour at a temperature of 750 deg C. 42. The process according to claim 1 further comprising: 43. The process according to claim 1 wherein said ceramic precursors are formed by the process comprising: 44. A process for immobilizing plutonium and uranium oxides in a ceramic form comprising pyrochlore, brannerite and rutile, which comprises the steps of: 45. A process for immobilizing actinides in a ceramic form comprising pyroclore, brannerite and rutile, which comprises the steps of: 46. The process according to claim 45 wherein said oxidizing step comprises: |
summary | ||
052895122 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in the schematic illustration of FIG. 1 that the invention is generally indicated by the numeral 10. Nuclear propulsion reactor 10 is generally comprised of reactor vessel 12, annular-shaped first core 14, cylindrical second core 16, and propellant nozzle 18. Reactor vessel 12 is formed as any suitable reactor pressure vessel known in the industry. First end 20 of reactor vessel 12 forms a plenum 22 that allows second core 16 to be in fluid communication with one end of first core 14. The second end 24 of reactor vessel 12 has propellant nozzle 18 attached thereto and in fluid communication with second core 16. A plenum 13 for the inlet propellant is also provided at the second end 24. As seen in the sectional view of FIG. 2, reactor vessel 12 may be provided with a neutron reflector 25 and control drums 26 between the reactor vessel wall and first core 14. Control drums 26 are arranged so as to be rotatable on their longitudinal axis. Each control drum 26 is provided with neutron absorber material 28 around a portion of its circumference for control of reactivity. Although only two control drums 26 are shown for ease of illustration it should be understood that a number of control drums would normally be spaced around the circumference of reactor vessel 12 when such control devices are incorporated into the reactor design. As seen in FIG. 2, first core 14 is annular in shape and provided with a plurality of fuel elements 30. In the preferred embodiment the propellant is heated directly by fuel elements 30 as the propellant travels through first core 14. For illustration purposes a particle bed reactor (PBR) fuel element design is shown. Each fuel element 30 is formed from an outer porous frit 32, inner porous frit 34, and fuel bed 36. Inner and outer frits 32, 34 are coaxial and held in position by end fittings in a manner known in the art. Fuel bed 36 in the annular space between frits 32, 34 is formed from a large number of relatively small spherical nuclear fuel particles. Each fuel element 30 is positioned inside a cylinder 38 such that there is a space between outer porous frit 32 and the inner surface of cylinder 38. During normal operations propellant/coolant flows into the inlet end of inlet channel 39 between outer porous frit 32 and cylinder 38, radially through outer frit 32, fuel bed 36, and inner frit 34 into the cylindrical space or exit channel 40 on the interior of inner frit 34, and then axially out the exhaust end of fuel element 30 through exit channel 40. The propellant/coolant is heated as it flows across fuel bed 36 and through exit channel 40. The details of only one fuel element 30 are shown for ease of illustration. Moderator material 42 is used in first core 14 between fuel elements 30 to enhance the fission reaction. A moderator such as beryllium hydride that has low specific mass, low neutron absorption, and high hydrogen concentration is preferred. FIG. 3 is an enlarged view of a portion of second core 16 seen in FIG. 2. Inner vessel wall 44 and insulation 46 separate first core 14 from second core 16. In the preferred embodiment second core 16 is formed from a cylindrical block 48 of a highly refractory fissionable carbide that is positioned in the axial space encompassed by first core 14. A plurality of axial passages 50 are provided through block 48 to allow the passage of propellant/coolant therethrough. The major metal component of block 48 is selected to optimize the refractory characteristics of the material. Examples of suitable metals are hafnium, tantalum, zirconium, and niobium. The fissionable component may be an isotope of uranium such as U.sup.233 or U.sup.235 or the such more reactive americium (Am.sup.242m). As an alternate to the use of passages 50, block 48 may be in the form of an open porosity carbide foam that would allow flow of propellant/coolant therethrough. FIG. 4 is also an enlarged view of a portion of second core 16 seen in FIG. 2 and illustrates an alternate embodiment of second core 16. In this embodiment, a plurality of conduits 52 are provided for flow of propellant/coolant therethrough. Heating of the propellant/coolant as it passes through conduits 52 may be accomplished by fissionable material incorporated into conduits 52 or by a fissionable gas contained in spaces 54 between conduits 52. Propellant nozzle 18 may be an y suitable type known in the art. Propellant nozzle 18 is attached to or in fluid communication with the second end 24 of reactor vessel 12. Propellant/coolant travelling through second core 16 is directed to propellant nozzle 18. In operation, propellant/coolant from a source not shown is directed to flow through nuclear fuel elements 30 in first core 14. As it travels through first core 14 the propellant/coolant is heated to a temperature near 2500 degrees K. As indicated by the arrows in FIG. 1, the propellant/coolant enters plunum 22 and is directed into second core 16 where it is heated to a higher temperature as it travels through second core 16 to propellant nozzle 18. Propellant nozzle 18 is designed to produce propulsive thrust as the heated and expanding propellant/coolant exits propellant nozzle 18. Control drums 26 provide a means of controlling reactivity. Control rods may also be used in first core 14. The fission reaction in first core 14 causes heating of the propellant/coolant as it passes therethrough. The annular shape of first core 14 provides a source of predominantly high energy leakage neutrons for driving the fission reaction in second core 16. In this manner first core 14 serves as the first stage for heating the propellant/coolant to near the present maximum possible exhaust temperature. The highly refractory material of second core 16 serves as a second stage for heating the propellant/coolant to an even higher temperature that increases the specific impulse and the thrust-to-weight ratio. It should be noted that the invention described above is intended to address the propulsive needs of vehicles designed for military space missions and for deep space exploration. For ease of illustration, details of such vehicles and means for supplying propellant/coolant known in the art are not shown. For maximum efficiency, liquified gas is normally used as a propellant since it quickly changes to its normal gaseous state during passage to the reactor and expands during heating by the reactor. This also serves the purpose of removing heat from the reactor and maintaining component temperatures within acceptable limits. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense. |
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051587416 | abstract | A liquid metal cooled nuclear fission reactor plant having a top entry loop joined satellite assembly with a passive auxiliary safety cooling system for removing residual heat resulting from fuel decay during shutdown, or heat produced during a mishap. This satellite type reactor plant is enhanced by a backup or secondary passive safety cooling system which augments the primary passive auxiliary cooling system when in operation, and replaces the primary cooling system when rendered inoperative. |
039376494 | summary | BACKGROUND OF THE INVENTION Tritium is a hydrogen atom containing one proton, two neutrons, and one electron. Radioactive tritium has a half-life of 12.33 years and emits beta particles during its decay. While the human skin will readily stop beta particles without any damage, tritium will easily vaporize and the inhalation of tritium is dangerous as internal body tissues are easily damaged by beta particles. In response to the increasing demands for electrical power within the United States, more atomic reactor generating plants are being built, particularly those having high temperature gas cooled reactors (HTGR). In HTGR's, there is a large production of tritium. Tritium is so pervasive, that it easily penetrates the steel tubing of the steam generator of the reactor and into the water system. Once into the water system there are several ways for tritium to escape into the atmosphere. To date, tritium has been removed from HTGR's only by unrestrained release into the atmosphere, or into the water disposal system, or otherwise into the surrounding environment. As more and larger HTGR's are built, the pollution of the environment through this indiscriminate discharge steadily increases and will soon create a significant problem unless remedied. In fact, the maximum permissible amount of release of radiation to the environment established by the Atomic Energy Commission will be exceeded by the rate of production of tritium in the large HTGR's already in the planning stage. SUMMARY OF THE INVENTION Accordingly, it is among the objects of this invention to: provide a safe process and system for the removal of radioactive tritium from high temperature gas cooled atomic reactors without polluting the environment and to provide a process and system for removal of tritium from any system containing an inert-to-oxygen circulating fluid which becomes tritiated. These and other objects of the invention are achieved by a process and system in which part of the reactor coolant which becomes permeated with tritium is continually removed and processed to remove the tritium. The process involves combining the removed reactor coolant under conditions of elevated temperature and pressure with gaseous oxygen, so as to result in a tritiated water vapor formation reaction from the tritium in the reactor coolant and the gaseous oxygen. The tritiated water vapor and the remaining gaseous oxygen are then successively removed by fractional liquefaction steps. The liquefied tritiated water vapor is then removed from the processing system and safely disposed of; the liquefied gaseous oxygen is used as cooling means in the water vapor liquefaction step and then used as the gaseous oxygen combined to form the water vapor; and the now untritiated reactor coolant is returned to the reactor for re-circulation. The processing system is designed against accidents through the inclusion of radiation monitors at points immediately after removal of the reactor coolant from circulation and immediately prior to its return to recirculation, and through pressure and temperature sensors connected through electronic controls to fast-acting pneumatic valves which immediately shut the processing system down in case of any malfunction. An additional provision is the heating of the reactor coolant prior to its return to be re-circulated by means of a heat exchange with ordinary circulating water, thus resulting in a supply of chilled water for use elsewhere in the reactor system and supporting environment. |
abstract | An embodiment of the invention relates to a method of analyzing a substance comprising the steps of: fabricating a structure comprising said substance and at least one graphene layer; carrying out at least one measurement step with respect to said structure; and analyzing the measurement result of said measurement step to receive at least one analytical result concerning said substance. |
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abstract | A transmission source loading apparatus for an imaging system utilizing a transmission source is disclosed. The source loading apparatus comprises a storage container for storing the transmission source, and a translation device. The translation device is adapted for advancing the transmission source from the storage container into a holder device for use of the imaging system. A gantry for an imaging system utilizing a transmission source is also disclosed. The gantry includes a gantry housing, a detector ring, a holder device for rotating the transmission source in a rotation path associated with the detector ring, and a transmission source loading apparatus. |
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051606950 | summary | FIELD OF THE INVENTION The invention pertains to a new physics process and method, and to associated apparatus for the creation of conditions under which nuclear fusion reactions can be made to occur and can be controlled, among charged particles capable of undergoing nuclear fusion. The invention thus involves two separate but related features: First is the conception of a new, unique and heretofore unrecognized set of physics processes that promote fusion reactions at high density among fusion fuel ions that are following converging spherical flow patterns, at operating conditions not previously thought to be capable of achieving or allowing such reactions or reaction densities, and; second, the conception of new and unique means of creating electric field structures for acceleration of such ions to achieve the necessary converging spherical flow. The general physics principles and conditions that are the subject of this invention can be applied with ANY means of accelerating fusion fuel ions, while the embodiments and conceptions of apparatus set forth in the preferred embodiments given here will apply most specifically to the acceleration of ions in a manner best and uniquely suited to exploit these physics processes. BACKGROUND OF THE INVENTION The central problem of creating useful controllable nuclear fusion reactions among ions is the necessity of confining a sufficient density of ions over a large enough volume of space, with high enough particle energy, to ensure that the reaction rate density between the ions is high enough to be interesting for both power generation and to overcome all radiative, collisional and other losses that may be associated with or inherent in the fact of the particles' confinement at high energy. Traditionally, two principal means have been examined to attempt the achievement of these conditions. These are "inertial" confinement and "magnetic" confinement. The major means of attempting inertial confinement has been the use of intense beams of laser light, focussed on the surface material of spheres made of or containing fusion fuels, with sufficient strength to vaporize, heat and "blow off" surface material and thus to provide a radial compressive force on the sphere surface. This force then can act to accelerate the sphere surface inwards, compressing and heating the material contained therein. If of sufficient strength this could, in principle, cause particle densities and temperatures (energies) to become high enough that fusion reactions may occur. The principal difficulty in this approach has been the attainment of stability during compression over a large enough volume of material, in a short enough time, that radiation and electron conduction losses do not dominate and prevent the achievement of the requisite conditions for fusion. This approach has not proven feasible to date, and is not of further interest here. Most of the world's fusion research efforts have been devoted to the magnetic confinement approach, in which strong magnetic fields are used to constrain the motion of fusion fuel ions (and electrons) along closed field lines in toroidal field geometries, for example, or along open field lines with large internal magnetic reflection characteristics, as in double-ended "cusp" mirror or solenoidal magnetic "bottle" confinement schemes. In these approaches, the forces acting to "contain" or "confine" the fusion fuel ions are always due to the interaction of their motion with the externally-imposed magnetic fields, and are thus principally at right angles to the direction of the particle motion, rather than oppositely-directed, as would be desireable for action against the particle motion. These magnetic approaches thus suffer from use of an indirect and therefore inefficient means of constraining ion loss motion towards the confining walls of the system. A more detailed discussion and summary of these and other related approaches to magnetic and non-electric inertial confinement of fusion fuel ions, and references to other writings on this topic is given by R. W. Bussard.sup.1 in U.S. Pat. No. 4,826,646, incorporated herein by reference, in connection with a description of an alternative electric inertial means of plasma confinement. This writing also describes the principal loss mechanisms confronting these "conventional" concepts for plasma confinement, and the general nature of the characteristics and limitations of these approaches. In the above patent it is shown that conventional magnetic confinement approaches to fusion power generation are practically unable to take advantage of the large energy gains (G=ratio of energy output to energy input per fusion reaction) naturally found in the fusion reactions between various reactive isotopes of the light elements These gains can be as large as G.apprxeq.1000-2000 for the fusion of deuterium (D or .sup.2 H) with tritium (T or .sup.3 H), the two heavy isotopes of hydrogen (p or .sup.1 H), according to D+T.fwdarw..sup.4 He+.sup.o n (+17.6 MeV), or up to G.apprxeq.50-100 for fusion between hydrogen (p) and boron-11 (.sup.11 B), p+.sup.11 B.fwdarw.3 .sup.4 He (+8.6 MeV). In spite of this, it is found that the large power requirements for confinement and plasma heating in magnetic confinement approaches place practical engineering limits on the energy gain potentially achievable to 2<G<5. Because of the difficulties inherent in the non-electric inertial and magnetic means for confining ions, some researchers turned to the use of more direct means of providing energy and motion to fusion fuels, by use of electric fields for their acceleration, and to spherically-convergent geometries for their densification by such motion. The simplest such system is that with pure spherical goemetry, in which a negative potential (-E.sub.w) is maintained at the center of a spherical shell by an electrode (cathode) mounted at the center. Positive ions introduced into this system will "fall down" the radial electric field toward the center, gaining energy and speed with nearly 100% efficiency in the process. In principle, this enables the achievement of large gain (G) from fusion reactions due to collisions at the system center. If the ions are moving on purely radial paths, they will stop only when the force of electrostatic repulsion between them is sufficient to overcome the kinetic energy gained in their fall "down" the potential well. The radius (r.sub.coul) at which this will occur is very small for particles that have gained energy from potential wells with energy depths and densities of interest for fusion (e.g. for E.sub.w .apprxeq.100 keV, r.sub.coul .ltoreq.1E-5 cm), and a consequent large increase in density with decreasing radius will result from the geomet ric radius-squared variation of area in the converging ion flow. However, a neutral (or near-neutral) plasma can not be confined by a static electric field of this type, because of charge separation and the resulting production of local dielectric fields that cancel the otherwise confining electrostatic field (Earnshaw's Theorem). Thus, the ion density that can be reached by this means is too small for fusion reactions at useful power levels. This difficulty can be overcome, and large ion densities achieved in plasmas of electrons and ions that are NOT locally neutral, by the use of inertial forces (particle kinetic energy) to create the confining field in a mixture of ions and electrons. One of the earliest such concepts was studied by Elmore, Tuck and Watson.sup.2, in 1959, who proposed to overcome the Earnshaw's Theorem limits (above) by injection of energetic electrons radially inward to the center of a spherical volume through a spherical shell screen grid system, as indicated in FIG. 1a. The grid 100 is to be held at a high positive potential relative to an electron-emitting outer surface shell 110 surrounding the grid, so electrons are injected into the interior grid space with the energy of the potential difference 120 between the grid and the outer shell. Electrons thus injected will converge to a central region 130 where their electrostatic potential at the sphere center is approximately equal to the grid injection energy. FIG. 1b shows the potential distribution in such a device. This large negative potential is then used to "trap" ions "dropped" into the well at the position of the electron injection grid 200, for ions so trapped will oscillate back and forth across the well at radius 200 (Rg) until central collisions result in fusion reactions, whose products 220 are sufficiently energetic to escape the well boundary, and deliver energy outside the well system. Non-reactive central collisions (i.e. scattering collisions) will not cause significant particle losses because they take place at the device center, where the only effect is to redirect the momentum vector of the colliding particles to new radial directions (assuming that the system is arranged so that central collisions have coincident center-of-mass and center-of-lab frames). The system they studied was unpromising, however, because no means were provided to inhibit the loss of electrons from the sphere outer surface, and because the model for radial energy distribution of the electrons was such (Maxwellian) that very inefficient well formation was inherent in the system concept. These two defects led to greatly excessive electron power losses, such that net power production by fusion was a practical impossibility in this system. In addition both Elmore, Tuck and Watson.sup.2, and Furth.sup.3 showed that the confinement would be unstable at ion densities of interest for fusion power; thus ion confinement by electron injection in purely inertial-electrostatic wells, with the energy distributions assumed in these studies, is not a useful approach to the attainment of fusion power. The limitations of electron injection were overcome by Farnsworth.sup.4 and Hirsch.sup.5, working with Farnsworth, who used ion injection rather than electron injection for the establishment of initial conditions for the formation of ion-trapping potential wells. The several-thousand-fold mass difference between these two species of charged particles allowed the attainment of much more stable field/ion-distribution structures than predicted for initial well formation by electron injection alone. As shown in FIG. 2a, Hirsch and Farnsworth proposed to use the (radial) injection of (heavy) ions at well depth energies (hundreds of keV) to form a spherically-symmetric virtual anode region 300 within the injection volume, which would then attract electrons from an electron-emitting grid screen 310 located outside this volume, to fall radially through the ionic virtual anode and form a spherically-symmetric interior virtual cathode 320 which then, in turn, would accelerate the ions further to convergence at the system center 330. In actual fact, however, their experiments utilized ion injection from six symmetrically-arranged ion "guns" 400 located in a cubical array around the surface of a sphere 410 which contained a screen grid 420 for electron emission (as described by Hirsch in two patents on the subject.sup.6), as shown in FIGS. 2b and 2c. These experiments achieved continuous fusion reaction rates of about 1E10 reactions/second, where EX designates 10 raised to the power X. The models used by Hirsch.sup.5 could not explain these high reaction rates (see e.g. Dolan et al.sup.7), and it was suspected that intersecting and colliding beam phenomena associated with the use of the tightly-focussed, opposing ion guns led to dominant phenomena different from those of the concentric, nested virtual electrode structures hypothesized by Hirsch/Farnsworth.sup.4,5 in their original descriptions of the concept. Theoretical models of electron and ion circulation and of associated potential well shape were examined by Black.sup.8, who showed that the hypothesized virtual electrode structures would not occur in ion/electron flows which had any finite angular (i.e. transverse) momentum in their motion across the potential well. A later study by Baxter and Stuart.sup.9 of the Hirsch/Farnsworth experiments emphasized the role played by multiple (ca.7-10) transits of ions across the well due to the reflection of ions by grid structures from opposing ion guns used in the experiments, but still remained inconclusive as to an explanation for the anomalously large observed fusion neutron production rates. In order to attain net power production (i.e. high gain, G) from fusion reactions induced by collisions at the center of such systems, Farnsworth, Hirsch and Bussard all showed that the electron current circulating across the system, and through the electron grid (virtual cathode) region, must reach very large values, equivalent to electron current recirculation ratios (G.sub.j) of G.sub.j .apprxeq.1E5 to 1E6 (circulating vs. injected electron current). The corollary ion flow recirculation ratio (G.sub.i) required was also shown to be in the range of G.sub.i .apprxeq.1E3 to 1E4, for the production of net fusion power. It is evident that these values can be attained only if electrons and/or ions are not removed by collisions with structure (e.g. grids) and/or walls of the system. But in the Hirsch/Farnsworth approach, as in the concept of Elmore, et al above, the existence of grid structure of significant solidity in the path of the circulating particle flows will always prevent the buildup of these large circulating currents needed to obtain large system power gain (G) values. Thus an inherent limitation of the Hirsch/Farnsworth approach is due to the ion gun structures required for ion injection, and of associated electron-emitting grid structures to provide the gross charge neutralization required to allow buildup of large ion currents and of large densities of both ions and electrons in recirculating electron and ion flow, as needed for large system gain. The very components required for supply of particles to the system thus prevent the attainment of the high recirculating densities required for large power output. This defect was recognized by Hirsch.sup.10, who tried to find a way to reduce structure-collision losses of electrons circulating through the system, by passing currents through the screen/grid wires or rods so as to provide "magnetic insulation" around them sufficient to prevent electrons from striking them as the electrons passed back and forth through the screen grid region. This did not appear to be promising, as proposed, for it introduced more complexity into the system structure and increased power requirements, without providing enough insulation to solve the structure-collision-loss problem. In addition, it introduced transverse momentum to the particle current streams, which further reduced their ability to converge towards a point by radial motion. Other work using electron injection to enhance magnetic confinement schemes was conducted by several researchers.sup.11, but is not relevant here. In reference to FIGS. 3a and 3b, a solution to most of these problems was given by Bussard.sup.1,12 who proposed a concept for a magnetically-confined, electron-injection-driven, negative potential well, which confines ions 520 injected at low energy by injectors 530 on the field axes, principally by inertial-electrostatic fields set up by high-energy electrons 540, supplied by electron guns 510, and confines these electrons without structure-collisions by use of special polyhedral point-cusp quasi-spherical magnetic fields 500 around the system outer surface. FIG. 3a shows a cross-section of the polyhedral system of FIG. 3b, taken on the plane X--X. A detailed study of this concept.sup.13 shows that such a system can work, and that high gain values (and their requisite large electron current recirculation ratios, G.sub.j .apprxeq.1E5-1E6) can be obtained if special polyhedral surface magnetic fields of sufficient strength (e.g. 2-20 kGauss) are arranged around the system. This concept and study was based on a general assumption of spherical convergence in ion and electron flow, with the ion motion at high convergence 610 dominated by ion transverse momentum content, and the electron motion inside a certain radius (the virtual cathode radius) dominated by the ion motion (the heavier ions pull the lighter electrons along, to avoid excessive positive charge buildup). Ion density increase with radial convergent motion under these conditions was taken to be varying approximately as 1/r.sup.2 to 1/r.sup.3, down to a (small) critical radius (r.sub.c) 620 at which ion radial motion had ceased, and all ion motion was then transverse and isotropic in a spherical surface sheet at that radius. This radius was shown to be determined by the average transverse momentum content of the ions at the system surface, after reaching steady-state from multiple traversals of the core, as compared with their radial momentum content at maximum radial speed (at well bottom). The ratio of critical radius to system radius (R) is then given by <r.sub.c >=(r.sub.c /R)=(E.sub.t /E.sub.r).sup.0.5, where E.sub.t and E.sub.r are mean transverse energy at the surface, and radial energy near the bottom of the potential well, respectively. System stability was assured by the large recirculating power flow, and by the existence of the externally-supplied polyhedral magnetic fields. However, the limited density increase possible under these convergence scaling laws and conditions leads to requirements for large electron current recirculation ratios (G.sub.j >1E5) which, in turn, require large quasi-spherical polyhedral surface fields 500 for electron confinement. Generation of these fields requires relatively large currents in the polyhedral windings 600 that define the magnet coil systems, and these lead to large ohmic power losses for use of normal conductors for the magnet coils. For use of DT fuels the losses are estimated as typically >20-30 Mwe for systems with reasonable gain (G), while use of advanced fuels such as p.sup.11 B may require magnet coil power of >60-100 Mwe for systems with minimally useful net gain. SUMMARY OF THE INVENTION Considering all of these difficulties and design limitations it appears that useful confinement and enhanced increase in density of ions can be achieved by an improvement on all prior concepts, by use of unique physics phenomena initiated and maintained by inertial forces on the confined ions, these in turn supplied by new and unique electrode means, or by other more conventional means of accelerating charged particles. The current invention accomplishes this by: (1) Using a substantially spherical electrostatic field geometry for acceleration of ions in radial motion, to yield a spherically-convergent circulating flow system for these ions, allowing their densification towards the center of the sphere, with consequent attraction of electrons both within and without the internal spherical region, which electrons act to partially neutralize the positive ionic charge and permit the attainment of high densities of ions due to the presence of the electrons thus attracted. This requires use of an electric field geometry which is everywhere spherical with respect to the system center towards which the ion densification occurs, and which does NOT have associated magnetic fields that can produce non-radial motion by interaction of the flowing particles with such fields. (2) Accelerating ions along radial lines towards the center of such a spherical volume at a speed and with such a flux density that conditions for initiation and maintenance of ion acoustic waves are created at small radius, with particle densities and energies such that the ion acoustic wavelength is small compared to the radius at which this initiation occurs, and with flow and velocity conditions such that the rate of change of ion acoustic wavelength with change in radial position of ions in the converging flow is simply directly proportional to the radial position, itself, thus ensuring resonance coupling of ion flow with these waves in a radial direction or mode within the sphere. (3) Accelerating ions as described in (2), above, in a system with ion flow and density conditions chosen so that the ion acoustic wavelength is (nearly) an exact integer divisor of the circumference of the sphere at the core radial position at which the onset of ion acoustic waves is made to occur, thus ensuring resonance coupling of ion flow with these waves in an azimuthal-tangential direction or mode around the sphere. (4) Using the resonant coupling of ion motion with ion acoustic waves thus formed in either radial and/or azimuthal-tangential modes, by operation at the special conditions required for their initiation as described above, to cause ion/wave collisional interactions on the scale of ion acoustic wavelengths within the small core radius; these short-range collisions then acting to trap and confine ions by collisional diffusion processes within the core, resulting in the buildup of very large ion densities within this core--very much larger (up to thousands of times) than otherwise possible by conventional simple Coulomb collisional interactions of ions with other ions in flow across the small radius of the resonant acoustic central spherical region. (5) Operating with sufficiently large spherically-convergent ion current, accelerating voltage (ion energy) and current density (particle flux) conditions such that the ion acoustic initiation radius referred to above is large enough that the number of ions contained therein will yield significant fusion reaction rates and power generation in excess of that required to accelerate the ions, make up for losses, and otherwise drive the system. (6) Providing electrons to the interior region of the sphere, by collisions with neutral gas within the spherical region, or by electron injection into this region or by emission from electron emitters placed spherically around it or from point/needle/button emitters on such spherical surface, so as to neutralize the buildup of positive charge density resulting from ion densification by convergence towards the center, and thus to allow a larger total number of ions to be focussed in the flow without significant ion energy losses due to repulsion from the creation of a strong positive virtual anode. (7) Adding ions to the system by direct injection of energetic ions and/or (indirectly) by addition of neutral gas to the ion injection region, which is then ionized by collisions with electrons or ions moving through the system, to attain ion densities needed for useful nuclear fusion reaction rates, and to make up for ions consumed by such reaction processes. (8) Using a concentric electrode array with minimum losses due to collisions with circulating particles, by use of wire frame electrodes arranged so as to form approximately equal areas on a spherical surface surrounding the central region of confined circulating ions, or by use of point "button" electrodes, arranged equispaced on a spherical surface around the system center, both arranged so as to provide spherical electrostatic potential surfaces around the center when energized by a source of potential difference, and configured so as to avoid the generation of any magnetic fields by currents through them. (9) Accelerating ions inward through such a potential difference, by causing them to appear (or be created) in the space between two concentric accelerating electrode surfaces, from collisional ionization with electrons accelerated in a direction away from the system center, which space is also the region in which ions or neutral particles may be added to the system, as in (7), above. (10) Using an external set of concentric electrodes, or a single electrode inside of and concentric to an external spherical shell wall bounding the system, located outside the ion accelerating electrodes, to provide an electric field of opposite sense to that required for inward acceleration of the ions, to decelerate electrons otherwise driven out of the system by the interior ion accelerating field, and thus to prevent their loss; or to use any other external means of preventing electron collisions with system structure and/or walls or of electron escape from the system of charged particles. It is the object of this invention to overcome limitations and deficiencies of previous concepts for electrostatic confinement of ions by increasing the density of ions in the central core, very greatly beyond that expected from the conventional spherical flow convergence and densification that characterizes the several prior concepts for electrostatic confinement of Elmore et al, Farnsworth/Hirsch, and Bussard. It is further the object of this invention to accomplish this great increase in density by utilizing unique physics effects created by operation of spherical converging ion flows in special ion acoustic resonant oscillation conditions over a dense central core, under which ions are trapped and the ion density is enhanced by internal collisional-diffusion processes, to achieve densities of such confined ions at values large enough to yield nuclear fusion reactions at useful rates. It is further the object of this invention to utilize these means for the confinement and densification in a collisional-diffusion enhanced core of energetic ions of a variety of types capable of undergoing fusion reactions, at particle energies in the range of 2-5 keV up to 400-600 keV, and to use these dense core ions for the generation of fusion power therein. It is further the object of this invention to arrange the electrodes for acceleration of ions into the spherical core region so that these intercept a minimum fraction of the ions which must pass through them in recirculating flow, and thus to keep ion/structure collision losses as low as possible, so that the number of ion transits across the system required for fusion reaction power generation in excess of losses is very much less than in previous concepts for electrostatic confinement. Any mechanism that can be used to achieve a great increase of central ion density in spherically-convergent ion flows in electrostatic confinement concepts for fusion power, will greatly reduce and may eliminate the need for large particle recirculation ratios. The present invention is such an improvement on all prior concepts, by use of a new and unique set of physics mechanisms governing interparticle collision phenomena within the small dense central core region of spherical inertial colliding flow systems, such that ion density therein may be enhanced by several thousand-fold (or more) above densities attainable in previous systems. This is here called the Inertial Collisional Compression (ICC) effect. Such increases, in turn, lead to increases in fusion reaction rates of up to several million-fold (varies as square of the density), with consequent reduction of the need to contain the charge-neutralizing electrons for many recirculating trips across the potential well in the system. In consequence, devices that use this new principle of inertial collisional compression (ICC) may be able to be constructed of quite simple electrode grids, without any of the complex or deleterious structures required for previous concepts of inertial-electrostatic confinement. |
043141579 | abstract | A safety lock for securing a radiation source in a radiography exposure device is disclosed. The safety lock prevents the inadvertent extension of the radiation source from the exposure device. The exposure devices are used extensively in industry for nondestructive testing of metal materials for defect. Unnecessary exposure of the radiographer or operator occurs not infrequently due to operator's error in believing that the radiation source is secured in the exposure device when, in fact, it is not. The present invention solves this problem of unnecessary exposure by releasingly trapping the radiation source in the shield of the radiography exposure device each time the source is retracted therein so that it is not inadvertently extended therefrom without the operator resetting the safety lock, thereby releasing the radiation source. Further, the safety lock includes an indicator which indicates when the source is trapped in the exposure device and also when it is untrapped. The safety lock is so designed that it does not prevent the return of the source to the trapped, shielded position in the exposure device. Further the safety lock includes a key means for locking the radiation source in the trapped position. The key means cannot be actuated until said radiation source is in said trapped position to further insure the safety lock cannot be inadvertently locked with the source untrapped and thus still extendable from the exposure device. |
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claims | 1. An extra-oral dental x-ray imaging system, for performing a partial CT or partial 3D image of a region of interest of an object, the system comprising:a) an x-ray source for exposing an object to x-rays so that the object may be imaged during the exposure;b) an x-ray imaging device suitable for producing multiple radiated image frames during at least part of the exposure;c) a first manipulator unit for moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit configured for enabling movement of both the x-ray source and the imaging device by selective rotation about at least one rotational axis located between a focal point of the x-ray source and the x-ray imaging device, wherein during the exposure the manipulator unit moves the imaging device and the x-ray source about the at least one rotational axis;d) a second manipulator unit configured for providing at least one of translation and rotation of the x-ray source; ande) a third manipulator unit configured for providing at least one of translating and rotating the imaging device,said second and third manipulators being separate from each other and separate from said first manipulator unit and configured for translation and rotation the imaging device and x-ray source independently of each other and independently of the first manipulator, and relative to the axis of rotation during at least part of the exposure so that during the exposure the rotational axis is virtually moved along a curve due to the at least one of translation and rotation of the x-ray source and of the imaging device respectively provided by the first and second manipulators. 2. An extra-oral dental x-ray imaging system according to claim 1, wherein,during the at least part of the exposure the rotational axis is virtually moved along the curve without physically moving the axis of rotation, byi) the first manipulator unit rotating the imaging device and the x-ray source along the path during the at least part of the exposure about the one rotational axis without the one rotational axis moving,ii) the second manipulator unit translating or rotating the x-ray source during the exposure,iii) third manipulator unit translating or rotating the at least part of the imaging device during the exposure, andthe curve defines a spiral. 3. An extra-oral dental x-ray imaging system according to claim 1, wherein through i) the first manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the first manipulator unit moving both the x-ray source and the imaging device by both selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the third manipulator unit rotating the imaging device during at least part of the exposure with respect to the rotational axis, during the exposure the geometry of the imaging device and the x-ray source is changed with respect to the rotational axis. 4. An extra-oral dental x-ray imaging system according to claim 1, wherein through i) the first manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the first manipulator unit moving both the x-ray source and the imaging device by both selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the second manipulator unit rotating the x-ray source during at least part of the exposure with respect to the rotational axis, during the exposure the geometry of the imaging device and the x-ray source is changed with respect to the rotational axis. 5. An extra-oral dental x-ray imaging system according to claim 1, wherein through i) the first manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the first manipulator unit moving both the x-ray source and the imaging device by both selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the third manipulator unit translating the imaging device during at least part of the exposure with respect to the rotational axis, during the exposure the relative geometry of the imaging device and the x-ray source changes to further increase the field of view. 6. An extra-oral dental x-ray imaging system according to claim 1, wherein through i) the first manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the first manipulator unit moving both the x-ray source and the imaging device by both selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the second manipulator unit translating the x-ray source during at least part of the exposure with respect to the rotational axis, during the exposure the relative geometry of the imaging device and the x-ray source changes to further increase the field of view. 7. An extra-oral dental x-ray imaging system according to claim 1, wherein through i) the first manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the first manipulator unit moving both the x-ray source and the imaging device by both selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the third manipulator unit translating and rotating the imaging device during at least part of the exposure with respect to the rotational axis, during the exposure the rotational axis is virtually moved along a spiral. 8. An extra-oral dental x-ray imaging system according to claim 1, wherein through i) the first manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the first manipulator unit moving both the x-ray source and the imaging device by both selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the second manipulator unit translating and rotating the x-ray source during at least part of the exposure with respect to the rotational axis, the rotational axis is virtually moved along the curve by defining a spiral. 9. An extra-oral dental x-ray imaging system according to claim 1, wherein through the third manipulator unit translating and rotating the imaging device during at least part of the exposure with respect to the rotational axis, during the exposure the rotational axis is virtually moved, without physically moving the axis of rotation, along the curve by defining a spiral. 10. An extra-oral dental x-ray imaging system according to claim 1, wherein through the second manipulator translating and rotating the x-ray source during at least part of the exposure with respect to the rotational axis, the rotational axis is virtually moved, without physically moving the axis of rotation, along a spiral. 11. An extra-oral dental x-ray imaging system according to claim 1, wherein through the second and third manipulator units translating and rotating respectively the x-ray source and imaging device during at least part of the exposure with respect to the rotational axis, the rotational axis is virtually moved without physically moving the axis of rotation. 12. An extra-oral dental x-ray imaging system, for performing a partial CT or partial 3D image of a region of interest of an object, the system comprising:a) an x-ray source for providing an x-ray beam for exposing an object to x-rays so that the object may be imaged during the exposure;b) an x-ray imaging device suitable for producing multiple radiated image frames during at least part of the exposure;c) a manipulator unit for moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit configured for enabling movement of both the x-ray source and the imaging device by selective translation and selective rotation about a rotational axis located between a focal point of the x-ray source and the x-ray imaging device, wherein during the exposure the manipulator unit moves the imaging device and the x-ray source in at least one of translation and rotation about the at least one rotational axis, the manipulator unit comprising i) a first manipulator configured for selective translation of both the x-ray source and the imaging device, ii) a second manipulator configured for selective rotational movement of both the x-ray source and the imaging device; andd) an additional manipulator, separate from said first and second manipulators, configured for translating or rotating at least one of i) the imaging device during at least part of the exposure with respect to the rotational axis, and ii) a component causing effectively the x-ray source to be translated or rotated during at least part of the exposure with respect to the rotational axis so that during the exposure the rotational axis is virtually moved, without physically moving the axis of rotation, along a curve. 13. An extra-oral dental x-ray imaging system according to claim 12, wherein the component is the x-ray source and the curve is a spiral. 14. An extra-oral dental x-ray imaging system according to claim 13, wherein through i) the manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit moving both the x-ray source and the imaging device by selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the additional manipulator translating the x-ray source during at least part of the exposure with respect to the rotational axis, during the exposure the geometry of the imaging device and the x-ray source is changed with respect to the rotational axis and the curve is a spiral. 15. An extra-oral dental x-ray imaging system according to claim 13, wherein through i) the manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit moving both the x-ray source and the imaging device by at least one of selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the additional manipulator rotating the x-ray source during at least part of the exposure with respect to the rotational axis, during the exposure the relative geometry of the imaging device and the x-ray source changes to further increase the field of view and the curve is a spiral. 16. An extra-oral dental x-ray imaging system according to claim 13, wherein through i) the manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit moving both the x-ray source and the imaging device by at least one of selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the additional manipulator translating and rotating the x-ray source during at least part of the exposure with respect to the rotational axis, the rotational axis is virtually moved, without physically moving the axis of rotation, along a spiral. 17. An extra-oral dental x-ray imaging system according to claim 12, wherein through i) the manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit moving both the x-ray source and the imaging device by at least one of selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the additional manipulator rotating the imaging device during at least part of the exposure with respect to the rotational axis, during the exposure during the exposure the geometry of the imaging device and the x-ray source is changed with respect to the rotational axis and the curve is a spiral. 18. An extra-oral dental x-ray imaging system according to claim 12, wherein through i) the manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit moving both the x-ray source and the imaging device by at least one of selective translation and selective rotation about the at least one rotational axis located between the focal point of the x-ray source and the x-ray imaging device, and ii) the additional manipulator translating the imaging device during at least part of the exposure with respect to the rotational axis, during the exposure the rotational axis is moved, without physically moving the axis of rotation, along a spiral. 19. An extra-oral dental x-ray imaging system according to claim 13, wherein through i) the manipulator unit moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, and ii) the additional manipulator translating and rotating the the imaging device during at least part of the exposure with respect to the rotational axis, during the exposure the rotational axis is virtually moved, without physically moving the axis of rotation and the curve is a spiral. 20. An extra-oral dental x-ray imaging system, for performing a partial CT or partial 3D image of a region of interest of an object, the system comprising:a) an x-ray source for exposing an object to x-rays so that the object may be imaged during the exposure;b) an x-ray imaging device suitable for producing multiple radiated image frames during at least part of the exposure;c) a manipulator unit for moving the imaging device and the x-ray source along a path between plural positions corresponding to plural radiated image frames during the exposure, the manipulator unit configured for enabling movement of both the x-ray source and the imaging device by selective rotation about one rotational axis located between a focal point of the x-ray source and the x-ray imaging device, wherein during the exposure the manipulator unit moves the imaging device and the x-ray source about the one rotational axis with the one rotational axis remaining physical fixed; andd) an additional manipulator unit configured for providing translation of the x-ray source and the imaging device, the additional manipulator unit being separate from the manipulator unit, the additional manipulator unit configured to translate the x-ray source and the imaging device relative to the one rotational axis during at least part of the exposure so that during the exposure the rotational axis is virtually moved along a curve without physically moving the one axis of rotation. 21. An extra-oral dental x-ray imaging system according to claim 20, wherein,the additional manipulator unit comprises:i) a first additional manipulator for translating the imaging device along one direction, during the at least part of the exposure with respect to the one rotational axis of rotation, andii) a second additional manipulator for translating the x-ray source along a second direction that is different from the first direction, during the at least part of the exposure with with respect to the rotational axis of rotation, andthe curve defines a spiral. |
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050900447 | claims | 1. An X-ray examination apparatus comprising: a bed; means for radiating X-rays to a patient lying on the bed; means for converting the X-rays radiated to the patient into an image; an arm rest, connected to one side of the bed, for platforming an arm of the patient thereon when a catheter is inserted into a blood vessel of the patient from the arm; and X-ray shield means, mounted on the arm rest, for shielding scattered X-rays to protect arms/hands of an operator handling the catheter, the X-ray shield means having a front wall facing a carcass of the patient, edge walls disposed at sides of the front wall in a manner to surround the operator's hands, and an opening formed in the front wall to platform the patient's arm on the arm rest. a bed; means for radiating X-rays to a patient lying on the bed; means for converting the X-rays radiated to the patient into an image; an arm rest, connected to one side of the bed, for platforming an arm of the patient thereon when a catheter is inserted into a blood vessel of the patient from the arm; X-ray shield means, mounted on the arm rest, for shielding scattered X-rays to protect arms/hand of an operator handling the catheter, the X-ray shield means having a front wall facing a carcass of the patient, edge walls disposed at sides of the front wall in a manner to surround the operator's hands, and an opening formed in the front wall to platform the patient's arm on the arm rest; and a cover, formed of an X-ray shielding material, for covering a bottom surface of the arm rest. a bed; means for radiating X-rays to a patient lying on the bed; means for converting the X-rays radiated to the patient into an image; an arm rest, connected to one side of the bed, for platforming an arm of the patient when a catheter is inserted into a blood vessel of the patient from the arm; and means for covering a bottom surface of the arm rest, formed of an X-ray shielding material. 2. The X-ray examination apparatus according to claim 1, wherein the arm rest comprises means for removably supporting the X-ray shield means. 3. The X-ray examination apparatus according to claim 2, wherein the removable supporting means includes hinge means for moving the shielding means from an upper surface of the arm rest sidewardly of the arm rest. 4. The X-ray examination apparatus according to claim 1, wherein the X-ray shield means is formed of an X-ray shielding material. 5. The X-ray examination apparatus according to claim 1, wherein the front wall has a height equal to or greater than a thickness of a body of the patient. 6. The X-ray examination apparatus according to claim 1, wherein the front wall has approximately the same width as the arm rest. 7. An X-ray examination apparatus comprising: 8. The X-ray examination apparatus according to claim 7, wherein the arm rest comprises means for slidably supporting the cover in a longitudinal direction of the arm rest. 9. The X-ray examination apparatus according to claim 8, wherein the slidably supporting means includes guide grooves formed in both side faces of the arm rest. 10. The X-ray examination apparatus according to claim 7, wherein the cover has a length which is equal to 1/3 to 1/2 the length of the arm rest. 11. The X-ray examination apparatus according to claim 7, wherein the cover comprises means for fixing itself to the arm rest at a desired longitudinal position. 12. The X-ray examination apparatus according to claim 11, wherein the fixing means includes a fixing screw which holds the cover in a static state to touch the bottom surface of the arm rest. 13. An X-ray examination apparatus comprising: |
abstract | A collimator and related methods are shown and described. The collimator can be a multi-divergent-beam collimator having a plurality of inverted, ordered sections of a cone-beam collimator reassembled in a substantially reversed order relative to the ordering of the cone-beam collimator. |
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description | This application claims priority to U.S. Provisional Patent Application No. 60/883,072, filed on Jan. 2, 2007. This invention was made with government support under Contract No. DE-FC07-051D14636 awarded by the Department of Energy. The government has certain rights in this invention. 1. Field of the Invention The present invention relates generally to nuclear reactor internals, more specifically to apparatus for maintaining the alignment of the nuclear reactor internals while permitting thermal growth. 2. Description of Related Art The primary side of nuclear reactor power generating systems which are cooled with water under pressure comprises a closed circuit which is isolated from and in heat-exchange relationship with a secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core supporting a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the vessel form a loop of the primary side. The primary side is also connected to auxiliary circuits, including a circuit for volumetric and chemical monitoring of the pressurized water. This auxiliary circuit, which is arranged branching on the primary circuit, makes it possible to maintain the quantity of water in the primary circuit by replenishing, when required, with measured quantities of water, and to monitor the chemical properties of the coolant water, particularly its content of boric acid, which is important to the operation of the reactor. The average temperature of the core components during full power reactor operation is approximately 580° F. (304° C.). Periodically, it is necessary to shut down the reactor system for maintenance and to gain access to the interior side of the pressure vessel. During such an outage, the internal components of the pressure vessel can cool to a temperature of approximately 50° F. (10° C.). The internal components of the reactor pressure vessel typically consist of upper and lower internals. The upper internals include a control rod guide tube assembly, support columns, conduits for instrumentation which enter the reactor vessel through the closure head, and a fuel assembly alignment structure, referred to as the upper core plate. The lower internals include a core support structure referred to as a core barrel, a core shroud that sits inside the core barrel and converts the circular interior of the barrel to a stepped pattern that substantially corresponds to the perimeter profile of the fuel assemblies within the core supported between a lower core support plate and the upper core plate. As an alternate to the core shroud, a bolted baffle former structure consisting of machined horizontal former and vertical baffle plates, has been employed. It is particularly important to maintain a tight alignment of the reactor internals upper core plate and a top plate of the shroud with the control rod drive mechanisms to assure that the control rods can properly scram; i.e., drop into the core, when necessary. This is particularly challenging when one considers the thermal expansion and contraction that has to be accommodated through power ramp-up and cool down sequences, where temperatures can vary between 50° F. (10° C.) and 580° F. (304° C.). In conventional designs, lateral alignment of the upper internals components was accomplished with a series of single pins located around the circumference of the core barrel. The upper core plate alignment pins fit in notches in the upper core plate and locate the upper core plate laterally with respect to the lower internals assembly. The pins must laterally support the upper core plate so that the plate is free to expand radially and move axially during differential thermal expansions between the upper internals and the core barrel. FIG. 1 is a simplified cross-section of such a conventional reactor design. A pressure vessel (10) is shown enclosing a core barrel (32) with a thermal shield (15) interposed in between. The core barrel (32) surrounds the core (14) which is held in position by an upper core plate (40). The upper core plate (40) is aligned by the alignment pins (19) which extend through the core barrel (32) into notches (21) in the upper core plate (40). The notches (21) permit the core barrel to grow with thermal expansion at a greater rate than the upper core plate (40) during start up without compromising the lateral position of the upper core plate (40). The installation sequence of the core shroud (17) in new advanced passive plant designs requires a modified design that will prevent lateral movement of both the upper core plate and the core shroud while enabling thermal growth and contraction between both the shroud and upper core plate and the core barrel, while maintaining rotational stability. Thus, it is an object of this invention to provide such a design that would facilitate the installation of the alignment apparatus, the core shroud and the upper core plate. This invention achieves the foregoing objective by providing a pressurized water nuclear reactor having a pressure vessel with a core region for supporting fuel assemblies. A core barrel is removably disposed within the pressure vessel around the core region. A core shroud is disposed within the core barrel between the core barrel and the fuel assemblies. The core shroud has an alignment slot that orients the core shroud with the core barrel. An upper support plate is removably disposed above the fuel assemblies and the core shroud. The upper core support plate also has an alignment slot for aligning the upper core support plate with the core barrel and the core shroud. An alignment plate is attached to the core barrel and is disposed within the alignment slot of the core shroud and within the alignment slot of the upper core support plate to maintain alignment of the upper and lower internals during reactor start up, shut down and continuous operation. Preferably, the alignment plate is attached to the inner surface of the core barrel and a reinforcing pad is disposed on the outside of the core barrel and attached to the alignment plate through the core barrel. In one embodiment, the reinforcement pad is attached to the alignment plate with at least two dowel pins that engage the reinforcement pad and the alignment plate through the core barrel. Preferably, the dowel pins are shrunk fit into the reinforcement pad, core barrel and alignment plate. The dowel pins desirably are positioned in spaced relationship with each other, one on top of the other; the top dowel pin is shrink-fitted to holes in both the core barrel and alignment plate, thus anchoring the alignment plate to the core barrel at this location. The bottom dowel hole in the alignment plate is designed to accommodate differential axial thermal growth between the core barrel and the alignment plate. This is accomplished by machining flat surfaces on the vertical faces of the dowel pins and alignment plate, and by enlarging one of the dowel pin holes in the alignment plate so that a gap exists between a top and bottom surface of one of the dowel pins and the alignment plate, allowing differential thermal growth in the vertical direction. In another embodiment, in addition to being secured by the dowel pins, the alignment plate and reinforcement pad are attached to the core barrel with threaded fasteners. The reinforcing pad is also welded to the core barrel, for example, with a fillet weld. Preferably, the back of the alignment plate that interfaces with the core barrel is machined to have a complementary curvature and the alignment plate is fit in a recess machined into the core barrel. Desirably, there are a plurality of alignment plates spaced around the core barrel with each being received within a corresponding slot in the core shroud and the upper core support plate. Desirably, the alignment plates on the inner surface of the core barrel are azimuthally aligned with corresponding inlet nozzles on the pressure vessel. The slots in the core shroud and upper core support plate may be fitted with inserts between the sides of the slots and the alignment plate so that a small clearance can be maintained between the sides of the slots and the alignment plate. Referring now to the drawings, FIG. 2 shows a simplified nuclear reactor primary system, including a generally cylindrical reactor pressure vessel (10) having a closure head (12) enclosing a nuclear core (14). A liquid reactor coolant, such as water, is pumped into the vessel (10) by pumps (16) through the core (14) where heat energy is absorbed and is discharged to a heat exchanger, typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown), such as a steam-driven turbine generator. The reactor coolant is then returned to the pump (16), completing the primary loop. Typically, a plurality of the above-described loops are connected to a single reactor vessel (10) by reactor coolant piping (20). An exemplary reactor design is shown in more detail in FIG. 3. In addition to a core (14) comprised of a plurality of parallel, vertical co-extending fuel assemblies (22), for purposes of this description, the other vessel internal structures can be divided into the lower internals (24) and the upper internals (26). In conventional designs, the lower internals function is to support, align and guide core components and instrumentation, as well as to direct flow within the vessel. The upper internals restrain or provide a secondary restraint for the fuel assemblies (22) (only two of which are shown for simplicity), and support and guide instrumentation and components, such as control rods (28). In the exemplary reactor shown in FIG. 3, coolant enters the vessel (10) through one or more inlet nozzles (30), flows downward through an annulus between the vessel and the core barrel (32), is turned 180° in a lower plenum (34), passes upwardly through a lower support plate (37) and a lower core plate (36) upon which the fuel assemblies (22) are seated and through and about the assemblies. In some designs the lower support plate (37) and lower core plate (36) are replaced by a single structure, the lower core support plate, at the same location as (37). The coolant flow through the core and surrounding area (38) is typically large, on the order of 400,000 gallons per minute at a velocity of approximately 20 feet per second. The resulting pressure drop and frictional forces tends to cause the fuel assemblies to rise, which movement is restrained by the upper internals, including a circular upper core plate (40). Coolant exiting the core (14) flows along the underside of the upper core plate and upwardly through a plurality of perforations (42). The coolant then flows upwardly and radially to one or more outlet nozzles (44). The upper internals (26) can be supported from the vessel or the vessel head and include an upper support assembly (46). Loads are transmitted between the upper support plate (46) and the upper core plate (40), primarily by a plurality of support columns (48). A support column is aligned above a selected fuel assembly (22) and perforations (42) in the upper core plate (40). Rectilinearly moveable control rods (28) typically including a drive shaft (50) in a spider assembly (52) of neutron poison rods are guided through the upper internals (26) and into aligned fuel assemblies (22) by control rod guide tubes (54). The guide tubes are fixedly joined to the upper support assembly (46) and connected by a split pin (56) force fit into the top of the upper core plate (40). The pin configuration provides for ease of guide tube assembly and replacement if ever necessary and assures that core loads, particularly under seismic or other high loading accident conditions are taken primarily by the support columns (48) and not the guide tubes (54). This assists in retarding guide tube deformation under accident conditions which could detrimentally affect control rod insertion capability. Though not shown in FIG. 3, the design of this invention includes a core shroud positioned inside the circular core barrel (32) that converts the circular inner profile of the core barrel to a stepped circumferential profile that matches the peripheral outline of the fuel assemblies (22) within the core. A portion of the shroud's stepped inner circumferential profile can be observed in FIG. 4, which provides a perspective view of a portion of the shroud (88) and upper core plate (40), with the alignment plate (94) of this invention in place within the slots (92) and (93) within the top shroud plate (90) and upper core plate (40), respectively. In FIG. 4, the core barrel has been removed for clarity. This invention presents a different design concept than the pins employed by conventional pressurized water reactor designs previously described with respect to FIG. 1, but still maintains the same functionality, i.e., radial and axial restraints for the upper core plate, in addition to supplying restraints for the core shroud components in the peripheral region around the core for the advanced passive AP1000 nuclear power plant design offered by Westinghouse Electric Company LLC. For the AP1000 nuclear power plant design, maintaining a tight alignment of the reactor internals upper core plate (40) and top shroud plate (90) with the control rod drive mechanisms is necessary to assure that the control rods can properly scram when necessary. The alignment plate (94) of this invention, shown in FIG. 4, provides not only rotational restraint to the upper internals that was provided by the previous pin design, but also provides alignment of the core shroud (88) at the top of shroud plate (90). In this embodiment, there are four alignment plate assemblies (94) located symmetrically around the periphery of the core barrel (32) at the same angular orientation as four inlet nozzles (30) on the pressure vessel. Symmetrically located does not necessarily mean that they are equally spaced around the pressure vessel nor at the same location as the inlet nozzles. In the AP1000 design, there are two inlet nozzles on either side and within the vicinity of an outlet nozzle, and there are two outlet nozzles diametrically opposed on the vessel. The alignment plates (94) are attached to the core barrel (32) with two dowel pins (96) and (98) and six one-inch hex cap screws (100). The hex screws (100) and dowel pins (96) and (98) are inserted through a reinforcing pad (110) (shown in FIG. 6) on the outside of the core barrel (32), the core barrel (32) and into the alignment plate (94). Attachment of the alignment plate (94) to the core barrel (32) is illustrated in FIG. 5 as viewed from the inside of the core barrel (32). Similarly, the attachment of the reinforcement pad (112) to the outside of the core barrel (32) is illustrated in FIG. 6. As shown in FIG. 6, a fillet weld 120 is made around the perimeter of the reinforcing pad (112), joining the reinforcing pad (112) to the core barrel (32). The fit up of the alignment plate (94) with the top shroud plate (90) and upper core plate (40) is shown in FIG. 4 with the core barrel removed for clarity. The alignment plate (94) is fit within the slots (92) and (93), respectively, in the top shroud plate (90) and the upper core plate (40). Inserts (118) are secured within the slots (92) and (93) on either side of the alignment plate (94) to maintain a snug fit to avoid rotational misalignment. During assembly, the upper dowel pin (96) is shrunk fit into the reinforcing pad (112), core barrel (32) and alignment plate (94). The bottom dowel pin (98) is shrunk fit through the reinforcing pad (112) and core barrel (32) only. The bottom dowel pin (98) alignment plate (94) interface is designed to accommodate differential axial thermal growth between the core barrel (32) and the alignment plate (94). As can be seen in FIG. 5, a gap exists between the top, bottom and side surfaces of the bottom dowel pin (98) and the alignment plate (94), allowing differential thermal growth in the vertical direction. It should be appreciated that though the lower dowel hole in the alignment plate is shown enlarged, the same functionality can be achieved by enlarging the upper dowel hole instead of the lower one. To assist in the radial positioning of the alignment plate (94) relative to the core barrel (32), the alignment plate (94) sits in a radial recess machined into the core barrel (32) to match the radius of the outside surface of the alignment plate (94). Alternatively, the back of the alignment plate (106) can be machined to match the curvature of the core barrel, or a combination of the two can be employed. 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 | The present application hereby claims priority under 35 U.S.C. §119 on German patent application numbers DE 10 2006 004 976.4 filed Feb. 1, 2006, DE 10 2006 004 604.8 filed Feb. 1, 2006, and DE 10 2006 037 255.7 filed Aug. 9, 2006, the entire contents of each of which is hereby incorporated herein by reference. Embodiments of the invention generally relate to a focus-detector arrangement of an X-ray apparatus for generating projective or tomographic phase contrast recordings of an observed region (=FOV=Field of View) of a subject. For example, an embodiment may relate to one having a radiation source which emits coherent or quasi-coherent X-radiation and irradiates the subject, a phase grating which is arranged behind the subject in the beam path of the radiation source and generates an interference pattern of the X-radiation in a predetermined energy range, and an analysis-detector system which detects at least the interference pattern generated by the phase grating in respect of its phase shift with position resolution. For X-ray imaging, two effects which occur when X-rays pass through matter are usually considered, namely the absorption of a particular component of the X-rays and the phase shift of the transmitted X-rays. In respect of the refractive index, which is given for X-rays byn=1−δ−iβ, (1)the absorption depends on the size of the imaginary decrement β, which is related to the mass absorption coefficient μ/ρ byμ/ρ=4πβ/λ, (2)where λ is the wavelength, μ is the linear absorption coefficient and ρ is the mass density. The phase shift follows from the real part of the refractive index 1−δ. The phase shift Δ of an X-ray wave in matter compared to a vacuum is given byΔ=2πδT/λ, (3)where T is the thickness of the material and δ is the real decrement of the refractive index. In X-radiography, the subject is exposed to X-rays and the transmitted intensity is recorded behind the object. With the aid of this measurement, projection images can be produced which show the absorption caused by the object. In X-ray tomography, more than one projection image is used in order to calculate a three-dimensional data set, which shows the spatial distribution of the absorption coefficients μ. For phase contrast radiography and phase contrast tomography, it is necessary to evaluate the phase shift caused by the object. Similarly as absorption imaging, a three-dimensional data set can be calculated which shows the spatial distribution of the real part of the refractive index 1−δ. Since the phase of a wave cannot be measured directly, the phase shift is firstly converted into a measurable intensity by interference of the wave to be studied with a reference wave. The practical conduct of such measurements, both in relation to projective recordings and in relation to tomographic recordings, is presented by way of example in the European patent application EP 1 447 046 A1 and in the German patent applications with the file references 10 2006 017 290.6, 10 2006 015 358.8, 10 2006 017 291.4, 10 2006 015 356.1 and 10 2006 015 355.3 of the same priority. The method presented there uses a phase grating placed in the beam path behind the subject, which acts as a diffraction grating and splits the X-rays into +1st and −1st order rays. In the wave field behind the phase grating, the diffracted rays interfere with one another to form an X-ray standing wave field. The subject causes local phase shifts, which deform the wavefront and therefore locally modify the amplitude, phase and offset of the standing wave field. By using a measurement which delivers information about the standing wave field, such as the phase, amplitude and average value of the standing waves, it is therefore possible to calculate the influence of the local phase shifts due to the subject. In order to scan the wave field with the requisite resolution, an analyzer grating is displaced stepwise over the wave field while the intensity is synchronously monitored pixel-wise by using a corresponding detector. In the European patent application EP 1 447 046 A1 cited above, parallel X-rays are used for scanning the subject. Considered superficially, it could be assumed that an arbitrary magnification effect would be achievable by using divergent radiation geometries and correspondingly positioning the subject in the beam path. But when considering the effect of the radiation being refracted by the subject, it is found that measurement of the phase shift no longer appears possible because it is to be expected that a “chaotic” pattern of the deviated rays will occur, which does not lead to an evaluatable image rendition. For this reason, no X-ray phase contrast measurements have actually been carried out in a magnifying geometry by using phase gratings. In at least one embodiment of the invention, a focus-detector arrangement is provided for X-ray phase contrast radiography and X-ray phase contrast tomography, which makes it possible to generate magnifying to highly magnifying projective and tomographic representations of the spatial distribution of the refractive index of a subject. In respect of X-ray phase contrast measurement with the aid of phase gratings and coherent or quasi-coherent X-radiation, the following should also essentially be pointed out: The emission of X-ray photons from laboratory X-ray sources (X-ray tubes, secondary targets, plasma sources, parametric X-ray sources, channeling radiation) as well as by conventional synchrotron radiation sources of the first to third generations is subject to stochastic processes. The emitted X-radiation therefore has no spatial coherence per se. In phase contrast radiography and tomography or any interference experiment, however, the radiation of X-ray sources behaves as coherent radiation when the observation angle at which the source appears to the observer or the object, the grating or the detector, is sufficiently small. The so-called spatial/transverse (lateral) coherence length Lc can be provided as a measure of the spatial or transverse coherence of an extended X-ray source: L c = λ a s . ( 4 ) Here, λ is the wavelength, s is the transverse source size and a is the source-observation point distance. The exact value is incidental; what is important is that the coherence length L is large compared to the (lateral) dimension of the spatial region from which rays are intended to interfere with one another. In the context of the patent application, the term coherent radiation is intended to mean radiation which leads to the formation of an interference pattern under given geometries and given distances of the X-ray optical gratings. It is self-evident that the spatial coherence and therefore the spatial coherence length is always determined by the trio of quantities: wavelength, source size and observation distance. With a view to compact formulation, this fact has been abbreviated to terms such as “coherent X-radiation”, “coherent X-radiation source” or “point source for generating coherent X-radiation”. The basis for these abbreviations is that the wavelength (or the energy E) of the X-radiation in the applications discussed here is limited by the desired penetrability of the subject on the one hand and the spectrum available in laboratory X-ray sources on the other hand. The distance a between the source and the observation point is also subject to certain restrictions in laboratory equipment for nondestructive material testing or medical diagnosis. This usually leaves only the source size s as a single degree of freedom, even though the relationships between source size and tube power likewise set narrow limits here. Higher-power radiation sources and therefore larger focus dimensions can be used in the focus-detector arrangement in question here if a suitably dimensioned source grating is used. The narrow slits of the source grating ensure that all the rays, which have to emerge from the same slit, comply with the requisite spatial coherence. Photons from the same slit can interfere with one another, i.e. be superposed with correct phase. Between the photons from different slits of the source grating, however, no correctly phased superposition is possible. Yet with suitable tuning of the source grating period g0 and the interference pattern period g2 as well as the spacing l of the source grating G0 and the phase grating G1, and the spacing d of the phase grating G1, and the interference pattern G2, to first approximation according tog0/g2=l/d, (5)correct superposition of the wave maxima and the wave minima of the standing wave field is possible at least in respect of intensity. In the abbreviated formulation of the patent application, the term “quasi-coherent radiation” or “quasi-coherent radiation source” is used in this context. The temporal or longitudinal coherence of the radiation is associated with the monochromaticity of the X-radiation or of the X-radiation source. The X-radiation of intense characteristic lines usually has a sufficient monochromaticity or temporal coherence length for the applications discussed here. Upstream monochromators or selection of the resonant energy via the bar height of the phase grating can also filter out a sufficiently narrow spectral range from a Bremsstrahlung spectrum or synchrotron spectrum, and thus satisfy the requirements for the temporal coherence length in the present arrangements. Contrary to the conventional wisdom that a magnifying structure of a focus-detector arrangement for phase contrast measurement is not possible, the Inventors have found that satisfactory image results can be achieved against all expectations. According to this discovery, in at least one embodiment, the Inventors provide a focus-detector arrangement of an X-ray apparatus for generating projective or tomographic phase contrast recordings of an observed region (=FOV =Field of View) of a subject, which comprises: a radiation source which emits a coherent or quasi-coherent X-radiation and irradiates the subject, a phase grating which is arranged behind the subject in the beam path of the radiation source and generates an interference pattern of the X-radiation in a predetermined energy range, and an analysis-detector system which detects at least the interference pattern generated by the phase grating in respect of its phase shift with position resolution, wherein the beam path of the X-radiation used diverges in at least one plane between the focus and the detector, i.e. corresponds to a fan beam. In another embodiment, the focus-detector arrangement may also be configured so that the beam path of the X-radiation used diverges two planes between the focus and the detector, and therefore corresponds to a cone beam. For a compact structure, it is particularly advantageous for there to be a divergence of the ray beam used of at least 5°, preferably at least 10° in at least one plane. For an application in the field of medical computer tomography, fan angles of more than 45° are even used. According to the divergence of the beam geometry used, the observed region of the subject—as seen in projection in the direction of the optical axis of the beam path—may be dimensioned smaller than the utilized region of the phase grating) downstream in the beam path, which in turn may be dimensioned smaller than the utilized region of the analysis-detector system downstream in the beam path. Of course, this also applies correspondingly with a reverse observation mode starting from the focus with increasing dimensioning. According to an example embodiment, the distance from the radiation source to the analysis-detector system is at least two times as great as the distance from the radiation source to the subject. This, by using a phase grating and the described analysis-detector system, for the first time allows an effectively magnifying phase contrast recording in which only the phase shift is represented in the image. With relevant requirements, this magnification factor may be extended to up to 10 times or even 1000 times magnification via an appropriate selection of distance between the X-ray source and the subject and between the X-ray source and the analysis-detector system. In the focus-detector arrangement, it is proposed that the following geometrical relationship be satisfied in respect of the periods of the phase grating and analysis grating: g 2 = 1 2 r 1 + d m r 1 g 1 , ( 6 ) where dm corresponds to the distance between the gratings, r1 corresponds to the distance between the radiation source and the first grating, g2 corresponds to the period of the analyzer grating, and g1 corresponds to the period of the phase grating. With the relationship r2=r1+dm, Equation (6) can also be rewritten as g 2 = 1 2 r 2 r 1 g 1 . It is furthermore proposed to position the analysis-detector system so that the analyzer grating, when the analysis-detector system includes a detector with an analyzer grating, or the entry side of the detector when the analysis-grating system includes a detector without an analyzer grating, is at a distance from the phase grating such that the standing wave field is maximally pronounced. The following applies to first approximation for this so-called Talbot distance: d m = ( m - 1 2 ) · g 1 2 4 · λ , ( 7 ) where: dm=distance from the phase grating to the analyzer grating, so-called Talbot distance; m=order of the Talbot-interference; m=1, 2, 3, . . . ; g1=period of the phase grating; λ=wavelength of the X-radiation used. Formula (7) describes the exact distance for a parallel beam. When using a cone beam, Formula (7) applies only to first approximation since the interference pattern spreads more and more with an increasing distance from the phase grating, as described in Formula (6). This corresponds in practice to a grating period g1 of the phase grating which becomes ever larger with an increasing distance. According to at least one embodiment of the invention, two different variants of the relative arrangement of the phase grating and the analysis-detector system can be set up in this embodiment of a focus-detector arrangement. If the phase grating is arranged closer to the analysis-detector system than to the subject in the radiation direction, then the grating period of the amplitude grating in the analysis-detector system will be smaller than the grating period of the phase grating, typically about half as large. In the alternative focus-detector arrangement in which the phase grating is arranged closer to the subject than to the detector in the radiation direction, it is possible to work with larger grating periods of the analyzer grating. It is even possible to work with a grating period of the analyzer grating which is greater than that of the phase grating. Both variants mentioned last may also be configured with an analysis-detector system which, instead of an analyzer grating, comprises a detector whose individual detector elements are furthermore designed to be strip-shaped with alignment according to the grating lines of the phase grating, in which case the strips must have a period of at most ⅓ of the corresponding period of an analyzer grating in order to be able to determine the phase shift of the X-ray in the detector element with a single measurement. In order to generate the coherent X-radiation, in a first alternative embodiment, the Inventors propose that the radiation source should have a focus which is designed as a microfocus in relation to the geometrical proportions of the focus-detector arrangement. According to another alternative embodiment, the radiation source may include an extended focus if an X-ray optical grating arranged in the beam direction, a so-called source grating, additionally ensures the required coherence. Although this entails a restriction in respect of the possible achievable resolution, the power can nevertheless be increased so that, for example, the required exposure times can be reduced. Although the variants mentioned above are example embodiments of the invention, all other known X-ray sources which generate coherent X-ray light—for example so-called free electron lasers, 4th generation synchrotrons—likewise fall within the scope of the invention, a divergent beam geometry respectively being a prerequisite. According to the discovery by the Inventors, they also propose that the focus-detector arrangement according to at least one embodiment of the invention be used in conjunction with an X-ray system for generating projective phase contrast recordings or in conjunction with an X-ray computer tomography system for generating tomographic phase contrast recordings, in each case with a magnifying representation of a subject. Such systems are usually employed in connection with the analysis of small samples, but also for detailed imaging in medical computer tomography or examination of small animals. It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to”, or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are interpreted accordingly. Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present 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 “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referencing the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, example embodiments of the present patent application are hereafter described. For better understanding, the basic principle of phase contrast measurement will be described below with FIGS. 1 to 2. FIG. 1 shows coherent radiation coming from a point-like radiation source or individually quasi-coherent radiation coming from a source grating, which passes through a subject or sample P, a phase shift taking place when passing through the subject P. When passing through the grating G1 an interference pattern is generated, as represented by the gray shading, which with the aid of the grating G2 leads to different radiation intensities per detector element on the downstream detector D and its detector elements Ei, Ej, an interference pattern or X-ray standing wave field being formed at a so-called Talbot distance. If the detector element Ei for example is considered as a function of the relative position xG of the analyzer grating G2 and the intensity I(Ei(xG)) is plotted as a function of the relative position xG, then a sinusoidal profile of the intensity I at this detector element Ei is obtained as shown in FIG. 2. If this measured radiation intensity I is plotted for each detector element Ei or Ej as a function of the offset xG, then the function I(Ei(xG)) or I(Ej(xG)) can be approximated for the various detector elements, which in the end form the geometrical X-ray between the focus and the respective detector element. The phase shift φ and the relative phase shift φij between the detector elements can be determined for each detector element from the functions. For each ray in space, the phase shift per detector pixel or ray considered can therefore be determined by at least three measurements with a respectively offset analyzer grating, from which either the pixel values of a projective recording can be calculated directly in the case of projective X-ray recordings. On the other hand, projections whose pixel values correspond to the phase shift are compiled in the case of a CT examination, so that with the aid of reconstruction methods known per se it is possible to calculate therefrom which volume element in the subject is to be ascribed to which component of the measured phase shift. Section images or volume data are thus calculated therefrom, which reflect the effect of the examined object in respect of the phase shift of X-radiation with position resolution. Since even minor differences exert a strong effect on the phase shift in this context, very detailed and high-contrast volume data can be obtained from materials which are relatively similar per se, in particular soft tissue. This variant of detecting phase shifts of the X-rays which pass through a subject, with the aid of a multiply offset analyzer grating and measuring the radiation intensity on a detector element behind the analyzer grating, means that at least three measurements of each X-ray have to be carried out with an analyzer grating respectively displaced by fractions of the grating period. In principle, it is even possible to make do without such an analyzer grating and use a sufficiently fine-structured detector instead, in which case the intensity losses due to absorption in the bars of the analyzer grating are obviated and the phase shift between the individual rays/pixels can be determined by a single measurement. In order to measure the phase contrast, it is necessary to use coherent or at least quasi-coherent radiation. This may be generated for example by a point-like focus or as a field of quasi-coherent radiation by a source grating behind a focus, which is designed to be flat, or by a corresponding grating-like configuration of the focal spot on the anode in order to replicate such a grating. The line orientation of the gratings should be selected so that the grating lines of the gratings provided, and the possibly provided strip structures of the detector elements, extend mutually parallel. It is furthermore advantageous, but not necessary, that the grating lines should be oriented parallel or perpendicularly to the system axis of the focus-detector system presented here. FIG. 3 shows a schematic representation of a focus-detector combination according to an embodiment of the invention having a focus F, which emits a divergent ray beam with the rays Si in the direction of a sample or subject P. After passing through the subject P the ray bundle, now broadened, strikes a first phase grating G1 in which an interference pattern is generated, which is evaluated by the downstream analysis-detector system with the analyzer grating G2 and the subsequent detector D. The evaluation by such an evaluation-detector system as presented here, having an analyzer grating and a downstream detector with a multiplicity of detector elements, takes place as was described in FIGS. 1 and 2. In order to improve the effectiveness of the analyzer grating G2, a highly absorbent material is additionally represented in the grating gaps of the grating G2. It will however be pointed out that analyzer gratings without such a filler in the grating gaps also belong to the scope of the invention. The relevant radial distances between the essential elements of the focus-detector combination are moreover represented below the figure, such as the radial distance r1, between the focus and the phase grating G1 and the radial distance r2 between the focus and the analysis-detector system. In order to describe the magnifying properties of the divergent rays, the distances between the focus or source and the sample QP and the distance between the source or focus and the analysis-detector system QD are likewise indicated. The magnification factor V is given by the distance ratio between the distance QD from the source or focus to the analysis-detector system and the distance QP from the source or focus to the sample, with V = QD _ QP _ . ( 8 ) The size of the projections of the scanned region in the subject (=FOV=Field of View) with respect to the utilized region of the subsequent phase grating G1 as well as to the utilized subsequent region of the analyzer-detector system also behave according to this geometrical situation in an embodiment of the inventive scanning of a subject. FIG. 4 represents a variant of a focus-detector system likewise according to an embodiment of the invention, in which the distance between the phase grating and the subsequent analysis-detector system is substantially increased. The Inventors have discovered that a larger Talbot distance can be achieved by selecting a higher Talbot order m and/or by increasing the phase grating period g1. Enlarging g1, moreover, also entails a larger period of the analyzer grating. Above all, however, the period of the standing wave field to be scanned and therefore also the period of the analyzer grating are increased by the geometrical enlargement. This reduces the aspect ratio and therefore facilitates production of the gratings. If the analysis-detector system is to be configured without an analyzer grating, then the spatial resolution requirements of the detector can advantageously be selected to be less stringent via the geometry as described above. Such a variant of a focus-detector system having a phase grating G1 for interference formation with a downstream analysis-detector system, in which the detector is divided into individual detector elements and these detector elements, which determine the position resolution of the detector, are furthermore subdivided into strip shapes according to the grating lines of the phase grating in order to measure the phase shift per detector element, is represented in FIG. 5. Here again, the distance between the phase grating G1 and the subsequent detector D is selected to be so large that it corresponds to the Talbot distance dm. FIGS. 6 and 7 represent a variant of a focus-detector system in which an additional source grating is interposed between the focus F and the subject P, so that quasi-coherent X-radiation can be generated even with an extended focus and it is therefore possible to work with a substantially higher power/intensity. This provides the opportunity to use such focus-detector systems also in conjunction with medically used projective X-ray equipment or computer tomographic systems. The mutual distance ratios of the gratings in FIGS. 6 and 7 correspond to the distance ratios of FIGS. 3 and 4. FIG. 8 represents a computer tomography system 1 by way of example of a medical application, which comprises one or optionally two focus-detector systems. A gantry housing 6 is represented, which contains a first X-ray tube 2 with a detector system 3 lying opposite, in which a phase grating as represented in the drawings described above is also integrated. Optionally, a further focus-detector system with a second X-ray tube 4 and a second detector system 5 may additionally be provided. As the subject, a patient 7 may be displaced through the opening in the gantry for the purpose of a scan along the system axis 9 with the aid of a displaceable patient table 8. The computer tomography system is controlled and evaluated with the aid of a computation and control unit 10, in which there is a memory which contains Programs Prg1, to Prgn. The evaluation of the recordings and their reconstruction may also be carried out in this control and computation unit 10. It should also be pointed out that the focus-detector systems presented here in the document are not only capable of carrying out phase contrast measurements, rather absorption measurements may also be carried out. Phase and absorption information is obtained when evaluating each individual pixel. It is to be understood that the features of the invention as mentioned above may be used not only in the combination respectively indicated, but also in other combinations or in isolation, without departing from the scope of the present invention. Example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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claims | 1. A decay heat removal system for a liquid metal reactor comprising:a reactor vessel containing a reactor core therein and including a hot pool for containing a high-temperature fluid discharged from the reactor core and a cold pool which is separated from the hot pool by a partition and contains a low-temperature fluid;an intermediate heat exchanger (IHX) for transferring heat from the hot pool to an external steam generation system and positioned in the hot pool, the IHX having an upper portion communicating via a guide pipe with the hot pool and a bottom portion communicating with the cold pool for discharging the fluid from the hot pool into the cold pool after extracting heat from said fluid;a cylinder surrounding the IHX and defining an annular space around the IHX, the cylinder positioned in the hot pool and having an open top portion extending above a level of the fluid in the hot pool, and a bottom portion communicating with the cold pool;the guide pipe extending through said annular space of the cylinder and communicating at a first end with the hot pool and communicating at a second end with the upper portion of the IHX for allowing passage of the fluid from the hot pool into the IHX;a decay heat exchanger (DHX) equipped with heat transfer tubes, positioned inside the annular space of the cylinder surrounding said IHX, spaced from the IHX and from the cylinder by a designated distance, and thermally connected to external air; anda pump arranged in the cold pool for pumping the fluid from the cold pool through the IHX to the reactor core and to the hot pool and evacuating the annular space of the cylinder through the bottom portion of the cylinder to lower a level of fluid in the cylinder under the level of the fluid in the hot pool and under the DHX by virtue of a pressure differential between the hot pool and the cold pool caused by normal operation of the pump, wherein, upon pump failure, the level of fluid in the cylinder rises to contact the DHX, thereby allowing conduction heat transfer from the IHX to the DHX and thus transferring reactor core decay heat to external air by the DHX. 2. The decay heat removal system as set forth in claim 1, wherein the DHX has heat transfer tubes which are spaced above the level of fluid in the cylinder when the pump operates normally. 3. The decay heat removal system as set forth in claim 1, wherein the DHX has heat transfer tubes which are coiled around an outer circumference of the IHX and separated from the IHX by a designated distance. 4. The decay heat removal system as set forth in claim 1, wherein a plurality of groups, each of which includes the IHX, the DHX and the cylinder, are installed in the reactor vessel which includes a single hot pool. 5. The decay heat removal system as set forth in claim 1, wherein the cylinder has a plurality of through holes formed in the bottom portion thereof, wherein the bottom portion of the cylinder passes through the partition between the hot pool and the cold pool of the reactor vessel, and is formed integrally with the partition. |
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description | This application claims priority to U.S. Provisional Patent Application Ser. No. 62/331,616, filed May 4, 2016, the disclosure of which is hereby incorporated by reference in its entirety. The field of the disclosure relates generally to radionuclide generators and, more particularly, to systems and methods for sterilizing sealed radionuclide generator column assemblies. Radioactive material is used in nuclear medicine for diagnostic and therapeutic purposes by injecting a patient with a small dose of the radioactive material, which concentrates in certain organs or regions of the patient. Radioactive materials typically used for nuclear medicine include Technetium-99m (“Tc-99m”), Indium-111m (“In-111”), Thallium-201, and Strontium-87m, among others. Such radioactive materials may be produced using a radionuclide generator. Radionuclide generators generally include a column that has media for retaining a long-lived parent radionuclide that spontaneously decays into a daughter radionuclide that has a relatively short half-life. The column may be incorporated into a column assembly that has a needle-like outlet port that receives an evacuated vial to draw saline or other eluant liquid, provided to a needle-like inlet port, through a flow path of the column assembly, including the column itself. This liquid may elute and deliver daughter radionuclide from the column and to the evacuated vial for subsequent use in nuclear medical imaging applications, among other uses. Prior to use in medical applications, radionuclide generators are sterilized such that when sterile eluant is eluted through the device, the resulting elution is also sterile and suitable for injection into a patient. At least some known sterilization methods use a vented column assembly for the sterilization process. The use of vented column assemblies increases the risks of radiological material (e.g., radiologically contaminated steam) being released from the column assembly, and moisture generated during the sterilization process re-entering the fluid line of the column assembly. In some instances, vented caps or covers are used to cover the outlet port of the elution assemblies to inhibit moisture from re-entering the column assembly. Such caps can increase the cost and complexity of the sterilization process. Accordingly, a need exists for improved systems and methods for sterilizing radionuclide generator column assemblies. This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. One aspect is a method of sterilizing a column assembly that includes a column having an interior containing a retaining media and a parent radionuclide retained by the retaining media. An inlet port is connected with the interior of the column, and an outlet port is connected with the interior of the column. The method includes sealing at least one of the inlet port and the outlet port to form a sealed column assembly such that fluid communication with the column interior though both the inlet port and the outlet port is prevented, and sterilizing the sealed column assembly to form a terminally-sterilized column assembly. In another aspect, a system includes a sterilizer defining a sterilization chamber, and a sealed column assembly is disposed within the sterilization chamber. The column assembly includes a column having an interior containing a retaining media and a parent radionuclide retained by the retaining media, and an elution flow path including an inlet line and an outlet line. Each of the inlet and outlet lines is in fluid communication with the interior of the column. The elution flow path is completely sealed such that fluid flow through the column interior is prevented. In yet another aspect, a method includes providing a sealed radionuclide generator column assembly including a column having an interior that contains a retaining media and a parent radionuclide retained by the retaining media. An elution flow path of the sealed column assembly is completely sealed such that fluid flow through the column interior is prevented. The method further includes placing the sealed column assembly within a sterilization chamber of a sterilizer, and sterilizing the sealed column assembly to produce a terminally-sterilized, sealed column assembly. Various refinements exist of the features noted in relation to the above-mentioned aspects. Further features may also be incorporated in the above-mentioned aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments may be incorporated into any of the above-described aspects, alone or in any combination. Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. FIG. 1 is a schematic view of a system 100 for manufacturing radionuclide generators. The system 100 shown in FIG. 1 may be used to produce various radionuclide generators, including, for example and without limitation, Technetium generators, Indium generators, and Strontium generators. The system 100 of FIG. 1 is particularly suited for producing Technetium generators. A Technetium generator is a pharmaceutical drug and device used to create sterile injectable solutions containing Tc-99m, an agent used in diagnostic imaging with a relatively short 6 hour radiological half-life, allowing the Tc-99m to be relatively quickly eliminated from human tissue. Tc-99m is “generated” via the natural decay of Molybdenum (“Mo-99”), which has a 66 hour half-life, which is desirable because it gives the generator a relatively long two week shelf life. During generator operation (i.e., elution with a saline solution), Mo-99 remains chemically bound to a core alumina bed (i.e., a retaining media) packed within the generator column, while Tc-99m washes free into an elution vial, ready for injection into a patient. While the system 100 is described herein with reference to Technetium generators, it is understood that the system 100 may be used to produce radionuclide generators other than Technetium generators. As shown in FIG. 1, the system 100 generally includes a plurality of stations. In the example embodiment, the system 100 includes a cask loading station 102, a formulation station 104, an activation station 106, a fill/wash station 108, an assay/autoclave loading station 110, an autoclave station 112, an autoclave unloading station 114, a quality control testing station 116, a shielding station 118, and a packaging station 120. The cask loading station 102 is configured to receive and handle casks or containers of radioactive material, such as a parent radionuclide, and transfer the radioactive material to the formulation station 104. Radioactive material may be transported in secondary containment vessels and flasks that need to be removed from an outer cask prior to formulation. The cask loading station 102 includes suitable tooling and mechanisms to extract secondary containment vessels and flasks from outer casks, as well as transfer of flasks to the formulation cell. Suitable devices that may be used in the cask loading station 102 include, for example and without limitation, telemanipulators 122. At the formulation station 104, the raw radioactive material (i.e., Mo-99) is quality control tested, chemically treated if necessary, and then pH adjusted while diluting the raw radioactive material to a desired final target concentration. The formulated radioactive material is stored in a suitable containment vessel (e.g., within the formulation station 104). Column assemblies containing a column of retaining media (e.g., alumina) are activated at the activation station 106 to facilitate binding of the formulated radioactive material with the retaining media. In some embodiments, column assemblies are activated by eluting the column assemblies with a suitable volume of HCl at a suitable pH level. Column assemblies are held for a minimum wait time prior to charging the column assemblies with the parent radionuclide. Following activation, column assemblies are loaded into the fill/wash station 108 using a suitable transfer mechanism (e.g., transfer drawer). Each column assembly is then charged with parent radionuclide by eluting formulated radioactive solution (e.g., Mo-99) from the formulation station 104 through individual column assemblies using suitable liquid handling systems (e.g., pumps, valves, etc.). The volume of formulated radioactive solution eluted through each column assembly is based on the desired Curie (Ci) activity for the corresponding column assembly. The volume eluted through each column assembly is equivalent to the total Ci activity identified at the time of calibration for the column assembly. For example, if a volume of formulated Mo-99 required to make a 1.0 Ci generator (at time of calibration) is ‘X’, the volume required to make a 19.0 Ci generator is simply 19 times X. After a minimum wait time, the charged column assemblies are eluted with a suitable volume and concentration of acetic acid, followed by an elution with a suitable volume and concentration of saline to “wash” the column assemblies. Column assemblies are held for a minimum wait time before performing assays on the column assemblies. The charged and washed column assemblies are then transferred to the assay/autoclave load station 110, in which assays are taken from each column assembly to check the amount of parent and daughter radionuclide produced during elution. Each column assembly is eluted with a suitable volume of saline, and the resulting solution is assayed to check the parent and daughter radionuclide levels in the assay. Where the radioactive material is Mo-99, the elutions are assayed for both Tc-99m and Mo-99. Column assemblies having a daughter radionuclide (e.g., Tc-99m) assay falling outside an acceptable range calculation are rejected. Column assemblies having a parent radionuclide (e.g., Mo-99) breakthrough exceeding a maximum acceptable limit are also rejected. Following the assay process, tip caps are applied to the outlet port and the fill port of the column assembly. Column assemblies may be provided with tip caps already applied to the inlet port. If the column assembly is not provided with a tip cap pre-applied to the inlet port, a tip cap may be applied prior to, subsequent to, or concurrently with tip caps being applied to the outlet port and the fill port. Assayed, tip-capped column assemblies are then loaded into an autoclave sterilizer 124 located in the autoclave station 112 for terminal sterilization. The sealed column assemblies are subjected to an autoclave sterilization process within the autoclave station 112 to produce terminally-sterilized column assemblies. Following the autoclave sterilization cycle, column assemblies are unloaded from the autoclave station 112 into the autoclave unloading station 114. Column assemblies are then transferred to the shielding station 118 for shielding. Some of the column assemblies are transferred to the quality control testing station 116 for quality control. In the example embodiment, the quality control testing station 116 includes a QC testing isolator that is sanitized prior to QC testing, and maintained at a positive pressure and a Grade A clean room environment to minimize possible sources of contamination. Column assemblies are aseptically eluted for in-process QC sampling, and subjected to sterility testing within the isolator of the quality control testing station 116. Tip caps are reapplied to the inlet and outlet needles of the column assemblies before the column assemblies are transferred back to the autoclave unloading station 114. The system 100 includes a suitable transfer mechanism for transferring column assemblies from the autoclave unloading station 114 (which is maintained at a negative pressure differential, Grade B clean room environment) to the isolator of the quality control testing station 116. In some embodiments, column assemblies subjected to quality control testing may be transferred from the quality control testing station 116 back to the autoclave unloading station 114, and can be re-sterilized and re-tested, or re-sterilized and packaged for shipment. In other embodiments, column assemblies are discarded after being subjected to QC testing. In the shielding station 118, column assemblies from the autoclave unloading station 114 are visually inspected for container closure part presence, and then placed within a radiation shielding container (e.g., a lead plug). The radiation shielding container is inserted into an appropriate safe constructed of suitable radiation shielding material (e.g., lead, tungsten or depleted uranium). Shielded column assemblies are then released from the shielding station 118. In the packaging station 120, shielded column assemblies from the shielding station 118 are placed in buckets pre-labeled with appropriate regulatory (e.g., FDA) labels. A label uniquely identifying each generator is also printed and applied to each bucket. A hood is then applied to each bucket. A handle is then applied to each hood. The system 100 may generally include any suitable transport systems and devices to facilitate transferring column assemblies between stations. In some embodiments, for example, each of the stations includes at least one telemanipulator 122 to allow an operator outside the hot cell environment (i.e., within the surrounding room or lab) to manipulate and transfer column assemblies within the hot cell environment. Moreover, in some embodiments, the system 100 includes a conveyance system to automatically transport column assemblies between the stations and/or between substations within one or more of the stations (e.g., between a fill substation and a wash substation within the fill/wash station 108). In the example embodiment, some stations of the system 100 include and/or are enclosed within a shielded nuclear radiation containment chamber, also referred to herein as a “hot cell”. Hot cells generally include an enclosure constructed of nuclear radiation shielding material designed to shield the surrounding environment from nuclear radiation. Suitable shielding materials from which hot cells may be constructed include, for example and without limitation, lead, depleted uranium, and tungsten. In some embodiments, hot cells are constructed of steel-clad lead walls forming a cuboid or rectangular prism. In some embodiments, a hot cell may include a viewing window constructed of a transparent shielding material. Suitable materials from which viewing windows may be constructed include, for example and without limitation, lead glass. In the example embodiment, each of the cask loading station 102, the formulation station 104, the fill/wash station 108, the assay/autoclave loading station 110, the autoclave station 112, the autoclave unloading station 114, and the shielding station 118 include and/or are enclosed within a hot cell. In some embodiments, one or more of the stations are maintained at a certain clean room grade (e.g., Grade B or Grade C). In the example embodiment, pre-autoclave hot cells (i.e., the cask loading station 102, the formulation station 104, the fill/wash station 108, the assay/autoclave loading station 110) are maintained at a Grade C clean room environment, and the autoclave unloading cell or station 114 is maintained at a Grade B clean room environment. The shielding station 118 is maintained at a Grade C clean room environment. The packaging stations 120 are maintained at a Grade D clean room environment. Unless otherwise indicated, references to clean room classifications refer to clean room classifications according to Annex 1 of the European Union Guidelines to Good Manufacturing Practice. Additionally, the pressure within one or more stations of the system 100 may be controlled at a negative or positive pressure differential relative to the surrounding environment and/or relative to adjacent cells or stations. In some embodiments, for example, all hot cells are maintained at a negative pressure relative to the surrounding environment. Moreover, in some embodiments, the isolator of the quality control testing station 116 is maintained at a positive pressure relative to the surrounding environment and/or relative to adjacent stations of the system 100 (e.g., relative to the autoclave unloading station 114). FIG. 2 is a perspective view of an example elution column assembly 200 that may be produced with the system 100. As shown in FIG. 2, the column assembly 200 includes an elution column 202 fluidly connected at a top end 204 to an inlet port 206 and a charge port 208 through an inlet line 210 and a charge line 212, respectively. A vent port 214 that communicates fluidly with an eluant vent 216 via a venting conduit 218 is positioned adjacent to the inlet port 206, and may, in operation, provide a vent to a vial or bottle of eluant connected to the inlet port 206. The column assembly 200 also includes an outlet port 220 that is fluidly connected to a bottom end 222 of the column 202 through an outlet line 224. A filter assembly 226 is incorporated into the outlet line 224. The column 202 defines a column interior that includes a retaining media (e.g., alumina beads, not shown). As described above, during production of the column assembly 200, the column 202 is charged via the charge port 208 with a radioactive material, such as Molybdenum-99, which is retained with the interior of the column 202 by the retaining media. The radioactive material retained by the retaining media is also referred to herein as the “parent radionuclide”. During use of the column assembly 200, an eluant vial (not shown) containing an eluant fluid (e.g., saline) is connected to the inlet port 206 by piercing a septum of the eluant vial with the needle-like inlet port 206. An evacuated elution vial (not shown) is connected to the outlet port 220 by piercing a septum of the elution vial with the needle-like outlet port 220. Eluant fluid from the eluant vial is drawn through the elution line, and elutes the column 202 containing parent radionuclide (e.g., Mo-99). The negative pressure of the evacuated vial draws eluant from the eluant vial and through the flow pathway, including the column, to elute daughter radionuclide (e.g., Tc-99m) for delivery through the outlet port 220 and to the elution vial. The eluant vent 216 allows air to enter the eluant vial through the vent port 214 to prevent a negative pressure within the eluant vial that might otherwise impede the flow of eluant through the flow pathway. After having eluted daughter radionuclide from the column 202, the elution vial is removed from the outlet port 220. The column assembly 200 shown in FIG. 2 is shown in a finally assembled state. In particular, the column assembly 200 includes an inlet cap 228, an outlet cap 230, and a charge port cap 232. The caps 228, 230, 232 protect respective ports 206, 214, 220, and 208, and inhibit contaminants from entering the column assembly 200 via the needles. In prior radionuclide generator production processes, needle closure is applied after a sterilization process such that the column assembly is vented during the sterilization process. Prior to final packaging, elution column assemblies of radionuclide generators intended for use in the medical industry are sterilized such that when sterile eluant is eluted through the device, the resulting elution is also sterile and suitable for injection into a patient. Known methods of sterilizing column assemblies include aseptic assembly, and autoclave sterilization of a vented column assembly. Aseptic assembly generally includes sterilizing components of the column assembly separately, and subsequently assembling the column assembly in an aseptic environment. Autoclave sterilization generally includes exposing a vented column assembly, having a column loaded with parent radionuclide, to a saturated steam, or a steam-air mixture environment. Autoclave sterilization provides advantages over aseptic assembly because it enables production of a terminally sterilized generator. In other words, autoclave sterilization produces a generator assembly that is sterilized in its final container, or at least that is sterilized with the flow path between the inlet port, the column, and the outlet port (i.e., the elution flow path) assembled in its final form, including any vented or non-vented caps over the inlet and outlet ports. Terminal sterilization provides significantly greater sterility assurance than aseptic assembly. As noted above, known methods of autoclave sterilization include exposing a vented column assembly to a saturated steam or a steam-air mixture environment. During this process, liquid that resides in the column assembly, including the column and tubes that extend between the column and the inlet and outlet ports may be heated to vapor form (e.g., steam) to kill and/or inactivate contaminants. The vent allows the introduction of steam and the release of vapors from the column during the sterilization process. However, because the column assembly is vented, radiological material (e.g., radiologically contaminated steam) may be released from the column assembly, and/or moisture generated during the sterilization process may re-enter the fluid line of the column assembly, which may adversely affect generator performance. A completely sealed, terminally-sterilized generator column assembly and systems and methods for producing completely sealed, terminally-sterilized generator column assemblies are disclosed. FIG. 3 is a perspective view of a completely sealed, terminally-sterilized generator column assembly 300, with a U-shaped elution line support 302, which supports the inlet and outlet lines 304, 306 and ports of the column assembly 300. A needle-like inlet port 308 and vent 310 of the column assembly 300 are covered and completely sealed by one of two cap plugs 312, and a needle-like outlet port 314 of the column assembly 300 is covered by the other of the cap plugs 312. Each of the cap plugs 312 is a solid, non-hollow, single-piece member constructed of an elastomeric material that is pierceable by the needle-like ports of the column assembly 300. The cap plugs 312 are constructed of a suitably elastomeric material such that when one of the needle-like ports of the column assembly 300 pierces one of the cap plugs 312, the cap plug 312 seals off the corresponding port. Suitable materials from which the cap plugs 312 may be constructed include, for example and without limitation, silicone. One particularly suitable material from which cap plugs 312 may be constructed is the commercially available silicone rubber sold by Wacker Chemie AG under the trade name Elastosil® 3003LR/20. A needle-like fill or charge port 316 is covered by a fill port stopper 318. The fill port stopper 318 may be constructed of the same or similar materials as the cap plugs 312. One particularly suitable material from which the fill port stopper 318 may be constructed is the commercially available silicone rubber sold by Wacker Chemie AG under the trade name Elastosil® 3003LR/50. A suitable method of producing the completely sealed, terminally-sterilized generator column assembly 300 of FIG. 3 includes completely sealing the elution flow path (including the inlet port 308, the inlet line 304, the outlet line 306, and the outlet port 314) of the column assembly 300 such that no fluid flow is permitted through the column 320 of the column assembly 300, and subjecting the sealed column assembly 300 to a sterilization process. In some embodiments, sealing the elution flow path of the column assembly 300 includes sealing each of the needle-like inlet and outlet ports 308, 314 of the column assembly 300 using, for example, the cap plugs 312. For example, with additional reference to FIG. 1, a cap plug 312 is placed over the outlet port 314 and/or the inlet port 308 of the column assembly 300 at the assay/autoclave loading station 110. The system 100 may include a dedicated capping station that uses automated or semi-automated tooling (e.g., telemanipulators) to apply the cap plugs 312 to the inlet port 308 and/or the outlet port 314 of the column assembly 300. Such a capping station may be located, for example, between an assay substation and an autoclave loading substation within the assay/autoclave loading station 110. In some embodiments, column assemblies may be provided with cap plugs 312 already applied to the inlet port 308. In such embodiments, a cap plug is not applied to the inlet port 308 at the assay/autoclave loading station 110. The method may also include sealing the charge or fill port 316 of the column assembly 300 using, for example, the fill port stopper 318. Referring again to FIG. 1, the fill port stopper 318 may be applied to the needle-like fill port 316 of the column assembly 300 after the assay process performed at the assay/autoclave loading station 110. The fill port stopper 318 may be applied to the column assembly 300 simultaneously with the outlet cap plug 312, before the outlet cap plug 312 is applied, or after the outlet cap plug 312 is applied to the column assembly 300. The fill port stopper 318 may be applied to the column assembly 300 within a capping station of the system 100 using automated or semi-automated tooling (e.g., a telemanipulator). When the cap plugs 312 and fill port stopper 318 are applied to the respective inlet and outlet ports 308, 314, and the fill port 316 of the column assembly 300, the column assembly 300 is completely sealed. That is, no fluid flow is permitted through the elution flow path, or through the interior of the column 320. In other words, fluid communication with the interior of the column 320 (and the parent radionuclide contained therein) is prevented. The completely sealed column assembly 300 is then subjected to a sterilization process that results in a completely sealed, terminally-sterilized column assembly 300. The sterilization process may be carried out in an autoclave sterilizer (e.g., sterilizer 124) located, for example, between the assay/autoclave loading station 110 and the autoclave unloading station 114 (shown in FIG. 1). The sterilization processes described herein may be performed in commercially available autoclave sterilizers, including, for example and without limitation, PST-series sterilizers available from Belimed. FIG. 4 is a perspective view of two example autoclave sterilizers 400 suitable for use in the system 100 of FIG. 1, and for carrying out the methods described herein. FIG. 5 is a schematic view of one of the autoclave sterilizers 400 connected to a controller 500 for controlling operation of the sterilizer 400. As shown in FIG. 4, each of the sterilizers 400 includes a generally rectangular enclosure 402 defining a sterilization chamber 404 in which a sterilization process is performed. In this embodiment, the enclosures 402 are made of stainless steel, specifically, 316L stainless steel, although the enclosures may be constructed of any other suitable material that enables the system 100 to function as described herein. In some embodiments, the sterilizers 400 and/or the enclosures 402 are positioned within a radiological containment chamber (i.e., a hot cell) to provide radiation shielding. In this embodiment, each of the enclosures 402 includes a plurality of tracks or rails 406 located within the sterilization chamber 404. The rails 406 are vertically spaced within the sterilization chamber 404, and are configured to receive carts 408 carrying racks (not shown in FIG. 4) of radionuclide generator column assemblies. Each of the sterilizers 400 also includes two sealing doors 410 located on opposite sides of the respective enclosure 402 for sealing access openings 412 to the sterilization chamber 404. In this embodiment, the sealing doors 410 are guillotine-style sealing doors, although the sealing doors 410 may have any other suitable configuration that enables the system 100 to function as described herein. Referring to FIG. 5, each of the autoclave sterilizers 400 includes a steam inlet 502 for introducing saturated steam into the sterilization chamber 404, and a compressed air inlet 504 for introducing compressed air into the sterilization chamber 404. A steam generator 506 is connected to the steam inlet 502, and a compressor 508 is connected to the compressed air inlet 504. The steam generator 506 generally includes a clean steam generator, such as a commercially available clean steam generator. In some embodiments, the autoclave sterilizers 400 include an insitu filter (not shown) for filtering compressed air before it is introduced into the sterilization chamber 404 through compressed air inlet 504. The autoclave sterilizers 400 also include a steam inlet valve 510 (generally, a first valve) connected between the steam generator 506 and the steam inlet 502 to control the supply of saturated steam into the sterilization chamber 404, and a compressed air inlet valve 512 (generally, a second valve) connected between the compressor 508 and the compressed air inlet 504 to control the supply of compressed air into the sterilization chamber 404. The steam inlet valve 510 and the compressed air inlet valve 512 may generally include any suitable actuatable valves that enable the autoclave sterilizers 400 to function as described herein, including, for example and without limitation, electrically-actuated valves and pneumatically actuated valves. Each of the steam inlet valve 510 and the compressed air inlet valve 512 is connected to the controller 500 for controlling operation of the respective valves. The autoclave sterilizers 400 also include a fan 514 for mixing steam and compressed air within the sterilization chamber 404. A motor 516 is connected to the fan 514 for controlling operation thereof. In this embodiment, the fan 514 is mounted to a top or ceiling of the enclosure 402, proximate to the steam inlet 502 and compressed air inlet 504. In this embodiment, each of the autoclave sterilizers 400 also includes a steam jacket 518 for controlling the temperature of the sterilization chamber 404. The steam jacket 518 is fluidly connected to source of pressurized steam, and is filled with pressurized steam to insulate the sterilization chamber 404 and facilitate maintaining a relatively constant temperature within the sterilization chamber 404. The sterilizers 400 may also include one or more sensors for monitoring conditions within the sterilization chamber 404. In this embodiment, each of the autoclave sterilizers 400 includes a temperature sensor 520 and a pressure sensor 522. The temperature sensor 520 and the pressure sensor 522 are connected to the controller 500 for providing feedback to the controller 500 about temperature and pressure conditions within the autoclave sterilizer 400. The temperature sensor 520 may be any suitable temperature sensor that enables the sterilizer 400 to function as described herein including, for example and without limitation, a resistance temperature detector. The pressure sensor 522 may be any suitable pressure sensor that enables the sterilizer 400 to function as described herein. In some embodiments, the pressure sensor 522 is a pressure transducer. The controller 500 is connected to each of the steam inlet valve 510, the compressed air inlet valve 512, and the fan motor 516 for controlling operation of the respective components. Also, as noted above, the controller 500 is connected to the temperature and pressure sensors 516 and 518 for monitoring temperature and pressure conditions within the sterilization chamber 404. In the example embodiment, the controller 500 is also connected to the steam generator 506 and the compressor 508 to control operation of the steam generator 506 and the compressor 508. The controller 500 is configured to control operation of at least the steam inlet valve 510 and the compressed air inlet valve 512 in response to temperature and pressure measurements received from the temperature sensor 520 and the pressure sensor 522, respectively. Specifically, the controller 500 controls the position and/or regulates each of the steam inlet valve 510 and the compressed air inlet valve 512 to control the supply of saturated steam and compressed air, respectively, into the sterilization chamber 404. FIG. 6 is a block diagram of the controller 500. The controller 500 may have any suitable controller configuration that enables the sterilizer 400 to function as described herein. In some embodiments, for example, the controller 500 is a PID controller. In this embodiment, the controller 500 includes at least one memory device 610 and a processor 615 that is coupled to the memory device 610 for executing instructions. In this embodiment, executable instructions are stored in the memory device 610, and the controller 500 performs one or more operations described herein by programming the processor 615. For example, the processor 615 may be programmed by encoding an operation as one or more executable instructions and by providing the executable instructions in the memory device 610. The processor 615 may include one or more processing units (e.g., in a multi-core configuration). Further, the processor 615 may be implemented using one or more heterogeneous processor systems in which a main processor is present with secondary processors on a single chip. As another illustrative example, the processor 615 may be a symmetric multi-processor system containing multiple processors of the same type. Further, the processor 615 may be implemented using any suitable programmable circuit including one or more systems and microcontrollers, microprocessors, programmable logic controllers (PLCs), reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), programmable logic circuits, field programmable gate arrays (FPGA), and any other circuit capable of executing the functions described herein. In this embodiment, the processor 615 controls operation of the autoclave sterilizer 400 by outputting control signals to at least the steam inlet valve 510, the compressed air inlet valve 512, and the fan motor 516. Further, in this embodiment, the processor 615 receives signals from the temperature sensor 520 and the pressure sensor 522 associated with the temperature and pressure, respectively, within the sterilization chamber 404. The memory device 610 is one or more devices that enable information such as executable instructions and/or other data to be stored and retrieved. The memory device 610 may include one or more computer readable media, such as, without limitation, dynamic random access memory (DRAM), static random access memory (SRAM), a solid state disk, and/or a hard disk. The memory device 610 may be configured to store, without limitation, application source code, application object code, source code portions of interest, object code portions of interest, configuration data, execution events and/or any other type of data. In this embodiment, the controller 500 includes a presentation interface 620 that is connected to the processor 615. The presentation interface 620 presents information, such as application source code and/or execution events, to a user 625, such as a technician or operator. For example, the presentation interface 620 may include a display adapter (not shown) that may be coupled to a display device, such as a cathode ray tube (CRT), a liquid crystal display (LCD), an organic LED (OLED) display, and/or an “electronic ink” display. The presentation interface 620 may include one or more display devices. The controller 500 also includes a user input interface 630 in this embodiment. The user input interface 630 is connected to the processor 615 and receives input from the user 625. The user input interface 630 may include, for example, a keyboard, a pointing device, a mouse, a stylus, a touch sensitive panel (e.g., a touch pad or a touch screen), a gyroscope, an accelerometer, a position detector, and/or an audio user input interface. A single component, such as a touch screen, may function as both a display device of the presentation interface 620 and the user input interface 630. In this embodiment, the user input interface 630 receives inputs associated with a desired exposure temperature, a desired exposure pressure, and a desired exposure time. In this embodiment, the controller 500 further includes a communication interface 635 connected to the processor 615. The communication interface 635 communicates with one or more remote devices, such as the temperature sensor 520 and the pressure sensor 522. In use, the sterilization process generally includes positioning the sealed column assembly 300 within the sterilization chamber 404 of the autoclave sterilizer 400, sealing the sterilization chamber 404, raising the temperature and pressure within the sterilization chamber 404 to a desired exposure temperature and exposure pressure, and exposing the sealed column assembly 300 to a mixture of steam and compressed air (also referred to as the “exposure phase”). The sealed column assembly 300 is exposed to the steam-air mixture for a suitable amount of time and at a suitable exposure temperature and pressure that enables the external surfaces of the needle-like ports, which are covered by the cap plugs 312 and the fill port stopper 318, to be sterilized, while matching chamber pressure with pressure formed within the sealed column assembly. In some embodiments, the exposure phase may be carried out at an exposure temperature of at least 100° C., at least 110° C., at least 120° C., at least 122° C., at least 124° C., at least 126° C., at least 128° C., at least 130° C., and even up to 140° C. In some embodiments, the exposure phase is carried out at an exposure temperature of between about 110° C. and about 130° C. In other embodiments, the exposure phase is carried out at an exposure temperature of between about 120° C. and about 140° C. In yet other embodiments, the exposure phase is carried out at an exposure temperature of between about 120° C. and about 130° C. In some embodiments, the exposure phase may be carried out at an exposure pressure of at least 2000 millibars (mbar), at least 2500 mbar, at least 2700 mbar, at least 2900 mbar, at least 3000 mbar, at least 3050 mbar, at least 3075 mbar, at least 3100 mbar, and even up to 3200 mbar. In some embodiments, the exposure phase is carried out at an exposure pressure of between about 2900 mbar and about 3200 mbar. In other embodiments, the exposure phase is carried out at an exposure pressure of between about 2800 mbar and about 3100 mbar. In yet other embodiments, the exposure phase is carried out at an exposure pressure of between about 3000 mbar and about 3100 mbar. Referring to FIGS. 4 and 5, the controller 500 may control the steam inlet valve 510 and the compressed air inlet valve 512 to raise the pressure and temperature within the sterilization chamber 404 to the desired exposure pressure and desired exposure temperature. In this embodiment, the controller 500 controls the steam inlet valve 510 by opening the steam inlet valve 510 to allow high temperature, saturated steam to enter the sterilization chamber 404 through the steam inlet 502, thereby raising the temperature of the sterilization chamber 404 to the desired exposure temperature. The controller 500 receives temperature feedback from the temperature sensor 520, and closes and/or regulates the steam inlet valve 510 once the desired exposure temperature is reached. Further, in this embodiment, the controller receives pressure measurements from the pressure sensor 522, and controls the compressed air inlet valve 512 to control chamber pressure to match the calculated pressure inside a sealed generator column assembly to balance pressures inside and outside the column assembly to prevent the column assembly from rupturing. The sealed column assembly 300 is exposed to the steam-air mixture environment for a suitable time that results in sterilization of all components and surfaces of the sealed column assembly 300, including the internal and external surfaces of the needle-like ports that are covered by the cap plugs 312 and the fill port stopper 318. In some embodiments, for example, the sealed column assembly 300 is exposed to the steam-air mixture environment for at least 10 minutes, at least 15 minutes, at least 20 minutes, at least 25 minutes, at least 30 minutes, at least 35 minutes, and even up to 45 minutes. In some embodiments, the sealed column assembly 300 is exposed to the steam-air mixture environment for an exposure time of between about 15 minutes and about 45 minutes, and, more suitably, for an exposure time of between about 20 minutes and about 40 minutes. In this embodiment, the steam-air mixture is formed in the sterilization chamber 404 by introducing sterile compressed air into the sterilization chamber 404 through the compressed air inlet 504, and mixing the compressed air with steam introduced into the sterilization chamber 404 via the steam inlet 502. In some embodiments, for example, regulated compressed air is fed through a sterile insitu filter into the sterilization chamber 404, and homogeneously mixed with saturated steam (introduced from the steam inlet 502) with the internal fan 514. In some embodiments, the rate at which the compressed air is introduced into the sterilization chamber 404 is controlled at a rate to maintain a partial pressure around the sealed column assembly at a pressure substantially equal to a partial pressure within the sealed column assembly. For example, suitable set-point pressures at which the sterilization process should be carried to prevent physical deformation of the column assembly may be experimentally determined. These values may be stored in the controller 500 (specifically, in the memory device 610 of the controller 500). The sterilization chamber pressure is then monitored using suitable pressure sensors or monitors (e.g., pressure sensor 522), and the rate at which compressed air is introduced into the sterilization chamber 404 is controlled using the controller 500 based on the sensed pressure within the sterilization chamber 404. For example, if the sensed pressure within the sterilization chamber 404 is too low (e.g., more than 30 mbar below the set-point pressure), compressed air is added, for example, by the controller 500 opening and/or regulating the compressed air inlet valve 512 until the sensed pressure reaches the set-point pressure. Further, if the sensed pressure within the sterilization chamber exceeds the set-point pressure by a preset threshold (e.g., more than 60 mbar above the set-point pressure), the flow of compressed air to the sterilization chamber 404 is terminated. In some embodiments, the sterilization process also includes monitoring the temperature within the sterilization chamber 404, and controlling the flow of saturated steam to the sterilization chamber 404 to adjust the temperature. In this embodiment, for example, the temperature within the sterilization chamber 404 is measured using the temperature sensor 520, and if the measured temperature is below a threshold temperature, high temperature saturated steam is added to the sterilization chamber 404. In this embodiment, the flow of steam to the sterilization chamber 404 is controlled by the controller 500, specifically, by controlling the steam inlet valve 510. In some embodiments, more than one sealed column assembly is sterilized at a time. In one embodiment, for example, up to 192 column assemblies are loaded into the sterilization chamber 404 of the autoclave sterilizer 400, and simultaneously subjected to a sterilization process. One example method of sterilizing a completely sealed column assembly includes: a) loading a plurality of column assemblies into the sterilization chamber of an autoclave sterilizer; b) gradually heating the sterilization chamber to an exposure temperature of between about 122° C. and about 130° C., while simultaneously raising the pressure in the sterilization chamber to an exposure pressure of between about 2800 mbar and about 3200 mbar; c) introducing compressed sterile air into the sterilization chamber and homogenously mixing the sterile air within the chamber to create a partial pressure equal to the pressure within the sealed column assemblies to prevent the column assemblies from rupturing; d) allowing the sterilization chamber temperature to stabilize for a stabilization period of between about 3 minutes and about 10 minutes; e) exposing the column assemblies to a steam-air mixture environment for an exposure time of at least 30 minutes; f) gradually cooling the sterilization chamber to a final temperature below 90° C., more suitably between about 50° C. and about 70° C., and g) removing the plurality of sealed column assemblies from the sterilization chamber. In some embodiments, the autoclave end-of-cycle F0 values are at least 40 minutes, at least 50 minutes, at least 60 minutes, at least 70 minutes, at least 80 minutes, at least 90 minutes, and even up to 120 minutes. By general comparison, end-of-cycle F0 values for previous autoclave sterilization processes are less than 20 minutes. The term “F0 value” refers to the number of equivalent minutes of steam sterilization at 250° F. (121° C.) delivered to a load or product (e.g., a column assembly). For example, if a cycle has an F0 value of 12, the sterilization effectiveness of that cycle is equal to 12 minutes at 250° F. (121° C.) regardless of the process temperature and time used in the cycle. Embodiments of the sterilization methods described herein can achieve Sterility Assurance Levels (SAL) up to about 10−78. This is significantly higher than SAL achievable with aseptic assembly (SAL around 10−6), or the prior autoclave sterilization processes (SAL around 10−14). As compared to prior sterilization processes, embodiments of the sterilization processes used to terminally sterilize the sealed column assembly 300 are carried out under unique conditions that facilitate sterilizing all components and surfaces of the sealed column assembly 300, including the needle-like inlet and outlet ports that are covered by the cap plugs 312. For example, embodiments of the sterilization processes described herein are carried out at generally higher temperatures, and for longer exposure times as compared to prior sterilization processes used on vented column assemblies. Moreover, embodiments of the present disclosure include introducing and mixing compressed air with saturated steam to maintain the pressure differential between the sealed column assembly and the sterilization chamber, and prevent rupture of the column assembly. The methods of the present disclosure provide several advantages over known column assembly sterilization procedures. For example, embodiments of the methods described herein are relatively cheaper and simpler because they do not require use of a vented outlet needle cover during the sterilization process. Additionally, methods of the present disclosure are relatively cleaner because the column assembly is completely sealed during sterilization, thereby inhibiting release of radiologically contaminated steam from the column assembly. Moreover, embodiments of the methods described herein significantly reduce the risk of moisture re-entering an open or vented port of the column assembly because all ports of the elution flow path are completely sealed during the sterilization process. When introducing elements of the present invention or the embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. |
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061817597 | summary | BACKGROUND OF THE INVENTION This invention relates to the detection of conditions in a nuclear-fueled electric power-generating unit, and more particularly, to methods and apparatus for estimating the effective neutron multiplication factor in a nuclear reactor. The power level of a nuclear reactor is generally divided into three ranges: the source or start-up range, the intermediate range, and the power range. The power level of the reactor is continuously monitored to assure safe operation. Such monitoring is typically conducted by means of neutron detectors placed outside and inside the reactor core for measuring the neutron flux of the reactor. Since the neutron flux at any point in the reactor is proportional to the fission rate, the neutron flux is also proportional to the power level. Fission and ionization chambers have been used to measure flux in the intermediate and power range of a reactor. Such fission and ionization chambers are capable of operation at all normal power levels, however, they are generally not sensitive enough to accurately detect low level neutron flux emitted in the source range. Thus, separate low level source range detectors are typically used to monitor neutron flux when the power level of the reactor is in the source range. U.S. Pat. No. 4,588,547 discloses a method and apparatus for determining the nearness to criticality of a nuclear reactor. That invention takes advantage of the fact that when the reactor is subcritical, the neutron flux generated by an artificial neutron source, and the direct progeny by fission, is higher than that generated by neutrons from natural neutron sources in the reactor fuel and progeny of those neutrons. However, that patent does not address the approach to criticality when a reactor approaches criticality due to withdrawal of control rods. During the approach to reactor criticality, the signals from the source range detectors are typically used to determine whether the reactor is critical or will achieve criticality before the scheduled or planned core conditions are achieved. Assemblies of control rods in the form of control banks, are used to regulate reactor activity through controlled absorption of the neutrons released in the fission process. When a reactor is to be made critical by withdrawal of the control banks, which is the typical method used for all reactor startups following the initial startup in each operating cycle, changes in control bank position cause changes in the magnitude of the source range detector signals which are not entirely indicative of core reactivity changes. This behavior makes it difficult for the reactor operator to use the source range detector information properly. Ideally the reactor operator would like to be able to not only determine whether the reactor is currently critical, or is likely to be critical before the planned critical conditions are achieved, but how close to critical the core actually is. In order to accurately determine how close the reactor is to critical, a means of using the source range detector signal information that does not rely only on the magnitude of the signal change from one control bank configuration to another is required. SUMMARY OF THE INVENTION This invention provides a method for determining the closeness to criticality of a nuclear reactor during start-up, comprising the steps of completing a control rod withdrawal step, thereby generating a change in an output signal of a neutron detector; measuring the output signal after the completion of the control rod withdrawal step and during a transient portion of the output signal; calculating the effective neutron multiplication factor (K.sub.eff) based upon the measured output signal and elapsed time between the output signal measurements; and determining the closeness to criticality of the nuclear reactor based upon the calculated value of the effective neutron multiplication factor (K.sub.eff). The invention also encompasses apparatus used to perform the above method. |
summary | ||
046719202 | abstract | A tool for maintaining ice baskets associated with a nuclear reactor system. The frame of the tool includes a platform which is disposed on a lattice support structure surrounding a selected and isolated basket. The tool includes an electric drill mounted for vertical reciprocation, in parallel axial relationship with the ice basket, and plural, selectively connectable auger shaft sections having a continuous helical fin thereabout which are connected in succession between the drill and a rotary drill bit, for drilling a hole of the required length, down through the ice within the ice basket. The drill then is maintained at an upper, vertically fixed position and a funnel positioned about the auger; ice chips or flakes are fed into the funnel while the drill is driven in reverse rotation, the auger conveying the ice to the bottom of the ice basket for filling lowermost voids and for filling successively higher voids as the auger is withdrawn. Clamping means are provided for clamping the protruding end of an auger section, during both the assembly of a successive auger section thereto and the disassembly of a successive auger section therefrom. |
051464810 | claims | 1. A substantially compressive stress free, pin-holes and defects free, continuous polycrystalline diamond thin membrane for X-ray lithography; said polycrystalline diamond membrane being substantially optically and X-ray transparent and having a substantially uniform thickness generally in the range of approximately 0.5 .mu.m to 4.0 .mu.m. a substantially compressive stress-free, pin-holes and defects free, continuous polycrystalline diamond thin membrane; said polycrystalline diamond membrane being substantially optically and X-ray transparent and having a substantially uniform thickness; a substantially X-ray absorbing pattern supported by said membrane; and a substrate supporting said membrane. preparing the surface of a supporting substrate comprising a material selected from the group consisting of silicon, polysilicon, silicon carbide, silicon nitride, silicon oxynitride, boron carbide, boron nitride, alumina, titanium carbide, titanium nitride, tungsten, molybdenum, tantalum and mixtures thereof by treating said substrate surface with a slurry of diamond particles and a volatile solvent placed in an ultrasonic bath for a predetermined period of time; placing said substrate into a hot filament chemical vapor deposition reactor chamber; pre-heating said substrate by electrically charging the pre-carburized filament network of said reactor to a temperature in the range of about 400.degree. C. to 650.degree. C. in the presence of an inert gas; maintaining said pre-heating temperature for a predetermined period of time; heating said substrate to a temperature in the range of approximately 650.degree. C.-700.degree. C. in the presence of a gaseous mixture of flowing hydrogen and carbon compounds; chemically vapor depositing a substantially optically and X-ray transparent, adherent and coherent polycrystalline diamond membrane having a substantially uniform thickness onto said substrate; cooling said substrate by extinguishing said deposition process and passing an inert gas over said substrate until the temperature of said substrate has reached substantially room temperature during said cooldown step; removing said substrate coated with a substantially compressive stress free polycrystalline diamond X-ray membrane from said reactor; applying an etch resistant mask to the back surface of the said substrate to define one or more openings; etching said back surface of said substrate by preferential chemical etchant; and recovering said compressive stress free, pin-holes and defects free, continuous polycrystalline diamond membrane supported by a substrate frame. 2. A X-ray lithography mask comprising: 3. The X-ray mask of claim 2 wherein the thickness of said polycrystalline diamond membrane is generally in the range of approximately 0.5 .mu.m to 4.0 .mu.m. 4. The X-ray mask of claim 2 wherein said polycrystalline diamond membrane has a diameter/thickness aspect ratio greater than 1,000. 5. The X-ray mask of claim 2 wherein said polycrystalline diamond membrane generally exhibits a tensile stress. 6. The X-ray mask of claim 2 wherein said polycrystalline diamond membrane generally exhibits a substantially wrinkle-free surface topography. 7. The X-ray mask of claim 2 wherein said substrate comprises a material selected from the group consisting of silicon, polysilicon, silicon carbide, silicon oxynitride, silicon nitride, boron carbide, boron nitride, alumina, titanium carbide, titanium nitride, tungsten, molybdenum, tantalum and mixtures thereof. 8. The X-ray mask of claim 2 wherein said X-ray absorbing pattern comprises a material selected from the group consisting of gold, nickel, tungsten, titanium, and tantalum or combination thereof. 9. A method for producing a substantially compressive stress free, pin-holes and defects free, continuous polycrystalline diamond X-ray membrane comprising: 10. The method of claim 9 wherein said diamond particles comprise 20 .mu.m to 100 .mu.m diamond powder. 11. The method of claim 9 wherein said diamond particles comprise 30 .mu.m to 35 .mu.m diamond powder. 12. The method of claim 9 wherein the distance between said substrate and said filament network is generally in the range of approximately 11 mm to 20 mm. 13. The method of claim 9 wherein the distance between said substrate and said filament network is generally in the range of approximately Il mm to 15 mm. 14. The method of claim 9 wherein the distance between said substrate and said filament network is generally in the range of approximately 11 mm to 15 mm. 15. The method of claim 9 wherein the flow rate of said inert gas during said pre-heating step is generally in the range of approximately 50 sccm-500 sccm for approximately 10 min. to 120 min. 16. The method of claim 9 wherein said carbon compound is selected from the group consisting of C.sub.1 -C.sub.4 saturated hydrocarbons, C.sub.1 -C.sub.4 unsaturated hydrocarbons, gases containing C and O, aromatic compounds and organic compounds containing C, H, and at least one of O and/or N. 17. The method of claim 9 wherein said carbon compound is methane. 18. The method of claim 13 wherein the concentration of said carbon compound in said gaseous mixture is generally in the range of approximately 0.2% to 5.0%. 19. The method of claim 13 wherein the concentration of said carbon compound in said gaseous mixture is generally in the range of approximately 0.5% to 2.0%. 20. The method of claim 9 wherein said flow rate of said gaseous mixture during said chemical vapor deposition step is generally in the range of approximately 10 sccm to 605 sccm. 21. The method of claim 9 wherein the operating pressure of said reactor during said chemical vapor deposition step is generally in the range of approximately 10 Torr. to 100 Torr. 22. The method of claim 9 wherein said substrate is rotated at approximately 1 to 10 revolutions/hour during said pre-heating and said chemical vapor deposition steps. 23. The method of claim 9 wherein the deposition rate for said polycrystalline diamond membrane is generally in the range of approximately 0.05-0.5 microns/hour. 24. The method of claim 9 wherein said chemical vapor deposition time is generally in the range of approximately 5-80 hours. 25. The method of claim 9 wherein the thickness of said polycrystalline diamond membrane is generally in the range of approximately 0.5 .mu.m-4 .mu.m. 26. The method of claim 9 wherein said polycrystalline diamond membrane has a diameter/thickness aspect ratio greater than 100. 27. The method of claim 9 wherein said polycrystalline diamond membrane generally exhibits a tensile stress. 28. The method of claim 9 wherein said polycrystalline diamond membrane generally exhibits a substantially wrinkle-free surface topography. 29. The X-ray mask of claim 8 wherein the absorbing pattern is deposited by physical vapor or chemical vapor deposition techniques. 30. The polycrystalline diamond thin membrane of claim 1 wherein said membrane has a diameter/thickness ratio greater than 1,000. 31. The polycrystalline diamond thin membrane of claim 1 wherein said membrane exhibits a substantially wrinkle-free surface topography. |
abstract | Method and apparatus and computer programs and computer medium for improving quality of a radiographic image of an object obtained by an X-ray apparatus containing an antidiffusion grid, placed between the object and a receiver of radiographic images, The grid is displaced in rectilinear translation in its plane on pickup of the image, between two positions according to a time displacement law which is a continuous curve with a time precision of approximately xc2x110% presenting at least five separate parts, the displacement taking place at constant speed over at least two parts and at variable speed over at least one part. |
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description | This application is the US-national stage of PCT application PCT/EP2007/002613, filed 23 Mar. 2007, published 4 Oct. 2007 as WO2007/110211, and claiming the priority of German patent application 102006013836.8 itself filed 24 Mar. 2006, whose entire disclosures are herewith incorporated by reference. The invention relates to a method of creating a safe permanent depository in a borehole produced by fusion drilling and having a lining formed by solidified melt, in particular a metallic lining. The invention further relates to an apparatus for creating a safe permanent depository comprising at least one borehole with a lining, in particular a metal lining from a casting. The invention should be used in particular for final storage of highly radioactive and/or highly toxic material, but is also suitable for storage of any other material. The invention further also relates to apparatuses as safe and cost-effective permanent depositories for low-level and medium-level radioactive materials and a bomb-proof holding and transport system for use between reactor or intermediate storage facility and a permanent depository shaft. The invention furthermore relates to apparatuses for controlling of a reactor core meltdown and automatic direct final storage of the molten core that has leaked out. The driving of boreholes, in particular so-called super-deep boreholes with bore diameters of constant size as far as the drilling target and in particular at depths of up to 20 km or more is known, for example, from EP 1 157 187 [U.S. Pat. No. 6,591,920] of the instant applicant, the content of which is integrated herein by reference in its entirety. The method described here can preferably be used in order to produce a borehole by fusion drilling and thereby provide the borehole with a seamless lining, in particular of metal. This object is attained according to the invention by a method in which in particular subcritical highly radioactive material for final storage is deposited in a lower area of the lined borehole, this lower area being separated after being filled from the rest of the borehole so that it subsequently moves independently toward the center of the earth. The object is further attained in that in a permanent depository apparatus at least one lower borehole region ( 1/7) of a lined borehole after filling with final depository material, in particular in subcritical condition, can be separated/is separated from the rest of the borehole, in order to sink as a result of autogenous heat generation and/or rock pressure and/or permanent weight under the effect of gravity and/or magma formation toward the center of the earth. As mentioned at the outset, the metal melt drilling method according to EP 1 157 187 represents a technically realizable drilling method with which in a continuous fusion drilling process production-ready extremely deep bores with large dimensionally stable borehole diameter can be produced quickly and cost-effectively up to depths of 20 km or more. With the continuous advance of the fusion drilling installation, in particular by magnetic slides, at the same time a seamless die-cast lining is produced from the metal melt acting as a drilling mud, which lining serves the magnetic slide as a “reaction rail” and transportation tube. These boreholes lined by die-casting, whether produced by this or another process, are used according to the invention as final depository. With the cited metal melt-drilling method running continuously at no time is an exposed, unlined borehole region present, since a strong-walled metal lining is directly constructed from the metal melt, which also serves as a “drilling head.” The stability of a borehole or borehole lined in this manner depends on the thickness of the metal wall, the prevailing pressure difference between the inner and outer wall and in particular the prevailing temperature. A borehole metal-lined in this manner can remain stable up to the rock temperature range of at least 600° C.-700° C., so that depths of around 20 km in the continental crust are to be expected. However, even under these temperature and pressure conditions the deep-seated rock is not present in a viscous form, but in a solid, albeit ductile form. The bore is preferably produced up to a depth at which the rock is ductile and in particular partial melts already form, the formation of which is further intensified by the autogenously generated heat of the embedded, heat-generating, highly radioactive material or in which in particular under the given temperature and pressure conditions, in the hot deep-seated rock the rock crystals are displaced with respect to a free, solid and in particular heavy metal body, on which the force of gravity of the earth acts more strongly than on the surrounding lighter surrounding rock. This can thus advantageously cause an accelerated migration of a separated lower borehole region that serves as a final depository zone. The migration speed of the entire separated lower borehole region or final depository zone is preferably promoted when the outer shape thereof is formed so as to widen downward conically so that the enormous lateral compressive forces become vertical thrust force. This migration according to the invention of the final depository zone in the form of a heavy metal body can be given, in addition, an acceleration by reduced friction from the increased internal temperature by means of the radioactive residual heat formation and/or by fluid collection in the metal mantel/deep-seated rock border area, in particular since these fluids can be supercritical under the prevailing temperature and pressure conditions and their frictional value is therefore drastically reduced. Advantageously, a final depository zone can slide downward in an accelerated manner under its gravitational force, surrounded by fluids or wetted by a fluid film, in particular like a glacier slides on its water film toward the valley. According to the invention, in the lower borehole region or the highly radioactive material finally deposited in the deepest part of the shaft can be filled up with a medium, for example, with molten lead as a moderator and/or heat compensation medium and/or pressure compensation medium, or the material to be finally deposited can be filled in. A lower borehole region thus filled up can be separated according to the invention as a final depository zone above the filling-in of the rest of the borehole by melting of the lining, in particular of the metal lining, e.g. over a length of several meters, and migrates as a whole out of the hot deep-seated rock toward the center of the earth, in particular under autogenous generation of heat and high permanent weight. The object of the invention is to overcome these disadvantages and to comply with the demand for the “best possible final depository.” The object of the invention is furthermore to provide a method and apparatus that offer a safe and cost-effective final depository directly on site and can be used in all countries, and in particular furthermore offer the possibility in the case of the burnthrough of a reactor of thus controlling the reactor core meltdown without polluting the environment. According to the invention, in the direct vicinity of a nuclear-power plant 18 or an intermediate storage facility 19 at least one borehole, for example, a borehole 10 that is 20 km deep, is sunk according to the described metal fusion-drilling method. The borehole 10 has a dome 20. An upper long region 7, e.g. more than three quarters of the borehole 10 thus produced, with in particular a continuous constant diameter, e.g. of preferably more than 0.5 meters, is provided with a lining, in particular a strong cast-metal lining preferably with good magnetic permeability, and according to the invention can be used as a final depository shaft, in order to conduct material to be stored into a lower smaller region 1, e.g. less than a quarter of the borehole 10. The lower borehole region 1, in particular the lower quarter or less, can be used hereby as a final depository zone, e.g. for highly radioactive and/or heat-developing materials or also other material. This borehole region 1 can preferably be in a ductile rock area or in the area of supercritical fluid conditions. Furthermore, the region 7 of the borehole lying above it can be used as a final depository for other material, e.g. for low-level and medium-level radioactive material, e.g. that accrues in the dismantling of a nuclear-power plant or another nuclear facility. Preferably the lower region used as a final depository zone 1 in the production of the borehole 10 can be formed in the area of the cast-metal lining such that the wall thickness is greater in the lower area than in the upper area, for example starts at 0.25 m and ends at the top at 0.05 m. This region 1 filled with highly radioactive and heat-generating elements 8, for instance spent fuel elements, surrounded by a mass 9 of heat-conducting and moderating material, for instance lead. The final depository zone 1 according to the invention can be separated from the rest of the borehole as a whole after filling with material to be finally disposed of and/or as required zone by zone, the separation of this zone 1 from the remaining zone 7 of the shaft 10 can advantageously occur by melting of a shaft wall area 4 in particular by radiation energy, which advantageously can come from a laser or a graphite emitter that can be moved upward and downward in the borehole via a magnetic slide device 14. The separation according to the invention by melting the borehole region 4 directly above the final depository zone 1 filled with highly radioactive material and preferably cast, for example, from molten lead can preferably be carried out such that this at the same time leads to the safe capping of the separated final depository zone 1 by the accumulating metal melt, which is deposited above the final depository zone and can form a metal cover or plug 5 and/or floats directly on the molten lead and with the remaining residue of the final depository zone lining forms a solid metal plug 6. The remaining lining-free melting area 4 in the borehole can optionally be filled up below the remaining region to form on a conical cast-iron tip 2 a new shaft tip 3 with a material (for example, borax) which promotes self-driving by migration through the hot bedrock. According to the invention, the upper shaft portion open at the bottom after separation can be closed with a cast metal filling, which serves as a new shaft tip 3 and preferably strengthened, e.g. by alloying elements, ensures the self-driving process. The final depository apparatus according to the invention preferably comprises a system 12 safely closed with respect to the biosphere, e.g. a transport tunnel that connects the final depository shaft 10 to the plant's reactor 17 and/or to the intermediate storage facility 19, such as, for example another magnetic slide system 14 (not shown). The transport tunnel 12 according to the invention between the reactor 17 and the final depository shaft 10, preferably bombproof and hermetically sealed off from the outside world, preferably also makes possible the construction of a catchment 13 and final depository apparatus for the event of a reactor meltdown, which greatly reduces the residual risk in the operation of nuclear-power plants and permits substantially longer running times of the nuclear facilities, so that the “golden end” of production time is extended in a favorable manner. The catchment and final deposition system 13 for the event of a reactor meltdown can be currently integrated into planning with new reactor constructions and thus designed in an optimal manner. With existing nuclear-power plants not provided with a ground protection of graphite tiles, an escape tunnel can preferably be built under the reactor foundation, which tunnel is preferably lined with graphite tiles and guides a reactor melt occurring unerringly into the sump 15 lying deeper, which can preferably also be lined with graphite tiles and is optionally additionally lined with special crucibles 16 of graphite such that the reactor melt flowing in is distributed in the graphite crucibles available and, after a decay time, can be conveyed via the automated transport system into the final depository. The catchment and final deposition system according to the invention for the event of a reactor meltdown 13 can be filled up with a medium 21 that is as far as possible inert with respect to radioactive radiation, heavier than air and lighter than the reactor melt. The contamination of the catchment and final deposition system 13 is thus preferably limited, and the medium can be pumped out after the final storage of the reactor melt and likewise finally stored. The advantages of the final storage method according to the invention with a direct permanent depository apparatus in situ on the site of nuclear facilities by means of boreholes according to the metal melt drilling method, compared to known methods and compared to a central final depository are as follows: 1. The driving and use of cost-effective permanent depository shafts for in particular highly radioactive materials directly at the location of production and/or storage saves high exploration costs in the search for and testing of suitable locations and saves valuable time, since every available location with nuclear facilities is suitable per se for the final depository method according to the invention described above, and the material to be finally stored reaches safe depths outside any influence of the biosphere. 2. The need for highly radioactive nuclear waste to travel in spite of the resistance by the general public is ended or can be restricted to marginal areas, to substantially reduce radiation exposure, the risk of accidents and the disposal costs for the general public. 3. Safe final storage of highly radioactive fuel elements up to the highly radioactive inventory of the nuclear-power plants in situ by self-driving via boreholes of a depth of, e.g. 15-20 km in historically manageable periods, with hermetic sealing from the biosphere and with high reduction of costs by fully automated sequences with shorter decay times, convince operators and the general public affected. 4. With the creation of final depositories at the main nuclear-power plant locations, the cost thereof is overall considerably lower than with a central final depository solution. At the same time, by burden-sharing, the problem is distributed over several locations, the resistance by the general public affected is reduced, since only the population at the nuclear facility locations is affected, and they have come to terms with nuclear energy anyway, and the risk and stress from the nuclear waste transports now no longer taking place are reduced. 5. The combination of direct final storage in situ with an integrated apparatus for controlling a reactor meltdown renders possible a substantial extension of the reactor runtimes and increases the acceptance of the final depository concept according to the invention among nuclear-power plant operators, politicians and the population of the locations affected. 6. Final storage in situ does not only bring relief from the population at the location in terms of risk and transport, but also creates jobs in the region with the construction of the final depository, which are guaranteed long-term by the complete dismantling of the nuclear facility. At the same time tax revenue is increased and guaranteed in the long term. 7. The acceptance by the general public with nuclear facilities for final depository locations in situ is achieved in particular by the self-driving of the highly radioactive material into the center of the earth never to return, since neither the region nor subsequent generations are left with an incalculable “evil inheritance,” while to the contrary the generation that enjoys the advantages of nuclear energy also assumes the burden of disposal. 8. The advantages across society of final storage by self-driving at the nuclear locations in situ via extremely deep bores and the development of the metal melt drilling methods ready for implementation associated as a prerequisite therewith are substantially outmatched by the creation of a completely new multi-billion market from the new metal melt drilling method base technology, of which the safe final storage is only one of the applications. 9. In addition to the greatest possible safety, the time and cost factors are important arguments for a permanent depository in situ: the costs for a borehole, e.g. 20 km deep with a capacity of 1 m3/m are estimated to be approx. = 200 m. The drilling time with the continuously operating metal melt drilling method alone is about six months, so that the rest of the year remains for transport to and from, and thus per year a 20 km borehole can be completed ready for production with a drilling installation. For each deep borehole, for example, 5×1000 m final depository zones with a final depository volume of approx. 5000 m3 can be used. With 24,000 m3 highly radioactive, heat-generating waste for the nuclear-power plants currently in existence in Germany, five final depositories according to the invention would be necessary with a total investment of 1 billion. This sum has already been invested in the construction of the Gorleben and Schacht Konrad locations, which turned out to be unsuitable as final depositories, and will have to be invested once again before they are usable as final depositories for low-level and medium-level radioactive material. 10. The cost of the search, testing and construction of a new central final depository to solve Germany's final depository problem will be at least twice as expensive according to current empirical values as the final depository solution in situ according to the invention, the cost of transport and the cost savings in dismantling the nuclear-energy facility not being included. The picture is similar with regard to the construction time scenario. For final depositories according to the invention, including the technical development of the magnetic slide metal melt drilling facilities up to technical readiness for use, a completion of 5 final depository shafts can be expected by 2020. The completion of a central final depository according to conventional mining methods, however, cannot be expected before 2030. |
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claims | 1. An EUV light source comprising:an EUV plasma production chamber comprising a chamber wall comprising an exit opening for the passage of produced EUV light focused to a focus point;a first EUV exit sleeve comprising a terminal end comprising an opening facing the exit opening;a first exit sleeve chamber housing the first exit sleeve and having an EUV light exit opening;a gas supply mechanism supplying gas under a pressure higher than the pressure within the plasma production chamber to the first exit sleeve chamber. 2. The apparatus of claim 1 further comprising:the first exit sleeve is tapered toward the terminal end opening. 3. The apparatus of claim 2 further comprising:the first exit sleeve is conical in shape comprising a narrowed end at the terminal end. 4. The apparatus of claim 3 further comprising:an EUV light receiving chamber housing the first exit sleeve chamber;a suction mechanism having a suction mechanism opening in the vicinity of the EUV exit opening of the first exit sleeve chamber removing EUV production material entering the EUV light receiving chamber through the EUV exit opening in the first exit sleeve chamber. 5. The apparatus of claim 3 further comprising:the EUV producing plasma production chamber comprising a second EUV exit sleeve comprising an exit opening facing an inlet opening of the first exit sleeve;a second exit sleeve chamber housing the second exit sleeve and having an EUV light exit opening;a suction mechanism removing EUV production debris from the second exit sleeve housing. 6. The apparatus of claim 5 further comprising:the second EUV exit sleeve opening comprising a different vacuum aperture. 7. The apparatus of claim 2 further comprising:the EUV producing plasma production chamber comprising a second EUV exit sleeve comprising an exit opening facing an inlet opening of the first exit sleeve;a second exit sleeve chamber housing the second exit sleeve and having an EUV light exit opening;a suction mechanism removing EUV production debris from the second exit sleeve housing. 8. The apparatus of claim 7 further comprising:the second EUV exit sleeve exit opening comprising a differential vacuum aperture. 9. The apparatus of claim 1 further comprising:the first exit sleeve is conical in shape comprising a narrowed end at the terminal end. 10. The apparatus of claim 9 further comprising:an EUV light receiving chamber housing the first exit sleeve chamber;a suction mechanism having a suction mechanism opening in the vicinity of the EUV exit opening of the first exit sleeve chamber removing EUV production material entering the EUV light receiving chamber through the EUV exit opening in the first exit sleeve chamber. 11. The apparatus of claim 9 further comprising:the EUV producing plasma production chamber comprising a second EUV exit sleeve comprising an exit opening facing an inlet opening of the first exit sleeve;a second exit sleeve chamber housing the second exit sleeve and having an EUV light exit opening;a suction mechanism removing EUV production debris from the second exit sleeve housing. 12. The apparatus of claim 11 further comprising:the second EUV exit sleeve exit opening comprising a differential vacuum aperture. 13. The apparatus of claim 1 further comprising:the EUV producing plasma production chamber comprising a second EUV exit sleeve comprising an exit opening facing an inlet opening of the first exit sleeve;a second exit sleeve chamber housing the second exit sleeve and having an EUV light exit opening;a suction mechanism removing EUV production debris from the second exit sleeve housing. 14. The apparatus of claim 13 further comprising:the second EUV exit sleeve exit opening comprising a differential vacuum aperture. 15. An EUV light source comprising:an EUV plasma production chamber;an EUV light collector within the chamber comprising a first focus and a second focus, plasma forming the EUV light being collected by the EUV light collector being formed in the vicinity of the first focus and as beam of exiting EUV light exiting the EUV light source chamber being focused to the second focus in the vicinity of an exit opening;a second focus alignment sensing mechanism comprising:an image detection mechanism imaging the second focus through the first focus and the collector;an alignment indicator indicating the position of the exiting beam in relation to the exit opening. 16. The apparatus of claim 15 further comprising:the image detection mechanism comprising a camera. 17. The apparatus of claim 16 further comprising:the exit opening comprising an exit aperture leading to an EUV light utilization apparatus and fixed in space in relation to the EUV utilization apparatus. 18. The apparatus of claim 17 further comprising:the alignment indicator comprising:a target positioned at the exit aperture. 19. The apparatus of claim 17 further comprising:the alignment indicator comprising:a contrast detector detecting contrast between the image of the primary focus and the image of the intermediate focus. 20. The apparatus of claim 16 further comprising:the alignment indicator comprising:a target positioned at the exit aperture. 21. The apparatus of claim 16 further comprising:the alignment indicator comprising:a contrast detector detecting contrast between the image of the primary focus and the image of the intermediate focus. 22. The apparatus of claim 15 further comprising:the exit opening comprising an exit aperture leading to an EUV light utilization apparatus and fixed in space in relation to the EUV utilization apparatus. 23. The apparatus of claim 22 further comprising:the alignment indicator comprising:a target positioned at the exit aperture. 24. The apparatus of claim 22 further comprising:the alignment indicator comprising:a contrast detector detecting contrast between the image of the primary focus and the image of the intermediate focus. 25. The apparatus of claim 15 further comprising:the alignment indicator comprising:a target positioned at the exit aperture. 26. The apparatus of claim 15 further comprising:the alignment indicator comprising:a contrast detector detecting contrast between the image of the primary focus and the image of the intermediate focus. |
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