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048067679 | summary | BACKGROUND OF THE INVENTION The present invention relates to an electron lens assembly employed in electron microscopes and others. More particularly, the invention is concerned with an electron lens assembly of an ultra-high vacuum structure. In general, in order that a specimen surface is to be observed in a clean state or environment within the electron microscope, it is necessary to sustain a vacuum on the order of 10.sup.-10 Torr within a space in which a specimen is placed. To this end, a so-called dry vacuum pump such as ion pump, turbo molecular pump or the like must naturally be used as the pump for generating vacuum. Further, such a column structure is required in which vacuum is generated only in the region constituting the passage for an electron beam. More specifically, the column has to be realized in such a structure in which outgassing sources such as electron lenses, deflecting coils and others are installed outside of the vacuum space by using a lining tube. Besides, in precedence to the use of the electron microscope, it is indispensable to heat the evacuated portions for the purpose of de-gassing H.sub.2 O or other molecules therefrom. Except for the objective lens, all structural components of other electron lenses inclusive of magnetic pole pieces can be installed outside of the vacuum space in a relatively simple arrangement since there is no necessity to insert any objects in these other electron lenses externally of the microscope. In contrast, in the case of the electron lens to serve as the objective lens, a specimen holder inclusive of a specimen, an objective aperture, cold fingers and others must be inserted between the magnetic pole pieces constituting parts of the objective lens. Thus, the objective lens is necessarily of a much complicated structure and presents many difficulties in creating the vacuum environment when compared with the other electron lenses. FIG. 1 of the attached drawings is a cross-sectional view showing a hitherto known structure of the objective lens assembly, wherein reference numeral 1 denotes an upper yoke member, 2 denotes a lower yoke member, 3 denotes an exciting coil, 4 denotes an upper magnetic pole piece, 5 denotes a lower magnetic pole piece, 6 denotes a coupling member of a non-magnetic material for combining together the magnetic pole pieces 4 and 5 in an integral structure, and 7 denotes a lens hold-down member. The elements 1, 2, 4, 5 and 7 cooperate to constitute a magnetic circuit, wherein a magnetic field is generated between the magnetic pole pieces 4 and 5, which serves as an electron lens. A specimen 8 is disposed between the magnetic pole pieces 4 and 5. The lens hold-down member 7 and the magnetic pole pieces 4 and 5 have respective bores formed therein to allow an electron beam to pass therethrough. The lower yoke member 7 is of a cylindrical structure having a hollow interior or through-hole for allowing the electron beam having passed through the electron lens constituted by the magnetic pole pieces 4 and 5 to pass through the yoke member 7. In operation, the electron beam enters the objective lens structure from above the lens hold-down member 7 and passes through an electron beam passage pipe 9 disposed within the hollow space defined by the through-hole to run to the succeeding stage of electron lens. Reference numeral 10 denotes a spacer formed of a non-magnetic material and provided with transverse bores 11 and 11' through which a specimen holder, objective aperture and others can be inserted. Reference numeral 12 denotes an O-ring for coupling the upper yoke member 1 to a portion of the column (not shown) to be disposed on the yoke member 1 in a vacuum-tight manner, 13 denotes an O-ring for joining vacuum-tightly the lower yoke member 2 and the spacer 10, and numerals 14 and 15 denote vacuum-tightly sealing O-rings for allowing an astigmatism correction element 16 to be disposed at a location close to the lower magnetic pole piece 5. Reference numeral 17 denotes a weld for joining vacuum-tightly the upper yoke member 1 and the spacer 10 by Heliarc welding. Accordingly, the upper yoke member 1 and the spacer 10 are realized in an integral structure such that they cannot be mechanically separated from each other. In contrast, the vacuum-tight connection between the lower yoke member 2 and the spacer 10 is assured by an O-ring seal 13, because it is necessary that the upper yoke member 1 and the lower yoke member 2 can be separated for accommodating the exciting coil 3. As will be seen from the above description, the vacuum tightness of the prior known electron lens assembly at the locations in the vicinity of the specimen is supposed to be assured by using the O-ring seals 13 to 15 which are each formed of a high molecular material having a melting point of about 150.degree. C. such as fluorine rubber commercially available under the designation "Byton" or the like. Accordingly, these O-ring seals are incapable of withstanding the heating at a temperature of about 200.degree. C. which is required for realizing an ultra-high vacuum on the order of 10.sup.-10 Torr. Further, the air may enter the electron lens assembly through these O-ring seals of the rubber material. Thus, the electron lens of the structure known heretofore suffers a problem that the ultra-high vacuum can not be attained. The inventors of the present invention have precedently proposed in JP-A-No. 60-158539 an objective lens structure in which these O-ring seals are eliminated. The objective lens structure according to this precedent proposal is shown in FIG. 2 of the accompanying drawings. Referring to FIG. 2, a gap is formed between a lower magnetic pole piece 5 and a lower yoke member 2, wherein a spacer 10 is so disposed as to extend into a space within the lower yoke member 2 by taking advantage of the gap so that the spacer can be connected to an electron beam path defining pipe 9 by welding. This structure is based on the results of experiments conducted by the inventors which showed that when the gap is at most about a tenth part of the inter-pole distance between the upper and lower magnetic pole pieces, no significant adverse influence is exerted to performance of the electron beam by the gap defined between the lower magnetic pole piece 5 and the lower yoke member 2. More specifically, since the inter-pole distance is about 10 mm, the distance between the lower magnetic pole piece 5 and the lower yoke member 2 can be held less than 1/10 of the inter-pole distance, provided that the extension of the spacer 10 has a thickness not greater than 0.5 mm. However, inspection conducted later on has proven that the thickness of the extension of the spacer on the order of 0.5 mm is inadequate for attaining the vacuum of 10.sup.-10 Torr because of penetration of the air or other gases. Further, it is a matter of cause that it is most preferable that there is provided no such gap. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electron lens assembly which can well withstand the heating at a temperature of about 200.degree. C. and thus allows an ultra-high vacuum to be realized. Another object of the present invention is to provide an electron lens assembly of a structure capable of withstanding an ultra-high vacuum. In view of the above objects, there is provided according to an aspect of the present invention an electron lens assembly which comprises at least a pair of magnetic pole pieces disposed in opposition to each other and each having a bore allowing an electron beam to pass therethrough, an exciting coil for producing a magnetic field between the magnetic pole pieces, a yoke coupled to the magnetic pole pieces and constituted by two divided parts or yoke members so that the exciting coil can be accommodated, at least one of the two yoke members being detachably coupled to one of the magnetic pole pieces, and a pipe disposed along the electron beam path for defining a passage for the electron beam except for a space defined between the magnetic pole pieces, wherein a metal O-ring is disposed on a surface of the detachable yoke member so as to prevent the air from entering the space defined by the opposite magnetic pole pieces along the surface of the detachable yoke member from a space accommodating the exciting coil, and the electron beam passage defining pipe is coupled integrally to the detachable yoke member. With the structure of the electron lens assembly mentioned above in which the electron beam passage defining pipe is integrally coupled to the yoke by welding, provision of an O-ring at this portion is rendered unnecessary, as in the case of the preceding proposal shown in FIG. 2. Thus, the electron lens assembly is imparted with the capability of fully withstanding the heating at a temperature of about 200.degree. C. Further, because the extension of the spacer required in the structure shown in FIG. 2 is rendered unnecessary, there arises no problem of penetration of the air through the extension of the spacer. Besides, since the yoke accommodating the exciting coil is realized by the separable yoke members combined through interposition of a metal O-ring which is excellent in the heat withstanding capability and the vacuum tight property, the electron lens assembly can sustain an ultra-high vacuum in addition to the capability of withstanding the heating at a temperature on the order of 200.degree. C. |
description | The present invention relates to Multi-leaf Collimators. A Multi-Leaf Collimator (MLC) is used in external beam radiation therapy in order to collimate the radiation beam to a chosen cross-sectional shape. The aim is to allow accurate delivery of the radiation to the tumour volume, and this is achieved by collimating the beam with an array of narrow elongate tungsten leaves, arranged side-by side and individually motorised in order to allow them to be moved longitudinally. This allows the collimator to define a desired shape. There are limitations on the longitudinal length of the leaves, dependent on their thickness. Generally, for a given leaf thickness (which does of course define the collimator resolution), there is a maximum feasible length of leaf. Beyond this length, difficulties arise in driving the leaf reliably. This therefore limits the maximum possible collimator aperture, and hence the size of the volume that can be treated. A compromise must therefore be reached between resolution and aperture. To allow for a greater aperture without compromising resolution, some MLCs mount the leaves on a secondary motion axis, usually referred to as a “carriage”. Thus, the leaves are supported on and movable relative to the carriage, and the carriage is mounted on and moveable longitudinally relative to a substrate. This allows collimated shapes to be made in a larger field size than that of a leaf alone. The movements are operated as two distinct axes, operating either on their own or sequentially. The present invention therefore provides a multi-leaf collimator for a radiotherapy apparatus, comprising a plurality of elongate leaves mounted in a carriage, the carriage being mounted on a substrate, wherein the leaves are independently moveable relative to the carriage in a longitudinal direction, and the carriage is moveable in that direction relative to the substrate, and a control apparatus arranged to receive a signal representing leaf positions relative to the substrate and being arranged to simultaneously control both the leaf positions relative to the carriage and the carriage positions relative to the substrate, in combination, so as to achieve the signalled leaf positions relative to the substrate. By allowing the carriage to be driven concurrently with the leaves, the speed of movement of the carriage can be added to that of the leaves. In this way, where leaves are required to make a long traverse they can do so more quickly. In a carriage-less MLC design, the leaf speeds are limited to that of the single leaf drive provided for each leaf. In a carriage MLC design according to the present invention, the complete leaf motion can be provided by the motion of the individual leaf together with the motion of the carriage that carries the leaves in that bank. In an conventional MLC incorporating a carriage, the usable leaf speed is still only provided by the individual leaf drives. The carriage position is set independently of the leaf positions and provides a “base point” from which the individual leaves then move. As a result, discontinuities arise during dynamic radiation delivery if the carriage has to be repositioned to allow the leaves to move to new positions not supported by the initial carriage positioning. Leaf travel and leaf speed are critical parameters in planning and delivering dynamic MLC treatments. Originally, when utilising static treatment shapes, the leaf speed was not critical as it did not alter the machine's ability to deliver the accurate treatment or significantly alter the overall delivery time. With the advent of tumour volume tracking, Volumetric Modulated Arc Therapy (VMAT) and/or Step and Shoot dynamic delivery, the leaves are required to move during delivery of the dose and the maximum usable leaf speed therefore becomes a much more important parameter. When tracking a tumour volume, the tracking error (i.e. the difference between target shape and the actual delivery shape) is directly related to the difference between required tracking speed and actual available speed. By definition, increasing the available tracking speed or leaf speed will reduce tracking error within faster tracking applications. When delivering a step and shoot dynamic delivery treatment, the treatment time is directly related to the speed at which the discrete collimating shapes are made because radiation is only delivered when all the leaves are in place. When delivering a true dynamic or VMAT delivery treatment, the treatment time is directly related to the speed at which the continuous (linearly interpolated) collimating shapes are made. The available speed of all axes (including the leaves) are used to calculate the actual dose rate used within the treatment to ensure a continuous and smooth treatment delivery. Increasing the available leaf speed allows potential selection of a faster dose rate in those instances where leaf motion is the limiting factor. Previous efforts have therefore been directed to increasing the maximum speed of travel of the leaves, and to extending the maximum length of leaves so that carriage movement during delivery is less likely to be required. Most MLCs have a means for sensing the current positions of the leaves relative to the substrate, such as an optical or mechanical positional feedback system. The control apparatus can therefore compare the current leaf positions to the signalled leaf positions, and move the leaves and the carriage accordingly. Each leaf can be moved according to a difference between the current leaf position and the signalled leaf position, and the carriage can be moved according to an average difference between the current leaf positions and the signalled leaf positions. The “average” can be a simple calculation such as the arithmetic mean of the respective set of leaf positions, or other arithmetic averages such as the median (or possibly the mode), or it can be a more complex function based on a suitable metric e.g. to maximise delivery speed or minimise tracking error while being bounded by parameters such as maximum speeds, physical limits, design rules etc. The invention also provides a corresponding method of operating a multi-leaf collimator. FIG. 1 shows an MLC 10 of the type to which the present application can be applied. A first bank 12 of elongate leaves 10 are arranged in a side-by-side array with their longitudinal edge arranged transverse to the beam, their depth arranged parallel to the beam, and their thicknesses transverse to the beam. Each leaf is mounted in a suitable guide (not shown) supported on a carriage 16. The guide is usually machined so as to support the upper and lower longitudinal edges of the leaves 14 and allow them to slide backwards and forwards in the longitudinal direction. A bank of motors 18, one for each leaf, each drive a leadscrew 20. Each leadscrew 20 engages with a captive nut or other threaded section within a leaf 14; thus as the motor 18 drives the leadscrew 20, this forces the captive nut along the leadscrew 20 and draws the relevant leaf 14 longitudinally backwards or forwards, depending on the direction of rotation of the motor. In this way, the leaves 14 can be driven so as to define a desired front profile 22 to the collimator. The carriage itself is mounted on a substrate 24 and is moveable in the same longitudinal direction. It is driven in a similar manner; a carriage screw 26 is driven by a motor 28 on the substrate 24 and engages with a captive threaded portion 30 on one side of the carriage 16. In this example, a duplicate carriage screw 32 is driven by a similar motor 34 and engages with a corresponding captive threaded portion 36 on the opposite side of the carriage 16, to provide a balanced drive. The entire arrangement is duplicated to form a second leaf bank 38 which is arranged on a diametrically opposite side of the beam. This defines a second collimator front 40. Between the two leaf banks 12, 38, a pair of variable collimator fronts 22, 40 are therefore defined and the beam can be shaped as desired. To move the leaves of an array to a new position, the motors 18 have hitherto been employed in order to adjust the positions of the leaves 14. However, we have observed that it is often necessary to move all the leaves by a similar amount and/or in the same direction. In this case, the motors 28, 34 can be employed in order to move the carriage 16 (and hence all the leaves 14) in the required direction. This means that if both the leaf motors 18 and the carriage motors 28, 34 are used together, the speed of movement of the leaves can be increased beyond that which the leaf motors 18 are capable of when operating alone. This invention therefore proposes that the leaf motion be defined as an integrated (single) axis, i.e. that the leaf axis is a composite of both the carriage position and the leaf position rather than being treated as a separate pair of axes. In addition, the leaf position servos are a composite of a leaf position servo and a carriage position servo. This can be referred to as a “dynamic integrated carriage system”. It is proposed the carriages are used to dynamically accommodate the “mean” leaf travel within a leaf bank by using the combined motion and speeds of the carriage and individual leaf drives. Dynamic Case In the case of a dynamic or step and shoot treatment, this implies that (according to a defined algorithm) the carriage position is pre-planned so as to minimise treatment time by moving into an optimal position, while (in addition) the individual leaf drives are moving to define the individual positions. This creates the possibility of cumulative leaf speeds greater than that of the individual carriage or leaf drives. This allows for reduction of treatment time, particularly for sequences of shapes where there is a significant common motion of individual leaves in a leafbank. Such common motion can be assisted by the carriage, through the leaves moving towards their position whilst the carriage is also moving, thus saving time. A further product of pre-planning the motion of the carriage is that motion discontinuities can be avoided during treatment, because the carriage is actively progressing to the optimal position for the next steps. In effect, the movement of the carriage that would be effected during a discontinuity is commenced in advance so that the carriage is already in position, in time. A variety of other metrics can be applied to achieving a treatment with the composite leaf and carriage motion described. Examples include leaf travel minimisation, leaf carriage minimisation, delivery time minimisation at the like. Tracking Case In the case of a tracking treatment, the treatment is necessarily reactive, so the motion of the carriage or leaves cannot be preplanned. In this case, the composite leaf and carriage servo is used to best track the tumour. The extra available speed is therefore utilised to minimise the tracking error. The reduction of tracking error is a design aim that is assumed will in turn improve the clinical effectiveness of the treatment. It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention. |
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041586026 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates the arrangement of components in a conventional liquid metal fast breeder reactor. The reactor includes a vessel 4 that contains a thermal shield 6, a plurality of fuel carrying subassemblies 10 and the primary coolant flowing through the reactor. The reactor uses partially enriched uranium (U-235) or plutonium (Pu-239) for fuel and the primary coolant is typically sodium at atmospheric pressure. The fuel is located in the core indicated by reference numeral 8 and is carried by those subassemblies 10 that pass through that area. Surrounding the core is a blanket of depleted uranium. The liquid sodium is pumped into the reactor 4, FIG. 1, through the inlet nozzles 12, 12'. The sodium entering through the inlet nozzle 12 passes into a lower plenum 13 and flows through the subassemblies 10 that penetrate the core area 8. The sodium entering through inlet nozzle 12' passes through the radial blanket subassemblies 10'. All of the subassemblies 10, 10' discharge the sodium into an upper plenum 14 where it thereafter flows out of the reactor through an outlet nozzle 15. The liquid sodium is maintained at essentially atmospheric pressure in the reactor by a blanket of inert gas 16 located in the upper portion of the reactor vessel. Typically, ten percent of the subassemblies in a liquid metal fast breeder reactor contain control rods and the other subassemblies contain either fuel or radial blanket elements. FIG. 2 illustrates one of the subassemblies that contains a control rod 22. This subassembly also includes a can 20 of hexagonal shape and a control rod drive shaft 24 that raises and lowers the control rod 22 with respect to the core 8. The rod drive shaft is connected to a rod drive mechanism (not shown) of conventional construction. The can is typically fabricated from stainless steel sheet stock and forms a conduit through which the sodium flows. The subassembly is terminated by an alignment stud 26 that maintains the lateral relationship of the subassembly with respect to a horizontal support plate (not shown). Referring to FIGS. 2-4, the control rod 22 is generally hexagonal in cross section and is freely movable within the can 20. The control rod consists of a plurality of elongate circular poison containing rods 28. Each rod is fabricated from boron carbide (B.sub.4 C) and is rigidly mounted by pins 29 between an upper and a lower support member 30, 32. The support members are rigidly mounted with respect to each other by a vertical support tube 34 that is surrounded by the poison rods 29. The upper support member 30, FIG. 4, has an upwardly projecting ring that forms a sealing surface 48 for the control rod as described in detail below. Referring to FIG. 4, the subassembly can 20 includes a separator plate 40 that forms the top of the subassembly. The separator plate contains an orifice 41 through which the control rod drive shaft 24 penetrates. To maintain alignment between the control rod 22 and the inside of the can 20, the drive shaft 24 has a plurality of centering vanes 42 that aid in seating the control rod 22 against the separator plate 40. The separator plate 40 further includes a downwardly projecting ring that forms a sealing surface 46. This sealing surface is engaged by a complementary sealing surface 48 located on the upper support member 30. When the two sealing surfaces 46, 48 are brought into contact as illustrated in FIG. 4, a fluid-tight seal is made. The complementary sealing surfaces are slightly rounded in order to prevent lateral displacement of the control rod with respect to the separator plate due to ordinary vibration. Such lateral displacement could break the seal and cause the control rod to drop as described below. The control rod 22, FIG. 4, is raised and lowered within the can 20 by a plurality of laterally disposed lifting bosses 38. The bosses are circular in cross section and engage a cam located on the inner surface of the side wall of the vertical support tube 34. FIG. 5 is an illustration of this cam and is a projection of the inner cylindrical surface of the support tube. The motion of the lifting bosses along the cam is described in detail below. OPERATION When sodium is being pumped through the reactor of FIG. 1, it enters the vessel 4 through one of the inlet nozzles 12, 12'. The sodium entering through nozzle 12 passes into a lower plenum 13 and flows through the subassemblies 10 containing fuel. The sodium entering through nozzle 12' flows through the subassemblies 10' containing radial blanket material. All of the subassemblies 10, 10' discharge into the upper plenum 14 and from there the sodium flows out of the reactor through the exit nozzle 15. The flow of sodium through the subassemblies causes a drop in pressure and in FIG. 1 the pressure P1 in the lower plenum 13 is substantially larger than the pressure P2 in the upper plenum 14. In a conventional liquid metal fast breeder reactor the differential pressure P1/P2 is typically about 100 PSI. The sodium that flows through the subassembly 10 containing the control rod 22, FIG. 2, enters the can 20 around the alignment stud 26. The flow of directed by the can, around the control rod and out through the orifice 41, FIG. 4. Orifice 41 leads directly to the upper plenum 14. If the control rod is positioned against the separator plate 40, a fluid-tight seal is made between the sealing surfaces 46, 48 and the differential pressure P1/P2 across the subassemblies is sufficient to retain the control rod in place. FIGS. 6-12 are schematic diagrams illustrating the operation of the preferred embodiment. Each figure depicts three adjacent subassemblies that pass through the core area 8, FIG. 1. The two outer subassemblies contain the fuel elements 8 and the inner subassembly houses the control rod 22. In each of the outer subassemblies the blanket areas are those areas that are located above and below the core 8 in FIG. 1. In all three subassemblies the primary coolant passes from the lower plenum 13, FIG. 1, into the bottom of the respective subassembly and flows out its top into the upper plenum 14. The presence of this flow is indicated by the arrows in the figures. In particular, FIG. 6 illustrates the reactor in a shut-down condition. The control rod 22 is positioned opposite the fuel and in a position to absorb the maximum number of neutrons. The control rod is supported by the control rod drive shaft 24 and the lifting bosses 38. There is a flow of primary coolant through the control rod subassembly that enters at the bottom and exits through the orifice 41. The control rod is maintained in position by a rod drive mechanism (not shown) that stops any further downward motion of the rod drive shaft 24. FIG. 7 diagrams the operation of the control rod 22 in regulating the power and the neutron flux in the reactor. The control rod 22 can be moved with respect to the fuel by raising and lowering the rod drive shaft 24. The position of the control rod with respect to the fuel controls the neutron flux and hence the power level. The control rod is supported in the same manner as FIG. 6 and coolant flows through the subassembly 10 and out the orifice 41. In FIG. 8 the procedure for locking the control rod 22 against the separator plate 40 is shown. The control rod drive shaft 24 and the lifting bosses 38 raise the control rod until the sealing surfaces 46, 48 come into contract. These sealing surfaces form a fluid-tight boundry and there is no flow of coolant out of the orifice 41. The differential pressure P1/P2 across the separator plate caused by the flow of primary coolant through the reactor locks the control rod in the position shown in FIG. 8. After the control rod 22 is locked against the separator plate 40, the control rod drive shaft 24 can be lowered to the position shown in FIG. 9. FIG. 9 illustrates the normal mode of operation of the preferred embodiment. The control rod subassembly can 20 is sealed and the flow of primary coolant through the orifice 41 is blocked. The differential pressure P1/P2 across the reactor maintains the sealing surfaces 46, 48 together. The control rod 22 thus remains up and out of the core. FIGS. 10-12 depict three of the ways a scram can be initiated by the preferred embodiment. In FIG. 10 a loss of primary coolant flow through the reactor initiates the scram. Prior to the loss of flow the control rod 22 and the control rod drive shaft 24 were positioned as shown in FIG. 9. That is to say, the lifting bosses 38 were positioned so as not to restrict the downward motion of the control rod. When a loss of flow occurs, the differential pressure P1/P2 across the reactor automatically decreases. Since it is merely the pressure drop across the separator plate that is holding the control up, the control rod 22 falls by gravity as indicated in FIG. 10. Motion of the rod drive shaft is not required. The control rod falls until the lifting bosses 38 engage the upper support member 30, FIG. 4, of the control rod or until the control rod comes to rest on a conventional support. The lifting bosses are positioned and the control rod is dimensioned so that the control rod 22 comes to rest opposite the fuel as illustrated in FIG. 6. This self-actuated motion shuts down the reactor. In FIG. 11 the scram is initiated when one of the reactor safety circuits or the reactor operator commands the rod drive mechanism (not shown) to scram the reactor. Upon receiving this command the rod drive mechanism releases the rod drive shaft 24 to drop by gravity or to descend under the force of a spring. This is the conventional mode of initiating a scram. When the control rod drive shaft 24 is either dropped or driven downward, the lifting bosses 38 engage the lower support member 32 of the control rod and the sealing surfaces 46, 48 are separated. This situation is illustrated in FIG. 11. When the sealing surfaces are separated, the differential pressure across the separator plate 40 is removed and the flow of coolant through the subassembly is restored. The control rod 22 then falls by gravity and comes to rest opposite the fuel as illustrated in FIG. 6. This type of scram can also be initiated by having the rod drive mechanism drive the rod drive shaft downward and thereby separate the sealing surfaces. FIG. 12 illustrates how the reactor can be scrammed when subjected to a severe lateral acceleration or impulse such as experienced during an earthquake. Typically, a severe lateral acceleration will cause the control rod to rock over or move laterally and force the sealing surfaces 46, 48 to separate slightly. The flow of primary coolant out of the orifice 41 is then reestablished and the differential pressure removed. The inside diameter of the vertical support tube 34 and the rod drive shaft are dimensioned to permit this type of movement. It should be noted that the preferred embodiment overcomes the problem of scramming the reactor during a severe earthquake when the upper reactor structure is displaced relative to the core. Such a displacement could prevent the control rod drive shaft from dropping and/or the rod drive mechanism from unlatching a conventional control rod and allowing it to drop. The preferred embodiment overcomes this problem because movement of the control rod drive shaft 24 is not required to initiate a scram. The scram is directly and inherently initiated by the action of the earthquake itself. Thus, the response of the control rod is an inherent reaction to the accident itself. Referring to FIG. 5, a cam 50 may be employed in order to enhance flexibility of operation by providing a means of breaking the seal without reducing the flow of sodium. FIG. 5 is a projection of the inner surface of the vertical support tube 34 and illustrates the raised surface of the cam as one of the lifting bosses 38 is sequenced by the various surfaces of the cam. In particular, when the control rod drive shaft 34 supports the control rod 22 as shown in FIG. 6 or raises the control rod as illustrated in FIG. 7, the lifting boss 38 engages the cam at point 52. If the control rod is sealed against the separator plate and the drive shaft 24 is lowered to the position illustrated in FIG. 9, the lifting boss moves from point 52 to point 54. When the lifting boss is located at point 54, it is out of vertical engagement with the control rod. The differential pressure P1/P2 across the separator plate 40 is pushing the control rod against the separator plate 40 and maintaining the two sealing surfaces 46, 48, FIG. 4, together. When a loss of flow accident occurs, the differential pressure P1/P2 decreases to effectively zero and the control rod drops by gravity, FIG. 10. The lifting boss in FIG. 5 remains at one elevation and the cam moves downward until the boss engages the cam at point 56. The vertical distance between points 54 and 56 is such that the control rod will come to rest opposite the fuel as shown in FIG. 6. If a scram is commanded by the reactor or by one of the reactor safety systems, FIG. 4, the seal between the separator plate 40 and the control rod 22 is broken by the downward motion of the rod drive shaft 24. In FIG. 5 the lifting boss moves downward from position 54 to position 58 where it engages the cam. The seal between the separator plate 40 and the control rod 22 can also be broken without flow interruptions and without having the control rod drop. That is to say, the mode of reactor control depicted in FIG. 9 can be shifted to that shown in FIG. 7. To effect this change, control rod drive shaft 24 can be lifted from point 54 to point 56 and then lowered to point 60. The motion of the boss is indicated by arrows in FIG. 5. When the lifting boss engages the cam surface at point 60, the seal can be broken by further downward motion of the control rod drive shaft. The control rod then drops and engages the boss at point 62 where it remains suspended by the rod drive shaft. The horizontal distance between points 60 and 62 is small and the motion of the control rod does not substantially affect the power level. Besides the slightly rounded sealing surfaces 46, 48, FIG. 4 used in the preferred embodiment, the present invention also contemplates varying the contour of the sealing surfaces to satisfy other design criteria. Contours having both concave and convex cross sections, triangular cross sections and knife edges can be used. In addition, the contour can be excluded and a flat surface used for sealing. It should also be noted that although the sealing surfaces 46, 48 in the preferred embodiment form a tight seal, the present invention does not required that the seal be fluid-tight. For example, the poison rods 28, FIG. 2, may require some flow of coolant in order to remove self-generated heat. Thus, a small aperture may be necessary in the control rod assembly 22 in order to allow coolant to reach the poison rods when the control rod is sealed against the separator plate, FIG. 9. Although this small aperture permits a flow of coolant to effectively flow across the separator plate, the aperture is dimensioned small enough that the differential pressure P1/P2 is not substantially reduced. The present invention also contemplates providing a follower attached below the control rod 22, FIG. 2, to fill the void in the reactor caused by the withdrawal of the control rod. The follower has the same shape as the control rod and is raised into the core area 8, FIG. 1, as the control rod is pulled out of the core. The follower is contructed of the same material as the blanket, thereby increasing breeding game and the "worth" or effectiveness of the control rod. The addition of the follower does not affect the sealing between the surfaces 46, 48 because the differential pressure P1/P2 across the separator plate is sufficiently large to retain both the follower and the control rod against the separator plate. Although the preferred embodiment is described in connection with a liquid metal fast breeder reactor, it is contemplated that this invention can be used on any comparable nuclear reactor. Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention. |
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abstract | The present invention provides an oxide-base scintillator single crystal having an extremely large energy of light emission, adoptable to X-ray CT and radioactive ray transmission inspection apparatus, and more specifically to provide a Pr-containing, garnet-type oxide single crystal, a Pr-containing perovskite-type oxide single crystal, and a Pr-containing silicate oxide single crystal allowing detection therefrom light emission supposedly ascribable to 5d-4f transition of Pr. |
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047626623 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the sole FIGURE of the drawing, there is shown a trigger device 10 comprising a closed vessel 11 containing a piston 12 slideably mounted in the vessel to divide it into two compartments 14 and 16. A pressurized fluid, preferably an inert gas, is contained within each of the compartments at substantially the same pressure. A connecting rod 18 is operatively connected to the piston 12, its other end being connected to an actuator means 28 so that movement of the piston 12 will activate the actuating means. A piston seal 20 acts to minimize fluid leakage between compartments 14 and 16 during activation of piston 12. A bellows arrangement 22 prevents leakage of the fluid from the system while allowing movement of the rod 18. A pipe 24 serves as vent means communicating with compartment 14. The pipe is normally closed by having a sealed tip 26 at its outward end. EXAMPLE The following example is set forth to more fully illustrate the preferred embodiment of the invention, but it is not intended as a limitation thereof. The cylinder 11 may vary in size, a large cylinder being pressurized at a lower pressure than a small cylinder. The pressure inside this cylinder conveniently varies from 100 to 1000 psi. Typically for use in a nuclear space reactor 30 the cylinder 11 will be from 6 to 12 inches in length and have a diameter of about 2 to 4 inches. The connecting rod 18 will typically be about 3 ft in length. Helium or argon is particularly preferred for use as the pressurizing gas. The reactor is equipped with beryllium or beryllium oxide reflectors about 10 inches on its inside, 18 inches on its outside and 14 inches high. About five pipes 24 are distributed throughout various parts of the spacecraft. These pipes are all connected to compartment 14 and each has a rupturable tip 26 at the end thereof. Upon reentry into the earth's atmosphere, a temperature of about 1650.degree.-2200.degree. C. (3000.degree.-4000.degree. F.) is encountered. The stainless steel tips at the end of tube 24, which are located for reentry burnoff, melt and rupture at temperatures above about 1400.degree. C. (2600.degree. F). Thereby compartment 14 is opened to vacuum, and piston 16 and rod 18 move in the direction of the arrow because of the difference in pressure created between compartments 14 and 16. Conveniently the motion of the connecting rods either introduces a beryllium carbide poison into the reactor or moves the reflectors away from the nuclear core. Either of these events will render the reactor subcritical. Although the invention has been described in terms of a preferred embodiment and a specific illustration, it will be obvious to those of ordinary skill in the art that various modifications and adaptations of the invention are possible without departing from the spirit and scope of the invention as claimed hereinbelow. For example, the thermally activated trigger device is not limited for use with any particular nuclear space reactor, but it is clear that the invention has applications in a wide variety of nuclear space reactors such as those useful for weather observation, communications, and surveillance, as well as for other apparatus and process applications. |
abstract | The present invention generally provides semiconductor substrates having submicron-sized surface features generated by irradiating the surface with ultra short laser pulses. In one aspect, a method of processing a semiconductor substrate is disclosed that includes placing at least a portion of a surface of the substrate in contact with a fluid, and exposing that surface portion to one or more femtosecond pulses so as to modify the topography of that portion. The modification can include, e.g., generating a plurality of submicron-sized spikes in an upper layer of the surface. |
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description | The present application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2010-0066762, filed on Jul. 12, 2010, the disclosure of which is expressly incorporated by reference herein in its entirety. 1. Field of the Invention The present invention relates, in general, to a shipping container for safely transporting a nuclear fuel assembly to a nuclear power plant, etc. after the nuclear fuel assembly has been produced and, more particularly, to a lid frame for a nuclear fuel assembly shipping container, which is equipped with gap compensators adapted to minimize a gap between a nuclear fuel assembly and a lid frame for clamping the nuclear fuel assembly in a shipping container, and a shipping container for nuclear fuel assemblies. 2. Description of the Related Art In general, nuclear fuels such as enriched uranium or mixed oxide need to be transported between various places, for instance a place where they are concentrated, a fuel rod producing place, and so on. For this transporting stage, the fuels are typically shaped like a small pellet. These fuels require a constant level of thermal insulation and structural strength to comply with international standards, and the control of their criticality is a main concern, and a mass of enriched fuel in a shipping container should be strictly restricted such that no dangerous situations occur. Due to this requirement, the volume of fuel that can be transported in a shipping container of a certain volume is strictly restricted. As a result, numerous shipping containers for transporting the nuclear fuel assembly have been disclosed. These shipping containers are generally designed so that a pair of lid frames are coupled to opposite long sides of the shipping container with the nuclear fuel assembly disposed therebetween so that the nuclear fuel assembly is clamped. The strength of the shipping container itself including the lid frames must be reliable, and thus the containers are typically formed of a metal material. Meanwhile, the nuclear fuel assemblies produced at present are not limited to one type but are classified into a variety of types. As such, they are different in size from each other. In contrast, the lid frames applied to the shipping container are designed to clamp one specific type of nuclear fuel assembly. Thus, to transport all types of nuclear fuel assemblies, the lid frames should be provided so as to correspond to these types. For this reason, the manufactured lid frames are not cost-effective, and it takes much manpower and time to replace the lid frames so that they are suited to the nuclear fuel assemblies. Furthermore, a storage space for storing the manufactured lid frames is needed. In addition, in the case of conventional nuclear fuel assembly shipping containers with clamps having the same size, since positions of spacer grids are different depending on the type of nuclear fuel assembly, the lid frames on which the clamps are disposed so as to correspond to the positions of the spacer grids should be used to transport different types of nuclear fuel assemblies. Accordingly, the lid frames should be provided depending on the type of nuclear fuel assembly. Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and embodiments of the present invention provide a lid frame for a nuclear fuel assembly shipping container which is equipped with gap compensators, and a shipping container for nuclear fuel assemblies, which allow various types of nuclear fuel assemblies to be clamped with one type of lid frame, and which allows various types of nuclear fuel assemblies to be transported by one type of shipping container. Embodiments of the present invention also provide a lid frame for a nuclear fuel assembly shipping container which is equipped with gap compensators, and a shipping container for nuclear fuel assemblies, which allow various types of nuclear fuel assemblies whose spacer grids are located at different positions to be transported using one type of lid frame. According to an aspect of the present invention, there is provided a lid frame for a nuclear fuel assembly shipping container, in which the shipping container includes a lower container in which a cradle is installed, an upper container detachably coupled to the lower container, and a base frame coupled to the cradle with at least one nuclear fuel assembly placed thereon. The lid frame can include: a plurality of supports installed apart from each other so as to surround the nuclear fuel assembly placed on the base frame; a plurality of clamps separated from each other, coupled to the supports so as to be perpendicular to the supports, rotatably hinged to the base frame, and configured to clamp the nuclear fuel assembly; and a plurality of gap compensators coupled to inner surfaces of the supports in order to compensate for a gap between the inner surfaces of the supports and the nuclear fuel assembly. According to another aspect of the present invention, there is provided a shipping container for nuclear fuel assemblies. The shipping container can include: a lower container in which a cradle is installed; an upper container detachably coupled to the lower container; a base frame coupled to the cradle with at least one nuclear fuel assembly placed thereon; and a pair of lid frames installed on opposite long sides of the base frame in order to clamp the nuclear fuel assembly placed on the base frame. Further, each lid frame can include: a plurality of supports installed apart from each other so as to surround the nuclear fuel assembly placed on the base frame; a plurality of clamps separated from each other, coupled to the supports so as to be perpendicular to the supports, rotatably hinged to the base frame, and configured to clamp the nuclear fuel assembly; and a plurality of gap compensators coupled to inner surfaces of the supports in order to compensate for a gap between the inner surfaces of the supports and the nuclear fuel assembly. Here, each gap compensator can have an “L” shape formed by an upper plate and a lateral plate so as to correspond to a shape of the lid frame. Further, each support can include support holes formed in an upper and lateral surfaces thereof; each gap compensator can include screw holes formed in the upper and lateral plates thereof; and the support holes can be aligned with the screw holes. Also, each gap compensator can be installed between the clamps coupled to the lid frame. The lid frame can further include press members coupled to press plate holding recesses formed in inner surfaces of the plurality of clamps including narrow clamps and wide clamps in order to press spacer grids of the nuclear fuel assembly. In addition, each press member can include: a press plate that is interposed between each clamp and each spacer grid; and adjustment screws, each of which passes through each clamp to be coupled to the press plate. According to another aspect of the present invention, the lid frame is installed in the shipping container to stably clamp the nuclear fuel assembly, and forms a lattice shape, so that it is possible to safely protect the nuclear fuel assembly compared to an existing method of clamping the nuclear fuel assembly only with clamps. Further, the gap compensators are installed to compensate for a gap between the lid frame and the nuclear fuel assembly, so that it is possible to compensate for the gap between the lid frame and the nuclear fuel assembly having a small size, and thus it is possible to prevent expansion of the nuclear fuel assembly when an accident takes place when the nuclear fuel assembly is being transported. Further, it is possible to transport various types of nuclear fuel assemblies using one type of shipping container without replacing the lid frame. Reference will now be made in greater detail to exemplary embodiments of the invention with reference to the accompanying drawings. FIG. 1 shows an appearance of a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention. The shipping container of this embodiment is configured so that a cross section of a lower container 100 and an upper container 200 is semi-circular such that at least one nuclear fuel assembly 10 can be held, and the lower container 100 and the upper container 200 are coupled so as to be opposite to each other. Here, each of the lower and upper containers 100 and 200 can be formed of a metal material strong enough to safely transport the nuclear fuel assembly 10. In detail, the shipping container of this embodiment is configured so that the upper container 200 is detachably coupled to the lower container 100, the lower and upper containers 100 and 200 are provided with flanges 110 and 210 on outer circumferences thereof, the flange of the lower container 100 has a plurality of assembly protrusions 111 protruding therefrom at regular intervals, and the flange of the upper container 200 is provided with a plurality of assembly holes 211 (see FIG. 2) so as to correspond to and be engaged with the protrusions 111. Further, the lower container 100 has a plurality of support legs 120 installed on an outer surface thereof at predetermined intervals so as to support the shipping container. The upper container 200 is provided with loading parts 220 on opposite long sides thereof. Each load part 220 is provided with lift holes 221 such that the upper container 200 can be lifted by, for instance, a crane. FIGS. 2 and 3 are exploded perspective views showing a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention, wherein the lower and upper containers 100 and 200 are separated from each other. FIG. 4 is a cross-sectional view showing a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention, wherein gap compensators 500 are installed between a lid frame 400 or 400′ and a nuclear fuel assembly 10. The lower container 100 is provided therein with a base frame 300 and a pair of lid frames 400 and 400′ so as to be able to stably support the nuclear fuel assembly 10. A cradle 130 is installed in the lower container 100 such that the base frame 300 can be placed on the cradle 130. The base frame 300 is placed on the cradle 130 with the nuclear fuel assembly 10 supported on an upper surface thereof. The cradle 130 has a plurality of supports 131 installed in a lengthwise direction at predetermined intervals. The cradle 130 is fixed to the lower container 100 by fasteners 134 such as screws. Here, buffers 140 formed of a rubber material are interposed between the lower container 100 and the cradle 130 in order to relieve external shocks that can be applied to the nuclear fuel assembly 10. Each buffer 140 is provided with a fastener hole (not shown) in the center thereof in a lengthwise direction. The fasteners 134 are fastened into the fastener holes through the cradle 130. Thereby, the cradle 130 is fixedly coupled to the lower container 100 so as to be able to absorb shocks. The lid frame 400 or 410′ includes supports 410 or 410′ stably surrounding the nuclear fuel assembly 10, narrow clamps 420 or 420′ and wide clamps 420a or 420a′ disposed on the supports 410 or 410′ at predetermined intervals, and end support plates 444 supporting opposite ends of the nuclear fuel assembly 10. The supports 410 or 410′ are separated from each other, and are installed in a lengthwise direction of the nuclear fuel assembly 10. Here, the supports 410 or 410′ are each provided with support holes 411 in upper and lateral surfaces thereof so as to correspond to screw holes 512 of each gap compensator 500, which will be described below. Each of the narrow clamps 420 or 420′ and the wide clamps 420a or 420a′ is hinged to the base frame 300 at one end thereof; so as to open outwardly when rotated along with the supports. Here, the narrow clamps 420 or 420′ and the wide clamps 420a or 420a′ are welded to the supports 410 or 410′, which are separated from each other, so as to be perpendicular to the supports 410 or 410′, and thus are integrally formed with the supports 410 or 410′ so as to be able to be rotated about the nuclear fuel assembly 10. Meanwhile, in this embodiment, the shipping container for transporting two nuclear fuel assemblies 10 at the same time has been described by way of example. The lid frames 400 and 400′ are installed on the base frame 300 on opposite long sides of a width direction of the base frame 300 so as to be rotatably opposite to each other. Further, each pair of narrow clamps 420 and 420′ or each pair of wide clamps 420a and 420a′ is configured to be fastened to each other, and is provided with male and female fasteners 421 and 421′ on free ends thereof so as to be engaged with each other, respectively. Further, the male and female fasteners 421 and 421′ are provided with bolting holes 422 and 422′ respectively, so that they can be firmly fixed to each other by a fixing bolt (not shown). Here, the narrow clamps 420 or 420′ are arranged so as to correspond to the spacer grids of the nuclear fuel assembly 10, so that they can stably clamp the nuclear fuel assembly 10. In this manner, the lid frame 400 or 400′ of this embodiment is configured so that the supports 410 or 410′, which are separated from each other, and the narrow clamps 420 or 420′ and the wide clamps 420a or 420a′, which are coupled to the supports 410 or 410′ at predetermined intervals respectively, have a lattice shape. Thus, the lid frames 400 and 400′ can be remarkably reduced in weight compared to a conventional lid frame where a pair of clamping frames is formed in a completely closed shape, and thus making transportation easier. Furthermore, the lid frames 400 and 400′ can also reduce the cost of production, which is advantageous from the economical point of view. Here, in the lid frames 400 and 400′, the narrow clamps 420 and 420′ and the wide clamps 420a and 420a′ are rotatably coupled so as to be able to surround the nuclear fuel assemblies 10 placed on the base frame 300, are symmetrically disposed on the supports 410 and 410′, which are separated from each other, at predetermined intervals in a lengthwise direction so as to be perpendicular to the supports 410 and 410′, and to clamp the respective nuclear fuel assemblies 10. Meanwhile, since the nuclear fuel assemblies 10 produced at present are not limited to one type but are classified into a variety of types, they are different in size from each other. Thus, to clamp each type of nuclear fuel assemblies 10 in the shipping container, the lid frames 400 and 400′ manufactured so as to suit each type of nuclear fuel assembly 10 are required. In this case, the manufactured lid frames 400 and 400′ are not cost-effective, and it takes a lot of manpower and time to replace the lid frames 400 and 400′ so as to suit them to the type of nuclear fuel assembly. Furthermore, a storage space for storing the manufactured lid frames 400 and 400′ is needed according to the type. For this reason, in the present invention, the gap compensators 500 are interposed between the lid frame 400 or 400′ and the nuclear fuel assembly 10 so as to be able to clamp various types of nuclear fuel assemblies 10 using one type of lid frames 400 or 400′ regardless of the type of nuclear fuel assembly 10. Each gap compensator 500 is bent in an “L” shape to form an upper plate 510 and a lateral plate 520 so as to correspond to the shape of the lid frame 400 or 400′, and is formed of aluminum so as to be able to minimize its weight while ensuring sufficient stiffness in the event of the gap compensation. The upper plate 510 is provided with screw holes 512, and thus is fixed to the lid frame 400 or 400′ by fixing screws S. Additionally, to further reduce the weight of the shipping container, the upper plate 510 of the gap compensator 500 can be provided with guide slots 511 in a lengthwise direction so as to correspond to the spacing between the supports 410 or 410′. Each gap compensator 500 constructed as described above is fixed with the fixing screws S so as to align the support holes 411, which are formed in the upper and lateral surfaces of the supports 410 or 410′included in the lid frame 400 or 400′, with the screw holes 512, which are formed in an upper plate and a lateral plate 510 and 520 of each gap compensator 500. The gap compensators 500 are installed between the narrow clamps 420 or 420′ and the wide clamps 420a or 420a′, both of which are coupled to the lid frame 400 or 400′. The narrow clamps 420 or 420′ and the wide clamps 420a or 420a′ are provided with press plate holding recesses 630 or 630′ formed in inner surfaces thereof at a predetermined depth in order to receive a press plate 610 configured to press the spacer grids of the nuclear fuel assembly 10. Thus, the nuclear fuel assembly 10 can be more stably clamped by press members 600 installed in the press plate holding recesses 630 or 630′. Each press member 600 includes the press plate 610, which is interposed between each of the clamps 420, 420′, 420a and 420a′ and each spacer grid, and extends in a lengthwise direction of the clamp in an approximately flat plate shape, and adjustment screws 620, each of which passes through each of the clamps 420, 420′, 420a and 420a′ to be coupled to the press plate 610. Thus, the press plate 610 is pressed or unpressed using the adjustment screws 620, so that the nuclear fuel assembly 10 can be firmly clamped to the lid frame 400 or 400′. Meanwhile, the press plate holding recesses 630 or 630′, each of which holds the flat-plate-shaped press plate 610, are formed inside each of the narrow clamps 420 or 420′ and the wide clamps 420a or 420a′. Here, a plurality of press plate holding recesses 630 or 630′, each of which holds the flat-plate-shaped press plate 610, is formed inside each of the wide clamps 420a or 420a′, and the flat-plate-shaped press plates 610 have the same dimensions as the press plate holding recesses 630 or 630′ formed inside each of the wide clamps 420a or 420a′ so as to be compatible with dimensions (width and length) of each of the wide clamps 420a or 420a′. These wide clamps 420a or 420a′ are formed so as to have a width that covers a change in position of each spacer grid of the nuclear fuel assembly to be transported. Thereby, in different types of nuclear fuel assemblies between which the position of each spacer grid is different, the spacer grid located at a different position can be fixedly pressed using the press plate 610. Accordingly, the lid frame 400 or 400′ can clamp and transport the different types of nuclear fuel assemblies without requiring a separate change in structure. In the state where the nuclear fuel assemblies 10 are stably clamped by the gap compensators 500 and the press members 600 of the lid frames 400 and 400′, when the nuclear fuel assemblies 10 are transported to a nuclear power plant, they can be transported without external shocks subjecting them to vibrations in the shipping container. Thereby, it is possible to prevent the nuclear fuel assemblies 10 from being damaged. Although exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. |
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claims | 1. A method of preparing fine patterns to be printed with an SLM, comprising the actions of:rasterizing an input pattern to a grayscale bitmap,applying an edge offset correction filter to at least two aligned pixels, including at least one pixel having a grey value and a light value pixel or a dark value pixel, wherein operation of the edge offset correction filter depends at least in part on the grey value and application of the edge offset correction filter increases a difference in illumination of at least one area element adjacent to an edge of the feature, located either on the dark side and/or one on the light side of the edge; andprojecting radiation from the aligned pixels of the SLM through a Fourier filter onto an object plane. 2. The method according to claim 1, wherein said light value corresponds to a value used to project a white pixel when the white pixel is surrounded by other white pixels. 3. The method according to claim 1, wherein said dark value corresponds to a value used to project a black pixel when the black pixel is surrounded by other black pixels. 4. The method according to claim 1, wherein application of the edge offset correction filter to the dark value pixel results in the dark value pixel having a negative amplitude. 5. The method according to claim 1, wherein application of the edge offset correction filter to the light value pixel results in the light value pixel having a lighter amplitude than used to project a white pixel when the white pixel is surrounded by other white pixels. 6. The method according to claim 1, wherein the edge offset correction filter, for at least some values of grey, is not symmetrical in lightening the light value and darkening the dark value. 7. The method according to claim 1, wherein the edge offset correction filter, for at least some values of grey, also changes the grey value. 8. The method according to claim 1, wherein the edge offset correction filter is a rule-based filter. 9. A method of preparing fine patterns to be printed with an SLM, comprising the actions ofrasterizing an input pattern to a grayscale bitmap,applying an edge offset correction filter to at least two aligned pixels, including at least one pixel having a grey value and a light value pixel or a dark value pixel, wherein operation of the edge offset correction filter depends at least in part on the grey value and application of the edge offset correction filter is changing the dark value pixel to a more negative amplitude and adjusts the grey value of the grey value pixel; andprojecting radiation from the aligned pixels of the SLM through a Fourier filter onto an object plane. 10. A method of preparing fine patterns to be printed with an SLM illuminated by partially coherent light, comprising the actions of:rasterizing an input pattern to a grayscale bitmap,applying an edge offset correction filter to at least three aligned pixels, including at least one pixel having a grey value and having on opposing sides a light value pixel and a dark value pixel, wherein operation of the edge offset correction filter depends at least in part on the grey value and application of the edge offset correction filter increases a difference between a complex amplitude of the light value pixel and the dark value pixel; andprojecting radiation from the aligned pixels of the SLM through a Fowier filter onto an object plane. 11. The method according to claim 10, wherein said light value corresponds to a value used, to project a white pixel when the white pixel is surrounded by other white pixels. 12. The method according to claim 10, wherein said dark value corresponds to a value used to project a black pixel when the black pixel is surrounded by other black pixels. 13. The method according to claim 10, wherein application of the edge offset correction filter to the dark value pixel results in the dark value pixel having a negative amplitude. 14. The method according to claim 10, wherein application of the edge offset correction filter to the light value pixel results in the light value pixel having a lighter amplitude than used to project a white pixel when the white pixel is surrounded by other white pixels. 15. The method according to claim 10, wherein the edge offset correction filter, for at least some values of grey, is not symmetrical in lightening the light value and darkening the dark value. 16. The method according to claim 10, wherein the edge offset correction filter, for at least some values of grey, also changes the grey value. 17. The method according to claim 10, wherein the edge offset correction filter is a rule-based filter. 18. A method of preparing fine patterns to be printed with an SLM projected through an optical path and projection optics pupil, comprising the actions of:rasterizing an input pattern to a grayscale bitmap,applying an edge offset correction filter to at least two aligned pixels, including at least one pixel having a grey value and light value pixel or a dark value pixel, wherein values of the edge offset correction filter substantially minimize the difference in the Fourier transform from projecting radiation from the aligned pixels of the SLM and a perfect binary mask or phase shifting mask over the projection optics pupil. |
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051184648 | abstract | An improved apparatus and method for ultrasonic inspection of materials through barriers such as gaps in manufactured parts is disclosed. The improvement herein is directed to enabling such ultrasonic testing to bridge ambient gaps such as intentionally formed gaps in composite structures having a first structure for originally receiving and transmitting sound separated by the gap from another structure to be inspected. Preferably, the gap is flooded with a gas having a predictable and optimum speed of sound relative to the material of the first and second structures. Sound is propagated to the first structure in a wave packet that is transmitted through the couplant fluid. The sound is generated in a wave packet having a spatial width at least twice the dimension of the gap to be bridged. The wave packet has a contained frequency having a wavelength (relative to the speed of sound of the gas flooding the gap) to create a constructively interfering standing wave node within the gap. The sound propagated to the gas-filled gap has a wavelength which is a half-integer with respect to the gap dimension. Sound passes through the first structure, creates a standing wave node in the gas-filled gap, passes into and acoustically interrogates the second structure for flaws and reflects. Reflected ultrasoound from the interrogated second structure again bridges the gap as a constructively interfering standing wave, passing through the primary structure and then through the couplant fluid to a transducer for receipt and analysis of the received ultrasound. |
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claims | 1. An extreme ultraviolet light generation apparatus comprising:A. a chamber in which extreme ultraviolet light is generated by a target substance being irradiated with a laser beam to generate plasma from the target substance;B. a vessel as a tubular member forming the chamber;C. a reference member supporting the vessel;D. a collector mirror configured to condense the extreme ultraviolet light in the chamber, the collector mirror being attached to the reference member in a replaceable manner and covered by the vessel to be housed in the chamber; andE. a vessel movement mechanism provided to the reference member and configured to move the vessel between a first position at which the vessel covers the collector mirror and a second position at which the vessel is retracted from the first position to expose the collector mirror. 2. The extreme ultraviolet light generation apparatus according to claim 1, wherein, in the reference member, an attachment surface to which the collector mirror is attached is tilted relative to the horizontal direction. 3. The extreme ultraviolet light generation apparatus according to claim 1, further comprising:F. a target sensor provided to the vessel and configured to measure the target substance in the chamber. 4. The extreme ultraviolet light generation apparatus according to claim 1, wherein the vessel movement mechanism includes a link member including a main shaft and a slide member configured to slide relative to the main shaft in the axial direction of the main shaft, one of the main shaft and the slide member being attached to the reference member, the other of the main shaft and the slide member being attached to the vessel, and moves the vessel relative to the reference member through the relative slide of the main shaft and the slide member. 5. The extreme ultraviolet light generation apparatus according to claim 4, wherein the link member is an air cylinder including a piston rod functioning as the main shaft, and a cylinder functioning as the slide member. 6. The extreme ultraviolet light generation apparatus according to claim 4, wherein the link member is a ball screw including a screw shaft functioning as the main shaft, and a nut functioning as the slide member configured to relatively slide in the axial direction of the screw shaft while being engaged with the screw shaft and relatively rotating about the axis of the screw shaft. 7. The extreme ultraviolet light generation apparatus according to claim 4, wherein the vessel movement mechanism includes a drive device configured to drive the link member. 8. The extreme ultraviolet light generation apparatus according to claim 1, wherein the vessel movement mechanism linearly moves the vessel between the first position and the second position. 9. The extreme ultraviolet light generation apparatus according to claim 8, wherein the vessel movement mechanism moves the vessel in the axial direction of the vessel. 10. The extreme ultraviolet light generation apparatus according to claim 8, wherein the vessel movement mechanism slides the vessel in a direction intersecting with the axial direction of the vessel. 11. The extreme ultraviolet light generation apparatus according to claim 1, wherein the vessel movement mechanism rotationally moves the vessel at movement between the first position and the second position. 12. The extreme ultraviolet light generation apparatus according to claim 11, whereinthe vessel is rotatably attached to the reference member through a hinge at one end of the attachment surface, andthe vessel movement mechanism rotationally moves the vessel with the hinge as a pivot. 13. The extreme ultraviolet light generation apparatus according to claim 11, wherein the vessel movement mechanism moves the vessel between the first position and the second position in combination of linear movement and rotational movement. 14. The extreme ultraviolet light generation apparatus according to claim 1, further comprising:G. a positioning mechanism configured to determine a position at which the vessel is attached to the reference member at the second position. 15. The extreme ultraviolet light generation apparatus according to claim 14, wherein the positioning mechanism includes a taper pin having an outer diameter that decreases from a base end side toward a leading end side, and an engagement hole to be engaged with the taper pin, one of the taper pin and the engagement hole being provided to the vessel, the other being provided to the reference member. 16. The extreme ultraviolet light generation apparatus according to claim 14, wherein the positioning mechanism is a ball spline including a spline shaft in which a key groove is formed in the axial direction, and a slider configured to slide relative to the spline shaft along the key groove, one of the spline shaft and the slider being attached to the vessel, the other being attached to the reference member. 17. The extreme ultraviolet light generation apparatus according to claim 1, further comprising:H. an O ring disposed between the attachment surface and an end face of the vessel, which faces the attachment surface at the first position, to seal a gap between the attachment surface and the end face. 18. The extreme ultraviolet light generation apparatus according to claim 17, wherein a ring groove to which the O ring is attached is formed on the attachment surface or the end face. 19. The extreme ultraviolet light generation apparatus according to claim 18, wherein a sectional shape of the attachment groove is a substantially trapezoid shape having a smaller width at an opening than inside the ring groove. |
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description | Embodiments of the present invention will be described below in detail with reference to the drawings. A first embodiment of the present invention will be described with reference to FIGS. 1 to 9. FIG. 2 is a conceptual block diagram showing an overall system configuration of a medical system including a radiation beam irradiator comprising a multi-leaf collimator of this embodiment and an accelerator. In the radiation beam irradiator, a radiation beam (also referred to simply as a xe2x80x9cbeamxe2x80x9d hereinafter), such as a charged particle beam, accelerated by an accelerator (synchrotron) 101 is outputted from a rotating irradiator 102 under control of a control unit 23 for irradiation to the diseased part of a patient K. By turning the rotating irradiator 102 about an axis of the rotation, the beam can be irradiated to the diseased part from a plurality of directions. (1) Outline and Operation of Synchrotron 101 The synchrotron 101 comprises a high-frequency applying apparatus 111 for applying a high-frequency magnetic field and electric field (referred to together as a xe2x80x9chigh-frequency electromagnetic fieldxe2x80x9d hereinafter) to the beam to increase the amplitude of betatron oscillation of the beam; deflecting electromagnets 112 for bending a track of the beam; quadrupole electromagnets 113 for controlling the betatron oscillation of the beam; hexapole electromagnets 114 for exciting resonance for exiting of the beam; a high-frequency accelerating cavity 115 for accelerating the beam; an inlet unit 116 for introducing the beam into the synchrotron 101, and outlet deflectors 117 for guiding the beam to exit the synchrotron 101. When the control unit 23 outputs an emission command to a pre-stage accelerator 104, the pre-stage accelerator 104 emits a beam of low energy in accordance with the emission command. The beam is guided to the inlet unit 116 of the synchrotron 101 through a beam transporting system, and then introduced to the synchrotron 101. The introduced beam goes around within the synchrotron 101 while its track is bent by the deflecting electromagnets 112. While the beam is going around within the synchrotron 101, it undergoes the betatron oscillation under actions of the quadrupole electromagnets 113. The oscillation frequency of the betatron oscillation is properly controlled in accordance with the amount of excitation of the quadrupole electromagnets 113 so that the beam stably orbits within the synchrotron 101. During the orbiting, a high-frequency magnetic field is applied to the beam in the high-frequency accelerating cavity 115, whereby energy is applied to the beam. As a result, the beam is accelerated and the beam energy is increased. When the energy of the beam orbiting within the synchrotron 101 is increased to a level of energy E, the application of energy to the beam in the high-frequency accelerating cavity 115 is stopped. At the same time, a gradient of the beam orbit is changed under well-known control by the quadrupole electromagnets 113, the hexapole electromagnets 114 and the high-frequency applying apparatus 111. The magnitude of the betatron oscillation is hence abruptly increased due to resonance, causing the beam to exit the synchrotron 101 through the outlet deflectors 117. In the above-described operation of the synchrotron 101, in accordance with the depth position of the diseased part inputted from a remedy scheduling unit 24 (described later in detail), the control unit 23 determines the energy E of the beam that is to be irradiated to the diseased part in a predetermined irradiating direction (usually the beam is irradiated in plural directions). Further, the control unit 23 calculates patterns of current values supplied to the deflecting electromagnets 112, the quadrupole electromagnets 113 and the high-frequency accelerating cavity 115 for accelerating the beam in the synchrotron 101 to a level of the energy E, and also calculates current values supplied to the high-frequency applying apparatus 111 and the hexapole electromagnets 114 for emitting the beam of the energy E. The calculated current values are stored in a storage means in the control unit 23 corresponding to levels of the energy E for each component, and are outputted to a power supply 108 or 109 when the beam is accelerated or exits. (2) Outline and Operation of Rotating Irradiator 102 The beam exiting the synchrotron 101 enters the rotating irradiator 102. The rotating irradiator 102 comprises a gantry 122, on which deflecting electromagnets 123, quadrupole electromagnets 124 and an outlet nozzle 120 are mounted, and a motor 121 for rotating the gantry 122 about a predetermined axis of rotation (see FIG. 2). The beam having entered the rotating irradiator 102 is introduced to the outlet nozzle 120 while the beam track is bent by the deflecting electromagnets 123 and the betatron oscillation is adjusted by the quadrupole electromagnets 124. The beam introduced to the outlet nozzle 120 first passes between scanning electromagnets 201, 202. Sinusoidal AC currents being 90 degrees out of phase are supplied to the scanning electromagnets 201, 202 from power supplies 201A, 202A. The beam passing between magnet poles of the scanning electromagnets 201, 202 is deflected by magnetic fields generated from the scanning electromagnets 201, 202 so that the beam makes a circular scan at a position of the diseased part. The beam having passed the scanning electromagnets 201, 202 is diffused by a diffuser 203 so as to have an enlarged diameter, and then passes a ridge filter 204A (or 204B). The ridge filter 204A (or 204B) attenuates the beam energy at such a predetermined rate that the beam energy has a distribution corresponding to a thickness of the diseased part. The radiation dose is then measured by a dosimeter 205. Thereafter, the beam is introduced to a porous member 206A (or 206B) that gives the beam an energy distribution corresponding to a bottom shape of the diseased part. Further, the beam is shaped by a multi-leaf collimator 200 in match with a horizontal shape of the diseased part, and then irradiated to the diseased part. Usually, as mentioned above, the beam is irradiated to the diseased part from a plurality of directions. This embodiment shows, by way of example, the case of irradiating the diseased part from two directions. Two ridge filters 204A, 204B are fabricated beforehand for each of the two irradiating directions corresponding to respective values of thickness of the diseased part determined by the remedy scheduling unit 24. Also, the porous members 206A, 206B are fabricated beforehand for each of the two irradiating directions corresponding to respective bottom shapes of the diseased part determined by the remedy scheduling unit 24. The fabricated ridge filters 204A, 204B are mounted on a rotating table 204C, and the fabricated porous members 206A, 206B are mounted on a rotating table 206C. An axis of rotation of the rotating table 206C is offset from the center of the beam track. By turning the rotating table 206C, therefore, the porous member 206A or 206B can be alternately arranged to lie across the beam track, and the beam having an energy distribution corresponding to each of the two irradiating directions can be formed. Additionally, the rotating table 206C is of the same construction as the rotating table 204C. When setting or changing the irradiating direction, an inclination angle signal corresponding to the irradiating direction is outputted from the control unit 23 to the motor 121, whereupon the motor 121 rotates the gantry 122 to an inclination angle indicated by the outputted signal and the rotating irradiator 102 is moved to a position where it is able to irradiate the beam to the diseased part from the selected irradiating direction. Also, the control unit 23 outputs, to the rotating tables 204C and 206C, signals for instructing them to arrange the ridge filter 204A (or 204B) and the porous member 206A (or 206B), corresponding to the selected irradiating direction, so as to lie across the beam track. The rotating tables 204C, 206C are rotated in accordance with the instruction signals. Then, a control signal corresponding to the selected irradiating direction is outputted from the control unit 23 to a collimator controller (leaf position control computer) 22. Responsively, the collimator controller 22 makes control such that, as shown in FIG. 3, a number of leaf plates 1 (described later in detail) provided in the multi-leaf collimator 200 are positioned in an opposing relation to provide a gap space G, which defines an irradiation area (field) F of a beam X in match with a horizontal shape of the diseased part as viewed in the selected irradiating direction. As a result, of the beam having reached the multi-leaf collimator 200 after passing the porous member 206A (or 206B), a component directing to other areas than the irradiation field F is shielded by the leaf plates, and the irradiation to an unnecessary part can be prevented. Important features of the present invention reside in mechanisms for driving the leaf plates of the multi-leaf collimator 200. Details of those features will be described below in sequence. (3) Basic Construction and Operation of Multi-leaf Collimator 200 FIG. 1 is a perspective view showing the detailed structure of the multi-leaf collimator 200; FIG. 4 is a front view as viewed in the direction of A in FIG. 1; FIG. 5 is a plan view of the multi-leaf collimator in a state where an upper coupling portion 201a (described later) and an upper support 7a (described later) of a leaf plate driver 200R (described later); and FIG. 6 is a plan view as viewed in the direction of B in FIG. 5. Referring to FIGS. 1, 4, 5 and 6, the multi-leaf collimator 200 comprises leaf plate driving body 200L and 200R. Each leaf plate driver 200L or 200R comprises a plurality (twelve in this embodiment, but the number may be greater than it) of leaf plates 1, which are movable to form the irradiation field F of the radiation beam and capable of shielding the radiation beam; an upper guide 3 and a lower guide 5 for receiving an upper sliding portion 1A and a lower sliding portion 1B of each leaf plate 1, respectively, and supporting them to be slidable in the longitudinal direction of the leaf plate 1 (left and right direction in FIG. 4); upper air cylinders 2 and lower air cylinders 4 capable of pressing the upper guide 3 and the lower guide 5 upward and downward, respectively; a support structure 7 including an upper support 7a and a lower support 7b for fixedly supporting the upper air cylinders 2 and the lower air cylinders 4, respectively, and an intermediate portion 7c connecting the upper support 7a and the lower support 7b; a motor 8 provided as a driving source for the leaf plates 1; a pinion gear 6 disposed coaxially with a drive shaft 8a of the motor 8 and connected to the drive shaft 8a on the side of the intermediate portion 7c; and a braking plate 9 brought into contact with the leaf plates 1 for holding them stationary by frictional forces (as described later in detail). The motor 8 is a known servo motor in this embodiment. A motor and a rotary encoder are coaxially arranged as an integral unit, and a pulse signal is outputted for each certain small angle of rotation. The upper air cylinders 2 and the lower air cylinders 4 are each constituted by a known single- or double-actuated air cylinder. For example, a piston is disposed in a cylindrical cylinder chamber, and a rod projecting out of the cylinder chamber is attached to the piston. In an operative condition, compressed air from a compressed air source is supplied to a bottom-side chamber, whereupon the piston is moved to the rod side by overcoming the biasing force of a spring disposed on the rod side. As a result, the rod is extended. Upon shift to an inoperative (stop) condition, the compressed air supplied to the bottom-side chamber is discharged (for example, by being made open to the atmosphere), whereby the piston is returned to the bottom side by the biasing force of the spring. As a result, the rod is contracted for return to the original position. The leaf plate 1 comprises upper and lower sliding portions 1A, 1B inserted in the upper and lower guides 3, 5, respectively, and a shield portion 1C coupling the upper and lower sliding portions 1A, 1B and shielding the radiation beam. The shield portions 1C of every two adjacent leaf plates 1 are arranged to be able to slide in a close contact relation. To that end, the upper and lower sliding portions 1A, 1B are each formed to have a smaller thickness than the shield portion 1C for securing spaces necessary for installing the upper and lower guides 3, 5. Also, to that end, the upper and lower guides 3, 5 and the upper and lower air cylinders 2, 4 associated with the adjacent leaf plates 1 are arranged in an alternately displaced relation (in a zigzag pattern), as shown in FIGS. 1, 5 and 6. A rack gear 12 is partly provided on an upper edge of the lower sliding portion 1B of each leaf plate 1 in the leaf plate driver 200L. The aforesaid pinion gear 6 is arranged in a position where it is able to engage (mesh) with the rack gear 12. On the other hand, the aforesaid braking plate 9 is disposed opposite to a lower edge of the upper sliding portion 1A of each leaf plate 1 in the leaf plate driver 200L. When moving the leaf plate 1, the lower air cylinder 4 is set to the operative condition and the upper air cylinder 2 is set to the inoperative (stop) condition, whereupon the leaf plate 1 is moved upward to mesh the rack gear 12 with the pinion gear 6, while the lower edge of the upper sliding portion 1A is moved away (disengaged) from an upper surface of the braking plate 9. By operating the motor 8 in such a state, the leaf plate 1 can slide in the predetermined direction through transmission of the driving force of the motor 8. Then, when stropping the leaf plate 1, the motor 8 is first stopped to cease the movement of the leaf plate 1. After that, by setting the upper air cylinder 2 to the operative condition and the lower air cylinder 4 to the inoperative condition, the leaf plate 1 is moved downward to release the rack gear 12 from mesh with the pinion gear 6, while the lower edge of the upper sliding portion 1A is partly brought into abutment against the upper surface of the braking plate 9. The leaf plate 1 is thereby positively held stationary at that position. Likewise, in the leaf plate driver 200R, a rack gear 12 is partly provided on a lower edge of the upper sliding portion 1A of each leaf plate 1, and the aforesaid braking plate 9 is disposed opposite to an upper edge of the lower sliding portion 1B. By setting the upper air cylinder 2 to the operative condition, the leaf plate 1 is moved downward to mesh the rack gear 12 with the pinion gear 6 so that the leaf plate 1 slides by the driving force of the motor 8, while the upper edge of the lower sliding portion 1B is moved away from a lower surface of the braking plate 9. Also, by setting the lower air cylinder 4 to the operative condition, the leaf plate 1 is moved upward to release the rack gear 12 from mesh with the pinion gear 6, while the upper edge of the lower sliding portion 1B is partly brought into abutment against the lower surface of the braking plate 9. The leaf plate 1 is thereby positively held stationary at that position. An upper coupling portion 201a, a lower coupling portion 201b, and an intermediate coupling portion 201c (see FIGS. 5 and 6) are disposed respectively between the upper supports 7a, between the lower supports 7b, and between the intermediate supports 7c of the leaf plate driving body 200L, 200R for coupling them. Of those coupling portions, the upper and lower coupling portions 201a, 201b have cutouts 202 formed therein to allow passage of the radiation beam. (4) Control System (4-1) Overall Construction FIG. 7 is a functional block diagram showing a system configuration of a control system in a medical system including the multi-leaf collimator 200 of this embodiment. In addition to the remedy scheduling unit 24, the control unit 23 and the collimator controller 22 mentioned above, the control system further comprises a leaf position driving actuator 14 (servo motor 8 in this embodiment) controlled in accordance with a rotation driving command and a driving stop command from the collimator controller 22; a driving force transmitting/cutoff mechanism 15 (upper and lower air cylinders in this embodiment) controlled in accordance with a driving force transmitting command and a driving force cutoff command from the collimator controller 22; a braking force transmitting/cutoff mechanism 16 (upper and lower air cylinders in this embodiment, described later in detail) controlled in accordance with a braking force transmitting command and a braking force cutoff command from the collimator controller 22; and a position detecting mechanism 19 (servo motor 8 in this embodiment, described later in detail) for outputting a position detected signal for each leaf plate 1 to the collimator controller 22. It is to be noted that, as described above, this embodiment is arranged to transmit or cut off the driving force from the pinion gear 6 and to cut off or transmit the braking force from the braking plate 9 at the same time, and switching between transmission and cut off of the driving force or the braking force is performed by the upper and lower air cylinders cylinders 2, 4. Consequently, the driving force transmitting/cutoff mechanism 15 and the braking force transmitting/cutoff mechanism 16 are constituted by a common mechanism. Further, the driving force transmitting command serves also as the braking force cutoff command, and the driving force cutoff command serves also as the braking force transmitting command. (4-2) Remedy Scheduling Unit 24 The remedy scheduling unit 24 comprises, for example, a computer, a plurality of display devices, an input device, and a patient database (the patient database may be separately prepared and connected to the unit 24 via a network). The remedy scheduling unit 24 has the function of aiding the remedy scheduling work to be made by a doctor as a pre-stage for carrying out actual irradiation. Practical examples of the remedy scheduling work include identification of the diseased part, decision of the irradiation area and the irradiating directions, decision of the radiation dose irradiated to the patient, and calculation of a dose distribution in the patient body. (A) Identification of Diseased Part In a diagnosis prior to the remedy, for example, three-dimensional image data of a tumor in the patient body is taken beforehand by an X-ray CT inspection and an MRI inspection. Those inspection data is given with a number for each patient, and is stored and managed as digital data in the patient database. In addition to the inspection data, the patient database also contains information such as the name of patient, the patient number, the age, height and weight of patient, the diagnosis and inspection records, historical data for diseases that the patient has suffered, historical data for remedies that the patient has taken, and remedy data. Stated otherwise, all data necessary for remedy of the patient is recorded and managed in the patient database. The doctor can access the patient database, as required, to acquire the image data of the diseased part and display the image data on the display devices of the remedy scheduling unit 24. Specifically, it is possible to display the image data of the diseased part as a three-dimensional image looking from any desired direction, and as a sectional image sliced at each of different depths looking from any desired direction. Further, the remedy scheduling unit 24 has the functions of assisting the doctor to identify the diseased part, such as contrast highlighting and area painting-out with a certain gradation level as a threshold for each image. The doctor identifies an area of the diseased part by utilizing those assistant functions. (B) Tentative Selection of Irradiation Area and Irradiating Directions Subsequently, the doctor makes an operation to decide the irradiation area that envelops the diseased part and includes an appropriate margin in consideration of a possibility that the diseased part may move in the patient body due to breathing, for example. Further, the doctor selects several irradiating directions out of interference with the internal organs highly susceptible to radiation, such as the spine. (C) Decision of Contour of Irradiation Field Based on the several irradiating directions, an image of the irradiation field looking from each irradiating direction is displayed, and the contour of the irradiation field covering the whole of a tumor is displayed in a highlighted manner. Also, a three-dimensional image of the diseased part is displayed, and a position of a maximum section and a three-dimensional shape subsequent to the maximum section are displayed. Those images are displayed on a plurality of display screens separately, or on one display screen in a divided fashion. Herein, the contour of the irradiation field decided provides basic (original) data for the irradiation field F shaped by the multi-leaf collimator 200, and the three-dimensional shape data subsequent to the maximum section provides basic (original) data for irradiation compensators, such as the porous members 206A, 206B. (D) Decision of Irradiating Direction and Radiation Dose Irradiated to Patient The remedy scheduling unit 24 has the function of automatically deciding a position of each leaf plate 1 of the multi-leaf collimator 200 based on information regarding the contour of the irradiation field, and can display the automatically decided position of each leaf plate 1 and an image of the maximum section of the irradiation field in a superimposed relation. At this time, the doctor can provide an instruction to finely change and adjust the position of each leaf plate 1 with reference to the superimposed images, or the position of each leaf plate 1 can be decided in response to an operation instruction provided by the doctor while the superimposed images are displayed. The decision result of the position of each leaf plate 1 is promptly reflected in the display on the display device. Based on both the leaf-plate set position information and the irradiation compensator information, the remedy scheduling unit 24 simulates a radiation dose distribution in the patient body and displays a calculation result of the dose distribution on the display device. On that occasion, irradiation parameters such as the radiation dose irradiated to the patient and the radiation energy are given by the doctor, and the simulation is performed for each of the selected several irradiating directions. The doctor finally selects the irradiating direction in which the most preferable result was obtained. The selected irradiating direction and the associated set position information for the leaf plates 1 of the multi-leaf collimator 200, irradiation compensator data, and irradiation parameters are stored in the patient database as remedy data specific to the patient. (4-2) Control Unit 23 and Collimator Controller 22 The control unit 23 comprises an input device and a display device, which serve as a user operation interface. Also, the control unit 23 is able to acquire the patient remedy data, including the set position information for the leaf plates 1 decided in the remedy scheduling unit 24, via network connection from the patient database associated with the remedy scheduling unit 24, and to display the acquired data on the display device for confirmation by the doctor, etc. Then, in practical irradiation, when a user of the set position information for the leaf plates 1 (a doctor or a radiotherapeutic engineer engaged in assisting the doctor""s remedy based on the remedy schedule), for example, inputs the start of irradiation remedy, the control unit 23 outputs a command for starting movement of the leaf plates to the collimator controller 22 in accordance with the set position information for the leaf plates 1. In response to the command from the control unit 23, the collimator controller 22 outputs necessary control commands to respective subordinating mechanisms, i.e., the leaf position driving actuator 14, the driving force transmitting/cutoff mechanism 15, and the braking force transmitting/cutoff mechanism 16. Upon receiving the movement start command, the collimator controller 22 controls those subordinating mechanisms so that eacg leaf plate 1 is moved to the predetermined set position. (4-3) Control of Leaf Plate Movement to Set Position The procedures for moving each leaf plate 1 by the collimator controller 22 will first be described with reference to FIG. 8 showing a control flow in this case. Referring to FIG. 8, the control flow begins when the collimator controller 22 receives the movement start command from the control unit 23. Note that this flow proceeds in parallel for each of the leaf plate driving body 200L, 200R concurrently. First, in step 10, the collimator controller 22 receives the set position information for each leaf plate 1 from the control unit 23 and stores it in a storage means (not shown). Then, in step 20, the driving force transmitting command (which serves also as the braking force cutoff command as described above) for transmitting the driving force to all the leaf plates 1 of the leaf plate driver 200L (or 200R) is outputted to the driving force transmitting/-cutoff mechanism 15 (all the upper and lower air cylinders 2, 4 in this embodiment). With this step, in the leaf plate driver 200L, the upper air cylinders 3 and the lower air cylinders 4 associated with all the leaf plates 1 are brought respectively into the inoperative condition and the operative condition (in the leaf plate driver 200R, the upper air cylinders 3 and the lower air cylinders 4 associated with all the leaf plates 1 are brought respectively into the operative condition and the inoperative condition). Thus, all the leaf plates 1 associated with the leaf plate driver 200L (or 200R) are moved away from the braking plate 9 and are meshed with the pinion gear 6. Next, in step 30, the collimator controller 22 outputs, to the leaf position driving actuator 14 (servo motor 8 in this embodiment), a rotation driving command (leaf advance command) to rotate the motor 8 in the leaf advancing direction (=inserting direction, i.e., direction to narrow the space gap G corresponding to the irradiation field F). Responsively, the motor 8 of the leaf plate driver 200L (or 200R) starts rotation, whereupon all the leaf plates 1 start moving forward in the inserting direction in a transversely aligned state. Then, in step 40, an amount of insertion (current position) of each leaf plate 1 is detected. Specifically, the collimator controller 22 receives a rotation signal (aforesaid pulse signal) outputted from the servo motor 8 which serves as the position detecting mechanism 19, and determines a rotation angle of the pinion gear 6 from the rotation signal. Further, the collimator controller 22 determines an amount of movement of each leaf plate 1 from both the rotation angle and a gear ratio of a rack-and-pinion mechanism comprising the pinion gear 6 and the rack gear 12, and totalizes the amount of movement from the origin, thereby obtaining current position information for each leaf plate 1. Subsequently, the control flow proceeds to step 50 where it is determined whether any of all the leaf plates 1 has reached the set position of the relevant leaf plate 1, which is defined by the leaf-plate set position information stored in the collimator controller 22. If not so, the control flow returns to step 20 for repeating the above-described steps in the same manner, and if so, the control flow proceeds to step 60. In step 60, the collimator controller 22 outputs a driving stop command (leaf stop command) to the leaf position driving actuator 14 (servo motor 8 in this embodiment). In accordance with that command, the rotation of the motor 8 is stopped and the movements of all the leaf plates 1 are stopped simultaneously. Thereafter, in step 70, the driving force cutoff command (which serves also as the braking force transmitting command as described above) is outputted to the driving force transmitting/cutoff mechanism 15 (upper and lower air cylinders 2, 4) associated with the leaf plate 1 that has reached the set position. With this step, in the leaf plate driver 200L, the lower air cylinder 4 and the upper air cylinder 3 associated with the relevant leaf plate 1 are brought respectively into the inoperative condition and the operative condition (in the leaf plate driver 200R, the lower air cylinder 4 and the upper air cylinder 3 associated with the relevant leaf plate 1 are brought respectively into the operative condition and the inoperative condition). Thus, the relevant leaf plate 1 is out of mesh with (disengaged from) the pinion gear 6, moves away (departs) from it, and is brought into contact with the braking plate 9. As a result, the relevant leaf plate 1 is held stationary at the set position with stability. Then, in step 80, it is determined whether all the leaf plates 1 associated with the leaf plate driver 200L (or 200R) have reached the set positions. If not so, the control flow returns to step 20 for repeating the above-described steps in the same manner until all the leaf plates 1 reach the set positions. More specifically, in step 20, the rotation of the motor 8 is started again, whereby all of the remaining leaf plates 1 start moving forward again while leaving the leaf plate 1 at the set position, which has reached there in above step 70. Then, through steps 20 to 70, the operations of stopping all the remaining leaf plates 1 upon one leaf plate 1 reaching the set position, cutting off the driving force (making disengagement) and transmitting the braking force for only the relevant one leaf plate 1, transmitting the driving force (making engagement) again and releasing the braking force again for the remaining leaf plates 1, and resuming insertion of the remaining leaf plates 1 are repeated until all the leaf plates 1 are completely moved to the set positions and the driving force is cut off for all the leaf plates 1. When all the leaf plates 1 have reached the set positions and the driving force is cut off for all the leaf plates 1, the determination in step 80 is satisfied and the collimator controller 22 outputs a leaf-plate insertion end signal to the control unit 23 in step 90, thereby completing the control flow. In the above-described steps, the current position information and the driving status of each leaf plate 1 under management of the collimator controller 22 are always transmitted to the control unit 23 and displayed on the display device of the control unit 23. (4-4) Return Control of Leaf Plate to Origin Position When the leaf plates have all been positioned to the set positions as described above and then irradiation of a radiation beam is ended, the control unit 23 outputs a leaf-plate return-to-origin command to the collimator controller 22 upon the end of irradiation remedy being instructed from the user of the set position information for the leaf plates 1. Upon receiving the return-to-origin command from the control unit 23, the collimator controller 22 controls the aforesaid subordinating mechanisms to move each leaf plate 1 for return to the origin position in a similar but reversed manner to that described above in (4-3). The procedures for returning each leaf plate 1 to the origin by the collimator controller 22 will be described with reference to FIG. 9 showing a control flow in this case. Referring to FIG. 9, the control flow begins when the collimator controller 22 receives the return-to-origin command from the control unit 23. Note that, similarly to the flow of FIG. 8, this flow also proceeds in parallel for each of the leaf plate driving body 200L, 200R concurrently. First, in step 110, the driving force transmitting command (which serves also as the braking force cutoff command) for transmitting the driving force to all the leaf plates 1 of the leaf plate driver 200L (or 200R) is outputted to the driving force transmitting/cutoff mechanism 15 (upper and lower air cylinders 2, 4). With this step, in the leaf plate driver 200L, the upper air cylinders 3 and the lower air cylinders 4 associated with all the leaf plates 1 are brought respectively into the inoperative condition and the operative condition (in the leaf plate driver 200R, the upper air cylinders 3 and the lower air cylinders 4 associated with all the leaf plates 1 are brought respectively into the operative condition and the inoperative condition). Thus, all the leaf plates 1 associated with the leaf plate driver 200L (or 200R) are moved away from the braking plate 9 and are meshed with the pinion gear 6. Next, in step 120, the collimator controller 22 outputs, to the leaf position driving actuator 14 (servo motor 8 in this embodiment), a rotation driving command (leaf retreat command) to rotate the motor 8 in the leaf retreating direction (=withdrawing direction, i.e., direction to widen the aforesaid space gap G). Responsively, the motor 8 of the leaf plate driver 200L (or 200R) starts rotation, whereupon all the leaf plates 1 start moving backward in the withdrawing direction in a transversely not-aligned state (position difference among the leaf plates 1 remain the same). Then, in step 130, an amount of withdrawal (current position) of each leaf plate 1 is detected. Specifically, as with the above case, the collimator controller 22 determines an amount of movement of each leaf plate 1 from a rotation signal outputted from the servo motor 8 which serves as the position detecting mechanism 19, and obtains current position information for each leaf plate 1 based on the determined amount of movement. In step 140, it is determined whether any of all the leaf plates 1 has reached the origin position. If not so, the control flow returns to step 120 for repeating the above-described steps in the same manner, and if so, the control flow proceeds to step 150. In step 150, the collimator controller 22 outputs a driving stop command (leaf stop command) to the leaf position driving actuator 14 (motor 8). In accordance with that command, the rotation of the motor 8 is stopped and the movements of all the leaf plates 1 are stopped simultaneously while they remain in the transversely not-aligned state. Instead of above steps 130 to 150, this embodiment may be modified such that, for example, a limit switch (not shown) is provided beforehand in the vicinity of the origin at a certain distance, and when one leaf plate 1 is withdrawn to a position near the origin and contacts the limit switch, a signal indicating the arrival of the relevant leaf plate 1 to the position near the origin is outputted from the limit switch to the collimator controller 22. In such a modified case, for example, at the timing at which the relevant leaf plate 1 is further withdrawn and an amount of withdrawal of the relevant leaf plate 1 from the time having received the above signal becomes equal to the distance from the limit switch to the origin, the driving stop command is outputted to the motor 8 so as to stop the movements of all the leaf plates 1 simultaneously. Thereafter, the control flow proceeds to step 160 where the driving force cutoff command (which serves also as the braking force transmitting command) is outputted to the driving force transmitting/cutoff mechanism 15 (upper and lower air cylinders 2, 4) associated with the leaf plate 1 that has reached the origin position. With this step, in the leaf plate driver 200L, the lower air cylinder 4 and the upper air cylinder 3 associated with the relevant leaf plate 1 are brought respectively into the inoperative condition and the operative condition (in the leaf plate driver 200R, the lower air cylinder 4 and the upper air cylinder 3 associated with the relevant leaf plate 1 are brought respectively into the operative condition and the inoperative condition). Thus, the relevant leaf plate 1 is out of mesh with (disengaged from) the pinion gear 6, moved away (departs) from it, and is brought into contact with the braking plate 9. As a result, the relevant leaf plate 1 is completely returned to the origin position and is held stationary there with stability. Then, in step 170, it is determined whether all the leaf plates 1 associated with the leaf plate driver 200L (or 200R) have returned to the origin positions. If not so, the control flow returns to step 110 for repeating the above-described steps in the same manner until all the leaf plates 1 return to the origin positions. More specifically, in step 110, the rotation of the motor 8 is started again, whereby all of the remaining leaf plates 1 are withdrawn again in the retreating direction while they remain in the transversely not-aligned state. Then, through steps 110 to 170, the operations of stopping all the remaining leaf plates 1 upon one leaf plate 1 returning to the origin position, cutting off the driving force (making disengagement) and transmitting the braking force for only the relevant one leaf plate 1, transmitting the driving force (making engagement) again and releasing the braking force again for the remaining leaf plates 1, and resuming withdrawal of the remaining leaf plates 1 are repeated until all the leaf plates 1 are completely returned to the origin positions and the driving force is cut off for all the leaf plates 1. When all the leaf plates 1 have returned to the origin positions and the driving force is cut off for all the leaf plates 1, the determination in step 170 is satisfied and the collimator controller 22 outputs a leaf-plate return-to-origin end signal to the control unit 23 in step 180, thereby completing the control flow. In the above-described steps, the current position information and the driving status of each leaf plate 1 under management of the collimator controller 22 are always transmitted to the control unit 23 and displayed on the display device of the control unit 23. In the foregoing description, the servo motor 8 in each of the leaf plate driving body 200L, 200R constitutes one driving means defined in Claim 1, and the pinion gear 6, all the upper and lower air cylinders 2, 4, and all the upper and lower guides 3, 5 cooperatively constitute driving force transmitting means that is capable of transmitting the driving force to a plurality of leaf plates at the same time and cutting off the driving force selectively for each leaf plate. Also, the servo motor 8 and the pinion gear 6 in each of the leaf plate driving body 200L, 200R constitutes one driving force generating means defined in Claim 2, which is provided to be capable of transmitting the driving force to the plurality of leaf plates at the same time. A pair of upper and lower air cylinders 2, 4 and a pair of upper and lower guides 3, 5, which are provided for each leaf plate 1, cooperatively constitute a plurality of engaging/disengaging means that are provided in a one-to-one relation to the plurality of leaf plates and are each capable of selectively engaging and disengaging a corresponding leaf plate with or from the one driving force generating means. Further, the braking plate 9 constitutes holding means capable of abutting against the leaf plates to hold the leaf plates in predetermined positions. Moreover, the collimator controller 22 constitutes control means, defined in Claim 8, for controlling the one driving means and the driving force transmitting means, and constitutes control means, defined in Claim 9, for controlling the one driving force generating means and the engaging/disengaging means. (5) Advantages of This Embodiment With the multi-leaf collimator of this embodiment, as described above (particularly in (3) and (4)), in each of the leaf plate driving body 200L and 200R, the driving force of the one common motor 8 can be transmitted to a plurality of leaf plates 1 at the same time, and the driving force can be selectively cut off for each leaf plate 1. When driving each leaf plate 1 from the origin position to the set position, the driving force is transmitted to the plurality of leaf plates 1 at the same time, causing all the leaf plates 1 to start movement simultaneously. Then, when one leaf plate 1 reaches the set position, the driving force applied to the relevant leaf plate 1 is cut off to leave it at the set position. By repeating such a step, all the leaf plates 1 are successively positioned to the set positions. Conversely, when returning all the leaf plates 1 to the origin positions from the set condition, the driving force is transmitted to all the leaf plates 1 in the different set positions at the same time, causing all the leaf plates 1 to start movement simultaneously while they remain in the transversely not-aligned state. Then, when one leaf plate 1 returns to the origin position, the driving force applied to the relevant leaf plate 1 is cut off to hold it at the origin position. By repeating such a step, all the leaf plates 1 are successively returned to the origin positions. Thus, since the leaf plates 1 can be successively positioned in each of the leaf plate driving body 200L and 200R while moving a plurality of leaf plates at the same time, a time required for completing the formation of the irradiation field, when the irradiation field is to be formed with high accuracy, can be shortened in comparison with a conventional structure wherein a number of leaf plates must be positioned one by one successively in each leaf plate driver. As a result, physical and mental burdens imposed on patients can be reduced. A second embodiment of the present invention will be described with reference to FIGS. 10 to 12. In this embodiment, the support structure of each leaf plate 1 is modified, and the driving force transmitting/cutoff mechanism 15 and the braking force transmitting/cutoff mechanism 16 are separately provided. The same components as those in the first embodiment are denoted by the same reference numerals, and a description of those components is omitted herein. FIG. 10 is a perspective view showing the structure of principal parts of a leaf plate driver 200R provided in a multi-leaf collimator of this embodiment. For the sake of simplicity, only three of total twelve leaf plates 1 are shown in FIG. 10. FIG. 11 is a front view as viewed in the direction of C in FIG. 10, and FIG. 12 is a perspective view showing the detailed structure of one leaf plate 1 in FIGS. 10 and 11. Referring to FIGS. 10, 11 and 12, in the leaf plate driver 200R provided in the multi-leaf collimator of this embodiment, a vertical position of each leaf plate 1 is always held constant. More specifically, an upper end 1a and a lower end 1b of each leaf plate 1 are contacted with respective rollers 26 rotatably provided on an upper projection 25A and a lower bottom plate 25B of a housing 25. Also, a lower edge of an upper sliding portion 1A and an upper edge of a lower sliding portion 1B of each leaf plate 1 are contacted with respective rollers 26 rotatably provided on upper and lower surfaces of an intermediate projection 25C of the housing 25. With such a structure, the leaf plate 1 is able to slide in the longitudinal direction thereof (left and right direction in FIG. 11) while its vertical displacement is restricted by the rollers 26. On the other hand, a position of each leaf plate 1 in the thickness direction thereof is maintained with such an arrangement that all the leaf plates 1 are sandwiched between a pressing mechanism 28 vertically provided on the housing lower bottom plate 25B and a housing body 25d disposed to extend in the vertical direction. More specifically, the pressing mechanism 28 includes a rotatable roller 28A, which is contacted with one of the total twelve leaf plates 1 positioned closest to the pressing mechanism 28. Though not shown, the housing body 25d also includes a rotatable roller, similar to the roller 28A, which is contacted with one of the twelve leaf plates 1 positioned closest to the housing body 25d. Thus, outermost two of the total twelve leaf plates 1 in the thickness direction thereof are restricted by the rollers from both sides, whereby the total twelve leaf plates 1 are each restricted from displacing in the thickness direction. On both lateral surfaces of the upper sliding portion 1A and the lower sliding portion 1B of each leaf plate 1, frictional sliding members 35A, 35B are provided in contact with the adjacent leaf plates 1. Since the pressing mechanism 28 applies a load for pressing all the leaf plates 1 toward the housing body 25d, the leaf plates 1 are held in a condition contacting with each other at the frictional sliding members 35A, 35B. The pressing load applied to the leaf plates 1 from the pressing mechanism 28 is adjusted such that the leaf plates 1 are slidable individually. A rack gear 12 is disposed at the top of the upper sliding portion 1A of each leaf plate through an air-cushion mechanism 31. A pinion gear 6 connected to the motor 8 is provided in an opposing relation to the rack gear 12 of each leaf plate 1. When compressed air is introduced to the air-cushion mechanism 31 through a piping system (not shown) and the air-cushion mechanism 31 is vertically expanded (=in operative condition), the rack gear 12 is raised up into mesh with the pinion gear 6 for transmitting the driving force. When the compressed air is discharged through a piping system (not shown), the air-cushion mechanism 31 is contracted and the rack gear 12 is out of mesh with the pinion gear 6, thereby disabling (cutting off) the transmission of the driving force. Stated otherwise, the air-cushion mechanism 31 provided for each leaf plate 1 fulfills the function of the driving force transmitting/-cutoff mechanism 15 described above in the first embodiment with reference to FIG. 7. Further, in this embodiment, an air cylinder 34 for moving a braking plate 9 up and down serves as the braking force transmitting/cutoff mechanism 16 shown in FIG. 7. More specifically, the air cylinder 34 is provided on the backside (underside) of the housing bottom plate 25B in a one-to-one relation to the leaf plates 1, and has a rod 34a penetrating the housing bottom plate 25B to project upward. The braking plate 9 is connected to a fore end of the rod 34a. As with the air cylinders 2, 4 used in the first embodiment of the present invention, the air cylinder 34 is constituted by a known single- or double-actuated air cylinder. When compressed air is supplied from a compressed air source to a bottom-side chamber, the rod 34a is extended (operative condition), the braking plate 9 is raised upward to such an extent that an upper surface of the braking plate 9 abuts against the leaf plate lower end 1b to produce braking force. The leaf plate 1 is hence stopped and held at that position by frictional force. Subsequently, when the compressed air supplied to the bottom-side chamber is discharged (for example, by being made open to the atmosphere), a piston is returned to the bottom side by the biasing force of a spring. As a result, the rod 34a is contracted (inoperative or stop condition) for return to the original position so that the leaf plate is made free (released) from the braking force. Thus, in this embodiment, the air cylinder 34 provided for each leaf plate 1 serves as the braking force transmitting/cutoff mechanism 16 described above in connection with FIG. 7. Additionally, the braking plate 9 comes into contact with the leaf plate 1 and generates frictional braking force only when the air cylinder 34 is operated to raise the braking plate 9 upward. While the above description is made in connection with, for example, the leaf plate driver 200R on one side, the leaf plate driver 200L on the other side is of the same structure. Control procedures for driving the leaf plates 1 in this embodiment having the above-mentioned construction are basically the same as those in the first embodiment described above with reference to FIGS. 8 and 9 except that the transmission/cutoff of the driving force and the transmission/cutoff of the braking force are separately controlled. More specifically, the procedures for moving the leaf plates 1 to the set positions, described above in connection with FIG. 8, and the procedures for returning the leaf plates 1 to the origin positions, described above in connection with FIG. 9, are modified as follows. In steps 20 and 110, a driving force transmitting command for transmitting the driving force to the leaf plates 1 is outputted to the air-cushion mechanism 31 that serves as the driving force transmitting/cutoff mechanism 15, and a braking force cutoff command is outputted to the air cylinder 34 that serves as the braking force transmitting/-cutoff mechanism 16. In accordance with those commands, the air-cushion mechanism 31 is brought into the operative condition and the air cylinder 34 is brought into the inoperative condition, respectively, whereby the braking plate 9 departs away from the leaf plate 1 and the pinion gear 6 meshes with the rack gear 12. Also, in steps 70 and 160, a driving force cutoff command for cutting off the driving force applied to the leaf plates 1 is outputted to the air-cushion mechanism 31, and a braking force transmitting command is outputted to the air cylinder 34. In accordance with those commands, the air-cushion mechanism 31 is brought into the inoperative condition and the air cylinder 34 is brought into the operative condition, respectively, whereby the braking plate 9 contacts with the leaf plate 1 and the pinion gear 6 is out of mesh with the rack gear 12. In the foregoing description, the pinion gear 6 and all the air-cushion mechanisms 31 in each of the leaf plate driving body 200L, 200R cooperatively constitute driving force transmitting means defined in Claim 1, which is capable of transmitting the driving force to a plurality of leaf plates at the same time and cutting off the driving force selectively for each leaf plate. Also, the air-cushion mechanisms 31 provided in each of the leaf plate driving body 200L, 200R in a one-to-one relation to the leaf plates 1 constitute a plurality of engaging/disengaging means that are provided in a one-to-one relation to the plurality of leaf plates and are each capable of selectively engaging and disengaging a corresponding leaf plate with or from the one driving force generating means. This embodiment can also provide similar advantages as those in the first embodiment of the present invention. While the driving force is transmitted in the first and second embodiments through meshing of the pinion gear 6 with the rack gear 12, the present invention is not limited to such an arrangement. For example, the arrangement may be modified such that a rubber roller having a cylindrical shape is provided instead of the pinion gear 6, the upper and lower edges of the upper and lower sliding portions 1A, 1B of each leaf plate 1 are each formed in an ordinary shape without the rack gear 12, and the rubber roller is brought into engagement with the upper and lower edges of the upper and lower sliding portions 1A, 1B for transmitting the driving force through frictional force produced upon the engagement. This modification can also provide similar advantages. Further, in the first and second embodiments, the upper and lower air cylinders 2, 4 or the air cylinders 34 are used as the driving force transmitting/cutoff mechanism 15 or the braking force transmitting/cutoff mechanism 16. Instead of those cylinders, however, known linearly reciprocating actuators provided with solenoid magnets (electromagnets) may be used. This modification can also provide similar advantages. While the first and second embodiments employ the servo motor 8 as the leaf position driving actuator 14, a stepping motor may be used instead. A stepping motor is a motor that rotates through a minute angle for each pulse when a pulse-shaped signal is applied as a drive signal to the motor. Usually, a rotation angle per pulse of the drive signal is reliably provided with high accuracy. In this modification, the drive signal for driving the stepping motor can be used instead of the rotation signal obtained from the servo motor 8 in the first and second embodiments. This modification can also provide similar advantages. In the first and second embodiments, the servo motor 8 functions also as the position detecting mechanism 19. However, the present invention is not limited to such an arrangement, and the position detecting mechanism 19 may be constituted by a linear encoder separately provided. A linear encoder comprises, for example, a rotary encoder, a wire, and a winding reel. The reel is rotated corresponding to the distance through which the wire is drawn out, and the rotary encoder connected to the reel generates a rotation signal. In this modification, the linear encoder is provided in the same number as the leaf plates 1 because it is connected to each leaf plate 1 in a one-to-one relation. Then, each linear encoder always outputs, to the collimator controller 22, pulse signals corresponding to the distance of movement of the leaf plate 1 connected to that linear encoder. Based on the known relationship between the pulse signal and the distance of movement of the leaf plate, the collimator controller 22 adds up the distance of movement of each leaf plate 1 and stores it therein as the position information. Furthermore, instead of the linear encoder, another type of linear displacement detector may be connected to each leaf plate 1. Other types of linear displacement detector include, for example, a linear scale, a linear potentiometer, and an LVDT (Linear Variable Differential Transformer). A linear scale comprises a linear rule and a reading head. The reading head moving over the linear rule optically or magnetically reads position symbols disposed on the rule with minute intervals, and outputs a pulse signal. A position detecting method based on a pulse signal is the same as the case described above. A linear potentiometer comprises a linear resistor and a slider linearly moving in slide contact with the resistor. Based on the fact that a resistance value between a terminal connected to one end the resistor and a terminal connected to the slider is given by a resistance value corresponding to the length of the resistor from the resistor terminal to the slider position, the resistance value is linearly changed depending on the distance through which the slider has moved. By connecting a power supply between both the terminals and measuring a voltage therebetween, the resistance value is read after transformation into voltage. In this case, the collimator controller 22 reads the voltage through an A/D converter and calculates the amount of movement of the slider (leaf plate) based on both the relationship between resistance value and voltage in a resistancexe2x80x94voltage converter and the linear relationship between displacement and resistance value, which is specific to the linear potentiometer. An LVDT comprises a unit made up of an excited primary coil and a secondary coil which are coaxially arranged side by side, and an iron core arranged to lie at the centers of the primary coil and the secondary coil and to extend in a straddling relation to both the coils. A linear displacement of the iron core connected to a measurement target is outputted as a change in an output voltage of the secondary coil, which is produced as the strength of coupling between the primary coil and the secondary coil changes. Design parameters are set such that the relationship between displacement and output voltage is linear and provides a constant gradient. Manners for reading the voltage and calculating the displacement are similar to those in the above case. According to the present invention, as described above, it is possible to shorten a positioning time required for forming an irradiation area with high accuracy using a number of leaf plates, and to reduce physical and mental burdens imposed on patients. |
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description | This application is a U.S. national phase under the provisions of 35 U.S.C. § 371 of International Patent Application No. PCT/EP14/78400 filed Dec. 18, 2014, which in turn claims priority of French Patent Application No. 1363261 filed Dec. 20, 2013. The disclosures of such international patent application and French priority patent application are hereby incorporated herein by reference in their respective entireties, for all purposes. The invention relates to the field concerning the synthesis of actinyl peroxides and hydroxo-peroxides More specifically, the invention relates to a process for synthesizing a mixed peroxide or hydroxo-peroxide of an actinyl, typically uranyl or neptunyl, and of at least one doubly, triply or quadruply charged metal cation. The mixed peroxide or hydroxo-peroxide thus synthesized is able to be subsequently converted via calcining to a mixed oxide of an actinide and of at least one metal, the invention also relating for a process for synthesizing said oxide. The invention further concerns a mixed peroxide or hydroxo-peroxide of an actinyl and of at least one doubly, triply or quadruply charged metal cation and to the use thereof for preparing a mixed oxide of an actinide and of at least this metal. The invention finds particular application in the production of mixed oxides of actinides suitable for the manufacture of nuclear fuel pellets such as mixed oxides of uranium and plutonium (U,Pu)O2, mixed oxides of uranium and neptunium (U,Np)O2, mixed oxides of uranium and americium (U,Am)O2, mixed oxides of uranium and curium (U,Cm)O2, or mixed oxides of uranium, americium and curium (U,Am,Cm)O2, or of transmutation targets. It also finds application in the decontamination of radionuclide-contaminated effluents from nuclear plants such as effluents from clean-up treatments of plant installations or soils, or from reprocessing of spent nuclear fuels, in particular for decontamination from lanthanides and/or strontium. Natural uranyl peroxides are known. These are studtite of formula UO4.4H2O or (UO2)(O2).4H2O and its dehydration product metastudtite of formula UO4.2H2O or (UO2)(O2).2H2O. It is acknowledged that these two peroxides are formed by hydrolysis of water to hydrogen peroxide. These are the sole peroxides of uranyl which do not contain any cation other than the uranium cation. They can be laboratory-synthesized by adding hydrogen peroxide to a solution comprising uranyl nitrate in nitric or sulfuric acid, at ambient temperature for studtite and at 70° C. for metastudtite. They can also be obtained by direct conversion of UO3 or U3O8 by hydrogen peroxide. Mixed peroxides and hydroxo-peroxides of uranyl and singly charged (Li+, Na+, K+, Rb+, Nb+ and Cs+) or doubly charged (Ca2+) metal cations as well as peroxides and hydroxo-peroxides in which uranyl is associated both with a singly charged metal cation and with a doubly charged metal cation (K+/Mg2+) are also known (Nyman et al., InorganicChemistry 2010, 49, 7748-7755, Reference [1]; Alcock et al., Journal of the Chemical Society A: Inorganic, Physical, Theoretical 1968, 1588, Reference [2]; Kubatko et al., InorganicChemistry 2007, 46, 3657-3662, Reference [3]; Unruh et al., Inorganic Chemistry 2009, 48, 2346-2348, Reference [4]). These mixed peroxides and hydroxo-peroxides of uranyl and singly/doubly charged metal cations are synthesized using so-called «direct synthesis» processes whereby typically a uranyl salt is reacted with a salt or hydroxide of the singly/doubly charged metal cation in the presence of hydrogen peroxide. It so happens that these processes do not work for the synthesis of mixed peroxides or hydroxo-peroxides of uranyl and triply or quadruply charged metal cations, and additionally that nobody to date has proposed an alternative process which would allow the synthesis of said peroxides or hydroxo-peroxides. Yet, insofar as metal peroxides and hydroxo-peroxides are compounds able to be converted to metal oxides by calcining, it would be desirable to be able to synthesize mixed peroxides and hydroxo-peroxides of uranyl and triply or quadruply charged metal cations, and in particular of uranyl and actinides(III) or (IV) for the subsequent production, from these mixed peroxides, and hydroxo-peroxides of mixed oxides of uranium and actinides(III) or (IV) suitable for use in the manufacture of nuclear fuels. The Inventors therefore set out to provide a process allowing the synthesis of mixed peroxides and hydroxo-peroxides of uranyl and triply or quadruply charged metal cations. A further objective was to provide a process that is relatively simple to implement and has a cost compatible with operation on an industrial scale. Yet, as part of their research, the Inventors ascertained that if a mixed peroxide or hydroxo-peroxide of uranyl and of at least one singly charged metal cation is contacted with a solution of a salt of a triply charged or quadruply charged metal cation, in fully surprising manner there occurs cationic exchange between the peroxide or hydroxo-peroxide and the salt so that the peroxide or hydroxo-peroxide with singly charged metal cation becomes a peroxide or hydroxo-peroxide with triply or quadruply charged metal cation. They additionally found that this cation exchange also occurs if the salt, the solution of which is contacted with the peroxide or hydroxo-peroxide, is a salt of a doubly charged metal cation such as a strontium salt. It is on these findings that the present invention is based. The subject of the invention is therefore firstly a process for synthesizing a compound C1 selected from mixed peroxides and hydroxo-peroxides of an actinyl and of at least one cation X1, wherein: the actinyl meets formula AnO2q+ where An is an actinide selected from uranium and neptunium, and q equals 1 (when An is neptunium(V)) or 2 (when An is uranium or neptunium(VI)); said at least one cation X1 is a double, triply or quadruply charged metal cation, provided however that this metal differs from An; which process comprises the reaction, in a solvent, of a salt of said at least one cation X1, e.g. a nitrate, chloride or sulfate, with a compound C2 selected from mixed peroxides and hydroxo-peroxides of the actinyl and of at least one singly charged cation X2, whereby compound C2 is converted to compound C1 by replacement of said at least one cation X2 by said at least one cation X1. It is to be understood that all the mixed peroxides and hydroxo-peroxides under consideration in the foregoing and in the remainder hereof can be in hydrated form, i.e. a form in which they are combined with molecules of water, or in anhydrous form. As indicated in the foregoing, the actinyl may be a uranyl or neptunyl, preference being given to uranyl. According to the invention, each cation X1 may be a cation of any metal able to form a doubly charged cation, triply charged cation and/or quadruply charged cation. Therefore it may be: a cation of an alkaline-earth metal namely: Be2+, Mg2+, Ca2+, Sr2+, Ba2+ or Ra2+; or a cation of a post-transition metal, for example: Al3+, Ga3+, In3+, Sn2+, Sn4+; Tl3+; Pb2+; Pb4+ or Bi3+; or a cation of a transition metal, for example: Sc3+, Ti4+, V3+, Cr3+, Mn2+, Mn3+, Mn4+, Fe2+, Fe3+, Co2+, Co3+, Ni2+, Cu2+, Zn2+, Y3+, Zr4+, Nb3+, Mo2+, Mo3+, Mo4+, Tc4+, Ru2+, Ru3+, Ru4+, Rh2+, Rh3+, Rh4+, Pd2+, Cd2+, Hf4+, Ta3+, Ta4+, W3+, W4+, Re2+, Re3+, Re4+, Os4+, Ir3+, Ir4+, Pt2+, Pt4+, Au3+ or Hg2+; or a cation of a lanthanide, for example: La3+, Ce3+, Ce4+, Pr3+, Nd3+, Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+ or Lu3+; or still a cation of an actinide, for example: Ac3+, Th4+, Pa3+, Pa4+, U3+, U4+, Np3+, Np4+, Pu3+, Pu4+, Am3+ or Cm3+. Each singly charged cation X2 may be any metal or non-metal, monoatomic or polyatomic singly charged cation. In particular, it may therefore be: a cation of alkaline metal, namely: Li+, Na+, K+, Rb+, Cs+ and Fr+; or a cation of a transition metal, for example: Cu+, Ag+, Au+ and Hg+; or still a polyatomic cation, for example: ammonium NH4+, alkylammonium such as methylammonium (CH3)NH3+ or ethylammonium (C2H5)NH3+, dialkylammonium such as dimethylammonium (CH3)2NH2+ or diethylammonium (C2H5)2NH2+, trialkylammonium such as trimethylammonium (CH3)3NH+ or triethylammonium (C2H5)3NH+, tetraalkylammonium such as tetramethylammonium (CH3)4N+ or tetraethylammonium (C2H5)4N+, hydrazinium N2H5+, oxonium H3O+, or still hydroxylammonium NH4OH+. According to the invention, the reaction of said at least one cation X1 with compound C2 is preferably performed by adding a solution of the salt of said at least one cation X1 to compound C2 and leaving the reaction mixture to stand preferably at ambient temperature for sufficient time to obtain the replacement of said at least one cation X2 by said at least one cation X1. Typically, 15 to 60 minutes are sufficient to reach a quantitative reaction. The solution of the salt of said at least one cation X1 is advantageously an aqueous solution, this aqueous solution preferably being prepared with deionized water to prevent any cations which may be contained in the water from perturbing the replacement of said at least one cation X2 by said at least one cation X1. After the reaction, compound C1 can be recovered, for example by vacuum filtration, washed, for example in ethanol, and dried. Preferably the process of the invention further comprises a synthesis of compound C2. This synthesis can be performed using any method proposed in the literature for the synthesis of a peroxide or hydroxo-peroxide of uranyl and of at least one singly-charged metal cation, or adapted from said method. In particular, this synthesis can be performed using a method which comprises the reaction of a first aqueous solution comprising a salt of the actinide An, e.g. a nitrate, chloride or sulfate, with a n alkaline second aqueous solution comprising a salt or hydroxide of said at least one cation X2 and hydrogen peroxide. This reaction is preferably conducted by adding the first solution to the second under agitation and advantageously in a receptacle held at a temperature in the order of 0 to 5° C., and leaving the reaction medium obtained to stand for sufficient time, typically one to ten hours, to obtain formation of compound C2. After the reaction, C2 can be recovered, for example by vacuum filtration, washed, for example in ethanol, and dried. According to one preferred provision of the invention, compound C1 meets following general formula (I):(X1m+)r1[(AnO2q+)n(O22−)p−x(OH−)2x](2p−qn)− (I)where: An and q are such as previously defined; m equals 2 (when X1 is a double charged cation), 3 (when X1 is a triply charged cation) or 4 (when X1 is a quadruply charged cation); n is an even integer, of 2 or higher; x is an integer equal to 0 (when compound C1 is a peroxide) or higher than 0 (when compound C1 is a hydroxo-peroxide); p is an integer higher than x; and n, p and r1 are such that:1.5≤p/n≤2; and0<r1=(2p−qn)/m (to heed the electroneutrality of compound C1). In which case, compound C2 meets following general formula (II):(X2+)r2[(AnO2q+)n(O22−)p−x(OH−)2x](2p−qn)− (II)where: An, q, n, x and p are such as previously defined; and0<r2=2p−qn. In the invention, it is preferred that, in above general formula (I) and, hence, above general formula (II), n should be an even integer ranging from 2 to 60 and better still from 16 to 60 (i.e. equaling 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58 or 60), in which case compound C1 is in the form of an open or closed cluster formed of n actinyl ions linked by peroxo or di-hydroxo bridges. Also, it is preferred that said at least one cation X1 should be a cation of an actinide, in particular a uranium cation (if An itself is not uranium), neptunium (if An itself is not neptunium), plutonium, thorium, americium or curium, or else a cation of a lanthanide, in particular a neodymium, cerium, gadolinium or samarium cation, whether or not compound C1 meets above general formula (I). Finally, it is preferred that said at least one cation X2 should be an ammonium cation, also whether or not compound C2 meets above general formula (II). For this purpose, it is sufficient for example to use ammonia as source of said at least one cation X2 for synthesis of compound C2. As previously mentioned, the metal peroxides and hydroxo-peroxides can be converted to oxides by calcining. A further subject of the invention is therefore a process for synthesizing a mixed oxide of an actinide An selected from uranium and neptunium, and of at least one metal able to form a doubly, triply or quadruply charged cation, the metal differing from An, which process comprises: synthesizing a mixed peroxide or hydroxo-peroxide of an actinyl of formula AnO2q+ where q equals 1 or 2, and of at least one doubly, triply or quadruply charged metal cation, using a process such as previously defined; and calcining the peroxide or hydroxo-peroxide thus synthesized. This calcining can be performed under different conditions depending on the type of mixed oxide it is desired to obtain having regard to the intended use thereof. For example, the Inventors have found that the calcining of a mixed hydroxo-peroxide of uranyl and neodymium leads to a mixed oxide when it is performed at a temperature in the order of 1 300 to 1 400° C. in air, whilst a mixed oxide having different oxygen stoichiometry is obtained when calcining is performed at a temperature in the order of 800 to 900° C. in a reducing atmosphere (e.g. H2/N2 3/97 v/v). Calcining conditions are therefore to be chosen as a function of the end use of the mixed oxide. Among the mixed peroxides and hydroxo-peroxides able to be obtained using the synthesis process of the invention, those meeting above general formula (I) have never, to the knowledge of the Inventors, been described in the literature. Therefore, a further subject of the invention is a mixed peroxide or hydroxo-peroxide of an actinyl and of at least one cation X1, wherein: the actinyl meets formula AnO2q+ where An is an actinide selected from uranium and neptunium, and q equals 1 or 2; said at least one cation X1 is a double, triply or quadruply charged metal cation, provided however that this metal differs from An; which peroxide or hydroxo-peroxide meets following general formula (I):(X1m+)r1[(AnO2q+)n(O22−)p−x(OH−)2x](2p−qn)− (I)where: m equals 2, 3 or 4; n is an even integer, of 2 or higher; x is an integer of 0 or higher; p is an integer higher than x; and n, p and r1 are such that 1.5≤p/n≤2 and 0<r1=(2p−qn)/m. Here too, it is preferred that n should be an even integer ranging from 2 to 60 and better still from 16 to 60, as it is also preferred that said at least one tout cation X1 should be a cation of an actinide, in particular a uranium, neptunium, plutonium, thorium, americium or curium cation, or else a cation of a lanthanide, in particular a neodymium, cerium, gadolinium or samarium cation. A further subject of the invention is the use of a mixed peroxide or hydroxo-peroxide of an actinyl and at least one cation X1, wherein: the actinyl meets formula AnO2q+ where An is an actinide selected from uranium and neptunium, and q equals 1 or 2; said at least one cation X1 is a doubly, triply or quadruply charged metal cation, provided however that this metal differs from An; which peroxide or hydroxo-peroxide is such as defined above; for the synthesis of a mixed oxide of the actinide and of the metal. Other characteristics and advantages of the invention will become better apparent on reading the remainder of the description below which relates to examples of synthesis of mixed peroxides and hydroxo-peroxides according to the invention and of mixed oxides by calcining these peroxides and hydroxo-peroxides. Evidently these examples are only given to illustrate the subject of the invention and do not in any way limit this subject. 1.1—Synthesis of the Mixed Hydroxo-Peroxide of Uranyl(VI) and Neodymium(III): The mixed hydroxo-peroxide of uranyl(VI) and neodymium(III)—hereafter called U32R-Nd—of following particular formula (Ia):Nd40/3[(UO2)32(O2)40(OH)24] (Ia),is synthesized in hydrated form by first synthesizing a mixed hydroxo-peroxide of uranyl(VI) and ammonium—hereafter called U32R-NH4—then substituting the ammonium cations of this hydroxo-peroxide by neodymium cations. Synthesis of Hydroxo-Peroxide U32R-NH4: A first aqueous solution of uranyl(VI) nitrate (UO2(NO3)2.6H2O) is prepared by dissolving 0.5 g of this nitrate in 6 mL of deionized water. This solution contains 0.996 mmol uranium(VI). In parallel, a second aqueous solution is prepared by mixing 4 mL of an aqueous solution comprising 4 mol/L ammonia (NH4OH) with 3 mL of 30% v/v aqueous solution of hydrogen peroxide (H2O2). The solution obtained contains 16 mmol of ammonia and 29.37 mmol of hydrogen peroxide. The first solution is added dropwise to the second under agitation, having placed the first solution over an ice bath. On completion of the addition, agitation is discontinued allowing rapid crystallisation of hydroxo-peroxide U32R-NH4. After 10 hours, crystallisation is quantitative. The solid formed is recovered by vacuum filtration and washed in 5 mL ethanol. Synthesis of Hydroxo-Peroxide U32R-Nd: An aqueous solution of neodymium(III) nitrate (Nd(NO3)3.6H2O) is prepared by dissolving 0.218 g of this nitrate in 10 mL of deionized water. This solution contains 0.497 mmol neodymium(III). This solution is poured into a beaker containing the solid previously obtained and left to stand. Thirty minutes later, the solid is recovered by vacuum filtration and washed in 5 mL of ethanol. It is formed of a powder and a few single crystals. The characterization of this solid given below shows that it is formed of a mixed hydroxo-peroxide of uranium(VI) and neodymium(III). 1.2—Synthesis of the Mixed Oxides of Uranium and Neodymium: Two mixed oxides of uranium and neodymium—hereafter called oxides 1 and 2—are synthesized by calcining the hydroxo-peroxide U32R-Nd obtained under item 1.1 above. Oxide 1 is obtained by performing this calcining in air at 1 400° C. for 12 hours (with temperature rise and decrease ramp rate of 300° C./h). It has the formula U0.71Nd0.29O2+δ, with (δ≥0). Oxide 2 is obtained by performing the calcining at 800° C., in a reducing atmosphere (H2/N2 3:97 v/v, with temperature rise and decrease ramp rate of 300° C./hour without any temperature hold). It has the formula U0.71Nd0.29O2+δ, with (δ≥0). 1.3—Characterization of Hydroxo-Peroxides U32R-NH4 and U32R-Nd: Single Crystal XRD Analysis: Analysis by single crystal X-ray diffraction of hydroxo-peroxide U32R-NH4 shows that this hydroxo-peroxide has a similar structure to that of the uranyl hydroxo-peroxide U32R-1 described by Sigmon et al., Journal of the American Chemical Society 2011, 131, 16648-16649, Reference [5], but differs therefrom in that it comprises a uranium atom in the centre of the U32R crown cluster. Single crystal XRD analysis of hydroxo-peroxide U32R-Nd shows that this hydroxo-peroxide has a similar structure to that of hydroxo-peroxide U32R-NH4 but differs therefrom in that it comprises Nd3+ ions to compensate the framework anion charge in replacement of the ammonium ions. As can be seen in FIG. 1, parts A and B, in which the neodymium atoms are substantiated by black circles, these atoms are present both inside the U32R crown but also outside this crown. In addition they are linked to the U32R crown via the oxygens of the uranyl ions of the hydroxo-peroxide. The Nd/U ratio determined with this analysis is 0.34. Powder XRD Analysis: As indicated in aforementioned Reference [5] for U32R-1 hydroxo-peroxide, hydroxo-peroxide U32R-NH4 very rapidly loses its crystallinity. As can be seen in FIG. 2, parts A and B, powder XRD analysis performed 10 minutes after obtaining this hydroxo-peroxide nevertheless gives an X-diffractogram (part B) corresponding to the one calculated (part A) from the structure such as determined by single crystal X-ray diffraction. One hour after it has been obtained, hydroxo-peroxide U32R-NH4 has become practically amorphous (part C). On the other hand, as shown by part D in FIG. 2, powder XRD analysis of hydroxo-peroxide U32R-Nd evidences much stronger crystallinity of this compound compared with that of hydroxo-peroxide U32R-NH4 and it is maintained over time due to inter-cluster links involving Nd3+ ions that are stronger than those existing with ammonium ions. ICP-AES and EDS Analyses: Analysis by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of hydroxo-peroxide U32R-Nd indicates a Nd/U ratio of 0.4. Analysis by energy dispersive spectrometry (EDS) indicates a Nd/U ratio of 0.42. These Nd/U ratios are slightly higher than the ratio obtained by single crystal X-ray diffraction which is 0.34, and can be accounted for: either by the presence of neodymium atoms in the single crystal occupying sites with low occupation rate and non-localised; or by under-estimated occupation rates; or still by the fact that the single crystals contain less neodymium than the whole powder. 1.4—Characterization of Oxide 1: Powder XRD Analysis: Powder XRD analysis of oxide 1 shows that this oxide is formed of a phase having a fluorine structure (FIG. 3). The lattice parameter of this oxide (a=5.4356(7) Å) is slightly lower than that of uranium dioxide UO2 (a=5,468(1) Å), indicating that the oxide is indeed a mixed oxide. TGA and HTXRD Analyses: The calcining temperature of 1 400° C. in air was set further to a study on the thermal decomposition of hydroxo-peroxide U32R-Nd that was carried out using thermogravimetric analysis (TGA) in air up to 1 300° C. (this corresponding to the maximum temperature of use of the equipment used) and by high temperature X-ray diffraction (HTXRD) in air up to 1 110° C. (this corresponding to the maximum temperature of use of the equipment used). As shown by the gravimetric curve in FIG. 4, TGA analysis of this hydroxo-peroxide shows that its decomposition is not complete at 1 300° C., as confirmed by HTXRD analysis which specifies thermal decomposition mechanisms up to 1 100° C. Therefore, as shown by the X-diffractogram in FIG. 5, α-UO3 crystallises on and after 575° C. in a mixture with a small proportion of fluorine phase denoted F in this Figure. Then at 800° C., α-UO3 is converted to α-U3O8 and the proportion of fluorine phase increases with temperature. Finally, U2O5 is obtained on and after 1 000° C. again in a mixture with a fluorine phase the quantity of which continues to increase with temperature. ICP-AES Analysis: ICP-AES analysis of oxide 1 indicates a Nd/U ratio of 0.42. Analysis by Castaing Microprobe: Mapping of a cross-section of the grains of oxide 1 is carried out using an electronic microprobe or Castaing microprobe on a pellet prepared by placing oxide 1 obtained under item 1.2 above in a resin, followed by polishing of this pellet. This mapping confirms that this oxide 1 is—a mixed oxide of uranium and neodymium with the simultaneous presence of uranium and neodymium within one same grain. Analysis by UV-Visible Spectrometry: An aqueous solution prepared by dissolving oxide 1 in concentrated phosphoric acid (H3PO4, 65% v/v) is analysed by UV-visible spectrometry. As shown by the spectrum in FIG. 6, uranium is present in this oxide at oxidation degrees IV and VI to compensate for the neodymium charge in the oxide of fluorine structure U0.71Nd0.29O2+δ, with (δ≥0). To conclude: by calcining in air at 1 400° C. the hydroxo-peroxide U32R-Nd obtained under item 1.1 above, a fluorine phase is obtained which corresponds to a mixed stoichiometric oxide having a composition close to U0.71Nd0.29O2+δ, with (δ≥0). 1.5—Characterization of Oxide 2: Powder XRD Analysis: Powder XRD analysis of oxide 2 shows that this oxide is formed of a phase having a fluorine structure (FIG. 7). The lattice parameter of this oxide (a=5.4484(4) Å) is slightly lower than that of uranium dioxide UO2 (a=5.468(1) Å), indicating the presence of a mixed oxide. Widening of the beams (compared with FIG. 3) can be accounted for by the fact that oxide 2 has a smaller particle size than oxide 1 because sintering phenomena are less present at 800° C. than at 1400° C. In addition, oxide 2 was obtained by calcining without a temperature hold whereas the calcining which led to oxide 1 was conducted with a 12-hour temperature hold. HTXRD Analysis: HTXRD analysis of the hydroxo-peroxide U32R-Nd was performed up to 800° C., in a reducing atmosphere (H2/N2 3/97 v/v). As shown in the X-diffractogram in FIG. 8 it can be seen that on and after 500° C. there occurs crystallisation of a sub-stoichiometric oxide with fluorine structure U0.71Nd0.29O2+δ, with (δ≥0)(▴). The beams between 2θ values ranging from 15° to 27° and the beam at 2θ=44° are those of the sample holder used for this analysis, namely a gold-leaf coated alumina crucible. Analysis by UV-Visible Spectrometry: An aqueous solution prepared by dissolving oxide 2 in concentrated phosphoric acid (H3PO4, 65% v/v) is analysed by UV-visible spectrometry. As shown in FIG. 9 which gives the UV-visible spectrum obtained for this solution (curve A) and the spectrum obtained for the solution of oxide 1 previously analysed under item 1.4 above (curve B), uranium is contained in the oxide at oxidation degrees IV and VI as in oxide 1. However the proportion of uranium(IV) in oxide 2 is much higher than in oxide 1. To conclude: by calcining at 800° C. in a reducing atmosphere the hydroxo-peroxide U32R-Nd obtained under item 1.1 ci-above, a fluorine phase is obtained which corresponds to a non-stoichiometric mixed oxide having a composition close to that of U0.71Nd0.29O2+δ, with (δ≥0). 2.1—Synthesis of the Mixed Hydroxo-Peroxide of Uranyl(VI) and Thorium(IV): The mixed hydroxo-peroxide of uranyl(VI) and thorium(IV)—hereafter called U32R-Th—having following particular formula (Ib):Th10[(UO2)32(O2)40(OH)24] (Ib),is synthesized in hydrated form by substituting the ammonium cations of hydroxo-peroxide U32R-NH4 by thorium cations. For this purpose, after synthesizing hydroxo-peroxide U32R-NH4 following the same operating protocol as described under item 1.1 above, an aqueous solution of thorium(IV) nitrate is prepared (Th(NO3)4.5H2O) by dissolving 0.285 g of this nitrate in 10 mL of deionized water. This solution contains 0.5 mmol of thorium(IV). It is poured into a beaker containing the hydroxo-peroxide U32R-NH4 previously obtained and left to stand. Thirty minutes later, the solid is recovered by vacuum filtration and washed in 5 mL ethanol. The characterization of this solid given below shows that it is formed of a mixed hydroxo-peroxide of uranium(VI) and thorium(IV). 2.2—Characterization of Hydroxo-Peroxide U32R-Th: Single crystal XRD analysis of hydroxo-peroxide U32R-Th shows that this hydroxo-peroxide has a similar structure to that of hydroxo-peroxide U32R-NH4 but differs from the latter in that it comprises Th4+ ions to compensate the framework anion charge in replacement of the ammonium ions. As can be seen in FIG. 10, parts A and B, in which the thorium atoms are substantiated by black circles, these atoms are present both inside the U32R crown cluster and outside this crown. In addition, they are linked to the U32R crown via the oxygens of the uranyl ions of the hydroxo-peroxide. The Th/U ratio determined under structural resolution analysis is 0.20. 3.1—Synthesis of the Mixed Hydroxo-Peroxide of Uranyl(VI) and Strontium(II): The mixed hydroxo-peroxide of uranyl(VI) and strontium(II)—hereafter called U32R-Sr—of following particular formula (Ic):Sr20[(UO2)32(O2)40(OH)24] (Ic),is synthesized in hydrated form by substituting the ammonium cations of a hydroxo-peroxide U32R-NH4 by strontium cations. For this purpose, after synthesizing hydroxo-peroxide U32R-NH4 following the same operating protocol as described under item 1.1 above, an aqueous solution of strontium(II) nitrate (Sr(NO3)4) is prepared by dissolving 0.212 g of this nitrate in 20 mL of deionized water. This solution contains 1 mmol of strontium(II). It is poured into a beaker containing the hydroxo-peroxide U32R-NH4 previously obtained and left to stand. Thirty minutes later, the solid is recovered by vacuum filtration and washed in 5 mL of ethanol. The characterization of this solid given below shows that it is formed of a mixed uranium(VI) and strontium(II) hydroxo-peroxide. 3.2—Characterization of Hydroxo-Peroxide U32R-Sr: Single Crystal XRD Analysis: Single crystal XRD analysis of hydroxo-peroxide U32R-Sr shows that this hydroxo-peroxide has a similar structure to that of hydroxo-peroxide U32R-NH4 but differs from the latter in that it comprises Sr2+ ions to compensate the framework anion charge in replacement of the ammonium ions. As can be seen in FIG. 11, parts A and B, in which the strontium atoms are substantiated by black circles, these atoms are present both inside the U32R crown and also outside this crown. In addition, they are linked to the U32R crown via the oxygens of the uranyl ions of the hydroxo-peroxide. The Sr/U ratio determined under structural resolution analysis is 0.42. ICP-AES Analysis: ICP-AES analysis of hydroxo-peroxide U32R-Sr gives a Sr/U ratio of 0.51. 4.1—Synthesis of the Mixed Peroxide of Uranyl(VI) and Neodymium(III): The mixed peroxide of uranyl(VI) and neodymium(III)—hereafter called U28-Nd—of following particular formula (Id):Nd20[(UO2)28(O2)42] (Id),is synthesized in hydrated form by first synthesizing a mixed peroxide of uranyl(VI) and ammonium—hereafter called U28-NH4—then substituting the ammonium cations of this peroxide by neodymium cations. Synthesis of U28-NH4 Peroxide: A first aqueous solution is prepared comprising 0.067 mol/L of uranyl(VI) nitrate (UO2(NO3)2.6H2O) by dissolving 0.625 g of this nitrate in 18.75 mL of deionized water, and 0.093 mol/L of ammonium oxalate ((NH4)2C2O4.H2O) by dissolving 0.250 g of this oxalate in the preceding mixture. The solution obtained contains 1.25 mmol of uranium(VI) and 1.75 mmol of ammonium. In parallel, a second aqueous solution is prepared comprising 1 mol/L of hydrogen peroxide by diluting 638 μL of 30% v/v hydrogen peroxide in 6.25 mL of deionized water. The solution obtained contains 6.25 mmol of hydrogen peroxide. Under agitation in a beaker, the second solution is added to the first. The pH of the reaction mixture being about 1.43, it is adjusted to 8 by adding 7.9 mL of 1M ammonia under agitation. The beaker is transferred to a hermetically sealed jar containing 33 mL methanol, allowing crystallisation of U28-NH4 peroxide by vapour diffusion and solvent modification. After two weeks, a solid corresponding to a mixture of powder and crystals is formed at the bottom of the beaker and is recovered by vacuum filtration and washed in 5 mL ethanol. Synthesis of U28-Nd Peroxide: An aqueous solution of neodymium(III) nitrate (Nd(NO3)3.6H2O) is prepared by dissolving 0.218 g of this nitrate in 10 mL of deionized water. This solution contains 0.497 mmol of neodymium(III). This solution is poured into a beaker containing the U28-NH4 peroxide previously obtained and left to stand. Thirty minutes later, the solid is recovered by vacuum filtration and washed in 5 mL ethanol. The characterization of this solid given below shows that it is formed of a mixed peroxide of uranium(VI) and neodymium(III). 4.2—Synthesis of the Mixed Oxide of Uranium and Neodymium A mixed oxide of uranium and neodymium—hereafter called oxide 3—is synthesized by calcining the U28-Nd peroxide obtained under item 4.1 above in air, at 1 400° C. for 12 hours (with a temperature rise and decrease ramp rate of 300° C./h). This oxide has the formula U0.73Nd0.27O2+δ, with (δ≥0). 4.3—Characterization of Peroxides U28-NH4 and U28-Nd: Single Crystal XRD Analysis: Single crystal XRD analysis of U28-NH4 peroxide shows that this peroxide has a structure similar to that of the uranyl peroxide U28 described by Burns et al., AngewandteChemie International Edition 2005, 44, 2135-2139, Reference [6]: it is a sphere with 28 uranium atoms composed of triperoxide bricks, the neutrality thereof being ensured by the ammonium ions. Powder XRD Analysis: U28-NH4 peroxide loses its crystallinity very rapidly. As can be seen in FIG. 12 parts A and B, powder XRD analysis performed 10 minutes after obtaining this peroxide nevertheless gives an X-diffractogram (part B) corresponding to the one calculated (part A) from the structure such as determined by single-crystal X-ray diffraction. In part B, the beams substantiated by a star (*) are those of the sample holder in polytetrafluoroethylene used for this analysis. As can be seen in FIG. 13, part C, powder XRD analysis of U28-Nd peroxide shows that it is amorphous. ICP-AES Analysis: ICP-AES analysis of U28-Nd peroxide gives a Nd/U ratio of 0.369. 4.4—Characterization of the Mixed Oxide of Uranium and Neodymium: Powder XRD analysis of oxide 3 shows that this oxide is formed of a phase having a fluorine structure (FIG. 13). The lattice parameter of this oxide (a=5.434(4) Å) is slightly lower than that of uranium dioxide UO2 (a=5.468(1) Å), indicating that this is indeed a mixed oxide. To conclude: by calcining in air at 1 400° C. the U28-Nd peroxide obtained under item 4.2 above, a fluorine phase is obtained which corresponds to a mixed oxide having a composition close to U0.73Nd0.27O2+δ, with (δ≥0). [1] Nyman et al., Inorganic Chemistry 2010, 49, 7748-7755 [2] Alcock et al., Journal of the Chemical Society A: Inorganic, Physical, Theoretical 1968, 1588 [3] Kubatko et al., Inorganic Chemistry 2007, 46, 3657-3662 [4] Unruh et al., Inorganic Chemistry 2009, 48, 2346-2348 [5] Sigmon et al., Journal of the American Chemical Society 2011, 131, 16648-16649 [6] Burns et al., AngewandteChemie International Edition 2005, 44, 2135-2139 |
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description | This application is a U.S. 371 Application from PCT/RU2017/000473 filed Jun. 30, 2017, the technical disclosures of which are hereby incorporated herein by reference. The invention relates to power engineering, in particular, to process control devices for ensuring reliable operation of the power plant equipment using process circuit water chemistry control means. Power plants, including nuclear power plants (NPPs) with water-cooled reactors, relate to highly technical and complex facilities. Given that the energy source at these facilities is a controlled nuclear fission reaction, closer attention is paid to assurance of safe and reliable operation of such power plants. Maintenance of the required water quality of the primary and secondary circuits of nuclear power plants is one of essential conditions ensuring safe, reliable and cost-efficient operation of NPPs (refer to NP-001-15 “General Safety Provisions for Nuclear Power Plants” at https://www.seogan.ru/np-001-15). Chemical control systems are designed to ensure receipt of the latest information about the water chemistry condition based on the measurements of the rated and diagnostic parameters of the process circuit aqueous media. Management of water chemistry quality indices is based on the data received from the chemical control systems. The scope or composition of the measured quality indices shall ensure receipt of sufficient information for relevant assessments of the current process circuit water chemistry condition and the corrosion of the equipment in these circuits. The collection, processing, archiving and display of the chemical control data shall be ensured by the system-level application of modern hardware and software products. (STO 1.1.1.03.004.0980-2014 “Water Chemistry of the Primary Circuit during Commissioning of the Nuclear Power Plant Unit under AES-2006 Project. Coolant Quality Standards and Supporting Means”. STO1.1.1.03.004.0979-2014 “Water Chemistry of the Secondary Circuit during Commissioning of the Nuclear Power Plant Unit under AES-2006 Project. Working Medium Quality Standards and Supporting Means” at http://www.snti.ru/snips_rd3.htm). A system for monitoring and protecting pipelines against corrosion is disclosed (refer to Patent RU2200895; IPC F16L 58/00; published on Mar. 20, 2003), including a pipeline; two to eight independent control channels, each containing a corrosion rate sensor comprising a corrosion measuring transducer and a sensor interface device; and an actuator for inhibitor injection comprising a dispenser and a dispenser interface device; wherein a microcontroller is integrated into each channel of the system connected to the device designed for control, processing and storage of information by a computer. The disadvantage of the disclosed system is its failure to ensure reliable operation of power plants, for example, for the primary and secondary circuits with water-cooled water-moderated power reactors (VVER type reactors) and pressurized water reactors (PWRs) at the design power, in transient modes or in cleaning, passivation and outage modes. The system does not take into account any essential differences in the parameters of the filling medium conditions and process circuit hydraulic characteristics, even within the same power plant, as compared to any pipeline route. A chemical control system for the coolant of a water-cooled reactor is disclosed (refer to JP2581833, IPC G01N 17/02, published on Feb. 12, 1997), including an electrochemical potential sensor installed in the coolant and connected to a potentiostat with its output further connected to a computer equipped with a memory unit and a monitor. The computer is connected to an actuator for gas or chemical reagent injection. The disadvantage of the disclosed system is arrangement of sensors in the active evaporation area, as well as directly in the neutron field. As is known, many materials, including elements of insulating materials and conductor wires of the sensors, when exposed to neutrons, change their physical and mechanical properties. The period of reliable operation of sensors of the disclosed system is clearly less than that in the neutron field compared to the duration of operation of similar equipment beyond its limits, and sensors may be replaced only during the shutdown of the power unit for refueling. In addition, in the active evaporation area, the measured values, especially the concentrations of dissolved gases, will fluctuate to a great extent. Averaging of these values in due course will lead to an underestimation of the actual amount of injected hydrogen and other reagents due to migration of the dissolved gases into bubbles, the capture of reagents by corrosion products then, when further concentrated and deposited, on the heat transfer surface of the fuel. Consequently, the hydrogen and other reagents metering control will be conservatively overestimated by the amount of an uncertainty related to dispersion in the readings of the disclosed system sensors. A power plant chemical control system is disclosed, which coincides with this engineering solution in the maximum number of essential features and is accepted as a prototype (EP0661538, IPC G01N 17/02, G21C 17/02, published on Jul. 5, 1995). The prototype system includes installation of a coolant electrochemical indication sensor in the reactor core and its connection for corrosion potential calculation to the measuring data processing and transmission unit with its output connected to the central computer system operating the actuator for hydrogen and chemical reagents injection. The system may also include a dissolved oxygen sensor, a hydrogen peroxide sensor, an electrical conductivity sensor, and a pH sensor. Location of the coolant electrochemical indicator sensor in the reactor core minimizes the transport lag time (the period of time between the sample exit from the sampling point and the achievement of the sampling sensor). The disadvantage of the disclosed system is that under the conditions of a powerful radiation field of the reactor core, the duration of operation of sensors and system elements is less compared to the duration of operation of similar equipment beyond its limits, and replacement of sensors and system elements is possible only during power unit shutdown for refueling. All elements of the system are to be replaced due to high induced activity, including electrodes of the polarization resistance sensor. At the same time, regular updating of the sensor surface state when changing them reduces the reliability of the predictive estimates of corrosion wear, since the overall corrosion decreases over time along the parabola, while corrosion properties of the medium remain unchanged. In case of water chemistry quality fluctuations, the response function of the replaced electrodes with the surface oxide film differing significantly from that formed on the surface of the circuit equipment over a long period, will be less reliable for substantiating the selection of quantitative characteristics and the use of the coolant parameters optimization means. The objective of this engineering solution is to develop such a power plant chemical control system that would ensure a longer service life of the sensors while maintaining reliable values of the rated and diagnostic parameters of the water media in process circuits at power, transient modes or in cleaning, passivation and outage modes. The stated objective is achieved by the fact that the power plant chemical control system includes at least one coolant electrochemical indication sensor electrically connected to the measurement data processing and transmission unit, with its output connected to a central programmable controller for the actuator for injection of hydrogen and chemical reagents. The coolant electrochemical indication sensor is of a flow type, its hydraulic input is connected by a sampling tube to the process circuit of the power plant, and its hydraulic output is hydraulically connected to the first heat exchanger and the first throttling device with a reversible coolant supply circuit in series. Removal of the coolant electrochemical indication sensor from the heavy-duty radiation field of the reactor core provides for a longer service life of the sensor. In this case, the sample coolant passing through the sensor is discharge into the drain line through the first heat exchanger to reduce the coolant temperature and the throttling device to reduce pressure and flow rate. In order to avoid a decrease in the flow rate of the coolant sample, and thus to extend the transport lag time due to the gradual clogging of the throttling device with iron corrosion products leading to reduction in the diameter of the throttling device opening, the throttling device is provided with a reversible coolant supply circuit that maintains a constant flow rate of the sample through the coolant electrochemical indication sensor. The reverse circuit is especially important when the reactor is operated in transient modes (start-up, shutdown), when the power unit capacity is changed, including emergency trips. Changes in the reactor/boiler unit power or switching of the pumps are accompanied by an increase in the coolant of suspended insoluble particles of corrosion products forming the surface loose and poorly adherent to the dense protective oxide films deposits under stationary conditions. The reversible circuit in these cases ensures maintenance of the constant sample flow through electrochemical sensors, which ensures receipt of reliable values of rated and diagnostic parameters of the aqueous media in the process circuits. The coolant electrochemical indication sensor may be made in the form of a flow-type sensor of the polarization resistance. The coolant electrochemical indication sensor may be made in the form of a flow-type sensor of the electrochemical potential. The coolant electrochemical indication sensor may be installed in the primary process circuit of the power plant. The working coolant electrochemical indicator sensor may be installed in the secondary process circuit of the power plant. The chemical control system of the power plant may include a dissolved oxygen sensor, and/or a dissolved hydrogen sensor, and/or an electrical conductivity sensor, and/or a pH sensor mounted between the second heat exchanger hydraulically connected to the process circuit of the power plant and the second throttling device or the installed after the throttling device. The coolant electrochemical indication sensors of this chemical control system of the power plant can be installed in the process circuits of various power plants: circulation circuits of boiling-type reactors, such as BWR (boiling water reactor) and RBMK (high power channel reactor), in the primary and secondary circuits of the NPPs with PWR and VVER reactors, in the circuits of thermal stations. But as an example, the power plant chemical control system of the primary circuit of a pressurized light-water reactor is considered below. The primary circuit of the power plant with a chemical control system (refer to FIG. 1) consists of a reactor pressure vessel (1) with a pressurizer (2), the primary circulation circuit equipment, including pipeline (3) for the heated coolant supply to the steam generator (4) and its return through the pipeline (5), the main circulation pump (6) through the pipeline (7) to the reactor pressure vessel (1). The system for controlling and maintaining the primary circuit water chemistry quality includes an outlet (8) and an inlet pipelines (9) connecting the reactor pressure vessel (1) to the equipment of the blowdown and makeup systems consisting of a regenerative heat exchanger (10), a coolant purification system on ion-exchange filters (11), and a make-up pump (12). The reactor pressure vessel (1) is hydraulically connected by a sampling tube (13) to the flow-type sensor (14) for the coolant electrochemical indication, for example, comprising a polarization resistance sensor “S1” (15) and an electrochemical potential sensor “S2” (16) that are hydraulically connected in series with the first heat exchanger (17) and the first throttling device (18) with a reversible coolant supply circuit (19). S1 (15) and S2 (16) may be connected in series (as shown in FIG. 1) or in parallel, depending on their structure and operating conditions. The first throttling device (18), for example, can be made in the form of a housing with inlet and outlet nozzles, wherein a set of throttling orifices is installed (not shown in the drawing). The hydraulic outlet of the first throttling device (18) is connected to the first drain line (20). The flow-type sensor “S1” (15) of the polarization resistance and the flow-type sensor “S2” (16) of the coolant electrochemical indication of the unit (14) (refer to FIG. 2) are electrically connected to the inlets of the first measurement data processing and transfer unit “U1” (21) with an outlet connected to a central computer, CPC (22), the control actuator “AD1” (23) for hydrogen injection and the actuator “AD2” (24) for injection of chemical reagents. The CPC (22) is equipped with a monitor (25) for visual control of the measurement data by the operator and making of managerial decisions during the power unit operation. S1 (15) and S2 (16), the first heat exchanger (17), the first throttling device (18) with a reversible circuit (19) and a measurement data processing and transfer unit “U1” (21) are located within the sealed reactor circuit and are not available for maintenance when operated at power. The chemical control system of the power plant may include (refer to FIG. 1), for example, a dissolved oxygen sensor “S3” (26), a dissolved hydrogen sensor “S4” (27), an electrical conductivity sensor “S5” (28) and a pH sensor “S6” (29) installed between the second heat exchanger (30) and the second throttling device (31), according to the structure of the first throttling device (18) (refer to FIG. 1), or may be installed after the second throttling device (31). S3 (26), S4 (27), S5 (28) and S6 (29) may be connected in parallel (as shown in FIG. 1) or in series, depending on their structure and operating conditions. The inlet of the second heat exchanger (30) can be hydraulically connected to the reactor pressure vessel (1) by removal from the tube (13) (one entry point) or by a sampling tube (32) (two entry points, as shown in FIG. 1). The second drain line (33) is designed for coolant samples passing through S3 (26), S4 (27), S5 (28) and S6 (29). S3 (26), S4 (27), S5 (28) and S6 (29) are electrically connected (refer to FIG. 2) to the second measurement data processing and transmission unit “U2” (34), the outlet of the U2 (34) is connected to the central computer (22). S3 (26), S4 (27), S5 (28) and S6 (29) are located outside of the sealed circuit of the reactor, and they are available for servicing when operated at power. Cooling of the sample in the second heat exchanger (30) creates acceptable operating conditions for the low-temperature sensors S3 (26), S4 (27), S5 (28) and S6 (29) and, in combination with the second throttling device (31), allows to reduce the pressure and to stabilize the sample medium flow rate, ensuring acceptable, according to the technical requirements, discharge of the spent sample into the second drainage line (33). FIG. 3 shows the first throttling device (18) with more detailed picture of the reversible coolant supply circuit (19). The reversible circuit (19) contains tubes (35, 36) for the reversible coolant sample supply and valves (37, 38, 39, 40) ensuring the reverse flow of the sample through the first throttling device (18). In case of forward direction of the sample flow through the first throttling device (18) towards the first drain line (20) (FIG. 1 and FIG. 2), the valves 37 and 38 are open and valves 39 and 40 are closed. The reverse flow of the sample through the first throttling device (17) during its flushing occurs if valves 37 and 38 are closed and valves 39 and 40 are open. This chemical control system of the power plant works as follows. The primary circuit coolant is automatically fed from the standard sampling points through the tube (13) to the set (14) of flow-type sensors for the electrochemical indication of the coolant containing, for example, S1 (15) for polarization resistance and S2 (16) for electrochemical potential; then the sample flow passes the first heat exchanger (17) and the first throttling device (18) with a reversible coolant supply circuit (19) for cleaning of the throttling device (18). The first heat exchanger (17) and the first throttling device (18) provide optimum values for the temperature, pressure and flow rate of the sample into the drain line (20). The signals from S1 (15) and S2 (16) are sent to the measurement data processing and transmitting unit U1 (21) and further to the CPC (22). At the same time, the working medium is fed through tube 32 (in one process connection option) or through tube 13 (in another process connection option) to the second heat exchanger (30) and passes at room temperature through S3 (26), S4 (27), S5 (28) and S6 (29) measuring the rated and diagnostic parameters related to the quality of the process circuit medium. The sample flow then passes through the second throttling device (31) and enters the drain line (33). The signals from S3 (26), S4 (27), S5 (28) and S6 (29) are sent to U2 (34) and then to the CPC (22). In the CPC (22), the processed measurement results of S (15), S2 (16), S3 (26), S4 (27), S5 (28) and S6 (29) are used to justify management decisions during power unit operation. Occasionally, the inner surfaces of the first throttling device (18) are cleaned from the iron corrosion products that are slightly adherent to the surface by changing the direction of the sample flow using valves 37, 38, 39, 40 of the reversible circuit (19). It is recommended to change the direction of the sample flow through the first throttling device (18) with a decrease in the sample flow rate by half compared to the initial value in the steady-state regime and, to prevent it, at the end of each transient mode stage. Regular flushing of the first throttling device (18) allows to keep the transport lag time and the stability of the sample flow to the sensitive elements of S1 (15), S2 (16), S3 (26), S4 (27), S5 (28) and S6 (29), which ensures receipt of reliable values of the rated and diagnostic parameters of the process circuit aqueous media during power operation, in transient modes or during washing, passivation and in outage modes. Selection of the values of rated and diagnostic quality parameters of the water chemistry of the process circuit by the criterion of the minimum corrosion activity of the filling medium and maintenance of the values within certain limits are required for safe operation of the power unit. In case of deviations in the parameter values beyond the established boundaries, actions are taken to correct violations within a specified time. If it is impossible to eliminate the causes for deviations in the measured parameter values of the process circuit within the specified period of time, decision is made to suspend or to stop further works at the power unit (STO 1.1.1.03.004.0980-2014 “Water Chemistry of the Primary Circuit during Commissioning of the Nuclear Power Plant Unit under AES-2006 Project. Coolant Quality Standards and Supporting Means”. STO1.1.1.03.004.0979-2014 “Water Chemistry of the Secondary Circuit during Commissioning of the Nuclear Power Plant Unit under AES-2006 Project. Working Medium Quality Standards and Supporting Means” at http://www.snti.ru/snips_rd3.htm). The following is a specific example showing the effectiveness of this power plant chemical control system, including sensors for the electrochemical parameters of the coolant of the power installation process circuits forming a complex with heat exchangers and throttling devices with a reversible coolant supply circuit. The production prototype of the corrosion monitoring complex was mounted on one of the power units with RBMK-1000 reactor (high-power channel-type reactors). The power unit with RBMK-1000 reactor is a single-circuit power plant of a boiling type. The coolant is light water (H2O) moving along the multiple forced circulation circuit connecting the channel-type reactor, the turbine and the main circulation pump. The circuit diagram of the multiple forced circulation circuit is similar to that shown in FIG. 1 (items 1, 4, 6). Organization of automatic sampling and supply of the sample to the power plant chemical control system are also similar (refer to FIG. 1, items 13, 16-20). The first option of the chemical control system production prototype configuration consisted of a cell with electrodes of an electrochemical potential sensor, a heat exchanger/cooler, a throttling device as a set of throttle orifices. The set of throttle orifices was designed to provide a pressure drop from 8 to 0.15 MPa and to maintain the coolant sample flow rate at about 20 dm3/h. The electrochemical potential was measured using a typical measuring transducer and 4-20 mA signal tapping to the recording system on the typical recording chart. The water chemistry quality complied with the regulatory document (STO 1.1.1.02.013.0715-2009 “Water Chemistry of the Main Process Circuit and Auxiliary Systems of Nuclear Power Plants with RBMK-1000 Reactors” at http://www.snti.ru/snips_rd3.htm). Quality parameters changed during power operation within the following limits: from 25 to 40 μg/kg for oxygen concentration; from 0 to 2 μg/kg for hydrogen concentration; from 7 to 10 μg/kg for iron corrosion products concentration; from 0.08 to 0.27 μS/cm for the specific electrical conductivity. During the first stage of the tests, under the power unit operation at nominal power, there was a reduction in the sample flow rate. The coolant sample flow through the complex reduced by half (up to 10 dm3/h) after 200 hours and to 3 dm3/h after 800 hours, which corresponds to an extension in the transport lag time by six times, up to approximately 5 minutes, with the sampling tube length of 10 meters from the sampling point to the sensor. The extended transport lag time has a negative effect on the reliability of the values of the rated and diagnostic parameters of the process circuit water media. The coolant sample flow rate of (17-19) dm3/h was restored as a result of the following procedures: disconnection of the complex from the multiple forced circulation circuit, removal of a set of throttling orifices from the complex, mechanical removal of iron corrosion products deposits from the internal surfaces of the set of throttling orifices, assembly of the set of throttling orifices, installation of the set of throttling orifices in the hydraulic circuit of the complex and its commissioning. Regular monitoring of the sample flow rate showed that the flow rate is gradually decreasing at almost the same rate as at the beginning of the test. A similar formation of deposits of iron corrosion products in the form of magnetic iron oxides was recorded in the regulating valve for feed water supply to the drum boiler of the combined-cycle gas-turbine unit at one of the combined heat and power plants. Cleaning the valve of deposits was required at least once a month. In order to eliminate these drawbacks, the hydraulic complex path was updated with arrangement of a reversible coolant supply circuit to a throttling device similar to that shown in FIG. 3. The upgraded complex with a throttling device with a reversible coolant supply circuit enabled to perform long-term tests (at least 5000 hours) at the rated power of the power unit, during start-up (48 to 144 hours) and shutdown (48 to 100 hours) periods. Quality indicators changed during the start-up and shutdown periods within the following limits: from 25 to 140 μg/kg for oxygen concentration; from 0 to 4 μg/kg for hydrogen concentration; from 20 to 100 μg/kg for iron corrosion products concentration; from 0.28 to 0.77 μS/cm for the specific electrical conductivity. Timely switching of the coolant flow direction through the throttling device allowed to maintain the flow rate within the limits from 15 to 18 dm3/h acceptable for measurement reliability. |
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054024579 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen a fuel assembly for a pressurized water reactor as is disclosed, for example, in Published European Application No. 0 364 623. The fuel assembly 1 contains, for example, 17.times.17 rods, a fuel assembly top end piece 2 with hold-down springs 3 and a fuel assembly bottom end piece 4. A number n (for example n=24) of the rods are guide rods or tubes 5, while a rod 5a is an instrumentation tube and remaining rods 7, 8, 9 and 10 are filled with fuel in the form of cylindrical pellets. Those rods are usually situated in a cross sectionally square grid configuration, while in the reactor core there is generally provided a predetermined number of fuel assemblies which are identical to one another. The fuel assemblies are disposed in a reactor pressure vessel and in each case a coolant K flows through them the direction of an arrow from bottom to top as shown. In this case the rods are held in a supporting structure which includes the fuel assembly top end piece 2 with the hold-down springs 3, the fuel assembly bottom end piece 4, the guide tubes 5 lying in between, for non-illustrated control rods and, depending on the type of fuel assembly, the central instrumentation tube 5a. Disposed on the guide tubes 5 are grid-shaped spacers 6, which have a square cross section with square sheet-like meshes or openings. Each of the rods is guided by a mesh of the grid, so that the rods are combined to form a bundle or cluster and are held in such a way that they can freely expand axially, while their lateral position in the meshes is fixed by corresponding spacing means, for example springs and dimples on the webs of the spacer. The laterally open construction of the fuel assembly permits cross-mixing of the coolant K, which makes its heating-up more uniform. In the case of a boiling water reactor, this cross-mixing is prevented by a channel which laterally surrounds the rods and extends from the bottom end piece to the top end piece. Control rods or other controllable absorber assemblies are disposed outside the channel, while the coolant K enters in liquid form through corresponding openings of the bottom end piece and flows as a liquid/vapor mixture through the passages in the top end piece 2. In this case one or more rods may be replaced by a water tube, through which liquid coolant flows and, under certain circumstances, may take up the cross section of a plurality of meshes of the spacer. In order to achieve uniform temperature loading and high utilization of the fuel with optimum cooling, it is an aim to attain a temperature at the fuel rods which is as uniform as possible in the radial direction and in the axial direction. However, when operating the reactor, different parts of different fuel rods develop different temperatures, so that temperature peaks occur in the fuel assembly both in the axial direction and in the radial direction. Therefore, it has already been proposed in German Published, Non-Prosecuted Application DE 15 64 697 A1 to use spacers with mixing vanes, which are intended to produce a uniform radial temperature distribution in pressurized water reactors by inducing a cross-flow through the individual fuel assembly and over the interspaces of the fuel assemblies. In FIG. 2, the grid structure of such a spacer is represented diagrammatically. In that case, the fuel rods 7 . . . 10 are each situated in a respective mesh of a grid. The meshes are formed by longitudinal webs 11, 12 and transverse webs 13, 14 which, in the case of a fuel assembly of square cross section, cross the longitudinal webs at a right angle. The fuel rods extend in a transverse or crossing plane perpendicular to the webs, while lateral surfaces thereof are aligned parallel to the rods. That structure produces flow subchannels 15, 16, which are surrounded by four rods in each case. In FIG. 2, the flow subchannels are represented by being alternately hatched and unhatched, so that a checkerboard-like array of hatched channels, which are referred to below as "black" channels and unhatched channels, which are referred to below as "white" channels, is produced. In a white channel, which is surrounded by the rods 7, 8, 9, 10, for example, the longitudinal web 12 may have two non-illustrated lateral lugs on both sides of the crossing transverse transverse web 13, at an edge thereof facing away from the stream of coolant. The two non-illustrated lateral lugs are bent in opposite directions laterally into the stream of coolant in such a way that a swirl symbolically represented by an arrow is produced in the "white" channel 15. In the black channels, the transverse webs 13, 14 likewise have lateral lugs in each case being disposed on both sides of the crossing longitudinal web. The lateral lugs are constructed as mixing vanes and protrude oppositely relative to each other obliquely into the stream of coolant. However, an arrow indicated in FIG. 2 shows that there the alignment of the swirl being produced is opposite to the alignment of the swirl in the white channels. This produces cross-flows, which in each case lead diagonally through the meshes of the grid and cross one another in the flow subchannels to form a rotational flow. In FIG. 2 there is already shown a checkerboard-like pattern for the flow subchannels, in which the crossing points of the webs and the mixing vanes are located. According to the invention, not all of the crossing points lie in an axial cross sectional plane of the fuel assembly, but instead at least two such crossing planes and at least two groups of crossing points are provided, with the crossing points of the one group lying in the one crossing plane, and the crossing points of the other group lying in the other crossing plane. The checkerboard pattern of FIG. 2 in this case is produced when the one crossing point in each case belongs to the one group, and the other crossing point belongs to the other group, with the two crossing points lying next to each other in the grid. In FIG. 2, the flow subchannel 16 and the other flow subchannels with the crossing points belonging to the first group are emphasized by the hatching and in FIGS. 3 and 4 the longitudinal web 11 and the transverse web 13 are represented by solid lines, while the webs 12 and 14 lying behind are drawn with broken lines. The parts of these webs lying in these hatched channels are likewise identified in FIGS. 3 and 4 by hatching. The longitudinal webs 11 and 12 run approximately in zigzag form and have slots 15 in their upper and lower regions through which the transverse webs 13 and 14, which likewise run in zigzag form and have insert slots 16 in their upper and lower regions, are inserted. As a result, virtually two groups of longitudinal webs and two groups of transverse webs are produced, with the longitudinal web 11 belonging to the one longitudinal web group and all of the other longitudinal webs of this one group being completely covered in FIG. 3 by the longitudinal web 11, while the other longitudinal web 12 belongs to the other group and covers all of the longitudinal webs of the other group. The two longitudinal webs which neighbor the longitudinal web of one group then in each case belong to the other group. In the same way, in FIG. 4 the transverse webs 13 and 14 belong to two transverse web groups and a transverse web of one group neighbors two transverse webs of the other group. The longitudinal webs in this case pass through the transverse webs at lines of intersection determined by the slots 15, 16 within specified zones A and C which are perpendicular to the fuel rods. Corresponding cross sectional planes I and II which are perpendicular to the rods pass through the zones. The planes consequently describe the axial position of the crossing points. Thus, the longitudinal webs and transverse webs extend in zigzag form between these zones A and C or the corresponding crossing planes I and II as follows: End edges M facing the stream of coolant K, that is to say the lower edges of the webs 11, 12, 13, 14 of FIGS. 3 and 4, run between extreme points situated in a plane I' that is upstream, and extreme points situated in a plane II' that is downstream. Similarly, end edges N of these webs facing away from the stream of coolant run between extreme points on the upstream plane I" and the downstream plane II". As FIGS. 3 and 4 show, in this case the downstream extreme points (plane II') of the end edge M facing the stream of coolant lie further downstream than the upstream extreme points (plane I") of the end edge N facing away from the stream of coolant. The hatched or "black" flow channels lying in a lower crossing plane I then contain a group of crossing points, which are formed either by the longitudinal web 11 (or another longitudinal web of this group) and the transverse web 13 (or another transverse web of this group) or else by a longitudinal web and a transverse web of the other group (for example web 12 and web 14). The other crossing points lie in the upper crossing plane II and in each case are formed either by a transverse web of the one transverse web group and a longitudinal web of the other longitudinal web group (for example the webs 12 and 13) or a longitudinal web of the one longitudinal web group and a transverse web of the other transverse web group (for example the webs 11 and 14). It can be seen that in the direction of the stream of coolant K, the flow cross section in the "black" flow subchannels is initially constricted increasingly in the zone A by the crossing webs and therefore in a flow subchannel which contains the lower crossing points and is identified by reference symbol L an increasing compression of the stream of coolant takes place in the zone A. In the "black" channels, the webs cross in this zone A. In the neighboring "white" flow subchannels, which contain only upper crossing points and are denoted by reference symbol H, the full flow cross section is still available in the zone A. The zone A is adjoined by a zone B, in which the overall flow cross section of the two channels remains approximately the same, with the flow cross section of the white channels being constricted (or "contracted") approximately to the same extent as that by which the flow cross section in the black channels is enlarged (or "expanded") again. In the plane II' there is a maximum contraction of the flow cross section for the white channels. In the zone C, the webs intersect in the white channels, while in the black channels there is an expansion or even the full, undisturbed flow cross section is again available. In any event, the overall flow cross section increases in the zone C in spite of the intersection of the two grid webs. Thus, in the direction of the stream of coolant K there is initially a contraction (and possibly already an expansion) only in some of the flow subchannels, while the other channels still do not exhibit any contraction or expansion. In the direction of the axial flow K, the same process then follows, with roles reversed: in those channels wherein the flow cross section was not constricted by crossing webs until now, there now occurs contraction or expansion, while in the other channels, in which contraction or expansion has already occurred, no further contraction or expansion now occurs. This has the overall effect of producing a significantly smaller flow resistance, with a certain mixing of the flows in the subchannels also already taking place. If the grid structure described with regard to FIGS. 3 and 4 is used as a spacer, springs and dimples or other non-illustrated spacing means are fastened on the webs, for holding the rods in the meshes of the grid. According to the same principle, the spacing means may also be distributed over a plurality of axial planes, in order to break up the cross sectional constriction as far as possible and not concentrate it on one plane. The cross sectional constriction is caused, for example, by springs and dimples. FIG. 5 shows a plan view of a spacer that is constructed in this way from longitudinal webs and transverse webs, with springs 18 and dimples 19. However, the grid structure of FIGS. 3 and 4 may also be used as a support for mixing vanes, in order to permit an axial and radial temperature compensation by corresponding swirling in the flow. Particularly suitable locations for these mixing vanes are zones B and D (planes I" and II"), since for instance in zone B, the contraction has already been completed there in each case in the one group of crossing points and the flow cross section is already expanding again ("black" flow channels), while in the neighboring ("white") flow channels virtually the full flow cross section is still available. Subsequently, turbulences and vortices may develop in the expanded stream of coolant, without leading to a high pressure loss. In FIG. 6, which is a plan view of the upper side of such a structure from above, facing away from the stream of coolant, it can be seen that at least some of the crossing points have at least one mixing vane inclined laterally with respect to the lateral surface of the webs. The mixing vanes are disposed on the edge of the webs facing away from the stream of coolant in each case. In the illustrated structure, in each case two neighboring crossing points have a pair of mixing vanes. For example, mixing vanes 20, 21 at a first of two crossing points, such as at the crossing of the webs 11 and 14 (or 12 and 13), are disposed on the edge of a first web 11, (or 12) while mixing vanes 23, 24 at a second of two crossing points are disposed on the edge of the web 13 (or 14) crossing the first web 11 (or 13). It is also possible to provide four such mixing vanes at each crossing point. FIG. 7 is a side view of the longitudinal web 11 and FIG. 8 is a side view of the transverse web 14. FIG. 9 is a side view without fuel rods and FIG. 10 is a perspective side view with fuel rods, through part of the mixing grid constructed according to FIGS. 6 to 8. In this case too, the (lower) end edge M of the webs facing the stream of coolant runs in zigzag form between the planes I' and II' on which its extreme points lie, while the extreme points of the (upper) end edge N facing away from the stream of coolant lie on the planes I" and II". In the case of this embodiment, the plane II' comes to lie virtually just as far downstream as the plane I". The lateral surfaces of the webs 11 to 14 extend between these end edges M and N and cross each other in the two zones A and C lying around the center planes I and II. The longitudinal webs are parallel to each other, but they form two groups which are offset from each other by one mesh width in each case, as is shown by the longitudinal web 11 of the one group and the longitudinal web 12 of the second group. A corresponding structure then also applies for the transverse webs. It can now be seen that the longitudinal webs in each case have the mixing vanes 20, 21 which are disposed at the upper crossings, i.e. in the plane II" while the mixing vanes 23, 24 disposed on the edge of the transverse webs 13 are disposed at the lower crossings, that is to say in the plane I". FIG. 10 shows a grid structure in a perspective representation together with rods situated in the meshes. In the case of pressurized water reactors, some of the rods are constructed as guide tubes for absorber assemblies or instrumentation tubes for guiding measuring lances or other instruments. Mixing vanes are preferably also provided on the webs supporting these rods, if the size of these guide tubes permits. In FIG. 10 it has therefore been assumed that all of the flow channels which can be seen have mixing vanes 30, 31, 32. These mixing vanes are situated on edges of webs having lateral surfaces 33, 34 which are aligned virtually parallel to the rods and which run transversely to the rods in the interspace between the rods. In this case, the mixing vanes 30, 31 belong to one group of crossing points, which lie in the lower crossing plane, while the mixing vane 32 belongs to another group, lying in the upper crossing plane. The number of mixing vanes depends on the flow conditions desired. Thus, under certain circumstances, a single mixing vane in each flow channel may suffice. However, it is advantageous if in each case a crossing point of a group having at least one mixing vane is respectively neighbored by a crossing point of the other group which likewise has at least one mixing vane. Often at least two mixing vanes, that are inclined in opposite directions with respect to the lateral surface of the webs, are considered necessary for each crossing point between fuel rods. In the case of the grid structure according to the invention, these two mixing vanes preferably lie in the same crossing plane. Thus, the edge of a web which has a corresponding, inclined mixing vane then also has a second vane, inclined in the opposite direction. In the case of the checkerboard pattern according to FIG. 2, a second crossing point which likewise has two mixing vanes comes to lie next to a first crossing point, in which a first web has the two mixing vanes. These mixing vanes of the neighboring, second crossing point are disposed on the edge of a second web facing away from the stream of coolant. The second web crosses the first web and is inclined in mutually opposite directions with respect to the lateral surfaces of the second web. In FIGS. 6 to 10, spacing assemblies are not represented, but they are always provided if such a mixing grid with its mixing vanes is used at the same time as a spacer for the fuel rods. It can be seen from FIG. 10 that--following the direction of a specific longitudinal web like web 11, i.e. following line I.sub.M --this web crosses the transverse web 14 and web 14' . . . of the first group of transverse webs at crossing points 114, 114' . . . which lie in a lower plane, while the crossing points 113, 113', 113" of longitudinal web 11 with transverse web 13 and the other webs 13', 13" . . . of the second group of transverse webs lie in an upper plane (line II.sub.M). Therefore, the crossing points are divided into two groups, according to different planes, and crossing points of the one group alternate with crossing points of the other group. This is true for the direction of each longitudinal web like 11, 12 as well as in the direction of each transverse web like 13, 13', 13", 14. This checkerboard-pattern applies for the mixing vanes, too: Vanes 32 (some of which are clearly visible in FIG. 10) lie in an upper plane and alternate with vanes 30, 31 (mostly invisible while covered by other elements in FIG. 10) lying in a lower plane. |
047524340 | summary | BACKGROUND OF THE INVENTION The invention relates to a coupling device between an elongate control bar, with longitudinal movement, intended for a nuclear reactor and a mechanism for driving the bar. It finds a particularly important, although not exclusive, application in light water cooled moderated reactors, using control bars comprising a cluster of parallel elements, containing a neutron absorbing material, which elements have a great length and so considerable flexibility and are suspended, at their upper end, from a piece generally called "spider". Control bar coupling devices are already known of the type comprising a gripper body having resilient gripping fingers, belonging to the mechanism and, on the bar, a terminal pommel for engagement by the fingers and a shoulder directed towards the pommel. The coupling device comprises an additional member, such as a sleeve, movable with respect to the gripper body between a position in which it allows resilient fingers to be released from the pommel and another position in which it locks the resilient fingers onto the pommel. In all these known coupling devices, the bar is simply suspended from the drive mechanism. Because of the very slender shape of the elements, because of their construction (generally a stack of pellets in a thin sheath), because of the disymmetrie and of the diversity of means for guiding them, considerable vibrations may appear during operation of the reactor. The coupling device cannot absorb the forces having a torque with respect to an axis passing through the gripping zone. The resilient blades work under poor conditions since, because of their very shape, they are only adapted for withstanding tractive forces. The inevitable clearances risk causing oscilltions and vibrations in the vertical direction. SUMMARY OF THE INVENTION It is an object of the invention to provide a releasable coupling devince in which the pommel of the control bar and the drive mechanism are connected against movement in any direction and any longitudinal clearance is taken up and external torques can be absorbed. To this end, there is provided a device of the above-defined type which comprises a sleeve movable with the mechanism, movable longitudinally with respect to the gripping fingers and having an end face bearingo n the shoulder of the pommel and comprises a prestressed spring exerting a force tending to move the sleeve away from the fingers so as to hold the end face of the sleeve firmly applied against the shoulder when the fingers are locked on the pommel. The gripper body and the fingers may be slidably received in the sleeve. This latter may then be formed with a recess allowing the fingers to spread apart and to release the pommel when an external force is exerted against that of the prestressed spring and overcomes the prestress. The gripper body may be associated with a central rod passing through the whole of the mechanism and having an abutting connection with a tubular rod, said abutting connection being situated at the end of the mechanism opposite said end face, the prestressed spring then being compressed between said tubular rod and the sleeve. The embodiment which has just been described has the advantage of simplicity. On the other hand, it subjects the tubular rod to compression forces which may cause it to buckle. This buckling may however be limited by disposing the tubular rod under compression inside a drive shaft fast with the sleeve and which co-operates with external drive means for moving it longitudinally. the external drive means may be electromechanical means, numerous embodiments of which are known. Such means are for example described in French Pat. No. 1,371,802. If it is desired to locate all components of the coupling device immediately above the pommel, it is possible to use another embodiment which involves no compression stress on rods or tubes or great length. A device may more especially be used in which the sleeve is fast with a slide situated inside the gripper body and having a surface for abutting connection with one end of the prestressed spring bearing on a slider having a disengageable abutting connection with the gripper body. The invention will be better understood from the following description of particular embodiments, given by way of examples. The description refers to the accompanyng drawings. |
claims | 1. A slurry dispensing system comprising: 1) a slurry mixer comprising a mixer outlet and a mixer recirculation port; and 2) a slurry dispenser fluidly connectable with said slurry mixer and comprising:a slurry bypass channel fluidly connectable with each of said mixer outlet and said mixer recirculation port;a metering chamber;a metering chamber inlet valve between said slurry bypass channel and said metering chamber;a metering chamber outlet valve for said metering chamber;a slurry inlet channel extending from said slurry bypass channel to said metering chamber, wherein said metering chamber inlet valve controls a flow through said slurry inlet channel to said metering chamber;an injection needle in fluid communication with said metering chamber; anda controller configured to execute a container slurry-loading sequence comprising closing said metering chamber outlet valve, thereafter opening said metering chamber inlet valve, thereafter closing said metering chamber inlet valve, thereafter opening said metering chamber outlet valve, and initiating a fluid flow through said injection needle after said metering chamber inlet valve has been closed. 2. The slurry dispensing system of claim 1, further comprising:at least one feed source fluidly connectable with said slurry mixer, wherein a fluid and a plurality of particles are directed into said slurry mixer by said at least one feed source, and wherein a discharge out of said mixer outlet comprises a slurry. 3. The slurry dispensing system of claim 1, wherein said slurry mixer comprises a horizontal mixer. 4. The slurry dispensing system of claim 1, further comprising:a pump between said mixer outlet and said slurry dispenser. 5. The slurry dispensing system of claim 4, wherein said pump comprises a peristaltic pump. 6. The slurry dispensing system of claim 1, wherein said slurry bypass channel comprises a dispenser inlet port and a dispenser recirculation port, wherein said slurry dispensing system further comprises:an outlet line extending between said mixer outlet and said dispenser inlet port; anda recirculation line extending between said dispenser recirculation port and said mixer recirculation port. 7. The slurry dispensing system of claim 6, wherein said slurry inlet channel intersects said slurry bypass channel between said dispenser inlet port and said dispenser recirculation port. 8. The slurry dispensing system of claim 1, wherein said injection needle extends through said slurry bypass channel and at least into said slurry inlet channel. 9. The slurry dispensing system of claim 8, wherein said injection needle extends through said slurry inlet channel and at least to said metering chamber. 10. The slurry dispensing system of claim 1, wherein said injection needle is disposed within a flow through said slurry bypass channel and is also disposed within a flow through said slurry inlet channel. 11. The slurry dispensing system of claim 10, wherein said injection needle is disposed transversely to said flow through said slurry bypass channel and is disposed parallel to said flow through said slurry inlet channel. 12. The slurry dispensing system of claim 1, wherein an effective outer diameter of said injection needle is smaller than an effective diameter of each of said slurry bypass channel and said slurry inlet channel. 13. The slurry dispensing system of claim 1, wherein said metering chamber inlet valve seals against said injection needle to fluidly isolate said slurry bypass channel from said metering chamber. 14. The slurry dispensing system of claim 1, wherein said slurry dispenser further comprises a fluid injector fluidly connectable with said metering chamber. 15. The slurry dispensing system of claim 14, wherein said fluid injector is configured to deliver a fluid to said metering chamber when said metering chamber inlet valve is closed and when said metering chamber outlet valve is open to facilitate removal of slurry from said metering chamber. 16. The slurry dispensing system of claim 14, wherein said fluid injector is configured to deliver a fluid to said metering chamber when said metering chamber inlet valve is closed and when said metering chamber outlet valve is open to flush said metering chamber. 17. The slurry dispensing system of claim 15, wherein said fluid is selected from the group consisting of air, water, or solvents. 18. The slurry dispensing system of claim 1, further comprising a container fluidly connectable with said slurry dispenser. 19. A slurry dispensing system comprising: 1) a slurry mixer comprising a mixer outlet and a mixer recirculation port; and 2) a slurry dispenser fluidly connectable with said slurry mixer and comprising:a slurry bypass channel fluidly connectable with each of said mixer outlet and said mixer recirculation port;a metering chamber;a metering chamber inlet valve between said slurry bypass channel and said metering chamber;a metering chamber outlet valve for said metering chamber;a slurry inlet channel extending from said slurry bypass channel to said metering chamber, wherein said metering chamber inlet valve controls a flow through said slurry inlet channel to said metering chamber; andan injection needle in fluid communication with said metering chamber, wherein said injection needle extends through said slurry bypass channel and at least into said slurry inlet channel, and wherein said injection needle extends through said slurry inlet channel and at least to said metering chamber. 20. The slurry dispensing system of claim 19, wherein said slurry bypass channel comprises a dispenser inlet port and a dispenser recirculation port, wherein said slurry mixer comprises a horizontal mixer, and wherein said slurry dispensing system further comprises:at least one feed source fluidly connectable with said slurry mixer, wherein a fluid and a plurality of particles are directed into said slurry mixer by said at least one feed source, and wherein a discharge out of said mixer outlet comprises a slurry;a peristaltic pump between said mixer outlet and said slurry dispenser;an outlet line extending between said mixer outlet and said dispenser inlet port; anda recirculation line extending between said dispenser recirculation port and said mixer recirculation port. 21. The slurry dispensing system of claim 20, wherein said slurry inlet channel intersects said slurry bypass channel between said dispenser inlet port and said dispenser recirculation port. 22. The slurry dispensing system of claim 19, wherein said injection needle is disposed transversely to a flow through said slurry bypass channel and is disposed parallel to said flow through said slurry inlet channel. 23. The slurry dispensing system of claim 19, wherein an effective outer diameter of said injection needle is smaller than an effective diameter of each of said slurry bypass channel and said slurry inlet channel. 24. The slurry dispensing system of claim 19, wherein said metering chamber inlet valve seals against said injection needle to fluidly isolate said slurry bypass channel from said metering chamber. 25. The slurry dispensing system of claim 19, wherein said slurry dispenser further comprises a fluid injector fluidly connectable with said metering chamber. 26. The slurry dispensing system of claim 25, wherein said fluid injector is configured to deliver a fluid to said metering chamber when said metering chamber inlet valve is closed and when said metering chamber outlet valve is open to facilitate removal of slurry from said metering chamber. 27. The slurry dispensing system of claim 25, wherein said fluid injector is configured to deliver a fluid to said metering chamber when said metering chamber inlet valve is closed and when said metering chamber outlet valve is open to flush said metering chamber. 28. A slurry dispensing system comprising: 1) a slurry mixer comprising a mixer outlet and a mixer recirculation port; and 2) a slurry dispenser fluidly connectable with said slurry mixer and comprising:a slurry bypass channel fluidly connectable with each of said mixer outlet and said mixer recirculation port;a metering chamber;a metering chamber inlet valve between said slurry bypass channel and said metering chamber;a metering chamber outlet valve for said metering chamber;a slurry inlet channel extending from said slurry bypass channel to said metering chamber, wherein said metering chamber inlet valve controls a flow through said slurry inlet channel to said metering chamber; andan injection needle in fluid communication with said metering chamber, wherein said injection needle is disposed within a flow through said slurry bypass channel and is also disposed within a flow through said slurry inlet channel, and wherein said injection needle is disposed transversely to said flow through said slurry bypass channel and is disposed parallel to said flow through said slurry inlet channel. 29. A slurry dispensing system comprising: 1) a slurry mixer comprising a mixer outlet and a mixer recirculation port; and 2) a slurry dispenser fluidly connectable with said slurry mixer and comprising:a slurry bypass channel fluidly connectable with each of said mixer outlet and said mixer recirculation port;a metering chamber;a metering chamber inlet valve between said slurry bypass channel and said metering chamber;a metering chamber outlet valve for said metering chamber;a slurry inlet channel extending from said slurry bypass channel to said metering chamber, wherein said metering chamber inlet valve controls a flow through said slurry inlet channel to said metering chamber; andan injection needle in fluid communication with said metering chamber, wherein said metering chamber inlet valve seals against said injection needle to fluidly isolate said slurry bypass channel from said metering chamber. |
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050698648 | claims | 1. A spring for positioning at least one of a plurality or nuclear fuel rods in a spacer usable in a fuel assembly of a nuclear power plant, the spacer provided with a plurality of ferrules, each ferrule having rod-contacting portions for holding at least one of said rods when said rod is biased against said rod-contacting portions by the spring, the spring comprising: a metallic strip having a width and a thickness, and having first and second ends, said ends spaced apart, said strip formed to include: a plurality of ferrules joined to each other, each ferrule having at least one rod stop for contacting at least one of said rods when said rod is in a preferred rod position biased against said rod stop, at least a first ferrule having a first slot defining an ear portion; at least a first spring for biasing a fuel rod towards said rod stop, said spring having a width and a thickness, and having first and second ends, said ends spaced apart, said spring formed to include: a plurality of ferrules joined to each other, each ferrule having rod stops for contacting at least one of said rods when said rod is in a preferred rod position biased against said rod stops, at least a first ferrule having a first slot defining two ear portions; a spring for biasing a fuel rod toward said rod stop, said spring having a width and a thickness, and having first and second ends, said ends spaced apart, said spring formed to include: a plurality of ferrules joined to one another, at least a first ferrule having a first slot defining two ear portions, at least a second ferrule having a second slot substantially without an ear portion, said second slot having a width; at least a first spring for biasing a fuel rod towards said rod stops, said spring having a width and a thickness, said width being less than the width of said second ferrule slot, said spring having first and second ends, said ends spaced apart, said spring formed to include: said second ferrule attached to said first ferrule in a position with said second slot aligned with said first slot so as to prevent disengagement of said spring from said ears. a metallic ribbon having a width and a thickness and having first and second ends, said ends spaced apart, said ribbon formed to include: 2. A spring as claimed in claim 1, wherein the width of said spring varies along the length of said spring. 3. A spring, as claimed in claim 1, wherein said rod-contacting portion includes an arch formed in said rod-contacting portion, and wherein the portion of the spring between said rod-contacting portion and said first and second legs is substantially flat. 4. A spring and spacer assembly for positioning at least one of a plurality of nuclear fuel rods, usable in a fuel assembly of a nuclear power plant, comprising: 5. An assembly, as claimed in claim 4, wherein at least a portion of said spring rotates about said contact between said first dimple and said ear portion upon flexing of said spring. 6. An assembly, as claimed in claim 4, wherein said length of said spring between said first and second dimples is about 0.8 inches. 7. An assembly, as claimed in claim 4, wherein said rod-contacting portion includes a ridge formed in said central region and wherein the said first and second legs are substantially flat. 8. An assembly, as claimed in claim 4, wherein said spring has a variable width along the length of said spring; the width being greatest in said central portion of spring, and being reduced in other portions of the spring. 9. An assembly, as claimed in claim 4, wherein the rod-to-rod spacing defined by said spacer is less than about 0.11 inch. 10. An assembly, as claimed in claim 4, wherein said spring provides a force to said rod of at least about one pound. 11. An assembly, as claimed in claim 4, wherein the rod-to-rod spacing of rod positions defined by said spacer is less than about 0.11 inch. 12. A spring and spacer assembly for positioning ar least one of a plurality of nuclear fuel rods, usable in a core assembly of a nuclear power plant, comprising: 13. An assembly, as claimed in claim 12, wherein said first and second loops each include a region for contacting said ears, and wherein said first and second loops each rotate about said regions upon flexing of said spring. 14. An assembly, as claimed in claim 12, wherein said plurality of ferrules define a plurality of preferred rod positions having a rod-to-rod spacing of less than about 0.11 inch. 15. A spring and spacer assembly for positioning at least one of a plurality of nuclear fuel rods, usable in a core assembly of a nuclear power plant, comprising: 16. An assembly, as claimed in claim 15, wherein at least one of said first and second loops includes a region for contacting said ear, and wherein said first and second loops each rotate about said regions upon flexing said spring. 17. An assembly, as claimed in claim 15, and wherein said spring has a variable width along the length of said spring, the width being greatest in said central portion of said spring and being reduced in other portions of said spring. 18. An assembly, as claimed in claim 15, wherein said plurality of ferrules define a plurality of preferred rod positions having a rod-to-rod spacing of less than about 0.11 inch. 19. A spring for positioning at least one of a plurality of nuclear fuel rods in a spacer usable in a core assembly of a nuclear power plant, the spacer defining a plurality of rod positions, the spring comprising: 20. A spring, as claimed in claim 19, wherein said first spacer-engagement loop includes a ridge for contacting an adjacent fuel rod. |
description | This application is a national phase of International Application No. PCT/FR2005/050647 entitled “Method And Device For Removing Inflammable Gases From A Sealed Chamber And Chamber Equipped With One Such Device”, which was filed on Aug. 4, 2005, which was not published in English, and which claims priority of the French Patent Application No. 04 51817 filed Aug. 8, 2004. The invention relates to a method and a device for removing inflammable gases, such as hydrogen, in a closed chamber containing radioactive matters, in the presence of solid or liquid organic compounds and possibly water capable of producing such gases, by radiolysis, or when the radioactive matters comprise compounds of this type and possibly water. The invention further relates to a closed chamber such as a receptacle, tank or container suitable for transporting or storing radioactive matters in the presence of organic compounds and possibly water, or comprising components of this type, said chamber being equipped with such a device for removing inflammable gases. The invention can be used in any closed chamber containing radioactive matters comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water. As a non-limiting example, these radioactive matters may be technological waste from a facility for fabricating or reprocessing fuel elements for a nuclear reactor or issuing from such a reactor. Nuclear installations such as facilities for fabricating fuel elements for nuclear reactors generate a certain quantity of scrap, called “technological waste”. This technological waste may comprise a very wide variety of objects and materials such as motor parts, filters, scrap metal, rubble, glass, etc. This waste may also contain organic matter based on cellulose, such as paper, wood, cotton, or in the form of plastics such as packaging bags made of vinyl or polyurethane, boots, gloves, and miscellaneous objects made of polymer materials. All these wastes may also contain small quantities of liquids such as water and organic liquids (oils, hydrocarbons, etc.). All these wastes in themselves constitute radioactive materials, because they consist of metal parts activated during their residence in the installations, organic or other materials contaminated by radioactive uranium or plutonium powder during their use in these installations. Technological waste is periodically removed to reprocessing and disposal centres. Their conveyance to these sites accordingly demands as many precautions as the transport of any other radioactive matter. In particular, the waste must be packaged and transported in containers or casks meeting the requirements of the regulations on the transport of radioactive matters on the public thoroughfare. In practice, transport is generally carried out by packing the technological waste in receptacles such as drums, bins or canisters, and by placing these receptacles in casks. The transport of technological waste raises a specific difficulty associated with the type of material transported. In fact, as explained above, this waste often contains organic matters, solid or in the form of residual liquids, or else a certain quantity of water, contaminated by uranium or plutonium, imparting a radioactive character to these materials. In fact, uranium and plutonium are emitters of α particles, which have the specific property of dissociating organic molecules to release gaseous compounds such as carbon monoxide, carbon dioxide, oxygen and nitrogen, as well as inflammable gases. This mechanism, called “radiolysis”, results in a dissociation of the molecules of the organic compounds containing carbon and hydrogen, like those comprised in plastics and hydrocarbons, or in a dissociation of the water molecules, with the production of hydrogen. The production of inflammable gases and particularly of hydrogen by radiolysis mainly raises problems when the technological waste is confined in a closed chamber of relatively limited volume. In fact, the radiolysis gases are then released in a confined volume, so that a high concentration of inflammable gases may be reached rapidly if the type of waste and the radiation intensity causes a significant production of these gases. The problem is particularly critical during transport, due to the fact that a large number of waste receptacles are generally placed in the same cask, in order to optimize transport capacity. In fact, this has the consequence of reducing the free space available in the cask for the inflammable gases which escape from the waste and the receptacles. It may also be observed that waste containment receptacles often themselves present a certain tightness, because they are closed by crimped lids that can be provided with seals. In this case, the inflammable gases preferably accumulate in the residual free space existing within each of the receptacles. Since these volumes are also very small, this can lead to high concentrations of inflammable gases in the containment receptacles themselves. In general, the inflammable gases produced by radiolysis form an explosive mixture when placed in the presence of other gases such as air, when their concentration exceeds a limit, called the “flammability limit”. The flammability limit varies according to the type of inflammable gas and according to the temperature and pressure conditions. In the case of hydrogen, the flammability limit in air is about 4%. This means that, if the hydrogen concentration in the air exceeds this level, a heat source or spark can suffice to ignite the mixture or to produce a violent explosion in a confined space. Various studies and observations have shown that the concentration of inflammable gases such as hydrogen, produced by radiolysis in a closed chamber containing radioactive matter comprising hydrogen-bearing components, can sometimes reach values of about 4% after a few days. This situation corresponds in particular to the case in which the technological waste emits intense α particles and contains numerous organic molecules. In fact, it is common for a cask to remain closed for a much longer time before being opened. This incurs the risk of accident, because a spark caused by impact or friction may be produced during transport in the chamber of the cask or in a receptacle filled with waste. In this eventuality, the ignition or explosion is liable to extend to the entire contents of the cask, implying the risk of a serious accident on the public thoroughfare. A comparable risk exists if the cask falls into an accidental situation of fire during its transport. Furthermore, the risk of accident subsists during the final operations of opening the cask and unloading the receptacles, and during their eventual opening. In fact, these operations demand numerous handling operations, which are potentially dangerous. It is therefore particularly important to take account of the risk of accumulation of inflammable gases in any closed chamber used to contain radioactive matter comprising hydrogen-bearing compounds. One technique for removing the inflammable gases such as hydrogen in a closed chamber such as a radioactive waste transport cask is essentially based on the introduction into the chamber of a catalyst for recombination of oxygen and hydrogen to water (or catalytic hydrogen recombiner), upon contact with which the hydrogen combines with the oxygen present in the air of the cavity to form water according to the catalytic hydrogen oxidation mechanism. Devices putting this technique into practice are described for example in documents EP-A-0 383 153 and EP-A-0 660 335. Document EP-A-0 383 153 describes a device for reducing the internal pressure in a radioactive waste storage receptacle. This device comprises a chamber placed in an opening of the wall or of the lid of the nuclear waste storage receptacle. The interior of this chamber receives a catalyst and comprises an opening communicating with the interior of the storage receptacle in which a sintered metal plug is placed. The catalyst is separated from the exterior by a metal fabric, a plate permeable to water vapour, or a lid of sintered metal. The hydrogen formed in the storage receptacle passes through the sintered metal plug and reaches the catalyst where the hydrogen is oxidized to water by the oxygen in the air. The catalyst used comprises a precious metal, for example palladium, on an inert support, for example alumina. In this document, use is made of an external oxygen source comprising ambient air, which is only feasible for hermetically closed chambers of perfectly sealed transport casks. Document EP-A-0 660 335 describes a device for reducing the overpressure in waste storage tanks, particularly radioactive waste producing hydrogen, in which a catalyst for recombination of hydrogen with oxygen and a desiccant are placed in a closed envelope placed inside the storage tank and communicating with its environment via a rupture disc. Inside the envelope are provided two separation sheets permeable to water vapour, below which two layers of desiccant are placed. In a first embodiment, two grids supporting the recombination catalyst are placed above the separation sheet. In a second embodiment, a layer of oxidant is placed above the separation sheet, kept in place by a separation sheet permeable to the gases. The desiccant is selected for example from silica gel, molecular sieves, dehydrated complexants such as for example copper sulphate or hygroscopic chemicals such as calcium chloride, magnesium sulphate, or phosphorus pentoxide, possibly on a support material. The recombination catalyst is selected in particular from catalysts coated with platinum or palladium. In this device, the recombiner becomes inoperative once all the oxygen in the chamber has been consumed. It has further been observed that these devices and methods, which use catalytic hydrogen recombiners, have the common feature of displaying lower efficiency particularly when the chamber contains carbon-bearing organic compounds. Hence a need exists for a method and a device for removing the inflammable gases, and particularly hydrogen, in a closed chamber containing radioactive matter comprising organic compounds, regardless of the types of organic compound and their carbon content, and possibly water. A need also exists for a method and a device for removing inflammable gases in a closed chamber, which serves to guarantee the removal of the inflammable gases, particularly of hydrogen over a long period, indeed a practically unlimited period. A further need exists for a method and a device for removing inflammable gases in a closed chamber, which is simple, reliable, safe, easy to use, does not demand lengthy and costly procedures, and which guarantees the effective removal of the inflammable gases such as hydrogen in a wide variety of conditions, that is, inter alia: in the presence of other radiolysis gases such as oxides like carbon monoxide and carbon dioxide, under irradiation and regardless of the type and intensity of this radiation, at various temperatures, these temperatures possibly being negative. It is an object of the invention to provide a method and a device which meet, inter alia, all the needs listed above. It is a further object of the invention to provide a method and a device which do not present the drawbacks, limitations, defects and disadvantages of the methods and devices of the prior art and which provide a solution to the problems raised by the methods and devices of the prior art, such as those described in documents EP-A-0 383 153 and EP-A-0 660 335. This object and others besides are achieved according to the invention, by a method for removing inflammable gases produced by radiolysis in a closed chamber containing radioactive matters comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water, in which the following are placed inside the chamber: a) a catalyst of at least one reaction for oxidizing the inflammable gases by oxygen contained in the chamber atmosphere, supported by an inert solid support, b) a catalyst of at least the reaction for oxidizing CO to CO2. The reaction of oxidation of the inflammable gases by the oxygen present in the chamber atmosphere is generally, and essentially, a reaction for oxidizing hydrogen to water. Preferably, the catalyst a) is a catalyst of at least the reaction for oxidizing hydrogen to water. The catalyst a) supported by an inert solid support is a first active product that permits the continuous removal of the inflammable gases and in particular of the hydrogen, produced by radiolysis of the molecules, organic compounds and possibly water inside the chamber. This removal is achieved by the reaction for oxidizing the inflammable gases with the oxygen present in the chamber atmosphere, and particularly by the reaction of recombination of the hydrogen with the oxygen in the chamber atmosphere to produce water. The catalyst a) of this oxidation reaction, which is supported by an inert solid support, can be a precious metal that is advantageously selected from the group consisting of platinum, palladium and rhodium. The precious metal is present in a quantity that is generally lower than 0.1% by weight. The catalyst a) of this oxidation reaction may also be a rare earth, selected advantageously from the lanthanide group, such as lanthanum. The support of catalyst a) is an inert solid support. Inert support means a support that does not react chemically with the compounds present in the chamber, the chamber atmosphere, and the other active products. Preferably, the support of catalyst a) is a microporous inert solid support. This microporous support is generally selected from possibly activated molecular sieves. The term activated is a commonly used term in this technical field, which means that the compound forming the molecular sieve, such as alumina, has undergone treatment, particularly heat treatment, so as, in particular, to increase its specific surface area. This molecular sieve is preferably made of a material selected from aluminas and activated aluminas. The microporous inert solid support generally has a high specific surface area, that is a specific surface area generally of at least 200 m2/g, and preferably of at least 300 m2/g. The catalyst b) is a second active product, it catalyses the reaction for oxidizing CO to CO2. Preferably, the catalyst b) is a specific catalyst of the reaction of oxidizing CO to CO2. Specific means that the kinetics of oxidation of CO to CO2 catalysed by b) is much higher than that catalysed by a). Preferably, the catalyst b) comprises a mixture of manganese dioxide MnO2 and copper oxide CuO. The method according to the invention uses a combination of two active products, specific catalysts a) and b), which has never been described in the prior art as represented in particular by documents EP-A-0 383 153 and EP-A-0 660 335. The method according to the invention, essentially due to the use of such a specific combination of active products, catalysts a) and b), meets the needs and requirements listed above and provides a solution to the problems raised by the methods of the prior art. In particular, the inventors have succeeded in demonstrating that the efficiency of the methods of the prior art is substantially reduced in the presence of other radiolysis gases such as carbon monoxide CO; this drop in efficiency is explained by a poisoning of the H2 oxidation catalyst, a) such as palladium, by the carbon monoxide CO. Accordingly, by combining the oxidation catalyst of the inflammable gases with a catalyst b) of the reaction of CO to CO2, one surprisingly succeeds in preventing the poisoning of catalyst a) for oxidizing the inflammable gases by CO. The catalyst b) ensures the continuous removal of the carbon monoxide, by oxidation, to produce carbon dioxide, which causes no problem of poisoning of the catalyst a). Nothing in the prior art tended to imply that the drop in efficiency of the catalyst basically resulted from the presence of CO in the chamber. The prior art contained no indication that would have led a person skilled in the art to associate with the catalyst a), such as a recombiner, commonly used in this technical field, a specific catalyst b). The method according to the invention serves to remove effectively, over a very long period, indeed a virtually unlimited period, the inflammable gases such as hydrogen, present in the closed chamber. It preserves very high efficiency regardless of the waste present in the chamber and particularly if the waste contains organic compounds comprising carbon and hydrogen that are liable to liberate both CO and hydrogen. The method according to the invention operates perfectly in the presence of various radiolysis gases which, in addition to hydrogen, include for example CO, CO2, etc. The method according to the invention similarly operates perfectly in a broad range of temperatures and in particular at negative temperatures and under irradiation regardless of the nature thereof. Optionally, in addition to the two catalysts a) and b) which are always present, an oxygen source c) is placed in the chamber. This oxygen source is an optional third active product that serves to contend with the lack of oxygen, once all the oxygen initially present in the chamber has been consumed. This oxygen source may be in gaseous form or in solid form. If the oxygen source is in solid form, it is generally selected from solid peroxides. These compounds release oxygen in the presence of water which, for example, is the water formed during the oxidation of hydrogen by the catalyst a). These solid peroxides are generally selected from peroxides of alkali and alkaline earth metals and mixtures thereof, such as calcium peroxide, barium peroxide, sodium peroxide, potassium peroxide, magnesium peroxide and mixtures thereof. If the oxygen source is in gaseous form, it is generally formed by replacing all or part of the chamber atmosphere by pure oxygen. Optionally, a hygroscopic microporous inert solid support d) is also placed in the chamber. The hygroscopic microporous inert solid support is a fourth optional active product, which serves to ensure the continuous lowering of the moisture content of the chamber atmosphere, by adsorption of water. Depending on the temperature, the quantity of water removed generally represents 15% to 30% of the weight of the hygroscopic microporous support. The residual moisture in the chamber is thus maintained at a low value, for example less than 10% (moisture content) up to the saturation of said support. This serves in particular to collect the free water produced by the oxidation reaction, in particular the oxidation of hydrogen, catalysed by the catalyst a) and which would not have been absorbed in the micropores of the solid support, such as alumina, of the catalyst a), which can generally absorb up to 30% of its weight of water. The hygroscopic microporous support is. preferably selected from molecular sieves. Advantageously, the molecular sieve of the microporous inert solid support d) is made of a material selected from materials of the aluminosilicate type (for example with the formula Na12[(AlO2)12(SiO2)12]X H2O, where X is up to 27, or 28.5% by weight of anhydrous product). The hygroscopic microporous support generally has a high specific surface area, that is of at least 200 m2/g, and preferably at least 300 m2/g. It should be observed that this fourth active product is particularly present if the third active product consists of a source of oxygen gas. In fact, in this case, the presence of water that has not been absorbed by the support of catalyst a) such as alumina, is not necessary to generate oxygen, as opposed to the case in which the oxygen source consists of a solid peroxide which liberates oxygen only in the presence of water. Preferably, the microporous inert solid support supporting the catalyst a); the catalyst b); and possibly the oxygen source c) and the hygroscopic microporous support d) take the form of discrete elements, or particles, such as for example crystals, beads or granules, which may take the form of a powder. Thus in a preferred embodiment of the invention, the inert solid, preferably microporous, support supporting the catalyst a); the catalyst b); and the hygroscopic microporous support d), if any, are fractionated into discrete elements, such as for example crystals, beads or granules, having an envelope diameter generally of between about 2 mm and about 20 mm. The expression “envelope diameter” means the diameter of a fictitious sphere forming the envelope of said element. The active product c) is advantageously in a finely divided form such as a powder. In general, the active products a), b) and possibly c) and d) are placed, mixed or separately, in at least one receptacle that is at least partially permeable, such as a textile envelope, a strainer, a metal grid, or a perforated receptacle, such as a cartridge. Preferably, the active products a) and b) are mixed. On the other hand, the active products c) and d) must be separated. It is possible, for example, to disperse each of the active products between two grids in the form of superimposed layers, or to form a single layer with a mixture of the two compulsory active products a) and b), each of the optional active products c) and d) being packaged separately, for example in the form of separate layers. Several receptacles, such as cartridges, can be placed in the same closed chamber in order to increase the exchange area. The mass ratio of catalyst b) to catalyst a) is generally from 1/1 to 1/10, and preferably from 1/2 to 1/4, this mass ratio generally being given for a ratio of generally about 1:11 of the CO flow rate to the H2 flow rate. The invention further relates to a device for removing inflammable gases produced by radiolysis in a closed chamber containing radioactive matters comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water, comprising: a) a catalyst of at least one reaction for oxidizing the inflammable gases by oxygen contained in the chamber atmosphere, supported by an inert solid support, b) a catalyst of at least the reaction for oxidizing CO to CO2, possibly an oxygen source c); possibly a hygroscopic microporous inert solid support d); a), b), c) and d) being such as defined above. Finally, the invention further relates to a closed chamber, suitable for containing radioactive matters comprising organic compounds and possibly water, or radioactive matter in the presence of organic compounds and possibly water, capable of producing inflammable gases, by radiolysis, said chamber further containing at least one device for removing inflammable gases as defined previously. The invention will be better understood from a reading of the detailed description that follows, provided for illustration and non-limiting, with reference to the drawings appended hereto in which: FIG. 1 is a graph that shows the hydrogen content (% by volume), in the chamber, measured by chromatography, as a function of time (t in hours) during the test performed in the example. The invention applies to any closed chamber, in which radioactive matters is placed comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water. Organic compound in the sense of the invention means a compound comprising at least one carbon atom, at least one hydrogen atom and possibly at least one other atom selected for example from atoms of nitrogen, sulphur, phosphorus, oxygen and halogens. This chamber may have any shape and dimensions, as well as a more or less high level of tightness, without going beyond the scope of the invention. It may in particular be a receptacle such as a drum or a cylindrical or parallelepiped-shaped container. Furthermore, the chamber may be equally intended for transport, storage or the treatment of the radioactive matter concerned. Furthermore, the radioactive matter placed in the closed chamber may consist of all radioactive materials comprising organic compounds and possibly water, or of all radioactive materials in the presence of organic compounds and possibly water. In general, the invention applies more particularly to the case where said organic compounds are compounds which, in addition to hydrogen, emit or produce CO and CO2, such as certain plastics. In fact, it has been demonstrated according to the invention that CO poisons the catalyst a) and could be removed effectively by the catalyst b) to preserve the efficiency of the catalyst a). As a non-limiting example, the radioactive matter may consist of technological waste from a plant for the reprocessing or fabrication of nuclear fuel elements. As already stated, such waste is contaminated by radioactive plutonium or uranium and may contain a certain fraction of water or of solid or liquid organic compounds such as cellulose materials, plastics or hydrocarbons. According to the invention, at least two active products are placed in the closed chamber containing the radioactive matter. One of these active products, called below “active product A”, is designed to remove, by continuous catalytic oxidation by the oxygen present in the chamber, the inflammable gases, such as hydrogen, produced by radiolysis in the chamber atmosphere, under the effect of the radiation emitted by the radioactive isotopes present in said materials. The second active product, called below “active product B”, is an active product designed to remove the carbon monoxide by continuous oxidation and form CO2. These two active products A and B may optionally be combined with one or two other active products. These two other optional active products comprise a third product, called below “active product C”, designed to provide a source of O2, serving to contend with the lack of oxygen once all the oxygen initially present in the chamber has been consumed; and a fourth product, called below “active product D”, consisting of an active product absorbing water. The active product A comprises an inert solid support, preferably microporous, supporting a precious metal (impregnated with a precious metal), such as palladium, platinum or rhodium. As a variant, the inert solid support, preferably microporous, can also support a rare earth (be impregnated with a rare earth) advantageously selected from the lanthanide group, such as lanthanum. The active product D consists of a hygroscopic microporous support. The inert solid support of the active product A, if this support is microporous, and the hygroscopic microporous support of the optional active product D, generally both consist of a molecular sieve with a large developed surface area defined by a specific surface area, for example equal to or greater than 200, indeed 300 m2/g. Thus, if the microporous support of the active product A is impregnated with a precious metal or a rare earth, it has a very large reaction area for the oxidation of the inflammable gases produced by radiolysis in the chamber atmosphere and more particularly hydrogen. In the active product A, the precious metal or rare earth is a catalyst of the reaction for continuous oxidation of the hydrogen, by the oxygen present in the chamber. Generally, the presence of less than 0.1% by weight of precious metal in the microporous catalytic support serves to obtain the desired effect. The preferred microporous inert support of active product A and the hygroscopic microporous support of the optional active product D generally consist, as stated above, of a molecular sieve preferably selected for the microporous support of the active product D from the group of aluminosilicates, with the formula Na12[(AlO2)12(SiO2)12]X H2, where X can be up to 27, representing 28.5% of the anhydrous product, and for the microporous support of the active product A, from aluminas, preferably activated. In the active product A, the high specific surface area of the preferred microporous support serves to maximize the catalysing action of the precious metal or the rare earth. In fact, a large reaction surface area is provided on a support material, by using very little catalytic compound and in reduced volumes. Upon contacting the microporous inert support supporting the catalyst (impregnated with catalyst), the hydrogen combines with the oxygen in the chamber, to form water. The water thus formed is trapped and fixed deep in the micropores of the preferred support of product A, by molecular capillarity. By way of example, such a support can absorb up to 30% of its mass of water. The excess water, not absorbed by the microporous support of the active product A, is possibly trapped in the micropores of the hygroscopic microporous support forming the active product D. This makes it possible to prevent any formation of free water, which is liable to be decomposed again by radiolysis, by restoring a portion of the hydrogen removed. In fact, the water trapped deep in the microporous supports is less subject to the effects of the radiation emitted in the chamber atmosphere than if the water were free water. Alternatively, if the active product D is not present, the excess free water not absorbed by the support of the catalyst a) can then react with an active product C comprising a solid peroxide to cause a release of oxygen. Furthermore, it should be observed that the oxidation method thus put into practice operates perfectly because the chamber atmosphere cannot reach a high moisture content. More precisely, the efficiency of the active product D serves to guarantee a relative humidity of less than about 10% in the chamber atmosphere. This ensures a maximum yield of the oxidation reactions using active products A and B. The active product B, which must be placed inside the chamber, comprises a mixture of metal oxides, preferably in the form of granules, which allows the continuous removal of CO by oxidation to CO2. A preferred product comprises a mixture of manganese dioxide MnO2 and copper oxide CuO. The mixture of manganese dioxide MnO2 and copper oxide CuO generally represents about 80% of the weight of the product B (generally about 66% of MnO2 and 14% of CuO). This active product B plays a particularly important role when the gases present in the chamber contain CO. In fact, and without wishing to be bound by any theory, it has accordingly been demonstrated that the active sites of the active product A are blocked by CO because the CO molecule is larger than the H2 molecule. Hence it is the CO that is preferably converted by the catalyst a) and not the hydrogen. In other words, the hydrogen is not recombined because the CO blocks the active sites of the catalyst a). If, in addition to the catalyst a), a catalyst b) is placed in the chamber, this permits a much faster oxidation of CO to CO2 than the catalyst a). The active sites of the catalyst a) are then more available for the oxidation of the inflammable gases and particularly of hydrogen. A catalyst that can be used as the active product B is the product sold under the name Carulite® by Zander. This is a mixture comprising CuO and MnO2 which specifically catalyses the oxidation reaction of CO to CO2. For example, Carulite® catalyses this reaction at a rate that is ten times faster than the catalyst a), so that the catalyst a) remains available for the reaction for oxidizing the inflammable gases and in particular for the reaction for oxidizing hydrogen to water. The mass ratio of the active product B to the active product A is generally from 1/1 to 1/10, and preferably from 1/2 to 1/4. This ratio is generally determined for a ratio of the CO flow rate to the H2 flow rate that is generally about 1/11; this flow rate ratio is the one generally produced by technological waste. The active product C, which is optional, is defined as being an oxygen source. This oxygen source is generally in gaseous form or in solid form. In the latter case, it is generally a solid compound of the peroxide family which liberates oxygen in the presence of water. This water is generally the water formed during the oxidation of hydrogen by the catalyst a) and which has not been absorbed by the preferably microporous inert solid support of the catalyst a). Accordingly, if the active product C is such a solid peroxide, it is preferable not to use active product D, so that the water remains available to react with the peroxide and liberate the oxygen. The solid peroxide is generally selected from peroxides of alkali and alkaline earth metals such as peroxides of calcium, barium, sodium, potassium, magnesium and mixtures thereof. The oxygen source in solid form is initially introduced into the chamber when an oxygen deficit is anticipated. In order to be easily used and packed in the chamber, the active products A, B, C and D generally take the form of discrete, elements or particles, such as granules, beads, crystals. Thus the microporous supports of the active products A, and possibly D, are advantageously fractionated into elements, particles, with small dimensions such as granules, beads or crystals. More precisely, each of the elements of the microporous supports preferably has an envelope diameter of between about 2 mm and about 20 mm. Each of said elements of microporous supports one (is impregnated with one) precious metal in the case of the active product A. The active product B is generally already in a fractionated form for example, that is to say generally in the form of granules of oxides MnO2 and CuO. When it is present, the active product C, if it is a solid product, generally takes the form of a powder. The fractionation of the microporous supports (active products A and D) and the already fractionated character of the active product B make it possible, optionally and as described more precisely below, to easily package at least one of the active products in various types of receptacle before placing them in the chamber. This fractionation also serves to maximize the efficiency of the properties of the microporous support, by further increasing the oxidation surface areas of the support of the active product A. In fact, when the hydrogen diffuses in the small elements forming the microporous catalytic supports, it is oxidized around the surfaces of all these elements. In other words, the total oxidation surface area corresponds to the sum of all the surface areas of the elements forming the support, which is much larger than the external surface area of the total volume occupied by said elements. The same argument applies to the fractionation of the supports of the active product D, which increases the water absorption surface areas. In consequence, the fractionation of the supports of the active product A and possibly D into small elements, the fractionated character of the active products B and C and the use of microporous materials with a high specific surface area combine to make the method according to the invention extremely efficient. The hydrogen is effectively oxidized on large surface areas, like the CO, and the water formed is trapped deep in the small elements, due to the capillarity properties of the microporous materials, particularly of the support material of the active product D. In a preferred embodiment of the invention, the microporous support of the active products A is activated alumina Al2O3, in the form of small granules. Activated alumina Al2O3 is a substance with a high specific surface area, more than 200 m2 per gram, indeed more than 300 m2/g. To obtain the best results, the alumina granules have an envelope diameter of a few millimeters, preferably of between about 2 mm and about 20 mm. In the case of the support of the active product A, the granules are slightly impregnated with precious metal (less than 0.1% by weight) or rare earth. Under these conditions, a quantity of granules impregnated with active product A corresponding to one liter by volume or about 800 g by weight, suffices to remove more than 400 liters of hydrogen in the free atmosphere of a closed chamber. In a particular application relative to the transport of radioactive matters, these matters are generally packed in receptacles such as drums lashed inside the container or cask. The active products are then advantageously placed inside these receptacles. This serves to remove the hydrogen directly where it is produced. Only a very small fraction of the hydrogen accordingly escapes from the receptacles to diffuse in the free volume of the container, where it is removed by the active products, also placed in small quantities in this free volume. If the receptacles are sealed, the active products can be placed in sufficient quantities exclusively inside these receptacles. In fact, the hydrogen concentration in the container atmosphere is then always insignificant because the hydrogen is removed in the receptacles and diffuses very little into the chamber of the container. It should be observed that the introduction of the active products into the receptacles serves to continue to prevent the accumulation of hydrogen after their final unloading. Moreover, if the receptacles are intended for storage on site for a long period, the active products can possibly be replenished to ensure the removal of hydrogen continuously on the storage site. In other words, the use of the method according to the invention is not limited to the removal of inflammable gases produced in a closed chamber during transport. In conclusion, the method according to the invention is particularly simple to use in combination with chambers of different types containing radioactive matter comprising organic components and possibly water. The handling operations necessary for placing the active products in the chamber are particularly simple and rapid to perform. The removal of the inflammable gases produced by radiolysis in the chamber is effectively guaranteed. Furthermore, the transport and storage times can be controlled very flexibly because it suffices to introduce appropriate quantities of active products into the chamber for the anticipated transport and/or storage period. The invention will now be described with reference to the following example, provided for illustration and non-limiting. This example illustrates the method of the invention using the following active products a) and b): active product a): alumina (microporous inert solid support) impregnated with palladium (catalyst) in the form of 3 mm beads and having a specific surface area of 300 m2/g; active product b): granules with the following chemical composition: 65% MnO2, 13% CuO, 9% Al2O3 and about 10% H2O. The granules are between 1 and 2 mm in size. The test was performed without active products c) and d). The test was performed as follows: A quantity of 25 grams of active product a) described above and a quantity of 12.5 g of active product b) described above (the products are packaged separately) were placed in a 20 liter chamber (Tedlar bag) containing 600 ml of hydrogen and 53 ml of carbon monoxide. The initial hydrogen concentration was about 5.6%. An H2/CO mixture was injected continuously with the following flow rates: 5.6 ml/h for carbon monoxide and 65 ml/h for hydrogen, representing an H2/CO flow rate ratio of 11.6. This ratio was representative of the ratio of flow rates of H2 and CO generated in a cask containing compacted waste produced by spent fuel reprocessing (of which the average composition was 90% of hulls and end-fittings and 10% of technological waste); the hydrogen and carbon monoxide flow rates were 2 liters/hour and 0.18 liters/hour, respectively. The test lasted 95 hours (up to the exhaustion of the oxygen present in the chamber). The hydrogen content in the chamber was measured throughout the test by chromatography. This content remained lower than 1% (by volume) throughout the test, as shown by the curve of the H2 content as a function of time (hours) shown in FIG. 1. |
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claims | 1. A fuel assembly for a nuclear reactor including:a plurality of elongated nuclear fuel rods having an extended axial length;at least a lowermost grid supporting said fuel rods in an organized array and having unoccupied spaces defined therein to allow a flow of fluid coolant there-through and past said fuel rods when said fuel assembly is installed in the nuclear reactor;a plurality of guide thimbles extending along said fuel rods through and supporting said grid;a bottom nozzle disposed below said grid, below lower ends of said fuel rods, supporting said guide thimbles and permitting the flow of fluid coolant into said fuel assembly, said bottom nozzle comprising a substantially horizontal plate extending transverse to the axis of the fuel rods and having an upper face directed toward said lowermost grid, said upper face of said plate having defined there-through a plurality of flow through holes extending completely through said plate for the passage of the fluid coolant from a lower face of said plate to the upper face of said plate, each of said coolant flow through holes in fluid communication with said unoccupied spaces; andsaid lowermost grid comprising a first, spaced, parallel arrangement of elongated straps extending along a plane substantially orthogonal to the axis of the fuel assembly and a second, spaced, parallel arrangement of elongated straps extending along the plane substantially orthogonal to the axis of the fuel assembly and perpendicular to the first, spaced, parallel arrangement of elongated straps in an egg-crate lattice arrangement that defines a plurality of cells therein through which the fuel rods and guide thimbles pass, each of a first plurality of said cells, through which the fuel rods pass, having walls respectively with a cell height along the axial dimension of the fuel assembly equal to the width of one of the first and second, spaced, parallel arrangement of elongated straps and a cell width along the elongated dimension of the corresponding, elongated strap, and a wall of each of the first plurality of said cells having at least two distinct protrusions that separately extend from the wall inwardly into the cell respectively at different elevations along the height of the wall of the first plurality of cells respectively laterally offset from the center of the cell wall from which the protrusions extend with the protrusions on each of the cell walls from which the protrusions extend arranged in an asymmetric pattern about both a horizontal and a vertical plane and spaced from the nuclear fuel rods at least at the beginning of life of the fuel assembly. 2. The fuel assembly of claim 1 wherein the lowermost grid is positioned substantially adjacent the bottom nozzle. 3. The fuel assembly of claim 2 wherein the bottom nozzle is a debris filter. 4. The fuel assembly of claim 1 wherein the protrusions on the walls from which protrusions extend are offset from one another along the width of the cell walls. 5. The fuel assembly of claim 1 including dimples on the lowermost grid that contact and support corresponding fuel rods substantially in a direction perpendicular to the axis of the fuel assembly. 6. The fuel assembly of claim 5 wherein the dimples and protrusions in each cell of the first plurality of cells are respectively offset from one another along the width of the cell walls. 7. The fuel assembly of claim 1 wherein at least some of the protrusions on the lowermost grid are located at a height along the cell wall coinciding with an elevation of a lower end plug on a corresponding fuel rod. 8. The fuel assembly of claim 7 wherein all of the lowermost protrusions in the at least one wall of the lower most grid are located at the height along the cell wall coinciding with the elevation of the lower end plug of the fuel rod. 9. The fuel assembly of claim 8 wherein substantially all of the protrusions in the at least one wall of the lower most grid are located at the height along the cell wall coinciding with the elevation of the lower end plug of the fuel rod. 10. The fuel assembly of claim 9 wherein substantially all of the protrusions in the at least one wall of the lower most grid are located at the height along the cell wall coinciding with the elevation of a solid portion of the lower end plug of the fuel rod. 11. The fuel assembly of claim 9 wherein substantially all of the protrusions are located at the height along the cell wall coinciding with an elevation below a cladding wall of the fuel rod. 12. The fuel assembly of claim 1 wherein the protrusions are located in proximity to corners of each of the first plurality of cells. 13. The fuel assembly of claim 1 wherein the protrusions are arches. 14. The fuel assembly of claim 13 wherein the arches are formed from a stamped portion of the cell wall connected to the cell wall at a base of the arch. 15. The fuel assembly of claim 13 wherein the arches are elongated with the elongated dimension of the arches extending laterally across a portion of the width of the cell walls of the first plurality of cells. 16. A grid for a nuclear fuel assembly comprising:a first, spaced, parallel arrangement of elongated straps extending along a plane substantially orthogonal to the axis of the fuel assembly;a second, spaced, parallel arrangement of elongated straps extending along the plane substantially orthogonal to the axis of the fuel assembly and perpendicular to the first, spaced, parallel arrangement of elongated straps in an egg crate lattice arrangement that defines a plurality of cells therein respectively through which either a fuel rod or a guide thimble passes; andeach of a first plurality of said cells, through which the fuel rods pass, having walls respectively with a cell height along the axial dimension of the fuel assembly equal to the width of one of the first and second, spaced, parallel arrangement of elongated straps and a cell width along the elongated dimension of the corresponding, elongated strap, and a wall of each of the first plurality of said cells having at least two distinct protrusions that separately extend from the wall inwardly into the cell respectively at different elevations along the height of the wall of the first plurality of cells respectively laterally offset from the center of the cell wall from which the protrusions extend with the protrusions on each of the cell walls from which the protrusions extend arranged in an asymmetric pattern about both a horizontal and a vertical plane and spaced from the nuclear fuel rods at least at the beginning of life of the fuel assembly. 17. A fuel assembly for a nuclear reactor including:a plurality of elongated nuclear fuel rods having an extended axial length;at least a lowermost grid supporting said fuel rods in an organized array and having unoccupied spaces defined therein to allow a flow of fluid coolant there-through and past said fuel rods when said fuel assembly is installed in the nuclear reactor;a plurality of guide thimbles extending along said fuel rods through and supporting said grid;a bottom nozzle disposed below said grid, below lower ends of said fuel rods, supporting said guide thimbles and permitting the flow of fluid coolant into said fuel assembly, said bottom nozzle comprising a substantially horizontal plate extending transverse to the axis of the fuel rods and having an upper face directed toward said lowermost grid, said upper face of said plate having defined there-through a plurality of flow through holes extending completely through said plate for the passage of the fluid coolant from a lower face of said plate to the upper face of said plate, each of said coolant flow through holes in fluid communication with said unoccupied spaces; andsaid lowermost grid comprising a first, spaced, parallel arrangement of elongated straps extending along a plane substantially orthogonal to the axis of the fuel assembly and a second, spaced, parallel arrangement of elongated straps extending along the plane substantially orthogonal to the axis of the fuel assembly and perpendicular to the first, spaced, parallel arrangement of elongated straps in an egg-crate lattice arrangement that defines a plurality of cells therein through which the fuel rods and guide thimbles pass, each of a first plurality of said cells, through which the fuel rods pass, having walls respectively with a cell height along the axial dimension of the fuel assembly equal to the width of one of the first and second, spaced, parallel arrangement of elongated straps and a cell width along the elongated dimension of the corresponding, elongated strap, and a wall of each of the first plurality of said cells having at least two distinct protrusions that separately extend from the wall inwardly into the cell respectively at different elevations along the height of the wall of the first plurality of cells respectively laterally offset from the center of the cell wall from which the protrusions extend with the protrusions on each of the cell walls from which the protrusions extend arranged in an asymmetric pattern about both a horizontal and a vertical plane and spaced from the nuclear fuel rods at least at the beginning of life of the fuel assembly and wherein the first plurality of said cells has at least one wall from which a spring extends into the cells to contact and support the corresponding fuel rods and the at least two distinct protrusions are positioned at elevations along the height of the wall from which the spring extends at elevations on either side of the spring. |
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044410255 | abstract | This invention relates to protective apparel for the human body, and in one embodiment comprises an x-ray protective apron having a main body portion and securing flaps to be wrapped around the body to secure the apron in place. The securing flaps are located approximately in the region of the small of the back when in the securing position and are characterized by being variable as to degree of tightness and by being oriented with their outermost ends in a downward direction when in the secured position, thereby effecting fastening of the apron to the body and varying weight distribution of the apron as between the wearer's shoulders and lower back. |
052271269 | summary | The invention relates to an improved internal structure of a fast neutron nuclear reactor. Fast neutron nuclear reactors of the integrated type comprise a main vessel enclosing the core of the reactor and an internal structure which are immersed in a liquid metal, usually constituted by sodium, for cooling the core. Intermediate heat exchangers and pumps for circulating the liquid metal cooling the core are also disposed inside the main vessel which is closed in its upper part by a very thick slab comprising throughway passages through which the exchangers and the pumps are introduced. The internal structure of the reactor disposed in the main vessel comprises in particular an inner vessel defining a zone of the main vessel receiving the hot liquid metal leaving the core and a zone receiving the cooled liquid metal issuing from the intermediate heat exchangers. The inner vessel comprises generally an assembly of shells coaxial with the main vessel in its upper part and a wall having a generally toroidal shape termed a step shaped area, in its lower part. The heat exchangers and the pumps extend through the step shaped area so that the lower inlet part of the pumps is immersed in the cooled sodium and the intermediate exchangers comprise openings on each side of the step shaped area for ensuring respectively the inlet and the outlet of the liquid metal cooling the core, termed primary fluid, circulating inside the heat exchanger. The primary fluid circulating inside the heat exchanger is cooled in thermal contact with a secondary fluid generally constituted by a liquid metal such as sodium. The secondary fulid heated by the primary fluid is circulated inside the intermediate heat exchangers and in a secondary circuit outside the main vessel of the reactor on which steam generators are disposed. Internal vessels of fast neutron neuclear reactors are known which have a step shaped area constituted by a single wall of toroidal shape whose meridian may have for example the shape of an ogive. In a reactor of known type at present in use, the plating resting on the bottom of the vessel supports the bed on which are fixed the fuel assemblies of the core and a false bed disposed around the bed on which rest the elements providing the lateral neutronic protection of the reactor. The lower part of the step shaped area of the inner vessel is fixed to the plating and the bed is supplied with hot liquid metal coming from the pumps, through piping extending through the plating in radial directions. Sealing devices are placed between the supply piping and the plating and between the bed and the support of the bed. The fact that the supply piping of the bed must extend through the plating, or possibly through the lower part of the inner vessel, complicates the design of the reactor and requires use of sealing devices such as bellows in the region of the passages of the piping to permit maintaining the pressure difference between the part of the vessel receiving the hot liquid sodium, or hot collector, and the part of the vessel receiving the cooled liquid, or cold collector. The lateral size of the sealing devices and of an intermediate support structure such as a bed support renders the design of the primary circuit of the reactor more difficult and results in radial dimensions of the elements of the reactor, and in particular of the main vessel, which may be large. The sealing devices which must be provided between the bed and the support element of the inner vessel such as the plating, for conducting the leakage flow of the primary fluid necessary for the cooling of the main vessel, may have a complex structure. Further, zones are formed around the bed in which the primary sodium is practically stagnant or flows at a low rate; the existence of these zones results in complex thermal stresses on the structures of the reactor during the transitional operating periods of the reactor. A first solution has been envisaged and disclosed in particular in the document FR-A-2,558,635. This solution consist in using a complex structure performing the functions of both the bed and the plating. However, it is still necessary in the case of such a structure to provide a lateral connection and a sealed passage for the primary sodium supply piping of the core. Further, the design of such a integrated structure which is heavy and hyperstatic may be complex; the hyperstatic nature of the structure renders it incapable of following in a satisfactory manner the thermal transitional periods in the course of the operation of the reactor. Lastly, the design of an integrated structure presents drawbacks when assembling or adjusting the reactor unit. An object of the invention is therefore to provide an internal structure of a fast neutron neuclear reactor comprising a main vessel enclosing the core of the reactor and the internal structure which are immersed in a liquid metal for cooling the core, the internal structure comprising an internal vessel defining a zone of the main vessel receiving the hot liquid metal issuing from the core and a zone receiving the cooled liquid metal and comprising a single wall or step shaped area of substantially toroidal shape in its lower part, a support element for the assemblies of the core and for feeding and distributing the liquid cooling metal in the core, termed bed, and a support element for the bed, or plating, resting on the bottom of the main vessel, said internal structure of being of simple design and avoiding the drawbacks of the aforementioned devices of the prior art. For this purpose, this step shaped area of the internal vessel is directly fixed by welding in its lower part to the upper part of the bed and the bed is connected to means for supplying cooling liquid metal in a zone located at its periphery and outside the internal vessel and the plating and rests on the plating through the medium of sliding supports one of which is located on the periphery of the bed and provides a cooling metal seal between the bed and the plating. In order to explain the invention, there will now be described, by way of a non-limitative example with reference to the accompanying drawings, an embodiment of an internal structure of a fast neutron nuclear reactor cooled by liquid sodium according the the invention. |
abstract | A semiconductor processing apparatus includes: a stage on which a substrate having a semiconductor film to be processed is to be mounted; a supply section that supplies a plurality of energy beams onto the semiconductor film mounted on the stage in such a way that irradiation points of the energy beams are aligned at given intervals; and a control section that moves the plurality of energy beams and the substrate relative to each other in a direction not in parallel to alignment of the irradiation points of the plurality of energy beams supplied by the supply section, and scans the semiconductor film with the irradiation points of the plurality of energy beams in parallel to thereby control a heat treatment on the semiconductor film. |
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050193260 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The field of the present invention relates to a mechanical apparatus for handling pellets and the like, as well as examining the external appearance of the handled material. 2. Prior Art In general, pellets to be loaded into nuclear fuel rods are manufactured by molding green compacts of uranium dioxide and similar nuclear fuel powders into a cylindrical form, then sintering. Because defects may develop on the surface of the pellets during the manufacturing process, it is necessary that they be inspected. In the past, inspection of such pellets has been carried out by visual examination by inspection personnel. During this inspection, pellets with surface flaws are removed. With such a method, however, it is necessary that each sintered pellet be individually examined in order to obtain reliable results. Such an inspection method is quite laborious and considerably inefficient, and furthermore, places considerable demands on the inspection personnel. With this in mind, various types of imaging equipment for examining the surfaces of the pellets have been proposed. With such methods, however, elaborate pellet handling devices are required to handle the pellets. Thus visualization and throughput of the pellets at a sufficiently high rate has not yet been achieved. SUMMARY OF THE INVENTION With the above described limitations of the prior art in mind, an object of the present invention is to provide an apparatus which can rapidly and smoothly rotate a pellet or the like about its axis while otherwise maintaining it in a fixed position, then eject the handled object. Furthermore, it is another object of the present invention to provide an apparatus which can inspect the surface of the pellet or other object while it is rapidly handled. Further objects of the present invention will become clear through the description of the preferred embodiments. To achieve the above objectives, the present invention provides a pellet handling apparatus equipped successively with a cylindrical roller and a slotted transfer roller which can freely rotate in the same direction. Furthermore, along with a pellet supply unit which is provided to supply pellets between the above mentioned cylindrical roller and the slotted transfer roller, a pellet transfer unit is provided at the above mentioned slotted transfer roller. Similarly, the present invention provides an external inspection apparatus which includes a circumferential surface inspection unit added to the above described assembly by which means the external circumferential surface of a pellet placed between the above mentioned cylindrical roller and slotted transfer roller may be inspected. Also included is a defective pellet discard unit as part of the above mentioned pellet discard unit by which means pellets judged to be defective by the above mentioned circumferential surface inspection unit are discharged. Moreover, the present invention as recited in claim 3 provides an external inspection apparatus in which a direction switching assembly is included on the first part of the above mentioned pellet supply unit, whereby the direction in which the pellet is conveyed is switched from the axial direction of the pellet to a direction perpendicular thereto. Also provided is a drying--rough sorting apparatus which dries and sorts the pellets after the above described switch in direction, and on this drying--rough sorting apparatus, an end surface inspection unit by which means the ends of the sorted pellets may be inspected. On the last portion of the above mentioned pellet discard unit, a pellet gathering assembly is provided to collect the pellets. The above described direction switching assembly includes a buffer tray upon which the pellets are placed arranged along their axes in multiple columns, as well as a pickup unit by which means the pellets on the buffer tray are grasped on their circumferential surface and conveyed. The above described drying--rough sorting apparatus includes a revolving conveyer unit by which means the pellets are rotated about their longitudinal axes while they are conveyed in a direction perpendicular to their longitudinal axes and a drying unit mounted on the revolving conveyer unit, and mounted on the rear portion of the drying unit, a rough sorting apparatus by which means the circumferential surfaces of the pellets are imaged from above and sorted on the basis of said image. The above mentioned end surface inspection unit has an intermittently rotating conveyer disk with pellet receiving grooves in its outer circumferential surface. While received in the grooves, each end of each pellet is independently imaged, and on the basis of these images, the pellets are judged as acceptable or not acceptable by means of an end surface evaluation unit. The end surface inspection unit also includes a defective pellet discard unit by which means pellets judged defective by the end surface evaluation unit are discarded. The above mentioned pellet gathering assembly includes a pellet placing unit which places and lines up a plurality of the pellets aligned in a direction perpendicular to their longitudinal axes. The pellet gathering assembly also includes an end surface pickup unit by which means the placed and aligned pellets are grasped by their end surfaces and conveyed. For the pellet handling equipment of the present invention as claimed in claim 1, the pellets are supplied from the pellet supply unit and are placed between the cylindrical roller and the slotted transfer roller which rotate in the same direction, and the pellets are thereby caused to revolve in this position. When the slotted transfer roller rotates to the position where its transfer slot meets the pellet, the pellet is received by the slot. For the external inspection apparatus of the present invention as claimed in claim 2, the pellets are supplied from the pellet supply unit and are placed between the cylindrical roller and the slotted transfer roller which rotate in the same direction, and while the pellets revolve in this position, their circumferential surfaces are inspected by the circumferential surface inspection unit. Those pellets judged to be defective are then discarded by the pellet discard unit. For the external inspection apparatus of the present invention as claimed in claim 3, through the action of a direction switching apparatus, the direction in which the pellets are conveyed is switched from the axial direction of the pellets to a direction perpendicular to the circumferential surface of the pellets. The pellets are then dried and rough sorted by means of the drying--rough sorting apparatus, after which the ends of the sorted pellets are inspected by means of the end surface inspection unit. The pellets are then placed between the cylindrical roller and the slotted transfer roller which rotate in the same direction, and while the pellets revolve in this position, their circumferential surfaces are inspected by the circumferential surface inspection unit. Those pellets judged to be defective are then discarded by the pellet discard unit while those judged as suitable collected by the pellet gathering assembly. With the above mentioned direction switching apparatus, the pellets are aligned in multiple columns on buffer trays, and through the action of a circumferential surface pickup unit, the pellets on the buffer tray, one from each column, are grasped on their circumferential surface and conveyed. The previously mentioned drying--rough sorting apparatus includes a revolving conveyer unit over which the pellets proceed in a direction perpendicular to their longitudinal axes while rotating about their longitudinal axes. As the pellets are conveyed, they are dried by the drying unit, and then through the action of the rough sorting unit, their circumferential surfaces are imaged. On the basis of the obtained images, the pellets are sorted as acceptable and defective. In the previously described end surface inspection unit, the pellets are received in grooves in the intermittently rotating conveyer disk, and while received in the grooves, the ends of the pellets are imaged, and on the basis of the images, the pellets are judged as acceptable or not acceptable by means of an end surface evaluation unit. Those pellets judged defective are then discarded by a defective pellet discard unit. With the above mentioned pellet gathering, the pellets are lined up in a direction perpendicular to their longitudinal axes by the pellet placing unit, after which a plurality of the pellets are grasped by means of the end surface pickup unit by their end surfaces and conveyed. |
051868903 | summary | BACKGROUND OF THE INVENTION The present invention relates to a nuclear fuel assembly for a fast breeder reactor, a reactor core wherein the nuclear fuel assembly is used as one of components, and a regulating method of coolant distribution of the reactor core, especially, to the core which is preferable to reduce a pressure drop of coolant of the reactor core of the fast breeder reactor and to improve thermal characteristics of the reactor core. As illustrated in FIG. 3, a nuclear fuel assembly (hereinafter called a fuel assembly) for a fast breeder reactor of the prior art was generally of a type of a fuel assembly which was composed of a wrapper tube 2 wherein a plurality of nuclear fuel rods 1 were arranged in triangle lattices with wire spacers 5 or grid spacers between an upper shield 6 and a lower shield 7. The fuel rod was composed of a cladding tube 4 with a small diameter containing a stack of nuclear fuel pellets 3. The wrapper tube 2 has a uniform inner width in all through the axial direction (vertical direction) of the fuel assembly. The reactor core of the fast breeder reactor was composed of a plurality of the fuel assemblies which were standing together vertically in the core region. The nuclear fuel pellets 3 can be divided into a blanket fuel pellet for breeding and a driver fuel pellet for driving the reactor. The blanket fuel pellets are inserted into each of an upper and a lower blanket region of the cladding tube 4, and the driving fuel pellets are inserted into a core region of the cladding tube 4. A gas plenum portion is formed at lower portion lower than the lower blanket portion of the cladding tube 4. A fuel assembly having a wrapper tube free structure wherein a structural material other than a part of or all of the wrapper tube 2 is deleted is also known. A reactor core is composed of a plurality of fuel assemblies which are standing together vertically in coolant. The fuel assembly comprises a plurality of nuclear fuel rods and a wrapper tube as a means of fuel containment. As for a reactor other than a fast breeder reactor, a technique for a boiling water reactor was disclosed in the JP-A-1-98994 (1989) and the JP-A-59-180389 (1984). The technique described above is close to the present invention in a point of an altered inner width of a nuclear fuel rod container (which is called a channel box in the technical field of the boiling water reactor). In the technique disclosed in the JP-A-1-98994 (1989), an inner width of the channel box is enlarged at a down-stream side of coolant while an outer width is maintained uniform. In the technique disclosed in the JP-A-59-180389 (1984), both of an inner and outer width of a channel box is enlarged continuously from an up-stream side of the coolant to a down-stream side of coolant in a reverse tapered shape. As general characteristics of a type of fuel assembly which had a wrapper tube 2 like a fuel assembly for a fast breeder reactor, the fuel assembly had to have a structure to wrap around a plurality of nuclear fuel rods 1 having a small diameter with a wrapper tube 2 and to settle a small gap between the fuel rods in order to make a reactor core compact and to improve a nuclear characteristics of the reactor, hence a large powered circulating pump was used for coolant circulation because of a large pressure drop of coolant of coolant flowing through a fuel bundle portion, wherein a plurality of nuclear fuel rods 1 are bundled, of the wrapper tube 2. And the wrapper tube 2 had to have a thick wall to sustain the fuel assembly structurally and to depress expansion in horizontal direction caused by neutron radiation and pressure difference between the inner side and the outer side of the wrapper tube 2 in operation. Further, the wrapper tube had a structure to maintain a gap properly between each next wrapper tube 2 even though the fuel assembly expanded in horizontal direction as described above in composing the reactor core by standing a plurality of fuel assembly together vertically in the core region of the reactor. One of the distinguished features of a fast breeder reactor from other type reactors is a phenomenon to cause a dislocation of chemical elements in materials of the wrapper tube and expansion at a portion of the wrapper tube (a middle portion of the wrapper tube) which is faced to a reactor fuel region by the neutron irradiation as burning of the nuclear fuel proceeds. Once the expansion is caused, as the wrapper tube has a closed shape in a horizontal section, both of the inner and the outer width of the wrapper tube are enlarged and a situation wherein a wrapper tube contacts with adjacent wrapper tubes is easily caused. The phenomenon of expansion is called a swelling. The swelling is more distinguished in the fast breeder reactor than in other reactors, and the swelling is different from a channel creep caused by a stress which is generated by a pressure difference between an inner and an outer side of a wrapper tube in other type reactors. In the fast breeder reactor, the middle portion of the wrapper tube expands in a horizontal direction by both of the stress generated by the pressure difference and the swelling. Therefore, although the gap between each of wrapper tubes standing together vertically in the reactor core might be settled closer at regions near both ends of the wrapper tube, a large gap was settled actually in consideration of the expansion in horizontal direction at the middle portion of the wrapper tube in the fast breeder reactor. The gap between each of next wrapper tubes 2 had been maintained with a pad 8 having a larger width than the outer width of the wrapper tube 2 at the portions of the upper and the lower shield 6, 7, locations. The setting of the wrapper tube 2 and the gap between each of wrapper tubes 2 resulted in a reduction of a flow area in the fuel assembly, and had been a cause to increase pressure drop of coolant of the reactor core. If pressure drop of coolant at the portion of fuel rod bundle in the fuel assembly can be reduced, a large reduction of pressure drop of coolant of reactor core as a whole becomes possible. On the other hand, a fuel assembly of wrapper tube free type has less pressure drop of coolant as much as an amount of pressure drop of coolant caused by wrapper tubes, but leakage and unbalancing flow of coolant among fuel assemblies are concerned because wrapper tubes are not existing in the fuel assembly even though distribution of coolant to each fuel assemblies composing of the reactor core is regulated in corresponding to output power of the each fuel assemblies, and an investigation on the composition of the fuel assembly is necessary to resolve the concerning. In a case wherein a technique disclosed in the JP-A-1-98994 (1989) is applied to a wrapper tube for a fast breeder reactor, a plurality of wrapper tubes have to be standing together vertically in a core region with the same large gap as a conventional reactor core in consideration of swelling etc. as the wrapper tube has a uniform outer width all through the total length from the top to the bottom without any exception at middle, upper and lower portion of the wrapper tube. Therefore, a coolant flow area in the wrapper tube has to be reduced reversely as much as a plurality of wrapper tubes occupies a wider area for standing in a limited core region with a large gap between each of wrapper tubes, and consequently, an increasing of pressure drop of coolant of the reactor core is easily induced. In a case wherein a technique disclosed in the JP-A-59-180389 (1984) is applied to a wrapper tube for a fast breeder reactor, a lower end of the wrapper tube is reduced in width, and the reduced portion of the lower end of the wrapper tube is fixed to a member composing an inlet of coolant (equal to the lower shield in the fast breeder reactor), and the width of the reduced portion will not be enlarged even though burning of the fuel is proceeded. Therefore, the reduced portion in width is maintained all through the burning period of the nuclear fuel from the beginning to the end of the period, and will be easily a cause to increase the pressure drop of coolant of the reactor core. Further, a technique to enlarge a width of a middle portion of a wrapper tube by placing a reverse tapered tube is equal to abandon a margin to accommodate expansion in the horizontal direction by swelling etc., which will be caused in the middle of burning period, from the beginning of the burning of the nuclear fuel as much as an amount of enlarged width, and a gap between each of the wrapper tubes has to be enlarged in order to avoid contact with adjacent fuel assemblies even though the expansion in the horizontal direction is occurred. Accordingly, a large area for the reactor core becomes necessary, and the technique is not suitable for the reactor core having a limited area. Therefore, in the technical field of the fast breeder reactor, the development of a fuel assembly which enable to distribute flow of coolant exactly and to decrease pressure drop of coolant in a reactor core having a small area as possible has been desired. SUMMARY OF THE INVENTION The first object of the present invention is to provide a low pressure drop of coolant type fuel assembly which enables to distribute flow of coolant of a fast breeder reactor exactly and to decrease pressure drop of coolant of a reactor core without enlarging the area of the reactor core as possible; the second object of the present invention is to provide a reactor core of the fast breeder reactor which enables to distribute flow of coolant exactly and to decrease the pressure drop of coolant of the reactor core without enlarging the area of the reactor core as possible; the third object of the present invention is to provide a means of fuel containment of the fast breeder reactor for reduction of the pressure drop of coolant of the fuel assembly; and the fourth object of the present invention is to provide a method to regulate the distribution of coolant in the fast breeder reactor which is effective to reduce difference of thermal output power among each of reactor core regions by using the fuel assembly described above. To achieve the first object described above, there is provided a first feature of is a fuel assembly for a fast breeder reactor comprising a plurality of nuclear fuel rods which are arranged in a means of fuel containment characterized that the means of fuel containment is a fuel assembly having a shape which is narrow in both inner and outer width at a middle portion of the means, and on the contrary, relatively wide in both inner and outer widths at closer portions to each of both ends of the means of fuel containment. In the present invention, the middle portion of the means which is faced to the middle portion of the nuclear fuel rods wherein temperature is high and irradiation dose is large shows a tendency to have a larger expansion coefficient in the horizontal direction than the closer portions to each of both ends of the means in reactor operation, and in considering of relatively small expansion coefficient at both ends portion, a larger width than a conventional width can be applicable to the both ends portion for reducing flow resistance of coolant through the means of fuel containment in reactor operation, and as the width of the middle portion of the means will be expanded and enlarged during use in reactor operation, an effect to reduce flow resistance along whole length of the means of fuel containment is obtained, and moreover the exact distribution of coolant is maintained as same as the conventional means because that the coolant flows through the means of fuel containment does not disperse to the externals. A second feature to achieve the first object described above is a fuel assembly for a fast breeder reactor comprising a plurality of nuclear fuel rods which are contained in a means of fuel containment characterized that the means of fuel containment is a fuel assembly of which shape is narrow in width between both of each inner faces and outer faces at a portion of the means which has larger swelling than another portion of the means, and by the second feature, a middle portion of the means of fuel containment where swelling is easily caused has a narrower width than another portion for accommodating the expansion by swelling and for preventing a mutual interference between fuel assemblies which are used in standing together in the reactor core after the expansion, on the other hand, other portion of the means where the swelling is relatively difficult to be caused has a wider width than a conventional means by utilizing a space for preventing the fuel assembly from a mutual interference with adjacent fuel assemblies caused by the expansion with swelling of the middle portion of the means, and consequently the means of fuel containment has a reduced flow resistance for coolant which flow through the means of fuel containment. A third feature to achieve the first object described above is a fuel assembly for a fast breeder reactor comprising a plurality of nuclear fuel rods which are contained in a means of fuel containment characterized that the means of fuel containment is a fuel assembly of which shape is narrower in width between both of each inner faces and outer faces at least at a portion of the means facing to a reactor core fuel portion of the nuclear fuel rod with respect to another portion of the means not facing to the reactor core fuel portion of the nuclear fuel rod, and by the third feature, temperature at the reactor core fuel portion of the nuclear fuel rod will be raised to the highest in use of the fuel assemblies standing together in the reactor, and the portion of the means facing to the reactor core fuel portion of the nuclear fuel rod expands wider than another portion of the means, but even though the expansion is caused, the portion of the means where the expansion is caused has the same narrow width as a conventional means for accommodating the expansion and will not cause any interference with adjacent fuel assemblies, and the another portion of the means has previously wider width than a conventional means by utilizing a space for preventing the fuel assembly from a mutual interference with adjacent fuel assemblies caused by the expansion, and consequently the means of fuel containment has a reduced flow resistance for coolant which flow through the means of fuel containment. A fourth feature to achieve the second object described above is a reactor core of a fast breeder reactor comprising a plurality of nuclear fuel assemblies standing together vertically in a reactor vessel which contains coolant characterized that at least one of the fuel assemblies is a fuel assembly for the fast breeder reactor relating at least to one of the features described above, as the flow resistance of coolant which flow through the fuel assembly is reduced, the reactor core itself of the nuclear reactor which comprises the fuel assembly as an element of the invention has an effect to reduce a pressure drop of the coolant flowing through the reactor core, and a distribution balance of coolant is still maintained because the distributed coolant flow essentially in a space surrounded with the means of fuel containment. A fifth feature to achieve the second object described above is the reactor core of the fast breeder reactor relating to the fourth feature is characterized in being loaded with the fuel assembly which is related to at least one of the features described above to a region of the reactor core wherein a relatively large output power is generated, and in addition to the effect brought by the fourth feature, as the fuel assembly having the reduced pressure drop of coolant is loaded into the region of the reactor core wherein the relatively large output power is generated, an effect that cooling by coolant is intensified and keeping thermal balance with surrounded thermal output power becomes easy is obtained. A sixth feature to achieve the third object described a means of fuel containment for a fast breeder reactor characterized in having a shape that the width of the middle portion of the means is narrow in both of inner and outer widths, and on the contrary, portions closer to each of both ends have a wider width than the middle portion in both of inner and outer widths, and the means of fuel containment has an enlarged width which enables to have a large flow area for reducing pressure drop of coolant at a portion which has a relatively smaller thermal expansion coefficient than the middle portion of the means in reactor operation, and the middle portion of the means of fuel containment gradually expands the width during the reactor operation, but as the expansion is expected previously and the width at the middle portion of the means is not enlarged, any interference between adjacent fuel assemblies would not be occurred in reactor operation, and moreover, owing to the enlargement of the flow area of the coolant with the thermal expansion of the width of the middle portion of the means of fuel containment during the reactor operation, the pressure drop of coolant owing to the means is reduced and hence an effect to reduce the pressure drop of coolant of the fuel assembly is obtained by using the means of fuel containment relating to the present invention. A seventh feature to achieve the first object described above is the fuel assembly for the fast breeder reactor is characterized in having a thinner wall thickness at a portion of the means of fuel containment which faces to the gas plenum portion of the nuclear fuel rod than the wall thickness of the middle portion of the means whereof a width between both of the inner and the outer faces respectively are narrower than the width of another portion, and as the gas plenum portion has a lower temperature and less irradiation dose than the portion where the nuclear fuel exists, the wall thickness at the portion of the means of fuel containment faced to the gas plenum portion of the nuclear fuel rod could be less than the wall thickness of other portion, and the wall thickness at the portion faced to the gas plenum portion can be reduced and an effect to reduce pressure drop of coolant of coolant by enlarging the flow area of coolant in the means of fuel containment as much as equivalent to the reduction in the wall thickness is obtained. An eighth feature to achieve the first object described above is the fuel assembly for the fast breeder reactor is characterized in having a shape that the width of the means of fuel containment is enlarged wider continuously from the middle portion of the means as closing toward the both ends of the means of fuel containment, and as the thermal expansion coefficient becomes continuously smaller as closing toward the both ends of the means even in middle portion of the means, the width of the means of fuel containment can be enlarged as much as equivalent to the decreasing of the thermal expansion coefficient and an effect to reduce pressure drop of coolant of coolant flowing through the means of fuel containment is obtained in addition to the effect of the first feature. A ninth feature to achieve the first object described above is the fuel assembly for the fast breeder reactor is characterized in having a shape that a wall thickness of the means of fuel containment becomes thinner as closing toward the both ends of the means in middle portion of the means, and in as the wall thickness of the means is reduced continuously according to the thermal expansion coefficient of the portion is decreased, the flow area of coolant in the means can be enlarged and an effect to reduce pressure drop of coolant of coolant is obtained in addition to the effect of the first feature. An tenth feature to achieve the fourth object is a method to regulate flow distribution of coolant in a reactor core of a fast breeder reactor which comprises composing the reactor core with a plurality of fuel assemblies standing together vertically in a reactor vessel which contains coolant, and making a difference of thermal output of each reactor core region preferable by distributing flow of the coolant to each of the fuel assemblies in the reactor depending on the difference of thermal output of the each reactor core region, characterized in comprising the steps of enlarging the flow area of coolant of the means of fuel containment at both portions close to both ends of the means, reducing the flow area of coolant of the means of fuel containment relatively small at middle portion of the means facing to the portion of reactor core fuel portion of a nuclear fuel rod, and regulating the flow distribution of coolant by changing the enlarging rate of the flow area of coolant, and, as a value of pressure drop of coolant which flow through the means of fuel containment can be fixed by the enlarging rate of the flow area of coolant of the means of fuel containment, a flow rate of the coolant is fixed depending on the enlarging rate, and consequently, the flow distribution of coolant can be regulated. In utilizing the method to regulate the flow distribution as described above, the difference of thermal output of the each reactor core region can be fixed preferably. |
abstract | A portable information terminal is separated from a charged particle beam irradiation apparatus for performing processing of a sample by irradiating the sample with a charged particle beam. The portable information terminal performs operation of a first operation item at a desired position and includes a display controller causing a display unit to display an image containing a graphical user interface (GUI) capable of operating the first operation item based on operation by a user, the first operation item being one or more operation items among a plurality of items operable in the charged particle beam irradiation apparatus. |
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description | This application is a continuation application of and claims priority to U.S. patent application Ser. No. 10/256,585, filed Sep. 27, 2002, now U.S. Pat. No. 6,855,930 titled “Defect Inspection Apparatus and Defect Inspection Method,” which in turn claims priority to Japanese Patent Application No. 2001-302108, filed Sep. 28, 2001, each of which is incorporated by reference herein in its entirety for all purposes. The present invention relates to a defect inspection apparatus and a defect inspection method, or in particular to a defect inspection apparatus and a defect inspection method using a technique suitable for inspection and analysis of a defect generated on a semiconductor wafer in the process of fabricating a semiconductor electronic circuit, in which an electron beam is radiated on a defective portion and the X-ray spectrum generated is analyzed. (1) Outline of Defect Analysis by EDX A method called EDX (Energy Dispersion X-ray Spectrum) is known as a conventional technique for analyzing the cause of the foreign particles generated on a semiconductor wafer during the semiconductor fabrication process. In this EDX method, an electron beam is radiated on a defect on a semiconductor wafer, and the energy dispersion (spectrum) of the X ray generated from a defective portion and the neighborhood thereof is analyzed to estimate the element composition of the foreign particles. Estimating the element composition of foreign particles is very important for specifying the source of the foreign particles and taking a protective measure against dust in the fabrication process. FIG. 2 is a diagram showing an example of the X-ray spectrum radiated from a defective portion and the neighborhood thereof upon radiation of an electron beam on a defect on a semiconductor wafer. With reference to FIG. 2, an explanation will be given of the fact that an element can be identified by analyzing the X-ray spectrum. The X-ray spectrum includes a continuous X ray and a characteristic X ray as shown in FIG. 2. The continuous X ray is an electromagnetic wave generated by the incident electron beam accelerated in the direction opposite to the direction of progression when it impinges on an object. The magnitude of energy lost by the impinging electrons is various, with the result that X rays having various energies are radiated. Upon impingement of electrons, the electrons around the atomic nucleus of the wafer obtain energy and are released out of the atomic nucleus. Then, an electron vacancy is formed in the trajectory of the atomic nucleus. The electrons in the outer shell having a higher energy level are trapped in this vacancy, and with the resulting extra energy, a characteristic X ray is generated. The energy level of the electrons is determined by the elements, and therefore the wavelength of the characteristic X ray radiated is determined by the elements. Thus, an element can be identified from the combination of the wavelengths of the characteristic X rays appearing in the spectrum. The wavelength of the characteristic X ray has been studied for long time, and the wavelength of the characteristic X ray generated by electron transition between different energy levels has already been determined for each element in the periodic table. The conventional EDX analyzer has such a function that the wavelength of the characteristic X ray of each element is stored in a library and the wavelength of the characteristic X ray extracted from the X-ray spectrum is collated with the library thereby to display a corresponding element and the peak position of the spectrum. The user can thus estimate the elements contained in the portion irradiated with the X ray. (2) Data Acquisition Procedure in EDX FIG. 3 is a flowchart for explaining the data acquisition procedure for a defective portion in EDX. Now, this data acquisition procedure for the detective portion will be explained. The data acquisition procedure is conducted typically by the operator determining whether or not EDX is to be carried out or not while observing the external appearance of the defective portion of a semiconductor wafer as an image under microscope. As shown in FIG. 3, the data acquisition for the defective portions is carried out by repeating, for each defect, a series of steps including (1) loading a semiconductor wafer, (2) moving the stage to a defective portion, (3) confirming the external appearance of the defective portion, (4) determining whether EDX is to be carried out or not, and (5) carrying out EDX. As an alternative, in the case where images of defective portions are collected beforehand using an automatic defect reviewing device, the operator confirms the images collected, selects a defective portion to be subjected to EDX, and carries out the EDX detection process for the selected defective portion. In connection with the foregoing description, a programming method for selecting a defective portion based on the size and type of foreign particles from a list of foreign particles detected by an inspection apparatus is described in JP-A-10-27833, etc. (3) Protective Measure Based on EDX Data FIG. 4 is a diagram for explaining a method of estimating the characteristic X ray unique to an element contained in a defect in actual analysis. Now, with reference to FIG. 4, an explanation will be given of a method of estimating the characteristic X ray unique to an element contained in a defect. In analyzing foreign particles on a product wafer (process wafer), the fact that the X-ray spectrum contains the characteristic X rays generated from the defect or the neighborhood thereof and a lower layer pattern sometimes makes it difficult to estimate the characteristic X ray unique to the element contained in the defect. In actual analysis, therefore, as shown in FIG. 4, for example, the operator detects the X-ray spectrum of the reference portion of an adjoining chip, and by visually comparing the X spectrum of the reference portion with that of the detective portion, estimates the composition of the element contained in the defective portion. Further, the operator estimates the cause of the defect based on the defect composition. As described above, the operator estimates the composition of the element contained in a defective portion and the cause of the defect by estimating the characteristic X ray unique to the element contained in the defect. In taking a protective measure against the defect, the operator is required to have a sufficient knowledge about the composition of a defect which may occur in each process and each fabrication unit through which a product wafer has been processed. Generally, therefore, it is not easy to estimate the cause of a defect. The problems of the conventional techniques described above will be explained below. (1) Number of Steps for Selecting an Object of EDX Analysis Analysis of a defective portion using EDX requires a long time. Specifically, the time required for collecting data on one point is much longer than the time required for the foreign particle inspection apparatus or the defective reviewing device. For examples, assume the presence of 600 defects on a semiconductor wafer having a diameter of 300 mm. The time required for defect detection by a foreign particle inspection apparatus is several minutes for the whole wafer surface, and the time required for collecting the images of all the defects by the defect reviewing device is one hour or two in total. The collecting the X-ray spectra of all defects due to EDX, on the other hand, requires at least several days. Thus, it is unrealistic to apply EDX for all the defects on a semiconductor wafer. Before carrying out EDX, therefore, it is necessary to manually select defects to be subjected to EDX from among the defects found by the inspection apparatus. However, the problem is that this defect selecting process consumes considerable labor. In the case where the work described with reference to FIG. 3 is conducted sequentially on each defect detected by the inspection apparatus, the operator is required to be engaged in the measurement work for long time. In the case where the images of defective portions are collected in advance by the automatic defect reviewing device, on the other hand, the image re-detection is not required but it is necessary for the EDX operator to confirm the images collected and to select defects subjected to EDX at the same time. This still poses the problem that many fabrication steps are required. (2) Estimation of Defect Composition for Process Wafer The method of analyzing the composition of the defective portion according to the prior art described with reference to FIG. 4 poses the problems described below. (a) The peak of the characteristic X ray attributable to the bedding or a lower layer pattern of the wafer cannot be identified automatically. As a result, the operator is required to conduct the work of comparing the spectra of the defective portions and the spectrum of the reference portion, thereby requiring a long time for the comparison work.(b) Long time is required for detecting the X-ray spectrum of the reference portion.(c) Even though the elements contained in the defective portion can be estimated, the information required for coping with the defect cannot be obtained directly. To take a protective measure against defects, it is necessary to introduce the past defect cases and the protective measures taken against them and to study the process to which the product of the particular type is subjected. Thus, it is not always easy to estimate the cause of a defect.(3) X-Ray Spectrum Detection Time The analysis of the defective portion using EDX requires a long time. Specifically, the time required for collecting data for each point is very long as compared with the corresponding time for the foreign particle inspection device or the defect reviewing device. The EDX often requires about one or two minutes to collect the X-ray spectrum for each defect. (4) Reduction of Objects of EDX Analysis There is no conventional method available for reducing the number of objects of EDX analysis to the required minimum. JP-A-10-27833 described above fails to disclose a method of removing, from the list of defects detected by the inspection apparatus, the defect sources requiring no analysis such as a detection error and a pattern defect erroneously detected by the inspection apparatus. Also, this patent publication contains no description about a method of selecting a representative one of defects for each defect type, e.g. selecting one largest defect for each defect type. Nor the same patent publication deal with any method of selecting a defect according to general defect features such as height, size or brightness. The object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a defect inspection apparatus and a defect inspection method in which a defect generated on a semiconductor process wafer is classified rapidly and reliably based on the external appearance and the composition thereof thereby to facilitate the execution of the protective measure against the cause of the defects. In order to achieve the object of the invention described above, according to one aspect of the invention, there is provided a defect inspection apparatus comprising: an X-ray spectrometer of energy dispersion type; means for analyzing a detected defect image acquired through a secondary electron detector and calculating the image features of the defect; a user interface for inputting the criterion (sampling rule) for determining whether the X-ray detection is to be carried out not for the image features of the defect; and a control computer for collating the image features output from the defect image analysis means with the criterion input for selecting the defects and giving an instruction to carry out the X-ray detection for a defect in keeping with the defect selection criterion. According to another aspect of the invention, there is provided a defect inspection apparatus comprising: an X-ray spectrometer of energy dispersion type; means for analyzing the X-ray spectrum detected and determining the peak position of the characteristic X ray; means for storing the reference data including the X-ray spectrum of the defective portion, the peak position of the characteristic X ray determined by the spectrum analysis means and the detected defect image; means for collating the peak position of the characteristic X ray determined by the spectrum analysis means with that of the characteristic X ray of the reference data stored in the reference data storage means and searching for the reference data having an analogous peak position; and a display screen for displaying the defect image and the X-ray spectrum of the reference data searched by the reference data search means. According to still another aspect of the invention, there is provided a defect inspection apparatus comprising: an X-ray spectrometer of energy dispersion type; means for extracting the features of the element composition from the X-ray spectrum detected; means for extracting the features of the detected image generated by the image generating means; and means for classifying defects based on the composition features extracted by the composition feature extraction means and the image features extracted by the image feature extraction means. According to yet another aspect of the invention, there is provided a defect inspection method using an X-ray spectrometer of energy dispersion type, comprising the steps of; inputting a criterion for determining whether the X-ray detection is to be carried out or not based on the image features of a defect; collating the calculated defect image features with the criterion; and detecting the X ray from the defect of an object satisfying the criterion. Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. A defect inspection apparatus and a defect inspection method according to an embodiment of the invention will be explained in more detail below with reference to the drawings. FIG. 6 is a diagram for explaining the concept of the semiconductor fabrication process including an inspection apparatus (reviewing device) according to an embodiment of the invention. In FIG. 6, reference numeral 61 designates a lithography step, numeral 62 an etching step, numeral 63 a deposition (film forming) step, numeral 64 a polishing (chemical mechanical polishing (CMP)) step, numeral 65 a cleaning step, numeral 66 an optical pattern inspection unit, numeral 67 a foreign particle inspection unit, numeral 68 a SEM pattern inspection unit, numeral 69 a reviewing device, numeral 6A a data management server, and numeral 6B a data base. The semiconductor fabrication process, as shown in FIG. 6, includes the lithography step 61, the etching step 62, the deposition step 63, the polishing step 64, the cleaning step 65 and the inspection step. In some cases, there are as many as several hundred steps in total. Various inspection units are used for the inspection step according to the object involved. The inspection units used include the optical pattern inspection unit 66 for inspecting whether a pattern defect is generated or not after etching, the foreign particle inspection unit 67 for inspecting whether foreign particles are generated or not after deposition (forming a film), and the SEM pattern inspection unit 68 for detecting a minute pattern defect. The various fabrication units for executing these steps are connected by LAN. The processing conditions of the semiconductor wafer are transferred to the data management server 6A through the LAN, and information on the steps of processing the semiconductor wafer is accumulated for each lot or wafer. Also, the defect coordinate data detected by various inspection units are transferred, together with the inspection conditions, to the data management server through the LAN and registered in the data base 6B. The inspection unit (reviewing device) 69 is for reviewing (analyzing) in detail the defects detected by the various inspection units described above. The reviewing device 69 receives, through the LAN, the defect coordinate data detected by the various inspection units, and subjecting the defect position thereof to the automatic defect review (ADR) with an electron beam image of high magnitude, makes it possible to observe the detective portion in detail. At the same time, the detected defect image is processed for measurement of the defect size and automatic defect classification (ADC). The reviewing device 69 also analyzes the element composition (EDX) of the detective portion by analyzing the spectrum of the X ray generated by electron beam radiation. Further, by referring to the wafer processing route information accumulated in the data management server, a candidate for the device that has caused the defect is displayed to support the analysis of the defect cause by the operator. Next, the job sequence for the reviewing device 69 will be briefly explained. Before reviewing, the operator sets the conditions for executing ADR/ADC (hereinafter referred to as the ADR/ADC execution conditions) and the conditions for executing EDX (hereinafter referred to as the EDX execution conditions). The review execution conditions include the conditions for detecting the electron beam image. The EDX execution conditions include the conditions for selecting the defects to be detected by EDX and the conditions for detecting the X ray. The operator loads the wafer to be inspected in the apparatus, and after setting the ADR/ADC conditions and the EDX conditions, gives a review start instruction. The reviewing device 69 detects the image of the defect to be reviewed, according to an instruction, and performs the process for calculating the defect feature amount and classifying the defects (ADR/ADC) by image processing. Then, in the case where there is a selected defect to be detected by EDX, the EDX is executed. The detected image and the X-ray spectrum are registered in the data base 6B. FIG. 5 is a block diagram showing a configuration of a reviewer. In FIG. 5, numeral 51 designates an electron gun, numeral 52 an electron lens, numeral 53 a deflection system, numeral 54 a deflection system control circuit, numeral 55 a control computer, numeral 56 a sample chamber, numeral 57 a vacuum system, numeral 58 a vacuum control circuit, numeral 59 an oil-sealed rotary pump, numeral 510 an object to be inspected, numeral 511 a work holder, numeral 512 an X-ray spectrometer, numerals 513, 515 a signal processing circuit, numeral 514 a secondary electron detector, numeral 516 a storage unit, and numeral 518 an electron beam image/X-ray detection system. The reviewing device 69 shown in FIG. 5 is configured of the electron beam image/X-ray detection system 518, the control computer 55 and the storage unit 516. [1] Electron Beam Image/X-Ray Detection System The electron beam image/X-ray detection system 518 radiates an electron beam on the object of inspection 510, and forms a secondary electron image by detecting the secondary electrons generated from the object, or forms an X-ray spectrum signal by detecting the X ray generated from the object. The electron beam image/X-ray detection system 518 is configured of a sample chamber 56, various detectors, a signal processing circuit, a control circuit, etc. The devices making up the electron beam image/X-ray detection system 518 will be explained below. The electron gun 51 is made up of a filament heated for emitting thermal electrons, a Wehnelt cathode for converging the electrons which otherwise might diverge, and an acceleration electrode (anode) for accelerating the converged electron beam. The thermal electrons emitted from the filament are accelerated toward the anode by the voltage of the bias electric field applied to the Wehnelt cathode. The electron lens 52 is for reducing the size of the electron source (electron beam) to several tens of Angstrom on the sample. As shown in simplistic way in FIG. 5, the electro-optic system normally includes two or three stages, in which the electron lens for the electron gun is called the convergence lens and the lens for the sample the objective lens. The deflection system (such as a deflection coil) for radiating the electron beam in deflected way is controlled by the control computer 55 through the deflection system control circuit 54 thereby to scan the electron beam spot two-dimensionally on the object substrate to be inspected. The sample chamber 56 has mounted therein a vacuum gauge 57 and is maintained in vacuum by being exhausted using the oil-sealed rotary pump 59 in compliance with a command from the vacuum control circuit 58. A sample 510 to be inspected such as a semiconductor circuit substrate is mounted and held on a work holder 511 in the sample chamber 56. The secondary electron detector 514 is for detecting the secondary electrons emitted from the surface of the substrate upon radiation of the electron beam thereon. Specifically, in the secondary electron detector 514, the primary electrons scan the wafer so that the secondary electrons are generated from the wafer surface. These secondary electrons are detected by being collected through the interior of the lens by the lens magnetic field. The detection signal of the secondary electron detector is amplified in the signal processing circuit 515, and after being A/D converted, transferred to the control computer 55 through a bus. The X-ray spectrometer 512 outputs an electrical signal corresponding to the energy of the X-ray quantum radiated from the wafer making up the sample to be inspected. This detection signal is amplified in the signal processing circuit 513, and after being A/D converted, is transferred to the control computer 55 through a bus. [2] Control Computer The control computer 55 has various functions including (a) a user interface (I/F) for inputting inspection conditions, (b) the function of controlling the electron beam image/X-ray detection system, (c) the function of processing the waveform data of the detection image and the X-ray signal, and (d) the function of displaying the detection image and the signal, and a data base. These functions will be sequentially explained below. (a) User I/F for Inputting the Inspection Conditions FIG. 7 is a diagram showing an input screen of the inspection conditions. With reference to this diagram, the inspection conditions will be explained. The inspection conditions include the following. (i) Object of Inspection The type, process, lot number, wafer number, etc. are designated. Based on the conditions thus designated, the control computer inquires the data management server of the information on the wafer to be inspected, and downloads the defect coordinate data, the processing start date and the like information through the LAN. (ii) Detection Conditions These conditions include the imaging magnification of the secondary electron image, the acceleration voltage of the electron beam, the probe current and the electron beam radiation diameter. Different conditions can be set for the detection of secondary electrons and the detection of EDX. (iii) Operating Conditions The conditions in general for executing ADR/ADC and EDX are set. The conditions include the defect detection sensitivity of ADR and the designation as to whether AF (Auto Focus) is executed or not. (iv) EDX Sampling Conditions This is a screen for setting the conditions for selecting the defects for which EDX is executed, from among the defects detected by the inspection apparatus. The user designates the select conditions based on the ID, size and type of the defect, as follows. Condition 1: Select the defects of designated ID. Condition 2: Select only the defects with the feature amount in a designated range. Condition 3: Select only the defects with the feature amount in designated order of size Condition 4: Select only the designated defect type. Condition 5: Conditions defined by a combination of the logical product, logical sum and negation of at least one of the conditions 1 to 4. The conditions 2 and 3 described above are for selecting a defect based on the feature amount calculated by the image processing based on the external appearance of the defect in the ADR/ADC execution stage. The feature amount is defined as the size of a defect, for example. The diameter of a typical electron beam for EDX is on the order of μm, while the diameter of a foreign particle defect on the semiconductor wafer to be analyzed is at least on the order of several tens of nm. Thus, an area other than the defect is unavoidably included in the electron beam radiation area. On the other hand, the larger a defect, the larger the proportion of the component of the EDX signal from the defective portion, and therefore the EDX data or the result of processing thereof is expected to increase in reliability, or the EDX signal may be obtained within a shorter time. For this reason, only those defects of a predetermined size or larger can be designated as an object of EDX. The condition 4 described above is for selecting a defect based on the result of classification of defects by ADR/ADC. Defects are classified, for example, into a round foreign particle, an acicular crystal, a cubic crystal or a scratch and a pattern open or pattern short. According to the conditions described above, the following conditions for selection can be designated. In this case, assumed that the defects can be classified into a foreign particle type A, a foreign particle type B, a foreign particle type C, a pattern defect, a nuisance detection or detection error and an unknown defect according to ADC, as follows. Selection condition 1: One each defect of maximum size is selected from each of the foreign particle type A, the foreign particle type B and the foreign type C, and ADR/ADC/EDX are executed. Selection condition 2: One each defect of a size not less than 3 μm is selected from each of the foreign particle type A, the foreign particle type B and the foreign type C, and ADR/ADC/EDX are executed. Selection condition 3: Only ADR/ADC is executed but not EDX for the pattern defect, the scratch defect and the detection error. Selection condition 4: For all unknown defects, ADR/ADC/EDX are executed. By designating the selection conditions described above, the operator can select any of the following modes: (1) EDX is intended to analyze the composition of a foreign particle defect, and therefore is not carried out for the pattern defect, the scratch defect or the detection error (selection condition 3); (2) The unknown defect is always analyzed in detail (selection condition 4); and (3) Even with regard to foreign particles, the requirement is sufficiently met by selecting a representative defect from each category (selection conditions 1 and 2). (b) Function of Controlling the Electron Beam Image/X-Ray Detection System In response to a review instruction issued by the operator through the user I/F for inputting the inspection conditions, the control computer 55 sets the electron beam image detection conditions in the electron beam image/X-ray detection system 518 and gives an instruction to detect an image. The electron beam image/X-ray detection system 518 moves the stage to the defect coordinate position based on the defect coordinate data of each defect and thus detects secondary electron images. The images thus detected are transferred to and stored in the control computer 55. Then, the control computer 55 sets the conditions for X-ray detection in the electron beam image/X-ray detection system 518 and gives an instruction for X-ray detection. The electron beam image/X-ray detection system 518 moves the stage based on the defect coordinate data for each defect designated in advance to be covered by EDX and detects the X ray. The X-ray spectrum thus detected is transferred to and stored in the control computer 55. The defects to be covered by EDX can be designated either before review or while checking the review images collected. (c) Function of Processing Waveform Data of Detection Image and X-Ray Signal FIG. 8 is a diagram for explaining the concept of the automatic defect classification process. With reference to FIG. 8, the function of processing the detected images and the waveform data of the X-ray signal will be explained. The control computer 55 processes the detected defect images and automatically classifies the defects. First, N image feature amounts of the defect are calculated from a defect image and the image is set as a corresponding point in the N-dimensional space of the feature amount. The image feature amount includes the defect size, the geometric feature such as the roundness, the average value of brightness, the texture feature such as dispersion and the phase-related feature such as whether the defect is located on the bedding or the pattern in the image. The category classification of samples in correspondence with the feature amount space is a subject that has long been studied in the field of pattern recognition, and various methods are known. Some examples include a classification method based on whether a feature amount is included in a range predetermined by the user, and a method in which a distribution model (for example, N-dimensional normal distribution) in the feature amount space is assumed and parameters (including the mean vector and the variance/covariance matrix for the N-dimensional normal distribution) included in the distribution model are estimated using a teaching defect image thereby to determine a discriminant function. With the functions described above, the reviewing device 69 automatically collects and classifies the images of defects. Thus, EDX can be carried out efficiently only for the defects meeting the conditions designated in advance by the operator. It was explained above that the conditions for selecting the defects to be subjected to EDX are set before review according to an embodiment of the invention. According to the invention, however, the conditions for selecting the defects to be subjected to EDX can be set alternatively while checking the review image after ADR/ADC. FIG. 9 is a diagram showing an example of a screen for setting the conditions for selecting the defects to be subjected to EDX. The use of this setting screen makes it possible to determine the selection conditions while checking the review image classification result and therefore an efficient selection is realized. (d) Function of Displaying Detection Images and Signals, and the Data Base Function FIG. 10 is a diagram showing an example in which the detection images collected automatically (ADR), the result of automatic classification (ADC) of the detection images and the result of detection of the X-ray spectrum (EDX) are displayed in a single display screen. The operator can observe the image and the EDX at the same time on the display as shown in FIG. 10, and consequently can analyze a defect rapidly and accurately. These detected data and the processing result are registered in the data base of the storage unit 516. Now, a second embodiment of the invention will be explained. According to the second embodiment of the invention, defects are classified and the cause of the defects estimated by EDX or by using both EDX and the image at the same time. The second embodiment described below has a similar hardware configuration to the first embodiment but is different from the first embodiment in the method of processing the detection signal and the configuration of the data base. In the second embodiment of the invention, the foreign particle information unique to the fabrication system having a dummy wafer (face plate wafer) for system management are collected and registered as reference information for defect classification. FIG. 1 is a flowchart for explaining the operation of processing the detection signal according to the second embodiment of the invention. With reference to FIG. 1, the processing operation will be briefly explained. The process is configured of two stages including learning and classification. (Learning) At the time of learning, the element composition of the foreign particles on the process QC wafer (the wafer charged on the line for the purpose of monitoring the fabrication system) is registered in the foreign particle data base for QC. The correspondence between each element and the wavelength of the characteristic X ray unique to the particular element is incorporated beforehand as a data base of the characteristic X rays for each element. (Step 1: Extraction of Peak Position of Characteristic X Ray) Te X-ray spectrum of a defective portion is detected, and the peak position of the characteristic X ray is extracted from the X-ray spectrum. FIG. 11 is a diagram for explaining a method of extracting the peak position of the characteristic X ray from the X-ray spectrum. As shown in FIG. 11, the X-ray spectrum is obtained as an X-ray energy and the X-ray quantum count N1 (E) corresponding to the particular energy. It is known that the process of releasing the X-ray quantum can be obtained in a model as a Poison process, and that in the case where the count of the continuous X rays registered in advance is N2 (E) for each energy, for example, the standard deviation σ is estimated as √{square root over ( )}N2 (E). By determining whether the count N1 (E) is included in the reliability range of 100*(1−α)% of the continuous X rays, therefore, the strength of the characteristic X ray can be determined. In the foregoing description, α can be set as a parameter in advance by the operator or built in the system in advance. (Step 2: Estimation of Elements Contained in Defective Portion) By collating the extracted peak position with the character X-ray data base by element, the elements contained in the defective portion are estimated. This estimation can be carried out by employing a method in which assuming that the extracted peak positions are given as {Pi: i=1, . . . , N}, the elements having each peak {Pi} of the characteristic X ray can be comprehensively listed at the time of collation with the data base X. (Step 3: Registration in Foreign Particle Data Base for QC (Quality Control)) The information for specifying a defect (type, process, wafer number, defect ID, etc.), the detection signal and the analysis result (type of elements estimated to be contained, the X-ray spectrum and detection image) are registered in the foreign particle data base for QC. As an alternative, the defects may be registered with the category assigned to them. (Classification) (Step 1: Extraction of Peak Position of Characteristic X Ray) The peak position of the characteristic X ray is extracted from the X-ray spectrum of a defect to be inspected. (Step 2: Estimation of Elements Contained in Defective Portion) The elements contained in the defective portion are estimated by collation with the data base in which the wavelength of the characteristic X ray of each element is registered. (Step 3: Comparison) The foreign particle defects for QC registered in the foreign particle data base for QC are searched for a defect having the same element, which defect is displayed. More specifically, the defect having the same element(s) as those estimated in step 2 as being contained in the defective portion is searched from the defects registered in the foreign particle data base for QC and is displayed. In the absence of such a defect, a signal indicating the absence of analogous defects is output. As an alternative, a defect which contains an element(s) that is (are) partially in common or is same may be output. In the case where the defect category is also registered in the foreign particle data base for QC, on the other hand, the category assigned to the registered defect is output at the same time. FIG. 12 is a diagram for explaining an example of the procedure for registering the reference information on the process QC wafer. With reference to FIG. 12, the procedure for registering the reference information for the process QC wafer will be explained. Each step of registering the reference information for the process QC wafer, as shown in the flowchart of FIG. 12, for example, is executed sequentially by the foreign particle inspection unit and the reviewing device. Normally, the inspection step is incorporated as an appearance inspection step once for every several to several tens of steps. The process QC wafer is inspected for defects by the foreign particle inspection unit following the completion of the process in the fabrication units A to D for executing the steps A to D shown in FIG. 12. The defects thus detected are reviewed by the reviewing device thereby to collect the images and the X-ray spectra. The defective models, the lot number, the wafer number, the image, the X-ray spectrum, the process of defect occurrence and the user defining category including the information obtained by the review are registered. The procedure described above completes the registration in the data base of the X-ray spectrum and the image information of the defects occurred in each step. FIG. 13 is a flowchart for explaining the operation of processing the detection signal according to a modification of a second embodiment of the invention. This modification will be explained below. The processing operation shown in FIG. 1 is different from that shown in FIG. 13 in that the processing operation shown in FIG. 13 makes it easy to take a protective measure against defects by searching and displaying the history of protective measures with reference to the data base of the history of the protective measures against foreign particles. The data base of the history of the protective measures against foreign particles has registered therein the information on the history of the protective measures taken against foreign particles generated in the past for each defect, including the wafer type, the process, the lot ID, the wafer ID, the defect ID and corresponding information on the protective measures (the defect sources, specific protective measures, dates at which the measures were taken, etc.). FIG. 14 is a flowchart for explaining the operation of processing the detection signal according to another modification of the second embodiment of the invention. This modification will be explained below. The example of the processing operation shown in FIG. 14 is to detect the X-ray spectrum of the reference portion as well as that of the defective portion, and by using it for classification, to make possible a very reliable classification. Specifically, in this example, and the X-ray spectrum of the defective portion is detected, the peak position of the characteristic X ray is extracted from the X-ray spectrum. Then, the reference X-ray spectrum is detected, and the peak position of the characteristic X ray is extracted from the X-ray spectrum. Further, the peak positions of the characteristic X rays obtained from the defective portion and the reference portion are compared with each other. In the case where comparison shows that a peak absent in the spectrum of the reference portion appears in the spectrum of the defective portion, the particular peak is regarded as the one unique to an element contained in the defective portion, and the element is estimated by reference to the characteristic X ray data base. In the case where comparison shows that the spectrum of the defective portion coincides with or is included in that of the reference portion, on the other hand, it is decided that the element contained in the defective portion is identical to the ions sputtered in the bedding, the pattern or the oxide film. Further, in the example shown in FIG. 14, the defects registered in the foreign particle data base are searched for an analogous defect. As an alternative, the data base storing the past information on the history of protective measures against foreign particles may be searched. FIG. 15 is a flowchart for explaining the operation of processing the detection signal according to still another modification of the second embodiment of the invention. This modification will be explained below. The processing operation shown in FIG. 15 is different from that shown in FIG. 14 that in the processing operation shown in FIG. 15, the X-ray spectrum of the reference portion is registered. The X-ray spectrum of the reference portion is defined as the X-ray spectrum detected at a specific point on the wafer before review. Normal points are considered to have the same element composition, though somewhat different from one detection point to another. Once a reference X-ray spectrum is detected for each product type and step, therefore, the element composition of the normal points can be registered in advance before review. FIG. 16 is a flowchart for explaining the operation of processing the detection signal according to yet another modification of the second embodiment of the invention. This modification will be explained below. The processing operation shown in FIG. 16 is different from that shown in FIG. 1 most significantly in that in the processing operation shown in FIG. 16, the automatic classification or the search is conducted using both the image information and the X-ray spectrum at the same time. Specifically, in the process shown in FIG. 16, the first step is to detect, at the time of learning, the X-ray spectrum of foreign particles on the process QC wafer and register it in the foreign particle data base as in the case explained with reference to FIG. 11. Then, at the time of classification, the X-ray spectrum of the defective portio is detected and the composition of the elements is estimated. At the same time, the feature amount of the image is also calculated by detecting the image of the defective portion. Next, the classification is carried out based on the element composition and the image feature amount. Assuming that the element composition is one of the feature amounts, the general classification and search method explained in the first embodiment is applicable. As a modification of the example described above, the result of classification by composition analysis and the result of classification by image can be combined with each other. FIG. 17 is a diagram showing an example of the screen for displaying the classification result by composition analysis and the classification result by image combined. In FIG. 17, “Class 1” and “Class 2” indicate the classification according to the elements contained in the defect. Defects having the same element composition may present different appearance depending on the process of defect generation. The external appearance of the defect generated by reaction in gas phase, for example, is different from that of the defect caused when a reaction product attached to the inner wall of the chamber drops. For taking a protective measure against defects, therefore, it is desirable to determine the dust generating process according to the external appearance of a defect as well as the dust-generating process based on the element composition of the defect. On the other hand, “Class A” and “Class B” indicate the classification based on the external appearance of defects. Defects having an analogous external appearance may have different compositions. Foreign particles generated in a different fabrication apparatus, for example, may assume a spherical shape due to the reaction in gas phase. In taking a protective measure against defects, therefore, it is desirable to estimate the dust-generating apparatus according to the element composition as well as the defect classification based on the appearance. The portions covered by both the classification of Class 1, Class 2 and Class A, Class B indicate a combination of the classification result by composition analysis and the classification result by image described above. The operator can estimate the dust source and the dusting process by observing the classification result based on the X-ray spectrum and the image information. As described above, the operator can change and optimize the EDX execution conditions dynamically according to the classification result indicated. Conditions for executing EDX include the acceleration voltage, for example. The higher the acceleration voltage, the broader the area in which the electron beam expands in the sample, thereby leading to the trend to generate the X rays from a wider area. Also, the higher the acceleration voltage, the larger the tendency toward a higher S/N, i.e. a higher ratio of the detection intensity of the characteristic X ray to that of the continuous X ray. As long as the X-ray detection area is not excessively large as compared with the size of the object of measurement, i.e. the defect size, therefore, the acceleration voltage is desirably higher. In accordance with the defect size, therefore, the acceleration voltage is changed. As explained above, the embodiments of the invention implement (2) to (5) of the following functions by the inspection apparatus constituting the reviewing device according to the invention: (1) the inspection function to detect the defect position from above the wafer to be inspected, (2) the defect review/automatic classification function to re-detect and classify the image at the defect position, (3) the sampling function to select the object of EDX analysis based on the review result, (4) the EDX function to subject the selected defect to EDX analysis, and (5) the function to collectively process the EDX analysis result and the image review result. Nevertheless, according to the invention, the functions of the inspection system including the inspection units can be shared in any other appropriate way. Some examples of the manner in which the functions of the inspection system are shared are: (I) to mount all the functions of (1) to (5) above on the inspection apparatus constituting a reviewing device, (II) to mount the function (1) on a corresponding inspection unit, the functions (2) and (3) on an inspection unit constituting a reviewing device, the function (4) on the analyzer, and the function (5) on the inspection server, and (III) to mount the function (1) on a corresponding inspection unit, the functions (2), (3) and (5) on an inspection unit constituting a reviewing device, and the function (4) on the analyzer. According to the embodiments of the invention, the number of steps for selecting the object to be subjected to EDX analysis can be reduced and the EDX can be executed efficiently. Specifically, the detection error made by the inspection apparatus and the pattern defects erroneously detected by the inspection apparatus can be removed automatically from the objects of EDX analysis. Also, the largest defect can be selected for each defect type, or otherwise a representative defect to be subjected to EDX analysis can be selected for each defect type. Further, defects can be selected according to ordinary defect features such as height, size or brightness. In addition, the embodiments of the invention described above can reduce the number of steps of analyzing the composition of the defective portion of a process wafer and estimating the cause of the defects. Further, the composition of the defective portion of a process wafer can be analyzed with highly reliability. What is more, defects can be classified according to the composition and the external appearance thereof, thereby making it possible to easily and accurately determine the cause of the defects and the manner in which they are generated. It will thus be understood from the foregoing description that according to the invention, the composition of the defective portion can be analyzed with higher rapidity based on the X-ray spectrum while at the same time easily and accurately determining the cause of the defects and the manner in which they are generated. It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. |
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059057718 | claims | 1. A repaired core shroud of a nuclear reactor, comprising: a circular cylindrical section of said core shroud having a crack therein; a first portion of said circular cylindrical section of said core shroud located on one side of said crack and having a first hole therethrough; a second portion of said circular cylindrical section of said core shroud located on another side of said crack and having a second hole therethrough; a member bridging said crack and having a first hole which is aligned with said first hole in said core shroud and a second hole which is aligned with said second hole in said core shroud; a first fastener installed in said aligned first holes; and a second fastener installed in said aligned second holes, wherein said member is fastened to said shroud at least in part by said first and second fasteners. a first fastener element having a threaded surface and a conical surface which is coaxial with said threaded surface; sleeve means comprising a longitudinal slot, an external surface which matches said first holes, an internal surface which matches said conical surface of said first fastener element and a flange which extends radially outward beyond said external surface; and a second fastener element having a threaded surface threadably engaged with said threaded surface of said first fastener element. placing a reinforcing member in a position adjacent said circular cylindrical section of said core shroud and bridging said crack; and forming first and second holes in said reinforcing member and first and second holes in said circular cylindrical section of said core shroud, said first hole in said circular cylindrical section of said core shroud being on one side of said crack and said second hole in said circular cylindrical section of said core shroud being on another side of said crack, said first and second holes in said circular cylindrical section of said core shroud being separated by a predetermined distance and said first and second holes of said reinforcing member being separated by said predetermined distance, the result of said placing and forming steps being that said first hole of said reinforcing member is aligned with said first hole in said circular cylindrical section of said core shroud and said second hole of said reinforcing member is aligned with said second hole in said circular cylindrical section of said core shroud, inserting a first fastener into said aligned first holes of said reinforcing member and said circular cylindrical section of said core shroud; securing said first fastener in place in said first holes of said reinforcing member and said circular cylindrical section of said core shroud; inserting a second fastener into said aligned second holes of said reinforcing member and said circular cylindrical section of said core shroud; and securing said second fastener in place in said second holes of said reinforcing member and said circular cylindrical section of said core shroud. 2. The repaired shroud as defined in claim 1, wherein said crack is located in a vertical weld seam. 3. The repaired shroud as defined in claim 1, wherein said crack is located in a circumferential weld seam. 4. The repaired shroud as defined in claim 1, wherein said first fastener comprises a first pin having a threaded portion with a longitudinal axis and an unthreaded portion with a surface of revolution about said longitudinal axis. 5. The repaired shroud as defined in claim 4, wherein said surface of revolution is conical. 6. The repaired shroud as defined in claim 4, wherein said first fastener further comprises first sleeve means having internal surface means which match said surface of revolution of said first pin and external surface means which match at least one of said first holes when said first sleeve means is in a first state, said internal surface means being in contact with said unthreaded portion of said first pin and said external surface means being in contact with said at least one of said first holes, and having flange means which can fit in said first holes when said first sleeve means is in a second state but not when said first sleeve means is in said first state. 7. The repaired shroud as defined in claim 6, wherein said first fastener further comprises a threaded nut threadably engaging said threaded portion of said first pin for blocking displacement of said first pin in one direction along said longitudinal axis, and said flange means blocks displacement of said first pin in a direction opposite to said one direction when said first sleeve means is in said first state. 8. The repaired shroud as defined in claim 6, wherein said first sleeve means comprises a sleeve having a longitudinal slot, said slotted sleeve being flexed in said first state and unflexed in said second state. 9. The repaired shroud as defined in claim 8, wherein said longitudinal slot extends the full length of said sleeve. 10. The repaired shroud as defined in claim 6, wherein said first sleeve means comprises a plurality of sleeve segments, each of said sleeve segments subtending an equal angle, the sum of said angles being less than 360.degree.. 11. The repaired shroud as defined in claim 1, wherein at least a portion of said first fastener is doped or coated with a noble metal. 12. The repaired shroud as defined in claim 1, wherein said member is a curved plate having a radius of curvature. 13. The repaired shroud as defined in claim 1, wherein said first fastener comprises: 14. The repaired shroud as defined in claim 13, wherein said first fastener element comprises a tapered shank having a conical surface and a threaded surface, and said second fastener element comprises a threaded bolt threadably engaged with said threaded surface of said tapered shank. 15. A method for repairing a circular cylindrical section of a reactor core shroud having a crack therein, comprising the steps of: 16. The method as defined in claim 15, wherein said inserting and securing steps are performed by remote manipulation on only one side of said shroud. 17. The method as defined in claim 15, wherein said secured first fastener exerts a radially outwardly directed contact load on the surface of said first hole in said shroud. 18. The method as defined in claim 15, wherein a first portion of said secured first fastener extends outside said first holes and inside said shroud and a second portion of said secured first fastener extends outside said first holes and outside said shroud. |
summary | ||
description | The present invention relates to a nuclear fuel assembly for boiling water reactors, of the type comprising a water channel extending along a longitudinal axis and having an upper section of larger cross-section area than a lower section and at least one fuel rod receiving groove extending longitudinally on the outer surface of the lower section, fuel rods extending longitudinally and disposed in an array around the water channel and fixing members for fixing at least one fuel rod to the water channel in the at least one groove below the upper section. A conventional nuclear fuel assembly for boiling water reactor comprises a bundle of fuel rods and a water channel arranged in a fuel channel, the water channel being surrounded by the fuel rods. In operation, water flows through the water channel and through the fuel channel, from lower end to upper end of the fuel assembly. Water serves as a moderator for the nuclear reaction and as a coolant. Water is progressively heated, so that water is in vapour-liquid phase nearby the upper end of the fuel assembly. The water channel enables to increase the moderator (water) to fuel ratio and the coolant amount near the central region of the fuel assembly. The moderator (water) to fuel ratio tends to decrease toward the upper end of the fuel assembly as the proportion of vapour increases in the water flow, namely in the water channel. The decrease of said ratio leads to a less efficient burning of the fuel in the upper region. Providing fuel rods of shorter length enables to reduce the amount of nuclear fuel in the upper region of the fuel assembly and to improve burning of the nuclear fuel in said upper section. Providing a water channel having an upper section of larger cross-section area enables to increase the amount of water in the upper region, to compensate the increase of vapour in the water flow, and to thus improve burning of the fuel rods. U.S. Pat. No. 5,202,085 describes a nuclear fuel assembly having a water channel surrounded by fuel rods. The water channel has a lower section having a cruciform cross-section occupying a region equivalent to five fuel rod cells and an upper section of square cross section occupying a region equivalent to nine fuel rod cells. The fuel rods comprise shorter fuel rods disposed adjacent the water channel beneath the upper region. However, such an arrangement makes it difficult to catch the shorter fuel rods located beneath the upper section, e.g. in view of replacing one of these fuel rods. An object of the invention is to provide a water channel for a nuclear fuel assembly for a boiling nuclear reactor which enables to improve burning of the fuel while making handling of the fuel rods more convenient. To this end, the invention provides a water channel of the above-mentioned type, wherein the at least one groove extends along the upper section such that a fuel rod received in fixing members is longitudinally extractable or insertable from the upper end side of the fuel assembly. In other embodiment of the invention, the water channel comprises one or more of the following features, taken in isolation or in any technically feasible combination: the or each groove is of constant width along the lower section and the upper section; the or each groove has a depth larger in the lower section than in the upper section; the or each groove is adapted to receive at least one fuel rod; the or each groove is adapted to receive at least two fuel rods side-by-side; the water channel has a main duct and at least two lateral ducts in fluid communication with the main duct along the whole length of the water channel, lateral ducts defining between them at least one fuel rod reception groove on the outer surface of the water channel; each lateral duct has a cross section area which is constant along the length of the water channel, and the main duct has a larger cross section area in the upper section than in the lower section; each lateral duct replaces at least one fuel rod in the array; each lateral duct replaces one fuel rod in the array; the main duct replaces at least one fuel rod in the array; the main duct replaces a square unit of several fuel rods in the array; the main duct replaces a four fuel rods square unit in the array; the water channel has four lateral ducts defining between them four fuel rod reception grooves around the water channel; the water channel has a cruciform cross section replacing fuel rods disposed in the diagonals of a fuel rods square unit of the array; the water channel replaces fuel rods disposed in the diagonals of a sixteen fuel rods square unit of the array. As illustrated on FIG. 1, the nuclear fuel assembly 2 is elongated along a longitudinal central axis L. Only an intermediate section of the fuel assembly 2 is represented on FIG. 1. In use, the fuel assembly 2 is placed in the core of a nuclear reactor with the axis L extending substantially vertically. In the following, the terms “lower” and “upper” refer to the position of the fuel assembly 2 in the reactor. The fuel assembly 2 comprises a bundle of nuclear fuel rods 4, 6 and a water channel 8 arranged in a fuel channel 10. The fuel rods 4, 6, the water channel 8 and the fuel channel 10 are elongated and extend longitudinally parallel to axis L. Each fuel rod 4, 6 comprises a tubular cladding filled with stacked nuclear fuel pellets. The water channel 8 is surrounded by the fuel rods 4, 6. The water channel is tubular and elongated along direction L. The water channel 8 comprises a tubular lower section 14 and a tubular upper section 16 of larger cross section area than the lower section 14. The fuel rods 4, 6 are arranged in an array and the water channel 8 replaces some of the fuel rods in the array. Fuel rods 4 are shorter than fuel rods 6. The shorter fuel rods 4 extend only along the lower section 14 without extending along the upper section 16. The longer fuel rods 6 extend along the lower section 14 and the upper section 16, i.e. substantially along the whole length of the water channel 8. The fuel assembly 2 comprises fuel rod supporting spacers 18 distributed along the length of water channel 8, only one spacer 18 being illustrated on FIG. 1. The spacer 18 is latticed and comprises a plurality of cells 20 for receiving the longer fuel rods 6 therethrough, and a central passage 22 for receiving the water channel 8 and the shorter fuel rods 4. The spacer 18 is guided by the water channel 8 and its axial movement is restricted, e.g. by welded spacer stops. The fuel assembly 2 comprises fixing members 24 for receiving the shorter fuel rods 4. The fixing members 24 are fixed along the lower section 14 of water channel 8 for fixing the shorter fuel rods 4 adjacent to the water channel 8. As illustrated on FIG. 2, each longer fuel rod 6 extends through a respective cell 20 and is supported transversally by the spacer 18 to maintain the transversal gap between the longer fuel rods 6. To this end, each cell 20 has protrusions protruding from the lateral walls of the cell 20 to contact the outer surface of the longer fuel rod 6 inserted through the cell 20. In the represented embodiment, the spacer 18 is arranged such that the cells 20 are disposed in a 10×10 lattice with the passage 22 replacing the sixteen cells square unit at the centre of the network. As illustrated on FIG. 3, the lower section 14 and the upper section 16 of the water channel 8 have cross sections of the same shape, upper section 16 having however a larger cross section area that lower section 14, as it will be explained later. The water channel 8 has a cruciform cross section and replaces eight fuel rods in the array, the branches of the cross corresponding to the two diagonals of a sixteen fuel rods square unit in the array. The water channel 8 has a main duct 26 and four lateral ducts 28 in fluid communication with the main duct 26 through transverse openings 30 extending along the whole length of the water channel 8. The main duct 26 has a substantially square section and replaces a four fuel rods square unit in the array, and each lateral duct 28 has a substantially square section and replaces one fuel rod in the array. Each lateral duct 28 is disposed at one of the four corners of the main duct 26 and aligned with the diagonals of the main duct 26. The water channel 8 has four grooves 32 provided on the outer surface 34 thereof and distributed around the longitudinal axis of the water channel 8. Each groove 32 is adapted to receive two shorter fuel rods 4 side-by-side. Each groove 32 is defined between two lateral ducts 28. Each groove 32 has a U-shaped cross section defined by a bottom wall 36 and two lateral walls 38. The bottom wall 36 externally defines the groove 32 and internally defines the main duct 26. Each lateral wall 38 externally defines the groove 32 and internally defines a lateral duct 28. The main duct 26 is thus defined by the bottom walls 36 of the grooves 32. The walls of the water channel 8 have a constant thickness along the length of the water channel 8. The varying cross section area of the water channel 8 is obtained via deformations of the walls of the water channel 8. In view of obtaining a larger cross section area in the upper section 16, the main duct 26 has a larger cross section area in the upper section 16 than in the lower section 14. To this end, the main duct 26 has a diverging section 40 at the junction between the lower section 14 and the upper section 16, in which the bottom walls 36 are inclined relative to the longitudinal axis of the water channel 8 and diverge from lower section 14 towards upper section 16. Each lateral duct 28 has a constant cross section area along the length of the water channel 8. Each groove 32 has a constant width W along the length of the water channel 8 (i.e. along the lower section 14 and the upper section 16) and a depth D larger along the lower section 14 than that d along the upper section 16. The water channel 8 is obtainable e.g. by extrusion. Each fixing member 24 comprises a tubular sleeve 42 adapted to receive a shorter fuel rod 4 therein, and inwardly protruding projections 44 adapted to contact the outer surface of a shorter fuel rod 4 passing trough the sleeve 42. Each fixing member 24 is fixed on the lower section 14 in one of the grooves 32, namely on the outer surface of the bottom wall 36 of the groove 32. Several fixing members 24 are distributed and aligned longitudinally along the lower section 14 for receiving a shorter fuel rod 4. As illustrated on FIG. 3, fixing members 24 are arranged in pairs, the fixing members of each pair being disposed side-by-side in the same groove 32 for receiving two shorter fuel rods 4. The fixing members 24 of each pair are separate. In an alternative, two adjacent fixing members 24 are connected one to the other and form a 2×1 fixing device. The depth of the groove 32 at the upper section 16 and the fixing members 24 are adapted such that the outer surface of each short fuel rod 4 does not radially interfere with the bottom wall 36 and lateral walls 38 of the groove 32. In operation, water flows through the water channel 8 and also through the fuel channel 10 between the fuel rods 4, 6. The water serves as a moderator for the nuclear reaction: it slows down the neutrons emitted by the fuel pellets contained in the fuel rods 4, 6. The water also serves as a coolant and exchanges heat with the fuel rods 4, 6. The water channel 8 surrounded by the fuel rods 4, 6 enables to increase the moderator (water) to fuel ratio and the coolant amount in a central region of the fuel assembly 2. The water flow is heated from the lower end to the upper end of the fuel assembly 2. At the upper end, the water flow is in vapour-liquid phase, the quantity of vapour increasing from lower end to upper end. Vaporized water is less efficient than liquid water as a moderator, and efficiency of fuel burning depends among others on the moderator to fuel ratio. The shorter fuel rods 4 reduce the amount of nuclear fuel in the upper region of the fuel assembly 2. The upper section 16 of larger cross section of the water channel 8 provides a greater amount of water in the upper region of the fuel assembly. As a result, it is possible to compensate a decrease of moderator to fuel ratio due to increasing amount of vaporized water. As illustrated on FIG. 5, each shorter fuel rod 4 can be gripped from the upper end of the fuel assembly 2 and slide upwardly through the groove 32 along the upper section 16 for extracting the short rod 4 without removing the water channel 8, e.g. in view of maintenance operations. A shorter fuel rod 4 can be inserted in the corresponding fixing member 24 in the same manner. This is due to the fact that the grooves 32 provided in the lower section 14 extend along the upper section 16 with a depth adapted so that a shorter fuel rod 4 will not interfere with the walls 36, 38, and specifically the bottom walls 36 upon longitudinal extraction or insertion. Maintenance operations can thus be conducted more easily. It is namely possible to replace a damaged shorter fuel rod 4, without extracting the water channel 8. The fixing members 24 dedicated to the shorter fuel rods 4 adjacent to the water channel 8 enable to simplify the shape of the spacers 18 despite the grooves 32, since it is possible to provide a passage 22 of square cross section. The spacers 18 can be the same along the lower section 14 and the upper section 16. The cruciform shaped cross section of the water channel 8 provides a good distribution of the water in a transverse plane of the fuel assembly 2. The main duct 26 is adjacent to eight fuel rods 4. Each lateral duct 28 is adjacent to seven fuel rods 4, 6. This distribution is obtained with a single water channel. The fuel assembly 2 can thus be manufactured economically. The water channel 8 is obtainable e.g. by extrusion. In the illustrated embodiment, the longitudinal axis of the water channel coincides with the longitudinal central axis of the fuel assembly. In an alternative, the longitudinal axis of the water channel is offset with respect to the longitudinal central axis of the fuel assembly 2. In alternative embodiments, the fuel rods 4, 6 are arranged in a square array having a different number of cells (e.g. 8×8, 9×9 . . . to 11×11 or more), the array has a different outer shape (e.g. hexagonal), the water channel has a different shape and replaces a different number of fuel rods in the array, and/or the water channel passage has a different shape and replaces a different number of fuel rods in the array. |
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claims | 1. A method of matching an image of a pattern on a semiconductor device produced by a semiconductor inspection system and a template comprising a bit map of CAD data, the method comprising the steps of:decomposing the edges of the pattern image;smoothing the edge-decomposed pattern image and the template; and matching the smoothed pattern image and the template. 2. The method according to claim 1, wherein the template is smoothed more strongly than the pattern image is. 3. A method of matching an image of a pattern on a semiconductor device produced by a semiconductor inspection system and a template comprising a bit map of CAD data, the method comprising the steps of:extracting the edges of the pattern image by breaking up the edges in a plurality of directions;smoothing each of the images of the edges broken up in the multiple directions;composing the smoothed edge images in the multiple directions; andmatching the composed pattern image and the template. 4. A computer program for an image processor for matching an image produced by a semiconductor inspection system and a template comprising a bit map of CAD data that is stored in advance, the computer program controlling the image processor such that the processor decomposes the edges of the image produced by the semiconductor inspection system, smoothes the edge-decomposed image and the template, and matches the smoothed image and the template. 5. An image processor controlled by the computer program of claim 4. 6. The computer program according to claim 4, wherein the image processor is controlled such that edges are extracted from the image in a plurality of directions, and the extracted edges in the multiple directions are composed prior to the matching process. 7. A semiconductor inspection system controlled by the computer program of claim 6. |
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052296164 | claims | 1. An exposure lamp for emitting incoherent far ultraviolet light to illuminate a substrate, said lamp enveloping a metal element which substantially consists of a single isotope of said metal element such that said incoherent far ultraviolet light is emitted on vaporization of said single isotope. 2. A lamp as claimed in claim 1, wherein said single isotope has a nuclear spin equal to zero. 3. A lamp as claimed in claim 1, wherein said metal element is an element selected from the group consisting of mercury (Hg), cadmium (Cd), zinc (Zn), and lead (Pb). 4. A lamp as claimed in claim 1, wherein said metal element is mercury and said single isotope is .sub.80 Hg.sup.196, .sub.80 Hg.sup.198, .sub.80 Hg.sup.199, .sub.80 Hg.sup.200, .sub.80 Hg.sup.201, .sub.80 Hg.sup.202, or .sub.80 Hg.sup.204. 5. A lamp as claimed in claim 1, wherein said metal element is lead and said single isotope is .sub.82 Pb.sup.204, .sub.82 Pb.sup.206, .sub.82 Pb.sup.207, or .sub.82 Pb.sup.208. 6. A lamp as claimed in claim 1, wherein said metal element is zinc and said single isotope is .sub.30 Zn.sup.64, .sub.30 Zn.sup.66, .sub.30 Zn.sup.67, .sub.30 Zn.sup.68, or .sub.30 Zn.sup.70. 7. A lamp as claimed in claim 1, wherein said metal element is cadmium and said single isotope is .sub.48 Cd.sup.106, .sub.48 Cd.sup.108, .sub.48 Cd.sup.110, .sub.48 Cd.sup.111, .sub.48 Cd.sup.112, .sub.48 Cd.sup.113, .sub.48 Cd.sup.114, or .sub.48 Cd.sup.116. 8. A lamp as claimed in claim 1, wherein said single isotope produces a light beam of said far ultraviolet light in a narrow bandwidth of less than 0.005 nm. 9. A lamp as claimed in claim 8, wherein said light beam produced by said single isotope has a wavelength of about 250 nm. 10. A lamp as claimed in claim 9, wherein said narrow bandwith and said wavelength of said light beam produced by said single isotope are effective when said lamp is utilized in combination in an exposure apparatus to illuminate a substrate for producing minimum pattern sizes of no more than 0.3 micron meters on said substrate. 11. A lamp as claimed in claim 1 further comprising means for receiving said far ultraviolet light as a beam of incoherent light and projecting said beam onto said substrate. 12. An exposure apparatus for use in exposing a substrate to manufacture a semiconductor device, said exposure apparatus comprising an exposure light source for emitting incoherent far ultraviolet light onto said substrate, said exposure light source comprising: a lamp enveloping a metal element which substantially consists of a single isotope such that said incoherent far ultraviolet light is emitted on vaporization of said single isotope. 13. An exposure apparatus as claimed in claim 12, wherein said single isotope has a nuclear spin equal to zero. 14. An exposure apparatus as claimed in claim 12, wherein said metal element is selected from the group consisting of mercury (Hg), lead (Pb), zinc (Zn), and cadmium (Cd). 15. An exposure apparatus as claimed in claim 12, wherein said metal element is mercury and said single isotope is .sub.80 Hg.sup.196, .sub.80 Hg.sup.198, .sub.80 Hg.sup.199, .sub.80 Hg.sup.200, .sub.80 Hg.sup.201, .sub.80 Hg.sup.202, or .sub.80 Hg.sup.204. 16. An exposure apparatus as claimed in claim 12, wherein said metal element is lead and said single isotope is .sub.82 Pb.sup.204, .sub.82 Pb.sup.206, .sub.82 Pb.sup.207, or .sub.82 Pb.sup.208. 17. An exposure apparatus as claimed in claim 12, wherein said metal element is zinc and said single isotope is .sub.30 Zn.sup.64, .sub.30 Zn.sup.66, .sub.30 Zn.sup.67, .sub.30 Zn.sup.68, or .sub.30 Zn.sup.70. 18. An exposure apparatus as claimed in claim 12, wherein said metal element is cadmium and said single isotope is .sub.48 Cd.sup.106, .sub.48 Cd.sup.108, .sub.48 Cd.sup.110, .sub.48 Cd.sup.111, .sub.48 Cd.sup.112, .sub.48 Cd.sup.113, .sub.48 Cd.sup.114, or .sub.48 Cd.sup.116. 19. An exposure apparatus as claimed in claim 12, further comprising optical means for receiving said far ultraviolet light from said light source as a beam of incoherent light and projection said beam onto said substrate. 20. A method of emitting far ultraviolet light from an exposure lamp to illuminate a substrate, said method comprising exciting an exposure lamp to vaporize a metal element in said lamp and produce a beam of incoherent far ultraviolet light, and selecting as said metal element a single isotope of said metal element so that said beam of incoherent far ultraviolet light has a wavelength of about 250 nm and a narrow bandwidth of less than 0.005 nm. |
claims | 1. An irradiation device for proton or ion beam therapy comprising:a radiation source (3) that comprises a cyclotron or synchrotron arranged horizontally in a first plane (E3) for generating a treatment beam;a beam guiding device (5) installed downstream of the cyclotron or synchrotron, wherein the beam guiding device guides the treatment beam from the cyclotron or synchrotron into a therapy room (7);wherein the therapy room (7) is arranged in a second plane (E1) located above the first plane (E3), and wherein the therapy room comprises a treatment site (9) and an access (17);wherein a floor (B) of the therapy room comprises an entrance region (E) that enables the treatment beam to enter the therapy room (7) in the second plane (E1), and wherein the entrance region (E) is arranged between the treatment site (9) and the access (17) in the second plane;wherein the therapy room comprises a shielding that surrounds, at least in part, the entrance region (E), and wherein the shielding is open towards the treatment site (9) in the second plane so that the access (17) is arranged on the open side of the shielding (33) that is facing away from the treatment site (9);wherein the beam guiding device (5) is configured to guide the treatment beam (13) from the first plane of the cyclotron or synchrotron into the second plane of the therapy room (7) via the entrance region (E), and wherein the treatment beam (13) is deflected between the access and the treatment site within the therapy room in such a way that the treatment beam is directed towards the treatment site (9) and in an opposite direction of the access (17); andwherein the therapy room comprises at least one labyrinth (L) positioned in the second plane, and wherein the labyrinth is laterally offset in relation to the treatment beam (13) proceeding in the therapy room (7) and laterally offset to the shielding (33). 2. The irradiation device according to claim 1, wherein said treatment beam (13) entering said therapy room (7) in said entrance region (E) is conducted to a beam deflecting device (SU) and/or to a beam forming device (SF), which is/are arranged in said therapy room (7). 3. The irradiation device according to claim 1, wherein said treatment beam (13) proceeds towards said entrance region (E) below or above said access (17). 4. The irradiation device according to claim 1, wherein said shielding (33) comprises two wall regions (33a, 33b), between which said entrance region (E) is located, one of which said wall regions (33a, 33b) may be part of a shielding wall (35) of said therapy room (7). 5. The irradiation device according to claim 2, wherein said beam deflecting device (SU) and/or said beam forming device (SF) is/are arranged between wall regions (33a, 33b) of said shielding (33). 6. The irradiation device according to claim 5, wherein said shielding (33) has a base section (33c) connecting wall regions (33a, 33b). 7. The irradiation device according to claim 6, wherein said base section (33c) has a shielding reinforcement (41). 8. The irradiation device according to claim 7, wherein said wall regions (33a, 33b) of said shielding (33) dilate towards said treatment site as seen downstream from said entrance region (E). 9. The irradiation device according to claim 1, wherein said shielding (33) is symmetrically constructed. 10. The irradiation device according to claim 1, wherein the labyrinth (L) is provided between said access (17) and said treatment site (9) on both sides of said shielding (33). 11. The irradiation device according to claim 1, wherein at least one room (15) is arranged on said second plane for pre-treatment and after-treatment of patients treated at said treatment site (9) and for the stay of other persons. 12. The irradiation device according to claim 11, wherein said treatment beam (13) directed out of said entrance region (E) towards said treatment site (9) is directed away from said at least one room (15). 13. The irradiation device according to claim 1, wherein said treatment beam (13) is directed in an angle onto said treatment site (9). 14. The irradiation device according to claim 1, wherein said treatment beam (13) proceeds in parallel to the floor (B) of said therapy room (7). 15. The irradiation device according to claim 1, wherein said beam guiding device (5) is arranged in a third plane (E2). 16. The irradiation device according to claim 1, wherein said therapy room is one of multiple therapy rooms (7/1, 7/2, 7/3, 7/4) that are arranged in a curved manner to each other. 17. The irradiation device according to claim 1, wherein said therapy room is one of multiple therapy rooms (7) that are arranged in parallel to each other. 18. The irradiation device according to claim 17, wherein said multiple therapy rooms are arranged offset to each other. 19. The irradiation device according to claim 1, wherein said therapy room is one of multiple therapy rooms that are mirrored arranged and/or formed. 20. An irradiation device comprising:a radiation source,a beam guiding device, anda therapy room into which a treatment beam is directed, said therapy room comprising a treatment site and an access,characterized in thatsaid therapy room is arranged in a first plane;a shielding is provided in said therapy room, said shielding being open towards said treatment site and associated with an entrance region of said treatment beam into said therapy room;said beam guiding device is configured to direct said treatment beam from a second plane located above or below said first plane into said therapy room, within which said treatment beam is deflected and directed towards said treatment site so that said treatment beam is directed away from said access; andsaid access is arranged on that side of said shielding which is facing away from said treatment site, wherein a line that is coincident with said treatment beam as directed towards said treatment site passes through said access. |
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051805456 | summary | FIELD OF THE INVENTION The invention relates to a lower end nozzle of a fuel assembly having a device for the retention of particles contained in the coolant fluid of nuclear reactors, especially pressurized-water nuclear reactors, and a fuel assembly having such an end nozzle. BACKGROUND OF THE INVENTION Pressurized-water nuclear reactors comprise a core consisting of prism-shaped assemblies arranged side by side in vertical position. The assemblies comprise a framework which is closed by means of end nozzles and in which are arranged the fuel rods held by spacer grids spaced apart from one another in the longitudinal direction of the assembly. The spacer grids constitute a regular network, some locations of which are occupied by guide tubes intended for receiving the absorbent rods of control clusters ensuring the control of the power released by the core of the nuclear reactor. At least some of the guide tubes are attached to the two end nozzles of the assembly by means of their end parts and ensure the junction between the components of the framework and the rigidity of this framework. One of the end nozzles of the assemblies, called the lower end nozzle, comes to rest on the lower core plate which is pierced with holes in the region of each of the assemblies, to allow the coolant water of the reactor to pass through the core in the vertical direction from the bottom upwards. The coolant flow for the fuel rods passes through the adaptor plate of the lower end nozzle via apertures called water passages, which are either circular (of a diameter approximately 7 to 10 mm) or of oblong (apertures approximately 10 mm wide by 15 to 50 mm long). Debris which may be present in the primary circuit of the reactor is liable to be carried along by the circulating pressurized water, and if it is of small size (for example, less than 10 mm), this debris can pass through the adaptor plate of the lower end nozzle, the water passages of which have a large cross-section. This debris can become jammed between the fuel rods and the cells of the first grid, i.e., of the lowermost spacer grid holding the rods in a regular array. This debris, subjected to the axial and transverse hydraulic stresses which are high in this zone, can produce wear on the jacket of the fuel rod resulting in a loss of sealing of this jacket and an increase in the rate of activity of the primary circuit of the reactor. Devices for filtering the coolant flow of the reactor, either during hot-running tests or during the operation of the reactor, are known in the art. In the case of hot-running tests, the filter elements can be attached to the lower core plate and arranged thereon in the position of the fuel assemblies, before fuelling of the core, as described, for example, in FR-A-2,577,345. In filtering during reactor operation, the filter elements are associated with the fuel assemblies and are generally arranged in their lower end nozzle. The filter elements fastened in the lower end nozzles of the fuel assemblies usually consist of sheet-metal or metal-wire structures making it possible to stop debris of a size smaller than the largest dimension of the cross-section of the passage between a fuel rod and a grid cell. Such filter elements are described, for example, in U.S. Pat. No. 4,664,880, U.S. Pat. No. 4,684,496 and EP-A-0,196,611. Such devices can be complex and introduce a relatively high head loss into the circulation of the coolant flow through the fuel assembly. Furthermore, these devices placed in the lower end nozzle of the assembly can be bulky and obstructive during loading and unloading of the core assemblies and during the dismounting and refitting of the guide tubes and lower end nozzle. Some fuel assemblies of recent design comprise a set of guide tubes (for example 16 out of 24) which are attached both to the upper end nozzle and to the lower end nozzle of the assembly, the rigidity of which they ensure, and a set of guide tubes which are attached to the upper connector only, of the assembly. The guide tubes of the second set which are freely engaged in the adaptor plate of the lower end nozzle perform only a guide function, and the lower end nozzle has, in the extension of these tubes, apertures which remain free. SUMMARY OF THE INVENTION The filter devices known from the prior art are unsuitable for this type of assembly. The object of the invention is, therefore, to provide a lower end nozzle of a nuclear fuel assembly, comprising an adaptor plate, supporting feet intended to come to rest on the lower core plate of the reactor, and a device for the retention of particles contained in the coolant flow of the reactor, consisting of a flat element performing the function of a filter grating, filtration of the fluid being carried out in the region of the end nozzle by means of the flat element, without introducing an excessive head loss into the circulation of the coolant flow, without increasing the bulk of the fuel assembly in the region of its lower end nozzle, and while at the same time preserving the possibility of dismounting this end nozzle easily. To this end the retention device consists of a filter plate pierced with holes and fastened against the bottom face of the adaptor plate. The invention likewise relates to a fuel assembly having a lower filtering end nozzle comprising a retention device, as defined above. Another object of the invention is to provide a fuel assembly with a filtering end nozzle, comprising a first set of guide tubes connected to the adaptor plate of its lower end nozzle and ensuring the rigidity of the framework of the assembly and a second set of guide tubes, not connected to the lower end nozzle and freely engaged in the adaptor plate of the lower end nozzle. According to the invention, the assembly has a debris retention device consisting of a filter plate pierced with holes and fastened against the lower face of the adaptor plate by fastening means engaged in apertures of the filter plate which are located opposite apertures passing through the adaptor plate in line with the guide tubes of the second set. |
abstract | Gamma radiation (22) is shielded by producing a region of heavy electrons (4) and receiving incident gamma radiation in such region. The heavy electrons absorb energy from the gamma radiation and re-radiate it as photons (38, 40) at a lower energy and frequency. The heavy electrons may be produced in surface plasmon polaritons. Multiple regions (6) of collectively oscillating protons or deuterons with associated heavy electrons may be provided. Nanoparticles of a target material on a metallic surface capable of supporting surface plasmons may be provided. The region of heavy electrons is associated with that metallic surface. The method induces a breakdown in a Born-Oppenheimer approximation Apparatus and method are described. |
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description | This application claims priority as a continuation application under 35 U.S.C. § 120 to PCT/CH2005/000345 filed as an International Application on 21 Jun. 2005 designating the U.S., the entire contents of which are hereby incorporated by reference in their entireties. The disclosure relates to the field of diagnostics of process devices, such as they are used in industrial or scientific processes, and in particular to the field of process device diagnostics using a sensed process variable of the process. Such a diagnostic device and diagnostic method is known from the patent publication U.S. Pat. No. 5,680,109. The device is connected to two impulse lines, which are coupled to a process fluid of a process, and either senses the two absolute pressures in the two impulse lines or one absolute pressure in one impulse line and one differential pressure between the two impulse lines. The device processes the pressure signals so as to extract from them vibration noise signals carried in the process medium (e.g., liquid, gas). Such vibration-related processed signals are then evaluated, with the evaluation ending in an output indicating that the impulse lines are not blocked or that at least one of the impulse lines are blocked. One goal of the disclosure is to create an alternative method for determining a blockage or other failure of at least one impulse line, and more general, to provide for a method for detecting a failure of a sensing means, which sensing means comprises at least one impulse line. In addition, a corresponding diagnostic device for detecting a failure of such a sensing means or impulse line shall be provided. Typically the impulse lines are to be connected to a transmitter, in particular to a pressure transmitter. A diagnostic device is disclosed for detecting a failure of a sensing means, which sensing means comprises at least one of first and a second impulse lines. The diagnostic device comprises a recording means for repeatedly recording pairs of two absolute pressure values, the absolute pressure values being related to absolute pressures in the first and the second impulse lines, respectively; a computation means for repeatedly computing, from a prescribable number of pairs of the two absolute pressure values, a correlation value representative of the correlation between the two absolute pressure values; a comparison means for comparing correlation values to at least one correlation threshold value; and an output means for outputting a diagnostic output depending on the result of the comparison. The correlation values are compared to a lower correlation threshold value and to an upper correlation threshold value. A diagnostic method is disclosed for detecting a failure of a sensing means, which sensing means comprises at least one of first and a second impulse lines. The method comprises the steps of: recording pairs of two absolute pressure values, the absolute pressure values being related to the absolute pressures in the first and a second impulse lines; computing, from a prescribable number of pairs of the two absolute pressure values, a correlation value representative of the correlation between the two absolute pressure values; comparing correlation values to a lower correlation threshold value and to an upper correlation threshold value; and outputting a diagnostic output depending on the result of the comparison. The reference symbols used in the figures and their meaning are summarized in the list of reference symbols. Generally, alike or alike-functioning parts are given the same reference symbols. The described embodiments are meant as examples and shall not confine the disclosure. According to the disclosure, the diagnostic device for detecting a failure of a sensing means, which sensing means comprises at least one of first and a second impulse lines, wherein the diagnostic device comprises a recording means for repeatedly recording pairs of two absolute pressure values, the absolute pressure values being related to absolute pressures in the first and the second impulse lines, respectively, a computation means for repeatedly computing, from a prescribable number of pairs of the two absolute pressure values, a correlation value representative of the correlation between the two absolute pressure values, a comparison means for comparing correlation values to at least one correlation threshold value, and an output means for outputting a diagnostic output depending on the result of the comparison. The corresponding method is a diagnostic method for detecting a failure of a sensing means, which sensing means comprises at least one of first and a second impulse lines, and the method comprises the steps of: recording pairs of two absolute pressure values, the absolute pressure values being related to the absolute pressures in the first and a second impulse lines, computing, from a prescribable number of pairs of the two absolute pressure values, a correlation value representative of the correlation between the two absolute pressure values, comparing correlation values to at least one correlation threshold value, and outputting a diagnostic output depending on the result of the comparison. Through this, it is possible to provide for reliable grounds for the diagnostic output of the diagnostic device, i.e., for the output indicating that there is a failure (blockage) in at least one of the two impulse lines or, more general, for the output indicating that there is a failure in the sensing means. The diagnostic device can be any device or combination of devices, which is capable of recording pressure values and processing them in the depicted way. It can be a transmitter (in particular a pressure or a flow velocity transmitter), a process monitoring device or process monitoring system, a controller or a process control system, a personal computer or a microprocessor or the like. The diagnostic device can be suitable for use in a process control environment. It can be implemented in a control system. The diagnostic device can be integrated in a transmitter, in a process monitoring device, in a controller or the like. The diagnostic device can, e.g., be realized in a flowmeter, a pressure transmitter (for absolute pressures) or differential pressure transmitter. The diagnostic output is related to a condition of the process, wherein the condition of the process is different from a measure for one or both of the absolute pressure values and also different from another process variable, which the sensing means would provide, like a differential pressure, a flow velocity or the like. The diagnostic output is related to the condition of a sensing means, in particular to the condition of an impulse line, which can be a part of a sensing means. The sensing means is designed for sensing a process variable of a process medium of a process, like an absolute pressure, a differential pressure, a flow velocity or the like of a liquid in a tubing system. In an exemplary embodiment the at least one correlation threshold value is derived from a statistical analysis of a number of correlation values obtained (recorded) during a training phase. In this exemplary embodiment, it is provided for a training phase (a prescribable time span), during which, under normal operating conditions, correlation values are recorded. These correlation values are then statistically analyzed, e.g., by calculating the (arithmetic) mean of the recorded correlation values and possibly also the variance of the correlation values. The at least one correlation threshold value can then be calculated on the basis of the statistical analysis. E.g., if the range of all possible correlation values is between 0 and 1, one correlation threshold value may be chosen as 0.5 times the mean correlation value as obtained during the training phase, or as the mean correlation value minus one time the variance, as obtained during the training phase (unless this would be smaller than 0). An aspect of this exemplary embodiment is, that the at least one correlation threshold value can be obtained automatically, and that the at least one correlation threshold value is chosen in direct dependence of the real process conditions. It is possible to choose correlation threshold values independent from the actual process conditions. A correlation threshold value may also be chosen, e.g., just in dependence of the viscosity of the process medium of the process. Preferably, the statistical analysis of the number of correlation values obtained during a training phase comprises fitting a statistical distribution function to the correlation values recorded during the training phase. In this way, a rather short training phase is sufficient for obtaining correlation threshold values that fit the process conditions very well. Advantageously, the correlation values are compared to a lower correlation threshold value and to an upper correlation threshold value. This is advantageous, because both, an exceedingly low and an exceedingly high correlation between the absolute pressure values, can indicate a failure of at least one of the impulse lines. In another exemplary embodiment, the computation means is designed for repeatedly computing, from a prescribable number of a first of the two absolute pressure values, a signal power value, and the comparison means is designed for comparing signal power values to at least one signal power threshold value, wherein signal power values are derived from a transform of the prescribable number of first pressure values into coefficients of a set of orthogonal functions. In such an exemplary embodiment, and if the first absolute pressure is measured at a first of the two impulse lines, it is possible, to detect, whether the first impulse line or the other impulse line is blocked, when it has been detected that exactly one of the two lines are blocked. The transform can be one of the group of Fourier transform and wavelet transform. Advantageously, the at least one signal power threshold value is obtained from a number of signal power values obtained during a training phase. An aspect of this exemplary embodiment is, that the at least one signal power threshold value can be obtained automatically, and that the at least one signal power threshold value is chosen in direct dependence of the real process conditions. Some statistical analysis, e.g. fitting of a distribution function, can be performed on the signal power values obtained during the training. In an exemplary embodiment, the diagnostic device comprises at least one sensing means for measurement of an absolute pressure, and for measurement of a differential pressure between the two impulse lines,and the two absolute pressure values are derived from measurements performed with the at least one sensing means. I.e., in that embodiment, the diagnostic device is capable to sense the pressure difference (differential pressure) between the pressure in the first and the pressure in the second impulse line, and, in addition, it is capable to sense an absolute pressure. That absolute pressure can, be the absolute pressure in one of the two impulse lines. In that case, the two absolute pressure values are readily at hand. A transmitter, in particular a pressure or flow velocity transmitter, according to the disclosure comprises a diagnostic device according to the disclosure and/or implements a diagnostic method according to the disclosure. An exemplary process control system according to the disclosure comprises a diagnostic device according to the disclosure and/or implements a diagnostic method according to the disclosure. An exemplary process monitoring device according to the disclosure comprises a diagnostic device according to the disclosure and/or implements a diagnostic method according to the disclosure. An exemplary process control environment according to the disclosure comprises a diagnostic device according to the disclosure and/or implements a diagnostic method according to the disclosure. FIG. 1 schematically illustrates a typical process control environment 1 with a diagnostic device 10. The diagnostic device 10 is comprised in a pressure transmitter 20, which is connected to two impulse lines 21,21′, through which it is coupled to a process medium 2 of the process control environment 1. The process medium 2 typically is a flowing fluid, symbolized in FIG. 1 by open arrows. The pressure transmitter 20 is designed to transmit an absolute pressure p+ and, in addition, a differential pressure dp. The absolute pressure p+ is the pressure in the first impulse line 21, which is upstream from the second impulse line 21′, in which there is an absolute pressure p−. The differential pressure dp is the absolute of the difference between p+ and p−, accordingly: dp=p+−p−. The pressure transmitter 20 can also be understood as a process monitoring device 20, which monitors a differential pressure and an absolute pressure in the process medium 2. The process medium 2 can be, e.g., a liquid like water or oil, which is contained in a tube 3. Process control devices like a pump 50 (including a pump control 51) and a valve 60 (including a valve control 61) are provided in the process control environment 1. The process control devices 10,20,50,60 are connected to a typically computer-based process control system 5. The process control system 5 can also be understood as a process control device 5, which (through the connection with the diagnostic device 10) incorporates (comprises) the diagnostic device 10. The pressure transmitter 20 as shown in FIG. 1 can be understood as an example of a diagnostic device 10 with a sensing means. FIG. 2 schematically shows a part of such a pressure transmitter 20. The sensing means 25 comprises the two impulse lines 21,21′, which are filled with process medium 2. The sensing means 25 comprises a sensing system (sensing element) 26. One process membrane 22 and one pressure transmission arm 23 are provided for each of the impulse lines 21,21′. The pressure transmission arms 23 (oil circuits 23) are filled with oil 24 as a sensing medium 24. The process membranes 22 are an interface between the impulse lines 21,21′ (containing process medium 2) and the oil circuits 23 (containing sensing medium 24). Through the pressure transmission arm 23 the absolute pressures p1 (corresponding to p+) and p2 (corresponding to p−) of the process medium (in the impulse lines 21,21′) are transferred to the sensing system 26. This allows to sense the differential pressure dp=p+−p−. Among others, the sensing system 26 may be based on one or more of the following principles, which allow to derive an electrically measureable signal from the differential pressure dp: Induction (the differential pressure modulates the inductance of a magnetic circuit) Piezoresistivity (the differential pressure modulates an output voltage of a piezoresistive element) Capacitance (the differential pressure modulates the capacity of an electric circuit). The signal derived that way is then digitized in a analogue-to-digital converter 27. It is related to the differential pressure dp between the two impulse lines 21,21′. For creating a combined absolute pressure and differential pressure transmitter 20, as it is indicated in FIG. 1, it is, e.g., possible to add another sensing element and a pair of pressure transmission arms to the device 10 shown in FIG. 2 (or, more precisely, to the sensing means 25 shown in FIG. 2). One pressure membrane would be an interface between, e.g. the first of the two impulse lines 21,21′ (containing process medium 2) and the oil circuit of that pressure transmission arm. The other pressure transmission arm would contain vacuum. Other ways of sensing the absolute pressure can be used, too. The signal obtained from the additional sensing element can then be digitized in another analogue-to-digital converter. It is related to the absolute pressure in that one of the impulse lines 21,21′, which is interfaced by the additional membrane, e.g., the absolute pressure p1=p+ would then be sensed. A microprocessor 15 of the diagnostic device 10 can then record the two digitized signals (differential pressure signal and absolute pressure signal) and derive diagnostic information from them. A diagnostic device 10 can be used to diagnose the condition and failures of the sensing means 25. In particular, the following failures may occur and can be detected by the diagnostic device 10: 1. At least one of the oil circuits 23 has a leak. 2. The interface between the two oil circuits 23 (usually an additional membrane) is damaged, so that the sensing medium 24 can flow between the two circuits 23. 3. At least one of the process membranes 22 is broken, so that the process medium 2 can flow into at least one of the pressure transmission arm. 4. At least one of the impulse lines 21,21′ is partially or completely plugged. Frequent reasons for a plugged impulse line (failure 4.) are: Solid material is present in the process medium 2 and blocks the impulse line. Some sedimentary process takes place in the impulse line and progressively plugs the impulse line (e.g., limestone). The process medium in the impulse line solidifies, typically because of low temperatures. (This can happen even if the process medium 2 in the rest of the process does not solidify, because the process medium 2 in the impulse lines 21,21′ is mainly still, whereas the process medium 2 in the process is usually flowing and therefore not still.) It is of considerable value to have diagnostic information on the condition of the sensing means 25 and in particular of the impulse lines. It is particularly valuable, if the diagnostic information can distinguish between (some of) the above-mentioned failure modes. It is advantageous for a diagnostic device, which uses at least two impulse lines (e.g., for a device using pressure and/or differential pressure signals derived from these at least two impulse lines), to have the impulse lines connected to the process at points, which are arranged close to each other. I.e., it is advantageous, when the locations at which the at least two impulse lines are coupled to the rest of the process medium, are in close proximity. The advantage is, that measured pressure values are small, fluctuations in the process fluid are mostly cancelled. How to get from p+ and dp to the diagnostic information? Firstly, from the sensed signals, two absolute pressure values must be extracted. When, as indicated in FIGS. 1 and 2, the first impulse line 21, at which the absolute pressure p+ is sensed, is located upstream from the second impulse line, in which there is the pressure p−, the absolute pressures p1,p2 are derived asp1=p+, and (3)p2=p+−dp. (4) When, on the other hand, the absolute pressure is sensed at the impulse line 21′, which is located downstream, the absolute pressures p1,p2 are derived asp1=p−+dp, and (3′)p2=p−. (4′) It is also possible to sense an absolute pressure at a third impulse line, which can be located very close to at least one of the other two impulse lines 21,21′. In that case, the second absolute pressure value can be obtained by adding or subtracting the differential pressure value dp to that absolute is pressure, depending on the location of the third impulse line with respect to the other impulse lines 21,21′. It is also possible to directly sense two absolute pressure values (which can render a differential pressure sensor superfluous). Yet, it is preferred to sense one absolute and one differential pressure, and use only two impulse lines, because this allows for high precision at moderate effort (moderate required resolution of the analogue-to-digital converter). FIG. 3 schematically shows an block diagram indicating steps performed in the diagnostic device during normal operation. In a recording means 100, absolute pressure values p1,p2 are repeatedly recorded. In more or less constant time intervals (e.g., 10 ms), p1-values and p2-values can be recorded. After some time, a (prescribable) number n of pairs of p1- and p2-values (e.g., n=20 pairs) are gathered, and a correlation value ρ can be computed from that series of values p1,p2 in a computation means 200. One possible way is to calculate the linear correlation coefficient ρ, which can be computed as follows: { ρ ( p 1 , p 2 ) = ∑ k = 0 n - 1 [ ( p 1 ( k ) - μ ( p 1 ) ) ( p 2 ( k ) - μ ( p 2 ) ) ] ∑ k = 0 n - 1 [ ( p 1 ( k ) - μ ( p 1 ) ) 2 ] ∑ k = 0 n - 1 [ ( p 2 ( k ) - μ ( p 2 ) ) 2 ] ( 1 ) μ ( p i ) = 1 n ∑ k = 0 n - 1 p i ( k ) i = 1 , 2 ( 2 ) μ(pi) is the (arithmetic) mean of the pressure value pi, wherein i can be 1 or 2; n is the number of pairs in the series of absolute pressure values used for the calculation. It is possible to use other formulas for calculating that correlation value, and it is also possible to calculate a different correlation value, e.g., the coefficient of quadratic correlation or a function of such a value, like, e.g., its inverse or its absolute. One advantage of the linear correlation coefficient is that its value cannot take arbitrary values, but only those between (and including) −1 and +1. For perfect positive correlation is ρ=1, for perfect negative correlation is ρ=−1, and for no correlation is ρ=0. If the diagnostic device is always in the same manner connected to impulse lines (with respect to the upstream/downstream location of the impulse lines), the values of the correlation values ρ can be confined to positive numbers. (Alternatively, it is also possible to proceed with the absolute value of ρ). Each correlation value is then, in a comparison means 400, compared to at least one correlation threshold value r. That correlation threshold value r is prescribable. If, e.g., the values of p can only be in the interval 0 to 1, r could be chosen as a lower limit for the correlation. e.g., r=0.4. The comparison would then mean to ask “ρ<r?”. In case the answer would be “yes”, an output means 500 would indicate a failure of one of the impulse lines 21,21′. Preferably, ρ is compared to two correlation threshold values r and R, with r being a lower limit and R being an upper limit. The comparison would then mean to ask “(ρ<r) or (ρ>R)?”. In case the answer would be “yes”, the output means 500 would indicate a failure of at least one of the impulse lines 21,21′. Otherwise, the diagnostic output provided by the output means 500 would indicate that there is no failure detected. In an exemplary embodiment, the at least one correlation threshold value is derived from data obtained during a training phase, as will be discussed below. Preferably, the means 100,200,400,500 are substantially realized in an adequately programmed microprocessor. In FIG. 4 a flow chart of a more elaborate diagnostic method is shown (steps performed in normal operation). It relates specifically to the detection of an impulse line failure due to plugging. After recording absolute pressure pairs p1,p2 and computing a correlation value ρ, that correlation value ρ is compared to a lower correlation threshold value r and to an upper correlation threshold value R, wherein the order of the two comparisons is not very important, but preferably, the second comparison is made only if the first comparison results in a “no”. If both comparisons (ρ<r and ρ>R) result in a “no”, the diagnostic output will indicate that none of the impulse lines is plugged. If ρ>R, the diagnostic output will indicate that both impulse lines are plugged. If ρ<r is the case, at least one impulse line is plugged (or has some failure). In that case, an analysis of one of the absolute pressure signals (here, e.g., p1) enables to give an indication, which one of the two impulse lines has a failure. Roughly speaking, if a significant decrease of the p1 signal has occurred, the impulse line associated with p1 is expected to be the plugged impulse line. Otherwise (i.e., no significant decrease of the p1 signal) the other impulse line is expected to be plugged. In the computation means 200, a signal power value Sp of the p1 signal (e.g., the directly sensed absolute pressure) is computed. Sp is a value derived from coefficients of a transform of a series of p1 values. I.e., a prescribable number N of p1-values is transformed (e.g., Fourier or wavelet), so as to obtain a number of coefficients, and Sp is obtained as a function of these coefficients. Preferably, Sp is obtained as the sum of the absolute value of selected Fourier coefficients, e.g., as the intensity in a prescribable frequency range. The Fourier coefficients X(k), with k being a frequency variable, and the Sp values can be calculated as follows: X ( k ) = ∑ t = 0 N - 1 x ( t ) ⅇ - j 2 π k N t ( 5 ) P ( k ) = { 2 X ( k ) 2 1 ≤ k ≤ N 2 - 1 X ( k ) 2 k = 1 , N 2 ( 6 ) Sp ( k 1 , k 2 ) = ∑ k = k 1 k 2 P ( k ) ( 7 ) Here, x(t) is the discrete time signal (absolute pressure value); Sp is the intensity within the frequency range ranging from k1 to k2; t is the time variable, e denotes the base of the natural logarithm, and j denotes the square root of −1. N is the number of absolute pressure values used for one transformation. The obtained Sp value is then, in the comparison means 400, compared to at least one signal power threshold value Spt. Depending on the result of the comparison, the diagnostic output will indicate, which one of the impulse lines is plugged. Thus, by analyzing not only the correlation of p1 and p2, but in addition also the signal power Sp of one absolute pressure value, it is possible not only to indicate that at least one impulse line is plugged, but also which one of the impulse lines is plugged, if only one is plugged. The signal power threshold value Spt is prescribable. The at least one signal power threshold value can be derived from a number of signal power values obtained during a training phase, which training phase can be the same training phase as the one for obtaining the correlation threshold value(s). An exemplary basic algorithm for the functioning of a diagnostic device 10 according to the disclosure is sketched in the block diagram in FIG. 5. First, the diagnostic device installed, i.e., mainly the diagnostic device is coupled to the process. Then follows a training phase, during which threshold values are generated. If then the nominal conditions in the process are unchanged, a measuring phase (normal operation) can be entered. If, at any time, the nominal conditions in the process are changed, e.g., through installation of a new process device, another training phase should be absolved before entering measurement mode again. FIG. 6 sketches steps performed during a training phase. The training is aimed at recording typical values of the correlation coefficient and preferably also of the signal power values of the absolute pressure at nominal operating conditions of the process. For a predetermined span of time, p1 and p2 values are recorded (from absolute pressure measurements, or from an absolute pressure measurement and a differential pressure measurement). From various series of p1,p2 value pairs, one correlation value ρ is calculated each. These correlation values are then statistically analyzed, e.g., by calculating the (arithmetic) mean of the correlation values and possibly also the variance of the correlation values. The at least one correlation threshold value can then be calculated on the basis of the statistical analysis. Preferably, this statistical analysis during the training phase comprises fitting a statistical distribution function to the distribution of correlation values obtained during the training phase. In case that the correlation values can have values only in the interval 0 to 1, the beta distribution could be applied. From the best-fitting (e.g., least-square-fit) distribution function, one or two correlation threshold values can be extracted. This has the advantage, that the at least one threshold value can be chosen with high precision on the basis of a relatively low number of correlation values determined during the training phase, and, in addition, the correlation threshold values will reflect the real process conditions very well. Furthermore, this allows to select the at least one threshold value such, that lower or higher correlation values occur with a prescribable probability. In parallel to the correlation threshold value related matters (or before or after), the at least one signal power threshold value Spt is determined. In analogy to the correlation threshold value, a number of signal power values Sp are obtained during the training phase (details are given above), and a statistical analysis of these allows for a well-defined selection of Spt. Another advantage of a statistical analysis of correlation values and/or signal powers obtained during the training with fitting of a statistical function is, that a diagnostic output can be provided with a “quality value”, which indicates the degree of confidence of the output. Through the flow of the process medium 2 (indicated by arrows in FIG. 1) and, in addition, through the process control devices 50,60, noise is generated in the process medium 2. Such noise can be sensed by means of the diagnostic device 10 in the transmitter 20. A change in the process conditions, e.g., a malfunction or failure of a process device 20,50,60, may be reflected in the sensed pressure signals. This can be used to detect failures of such process devices 20,50,60 by means of a diagnostic device and a diagnostic method as described above. It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein. List of Reference Symbols 1process control environment 2process medium, process fluid 3tube 5process control system, process control device 10diagnostic device 15microprocessor 20transmitter, pressure transmitter, differential and absolutepressure transmitter, 21(first) impulse line 21(second) impulse line 22process membrane 23pressure transmission arm, oil circuit 24sensing medium, oil 25sensing means 26sensing element, sensing system 27A/D converter 50pump 51pump control 60valve 61valve control100recording means200computation means400comparison means500output meansktransform variable, frequencyk1,k2limit values in transform space, frequency limitsdpdifferential pressure value (p+ − p−)p1(first) absolute pressure valuep2(second) absolute pressure valuep+absolute pressure value (measured upstream)pabsolute pressure value (measured downstream)rcorrelation threshold value, lower correlation threshold valueRcorrelation threshold value, upper correlation threshold valueSpsignal power valueSptsignal power threshold valuettimeX(k)transform, discrete transform, discrete Fourier transform,coefficientx(t)process variable value (taken at various times), pressure valueρcorrelation value |
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claims | 1. A grid holder for retaining a specimen grid, the grid holder comprising:a body sized to hold one or more specimen grids, the body comprising a slot in its interior, the slot including sides for receiving the specimen grid, wherein the specimen grid is a flat disk or a partial disk with edges and a pair of opposing faces, wherein one face of the specimen grid optionally has a specimen thereon;wherein the slot is sized to receive the specimen grid through an open top end of the slot, the slot having sides tapering from the top end to a bottom end of the slot, such that the bottom end of the slot is smaller than the specimen grid; andwherein the slot further is configured to contact the specimen grid along at least a portion of edges of the specimen grid to secure the specimen grid by engagement of the edges of the specimen grid with the sides of the slot, wherein the opposing faces of the grid do not contact the slot. 2. The grid holder of claim 1, wherein the grid is made of a resilient deformable material and the interior of the slot is configured to deflect the grid sideways as the grid is inserted into the slot, so that the grid exerts tension against the interior of the slot to hold the grid within the slot. 3. The grid holder of claim 1, wherein the bottom of the slot is closed. 4. The grid holder of claim 1, wherein the bottom of the slot is open. 5. The grid holder of claim 4, wherein the slot is configured to permit the exposure of the grid within the slot to one or more reagents, chemical treatments, preparation compounds or treatment environments to prepare any specimen held on the grid for examination. 6. The grid holder of claim 4, wherein the body is made of a chemically resistant material. 7. The grid holder of claim 1, wherein the body of the grid holder is made of a resilient deformable material and the material within the slot deflects in response to the insertion of the grid and exerts tension on the grid to retain the grid within the slot. 8. The grid holder of claim 1, wherein the slot is sized to so that insertion of the grid into the slot causes the grid to deflect and a resistance to deflection of the grid exerts tension on the sides of the slot to hold the grid within the slot, the slot further being configured so that deformation of the grid does not bring areas of the side of the grid that are distant from the edge into contact with the grid holder. 9. The grid holder of claim 1, wherein the grid is an electron microscope grid. 10. The grid holder of claim 4, wherein the grid is an electron microscope grid. 11. The grid holder of claim 1, the body further comprising a plurality of slots. 12. The grid holder of claim 1, further comprising the grid holder being made of a suitable material to retain the grid for processing, storage and analysis of a specimen on the grid, so that a grid need not be removed from the grid holder once placed in the slot. 13. The grid holder of claim 1, further comprising a cap configured to close off the open top of the slot. 14. The grid holder of claim 13, the cap further comprising a tab configured to extend into the slot and maintain the grid in position within the slot when the cap is closing off the open top of the slot. 15. The grid holder of claim 13, wherein the cap is attached to the grid holder by a living hinge. 16. The grid holder of claim 1, wherein the grid holder includes a plurality of slots and indicia are included corresponding to each slot. 17. A device for retaining a thin aperture, the device comprising:a body sized to hold one or more thin apertures, the body comprising a slot in its interior, the slot including sides for receiving the thin aperture, wherein the thin aperture is a flat disk with edges and a pair of opposing faces;wherein the slot is sized to receive the thin aperture through an open top end of the slot, the slot having dies tapering from the top end to a bottom end of the slot, such that the bottom end of the slot is smaller than the thin aperture; andwherein the slot is configured to contact the thin aperture along at least a portion of the edges of the thin aperture to secure the thin aperture to allow sideways deformation of the aperture without opposing faces of the thin aperture contacting the slot. 18. The device of claim 17, wherein the grid is made of a resilient deformable material and insertion of the grid within the slot causes the grid to deform and exert pressure against the opposing sides of the slot along opposing edges of the grid. 19. The device of claim 17, wherein the body is mode of a resilient deformable material and insertion of the grid within the slot causes the opposing sides of the slot to deform and exert pressure on the opposing edges of the grid to secure the grid with the slot. 20. A device for retaining a thin disk, the device comprising:a body sized to hold one or more thin disks, the body comprising a slot formed in its interior, the slot including sides for receiving the thin disk, wherein the thin disk has edges and a pair of opposing sides and is made of a resilient deformable material;wherein the slot is sized to receive the thin disk through an open top end of the slot, the slot having sides tapering from the top end to a bottom end of the slot, such that the bottom end of the slot is smaller than the thin disk; andwherein the slot is configured to contact the thin disk along at least a portion of the edges of the disk and to allow sideways deformation of the disk without opposing faces of the thin disk contacting the slot. 21. The grid holder of claim 1, wherein the body of the grid holder is a capsule and the slot is formed in the interior of the capsule. 22. The grid holder of claim 1, wherein the grid holder comprises a plurality of slots within the body of the grid holder for holding a plurality of sample grids. |
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abstract | A system for inspecting nuclear fuel pellets is provided. The inspection system is configured to use X-ray radiation at one or more energies to probe nuclear fuel pellets disposed within a nuclear fuel rod for nuclear fuel pellet defects. In some implementations of the inspection system, a nuclear fuel rod manufacturing facility may be able to integrate the inspection system for fully or partially automated inspection of all fuel rods produced within the facility. |
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044951450 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is a loading probe for loading nuclear fuel rods with spherical nuclear fuel. The probe is part of an overall loading system described in copending application Ser. No. 327,817 entitled "Spherical Nuclear Fuel System" filed on Dec. 7, 1981 by the same inventor and assigned to the same assignee as the present application and incorporated herein by reference. The overall system is shown in FIGS. 1 and 3. FIG. 1 shows the system viewed from the front. A fuel cladding rod 2 to be loaded with fuel is held vertically upright by a fuel rod support clamp 4. Because of the length of the fuel rods 2, the rods 2 may be set in pit 1 in the building floor. The support clamp 4 is fixed to a vibrator 6 driven by vibrator motor 8. The vibrator 6 rests on a frame 10. The frame 10 is vertically adjustable to give the vibrator 6 a vertical travel of several feet. This allows the loading system to accomodate fuel cladding rods 2 of different lengths. The open upper end of the fuel cladding tube 2 is attached to an adaptor 18 with an airtight connection. The adaptor 18 is mounted to the glove box 22 via a bellows arrangement so that the fuel tube 2 is flexibly mounted to the glove box 22 allowing the fuel tube 2 to vibrate in response to the vibrator 6 while the tube is being loaded. The adaptor 18 is connected to the glove box 22 with a vacuum valve 24 so that the adaptor 18 and fuel tube 2 combination may be isolated from the glove box 22 forming an airtight combination. The glove box 22 is an enclosure capable of being made airtight which receives the nuclear fuel through the entrance vacuum valve 26. The glove box includes windows 28 and hinged glove box covers 30. Opening the glove box covers 30 reveals gloves (not shown) mounted to the glove box 22 which allows the operator to accomplish manipulation within the glove box 22 while still retaining the inert atmosphere within the glove box 22. On the upper side and connected to the glove box 22 is the rod loading assembly cover 32. The rod loading assembly cover 32 is of sufficient length to allow the rod loading assembly 34 to rise high enough so that it is free of the fuel cladding tube 2. FIG. 3 shows a side view of the glove box and fuel cladding tube assembly. After entering the glove box through the vacuum valve 26, the fuel proceeds to the weighing station. Referring to FIGS. 3, 4, and 5 shows the passage of the spherical nuclear fuel from the entrance vacuum valve 26 to the loading hoppers 60 and 62 of the weighing stations. The nuclear fuel spheres enter the glove box 22 through the entrance vacuum valve 26 in containers large enough to hold sufficient fuel for about six fuel tubes 2. The fuel containers 36 indicated by the dotted lines, move along the rollers 40 of the transport conveyor 38, which may be powered or non-powered. After coming to rest on the conveyor 38, the fuel is lifted vertically upward by the overhead transport system 42. The over head transport system 42 is capable of lifting the fuel container 36 from the transport conveyor 38 and moving it from right to left and back and forth within the glove box 22. The overhead transport conveyor 38 includes a rotating drum 43 around which is wrapped a cord 44 for raising and lowering the spheres. The containers 36 are moved one at a time from the transport conveyor 38 to the loading hoppers 60 and 62 of the weighing scales. In the preferred embodiment, three sizes of spheres are used, which are referred to herein as fines, mediums and large. There are three weighing stations, one corresponding to each of the sphere sizes. However, only two of the PG,6 weighing stations, the fines 64 and mediums 66 are shown for clarity. The mediums weighing station 66 is shown in FIG. 3 by the dotted figure in the load position for receiving fuel. The fuel container 36 are attached to the transport lid 43 and moved by the overhead transport system 42 to each of the weighing stations where the fuel spheres are deposited into the hoppers 60 and 62 of the scales. The mediums 65 and large 66 weighing stations are mounted on one platform and move from side to side by the drive motor 68. In addition, the weighing stations move up and down by the drive mechanism 72, the glove box 22 providing a recess 74 for the support shaft 76 when the station is lowered. The fines weighing station 64 moves front to back driven by the drive motor 78 within the glove box 22 as well as side to side motion driven by motor 70. As noted above, the mediums 66 and large 65 weighing stations are mounted on one platform moved toward the glove box opening for loading. In addition, the weighing stations loading hoppers 61 and 62 are lowered to accommodate the fuel containers 36 which are moved to the weighing stations by the overhead fuel transport 42. The fines weighing system 64 is mounted independently of weighing stations 65 and 66 and moves toward the back of the glove box 22, then to the right and down for loading. The fuel spheres containers 36 are picked up by the overhead transport system 42 and positioned on top of the weighing station hoppers. The spheres are released into the loading hoppers 60, 61 and 62. Spheres of each size are dropped into the weighing scales hoppers 80 and 82 in incremental amounts by the stepper motors 84 and 86. When predetermined amounts of fuel spheres are received by the scale hoppers 80 and 82 as indicated by the weighing means 79 and 81 the flow ceases (Recall only two of the three weighing scales are shown in the Figures). These predetermined amounts of fuel spheres are sufficient to fill one fuel rod 2. These fuel spheres are then transferred to the hoppers 92, 94, and 96 of the feeding probe 34. The feeding probe 34 is a device for depositing the three different sizes of spheres into the fuel rod 2 in a controlled manner so that the correct uniform density is achieved in the rod 2. Referring to FIGS. 4 and 6, the probe 34 includes three funnels 92, 94 and 96 into which each of the three quantities of fuel is discharged from the weighing scale hoppers 80, 81 and 82. In FIG. 6, only two 92 and 94 of the three funnels are shown for clarity. The funnels are spaced about 60.degree. apart and are all identical except for the ability to accommodate different sized spherical fuel. The three funnels 92, 94 and 96 are connected to the probe hopper 98 via three solenoid valves 100. There is one solenoid valve 100 for each funnel. The probe hopper 98 is divided into three sections 102, 104 and 106. The fuel spheres, after being released by the solenoid valves 100, pass through a regulator gate 114 shown in FIG. 9. The gate 114 is releasably attached by conventional ball plunger means 115 to the hopper 98 so as to restrict the passage-way 116 connecting the funnels 92 to the sections 102, 104 and 106 of the probe hopper 98. Referring to FIG. 11, the gate 114 includes an opening of height h and width w. These dimensions are selected according to the size of nuclear fuel spheres and the desired rate of flow into the probe hopper 98. The rate of flow of each of the fuel spheres is determined so that upon emergence from the probe 34 within the fuel rod 2, the maximum randomness of the three different size spheres is achieved. The probe hopper is connected to tubing 108, 110 and 112. Each of these tubes corresponds to one of the sections of the probe hopper 98 which, in turn, corresponds to one of the funnels 92, 94 and 96. In the particular embodiment shown in FIGS. 6 and 10, two of the tubes 108 and 110 are of the same circular cross-section. These tubes are used for the two smallest diameter fuel. The largest fuel sphere is carried by the tube 112 of elliptical cross section. The outer surface of lower end of each of the tubes 108, 110 and 112 is extended into scoops as shown in FIGS. 8 and 10. The scoop shaped extensions terminate into points 116 and 117 toward the axis through the center of the three tubed arrangement. The extensions of tubes 108 and 110 for the two smaller tubes join together to form one common point 117. These extensions help in the mixing of the fuel spheres to provide a random distribution of packing of the fuel tube. To further enhance the randomness of distribution of the three different sized spheres and improve the uniformity of packing of the fuel rod 2, a cone shaped piece 118 is fixed to the lower end of the fuel tubes 108, 110 and 112 by two cylindrical rod members 130 as shown in FIG. 8. The cone 118 is fixed to the rods 130 by conventional means. Alternatively, as shown in FIGS. 6 and 7, the cone 118 may be fixed to the lower end of the fuel tubes 108, 110, and 112 by a cylindrical collar 119. The collar overlaps and is welded to the lower end of the fuel tubes. The cone 118 is fixed to the other end of the collar 118 with the point of the cone 118 along the axis of the collar and pointed toward the probe 34. The cone 118 is welded at several points 121 but leaving a gap 123 between the cone 118 and collar 119 so that the fuel spheres may emerge from the probe 34. After the probe is loaded, the weighing stations are moved out of the way of the fuel feeding probe 90 and the solenoid valves 100 are opened. The fuel spheres descend through the valve 100, the regulator gate 114 and the tubing 108, 110 and 112. As the fuel reaches the bottom of the fuel rod 2, the probe 90 is raised at a rate so that the bottom of the fuel probe 90 remains just above the ascending fuel column. That is, the spheres are deposited on top of the fuel column such that the end of the probe remains between about 1 and 5 in above the ascending fuel column. The probe 34 is raised and lowered by means 33 through a cable 35 attached to Bracket 31 of the probe 34. Copper tubes 132 guide the feeding probe 90 up and down. The copper tubes 132 in combination with wires 134 provide the electrical contact to operate the solenoids 100. The vibrator 6 is in operation while the fuel rod 2 is being loaded. After the loading is completed and feeding probe 90 is clear of the fuel rod 2, the rod is removed from the support clamp 4. A new fuel rod is placed in the clamp 4 and process is started again. EXAMPLE For fuel spheres having diameters 30 .mu.m, 200 .mu.m, and 1200 .mu.m, the dimensions for the opening in the regulator gate is d=0.504 for all three gates and h=0.020 in, 0.032 in and 0.1 in. |
060524316 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray converging mirror located at the vicinity of the X-ray source for reflecting X-ray beams emitted from the X-ray source in an X-ray irradiation position direction in the X-ray irradiation device to provide an improved X-ray system, such as an X-ray analysis microscope. 2. Description of Related Art In recent years, X-ray analysis microscopes have begun to be used in the analysis of biological tissues, such as plants and small animals as well as minerals or in the field of various analysis and quality control of semiconductor packages and electronic parts. In an X-ray analysis microscope, it is necessary to irradiate microscopic portions of specimens with fine X-ray beams, which are important for analysis as a probe. Conventionally, fine X-ray beams are generated using a microfocus X-ray tube, such as an X-ray converging mirror for converging and focusing fine X-ray beams at an X-ray irradiation position, for example, ellipsoid of revolution type reflecting mirrors, as shown in Japanese Patent Publications No. Hei 4-6903, Hei 5-27840, and Hei 5-43080 have been used. FIG. 3 schematically shows an ellipsoid of revolution type reflecting mirror where an X-ray source 4 is installed at a first focal point of the ellipsoid of revolution type reflecting mirror 30. A specimen 32 is installed at a second focal point of the mirror 30. Of the X-beams mitted from the X-ray source 31, those reflected on the reflecting surface of the mirror 30 are all converged to the specimen 32 surface. However, because X-ray beams impinging in the vicinity of the central portion of the mirror 30, as in the case of X-ray beams shown with numeral 33, have a small incidence angle a with respect to the reflecting surface tangent 34 when an ellipsoid of revolution type mirror 30 is used for an X-ray converging mirror, the reflectivity at the reflecting surface is high and the ratio of the X-rays impinging in the specimen 32 (X-ray efficiency) is high. But in the case of the X-ray beams shown with numeral 35 impinging in the vicinity of the X-ray source 31 of the mirror 30, they have a large incidence angle .beta. with respect to the reflecting surface tangent 36, and a problem exists in that the X-ray permeability at the reflection surface is high and the X-ray efficiency is low. OBJECTS AND SUMMARY OF THE INVENTION This invention is made with the above-mentioned matter taken into account, and it is the main object of this invention to provide an X-ray converging mirror that can reflect X-ray beams satisfactorily in the X-ray irradiation position direction in the vicinity of the X-ray source. It is another object of the present invention to provide an improved X-ray analysis system, such as an energy-dispersive fluorescent X-ray analytical microscope, which includes a fluorescent X-ray detector, an X-ray guide tube, a sample stage, a transmitted X-ray detector, and appropriate processing systems to render a mapping image of the sample. In order to achieve the above-mentioned objects, this invention relates to an improved X-ray converging mirror installed in the vicinity of the X-ray source to reflect X-ray beams emitted from the X-ray source in the X-ray irradiation position direction. The X-ray converging mirror is characterized by a cross-sectional profile of the mirror, which is a curve expressed by the following expression EQU x=y tan .theta.[1-ln(y/b)] .theta. is set to the critical angle or less, PA1 ln is the natural logarithm, and x, y, and b are positions on a coordinate system. In the X-ray converging mirror of the above configuration, the reflectivity of X-ray beams in the vicinity of the X-ray source becomes high and the X-ray intensity also increases. Consequently, it is possible to obtain an X-ray converging mirror with an excellent X-ray efficiency. |
051749459 | abstract | A fusion power generating device is disclosed having a relatively small and inexpensive core region which may be contained within an energy absorbing blanket region. The fusion power core region contains apparatus of the toroidal type for confining a high density plasma. The fusion power core is removable from the blanket region and may be disposed and/or recycled for subsequent use within the same blanket region. Thermonuclear ignition of the plasma is obtained by feeding neutral fusible gas into the plasma in a controlled manner such that charged particle heating produced by the fusion reaction is utilized to boot-strap the device to a region of high temperatures and high densitities wherein charged particle heating is sufficient to overcome radiation and thermal conductivity losses. The high density plasma produces a large radiation and particle flux on the first wall of the plasma core region thereby necessitating replacement of the core from the blanket region from time to time. A series of potentially disposable and replaceable central core regions are disclosed for a large-scale economical electrical power generating plant. |
claims | 1. A CT scanner comprising:at least one source of X-rays within an x-ray spectra;a detector array comprising a plurality of detectors; andan X-ray filter mask arrangement disposed between the at least one source of X-rays and detector array so as to modify the spectra of the X-rays transmitted from the at least one source through the filter mask arrangement to at least some of the detectors so that the X-ray spectra detected by at least one set of detectors is different from the X-ray spectra detected by at least one other set of detectors;wherein the CT scanner has X, Y and Z-axes, wherein the X and Y-axes define a scanning plane, and the Z-axis defines the axis of rotation of the at least one source of X-rays and detector array, and the CT scanner further comprises a processor arrangement configured so as to process signals from the detectors to generate interpolated data so that the set of interpolated data representing interpolated values is provided in accordance with a four point Lagrange interpolation along the X-axis. 2. A CT scanner according to claim 1, wherein the at least one source of X-rays is a source providing x-rays of a first energy spectra, and the filter mask arrangement provides x-rays of a second and different energy spectra so that some of the detectors receive x-rays of the first energy spectra and some of the other detectors receive x-rays of the second energy spectra such that use of the filter mask arrangement converts a single energy scanner into a dual energy scanner. 3. A CT scanner according to claim 1, wherein the at least one source of X-rays is a source providing a first set of x-ray energy spectra, and the filter mask arrangement provides x-rays of a second and different set of x-ray energy spectra so that some of the detectors receive x-rays of the first set of energy spectra, and some of the other detectors receive x-rays of the second set of energy spectra such that use of the filter mask arrangement increases the number of projections associated with different x-ray energy spectra. 4. A CT scanner according to claim 1, wherein the at least one source of X-ray includes an x-ray tube with a flying focal spot. 5. A CT scanner according to claim 1, wherein the X-ray filter mask arrangement is disposed between scanning objects and the detector array. 6. A CT scanner according to claim 1, wherein the X-ray filter mask arrangement is disposed between scanning objects and the at least one source of X-rays. 7. A CT scanner according to claim 1, wherein the X-ray filter mask arrangement includes a checker board pattern. 8. A CT scanner according to claim 1, wherein the CT scanner further includes a processor arrangement configured so as to interpolate data received by the detectors corresponding to one X-ray spectrum to generate the data corresponding to the remaining detectors that correspond to other X-ray spectra and apply an image reconstruction algorithm using the interpolated data for reconstruction. 9. A CT scanner according to claim 8, wherein the CT scanner has an X, Y and Z-axes, wherein the X and Y-axes define a scanning plane, and the Z-axis defines the axis of rotation of the at least one source of X-rays and detector array, and the CT scanner further comprises a processor arrangement configured so as to process signals from the detectors to generate interpolated data so that the set of interpolated data representing interpolated values is provided in accordance with an interpolation technique along the Z-axis. 10. A CT scanner according to claim 8, wherein the CT scanner has an X, Y and Z-axes, wherein the X and Y-axes define a scanning plane, and the Z-axis defines the axis of rotation of the at least one source of X-rays and detector array, and the CT scanner further comprises a processor arrangement configured so as to process signals from the detectors to generate interpolated data so that the set of interpolated data representing interpolated values is provided in accordance with a four point Lagrange interpolation along the X-axis. 11. A CT scanner according to claim 1, wherein the CT scanner further includes a processor arrangement configured so as to apply a reconstruction algorithm with steps modified to reconstruct data received by the detectors corresponding to one X-ray spectrum. 12. A CT scanner according to claim 11, wherein the reconstruction algorithm is a nutated slice reconstruction algorithm. |
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040100685 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to nuclear reactor power plants and more particularly to the removal of radioactive contaminants from the coolant of a liquid metal-cooled fast breeder nuclear reactor. 2. Description of the Prior Art In a nuclear reactor power plant electricity is generated from heat which is produced by fission of fissile materials. In an initial phase of this process a reactor coolant, such as liquid sodium, is used to remove the heat from fuel elements which contain the fissile materials. The reactor coolant circulates through a closed flow system known as the primary system which is made up of a main coolant circulating pump, either a heat exchanger or a steam generator, reactor vessel, and connecting piping arranged in series flow connection. The primary system is closed in the interest of safety since a closed system prevents the release, to the environment, of radioactive particles should the primary system become contaminated. One way that the contamination may occur is by release of radioactive fission products from failed fuel elements. Another way is from the use of vented fuel elements which operate by purposely allowing the release of fission products rather than trying to keep them contained. In the past, the radioactive contamination was removed, although not effectively, by a cold trapping technique which operates by lowering the temperature of a diverted portion of the reactor coolant causing the contamination to precipitate out of solution. Recently, however, major advances were made in the art by using the cold trapping technique in conjunction with adding certain chemicals or reactants to the hot reactor coolant to enhance the precipitation of the contamination. That is, high concentrations of reacting chemicals or isotopic diluents are mixed with a diverted stream of reactor coolant and the radioactive contamination, in the form of isotopically exchanged or insoluble compounds, are precipitated out of solution in a cold trap. The addition of non-radioactive iodine for example, to hot liquid sodium removes as much as 99.9% of the radioactive isotopes, iodine-131 and iodine-125. Also, the addition of hydrogen to hot liquid sodium removes essentially all of the tritium, cesium-137 and iodine-131 from the reactor coolant. Even these recently employed methods, however, have certain disadvantages. A principal disadvantage is that the amount of radioactive contamination removed is quite small relative to the amount of reactants or additives used. This means that the precipitant in the cold trap consists primarily of unreacted chemicals and unexchanged isotopic diluents. Consequently, the cold trap must be large and must either be replaced or cleaned on a frequent basis. This severely limits the availability of the plant for the production of electrical energy. The present invention eliminates this highly undesirable feature of the prior art. SUMMARY OF THE INVENTION The invention described herein consists of an oscillating cold trap system in which one trap is loaded with reactants while a second trap, in series flow connection thereto, is used to precipitate the radioactive contamination and the excess reactants. When the reactants in the first trap are exhausted, the direction of flow is reversed; the heating and cooling of the traps are also reversed. The second cold trap then acts as the reactant supply, while the first cold trap operates to remove the impurities by precipitation. When the excess reactant has been exhausted from the second cold trap, the flow is again switched, reversing the roles of the two cold traps. The system is continuously and reversibly operated in this manner until the reactants can no longer be used to precipitate radioactive contamination contained within the reactor coolant. Sodium hydride, sodium oxide, and sodium iodide are typical reactants loaded into the oscillating cold trap system. These will effectively and efficiently remove such radioactive contamination as tritium, barium-140, cesium-141, zirconium-95, iodine-131 and iodine-125. |
abstract | A radiation system for generating a beam of radiation that defines an optical axis is provided. The radiation system includes a plasma produced discharge source for generating EUV radiation. The discharge source includes a pair of electrodes constructed and arranged to be provided with a voltage difference, and a system for producing a plasma between the pair of electrodes so as to provide a discharge in the plasma between the electrodes. The radiation system also includes a debris catching shield for catching debris from the electrodes. The debris catching shield is constructed and arranged to shield the electrodes from a line of sight provided in a predetermined spherical angle relative the optical axis, and to provide an aperture to a central area between the electrodes in the line of sight. |
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055704018 | abstract | An improved containment configuration for a boiling water reactor in which the wetwell airspace is divided into a multiplicity of chambers through the use of wetwell airspace divider partitions. The partitions extend to below the water level of the suppression pool so that the gas in one airspace chamber cannot communicate with another airspace chamber. Each wetwell airspace chamber can be placed in flow communication with the drywell via a respective open vacuum breaker. When one vacuum breaker fails in the open position or when wetwell/drywell steam bypass leakage into one chamber occurs, the pressure differential between the wetwell airspace chamber and the drywell drops. However, because the leaking chamber is isolated, the pressure differential between the drywell and the other chambers is unaffected. Thus, the PCC heat exchangers corresponding to non-leaking chambers can continue to operate effectively, even if the PCC heat exchanger corresponding to the leaking chamber is rendered ineffective. |
039649695 | abstract | An internal core tightener which is a linear actuated (vertical actuation motion) expanding device utilizing a minimum of moving parts to perform the lateral tightening function. The key features are: (1) large contact areas to transmit loads during reactor operation; (2) actuation cam surfaces loaded only during clamping and unclamping operation; (3) separation of the parts and internal operation involved in the holding function from those involved in the actuation function; and (4) preloaded pads with compliant travel at each face of the hexagonal assembly at the two clamping planes to accommodate thermal expansion and irradiation induced swelling. The latter feature enables use of a "fixed" outer core boundary, and thus eliminates the uncertainty in gross core dimensions, and potential for rapid core reactivity changes as a result of core dimensional change. |
claims | 1. A target unit for producing Cu67 radioisotope comprising:a cage body releasably coupled to a screw-on cap; anda ceramic capsule containing a solid Zn68 target ingot and having one open end and one closed end and defining an interior chamber for the target ingot;wherein the ceramic capsule is releasably contained between the cage body and the screw-on cap with a lid disposed on the open end of the capsule and a washer positioned between the lid and the screw-on cap, wherein the screw-on cap and the washer provide a water-tight seal between the lid and the capsule; the interior of the ceramic capsule is in intimate physical contact with the solid Zn68 target ingot; and the Zn68 of the target ingot is free of traces of residual oxygen that interfere with contact of the Zn68 to the capsule. 2. The target unit of claim 1, wherein the cage body and the screw-on cap are composed of aluminum. 3. The target unit of claim 1, wherein the cage body and the screw-on cap are composed of different alloys of aluminum to minimize the possibility of thread galling. 4. The target unit of claim 1, wherein the cage body and the screw-on cap are each composed of different alloys of aluminum selected from the group consisting of 6061 Al and 2024 Al. 5. The target unit of claim 1, wherein the cage body includes apertures to allow cooling water to contact the capsule during irradiation thereof to prevent melting or partial melting of the zinc target ingot during the irradiation. 6. The target unit of claim 1, wherein the ceramic capsule is composed of a material selected from the group consisting of alumina and aluminum nitride. 7. The target unit of claim 1, wherein the capsule is composed of alumina. 8. A target unit for producing Cu67 radioisotope comprising:a cylindrical cage body with a threaded open end;a screw-on cap threaded to mate with the threaded open end of the cage body;a ceramic capsule having one open end and one closed end, and defining an interior chamber containing a Zn68 target ingot in intimate physical contact with the capsule;a removable lid covering the open end of the capsule; anda gasket disposed between the open end of the capsule and the lid;wherein the ceramic capsule, the lid, and the gasket are arranged within the interior cavity of the cage body with the lid in contact with the screw-on cap when the cage body is mated with the screw-on cap, so that the screw-on cap applies a pressure on the lid and gasket sufficient to form a water-tight seal over the open end of the capsule when the unit is fully assembled for use; and the Zn68 of the target ingot is free of traces of residual oxygen that interfere with contact of the Zn68 to the capsule. 9. The target unit of claim 8, wherein the cage body and the screw-on cap are composed of aluminum. 10. The target unit of claim 8, wherein the cage body and the screw-on cap are composed of different alloys of aluminum to minimize the possibility of thread galling. 11. The target unit of claim 8, wherein the cage body and the screw-on cap are each composed of different alloys of aluminum selected from the group consisting of 6061 Al and 2024 Al. 12. The target unit of claim 8, wherein the cage body includes apertures to allow cooling water to contact the capsule during irradiation thereof to prevent melting or partial melting of the zinc target ingot during the irradiation. 13. The target unit of claim 8, wherein the ceramic capsule is composed of a material selected from the group consisting of alumina and aluminum nitride. 14. The target unit of claim 8, wherein the capsule is composed of alumina. 15. The target unit of claim 8 wherein the gasket is composed of graphite. |
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058870415 | claims | 1. An automated system for identifying at least one of a plurality of nuclear power plant components of a nuclear power plant, said nuclear power plant components having at least one component identifier positioned therewith, said system comprising: camera means for inputting a first image including at least one of said nuclear power plant components and providing an input signal therefrom; digitization means for generating a second image of said at least one of said nuclear power plant components from the input signal, with the second image being a digitized image including a plurality of pixel elements; means for locating said component identifier of said at least one of said nuclear power plant components from said pixel elements; and determining means at least for determining said component identifier, said determining means comprising: means for locating a third image of the identification characters in the second image, means for convolving an edge filter over the third image to produce an edge image, means for selecting one of the predetermined characters, means for convolving the edge image with an edge image representation of the selected predetermined character to produce an edge convolution surface, means for convolving the third image with an intensity representation of the selected predetermined character to produce an intensity convolution surface, means for subtracting the edge convolution surface from the intensity convolution surface to produce a difference image, means for determining the location where the intensity representation and the edge image representation of the selected predetermined character collectively best match the third image and the edge image, and means for determining a confidence value of the match between the selected predetermined character and the third image from the difference image. means for producing a binary image from the third image, means for producing an image having a standard size from the binary image, and means for determining the best match between the image having the standard size and each of the predetermined characters. means for convolving a segmented character template with each of the plural segments, means for determining a confidence value) corresponding to each of the segments, and means for determining a confidence value) for said one of the identification characters from the confidence values) of the segments. inputting a first image of at least a portion of said nuclear power plant component including said component identifier; generating a second image of said nuclear power plant component from the first image, with the second image being a digitized image including a plurality of pixel elements; locating said component identifier of said nuclear power plant component from said pixel elements; determining a first intermediate recognition of said component identifier, determining a second intermediate recognition of said component identifier, and recognizing said component identifier employing said first and second intermediate recognitions. determining a plurality of intermediate recognitions of said component identifier including a confidence value corresponding to each of the intermediate recognitions; determining unique ones of the intermediate recognitions; summing the confidence values corresponding to the unique intermediate recognitions; and recognizing said component identifier as the unique intermediate recognition having the largest summed confidence value. 2. The system of claim 1 wherein each of the outputs includes an intermediate identifier and a corresponding confidence value; and wherein said means for combining the outputs includes means for recognizing said component identifier as the intermediate identifier having the largest confidence value. 3. The system of claim 2 wherein said means for recognizing said component identifier includes 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 said component identifier as the unique intermediate identifier having the largest summed confidence value. 4. The system of claim 1 wherein said component identifier includes at least one identification character; and wherein said determining means includes means for recognizing the identification character. 5. The system of claim 4 wherein said at least one identification character includes a plurality of alphanumeric characters. 6. The system of claim 1 wherein said nuclear power plant includes a nuclear reactor core; wherein said nuclear power plant components include nuclear fuel assemblies; wherein said means for locating determines a location of said component identifier of one of said nuclear fuel assemblies in the nuclear reactor core; and wherein said determining means includes means for inputting predefined component identifiers of said nuclear fuel assemblies in said nuclear reactor core, and means for verifying said component identifier of one of said nuclear fuel assemblies with a corresponding one of said predefined component identifiers. 7. The system of claim 1 wherein said nuclear power plant includes a nuclear reactor core; wherein said nuclear power plant components include nuclear fuel assemblies; wherein said means for locating determines locations of said component identifiers of an adjacent pair of said nuclear fuel assemblies in the nuclear reactor core; and wherein said determining means includes means for determining a gap between the pair of said nuclear fuel assemblies. 8. The system of claim 7 wherein said determining means includes means for inputting at least one of a minimum gap and a maximum gap between the pair of said nuclear fuel assemblies, and means for verifying the gap between said pair with said at least one of the minimum and maximum gaps. 9. The system of claim 1 wherein at least one of said recognizer means includes convolution means for recognizing said component identifier. 10. The system of claim 9 wherein said component identifier of said nuclear power plant components includes a plurality of identification characters selected from a plurality of predetermined characters; and wherein said convolution means includes: 11. The system of claim 10 wherein said convolution means further includes means for evaluating the third image with each of the predetermined characters. 12. The system of claim 1 wherein one of said recognizer means includes means employing a Karhunen-Loeve expansion for recognizing said component identifier. 13. The system of claim 1 wherein said component identifier of said nuclear power plant components includes a plurality of identification characters selected from a plurality of predetermined characters; wherein said determining means further includes means for locating a third image of the identification characters in the second image; wherein the third image includes a plurality of pixels each of which has a plural bit gray-level value; and wherein one of said recognizer means includes identification character recognizer means comprising: 14. The system of claim 13 wherein said identification character recognizer means further includes means for determining a confidence value of the match between the predetermined characters and the image having the standard size. 15. The system of claim 1 wherein said component identifier includes a plurality of identification characters; wherein said determining means further includes means for locating a third image of the identification characters in the second image; wherein one of said recognizer means includes segmented convolution recognizer means for segmenting the third image into a plurality of segments and determining one of the identification characters therefrom. 16. The system of claim 15 wherein said segmented convolution recognizer means includes: 17. The system of claim 1 wherein said nuclear power plant components include nuclear fuel assemblies; wherein said nuclear fuel assemblies include a spring clamp; and wherein said component identifier is located on the spring clamp. 18. The system of claim 17 wherein the spring clamp includes a plurality of screw hole locations and a plurality of edges; wherein said means for locating said component identifier includes first convolution means for determining the location of said nuclear fuel assembly from the screw hole locations, and second convolution means for alternatively determining the location of said nuclear fuel assembly from the edges. 19. A method for identifying a nuclear power plant component of a nuclear power plant, said nuclear power plant component having a component identifier positioned therewith, said method comprising the steps: 20. The method of claim 19 further comprising: |
051732173 | description | With reference to FIG. 1 a containment for the disposal of radioactive waste material comprises an outer container 1, which can be of carbon or stainless steel, housing a crate 2, which can be wood, and which in turn, houses a used glove box 3. The glove box 3 can contain a variety of contaminated radioactive products such as gloves, tissues, tools in addition to fixed or loose in-box process equipment. The container 1 has a lid 4 provided with an entry port 5 which is shown in greater detail in FIG. 2. The port 5 comprises a support tube 6 which extends through the lid 4 and is secured by webs 7 in a well 8 in the lid 4. The end of the tube 6 within the container 1 is closed by a bursting disc 9, conveniently of aluminum, which is bonded to the end of the tube 6. A vent coupling 10 is mounted in the lid 4 at the well 8. A locking screw 11 is provided at or adjacent the end of the tube 6 outside the container 1. Finally, a cover plate 12 for the well 8 is provided and a sealing ring or compound is introduced between the plate 12 and the lid 4 before the plate 12 is clamped in position by means of screws 13. FIGS. 3 and 3a show respectively a front elevation and section of a cabinet 14 for mounting on the lid 4 at the port 5. The cabinet 14 support an electric drive motor 15 displaceable vertically within the cabinet 14 by means of a hand lever 16 cooperable with racks 17 fixedly mounted on a wall of the cabinet 14. The vertical displacement of the motor 15 is controlled by a counter-weight 18. Power for the drive motor 15 is supplied through a control box 19 mounted on the exterior of the cabinet 14. An opening 20 in a wall provides controlled access to the interior of the cabinet 14. The motor 15 drives a socket 21 and as shown in FIGS. 4 and 4a one end of a hollow stem 22 is releasably engageable in the socket 21. A cutter tool 23 is fixedly secured to the opposite end of the hollow stem 22. A plurality of radial bores (not shown) extend through the cutter tool 23 and the wall of the stem 22 to communicate with the interior of the stem 22. Referring again to FIG. 3a, a grout feed pipe 24 extends into the cabinet 14 and has a length to reach the floor of the cabinet 14. The end of the pipe 24 within the cabinet 14 is provided with a releasable coupling 25 capable of cooperating with an associated coupling (not shown) at the upper end of the hollow stem 22 (see FIG. 4). A further pipe 26 within the cabinet 14 cooperates with the vent coupling 10 (see FIG. 2) in the well 8 of the lid 4. The pipe 26 passes through an opening in the floor of the cabinet 14. The opening cooperates with the well 8 in the lid 4 to permit the cutter tool 23 to enter into the tube 6. The stem 22 is supported at the tube 6 by a bearing block 27 which permits axial and rotational movement of the stem 22. The block 27 is clamped in position in the tube 6 by the locking screw 11 (FIG. 2). In use, the cabinet 14 is positioned on the container 1 and over the entry port 5. With the hollow stem 22 carrying the cutter tool 23 engaged in the coupling socket 21, the drive motor 15 is lowered to cause the tool 23 to break through, in succession, the bursting disc 9 at the bottom of the tube 6, the wall of the crate 2 and the wall of the glove box 3. The downward motion is continued until the socket 21 reaches the tube 6. The socket 21 is then released from the stem 22 by lifting the motor 15 back to its initial position and the coupling 25 at the end of the grout feed pipe 24 is engaged with the coupling at the upper end of the stem 22 at the tube 6. Grout slurry is pumped along the pipe 24 to pass along the hollow stem 22 and emerge through the radial bores at the opposite end of the stem 22 into the interior of the glove box 3. The contents of the glove box 3 are immersed in the grout slurry which progressively fills the complete containment of glove box 3, crate 2 and container 1. Air displaced upon filling by the grout slurry is expelled through the vent pipe 26 coupled to the coupling 10. When the containment is filled the grout feed pipe 24 is released from the end of the stem 22 at the well 8 in the lid 4, and the cover plate 12 is secured in position. The stem 22 remains within the containment and forms a part of the contents thereof which are embedded in the grout when set. The end product comprises a solid block containing waste products including the glove box 3 and its contents. The containment can include more than one glove box. For example, the containment can comprise an outer container capable of accommodating a plurality of crates and/or glove boxes and having a corresponding plurality of entry ports and a corresponding plurality of cutting means maybe provided. |
048658006 | abstract | A fuel assembly grid inspection apparatus includes a precision noncontact measurement device having a source of illumination and a viewing system which defines an inspection field of view. The viewing system is adapted to view and record one or more images of an object, such as a fuel assembly grid, located in the field of view to provide information from actual measurements of the grid which can be calculated to determine whether or not it comes within acceptable tolerances of the measurements of a standard grid of the same design. The apparatus also includes a universal fixture adapted to support any one of a variety of grids of different designs within the field of view such that portions of the fixture within the field of view are substantially transparent to the viewing system. The viewing system and the fixture are movable relative to each other in X, Y, and X directions for achieving a complete inspection of all parts of the grid. Typically, the grid being inspected has at least a pair of vertically displaced fuel rod contacting dimples disposed in each of a plurality of cells defined in the grid. The dimples are inspected for perpendicularity with respect to each other by using the viewing system to view them at separate instances but from the same location within the field of view. |
052166996 | abstract | An X-ray microscope has an X-ray filter for transmitting a wavelength between 43.7 and 65 .ANG. and a light source for emitting ultraviolet light of a wavelength of at least 100 nm in an optical path so that a specimen is irradiated with X rays and an image of an object is formed by an X-ray detector, in which the ultraviolet light is reflected from the X-ray filter to irradiate the specimen. Thus, the X-ray microscope allows biological observation to be made with a transmitted microscopic image of high quality and has advantages in design and choice of materials in fabricating its system. |
claims | 1. A method of preparing a spherical nuclear fuel particle, which method includes the step of depositing at least two adjacent series of spherically continuous layers around a kernel of fissile material to form a spherical nuclear fuel particle, each series comprising a layer of pyrolytic carbon contiguous with a layer of silicon carbide and each layer having a thickness of at most 9 micrometers, with alternate layers of pyrolytic carbon and silicon carbide thus being deposited around the kernel. 2. The method as claimed in claim 1, in which each layer has a thickness of between 3 micrometers and 9 micrometers. 3. The method as claimed in claim 2, in which each layer of silicon carbide has a thickness of between 3 micrometers and 6 micrometers. 4. The method as claimed in claim 2, in which each layer of pyrolytic carbon has a thickness of between 4 micrometers and 9 micrometers. 5. The method as claimed in claim 1, in which the layers are deposited by chemical vapor deposition techniques. 6. The method as claimed in claim 5, in which the deposition of layers is carried out at a pressure of between 1.3 kPa and 2.5 kPa. 7. The method as claimed in claim 6, in which the deposition of layers is carried out at a pressure of 1.7 kPa. 8. The method as claimed in claim 1, in which the deposition of the pyrolytic carbon and silicon carbide layers takes place as a continuous process, the method including switching between chemical precursors for deposition of the pyrolytic carbon and silicon carbide layers respectively such that transition zones comprising pyrolytic carbon mixed with silicon carbide are formed between each layer of pyrolytic carbon and a contiguous layer of silicon carbide. 9. The method as claimed in claim 8, in which the transition zones between each layer of pyrolytic carbon and its contiguous layer of silicon carbide have a thickness of between 0.5 micrometers and 2 micrometers. 10. The method as claimed in claim 1, which includes the prior step of forming a plurality of kernels of uranium dioxide by atomising a uranyl nitrate solution to form microparticles, followed by baking the microparticles at high temperature, to yield uranium dioxide microparticles. 11. The method as claimed in claim 1, in which the deposited silicon carbide is of the beta polytype. 12. The method according to claim 1, in which the kernel has a diameter of 500 micrometers. 13. A method of preparing a spherical nuclear fuel particle, which method includes the step of depositing at least two adjacent series of spherically continuous layers around a kernel of fissile material to form a spherical nuclear fuel particle, each series comprising a layer of pyrolytic carbon contiguous with a layer of silicon carbide and each layer having a thickness of at most 9 micrometers, with alternate layers of pyrolytic carbon and silicon carbide thus being deposited around the kernel, with the deposition of the pyrolytic carbon and silicon carbide layers taking place as a continuous process by switching between chemical precursors for deposition of the pyrolytic carbon and silicon carbide layers respectively such that transition zones comprising pyrolytic carbon mixed with silicon carbide are formed between each layer of pyrolytic carbon and a contiguous layer of silicon carbide. 14. The method as claimed in claim 13, in which the transition zones between each layer of pyrolytic carbon and its contiguous layer of silicon carbide have a thickness of between 0.5 micrometers and 2 micrometers. 15. A method of preparing a spherical nuclear fuel particle, which method includes the step of depositing at least two adjacent series of spherically continuous layers around a kernel of fissile material to form a spherical nuclear fuel particle, each series comprising a layer of pyrolytic carbon contiguous with a layer of silicon carbide and each layer having a thickness of at most 9 micrometers, with alternate layers of pyrolytic carbon and silicon carbide thus being deposited around the kernel, the method including a prior step, preceding the step of depositing at least two adjacent series of spherically continuous layers around the kernel of fissile material, of forming a plurality of kernels of fissile material. 16. A method according to claim 15, in which the fissile material is uranium dioxide. 17. A method according to claim 1, in which the fissile material is uranium dioxide. 18. A method according to claim 13, in which the fissile material is uranium dioxide. |
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061954063 | 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 pressurizer 1, which usually forms part of a nuclear power plant with a pressurized water reactor, where it is connected to a hot part or system 12 of a primary circuit through a volume-compensation line 2. If the pressure in the primary circuit were to be too high, water, which can be branched off from a cold part of the primary circuit, is sprayed into the pressurizer 1. To this end, a spray line 3 leads from the cold part or system 13 and ends in the pressurizer 1. A spray valve 4 with a controllable or ON/OFF actuator 5 is disposed in the spray line 3 outside the pressurizer 1. The spray valve 4 is controlled according to the pressure in the primary circuit. Water levels 6a, 6b for zero load and normal operation of the nuclear power plant are indicated in the pressurizer 1. Heater rods 11 are disposed in a lower section of the pressurizer 1. The spray line 3 runs from outside a casing 7 of the pressurizer 1 through a wall of a lower cylindrical part of the casing 7, into an interior of the casing 7, at an oblique angle with respect to the wall. Inside the casing, the spray line 3 runs continuously upward and ends at its geodetically highest point. The spray line 3 is guided along an inner wall surface of the casing 7. The spray line 3 has spray nozzles 8 in the region of its highest point. This portion of the spray line 3 which has the spray nozzles 8 is directed upward at an angle. Water is advantageously sprayed into the pressurizer 1 from its upper region through the use of this configuration. Nevertheless, when the spray valve 4 is closed it is impossible for any part of the spray line 3 between the spray valve 4 and the spray nozzles 8 to become empty. Consequently, it is also impossible for any steam to penetrate into the spray line 3 and condense therein, and there is no possibility of temperature fluctuations or exposure to radiation in the spray line 3. In particular, the spray line 3 inside the pressurizer 1 is only exposed to a slight pressure difference between its interior and its exterior, so that a relatively thin spray line 3 is sufficient, yet there is no risk of the spray line being fractured. Even in the unlikely event of a fracture of the spray line 3 inside the pressurizer 1, the small pressure difference means that there is no possibility of secondary damage caused by recoil effects. FIG. 2 is an enlarged view of a portion of FIG. 1 which shows the structure that allows the spray line 3 to be guided through the wall of the casing 7 at an oblique angle. Inside the casing 7, the spray line 3 is connected to the wall of the casing 7 by clamps 9, which allow the spray line 3 to move in axial direction but do not allow it to rotate. Due to the small pressure differences between the interior and the surroundings of the spray line 3, a relatively thin-walled spray line 3 is sufficient inside the pressurizer 1. A larger wall thickness is required outside the pressurizer 1. A fixed point 10 for the spray line 3 is disposed in the region of the inclined passage through the wall. FIG. 3 shows another embodiment for guiding the spray line 3 through the wall of the casing 7. The FIG. 3 embodiment differs from the embodiment according to FIG. 2 only in that the spray line 3 is guided through the wall at right angles thereto. Although this requires a more complex path for the line as compared to the embodiment according to FIG. 2, the region where it is guided through the wall is simplified. FIG. 4 shows the most advantageous way of guiding the spray line 3 through the wall of the casing 7. The spray line 3 is guided through with slight curvatures at right angles to the wall of the casing 7, in a dome-like part 7a of the casing 7, which closes off the casing 7 at the bottom. In this embodiment, the spray line 3 is also disposed in an inexpensive, stable manner inside the pressurizer 1 over as long a distance as possible. This is because the spray line 3 cannot be guided into the pressurizer 1 directly from below, since that is where the heater rods 11, which are also shown in FIG. 1, are disposed. |
abstract | A reflective optical element and an EUV lithography appliance containing one such element are provided, the appliance displaying a low propensity to contamination. The reflective optical element has a protective layer system includes at least two layers. The optical characteristics of the protective layer system are between those of a spacer and an absorber, or correspond to those of a spacer. The selection of a material with the smallest possible imaginary part and a real part which is as close to 1 as possible in terms of the refractive index leads to a plateau-type reflectivity course according to the thickness of the protective layer system between two thicknesses d1 and d2. The thickness of the protective layer system is selected in such a way that it is less than d2. |
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description | The subject matter of this application is related to the subject matter in a co-pending non-provisional application by Dan Vacar, David K. McElfresh, Kenny C. Gross, and Leoncio D. Lopez entitled, “Characterizing Degradation of Components During Reliability-Evaluation Studies,” having serial number 11/452,632, and filing date 13 Jun. 2006 1. Field of the Invention The present invention relates to techniques for monitoring the health of a computer system. More specifically, the present invention relates to a method and apparatus for determining whether a computer system is at the onset of degradation by monitoring a difference function for the variance of a monitored telemetry variable. 2. Related Art An increasing number of businesses are using computer systems for mission-critical applications. In such applications, a component failure can have a devastating effect on the business. For example, the airline industry is critically dependent on computer systems that manage flight reservations, and would essentially cease to function if these systems failed. Hence, it is critically important to monitor the health of components within the computer system so that remedial actions can be performed on components that are at the onset of degradation. One technique for monitoring the health of components within the computer system is to monitor telemetry variables generated within the computer system. These telemetry variables can include physical signals generated by transducers: such as temperature, voltage, current, and vibration, and can include software signals monitored by an operating system such as: hard disk activity, central processing unit (CPU) load, and memory usage. Existing health-monitoring techniques detect changes in the mean value of the monitored telemetry variables. One embodiment of the present invention provides a system that monitors the health of a computer system. During operation, the system receives a first-difference function for the variance of a time series for a monitored telemetry variable within the computer system. The system then determines whether the first-difference function indicates that the computer system is at the onset of degradation. If so, the system performs a remedial action. In one embodiment, prior to receiving the first-difference function, the system receives the variance of the time series for the monitored telemetry variable. Next, the system calculates a residual function of the variance of the time series for the monitored telemetry variable. The system then calculates the first-difference function from the residual function of the variance. In one embodiment, prior to receiving the variance for the time series for the monitored telemetry variable, the system receives the time series for the monitored telemetry variable. The system then calculates the variance of the time series for the monitored telemetry variable. In one embodiment, while calculating the first-difference function of the time series, for each time point within the time series, the system subtracts a value of the time series at a previous time point from the value of the time series at a present time point. In one embodiment, the system divides the result of the subtraction by the value of a length of a time interval between the previous time point and the present time point. In one embodiment, while calculating the residual function for a time series, for each time interval in the time series, the system (1) calculates a running average of values for the time series up to and including a present time interval; and (2) subtracts the running average from a value of the time series at the present time interval. In one embodiment, while determining whether the first-difference function indicates that the computer system is at the onset of degradation, the system determines whether the first-difference function exceeds a specified threshold. In one embodiment, while determining whether the first-difference function indicates that the computer system is at the onset of degradation, the system performs a Sequential Probability Ratio Test (SPRT) on the first-difference function. The system then determines whether the SPRT generates an alarm. In one embodiment, the SPRT can include one or more of: a positive variance first-difference test, which generates an alarm if the first-difference function for the variance of the time series for the monitored telemetry variable is increasing; and a negative variance first-difference test, which generates an alarm if the first-difference function for the variance of the time series for the monitored telemetry variable is decreasing. In one embodiment, while performing the remedial action the system performs one or more of the following actions: recording a time when the onset of degradation occurred; notifying a system administrator that the computer system is at the onset of degradation; shutting down the computer system; backing up data stored on the computer system; failing-over to a redundant computer system; replacing one or more components which are at the onset of degradation; and performing other remedial actions. The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. The data structures and code described in this detailed description are typically stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. This includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing computer readable media now known or later developed. Overview One embodiment of the present invention detects precursor failure mechanisms that do not show up as anomalies in the mean value or in the correlation patterns for telemetry variables. More specifically, one embodiment of the present invention detects failure mechanisms that appear as changes in the variance (including the degree of spikiness or burstiness) of monitored telemetry variables. One embodiment of the present invention proactively detects and monitors the evolution of computer system failure mechanisms through a binary-hypothesis test that continuously monitors the digitized rate-of-change of the variance for monitored telemetry variables. In doing so, the present invention can detect anomalies that show up as a change-in-gain, change-in-variance, or change-in-spikiness/burstiness, without a change-in-mean value. One embodiment of the present invention detects increases in the variance of a monitored telemetry variable and quantifies the rate of increase in the variance. Another embodiment of the present invention detects decreases in the variance of a monitored telemetry variable and quantifies the rate of decrease in the variance. Note that decreases in variance include the case where physical transducers degrade with what are known as “stuck-at” failures. Note that for the sake of clarity, the present invention is described in terms of “telemetry variables,” which can generally include, but are not limited to, sensor signals generated by physical sensors or software sensors, instrumentation signals, inferential variables which are inferred from sensor signals or inferred from other variables or signals, and any other variable or signal that can be used to determine the health of a computer system or a component. Computer System FIG. 3 presents a block diagram illustrating a computer system 300 in accordance with an embodiment of the present invention. Computer system 300 includes processor 301, memory 302, storage device 303, and real-time telemetry system 304. Processor 301 can generally include any type of processor, including, but not limited to, a microprocessor, a mainframe computer, a digital signal processor, a personal organizer, a device controller and a computational engine within an appliance. Memory 302 can include any type of memory, including but not limited to, dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, read only memory (ROM), and any other type of memory now known or later developed. Storage device 303 can include any type of non-volatile storage device that can be coupled to a computer system. This includes, but is not limited to, magnetic, optical, and magneto-optical storage devices, as well as storage devices based on flash memory and/or battery-backed up memory. In one embodiment of the present invention, real-time telemetry system 304 is separate from computer system 300. Note that real-time telemetry system 304 is described in more detail below with reference to FIG. 4. Real-Time Telemetry System FIG. 4 illustrates real-time telemetry system 304 in accordance with an embodiment of the present invention. Referring to FIG. 4, computer system 300 can generally include any computational device including a mechanism for servicing requests from a client for computational and/or data storage resources. In one embodiment, computer system 300 is a high-end uniprocessor or multiprocessor server that is being monitored by real-time telemetry system 304. Real-time telemetry system 304 includes telemetry device 400, analytical re-sampling program 401, sensitivity analysis tool 402, and SPRT module 403. Telemetry device 400 gathers information from the various sensors and monitoring tools within computer system 300. In one embodiment, telemetry device 400 directs the signals to a remote location that contains analytical re-sampling program 401, sensitivity analysis tool 402, and SPRT module 403. In another embodiment of the present invention, one or more of analytical re-sampling program 401, sensitivity analysis tool 402, and SPRT module 403 are located within computer system 300. Analytical re-sampling program 401 ensures that the monitored telemetry variables have a uniform sampling rate. In doing so, analytical re-sampling program 401 uses interpolation techniques, if necessary, to fill in missing data points, or to equalize the sampling intervals when the raw data is non-uniformly sampled. After the telemetry variables pass through analytical re-sampling program 401, they are aligned and correlated by sensitivity analysis tool 402. For example, in one embodiment of the present invention sensitivity analysis tool 402 incorporates a novel moving window technique that “slides” through the telemetry variables with systematically varying window widths. The system systematically varies the alignment between sliding windows for different telemetry variables to optimize the degree of association between the telemetry variables, as quantified by an “F-statistic,” which is computed and ranked for all telemetry variable windows by sensitivity analysis tool 402. While statistically comparing the quality of two fits, F-statistics reveal the measure of regression. The higher the value of the F-statistic, the better the correlation is between two telemetry variables. The lead/lag value for the sliding window that results in the F-statistic with the highest value is chosen, and the candidate telemetry variable is aligned to maximize this value. This process is repeated for each telemetry variable by sensitivity analysis tool 402. Telemetry variables that have an F-statistic very close to 1 are “completely correlated” and can be discarded. This can result when two telemetry variables are measuring the same metric, but are expressing them in different engineering units. For example, a telemetry variable can convey a temperature in degrees Fahrenheit, while a second telemetry variable conveys the same temperature in degrees Centigrade. Since these two telemetry variables are perfectly correlated, one does not contain any additional information over the other, and therefore, one may be discarded. Some telemetry variables may exhibit little correlation, or no correlation whatsoever. In this case, these telemetry variables may be dropped because they add little predictive information. Once a highly correlated subset of the telemetry variables has been determined, they are combined into one group or cluster for processing by the SPRT module 403. One embodiment of the present invention continuously monitors a variety of telemetry variables (e.g., sensor signals) in real time during operation of the server. (Note that although we refer to a single computer system in this disclosure, the present invention can also apply to a collection of computer systems). These telemetry variables can also include signals associated with internal performance parameters maintained by software within the computer system. For example, these internal performance parameters can include, but are not limited to, system throughput, transaction latencies, queue lengths, central processing unit (CPU) utilization, load on CPU, idle time, memory utilization, load on the memory, load on the cache, I/O traffic, bus saturation metrics, FIFO overflow statistics, and various operational profiles gathered through “virtual sensors” located within the operating system. These telemetry variables can also include signals associated with canary performance parameters for synthetic user transactions, which are periodically generated for the purpose of measuring quality of service from the end user's perspective. These telemetry variables can additionally include hardware variables, including, but not limited to, internal temperatures, voltages, currents, and fan speeds. Furthermore, these telemetry variables can include disk-related metrics for a remote storage device, including, but not limited to, average service time, average response time, number of kilobytes (kB) read per second, number of kB written per second, number of read requests per second, number of write requests per second, and number of soft errors per second. In one embodiment of the present invention, the foregoing telemetry variables are monitored continuously with one or more SPRT tests. In one embodiment of the present invention, the components from which the telemetry variables originate are field replaceable units (FRUs), which can be independently monitored. Note that all major system components, including both hardware and software components, can be decomposed into FRUs. (For example, a software FRU can include: an operating system, a middleware component, a database, or an application.) Also note that the present invention is not meant to be limited to server computer systems. In general, the present invention can be applied to any type of computer system. This includes, but is not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a personal organizer, a device controller, and a computational engine within an appliance. Detecting Changes in Variance One embodiment of the present invention computes the first-difference function of the variance estimates for digitized time-series telemetry variables under surveillance. In one embodiment of the present invention, the time-series signals are “residuals” formed by subtracting the mean value of a monitored telemetry variable from the value of the monitored telemetry variable. Note that the first-difference function of the variance is a numerical approximation of the derivative of the sequence of variance estimates. In one embodiment of the present invention, a sequential probability ratio test (SPRT) is used to monitor first-difference function of the variance of a telemetry variable. In one embodiment, the SPRT generates a warning flag if the variance of the telemetry variable is increasing (positive variance first-difference function SPRT). In another embodiment, the SPRT generates a warning flag if the variance of the telemetry variable is decreasing (negative variance first-difference function SPRT). Note that more than one SPRT test can be used at the same time. A comparison of SPRT alarms issuing from a positive variance-derivative SPRT and/or a negative variance first-difference function SPRT provides a wealth of diagnostic information on a class of failure modes known collectively as a “change-in-gain without a change-in-mean”. For example, if the positive variance-derivative SPRT triggers warning flags, it is an indication that there has been a sudden increase in the variance (or degree of spikiness or burstiness) of the process. If this SPRT subsequently ceases triggering warning flags, it is an indication that the degradation mode responsible for the increased noisiness has gone to completion. Such information can be beneficial in root causing the origin of the degradation and helping to eliminate the degradation mechanism from future product designs. Similarly, if the negative variance first-difference function SPRT starts triggering alarms, there is a decrease in variance for the process. If the negative variance first-difference function SPRT ceases issuing warning flags, it is an indication that the degradation mode has gone to completion. In safety critical processes, this failure mode (decreasing variance without a change in mean) is dangerous in conventional systems that are monitored only by threshold limit tests. The reason it is dangerous is that a shrinking variance, when it occurs as a result of a transducer that is losing its ability to respond, never trips a threshold limit. (Whereas degradation that manifests as a linear decalibration bias, or even an increasing variance, will eventually trip a high or low threshold limit and sound a warning). A sustained shrinking variance, which can occur, for example, when oil-filled pressure transmitters leak their oil, or electrolytic capacitors leak their electrolyte, never trips a threshold, but can be detected by the positive and negative variance first-difference function SPRT tests. FIG. 5 presents a flow chart illustrating the process of using the first-difference function for the variance of telemetry variables to monitor the health of a computer system in accordance with an embodiment of the present invention. The process begins when the system monitors telemetry variables (step 500). In one embodiment of the present invention, the telemetry variable is a variance function of the monitored telemetry variable. In another embodiment of the present invention, the system receives a time series for the monitored telemetry variable and calculates a variance function of the time series for the monitored telemetry variable. Next, the system calculates a running average for each monitored telemetry variable (step 501). The system then calculates residuals for the telemetry variables (step 502) to produce residuals 503. In one embodiment of the present invention, the system calculates residuals for the telemetry variables by subtracting the running average for each monitored telemetry variable from the corresponding monitored telemetry variable. Next, the system calculates the first-difference function for the residuals of the variance for the monitored telemetry variables (step 504). In one embodiment of the of the present invention, for each time point within the time series for the telemetry variable, the system calculates the first-difference function by subtracting a value of the time series at a previous time point from the value of the time series at a present time point. In one embodiment of the present invention, the system divides the result of the subtraction by the value of a length of a time interval between the previous time point and the present time point. The system then performs a Sequential Probability Ratio Test (SPRT) on the first-difference functions (step 505). Note that the system also receives alpha and beta values 506 for the SPRT. (SPRTs are described in more detail below.) If an alarm is generated by the SPRTs (step 507, yes), the system records the time of failure (step 508), and continues monitoring the telemetry variables (step 509). If no alarm is generated by the SPRTs (step 507, no), the system continues monitoring the telemetry variables (step 509). In one embodiment of the present invention, a remedial action is also performed in step 508. In one embodiment of the present invention, the remedial action can involve performing one or more of: recording a time when the onset of degradation occurred; notifying a system administrator that the computer system is at the onset of degradation; shutting down the computer system; backing up data stored on the computer system; failing-over to a redundant computer system; replacing one or more components which are at the onset of degradation; and other remedial actions. Accelerated-Life Studies For devices undergoing accelerated-life studies, it is often desirable to supply power to the devices under test while they are in the stress-test chambers. Even though it may not be possible to apply the full pass/fail functional testing to the devices inside the stress-test chamber, a change in the electrical behavior of the device can be detected by monitoring the signatures of the electrical current being applied to the devices. Note that subtle anomalies in the noise-signature time-series of the current for the device appear when the device degrades and/or fails. Also note that the current to the device can provide an indirect measure of the health of a device. More specifically, the current-noise time series can be used as an “inferential variable” for high-resolution annunciation of the onset of degradation and, in many cases, the exact point of failure in time in the components undergoing accelerated-life studies. FIG. 6 illustrates an in-situ reliability stress-test chamber 600 in accordance with an embodiment of the present invention. A component under test 601, which can be any type of device from a computer system, is placed inside stress-test chamber 600. Note that component under test 601 can include, but is not limited to: power supplies, capacitors, sockets, integrated circuit chips, hard drives, and transceivers. Stress control module 602 applies and controls one or more stress variables to the stress-test chamber 600. These stress variables can include, but are not limited to: temperature, humidity, vibration, voltage, chemical/environmental, and radiation. In one embodiment of the present invention, stress control module 602 applies sufficient stress factors to stress-test chamber 600 to create accelerated-life studies for the component under test 601. The same setup can also be applied to early failure rate studies of a component, burn-in screens of a component and repair-center reliability evaluations of a returned component. As is shown in FIG. 6, stress-test chamber 600 can contain multiple units (specimens) of component under test 601, wherein an array of nine specimens 603 of component under test 601 are shown. Stress-test chamber 600 provides a supply of power to each specimen of component under test 601, and obtains telemetry variable outputs (e.g., inferential variables) from each specimen. The telemetry variable outputs are coupled to a fault-monitoring module 604. In one embodiment of the present invention, fault-monitoring module 604 is a Continuous System Telemetry Harness (CSTH). Note that the output data series can be either processed in real-time or post-processed. In one embodiment of the present invention, fault-monitoring module 604 analyzes the output data series in real-time while the telemetry variables are being collected from all of the specimens 603 of component under test 601, and predicts the likelihood of failure for each of specimens 603. In another embodiment of the present invention, fault-monitoring module 604 post-processes the output data series at a later time and detects whether failures have occurred at an earlier time, and if so, determines the time of failures. Note that the output data series can include but is not limited to: a time-series, a number of cycles, and a number of incidents. Furthermore, note that the telemetry variable from each specimen of the component can include current, voltage, resistance, temperature, and other physical variables. Also, note that all of the specimens 603 in stress-test chamber 600 can be tested at the same time and under the same conditions. Moreover, instead of testing multiple individual components, the stress-test chamber can be configured to test a single component. One embodiment of the present invention uses an ultra-sensitive sequential detection technique called the Sequential Probability Ratio Test (SPRT) for telemetry variable surveillance to accurately identify the onset of component degradation and/or failure. Moreover, a tandem SPRT can be run on the derivative of the telemetry variable's time series to accurately assess the time of complete of failure. The combination of tandem SPRTs that monitor the telemetry variables provides a robust surveillance scheme which has the capability to: 1. detect the onset of degradation in any individual component under stress, even when the overall functionality of that component cannot be measured directly; and to 2. detect the time of complete failure for any component under stress. In one embodiment of the present invention, information from the tandem SPRT analyses is combined with discrete-time ex-situ pass/fail testing to construct a detailed population failure distribution. One embodiment of the present invention lessens the constraints on the tradeoff between the number of units under test and the duration of the experiments, while yielding much higher resolution information on the dynamic evolution of the health of the components as a function of age and cumulative stress. This higher resolution facilitates higher confidence in selecting a mathematical model that accurately predicts the long-term reliability of the component for a time point beyond the number of hours the component was actually tested. Also note that the present invention minimizes expensive ex-situ functional evaluations. FIG. 7 presents a flow chart illustrating the process of using the first-difference function for the variance of telemetry variables to detect the onset of degradation in components during reliability-evaluation studies in accordance with an embodiment of the present invention. The process begins when the system monitors telemetry variables (step 700). In one embodiment of the present invention, the telemetry variable is a variance function of the monitored telemetry variable. In another embodiment of the present invention, the system receives a time series for the monitored telemetry variable and calculates a variance function of the time series for the monitored telemetry variable. Note that FIG. 5 and FIG. 7 are different. FIG. 5 illustrates the process of monitoring a number of distinct telemetry variables for a single computer system or a single component. In contrast, FIG. 7 illustrates the process of monitoring a single telemetry variable from a number of specimens of a component. In one embodiment of the present invention, the process illustrated in FIG. 7 can be performed on one or more telemetry variables across a number of specimens of a component. Next, the system calculates a running average across all monitored telemetry variables (step 701). The system then calculates residuals for the telemetry variables (step 702) to produce residuals 703. In one embodiment of the present invention, the system calculates residuals for the telemetry variables by subtracting the running average for all monitored telemetry variable from each monitored telemetry variable. Next, the system calculates the first-difference function for the residuals of the variance for the monitored telemetry variables (step 704). In one embodiment of the of the present invention, for each time point within the time series for the telemetry variable, the system calculates the first-difference function by subtracting a value of the time series at a previous time point from the value of the time series at a present time point. In one embodiment of the present invention, the system divides the result of the subtraction by the value of a length of a time interval between the previous time point and the present time point. The system then performs a Sequential Probability Ratio Test (SPRT) on the first-difference functions (step 705). Note that the system receives alpha and beta values 706 for the SPRT. Note that SPRTs are described in more detail below. If an alarm is generated by the SPRTs (step 707, yes), the system records the time of failure (step 708). The system then determines whether the reliability-evaluation study should be altered (step 710). If so, the system stops and alters the reliability-evaluation study (step 711). The system then continues monitoring the telemetry variables (step 709). If the system determines that the reliability-evaluation study should not be altered, the system continues monitoring the telemetry variables (step 709). If no alarm is generated by the SPRTs (step 707, no), the system continues monitoring the telemetry variables (step 709). SPRT (Sequential Probability Ratio Test) The Sequential Probability Ratio Test is a statistical hypothesis test that differs from standard fixed sample tests. In fixed-sample statistical tests, a given number of observations are used to select one hypothesis from one or more alternative hypotheses. The SPRT, however, examines one observation at a time, and then makes a decision as soon as it has sufficient information to ensure that pre-specified confidence bounds are met. The basic approach taken by the SPRT technique is to analyze successive observations of a discrete process. Let yn represent a sample from the process at a given moment tn in time. In one embodiment of the present invention, the sequence of values {Yn}=y0, y1, . . . , yn comes from a stationary process characterized by a Gaussian, white-noise probability density function (PDF) with mean 0. (Note that since with the sequence is from a nominally stationary processes, any process variables with a nonzero mean can be first normalized to a mean of zero with no loss of generality). The SPRT is a binary hypothesis test that analyzes process observations sequentially to determine whether or not the telemetry variable is consistent with normal behavior. When a SPRT reaches a decision about current process behavior (i.e., the telemetry variable is behaving normally or abnormally), the system reports the decision and continues to process observations. For each of the eight types of tandem SPRT tests described below, the telemetry variable data adheres to a Gaussian PDF with mean 0 and variance σ2 for normal signal behavior, referred to as the null hypothesis, H0. The system computes eight specific SPRT hypothesis tests in parallel for each telemetry variable monitored. One embodiment of the present invention applies a SPRT to an electrical current time-series. Other embodiments of the present invention apply a SPRT to other telemetry variables, including voltage, internal temperature, or stress variables. The SPRT surveillance module executes all 8 tandem hypothesis tests in parallel. Each test determines whether the current sequence of process observations is consistent with the null hypothesis versus an alternative hypothesis. The first four tests are: (SPRT 1) the positive-mean test, (SPRT 2) the negative-mean test, (SPRT 3) the nominal-variance test, and (SPRT 4) the inverse-variance test. For the positive-mean test, the telemetry variable data for the corresponding alternative hypothesis, H1, adheres to a Gaussian PDF with mean +M and variance σ2. For the negative-mean test, the telemetry variable data for the corresponding alternative hypothesis, H2, adheres to a Gaussian PDF with mean −M and variance σ2, For the nominal-variance test, the telemetry variable data for the corresponding alternative hypothesis, H3, adheres to a Gaussian PDF with mean 0 and variance Vσ2 (with scalar factor V). For the inverse-variance test, the telemetry variable data for the corresponding alternative hypothesis, H4, adheres to a Gaussian PDF with mean 0 and variance σ2/V. The next two tandem SPRT tests are performed not on the raw telemetry variables as above, but on the first difference function of the telemetry variable. For discrete time series, the first-difference function (i.e., difference between each observation and the observation preceding it) gives an estimate of the numerical derivative of the time series. During uninteresting time periods, the observations in the first-difference function are a nominally stationary random process centered about zero. If an upward or downward trend suddenly appears in the telemetry variable, SPRTs number 5 and 6 observe an increase or decrease, respectively, in the slope of the telemetry variable. For example, if there is a decrease in the value of the telemetry variable, SPRT alarms are triggered for SPRTs 2 and 6. SPRT 2 generates a warning because the sequence of raw observations drops with time. And SPRT 6 generates a warning because the slope of the telemetry variable changes from zero to something less than zero. The advantage of monitoring the mean SPRT and slope SPRT in tandem is that the system correlates the SPRT readings from the eight tests and determines if the component has failed. For example, if the telemetry variable levels off to a new stationary value (or plateau), the alarms from SPRT 6 cease because the slope returns to zero when the raw telemetry variable reaches a plateau. However, SPRT 2 will continue generating a warning because the new mean value of the telemetry variable is different from the value prior to the degradation. Therefore, the system correctly identifies that the component has failed. If SPRTs 3 or 4 generates a warning, the variance of the telemetry variable is either increasing or decreasing, respectively. An increasing variance that is not accompanied by a change in mean (inferred from SPRTs 1 and 2 and SPRTs 5 and 6) signifies an episodic event that is “bursty” or “spiky” with time. A decreasing variance that is not accompanied by a change in mean is a common symptom of a failing component that is characterized by an increasing time constant. Therefore, having variance SPRTs available in parallel with slope and mean SPRTs provides a wealth of supplementary diagnostic information. The final two tandem SPRT tests, SPRT 7 and SPRT 8, are performed on the first-difference function of the variance estimates for the telemetry variable. The first-difference function of the variance estimates is a numerical approximation of the derivative of the sequence of variance estimates. As such, SPRT 7 triggers a warning flag if the variance of the telemetry variable is increasing, while SPRT 8 triggers a warning flag if the variance of the telemetry variable is decreasing. A comparison of SPRT alarms from SPRTs 3, 4, 7, and 8, gives a great deal of diagnostic information on a class of failure modes known collectively as a “change-in-gain without a change-in-mean.” For example, if SPRTs 3 and 7 both trigger warning flags, it is an indication that there has been a sudden increase in the variance of the process. If SPRT 3 continues to trigger warning flags but SPRT 7 ceases issuing warning flags, it is an indication that the degradation mode responsible for the increased noisiness has gone to completion. Such information can be beneficial in root causing the origin of the degradation and eliminating it from future product designs. Similarly, if SPRTs 4 and 8 both start triggering alarms, there is a decrease in variance for the process. If SPRT 4 continues to issue warning flags but SPRT 8 ceases issuing warning flags, it is an indication that the degradation mode has gone to completion. In safety-critical processes, this failure mode (decreasing variance without a change in mean) is dangerous in conventional systems that are monitored only by threshold limit tests. The reason it is dangerous is that a shrinking variance, when it occurs as a result of a transducer that is losing its ability to respond, never trips a threshold limit. (In contrast degradation that manifests as a linear decalibration bias, or even an increasing variance, eventually trips a high or low threshold limit and sounds a warning). A sustained decreasing variance, which happens, for example, when oil-filled pressure transmitters leak their oil, or electrolytic capacitors leak their electrolyte, never trips a threshold in conventional systems, but will be readily detected by the suite of 8 tandem SPRT tests taught in this invention. The SPRT technique provides a quantitative framework that permits a decision to be made between the null hypothesis and the eight alternative hypotheses with specified misidentification probabilities. If the SPRT accepts one of the alternative hypotheses, an alarm flag is set and data is transmitted. The SPRT operates as follows. At each time step in a calculation, the system calculates a test index and compares it to two stopping boundaries A and B (defined below). The test index is equal to the natural log of a likelihood ratio (Ln), which for a given SPRT is the ratio of the probability that the alternative hypothesis for the test (Hj, where j is the appropriate subscript for the SPRT in question) is true, to the probability that the null hypothesis (H0) is true. L n = probability of observed sequence { Y n } given H j is true probability of observed sequence { Y n } given H 0 is true ( 1 ) If the logarithm of the likelihood ratio is greater than or equal to the logarithm of the upper threshold limit [i.e., ln(Ln)>ln(B)], then the alternative hypothesis is true. If the logarithm of the likelihood ratio is less than or equal to the logarithm of the lower threshold limit [i.e., ln(Ln)<ln(A)], then the null hypothesis is true. If the log likelihood ratio falls between the two limits, [i.e., ln(A)<ln(Ln)<ln(B)], then there is not enough information to make a decision (and, incidentally, no other statistical test could yet reach a decision with the same given Type I and II misidentification probabilities). Equation (2) relates the threshold limits to the misidentification probabilities α and β: A = β 1 - α , B = 1 - β α ( 2 ) where α is the probability of accepting Hj when H0 is true (i.e., the false-alarm probability), and β is the probability of accepting H0 when Hj is true (i.e., the missed-alarm probability). The first two SPRT tests for normal distributions examine the mean of the process observations. If the distribution of observations exhibits a non-zero mean (e.g., a mean of either +M or −M, where M is the pre-assigned system disturbance magnitude for the mean test), the mean tests determine that the system is degraded. Assuming that the sequence {Yn} adheres to a Gaussian PDF, then the probability that the null hypothesis H0 is true (i.e., mean 0 and variance σ2) is: P ( y 1 , y 2 , … , y n ❘ H 0 ) = 1 ( 2 πσ 2 ) n / 2 exp [ - 1 2 σ 2 ∑ k - 1 n y k 2 ] ( 3 ) Similarly, the probability for alternative hypothesis H1 is true (i.e., mean M and variance σ2) is: P ( y 1 , y 2 , … , y n ❘ H 1 ) = 1 ( 2 πσ 2 ) n / 2 exp [ - 1 2 σ 2 ( ∑ k - 1 n y k 2 - 2 ∑ k - 1 n y k M + ∑ k - 1 n M 2 ) ] ( 4 ) The ratio of the probabilities in (3) and (4) gives the likelihood ratio Ln for the positive-mean test: L n = exp [ - 1 2 σ 2 ∑ k - 1 n M ( M - 2 y k ) ] ( 5 ) Taking the logarithm of likelihood ratio given by (5) produces the SPRT index for the positive-mean test (SPRTpos): SPRT pos = - 1 2 σ 2 ∑ k - 1 n M ( M - 2 y k ) = M σ 2 ∑ k - 1 n ( y k - M 2 ) ( 6 ) The SPRT index for the negative-mean test (SPRTneg) is derived by substituting −M for each instance of M in (4) through (6) above, resulting in: SPRT neg = M σ 2 ∑ k - 1 n ( - y k - M 2 ) ( 7 ) The next two SPRT tests examine the variance of the sequence. This capability gives the SPRT module the ability to detect and quantitatively characterize changes in variability for processes, which is vitally important for 6-sigma QA/QC improvement initiatives. In the variance tests, the system is degraded if the sequence exhibits a change in variance by a factor of V or 1/V, where V, the pre-assigned system disturbance magnitude for the variance test, is a positive scalar. The probability that the alternative hypothesis H3 is true (i.e., mean 0 and variance Vσ2) is given by (3) with σ2 replaced by Vσ2: P ( y 1 , y 2 , … , y n ❘ H 0 ) = 1 ( 2 π V σ ) n / 2 exp [ - 1 2 V σ 2 ∑ k - 1 n y k 2 ] ( 8 ) The likelihood ratio for the variance test is given by the ratio of (8) to (3): L n = V - n / 2 exp [ - 1 2 σ 2 1 - V V ∑ k - 1 n y k 2 ] ( 9 ) Taking the logarithm of the likelihood ratio given in (9) produces the SPRT index for the nominal-variance test (SPRTnom): SPRT nom = 1 2 σ 2 ( V - 1 V ) ∑ k - 1 n y k 2 - n 2 ln V ( 10 ) The SPRT index for the inverse-variance test (SPRTinv) is derived by substituting 1/V for each instance of Vin (8) through (10), resulting in: SPRT inv = 1 2 σ 2 ( 1 - V ) ∑ k - 1 n y k 2 + n 2 ln V ( 11 ) The tandem SPRT module performs mean, variance, and SPRT tests on the raw process telemetry variable and on its first difference function. To initialize the module for analysis of a telemetry variable time-series, the user specifies the system disturbance magnitudes for the tests (M and V), the false-alarm probability (α), and the missed-alarm probability (β). Then, during the training phase (before the first failure of a component under test), the module calculates the mean and variance of the monitored variable process signal. For most telemetry variables the mean of the raw observations for the telemetry variable will be nonzero; in this case the mean calculated from the training phase is used to normalize the telemetry variable during the monitoring phase. The system disturbance magnitude for the mean tests specifies the number of standard deviations (or fractions thereof) that the distribution must shift in the positive or negative direction to trigger an alarm. The system disturbance magnitude for the variance tests specifies the fractional change of the variance necessary to trigger an alarm. At the beginning of the monitoring phase, the system sets all eight SPRT indices to 0. Then, during each time step of the calculation, the system updates the SPRT indices using (6), (7), (10), and (11). The system compares each SPRT index is then compared to the upper [i.e., ln((1−β)/α] and lower [i.e., ln((β/(1−α))] decision boundaries, with these three possible outcomes: 1. the lower limit is reached, in which case the process is declared healthy, the test statistic is reset to zero, and sampling continues; 2. the upper limit is reached, in which case the process is declared degraded, an alarm flag is raised indicating a sensor or process fault, the test statistic is reset to zero, and sampling continues; or 3. neither limit has been reached, in which case no decision concerning the process can yet be made, and the sampling continues. The advantages of using a SPRT are twofold: 1. early detection of very subtle anomalies in noisy process variables; and 2. pre-specification of quantitative false-alarm and missed-alarm probabilities. The foregoing descriptions of embodiments of the present invention have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims. |
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claims | 1. A mirror, having an optical effective surface and comprising:a mirror substrate;a reflection layer stack that reflects electromagnetic radiation incident on the optical effective surface;at least one piezoelectric layer arranged between the mirror substrate and the reflection layer stack;a first electrode arrangement situated on a side of the piezoelectric layer facing the reflection layer stack, and a second electrode arrangement situated on a side of the piezoelectric layer facing the mirror substrate, wherein the first electrode arrangement and the second electrode arrangement are arranged to apply an electric field to the piezoelectric layer that produces a locally variable deformation in the piezoelectric layer;wherein the first electrode arrangement and the second electrode arrangement each respectively has a plurality of electrodes, and wherein each of the electrodes has a respective lead configured to apply an electrical voltage relative to a respective other of the electrode arrangements; anda first mediator layer assigned to the first electrode arrangement and a second mediator layer assigned to the second electrode arrangement, wherein each of the mediator layers is arranged to set a respective continuous electrical potential profile along the respective electrode arrangement; andwherein the first and the second mediator layers differ from one another in average electrical resistance by a factor of at least 1.5. 2. The mirror as claimed in claim 1, wherein the mediator layers differ from one another in the average electrical resistance by a factor of at least 3. 3. The mirror as claimed in claim 1, wherein the mediator layers differ from one another in average thickness. 4. The mirror as claimed in claim 1, the mediator layers differ in stoichiometry from one another. 5. The mirror as claimed in claim 1, wherein at least one of the mediator layers comprises titanium dioxide (TiO2), LaCoO3, LaMnO3, LaCaMnO3 or LaNiO3. 6. A mirror, having an optical effective surface and comprisinga mirror substrate;a reflection layer stack that reflects electromagnetic radiation incident on the optical effective surface;at least one piezoelectric layer, arranged between the mirror substrate and the reflection layer stacka first electrode arrangement situated on a side of the piezoelectric layer facing the reflection layer stack, and a second electrode arrangement situated on a side of the piezoelectric layer facing the mirror substrate, wherein the first electrode arrangement and the second electrode arrangement are arranged to apply an electric field to the piezoelectric layer that produces a locally variable deformation in the piezoelectric layer; andat least one mediator layer assigned to at least one of the electrode arrangements and having a controllable electrical conductivity for setting a temporally variable continuous electrical potential profile along the at least one electrode arrangement. 7. The mirror as claimed in claim 6, further comprising at least one control electrode arranged to control the electrical conductivity of the mediator layer. 8. The mirror as claimed in claim 6, further comprising a plurality of mutually independently operable control electrodes arranged to control the electrical conductivity of the mediator layer. 9. The mirror as claimed in claim 1, configured for an operating wavelength of less than 30 nm. 10. The mirror as claimed in claim 1, configured for a microlithographic projection exposure apparatus. 11. An optical system configured as an illumination device or a projection lens of a microlithographic projection exposure apparatus, comprising a mirror as claimed in claim 1. 12. An optical system, comprising at least two mirrors,wherein each of the mirrors has a respective optical effective surface, a respective mirror substrate and a respective reflection layer stack that reflects electromagnetic radiation incident on the respective optical effective surface;wherein each of the mirrors has a respective piezoelectric layer arranged in each case between the respective mirror substrate and the respective reflection layer stackwherein each of the mirrors has a respective first electrode arrangement situated on a side of the respective piezoelectric layer facing the respective reflection layer stack, and a respective second electrode arrangement situated on a side of the respective piezoelectric layer facing the respective mirror substrate;wherein each of the mirrors has at least one respective mediator layer arranged to set a respective continuous electrical potential profile; andwherein each of the respective mediator layers has a respective average electrical resistance, such that the respective average electrical resistances differ from one another by a factor of at least 1.5. 13. The optical system as claimed in claim 12 and configured as an illumination device or as a projection lens of a microlithographic projection exposure apparatus. 14. The optical system as claimed in claim 12, wherein the mediator layers differ from one another such that the respective average electrical resistances differ by a factor of at least 5. 15. A microlithographic projection exposure apparatus comprising an illumination device and a projection lens, wherein at least one of the illumination device and the projection lens comprises an optical system as claimed in claim 12. |
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042319765 | abstract | Ceramic plutonium-uranium fuels are made by sintering wet-chemical microspheres of plutonium-uranium solid-solution oxides, carbides, nitrides, or the like, or by sintering separate plutonium- and uranium-compound microspheres mixed together, the uranium compound alternatively being in a fine-grained to pulverulent form. |
claims | 1. A detector system for x-ray imaging, said detector system comprising:a detector having a plurality of adjacent edge-on detector modules, wherein:each of said edge-on detector modules comprises a first edge that is adapted to be oriented towards an x-ray source and a front-side running essentially parallel to the direction of incoming x-rays, said front-side comprising at least one charge collecting electrode and routing traces connecting the at least one charge collecting electrode with front-end electronics; andat least a subset of said plurality of adjacent edge-on detector modules being pairwise arranged, front-side to front-side, whereby a front-side to front-side gap is defined between the front-sides of said pairwise arranged edge-on detector modules; and whereineach said pairwise arranged edge-on detector modules include an anti-scatter collimator arranged in the x-ray path between said x-ray source and said edge-on detector modules and overlapping said front-side to front-side gap, said anti-scatter collimator being arranged to protect the front-side surface of both detector modules in each said pairwise arranged edge-on detector module from damaging x-rays, andeach pair of said pairwise arranged edge-on detector modules further include an anti-scatter foil located in said front-side to front-side gap between the front-sides of said pairwise arranged edge-on detector modules. 2. The detector system according to claim 1, wherein said anti-scatter collimator comprises a collimator of a high Z material. 3. The detector system according to claim 2, wherein said front-side to front-side gap comprises an anti-scatter foil. 4. The detector system according to claim 2, wherein said anti-scatter foil comprises a high Z anti-scatter foil. 5. The detector system according to claim 2, wherein the backside of at least one edge-on detector module of said pairwise arranged edge-on detector modules is arranged to face the backside of a corresponding edge-on detector module in such a way that a back-side to back-side gap is formed between said edge-on detector module and said corresponding edge-on detector module. 6. The detector system according to claim 1, wherein said anti-scatter foil is attached to the front-side surfaces of both edge-on detector modules of each pair of said pairwise arranged edge-on detector modules. 7. The detector system according to claim 6, wherein said anti-scatter foil comprises a high Z anti-scatter foil. 8. The detector system according to claim 1, wherein said anti-scatter foil comprises a high Z anti-scatter foil. 9. The detector system according to claim 1, wherein the front side volume protected by said anti-scatter collimator exceeds 1% of the total detector volume. 10. The detector system according to claim 1, wherein the backside of at least one edge-on detector module of said pairwise arranged edge-on detector modules is arranged to face the backside of a corresponding edge-on detector module in such a way that a back-side to back-side gap is formed between said edge-on detector module and said corresponding edge-on detector module. 11. The detector system according to claim 10, wherein said back-side to back-side gap comprises an attenuating material. 12. The detector system according to claim 11, wherein said attenuating material comprises a material having similar attenuation characteristics as the semi-conducting material used for the detector modules. 13. The detector system according to claim 1, wherein said edge-on detector modules comprises edge-on detector modules of a semi-conducting material. 14. The detector system according to claim 13, wherein said semi-conducting material comprises silicon. 15. The detector system according to claim 14, wherein said attenuating material comprises silicone. 16. The detector system according to claim 1, wherein the detector system is arranged to provide improved charge collection. 17. The detector system according to claim 1, wherein,each said anti-scatter collimator has a front face portion arranged facing the directly incoming x-rays and a rear face portion facing front sides of the pairwise arranged edge-on detector modules and the said front-side to front-side gap therebetween,a width of the rear face portion being greater than a width of said front-side to front-side gap adjacent said rear face portion, the rear face portion covering both said front-side to front-side gap and a portion of front sides of each of the pairwise arranged edge-on detector modules, the rear face portion thereby covering and protecting the front side volume of the pairwise arranged edge-on detector modules against the directly incoming x-rays. |
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046831100 | claims | 1. An apparatus for consolidating spent fuel rods from spent fuel assemblies, comprising: a container having a front wall, a back wall, side walls connected between the front and back walls, a bottom, and a plurality of stationary flutes along the front wall, the plurality of stationary flutes defining a plurality of channels along the front wall, each channel being sized to accept a fuel rod, the flutes and the channels being stationary; a plurality of springs, the springs being aligned with and bearing against the flutes and the channels when no fuel rods have been inserted into the container and the springs are located proximate the front wall, each spring being capable of maintaining a fuel rod in a preselected location in the container; support means located within the container for supporting the springs, the support means being movable within the container in a substantially horizontal direction between the front and back walls of the container; and positioning means for positioning the support means between the front and back walls of the container, the positioning means permitting the support means to take nondiscrete positions between the front and back walls. installing a first row of fuel rods in the first row of locations, the springs bearing against the first row of fuel rods and the flutes, the springs maintaining the first row of fuel rods in position after the first row of fuel rods has been installed, the first row of fuel rods and the flutes defining a second row of locations; installing a second row of fuel rods in the second row of locations, the springs bearing against the first row of fuel rods and the second row of fuel rods, the springs maintaining the first and second rows of fuel rods in position after the second row of fuel rods has been installed, the first and second rows of fuel rods defining a third row of locations, the first row of fuel rods being located between the associated springs and the channels, the second row of fuel rods being located between the associated springs and the flutes, whereby the third row of locations is defined by the first and second rows of fuel rods; and permitting the support means to take nondiscrete positions between the front and back walls of the container. moving the support means toward the back wall after the first row of fuel rods has been installed; and moving the support means toward the back wall after the second row of fuel rods has been installed. 2. An apparatus as defined in claim 1, wherein the springs are arranged in a first row and a second row running between the side walls. 3. An apparatus as defined in claim 1, wherein each of the springs is a resilient finger, each finger extending outwardly from the support means toward the front wall. 4. An apparatus as defined in claim 1, wherein the support means includes a sheet and the springs are mounted on the sheet. 5. An apparatus as defined in claim 1, wherein the support means includes a first plate and a second plate, said springs being mounted on the first and second plates. 6. An apparatus as defined in claim 5, wherein the springs are arranged in a first row and a second row, the first row being mounted on the first plate and the second row being mounted on the second plate. 7. An apparatus as defined in claim 1, wherein said flutes are formed in the front wall. 8. An apparatus as defined in claim 1, wherein said flutes are formed in a sheet and the sheet is positioned adjacent to the front wall. 9. An apparatus as defined in claim 1, wherein the front and side walls each have an angular lip. 10. An apparatus as defined in claim 9, wherein the support means includes a sheet with an angular lip. 11. An apparatus as defined in claim 1, further comprising means for locking the positioning means in a position between the front and back walls. 12. An apparatus as defined in claim 1, wherein the positioning means includes a first plate and a second plate, a plurality of resilient elements being connected between the first plate and the second plate, the first plate abutting the support means, and adjusting means connected to said second plate for adjusting the position of the second plate. 13. An apparatus as defined in claim 12, wherein the adjusting means includes a pantograph. 14. An apparatus as defined in claim 12, wherein the adjusting means includes means for automatically adjusting the position of the second plate in response to a control signal. 15. An apparatus as defined in claim 1, wherein the bottom has a plurality of holes formed therein permitting water to flow through fuel rods inserted in the container. 16. An apparatus as defined in claim 15, wherein the holes are aligned with interstitial channels defined by fuel rods inserted in the container. 17. An apparatus as defined in claim 15, wherein the front, back, and side walls each have a plurality of holes, the holes in the walls being located at a level above the level of an inserted fuel rod. 18. An apparatus as defined in claim 15, further comprising a screen plate with a multiplicity of holes, the screen plate being positioned between the bottom and an inserted fuel rod. 19. An apparatus as defined in claim 1, wherein the positioning means includes a plurality of resilient elements, the resilient elements being positioned between the support means and the back wall, the resilient elements urging the support means toward the front wall. 20. An apparatus as defined in claim 19, wherein each resilient element is a wave-shaped spring. 21. An apparatus as defined in claim 19, wherein each resilient element is a leaf spring. 22. An apparatus as defined in claim 19, wherein each resilient element is a conical coil spring. 23. An apparatus as defined in claim 19, wherein each resilient element is a torsional spring. 24. An apparatus as defined in claim 1, wherein the positioning means includes means for producing a substantially constant force against the support means and for urging the support means toward the front wall. 25. An apparatus as defined in claim 1, further comprising a frame, the frame being capable of holding the container and at least one fuel assembly. 26. An apparatus as defined in claim 1, further comprising a removable cover for the container. 27. An apparatus as defined in claim 26, wherein the cover includes a plurality of holes. 28. A method for packing spent fuel rods in an apparatus including a container having a front wall, a back wall, side walls connected between the front and back walls, the container also having a plurality of stationary flutes positioned adjacent to the front wall, the plurality of flutes defining a plurality of channels, the flutes and channels defining a first row of locations along the front wall, the apparatus also including a plurality of springs and support means for supporting the plurality of springs, the springs being aligned with and bearing against the flutes and the channels when no fuel rods have been inserted into the container and the support means is located proximate the front wall, comprising the steps of: 29. A method as defined in claim 28, further comprising the step of installing a third row of fuel rods in the third row of locations, the springs bearing against the second row of fuel rods and the third row of fuel rods, the springs maintaining the first, second, and third rows of fuel rods in position after the third row of fuel rods has been installed. 30. A method as defined in claim 28, further comprising the steps of: 31. A method as defined in claim 30, wherein the first moving step includes automatically moving the support means toward the back wall after the first row of fuel rods has been installed in response to a first control signal, and wherein the second moving step includes automatically moving the support means toward the back wall after the second row of fuel rods has been installed in response to a second control signal. 32. A method as defined in claim 28, further comprising the step of removing the support means and the springs after a last row of fuel rods has been installed. 33. A method as defined in claim 28, further comprising the step of convectively cooling the fuel rods in the container. 34. A method as defined in claim 28, further comprising the step of locking the support means in a position between the front and back walls. 35. A method as defined in claim 28, wherein, after the first installing step, fuel rods in the first row of fuel rods are in contact with the front wall, and wherein, after the second installing step, fuel rods in the second row of fuel rods are in contact with fuel rods in the first row of fuel rods. 36. A method as defined in claim 28, wherein each installing step includes inserting one fuel rod at a time into the container. 37. A method as defined in claim 30, wherein the first moving step includes manually moving the support means toward the back wall after the first row of fuel rods has been installed and after a first sensory perceptible indication has been received, and wherein the second moving step includes manually moving the support means toward the back wall after the second row of fuel rods has been installed and after a second sensory perceptible indication has been received. 38. A method as defined in claim 28, wherein the first installing step includes installing the rods such that a rod in the first row of fuel rods is spaced apart from adjacent rods in the first row of fuel rods and wherein the second installing step includes installing the rods such that a rod in the second row of fuel rods is spaced apart from adjacent rods in the second row of fuel rods. |
summary | ||
abstract | The invention relates to a thermosetting resin composition including a radically curable resin mixture of: |
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claims | 1. A circuit comprising:a periodic Performance Monitor Counter (PMC), the periodic PMC being configured to count performance signals from a component of a computer system for a predetermined period of time; anda first count comparator hardware coupled to the periodic PMC, wherein in response to the first count comparator hardware determining that the number of performance signals stored in the periodic PMC is outside of a first predetermined range of numbers, the first count comparator hardware generates a first action signal to evoke a performance adjustment to a computer logic whose performance signals are being monitored by the periodic PMC. 2. The circuit of claim 1, further comprising:a PMC reset controller, wherein the PMC reset controller clears the periodic PMC after the predetermined period of time. 3. The circuit of claim 1, further comprising:a counter selector coupled to the first count comparator hardware;a first counter and a second counter coupled to the counter selector, wherein the counter selector is capable of selectively toggling between the first and second counters to store a current first action signal count stored in the periodic PMC, such that one of the first and second counters stores a previous period's first action signal count from the first count comparator hardware and the other of the first and second counters stores a current period's first action signal count from the first count comparator hardware; and a second count comparator coupled to the first and second counters, wherein the second count comparator issues an action signal in response to a difference between the performance signal counts in the first and second counters being outside of a second predetermined range of numbers. 4. The circuit of claim 1, wherein the computer system is a microprocessor. 5. The circuit of claim 1, wherein the action signal is an external trigger used to control an event capture by a logic analyzer that is external to the computer system. 6. The circuit of claim 1, wherein the action signal generates an internal trigger for use with an internal trace array. 7. The circuit of claim 1, wherein the action signal generates a new performance event that is stored in a performance event PMC, wherein the performance event PMC stores a total number of action signals that reflect the number of times that the performance signals exceed the first predetermined range of numbers. 8. A circuit comprising:a periodic Performance Monitor Counter (PMC), the periodic PMC being configured to count performance signals from a component of a computer system;a counter selector coupled to the periodic PMC;a first counter and a second counter coupled to the counter selector, wherein the counter selector is capable of selectively toggling between the first and second counters to store a current performance signal count stored in the periodic PMC, such that one of the first and second counters stores a previous period's performance signal count from the periodic PMC and the other of the first and second counters stores a current period's performance signal count from the periodic PMC; and a count comparator coupled to the first and second counters, wherein the count comparator issues an action signal in response to a difference between the performance signal counts in the first and second counters being outside of a predetermined range of numbers. 9. The circuit of claim 8, further comprising:a clock cycle counter coupled to the count comparator, wherein the clock cycle counter controls when the performance signal counts in the first and second counters are compared. 10. The circuit of claim 8, wherein the computer system is a microprocessor and wherein the action signal causes a chiplet in the microprocessor to perform a specific action. 11. The circuit of claim 8, wherein the action signal is an external trigger used to control an event capture by a logic analyzer that is external to the computer system. 12. The circuit of claim 8, wherein the action signal generates an internal trigger for use with an internal trace array. 13. The circuit of claim 8, wherein the action signal generates a new performance event that is stored in a performance event PMC, wherein the performance event PMC stores a total number of action signals that reflect the number of times that the performance signals exceed the predetermined range of numbers. 14. A method for capturing a change in performance in a computer logic using a Performance Monitoring Counter (PMC), the method comprising:storing in a first hardware counter a starting count of performance events captured by a PMC;storing in a second hardware counter an ending count of performance events captured by the PMC;comparing the counts of performance events in the first and second hardware counters; andgenerating an action signal if a first derivative of the performance event counts in the first and second hardware counters is outside a first predetermined range of values. 15. The method of claim 14, further comprising:storing the first derivative of the performance event counts in the first and second hardware registers in a third hardware counter;storing a subsequent first derivative of the performance event counts in the first and second hardware counters in a fourth hardware counter; andin response to a second derivative of the first derivative and the subsequent first derivative being outside of a second predetermined range of values, generating the action signal. 16. A method comprising:storing in a first hardware counter a starting count of performance events captured by a Performance Monitoring Counter (PMC);storing in a second hardware counter an ending count of performance events captured by the PMC;comparing the counts of performance events in the first and second hardware counters;using hardware to calculate a first derivative that reflects a rate of change in performance events;deriving the first derivative to obtain a second derivative that reflects a delta in the rate of change in performance events; andgenerating an action signal if the first derivative of the performance event counts in the first and second hardware counters is outside a first predetermined range of values. 17. The method of claim 16, further comprising: using the second derivative to prompt a configurable action. 18. The method of claim 17, wherein the configurable action is a chip inhibit. 19. The method of claim 17, wherein the configurable action is a trigger for a logic analyzer. |
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abstract | A heating laser beam is emitted to a cracked portion to remove moisture from the cracked portion, and subsequently, a welding laser beam is emitted to the cracked portion to heat and melt the cracked portion. The heating laser beam and the welding laser beam are emitted to an entire surface of the cylindrical body inside the reactor such as a stub tube penetrating through and fixed to a reactor bottom portion and a crack of the welded portion between the cylindrical body and the reactor bottom portion to thereby prevent a new crack from occurring and reactor water from leaking. |
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claims | 1. A power generation system, comprising:a power source comprising an input and an output;a thermal/electrical power converter including a compressor with an output coupled to said input of said power source;a power plant with an input coupled in series with an output of said thermal/electrical power converter, wherein said thermal/electrical power converter and said power plant are configured to serially convert thermal power produced at said output of said power source into electricity; andan inert gas reservoir tank coupled to an input of said compressor via a reservoir tank control valve and to said output of said compressor via another reservoir tank control valve, said reservoir tank control valve and said another reservoir tank control valve being configured to regulate a temperature of said output of said thermal/electrical power converter. 2. The power generation system as recited in claim 1 further comprising a counterflow heat exchanger with an input coupled to said output of said power source, and an output coupled to an input of a gas turbine of said thermal/electrical power converter. 3. The power generation system as recited in claim 2 wherein said power source is an inert gas power source that provides a first inert gas to said input of said counterflow heat exchanger to transfer thermal energy to a second inert gas at said output of said counterflow heat exchanger. 4. The power generation system as recited in claim 3 wherein said first inert gas is helium and said second inert gas is argon or a mixture of argon and helium. 5. The power generation system as recited in claim 3 wherein said second inert gas has an average molecular weight equal to or greater than an average molecular weight of air. 6. The power generation system as recited in claim 3 further comprising a circulating pump configured to circulate said first inert gas between said inert gas power source and said counterflow heat exchanger. 7. The power generation system as recited in claim 6 further comprising a filter coupled between another output of said counterflow heat exchanger and an input of said circulating pump. 8. The power generation system as recited in claim 3 further comprising another inert gas reservoir tank coupled to said inert gas power source. 9. The power generation system as recited in claim 1 further comprising a heat exchanger having an input coupled to an output of a gas turbine, an output coupled to said input of said compressor, and said output coupled to said power plant. 10. The power generation system as recited in claim 1 wherein said thermal/electrical power converter and said power plant are thermally coupled in series and electrically coupled in parallel. 11. A method, comprising:providing a power source comprising an input and an output;coupling an output of a compressor of a thermal/electrical power converter to said input of said power source;coupling an output of said thermal/electrical power converter in series with an input of a power plant, wherein said thermal/electrical power converter and said power plant are configured to serially convert thermal power produced at said output of said power source into electricity; andcoupling an inert gas reservoir tank to an input of said compressor via a reservoir tank control valve and to said output of said compressor via another reservoir tank control valve, said reservoir tank control valve and said another reservoir tank control valve being configured to regulate a temperature of said output of said thermal/electrical power converter. 12. The method as recited in claim 11 further comprising coupling said output of said power source to an input of a counterflow heat exchanger, and coupling an input of a gas turbine of said thermal/electrical power converter to an output of said counterflow heat exchanger. 13. The method as recited in claim 12 wherein said power source is an inert gas power source and further comprising providing a first inert gas via said inert gas power source to said input of said counterflow heat exchanger to transfer thermal energy to a second inert gas at said output of said counterflow heat exchanger. 14. The method as recited in claim 13 wherein said first inert gas is helium and said second inert gas is argon or a mixture of argon and helium. 15. The method as recited in claim 13 wherein said second inert gas has an average molecular weight equal to or greater than an average molecular weight of air. 16. The method as recited in claim 12 further comprising circulating said first inert gas via a circulating pump between said inert gas power source and said counterflow heat exchanger. 17. The method as recited in claim 16 further comprising coupling another output of said counterflow heat exchanger to an input of said circulating pump via a filter. 18. The method as recited in claim 13 further comprising coupling another inert gas reservoir tank to said inert gas power source. 19. The method as recited in claim 11 further comprising:coupling an input of a heat exchanger to an output of a gas turbine,coupling an output of said heat exchanger to said input of said compressor, andcoupling said output to said power plant. 20. The method as recited in claim 11 wherein said thermal/electrical power converter and said power plant are thermally coupled in series and electrically coupled in parallel. |
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051608472 | claims | 1. A dynamic multivane electron arc beam collimator for defining the electron field of an electron beam emitted by a linear accelerator for use in electron arc therapy, said collimator comprising: (a) a plurality of vanes positioned and adapted to define an electron aperture which defines said electron field, (b) a plurality of vane movement means associated with said vanes for moving said vanes to dynamically define said electron aperture and to thereby dynamically define said electron field, and (c) a plurality of local controllers to control said vane movement means through distributed processing; (a) a plurality of vanes positioned and adapted to define an electron aperture which defines said electron field, (b) a plurality of vane movement means associated with said vanes for moving said vanes to dynamically define said electron aperture and to thereby dynamically define said electron field, (c) a plurality of local controllers to control said vane movement means, and (d) a housing; wherein said vanes, vane movement means and local controllers are housed within said housing; wherein said collimator is portable; and wherein said collimator is attachable to and detachable from the head of said linear accelerator. (a) a plurality of vanes positioned and adapted to define an electron aperture which defines said electron field, (b) vane movement means for moving said vanes to dynamically define said electron aperture and to thereby dynamically define said electron field, and (c) a local controller to control said vane movement means and to thereby control movement of said vanes; wherein said vanes, said vane movement means and said local controller are combined to form a unit which is attachable to and detachable from the head of said linear accelerator; and wherein said local controller provides local intelligence to said unit. (a) a dynamic multivane electron arc beam collimator comprising: wherein (i), (ii) and (iii) are adapted to provide independent and simultaneous movement of each vane; wherein said vanes are divided into two parallel vane rows to form a plurality of vane pairs; wherein each vane pair is comprised of two opposing vanes which can be moved linearly to dynamically define an opening between said vanes of said pair; and wherein the vane pair openings defined by said vane pairs collectively define said electron aperture. (b) means for selecting a treatment arc and dividing said treatment arc into a plurality of arc segments defined by reference angles; (c) means for determining preferred vane pair openings for each arc segment and for representing said preferred vane pair openings as vane position data for each arc segment; (d) means for monitoring current treatment angle of the linear accelerator during linear accelerator rotation to detect reference angles when encountered by such rotation, and (e) means for sequentially transmitting to the local controllers of said collimator the vane position data of each arc segment when the reference angle identifying the arc segment is encountered by linear accelerator rotation; 2. A collimator in accordance with claim 1 wherein said vanes are divided into two parallel vane rows to form a plurality of vane pairs; wherein each vane pair is comprised of two opposing vanes which can be moved linearly to dynamically define an opening between said vanes of said pair; and wherein the vane pair openings defined by said vane pairs collectively define said electron aperture. 3. A collimator in accordance with claim 2 wherein the number of said vane pairs ranges from 3 to 71. 4. A collimator in accordance with claim 2 wherein the number of said vane pairs ranges from 5 to 31. 5. A collimator in accordance with claim 2 wherein (a), (b) and (c) are combined to form a unit that is attachable to and detachable from the head of said linear accelerator. 6. A collimator in accordance with claim 2 wherein the number of said vane is an odd number; and wherein the target treatment area is located and centered with respect to the center vane pair. 7. A collimator in accordance with claim 1 wherein each local controller controls one or more of the vane movement means. 8. A collimator in accordance with claim 1 wherein the vane movement means further comprises a vane position monitoring means to monitor the position of the vane associated with the vane movement means. 9. A collimator in accordance with claim 8 wherein the vane position monitoring means is a potentiometer. 10. A collimator in accordance with claim 1 wherein said collimator further comprises a housing for (a), (b) and (c); and wherein said housing is attachable to the head of the linear accelerator and detachable from the head of the linear accelerator. 11. A collimator in accordance with claim 1 wherein said collimator further comprises a noncontact communication means for communication with a remote host controller. 12. A collimator in accordance with claim 11 wherein said noncontact communication means comprises an infra-red transceiver. 13. A collimator in accordance with claim 1 wherein said collimator further comprises a local power source. 14. A collimator in accordance with claim 1 wherein said local controllers are networked as nodes on a common network. 15. A collimator in accordance with claim 1 wherein said vane movement means are local to said vanes. 16. A portable dynamic multivane electron arc beam collimator for defining the electron field of an electron beam emitted by a linear accelerator for use in electron arc therapy, said collimator comprising: 17. A dynamic multivane electron arc beam collimator for defining the electron field of an electron beam emitted by a linear accelerator for use in electron arc therapy, said collimator comprising: 18. A dynamic multivane electron arc beam collimation system for defining the electron field of an electron beam emitted by a linear accelerator for use in electron arc therapy, said collimation system comprising; |
050826174 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a neutron activated heat source, in particular, an isotopic heat source using the isotope thulium-170. 2. Description of Related Art Isotopic heat sources use the release of energy from a radioactive isotope. The isotope is created either as a result of fission or by irradiating a target material with neutrons in a nuclear reactor. In neutron irradiation, the target atomic nuclei capture irradiating neutrons and are converted into a neutron activated isotope. The target material is chosen to provide the energy release rate and decay characteristics of interest in the activated target. This energy release can be absorbed as heat and exploited for many uses, such as for a power conversion system. Typically, reactor target materials are formed into thin flat disks. During irradiation, neutrons are highly absorbed at the target surface, resulting in fewer neutrons available for absorption in the center of the target. The reduction in neutrons, called flux depression, results in lower activation in the target center compared to the target surface. Thin targets provide a more efficient use of target material by reducing flux depression. Targets may contain a material that acts as a moderator during irradiation. Neutrons that pass through the target atoms unabsorbed can collide with moderator atoms, slow down, and become more susceptible to capture by other target nuclei. Moderators thereby increase the efficiency of the production of the activated isotope. An ideal amount of moderation causes the neutron energy distribution to peak in the energy region of high cross-section for the target material. Isotopic heat sources are useful when combined with a power conversion system because the energy release is reliable, and the power output diminishes in a known manner as the isotope decays. The heat sources have greater energy density, by several orders of magnitude, than chemical batteries. Depending on the half-life of the isotope, the heat sources can be used for months or years, rather than having a life of hours or weeks that is typical of a chemical battery. The sources are compact and portable, which is especially useful for exploration or surveillance in remote areas such as Antarctica, in space, or underwater. Presently, isotopic heat sources are available that use isotopes such as strontium-90, cobalt-60, and plutonium-238. These isotopes are environmentally hazardous because they are easily dispersed, and their half-lives are on the order of years. Thulium-170 has also been considered as a fuel for heat sources. Targets with stable thulium-169 are irradiated and converted into thulium-170 (and thulium-171, etc.). Thulium-169 has a high neutron cross-section, lowering the irradiation time (and cost) needed to produce thulium-170. Thulium is advantageous as a fuel because of its refractory properties; that is, thulium is very stable at high temperatures and has a high melting point (heat of fusion). Thulium-170 is a better heat source from an environmental standpoint because of its relatively short half-life (129 days), its chemical stability, and refractory nature. Several isotopic heat sources using thulium-170 have been developed. The thulium fuel has been in the form of thulium hydride, thulium metal, thulium oxide, and a mixture of thulium oxide and thulium metal. The thulium fuel is usually encapsulated or encased in a material with a high melting point and low neutron cross-section. These materials are usually metals or high atomic weight (high Z) materials, such as molybdenum, tantalum, tungsten, zirconium, steel, nickel, or platinum-rhodium alloy. The casings provide containment of the target material before and after irradiation. Using high Z material to encapsulate targets presents several problems: the heat source weight is increased, pre-fabrication of the capsules is needed, and high Z materials produce more bremsstrahlung radiation after target irradiation than low Z materials. Accordingly, a more useful heat source would comprise a refractory fuel with a short half-life and a diluent of low atomic weight (low Z) material. The low Z material would reduce the weight of the heat source. The low Z material would also produce less bremsstrahlung radiation than a high Z material, requiring less shielding. The reduction in shielding and source weight is advantageous in creating portable power sources. Individual thulium fuel parts would not be encapsulated, minimizing pre-fabrication time and expense. Suitable containment would be provided by an outer vessel containing all of the thulium fuel parts. SUMMARY OF THE INVENTION The present invention provides a heat source fuel stack that is internally moderated during irradiation and requires minimal shielding due to minimal production of bremsstrahlung radiation. The fuel stack needs little or no post-activation handling, which saves time and prevents prolonged radiation exposure. The invention also provides a heat source apparatus for efficient heat removal. The fuel stacks comprise an isotopic fuel and a low atomic weight diluent. The fuel, preferably thulium oxide, is refractory and produces an isotope during neutron irradiation with a relatively short half-life. The diluent is refractory and heat conductive, preferably graphite. A stack of thulium oxide fuel and graphite disks is irradiated in a reactor in a conventional manner to form a fuel stack. In the described embodiment, the heat source apparatus comprises heat pipes for heat removal, a heat block, holes in the heat block for inserting irradiated fuel stacks and heat pipes, a structural container, insulation, and radiation shielding. The irradiated fuel stacks and heat pipes are mounted in the heat block. The heat block, preferably made of graphite, is encased in a sealed structural container that is surrounded by layers of insulation and shielding. The heat pipes extend beyond the container and shielding and contain a heat pipe working fluid. The working fluid transfers heat from the heat source to a heat exchanger. A single phase gas restricts the flow of the heat pipe working fluid at an established interface. The low atomic weight diluent in the fuel stack has several advantages. In the preferred embodiment, graphite dilutes the thulium oxide fuel and acts as a moderator, increasing the efficiency of thulium-170 production. Graphite and other low Z materials do not produce as much bremsstrahlung radiation as high Z materials; therefore, the fuel stacks require less shielding, reducing the weight of the heat source. Graphite is also an excellent heat conductor, increasing heat removal efficiency. In the preferred embodiment, the heat source apparatus provides two passive mechanisms for containment and heat dissipation in the case of source overheating. In the first mechanism, the heat pipes are oversized in length to permit passive cooling. A heat pipe working fluid circulates in the heat pipes between the heat source and the heat exchanger. Beyond the heat exchanger, the heat pipe contains a single phase gas. The interface between the working fluid and the single phase gas is preferably located at the heat exchanger. If the heat source temperature increases, the working fluid vapor pressure increases and moves the working fluid-gas interface away from the heat source so the heat pipes have more surface area for cooling. As a second mechanism for providing containment and cooling, the insulation layer is designed to fail at a temperature below the failure temperature of the inner container and its contents. The present invention has many potential uses. The heat source coupled with a power conversion system provides a reliable, refuelable and relatively long-lasting power source. This type of power system could be used for autonomous or remotely controlled vehicles. These power sources are particularly useful for exploration or surveillance in remote environments such as space or underwater. |
claims | 1. An electron beam apparatus with an aberration corrector, said apparatus comprising:an electron optical system which has at least an electron gun for emitting an electron beam, a condenser lens, an objective lens for converging an electron beam onto a surface of a specimen, and a scanning deflector for causing the converged electron beam to scan the surface of the specimen;said aberration corrector composed of a plurality of combined multipole lenses; anda computer for controlling at least one of the electron optical system and said aberration corrector, said computer having a first scan mode for enabling operation of said aberration corrector and a second scan mode for disabling the operation of said aberration corrector and controlling said objective lens, said condenser lens, or said aberration corrector such that an object point of the objective lens does not substantially change in either of the modes. 2. An electron beam apparatus with an aberration corrector, said apparatus comprising:an electron optical system which has at least an electron gun for emitting an electron beam, a condenser lens, an objective lens for converging an electron beam onto a surface of a specimen, and a scanning deflector for causing the converged electron beam to scan the surface of the specimen;said aberration corrector composed of a plurality of combined multipole lenses; anda computer for controlling at least one of the electron optical system and said aberration corrector, said computer having a first scan mode for enabling operation of said aberration corrector and a second scan mode for disabling the operation of said aberration corrector and controlling said objective lens, said condenser lens, or said aberration corrector such that an object point of the objective lens does not substantially change in either of the modes by switching a magnetization intensity of said condenser lens in association with ON/OFF modes of the aberration corrector. 3. An electron beam apparatus with an aberration corrector according to claim 1, wherein in said second scan mode, operation of said multipole lenses is disabled. 4. An electron beam apparatus with an aberration corrector according to claim 2, wherein in said second scan mode, operation of said multipole lenses is disabled. 5. An electron beam apparatus comprising:an electron optical system which has at least an electron gun for emitting an electron beam, a condenser lens, an objective lens, and a scanning coil;an aberration corrector composed of a plurality of combined multipole lenses; anda computer controlling at least one of the electron optical system and the aberration corrector,wherein said computer has a ON mode for enabling operation of said multipole lenses and a OFF mode for disabling the operation of said multipole lenses and controlling at least one of the electron optical system and the aberration corrector such that an object point of the objective lens does not substantially change in either of the modes. 6. An electron beam apparatus according to claim 5, wherein said computer controls said objective lens, said condenser lens, or said aberration corrector such that said object point of the objective lens does not substantially change in either of the modes. 7. An electron beam apparatus according to claim 5, further comprising a mechanism for detecting a secondary electron and a reflected electron and forming an image in said ON mode for enabling operation of said multipole lenses and in said OFF mode for disabling the operation of said multipole lenses. 8. An electron beam apparatus according to claim 5, wherein said computer controls at least one of said electron optical system and said aberration corrector based on an image which detects secondary electrons or reflected electrons in said ON mode for enabling operation of said multipole lenses and in said OFF mode for disabling the operation of said multipole lenses. |
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description | This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0052214, filed on Apr. 14, 2015, the disclosure of which is incorporated herein by reference in its entirety. 1. Field of the Invention The present invention relates to a method for synthesizing lithium-titanium oxide using a solid state method, and more specifically to a method for synthesizing lithium-titanium oxide, which is used for a breeding material in a nuclear fusion reaction and represented by Li2TiO3, using a solid state method. 2. Discussion of Related Art Among deuterium and tritium which are used as fuels of a nuclear fusion reactor, tritium is generated by a reaction of neutrons and lithium because it is not present in nature. A material generating tritium is referred to as a breeding material, and a breeding material including lithium in a solid state is referred to as a solid breeding material. Representative examples of the solid breeding material include lithium oxide (Li2O), lithium-aluminum oxide (Li2AlO2), lithium-zirconium oxide (Li2ZrO3), lithium-titanium oxide (Li2TiO3), lithium-silicon oxide (Li4SiO4), etc. Especially, among these solid ceramic breeding materials, lithium-titanium oxide (Li2TiO3) is now known to have advantages in that it has high stability at a high temperature and is capable of generating tritium at a low temperature. However, lithium-titanium oxide which has been commercialized is expensive, and includes impurities such as cobalt which is a long-period element, and thus is disadvantageous in that it is difficult to be reused as a breeding material. Further, when lithium-titanium oxide is formed by a solid state synthesis method, it is difficult to control the reduction of a particle size for ensuring the ease of tritium emission. The present invention has been made to solve the aforementioned problems, and an object of the present invention is to provide a method for synthesizing lithium-titanium oxide, which may be prepared to have fine particles, and used as a recyclable breeding material, using a solid state method. Provided is a method for synthesizing lithium-titanium oxide using a solid state method according to an example of the present invention. The synthesis method includes: mixing lithium oxide (Li2O) and titanium oxide (TiO2) in a solvent; separating a solid material which includes lithium oxide and titanium oxide from the solvent; drying the solid material separated from the solvent; and performing a heat treatment on the solid material. A molar ratio of lithium oxide to titanium oxide may be 1:0.940 or more to less than 1:1. A molar ratio of lithium oxide to titanium oxide may be in the range of 1:0.940 to 1:0.944. Titanium oxide may have an anatase crystal structure. A molar ratio of lithium oxide to titanium oxide may be 1:0.942 when titanium oxide has a rutile crystal structure. The heat treatment may be performed at 600° C. or more to less than 800° C. The heat treatment may be performed at 670° C. or more to less than 800° C. The heat treatment may be performed for 12 hours or more. Titanium oxide may have an anatase crystal structure. Lithium-titanium oxide prepared in the performing of the heat treatment may have a Li2TiO3 structure. The solvent may include an alcohol. Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. While the present invention is shown and described in connection with exemplary embodiments thereof, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Hereinafter, the present invention will be described in detail in conjunction with the appended drawings. FIG. 1 is a flow chart for illustrating a method for synthesizing lithium-titanium oxide according to an example of the present invention. Referring to FIG. 1, first, lithium oxide (Li2O) and titanium oxide (TiO2) are mixed in a solvent to prepare lithium-titanium oxide according to the present invention (S110). Here, mixing may be performed such that the molar ratio of lithium oxide to titanium oxide is 1:0.940 or more to less than 1:1. A mixing process is performed by a wet process using a solvent. Lithium oxide and titanium oxide may be wet-milled in the mixing process. The mixing process may be performed by ball-milling. The solvent used in the mixing process may include an alcohol. For example, lithium oxide and titanium oxide may be mixed in isopropyl alcohol (IPA). Here, the mixing process may be performed for 4 to 5 hours. When the molar ratio of lithium oxide to titanium oxide is less than 1:0.940 or 1:1 or more, compounds such as LiTiO2, TiO2 or the like are included as impurities in a final product in addition to lithium-titanium oxide having a Li2TiO3 structure. When these impurities are contained, the final product may not be used as a breeding material because the purity is reduced, and thus the molar ratio of lithium oxide to titanium oxide is preferably 1:0.940 to 1:1. More preferably, the molar ratio of lithium oxide to titanium oxide may be in the range of 1:0.940 to 1:0.944. Most preferably, the molar ratio of lithium oxide to titanium oxide may be 1:0.942. Any titanium oxide having a rutile structure or an anatase structure may be used as titanium oxide. However, titanium oxide having an anatase crystal structure is more suitable for preparing lithium-titanium oxide which is controlled to have a fine particle size as a breeding material. When titanium oxide having a rutile crystal structure is used as titanium oxide, highly crystalline lithium-titanium oxide without impurities may be prepared when the molar ratio of lithium oxide and titanium oxide is 1:0.942. A solid material is separated from a solvent in a mixed solution of lithium oxide and titanium oxide (S120), and then the solid material separated from the solvent is dried (S130). The mixed solution includes a liquid material and a solid material, and the solid material may be obtained by separation from the liquid material. The liquid material in the mixed solution is a solvent used in the mixing process, and the solid material includes lithium oxide and titanium oxide. In an example, the solid material may be separated from the mixed solution by centrifugation. After the solid material is separated, the solvent remaining in the solid material is removed by a drying process. Here, the drying process may be performed in a vacuum, and may be performed at 50 to 70° C. for 5 to 7 hours. Thereafter, a heat treatment is performed on the obtained solid material (S140) to prepare lithium-titanium oxide according to the present invention. Lithium oxide reacts with titanium oxide in the solid material by a heat treatment process, and thereby lithium-titanium oxide having a Li2TiO3 crystal structure is prepared. The heat treatment process may be performed at 600 to 800° C. When the heat treatment process is performed at less than 600° C., lithium-titanium oxide with high purity is difficult to be obtained because lithium-titanium oxide as a final product includes impurities. Further, when the heat treatment process is performed at 800° C. or more, lithium-titanium oxide having a Li4Ti5O12 crystal structure in addition to a Li2TiO3 crystal structure is generated, and thus availability as a breeding material may be reduced. Accordingly, the heat treatment process may be performed at 600° C. or more to less than 800° C., preferably, at 670° C. or more to less than 800° C., and most preferably, at 700° C. The heat treatment process may be performed in an air atmosphere after pouring a solid material into a quartz crucible and putting it into a box oven. Here, the heat treatment process may be performed for 2 to 24 hours. As described above, in lithium-titanium oxide according to the present invention, lithium oxide and titanium oxide are reacted by a solid state method such that lithium-titanium oxide which is a final product may be easily controlled to have a fine particle size, and lithium-titanium oxide having a uniform particle size may be prepared. Moreover, spherical lithium-titanium oxide may be easily prepared according to the preparation method of the present invention. Hereinafter, the present invention will be described in detail in conjunction with examples in which lithium-titanium oxide is prepared according to the preparation method of the present invention. Preparation of Samples LTA-0 to LTA-5 and Comparative Sample CLTA-1 Lithium oxide (Li2O) and titanium oxide (TiO2) having an anatase crystal structure were mixed in the molar ratio of 1:0.940, and ball-milled in 100 mL of isopropyl alcohol (IPA) at a rate of 300 rpm for 3 hours. Subsequently, a solid material was separated using a centrifuge, was vacuum-dried at 60° C. for 6 hours, and a heat treatment was performed thereon at 700° C. for 12 hours to prepare lithium-titanium oxide (sample LTA-0) according to Example LTA-0 of the present invention. Samples LTA-1 to LTA-5 and comparative sample CLTA-1 were prepared in substantially the same manner as sample LTA-0 by controlling molar ratio conditions as shown in the following Table 1. TABLE 1Molar ratio ofHeat treatmentlithium oxide totemperatureHeat treatmentClassificationtitanium oxide(unit: ° c.)time (unit: hours)LTA-01:0.94070012LTA-11:0.941LTA-21:0.942LTA-31:0.943LTA-41:0.944LTA-51:0.945CLTA-11:0.938 Analysis of Samples LTA-0 to LTA-5 and Comparative Sample CLTA-1 A diffraction angle (2θ) with respect to a CuK-alpha characteristic X-ray wavelength was measured through XRD (x-ray diffraction) analysis for each of samples LTA-0 to LTA-5 and comparative sample CLTA-1. The results were shown in FIGS. 2 and 3. FIG. 2 is an XRD graph of samples LTA-0 to LTA-4, and FIG. 3 is an XRD graph of sample LTA-5 and comparative sample CLTA-1. An x-axis represents a diffraction angle (2θ, unit: degrees) and a y-axis represents intensity (unit: arbitrary unit) in each of FIGS. 2 and 3. Peaks of LiTiO2 (JCPDS No. 74-2257), TiO2 (JCPDS No. 21-1276) and Li2TiO3 (JCPDSNo. 77-8280) are illustrated together as a reference for peaks in the XRD graph in FIGS. 2 and 3. Referring to FIG. 2, each of samples LTA-0 to LTA-4 has a main peak corresponding to that of Li2TiO3 at a diffraction angle (2θ) in the range of 5 to 20 degrees. Especially, it may be determined that the main peak of each of samples LTA-0 to LTA-4 results from Li2TiO3, and not from Li4Ti5O12. That is, it may be known that highly crystalline Li2TiO3 was prepared. Furthermore, each of samples LTA-0 to LTA-4 may be determined to have no main peak corresponding to that of TiO2. Referring to FIG. 3, it may be determined that sample LTA-5 shows substantially the same result as those of samples LTA-0 to LTA-4, and comparative sample CLTA-1 in which the molar ratio of lithium oxide and titanium oxide is 1:0.938 has a main peak resulting from Li2TiO3, but the intensity thereof is close to almost 50% of that of sample LTA-5. That is, it may be determined that, since low crystalline Li2TiO3 is prepared when the molar ratio of lithium oxide and titanium oxide is 1:0.938 under the same heat treatment temperature and time conditions, lithium-titanium oxide which is suitable as a breeding material may be prepared when the molar ratio is at least more than 1:0.938, and specifically is 1:0.940. According to the description of FIGS. 2 and 3, it may be experimentally determined that lithium-titanium oxide with high availability as a breeding material may be prepared only if the molar ratio of lithium oxide and titanium oxide is at least 1:0.940. Especially, it may be determined that highly crystalline Li2TiO3 may be prepared when the molar ratio is in the range of 1:0.940 to 1:0.944. Preparation of Samples LTA-5 to LTA-9 Lithium oxide (Li2O) and titanium oxide (TiO2) were mixed in the molar ratio of 1:0.942, and ball-milled in 100 mL of isopropyl alcohol (IPA) at a rate of 300 rpm for 3 hours. Subsequently, a solid material was separated using a centrifuge, was vacuum-dried at 60° C. for 6 hours, and the dried material was ground in an agate mortar and prepared in powder form. A heat treatment was performed on the powder at 650° C. for 2 hours to prepare lithium-titanium oxide (sample LTA-6) according to Example LTA-6 of the present invention. Samples LTA-7 to LTA-10 were prepared in substantially the same manner as sample LTA-6 by controlling heat treatment temperature conditions as shown in the following Table 2. TABLE 2Molar ratio ofHeat treatmentlithium oxide totemperatureHeat treatmentClassificationtitanium oxide(unit: ° c.)time (unit: hours)LTA-61:0.94265024LTA-7660LTA-8670LTA-9680LTA-10700 Analysis of Samples LTA-6 to LTA-10 A diffraction angle (2θ) with respect to a CuK-alpha characteristic X-ray wavelength was measured through XRD analysis for each of samples LTA-6 to LTA-10. The results were shown in FIG. 4. FIG. 4 is an XRD graph of samples LTA-6 to LTA-10. In FIG. 4, an x-axis represents a diffraction angle (2θ, unit: degrees) and a y-axis represents intensity (unit: arbitrary unit). Peaks of TiO2 Rutile (JCPDS No. 21-1276), LiTiO2 (JCPDS No. 74-2257) and Li2TiO3 (JCPDS No. 77-8280) are illustrated together as a reference for peaks in the XRD graph in FIG. 4. Referring to FIG. 4, each of samples LTA-6 to LTA-10 has a main peak corresponding to that of Li2TiO3 at a diffraction angle (2θ) in the range of 5 to 20 degrees. Further, it may be determined that each of samples LTA-6 to LTA-10 has a main peak corresponding to that of TiO2 at a diffraction angle (2θ) in the range of 25 to 30 degrees. It may be determined that the intensity of the main peak of TiO2 is reduced while a heat treatment temperature increases from 650 to 700° C., under the same molar ratio and heat treatment time conditions. That is, the intensity of the main peak of TiO2 at each of 650° C., 660° C., 670° C. and 680° C. has decreased, and no peak is substantially shown at 670 to 700° C. As may be seen from FIG. 4, a heat treatment is preferably performed at 650 to 700° C., more preferably at 670° C. or more to less than 800° C., and most preferably at 700° C. to obtain highly crystalline Li2TiO3. Preparation of Samples LTA-11 and LTA-12 Lithium oxide (Li2O) and titanium oxide (TiO2) were mixed in the molar ratio of 1:0.942, and ball-milled in 100 mL of isopropyl alcohol (IPA) at a rate of 300 rpm for 3 hours. Subsequently, a solid material was separated using a centrifuge, was vacuum-dried at 60° C. for 6 hours, and the dried material was ground in an agate mortar and prepared in powder form. A heat treatment was performed on powders at 700° C. for 2 hours to prepare lithium-titanium oxide (sample LTA-11) according to Example LTA-11 of the present invention. Samples LTA-11 and 12 were prepared by a controlling heat treatment times as shown in the following Table 3. TABLE 3Molar ratio ofHeat treatmentlithium oxide totemperatureHeat treatmentClassificationtitanium oxide(unit: ° c.)time (unit: hours)LTA-111:0.9427002LTA-126LTA-212LTA-1024 Comparison and Analysis of Samples LTA-11 and LTA-12 and Samples LTA-2 and LTA-10 A diffraction angle (2θ) with respect to a CuK-alpha characteristic X-ray wavelength was measured through XRD analysis for each of samples LTA-2 and LTA-9 to LTA-11. The results were shown in FIG. 5. Peaks of TiO2 Rutile (JCPDS No. 21-1276), Li2TiO3 (JCPDS No. 77-8280) and LiTiO2 (JCPDS No. 74-2257) are illustrated together as a reference for peaks in the XRD graph in FIG. 5. FIG. 5 is an XRD graph of samples LTA-2 and LTA-10 to LTA-12. Referring to FIG. 5, it may be determined that lithium-titanium oxide having a more pure Li2TiO3 structure may be prepared in the case in which the heat treatment time is 12 to 24 hours (samples LTA-2 and LTA-10) as compared to the case in which the heat treatment time is 2 to 6 hours (samples LTA-11 and LTA-12), under the same heat treatment temperature conditions. Accordingly, the heat treatment is preferably performed for 12 hours or more, and especially, for about 24 hours. Preparation of Sample LTR-1 Sample LTR-1 was prepared in substantially the same manner as sample LTA-2 except that TiO2 having a rutile structure was used instead of TiO2 having an anatase structure. Comparison and Analysis of Sample LTA-2 and Sample LTR-1 A diffraction angle (2θ) with respect to a CuK-alpha characteristic X-ray wavelength was measured through XRD analysis for each of sample LTA-2 and sample LTA-1. Further, a scanning electron microscopy (SEM) image of each of sample LTA-2 and sample LTA-1 was taken. The results were respectively shown in FIGS. 6 and 7. Peaks of Li4Ti5O12 (JCPDS No. 49-0207), TiO2 Rutile (JCPDS No. 21-1276), TiO2 Anatase (JCPDS No. 21-1272) and Li2TiO3 (JCPDS No. 77-8280) are illustrated together as a reference for peaks in the XRD graph in FIG. 6. FIG. 6 is an XRD graph of samples LTA-2 and LTR-1. Referring to FIG. 6, it may be determined that both of samples LTR-1 and LTA-2 have main peaks corresponding to that of Li2TiO3. That is, it may be determined that highly crystalline Li2TiO3 may be prepared in both of the case in which when TiO2 with a rutile structure is used and the case in which TiO2 with an anatase structure is used. SEM images of FIG. 7 are SEM images in which the scale bar is 1 μm, FIG. 7(a) is an image of sample LTR-1, and FIG. 7(b) is an image of sample LTA-2. Referring to FIG. 7, it may be determined from both of samples LTR-1 and LTA-3 that spherical lithium-titanium oxide having a uniform particle size was formed. However, it was determined that lithium-titanium oxide having a smaller particle size was formed in the case of sample LTA-2 in which TiO2 having an anatase structure was used as compared to the case of sample LTR-1 in which TiO2 having a rutile structure was used. Analysis of Components of Commercially Available Product and Samples LTA-2 and LTR-1 Lithium-titanium oxide in powder form manufactured by Japan Pure Chemical Co., Ltd., and sample LTA-2 and sample LTR-1 prepared according to the present invention were prepared. Analysis of components of each sample was performed according to an inductively coupled plasma method. The results were shown in Table 4. TABLE 4Productmanufactured byJapan PureType of elementChemical Co., Ltd.LTA-2LTR-1Al 5.49 ppm33.18 ppm30.89 ppmCo629.11 ppm ——Ca70.07 ppm47.08 ppm82.16 ppmCr34.57 ppm2.990.731 ppmFe 6.54 ppm——Mg20.92 ppm12.8868.83 ppmB—0.2990.062 ppmNa144.40 ppm 60.97 ppm33.43 ppmZr—339.6 ppm 3139 ppm Referring to Table 4, it may be determined that the commercially available product contains a large amount of cobalt which is a long-period element while no cobalt was detected in samples LTA-2 and LTR-1 prepared according to an example of the present invention, and although each of samples LTA-2 and LTR-1 includes aluminum, an amount of aluminum is in an acceptable range. That is, lithium-titanium oxide prepared according to the present invention may be easily reused. Preparation of Samples LTR-2 to LTR-4 Samples LTR-2 to LTR-4 were prepared in substantially the same manner as sample LTR-1 except for the molar ratio of lithium oxide to titanium oxide having a rutile structure. Each sample was prepared according to Table 5. TABLE 5Molar ratio ofHeat treatmentlithium oxide totemperatureHeat treatmentClassificationtitanium oxide(unit: ° c.)time (unit: hours)LTR-11:0.94270012LTR-21:0.945LTR-31:0.943LTR-41:0.938 Comparison and Analysis of Samples LTR-1 to LTR-4 A diffraction angle (2θ) with respect to a CuK-alpha characteristic X-ray wavelength was measured through XRD analysis for each of samples LTR-1 to LTR-4. Each result was shown in FIG. 8. Peaks of TiO2 Rutile (JCPDS No. 21-1276), LiTiO2 (JCPDS No. 74-2257) and Li2TiO3 (JCPDS No. 77-8280) are illustrated together as a reference for peaks in the XRD graph in FIG. 8. FIG. 8 is an XRD graph of samples LTR-1 to LTR-4. Referring to FIG. 8, it may be determined that the intensity of the main peak of Li2TiO3 is low when the molar ratio is less than 1:0.940 like sample LTR-4 while titanium oxide having a rutile structure is used as a starting material, under the same heat treatment temperature and time conditions. That is, the reaction is preferably performed with lithium oxide and titanium oxide in the molar ratio of at least 1:0.940 or more. However, since samples LTR-2 to LTR-4 have main peaks resulting from TiO2, it may be determined that the molar ratio of lithium oxide to titanium oxide is most preferably 1:0.942 like sample LTR-1 when titanium oxide having a rutile structure is used to prepare lithium-titanium oxide with high purity and high crystallinity. The description of the presented embodiments is provided so that those skilled in the art of the present invention use or implement the present invention. It will be apparent to those skilled in the art that various modifications of the embodiments will be apparent to those skilled in the art and general principles defined herein can be applied to other embodiments without departing from the scope of the present invention. Therefore, the present invention is not limited to the embodiments presented herein, but should be analyzed within the widest range which is associated with the principles and new features presented herein. According to a method for synthesizing lithium-titanium oxide using a solid state method of the present invention, lithium-titanium oxide (Li2TiO3) which can be controlled for grain refining to ensure the ease of tritium emission may be realized and used as a recyclable breeding material can be prepared. It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers all such modifications provided they come within the scope of the appended claims and their equivalents. |
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047956062 | abstract | An inspection system for detecting leakage from for example the primary vessel (11) of a nuclear reactor includes a camera (29) carried by an umbilical cable (28) which can be fed through a duct assembly (22) comprising a series of tubular sections (23) connected endwise by flexible bellow (24). A guide track (18) extends around the top of the vessel (11) and each duct section (23) is provided with wheels (25) which engage the track (18). A curved guide tube (17) feeds the duct sections (23) from a vertical entry position (15) in the roof (13) into a horizontal track-engaging disposition. The track (18) includes spaced flanges (20b, 21b) through which the umbilical cable can extend and depend downwardly into the annular space between the primary vessel (11) and a surrounding guard vessel (12). |
047598964 | abstract | A method and apparatus is disclosed for reducing the exposure of pressure vessel welds to fast neutron fluxes. Localized peripheral core areas are provided with rod assemblies which may be made up of nuclear absorbing materials, nuclear reflecting materials, or any combination thereof, and of any desired length so as to reduce the exposure of the welds to such fast neutron fluxes. The rod assemblies are precisely tailored consistent with nuclear calculations to provide the desired effect without substantially reducing core ratings or adversely affecting reactor shutdown margins. |
claims | 1. An apparatus for radiographing an object, comprising: an X-ray radiation unit for radiating X-ray; a grid arranged in an X-ray radiation path; a grid movement controller for changing a movement speed of the grid by changing a turn speed of a motor, comprising a link mechanism for changing a turn movement of the motor into a straight movement of the grid; a sensor unit for converting the X-ray into image data; an input unit for inputting information relating to a region of a body; and an imaging controller for controlling (i) the time for the X-ray radiation unit to start radiating the X-ray, (ii) the time for the grid movement controller to start rotating the motor, and (iii) the time for the sensor unit to start storage, by associating one with another, wherein the imaging controller (a) selects a standard radiation exposure time and the turn speed based on the information input into the input unit, (b) controls the radiation exposure starting time of the X-ray radiation unit based on the selection, and (c) causes the grid movement controller to rotate the motor at the turn speed, wherein the standard radiation exposure time is selected based on the maximum X-ray radiation time to be determined according to the region of the body, and wherein the imaging controller is configured such that it controls the radiation exposure starting time of the X-ray radiation unit so that the standard radiation exposure time will be y divided by a ratio of m:n, where y is the time interval between the minimum X-ray radiation time and the maximum X-ray radiation time, m and n are natural numbers, and the minimum X-ray radiation time and the maximum X-ray radiation time are determined according to the region of the body. 2. An apparatus according to claim 1 , wherein the minimum X-ray radiation time is the time from when radiation starts until when the grid moves a predetermined distance, and the maximum X-ray radiation time is the time from when radiation starts until when the grid starts a turn movement. claim 1 3. An apparatus according to claim 2 , wherein the predetermined distance is determined so that the value of the predetermined distance multiplied by a pitch of a lead foil of the grid will be a predetermined value. claim 2 4. An apparatus according to claim 1 , further comprising a display unit for displaying one or more combinations of the minimum X-ray radiation time and the maximum X-ray radiation time, and the standard radiation exposure time. claim 1 5. An apparatus according to claim 1 , wherein m is 5 and n is 2, and wherein the standard radiation exposure time is y/(5/2). claim 1 |
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050842285 | description | DESCRIPTION OF PREFERRED EMBODIMENT As shown in FIG. 1, part of a vessel head 1 of a pressurized-water nuclear reactor is penetrated by an opening 2 in which a follower 3 is fastened leak-tightly by welding, the follower having a part projecting below the vessel head ensuring the guidance of a thermocouple column 5, and a part projecting above the vessel head 1 forming a widened part 4, on the outer surface of which is machined a screw thread 4a. The fastening and sealing device 6 of the thermocouple column 5 is fastened onto the widened part 4 via its lower part 7 having a tapped bore which can be engaged onto the threaded part 4a of the widened part 4. Mounting is thus ensured of the bearing unit of the sealing device of the thermocouple column at the end of the follower 3. The widened part 4 of the follower and the lower part 7 of the bearing unit 6 of the sealing device have circular seams 4', 7' which coincide when the part 7 is screwed fully onto the widened part 4. The seams 4' and 7' are joined by welding so as to ensure the leaktightness of the screwed joint between the pieces 4 and 7. The head and the followers or penetrating adaptors 3 are made in the workplace and transported to the site where the nuclear reactor is being installed. The fastening and sealing devices of the thermocouple columns 5, on the other hand, are attached and fastened to the upper ends of the followers on the site of the reactor. The lower part 7 of the bearing unit of the sealing device 6 is fastened onto the end of the follower so as to be capable of being disassembled if necessary, by fusing the joining zone of the seams 4' and 7'. This disassembly is, however, only carried out for repairs or in exceptional cases for servicing the penetration of the thermocouple column. The bearing unit of the sealing device has an upper part 8 which is mounted leaktightly on the lower part 7, a metal seal 10 with a special shape being placed therebetween, the parts 7 and 8 of the bearing unit being assembled by a clamping bracket 12 with three parts which can be assembled and clamped by screws introduced into openings 13 traversing opposite ears situated at the end of the three parts in the shape of sectors having an angle of aperture of 120.degree.. The clamping bracket has, on its inner part, tapered areas in clamping contact with corresponding tapered areas machined on end widened parts 7a and 8a of the lower part 7 and of the upper part 8, respectively, of the bearing unit of the sealing device. The follower 3 and the bearing unit of the sealing device have a tubular shape and arranged in each other's extension so as to provide a passage for the thermocouple column 5 formed by a tube for supporting and securing a set of thermocouples 15. The thermocouple column 5 has a bearing and sealing piece 16 at its upper end, inside the bearing unit, this piece 16 being machined in order to form a joint area 16a with a tapered shape intended to interact with a corresponding tapered shoulder machined inside the bore of the upper part 8 of the bearing unit. A sealing strip is inserted between the two coinciding tapered areas. Above the solid piece 16, the thermocouple column has a part projecting relative to the end of the upper part 8 of the bearing unit in which is machined a throat enabling the securing of a traction ring 18 formed from two half-rings which may be engaged laterally into the annular throat. A pressure plate 19 has axially engaged compression screws 20 and a rim which engages beneath the traction ring 18. The end of the compression screws 20 bears against the upper surface of the part 8 of the bearing unit of the sealing device. It will be readily understood that, upon screwing the compression screws 20, the compression plate is caused to rise and to bear beneath the traction ring 18 of the thermocouple column 5. The thermocouple column is thus caused to rise inside the bore of the bearing device 7, 8 and the sealing strip associated with the tapered area 16a of the thermocouple column to bear against the corresponding shoulder machined in the bore of the upper part 8 of the bearing unit. Leaktight fastening of the thermocouple column inside its bearing unit is thus obtained. In order to disassemble the thermocouple column, the screws 20 are loosened, the compression plate 19 and the traction ring 18 are separated from the upper part of the thermocouple column 5, and the elements of the clamping bracket 12 are then separated. It is then possible to slide the upper end part 8 of the bearing unit about the outer surface of the thermocouple column 5 in order to completely free this thermocouple column, which may be disassembled, or the sealing strip of which associated with the tapered area 16a may be changed. As explained above, these operations may be lengthy and difficult and even impossible when the clamping elements are seized up. FIG. 2 shows an alternative embodiment of the upper part of the bearing unit of the sealing device enabling the thermocouple column to be disassembled more easily. The lower part 21 of the bearing unit is identical to the lower part 7 of the bearing unit of the sealing device according to the prior art shown in FIG. 1. This lower part 21 is mounted on the upper part 23 by a clamping bracket 22 identical to the bracket 12 of the embodiment shown in FIG. 1. A seal 24 is inserted between the upper end of the part 21 and the lower end of the part 23. According to the invention, the upper part 23 of the bearing unit has two successive tubular sections 25 and 26 superposed in the axial direction. The first section 25 has, in its lower part, a widened part 27 having a tapered bearing surface 27a against which a corresponding clamping surface of the bracket 22 is applied. The first section 25 has, in its upper, diametrically widened part, an annular throat 28 open on its outer lateral surface and having a certain depth in the radial direction. The part of the diametrically widened piece 25 also has axial openings 29 which open in the annular throat 28 and traverse the whole of the diametrically widened part of the piece 25. The upper part 23 of the bearing unit has a second section 26 superposed on the section 25, an annular sealing strip 31 being placed therebetween, this upper part 26 having a diameter which is substantially equal to the diameter of the part with a widened diameter of the piece 25 and being traversed by openings 32 arranged so as to come into alignment with the openings 29 of the piece 25 when these two pieces are superposed and placed in a desired relative orientation about the axis 33 of the thermocouple column and of the penetration. In order to assemble the two sections 25, 26 of the upper part 23 of the bearing unit which have corresponding centering elements, an annular mounting piece 30 formed from two half-rings is introduced laterally into the annular opening 28 of the section 25. The annular piece 30 has four tapped holes 35 arranged so as to come into alignment with the openings 29 and 32 in the assembled position of the upper part 23 of the bearing unit. Four screws 36, are engaged into the openings 32 and 29 placed to coincide and screwed into the tapped holes 35 of the piece 30. The screws 36 ensure the mounting of the two sections 25 and 26 and the clamping of the seal 31. As can be seen from FIGS. 2 and 3, a pressure plate 37 in the shape of a disc is introduced around the upper part of the thermocouple column 40, above the upper surface of the section 26. Four compression screws 41 are screwed inside tapped holes traversing the compression plate 37 in positions situated at 90.degree. from each other. The compression plate 37 also has four openings 42 placed at 90.degree. from each other about the axis 33 of the penetration and of the thermocouple column 40 enabling access to the heads of the screws 36 in order to tighten or loosen the screws 36. The upper part of the thermocouple column 40 has a throat 44 serving as a housing for a traction ring 45 formed from two half-rings which can be engaged laterally into the throat 44. The compression plate 37 has a central annular cavity which is capable of engaging with the traction ring 45 in the high position 37' of this plate shown in dot-dashed lines in FIG. 2. The screws 41 bear with their head 41a against the upper surface of the section 26 of the bearing unit. The screws 41 also have a profiled part 41b which enables them to be screwed or unscrewed by means of a hand tool such as a wrench. In FIG. 2, the thermocouple column 40 has been shown in its low position where its bearing and sealing area 47 with a slightly tapered shape is at a distance from the corresponding bearing shoulder 48 machined in the section 26 of the bearing unit. A sealing strip 47' with a slightly tapered shape rests against the bearing area 47. By screwing the screws 41 which bear with their head 41a against the upper part of the section 26, the compression plate 37 is caused to rise; this exerts a tensile force on the ring 45 so as to raise the thermocouple column 40 until the seal 47' comes into contact with the bearing shoulder 48 of the section 26. The seal 47' is then clamped at the desired pressure, for example by means of a torque wrench. The sealing strip 47' of the thermocouple column 40 is clamped at a first pressure, enabling leaktightness to be ensured in the region of the thermocouple column during the rise in pressure inside the vessel of the nuclear reactor. When the pressure of the cooling water of the nuclear reactor reaches 70 bars, the screws 41 are tightened again, inasmuch as the pressure inside the vessel of the nuclear reactor causes a further rise of the thermocouple column 40 and a further crushing of the seal 47'. The compression plate 37 of the traction unit of the thermocouple column 40 is then no longer in contact with the traction ring 45, and it is therefore necessary to perform a complementary screwing-in of the screws 41 in order to ensure the leaktight clamping of the thermocouple column in case the pressure tends to reduce inside the vessel of the reactor. It is also possible to exert a tensile force on the upper part of the thermocouple column 40, before the screws 41 are tightened, in order to ensure compression of the corresponding seal 47' during the operation of the reactor at the nominal power and to perform the tightening of the screws 41 in a single operation. FIG. 2A shows a compression screw 41 on a larger scale, with its head 41a resting against the upper surface of a cavity 49 machined on this upper surface. A washer 50 arranged about the screw head 41a has a part 50a which can be folded back and which locks the screw 41 against rotation, inside a cavity 51 machined on the upper surface of the section 26 of the upper part of the bearing unit. The compression plate 37 is traversed by openings 53 arranged exactly vertically above the cavities 51 for locking the screws 41 so as to enable the passage of a tool performing the folding back of the part 50a of the washer 50 into the cavity 51 in order to ensure the locking of the screw 41 against rotation. The device according to the invention enables the thermocouple column to be disassembled easily and quickly, for example prior to the opening of the head or for the purpose of changing the sealing strip 47' of the bearing area of the thermocouple column. When the vessel of the reactor is depressurized, the screws 41 are loosened so as to lower the pressure plate from its high position 37', to its low position 37 shown in solid lines in FIG. 2. Simultaneously, the thermocouple column returns to its low position, shown in FIG. 2, where the bearing area 47 of this column is separated from the bearing shoulder 48 of the section 26 by a certain distance (for example 17 mm). The screws 36 are then unscrewed by introducing a tool through the corresponding openings 42 of the plate 37. When the screws 36 are freed from the threaded holes 35 of the mounting piece 30, the upper section 26 of the end part of the bearing unit may be separated from the lower section 25 simply by lifting it, after the two-part traction ring 45 has been disassembled. There is thus no need to disassemble the bracket 22 and the lower section 25. In the event that the screw thread of at least one of the screws 36 is seized up inside the mounting piece 30, the screw 36 may be cut at the level of a space for the passage of a tool 34, provided between the pieces 25 and 26. The upper section 26 is then separated from the lower section 25 and the parts of the screws remaining in the piece 25 are removed by drilling. The two-part piece 30 may then be extracted from the housing 28 of the piece 25. When reassembling, only the piece 30 and the screws 36 need to be replaced by new elements. The invention therefore allows a thermocouple column to be disassembled quickly and easily, for example in order to have access to the sealing strip of this column. This disassembly may be performed by simple operations, even in the event of the assembly screws being seized up. Sections 25 and 26 of the upper part of the bearing unit 23 may have different configurations, the number of screws for carrying out the assembly of the two sections may be other than four (but no less than three) and, similarly, the number of compression screws 41 for the traction unit of the thermocouple column may be other than four but no less than three. The lower section of the bearing unit and the piece 21 for mounting on the follower may be produced in a single tubular piece, mounting of these two pieces by a bracket no longer being necessary for disassembling the thermocouple column. Lastly, the invention can be applied to any pressurized-water nuclear reactor having instrumentation columns penetrating the vessel head, it being possible for these instrumentation columns to be other than thermocouple columns. |
summary | ||
abstract | A soft X-ray microscope includes a table (10); a housing (20) installed to the upper side of the table (10) and having a partition (22); a light source chamber (30) installed lower than the partition (22) of the housing (20) to project a light to liquid jetted under a high pressure to generate plasma; a mirror chamber (40), installed above the partition (22) of the housing (20), in which first and second mirror (410 and 430) are respectively installed to upper and lower sides of a holder (420) for storing a living sample, the soft X-ray generated by the plasma generated in the light source chamber (30) illuminates the living sample, and the soft X-ray penetrated the living sample is amplified to obtain an image in an image capturing chamber; and an image capturing chamber (50) installed to the upper side of the housing (20) to amplify a light image signal amplified through the mirror chamber (40) and to capture the light image on an external screen to allow distinguishing the light image from exterior. |
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052456420 | summary | BACKGROUND OF THE INVENTION This invention relates to the operation and safety of water cooled nuclear fission reactors, and in particular to measures for reducing the hazards of possible exposure of operating and maintenance personnel to a source of radiation dispersed throughout the coolant water circulating system of such nuclear reactors. A significant potential hazard in water cooled nuclear fission reactors, such as boiling water reactors, is the spread of radioactive substances throughout the circulating system for the reactor coolant water. Operating personnel and maintenance workers can be subjected to radiation from such extensively dispersed radioactive substances within and about many areas or locations of the nuclear reactor plant. Increased radiation and its dispersion within a reactor plant presents both an elevated health hazard and economic liability due to restricted work time exposure for workers in such area of radiation presence. Cobalt, derived from a number of different alloys commonly employed in components of the reactor's mechanisms or structures, is subject to induced radioactivity, especially the cobalt-60 isotope. This radioactive cobalt-60 isotope, or ions or compounds thereof, can be carried in the circulating coolant water flowing through the coolant water circuit whereby the radioactive substances are spread and deposited throughout the cooling water circuit or primary loop system of the reactor plant. Such radioactive substances are prone to become taken up and incorporated into the normally occurring oxide films which form and progressively accumulate on the inner coolant water retaining structural surfaces that provide the reactor coolant water circuit. A number of proposals or potential solutions to this problem of dispersion of radioactive substances throughout the coolant water circuit or system and incorporation into the inherently produced oxide films forming over the surfaces of structures providing the coolant water circuit or system have been considered or made. One approach to controlling the potentially hazardous cobalt source of such radiation has been the application of zinc as disclosed in several U.S. patents, for example U.S. Pat. Nos. 4,756,874, issued Jul. 12, 1988 and 4,759,900, issued Jul. 26, 1988. The disclosure and contents of the aforesaid patents are incorporated herein by reference. SUMMARY OF THE INVENTION This invention comprises a method for controlling Co-60 isotope radiation contamination occurring on the surfaces of structures providing a coolant water circuit or system of a water cooled nuclear fission reactor plant. The method of this invention comprises the application of chemical measures or agents and physical conditions which impede buildup of the Co-60 isotope on the surface of metal components or structures that provide the primary coolant water system for the typical circulation of coolant water in a water cooled nuclear fission reactor. |
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056152396 | summary | FIELD OF THE INVENTION This invention relates generally to nuclear reactors and, more particularly, to apparatus for enabling detection of core differential pressure and injection of a neutron absorbent into a core of a nuclear reactor. BACKGROUND OF THE INVENTION Known apparatus for enabling detection of core differential pressure and injection of a neutron absorbent into a core of a nuclear reactor generally includes two separate tubes, or conduits, constructed of stainless steel having a high carbon content. In one particular embodiment, one tube has a smaller diameter than the other tube, and the smaller diameter tube is positioned within the larger diameter tube to form a tube assembly. The tube assembly extends in the reactor pressure vessel (RPV), from an opening formed in the RPV wall to a socket. A first tube extends from the socket to an elevation within the pressure vessel above the core plate, and the open end of the first tube within the pressure vessel is exposed to pressures at the elevation above the core plate. The first tube is in flow communication with the larger diameter tube. A second tube extends from the socket and to an elevation below the core plate. The open end of the second tube within the pressure vessel is exposed to pressures at the elevation below the core plate. The second tube is in flow communication with the smaller diameter tube. In the one embodiment, at the exterior of the vessel wall at the location of the opening, a nozzle extends from the wall. The nozzle has a bore with a diameter greater than the outer diameter of the smaller diameter tube. The opening in the vessel wall has a diameter about substantially equal to the diameter of the bore. The smaller diameter tube extends through the opening in the wall and into the nozzle bore. A first port of the nozzle is in flow communication with the channel of the smaller diameter tube and a second port of the nozzle is in flow communication with the larger diameter tube. Pressure meters may be attached to the first and second ports of the nozzle. In operation, the pressures within the pressure vessel at the elevations of the open ends of the tubes are communicated through the tubes to the pressure meters coupled to the nozzle ports. Utilizing the pressure readings from the respective pressure meters, a core differential pressure may be determined. Core differential pressure, as is well known, may be utilized to control reactor operations. In addition, in the event that a liquid neutron absorbent must be injected into the reactor pressure vessel, the absorbent may be injected into the smaller diameter tube at the first nozzle port. The liquid neutron absorbent will flow through the smaller diameter tube and into the pressure vessel from the open end of such tube. As a result, the neutron absorbent will be injected into the reactor pressure vessel at an elevation below the core plate, which generally is a desirable location for injection of such an absorbent. With respect to known differential pressure and standby liquid control line apparatus, creviced weld connections typically are used to weld the stainless steel tubes to support brackets. In addition, sockets and other connectors may be used in order to position the tubes in the desired locations and elevations within the core, and the tubes typically are welded to such sockets and connectors. The use of such welds, in combination with the high carbon content stainless steel tube material and exposure to the reactor environment, may result in intergranular stress corrosion cracking (IGSCC) of the tubes. Of course, such IGSCC could lead to a failure of one or both of the tubes. Failure of the inner, smaller diameter, tube of the tube assembly may result in the loss of the ability to determine the core differential pressure. Failure of the outer, larger diameter, tube of the tube assembly could possibly result in an inaccurate core differential pressure reading, particularly if the discharge water flow from a jet pump impinges on the failed region of the outer robe. An inaccurate core differential pressure reading, or total loss of the ability to obtain such reading, may adversely affect reactor operation, including even possibly requiring shutting down the reactor to perform repairs. It would therefore be desirable to provide a core differential pressure and neutron absorbent injection apparatus which reduces the possibility for IGSCC, thereby reducing the possibility for failure of the apparatus. In addition, it would be desirable to provide such an apparatus which can be utilized to replace existing core differential pressure and neutron absorbent injection apparatus presently installed in nuclear reactors in the event that a failure is ever detected or suspected. SUMMARY OF THE INVENTION These and other objects are attained by a core differential pressure and liquid control line apparatus which includes, in one embodiment, a tube assembly having a first portion configured to be positioned within and extend through an opening in the pressure vessel wall and into the bore of the nozzle. The first tube portion has a diameter less than the diameter of the nozzle bore and less than the diameter of the opening in pressure vessel wall. As a result, an annulus in flow communication with the nozzle bore is formed between the first tube portion and the pressure vessel wall opening. The tube assembly further includes a second, L-shaped, tube portion. A first shrink coupling couples one end of the first tube portion to one end of the second tube portion. The shrink coupling may be a Tinel type coupling, which is generally known in the art. The assembly also includes a third tube portion having its open end configured to be positioned at an elevation above the core plate. Particularly, the third tube portion extends through an opening in the core plate so that the open end of the third tube portion is at an elevation above the core plate. A second shrink coupling couples the other end of the third tube portion to one end of the second tube portion. The nozzle, which may be integrally formed with vessel wall, includes a first port in flow communication with the tube assembly. The nozzle also includes a second port in flow communication with the above described annulus. In operation, and to determine core differential pressure, the pressure at an elevation above core plate is communicated through the tube assembly to the first port of the nozzle. The pressure below the core plate is communicated through the annulus to the second port in the nozzle. Using such pressures, the core differential pressure can be determined. To inject a neutron absorbent into the vessel below the core plate, such absorbent may be injected through the second port of the nozzle and into the annulus. Such absorbent will flow through the annulus and will be injected into the core at the location where the annulus opens into the interior of the pressure vessel. The neutron absorbent may, for example, be liquid pentaborate. The likelihood for failures is believed to be reduced with the apparatus described above as compared to the known apparatus described hereinbefore. For example, the number of welds is significantly reduced when the above described apparatus is used as compared to the number of welds required with known apparatus. In addition, with the above described apparatus, a tube assembly having a smaller diameter tube inserted within a larger diameter tube is eliminated. Elimination of this tube within a tube configuration is believed to simplify installation and reduce costs. Further, the above described apparatus can be used to replace the known apparatus in the event that if a failure is detected in such known apparatus. |
056335083 | summary | OBJECT OF THE INVENTION The present invention relates to radiation attenuation shielding, and in particular to providing a low maintenance, high durability shield for shielding nuclear waste. BACKGROUND OF THE INVENTION Nuclear energy has been used as a power source for approximately the last 50 years. The nuclear reactors providing that power have been producing waste since that time. That waste has created significant problems. There are approximately 110 active nuclear reactors in the United States, each producing an average of 20 metric tons of nuclear waste. A nuclear power facility ordinarily stores this waste in an on-site indoor water pool. However, these facilities are quickly reaching their storage capacity. By 1998, 32 nuclear reactors will have no more indoor water pool storage capacity. To address this problem, the federal government in 1982 enacted the Nuclear Waste Policy Act which mandated that the federal government accept nuclear waste beginning Jan. 31, 1998. As of today, the federal government does not have a concise definitive plan in place to deal with the nuclear waste it will receive. Indeed, the proposed federal repository site at Yucca Mountain is years behind schedule. Further, because of earthquakes and transportation problems there is no guarantee that the Yucca Mountain facility will ever be completed. Adding to the problem of excess nuclear waste is the fact that many nuclear power plants are likely to close in the next two decades. When these reactors are closed, the waste at those power plants must also be handled. The disposal of nuclear waste raises serious questions regarding public safety. The recognized harm (for example, cancer) caused by high levels of radiation exposure have caused a great deal of public concern about radiation from nuclear power plants and about radiation generally. This public concern and other concerns have made it difficult for public utilities to create permanent nuclear waste facilities. For example, permanent facilities may involve storing the nuclear waste below ground level which raises issues related to underground water contamination. Underground facilities are also difficult to monitor and maintain and make retrieving the waste for reprocessing difficult. To address these problems, many utilities are pressing the federal government to license rugged above-ground containers for either temporary or permanent storage. Rugged above-ground containers are called dry casks, and to date, are only temporary in nature. Dry casks are ordinarily constructed from concrete and steel and are placed on a concrete base. The nuclear waste is then placed in the cask. An example of one such cask is disclosed in U.S. Pat. No. 4,527,066 to Dyek entitled "CONCRETE SHIELDING HOUSING FOR RECEIVING AND STORING A NUCLEAR FUEL ELEMENT CONTAINER." Other casks are available in the prior art as well. Above-ground storage in casks raise significant public concerns as well. The public concerns are exacerbated by the fact that facilities which were designed to be temporary are quickly becoming considered to be permanent. The concerns include the possible discontinuance of maintenance, sabotage, and difficulties in transportation. Maintenance of these above-ground casks is critical because of their concrete construction. With proper maintenance, scientists have speculated that concrete used in nuclear applications may have a service life of up to 60 years. See Hookham & Bailey, Long Term Durability Considerations for Nuclear Power Plant Structures 1990. However, if a facility is permanent, 60 years is a very short time as compared to the long-term toxicity of nuclear waste. Problems associated with concrete structures include cracking and deterioration. These problems are caused in part by freeze/thaw cycling of water in addition to the additional corrosive affects caused by acid rain. As concluded by Hookham and Bailey, without proper maintenance these environmental factors will eventually render a concrete structure unsafe. When these problems occur, the concrete must be repaired and/or replaced. To properly perform maintenance, the dry cask must be continually monitored so that cracks and erosion can be repaired immediately. The process of continually monitoring and repairing is extremely costly. As budgets are cut back, additional concerns arise because these concrete structures may fall out of repair thereby shorting their useful life. If maintenance is discontinued, the structure would erode thereby compromising its integrity. Because the potential harm which would be caused by a nuclear radiation leak is so great, facilities must protect against sabotage or attack. Sabotage may take the form of launched projectiles, or direct attack by suicide or truck bombers. Thus, storage facilities must provide a high degree of security. Safe transportation of nuclear waste is also an issue which must be addressed. The primary issue related to transportation is the public's unwillingness to allow high sources of radiation traveling past homes and exposing people to the radiation. To avoid these problems, nuclear power plants prefer to store waste on site. Therefore, a need has arisen to prevent the potential harm to the public should maintenance of these temporary facilities cease, or should the temporary casks be compromised. A further need has arisen to make the temporary sites which are becoming permanent safer. SUMMARY OF THE INVENTION The present invention provides for a method and construction to shield radiation. The method includes the steps of surrounding a source of radiation with a granite wall. The wall of the present invention includes a construction not heretofore used with granite. That construction shields a source of radiation being positioned on ground level. The secondary attenuation shield includes a plurality of granite foundation blocks where the granite foundation blocks have a top surface including a first mating portion. The foundation blocks are positioned partially below ground level and are positioned to form a wall. A plurality of block sections having a top and bottom surface where the bottom surface includes a second mating portion cooperative in interfacing with the first mating portion of the foundation blocks are positioned on the foundation blocks so that the foundation blocks and the block sections obstruct the source of radiation. In the preferred embodiment, horizontally adjacent blocks also include cooperative mating portions to interlock horizontally adjacent blocks. |
abstract | A method is described for producing a micro-gripper, which comprises a base body and a gripping body connected integrally to the base body, which projects beyond the base body and provides a receptacle slot on a free end area in such a way that a micrometer-scale or sub-micrometer-scale object may be clamped in the receptacle slot for gripping and holding, as well as a micro-gripper according to the species. |
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description | The present invention relates to an alloy technology, and in particular, to a radiation resistant high-entropy alloy and a preparation method thereof. A structural material used in the nuclear power plant is usually required to have good comprehensive performance, for example, excellent mechanical properties and radiation resistance. The radiation resistance of fuel cladding materials used in nuclear reactors is particularly important. High-dose neutron irradiation produced by nuclear reactions results in vacancies, dislocation, element segregation in a material, and aggregation of H and He atoms produced by transmutation reactions can further cause material swelling, hardening, embrittlement, and even lead to a material failure. At present, fuel cladding materials and key metal components used in the nuclear power plant all suffer lattice expansion and radiation hardening damage under irradiation, which accelerates the metal failure process. An objective of the present invention is to propose a radiation resistant high-entropy alloy in view of the foregoing problem that existing conventional alloy has poor irradiation performance. The irradiation performance of the alloy is far better than that of the conventional alloy and has good mechanical properties in an as-cast condition. To achieve the above objective, the present invention adopts the following technical solution: A radiation resistant high-entropy alloy is prepared, where its general formula is TiZrHfVMoTaxNby, in which 0.05≤x≤0.25, 0.05≤y≤0.5, and x and y are molar ratios. Further, in the general formula TiZrHfVMoTaxNby, 0.1≤x≤0.2, and 0.1≤y≤0.2. Another objective of the present invention is to provide a preparation method of a radiation resistant high-entropy alloy, including the following steps: stacking Ti, Zr, Hf, V, Mo, Ta, and Nb in order, and conducting vacuum levitation induction melting or vacuum arc melting to obtain the radiation resistant high-entropy alloy. Further, the melting process includes the following steps: during fusion alloying, placing Ti, Zr, Ta, and V bottommost, and placing Nb, Mo, and Hf uppermost. Further, in the melting process, vacuumizing is conducted to reach 5×10−3 to 3×10−3 Pa, and back-filing with argon gas to 0.03 to 0.05 MPa is conducted. Further, alloy ingots are turned and melted five to seven times during vacuum arc melting, to ensure composition uniformity. Further, alloy ingots are turned and melted four to six times during vacuum levitation induction melting, to ensure composition uniformity. Further, Ti, Zr, Hf, V, Ta, Nb, and Mo are all industrial grade pure raw materials with a purity of over 99.5 wt %. Another objective of the present invention is to provide an application of the radiation resistant high-entropy alloy in fuel cladding materials in the nuclear power plant reactor or key metal components of the nuclear power plant. The radiation resistant high-entropy alloy in the present invention has a scientific and reasonable formula and an efficient preparation method. Compared with the prior art, the radiation resistant hardening alloy of the present invention has the following advantages: 1. The radiation resistant high-entropy alloy in the present invention contains specific element selection and composition, where the elements Mo, Nb, Ta, and V can improve the high-temperature properties of the alloy; the element Ti can improve the corrosion resistance of the alloy; the element Zr has excellent neutron penetrability; and the element Hf can improve the service temperature of the alloy. 2. The alloy has excellent mechanical properties in an as-cast condition, the ingots obtained by vacuum levitation induction melting or vacuum arc melting are of a single-phase BCC structure, and do not need to be subjected to any heat treatment process and deformation strengthening process. At room temperature, the engineering compressive yield strength of the alloy is up to 1.1 Gpa, and a compression rate and elongation thereof are greater than 50%. 3. The radiation resistant high-entropy alloy in the present invention has excellent ion-irradiation hardening resistance, and it is detected by an ion irradiation experiment that almost no irradiation hardening occurs in the alloy in the present invention. 4. The density of bubbles produced after helium ion irradiation on the high-entropy alloy in the present invention is an order of magnitude lower than that of conventional alloy. 5. After helium ion irradiation, the lattice constant of the alloy in the present invention decreases abnormally, while this is quite different from a case in which lattices of the conventional alloy expands and the lattice constant the conventional alloy increases after irradiation. 6. Elements in the radiation resistant high-entropy alloy in the present invention are easy to obtain, and the preparation method of the alloy is efficient, and only conventional vacuum arc smelting or vacuum electromagnetic suspension induction smelting needs to be used. The alloy can achieve excellent mechanical properties without being subject to heat treatment and a subsequent complex processing technology. To sum up, the radiation resistant high-entropy alloy in the present invention has excellent performance: The lattice constant of the high-entropy alloy decreases abnormally after irradiation, the high-entropy alloy does not suffer hardening damage after irradiation, the density of helium bubbles of the high-entropy alloy is far lower than that of the conventional alloy. Therefore, the high-entropy alloy has a broad application prospect in nuclear industry. The present invention is further described below with reference to the following embodiments: This embodiment discloses a radiation resistant high-entropy Ti—Zf—Hf—V—Mo—Nb—Ta alloy, where its general formula is TiZrHfVMoNb0.1Ta0.1. A specific preparation method of TiZrHfVMoNb0.1Ta0.1 includes: stacking raw materials Ti, Zr, Hf, V, Mo, Nb, and Ta in order according to a molar ratio shown by the general formula, where Ti, Zr, Hf, V, Mo, Nb, and Ta are all industrial grade pure raw materials with a purity of over 99.5 wt %; conducting vacuum levitation induction melting or vacuum arc melting; during fusion alloying, placing Ti, Zr, V, and Ta bottommost, and placing Nb, Mo, and Hf uppermost; and conducting vacuumizing to reach 5×10−3 Pa, and back-filing with argon gas to 0.05 MPa. Each alloy ingot is melted at least five times during arc melting, to ensure composition uniformity. FIG. 1 shows relationships between average nano-indentation hardness and indentation depths at 600° C. before and after irradiation according to Embodiment 1, and shows that a radiation hardening damage behavior of conventional alloy does not occur on the alloy after irradiation. FIG. 2 shows sizes and density of helium bubbles at 600° C. under different doses of irradiation according to Embodiment 1, and shows that the density of helium bubbles of the alloy after irradiation is lower than that of conventional alloy. FIG. 3 shows XRD diffraction analysis patterns of TiZrHfVMoNb0.1Ta0.1 before and after irradiation experiments according to this embodiment. FIG. 4 shows a variation trend of a lattice constant of radiation resistant high-entropy alloy as an irradiation dose changes according to this embodiment. FIG. 3 and FIG. 4 show that the lattice constant of the alloy after irradiation decreases, while the lattice constant of conventional alloy after irradiation increases, and therefore an irradiation behavior of the alloy is quite different from that of the conventional alloy. An alloy irradiation experiment process is as follows: First, a sample of the irradiation resistant high-entropy alloy in this embodiment is cut into slices with a thickness of 1 mm (10 mm×6.5 mm) and is subjected to double-sided fine grinding and single-side polishing. Then, a test sample is placed in an aqueous solution containing 50% H2SO4 and 40% glycerol for electropolishing at a voltage of 36V for 10 seconds, and is subjected to ultrasonic cleaning with acetone, anhydrous ethanol, and deionized water. An irradiation experiment is conducted on the prepared sample at 600° C., where helium ion irradiation with energy of 3 MeV is adopted, and irradiation doses are 5×1015, 1×1016, and 3×1016 ions/cm2, respectively. FIG. 5 shows a compression curve of radiation resistant high-entropy alloy at room temperature according to Embodiment 1, and shows excellent mechanical properties of the alloy. This embodiment discloses a radiation resistant high-entropy alloy, where its general formula is TiZrHfVMoNb0.2Ta0.2. A preparation method of the radiation resistant high-entropy alloy in this embodiment is the same as that in Embodiment 1. It is detected that TiZrHfVMoNb0.2Ta0.2 in this embodiment and TiZrHfVMoNb0.1Ta0.1 in Embodiment 1 both have excellent mechanical properties and radiation resistance, and can be widely applied to fuel cladding materials in the nuclear power plant reactor or key metal components of the nuclear power plant. The present invention is not limited to description of the radiation resistant high-entropy alloy according to either of claims 1 and 2, where changes in x and y and modifications made to the preparation method all fall within the protection scope of the present invention. Finally, it should be noted that the foregoing embodiments are merely intended for describing the technical solutions of the present invention, but not for limiting the present invention. Although the present invention is described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some or all technical features thereof, without departing from the scope of the technical solutions of the embodiments of the present invention. |
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abstract | A process for the electrochemical dissolution of a metallic structure having a plurality of electrically conducting components comprises utilising the structure as a sacrificial electrode in an electrochemical cell so as to dissolve at least part of the strcuture. The process is characterised in that, prior to the use of the structure as a sacrificial electrode, molten metal is allowed to solidify about the structure so as electrically to connect together the components. |
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description | This application claims priority from U.S. Provisional Patent Application No. 61/843,092 filed on Jul. 5, 2013, U.S. Provisional Patent Application No. 61/900,455, filed on Nov. 6, 2013, and U.S. Provisional Application No. 61/946,074 filed on Feb. 28, 2014, all of which are relied upon and incorporated herein in their entirety by reference. Technical Field The invention relates to the field of charged particle radiation therapy. More specifically, the invention relates to the field of spot scanned ion therapy. More specifically, the invention relates to a charged particle system for the irradiation of a target of tissues that may be cancerous. The invention also relates to a method for irradiation of a target with a particle pencil beam. Related Art In charged particle radiation therapy, a number of irradiation techniques are known today. The most common form of radiation therapy currently is photon therapy. However, photon therapy comes with several complications. For one, when using photon therapy, the applied photon beam passes through a targeted tumor and exits the patient through healthy tissue distal to the tumor. The exiting of the photon beam or dose through the healthy tissue increases the difficulty in preventing radiation damage to the healthy tissue. The radiation damage caused by the exiting dose through healthy tissue also is a limiting factor when designing an effective tumor treatment plan. Ion therapy, which includes proton therapy and argon, carbon, helium and iron ion therapy, amongst others, provides some advantages over photon therapy. For one, ion therapy can result in a lower total radiation energy, termed integral dose, being deposited in a patient for a given tumor dose in relation to photon therapy. The integral dose reduction is significant because it reduces the probability of stochastic effects, i.e., patients developing secondary malignant neoplasms following irradiation of non-tumor tissue. Young patients with high probabilities of long term survival have a higher probability of developing secondary malignant neoplasms than older patients since the probability of development is related to the time elapsed post-therapy. Thus, the reduction of radiotherapy doses to non-tumor tissues in children is a particularly important advantage of ion therapy. The integral dose reduction for proton therapy relative to photon therapy has been quantified for parameningeal paraorbital rhabdomyosarcoma and spinal neuraxis in children with medulloblastoma, resulting in a reduction in the probability of radiation-induced secondary malignancies by factors of ≧2 and 8-15, respectively. Proton therapy is expected to reduce the probability of occurrence of secondary malignant neoplasms in adults as well. For example, the probability of a secondary malignant neoplasm is decreased by 26% to 39% for prostate patients receiving proton therapy versus intensity modulated photon therapy. The second clinical advantage of ion therapy over photon therapy is that radiation dose to healthy tissues is reduced sufficiently such that deterministic effects (i.e., complications whose magnitude is related to the radiation dose delivered) may be reduced relative to photon therapy. Examples of deterministic effects are skin erythema and xerostomia. The reduction in deterministic effects has been demonstrated in multiple studies in which tumor dose conformity has been shown to be comparable to that of photon therapy, but healthy tissue sparing for proton therapy is superior. Healthy tissues associated with multiple tumor sites have been shown to be spared of more dose by proton than photon therapy, including paraspinal sarcomas, head-and-neck malignancies, meningioma, cervix, medulloblastoma, paranasal sinus, and prostate. Spot scanning (SS), an advanced form of ion therapy delivery, has some advantages over traditional ion therapy. Conventional proton therapy beams for treating patients are typically generated using either passive scattering or uniform dynamic scanning. With passive scattering, one or more range compensators and a range modulator are used to spread a proton pencil beam into a beam that produces a spatially uniform dose distribution laterally and in depth. The range modulator may be a spinning propeller, wedge, or ridge filter, and produces a spread out Bragg peak (SOBP). The field is shaped laterally to the central beam axis with a custom-designed aperture, block, or multi-leaf collimator (MLC), and is shaped in depth to match the distal edge of the treatment volume using a patient-specific compensator. Single and double scattering systems exist, the latter typically providing larger regions of uniform dose than the former. Uniform dynamic scanning uses a magnetically scanned pencil beam and dynamic energy modulation to generate proton fields which, when averaged over time, have a uniform intensity in space. Field shapes are defined by apertures or blocks in a similar manner as with passive scattering. In SS ion therapy, the treatments are delivered with pencil beams, usually produced by a beam generator (e.g., a cyclotron), that are magnetically scanned to deliver dose in the target. The size of the pencil beam in SS is generally much smaller than uniform dynamic scanning. The use of pencil beams allows the beam shape to be defined using the scanning magnets rather than an aperture. This pencil beam spot scanning technique represents an advance over the single or double scattering technique, wherein a scattered broad beam is shaped by a patient specific collimator or aperture, so that it corresponds to the shape of the target to be treated. As a result, the lateral falloff of dose distributions delivered with spot scanning without an aperture is dependent on the size of the incoming pencil beam and interactions of the beam in the patient. Additionally, in SS, the beam intensity, when averaged over time, is not required to be uniform. This allows intensity modulated proton therapy (IMPT) to be delivered. With IMPT, several fields can be optimized simultaneously such that the sum of all fields will yield a uniform dose to the target while minimizing the dose to surrounding normal structures. However, proton SS systems have low-energy (≦160 MeV) lateral beam intensity profiles that are less sharp than those of photon therapy systems, thus more of the radiation dose is typically deposited lateral to the tumor for low-energy treatments (i.e., the lateral penumbra of a pencil beam is larger than the penumbra of a collimated broad beam). As a result, proton SS is superior to photon therapy in integral dose delivered and inferior to conventional proton therapy in dose delivered lateral to the tumor for low-energy treatments. The degree of inferiority imposed by the latter property is dependent upon the energy of the ion beam, as low energy beams tend to be broader than higher energy beams due to the physical properties of the system used to transport the ion beam from the accelerator to the patient. Therefore, attempts have been made to reduce the size of the penumbra. For example, a device to reduce the penumbra of a pencil beam spot scanning is disclosed in U.S. Patent Application Publication No. US 2013/0043408. However, the device consists of a patient specific collimator or aperture to be inserted in the beam line. A patient specific collimator means an individual collimator for each patient has to be constructed, adding to the overall cost of treatment. MLCs have been used with pencil beam spot scanning, but MLCs are complex to develop and require a lot of space such that MLCs are prevented from being positioned in a very close proximity to the patient. In addition, the weight of such an MLC requires a strong mechanical structure to support it. Therefore, there is a need for a system and method for the application of SS ion therapy that reduces the radiation dose delivered to healthy tissues outside the target boundary. In addition, there is a need for a system that allows the application of SS ion therapy at areas of a patient in which access is difficult (e.g., areas around the neck and head due to the location of the patient's shoulders). There is also a need for a simplified and cost effective device for reducing the lateral penumbra of a beam from a SS system. It is an object of the invention to provide a particle radiation therapy system for irradiation of a target through spot scanning that reduces the delivery of dose outside the target boundary. A further objective is to provide a compact system for delivery of spot scanning (SS) therapy to difficult areas of a patient. The invention is a system and process for improving SS ion therapy by reducing the delivery of the SS ion therapy dose outside of the target boundary. In an exemplary aspect, the invention improves SS ion therapy of cancerous tumors by reducing the radiation dose delivered to healthy tissues lateral to the target. In an aspect, the SS ion therapy is delivered by an ion therapy source. In an exemplary aspect, the ion therapy source produces a particle pencil beam. In an aspect, the particle pencil beam can be characterized by a phase space. In an aspect, the ion therapy source of the system comprises a beam generator for generating the pencil beam. In an aspect, the ion therapy source of the system further comprises a spot scanning system configured for performing a number of spot irradiations by sequentially directing and delivering said pencil beam to a number of spot locations in said target. In such aspects, the spot scanning system can comprise one or more scanning magnets. In an aspect, the system delivers Dynamically-Trimmed Spot Scanning (DTSS). In such aspects, the system includes an irradiation controller for controlling the delivery of a dose during said spot irradiations and a beam intercepting system for intercepting a portion of the pencil beam during one or more of the number of spot irradiations so as to modify the phase space of the pencil beam. The beam intercepting system of DTSS system can include a dynamic trimming collimator (DTC) that is configured to intercept a portion of the pencil beam that shapes the particle pencil beam. In such aspects, the DTC is located downstream of the one or more scanning magnets of the spot scanning system. In an aspect, the DTC can comprise at least one trimmer configured to intercept the beam. In an aspect, the beam intercepting element can comprise a thickness and shape adapted for changing the phase space of the pencil beam. Depending on the thickness and shape of the at least one trimmer, the transverse beam phase shape and/or longitudinal beam shape can be changed. In an aspect, the thickness and the shape of the at least one trimmer is configured to block a portion of the pencil beam so as to change the transverse beam size of the pencil beam. In another aspect, the thickness and shape of the at least one trimmer can be configured to modify the energy and/or energy spread of the pencil beam. In another aspect, the thickness and the shape of the at least one trimmer is configured to modify the energy and/or energy spread of the pencil beam. In an exemplary aspect, the thickness and shape of the at least one trimmer is configured to both changes the transverse beam size and the energy and/or energy spread of the pencil beam. In an aspect, the at least one trimmer can be configured to move along a first axis of motion and a second axis of motion to intercept a portion of the pencil beam. In an aspect, the trimmer can be configured to move across axes that are perpendicular to the central axis of the pencil beam. In an aspect, the trimmer can be configured to move along an axis that is parallel to the central axis of the pencil beam. In an aspect, the movement of the trimmer can be done through a driving mechanism configured to support the at least one trimmer. In an aspect, the at least one trimmer can comprise a plurality of trimmers. In an aspect, each of the trimmers is mounted to a driving mechanism. During the ion therapy, the trimmers can move in synchrony with the scanned ion beam. In an aspect, the DTC can utilize a plurality of trimmers that are configured to rapidly move along a path perpendicular to the axis of a pencil beam. In an aspect, the DTC can include a driving controller for controlling the driving mechanism of each trimmer to place the trimmer at a pre-defined position for the interception of the pencil beam. The pre-defined positions can correspond to positions for intercepting the beam while performing a spot irradiation. In an aspect, the driving controller can include a control interface for receiving parameters for the positioning of the trimmer along the first axis and second axis of motion. In an exemplary aspect, the parameters can include at least first and second parameters for the first and second axes. In an aspect, the DTSS can include a position planning controller configured for defining, for one or more of the spot irradiations, corresponding pre-defined positions for positioning the at least one trimmer. In an aspect, the first axis and the second axis may correspond to two non-parallel translation axes. In such aspects, the first parameter and the second parameter may correspond to coordinate positions along the translation axes. In another aspect, the first axis and the second axis may correspond to a translation axis and a rotation axis. In such an aspect, the rotation axis is preferably essentially perpendicular to the translation axis. Further, in such an aspect, the first parameter corresponds to a coordinate position along the translation axis and the second parameter corresponds to a rotation angle with respect to the rotation axis. It is an advantage of embodiments of the present invention that by using a first and second axes of motion allows for the same at least one trimmer to be moved to various pre-defined positions for intercepting the pencil beam. The interception of the pencil beam can be defined by defining the exact position of the trimmer within pencil beam. In an aspect, the DTC can be configured to be small enough to position the trimmers within several centimeters of the patient's skin, even when treating sites such as the head and neck. In an aspect, the ability to be able to position the trimmers in various positions multiple times allows for a minimal number of trimmers to be used, reducing the overall size of the DTC. In another aspect, the trimmer rods can be configured to partially block the ion beam, which can increase the sharpness of the beam. The increase in beam sharpness results in a concurrent decrease in the radiation dose that spills laterally out of the target tissue and into adjacent normal tissue. Such an improvement is useful in the field of radiation oncology, as DTSS is a solution to the well-known problem that shallowly-penetrating ion beams, especially proton beams, deliver lateral radiation doses that are inferior to those of photon therapy. In an aspect, the driving controller can be configured to interface with an irradiation controller for receiving a signal indicating a beam on/beam off status information and whereby the driving controller is configured to allow motion of the trimmer only when the beam is in an off status. In other words, the trimmer is only moved in between spot irradiations and not during spot irradiations. In such aspects, a simplified irradiation control system can be utilized. These and other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention. Both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute part of this specification, illustrate several embodiments of the invention, and together with the description serve to explain the principles of the invention. In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises,” means “including but not limited to,” and is not intended to exclude, for example, other additives, components, integers or steps. “Exemplary” means “an example of” and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes. Disclosed are components that can be used to perform the disclosed methods and systems. These and other components are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these components are disclosed that while specific reference of each various individual and collective combinations and permutation of these may not be explicitly disclosed, each is specifically contemplated and described herein, for all methods and systems. This applies to all aspects of this application including, but not limited to, steps in disclosed methods. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the disclosed methods. As will be appreciated by one skilled in the art, aspects of the current invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. In an aspect, the current invention can include a combination of physical components configured to perform certain steps and functions (e.g., generating ion beams, moving trimmers configured to shape ion beams, etc.) that are controlled by a combination of hardware and software components. Furthermore, components of the methods and systems may take the form of a computer program product on a computer-readable storage medium having computer-readable program instructions (e.g., computer software) embodied in the storage medium. Any suitable computer-readable storage medium may be utilized including hard disks, CD-ROMs, optical storage devices, or magnetic storage devices. Further, components and methods utilized by the present invention as described below can be performed in a program environment, which may incorporate a general-purpose computer or a special purpose device, such as a hardware appliance, controller, or hand-held computer. In addition, the techniques of the components described herein can be implemented using a variety of technologies known in the art. For example, the methods may be implemented in software executing on a computer system, or implemented in hardware utilizing either a combination of microprocessors or other specially designed application specific integrated circuits, programmable logic devices, or various combinations thereof. Some aspects of the methods and systems are described below with reference to block diagrams and flowchart illustrations of methods, systems, apparatuses and computer program products. It will be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, respectively, can be implemented by computer program instructions. These computer program instructions may be loaded onto a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions which execute on the computer or other programmable data processing apparatus create a means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including computer readable instructions for implementing the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Accordingly, blocks of the block diagrams and flowchart illustrations support combinations of means for performing the specified functions, combinations of steps for performing the specified functions, and program instruction means for performing the specified functions. It will also be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, can be implemented by special purpose hardware-based computer systems that perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. As illustrated in FIGS. 1-27, aspects of the present invention are directed at a charged particle radiation system 10. In an exemplary aspect, the charged particle radiation system 10 comprises a spot scanning (SS) ion therapy system 10 configured to apply ion therapy 20 on at least one target 30 with a reduction of the radiation outside of the target zone. In an exemplary aspect, the SS ion therapy system 10 is configured to apply the ion therapy 20 on cancerous targets 30 while reducing the dose delivered to healthy tissues lateral to the target. In an aspect, the SS ion therapy system 10 is configured to deliver Dynamically-Trimmed Spot Scanning (DTSS). The SS ion therapy system 10 utilizes a dynamic trimming collimator (DTC) 40 to apply the ion beam 20 from an ion therapy source 50 in a narrowly focused manner. During DTSS delivery, a narrow ion beam 20 with a given energy, which determines the penetration depth, is magnetically scanned by components of the ion therapy source 50 across a patient's target volume. The scanning pattern is often in a line-by-line raster pattern, but can be arbitrarily defined to deviate from a raster pattern. However, since the ion therapy source 50 cannot perfectly focus the beam 20 on a target 30, when the beam 20 is placed near the edge of the target, some radiation dose spills outside of the target and into normal tissue. The DTC 40 assists the ion therapy source 20 by limiting such spillage of radiation. In other words, the DTC 40 enables the delivery of DTSS radiation dose distributions that spare normal tissue adjacent to tumors/targets 30 more effectively than the dose distributions generated by conventional SS. A system controller 60 can control the operation of the DTC 40 and the ion therapy source 50, as shown in FIGS. 1 and 2, discussed in more detail below. As shown in FIG. 2, the ion therapy source 50 of the SS ion therapy system 10 comprises a beam generator 52 for generating the ion beam 20 for use with spot scanning. In an aspect, the beam generator 52 is configured to generate a proton particle pencil beam 20. The ion particle pencil beam 20 can have a wide range of energy. As known, the energy of the particle pencil beam 20 can determine the penetration depth of the beam 20 within the target 30, discussed in detail below. In an aspect, an irradiation controller 62 can be configured to control the delivery of a radiation dose to the various spot locations of the target 30. In an aspect, the irradiation controller 62 can take the form of a module 62 within the system controller 60 of the SS ion therapy system 10. In an aspect, the particle pencil beam 20 is characterized by a beam phase space. The beam phase space can be defined at given positions along a traveling path of the beam. As well known in particle beam optics, the beam phase space of an energetic particle beam is defined through the position distribution and momentum distribution of the particles within the beam. In general, the phase space can be divided in a transverse beam phase space and a longitudinal beam phase space. The transverse phase space defines the transverse extension of the beam 20 with respect to a central travelling direction, or central axis 22, of the beam. A physical quantity that can for example be measured is the transverse beam size. In the longitudinal direction, perpendicular to the transverse direction, the longitudinal phase space can be defined by the averaged particle energy or averaged momentum in the beam travelling direction and by the associated energy spread or momentum spread. In an aspect, the ion therapy source 50 further includes a spot scanning system 54 configured for performing a number of spot irradiations by sequentially directing and delivering the ion beam 20 to a number of spot locations in the target 30. In an aspect, the spot scanning system 54 includes means for scanning the pencil beam 20 over the target 30. In an aspect, the spot scanning system 54 includes one or more electromagnets 56 designed for scanning the particle beam 20 over the target 30. In an aspect, the at least one electromagnet 56 comprises two electromagnets 56 for scanning in an X and Y directions, respectively. In another aspect, a single scanning magnet 56 configured to scan in the X and Y directions can be used. In an additional aspect, the scanning magnets can be superconducting. A spot scanning (SS) system controller 64 can be utilized to control the spot scanning system 54, including the positioning of the scanning magnets. In an aspect, the SS system controller 64 can take the form of a module within the system controller 60. In another aspect, the irradiation controller 62 can be configured to control the operations of the spot scanning system 54 and the SS system controller 64. As illustrated in FIGS. 1-2, the SS ion therapy system 10 of the present invention includes a dynamic trimmer collimator (DTC) 40. The DTC 40 is configured to intercept a portion of the pencil beam 20 during a spot irradiation so as to modify the phase space of the pencil beam 20. In an aspect, the DTC 40 is located downstream of the spot scanning system 54. In an exemplary aspect, the DTC 40 is located downstream of the scanning magnets 56 of the spot scanning system 54. In an aspect, the DTC 40 includes at least one trimmer 42 that is located downstream of the magnet(s) 56 of the spot scanning system 54. In an aspect, the at least one trimmer 42 is configured to intercept a portion of the pencil beam 20. In an aspect, the trimmer 42 has a thickness and shape for changing the phase space of the pencil beam 20. In an aspect, the thickness of the trimmer 42 will depend on the energy of the pencil beam 20 that is utilized by the system 10. In an aspect, the proton energies for use in proton therapy can vary between 70 MeV and 250 MeV. The thickness of the trimmer 42 can be selected to, for example, block particles having an energy lower than 160 MeV. In an aspect, the trimmer 42 can be supported by a driving mechanism 44. In an aspect, the driving mechanism is configured to move the trimmer 42. In an aspect, the driving mechanism 44 is configured to have at least two degrees of freedom for moving the trimmer 42 to a pre-defined position for intercepting a portion of the pencil beam 20 during a spot irradiation. In such aspects, the driving mechanism comprises a first axis of motion and a second axis of motion configured for moving the trimmer 42 to a pre-defined position for intercepting a portion of the pencil beam 20 during the spot irradiation. In an aspect, the trimmer 42 can either change the transverse beam phase space or the trimmer 42 can change the longitudinal beam phase space, depending on the geometry of the trimmer 42. For example, if a trimmer 42 has a water equivalent thickness that is larger than the water equivalent range of the pencil beam 20, then, by partially inserting the trimmer 42 into the pencil beam 20, part of the pencil beam 20 will be stopped in the trimmer 42 so that the remaining portion of the beam 20 has a modified transverse phase space. For example, by cutting part of the beam 20 laterally, the lateral beam shape of the pencil beam 20 can be modified. In this way, the lateral penumbra can be improved. Alternatively, in another aspect, by using a trimmer 42 that includes portions having a water equivalent thickness that is smaller than the water equivalent range of the pencil beam 20, the pencil beam 20 will not be stopped in such portions of the trimmer 42, but the remaining pencil beam 20 will have a modified longitudinal phase space. For example, the energy of the remaining beam can be shifted by a given amount or the energy distribution of the remaining beam can be modified. For modifying the longitudinal phase space, the trimmer 42 can have either a fixed constant thickness (e.g., a trimmer 42 with a rectangular shape) or it can have a variable thickness. For example, a trimmer 42 having a variable thickness (e.g., a trimmer 42 having a triangular shape) can be used to allow varying the longitudinal phase space relative to the position of the pencil beam 20 and the trimmer 42. In an aspect, the trimmer 42 can be configured to intercept only a portion of the pencil beam 20. In another aspect, the trimmer 42 can be configured to intercept the entire pencil beam 20. In an aspect, the axis of motion of the driving mechanism 44 can be a translation axis. In another aspect, the axis of motion can be a rotation axis. Detailed embodiments using either multiple translation axes or using a combination of translation axes, rotation axes, or others, will be described below. The driving mechanism 44 can include, but is not limited to, electrical motors, hydraulic motors, and the like. In an exemplary aspect, the driving mechanism 44 is configured to move in at least two axes of motion such as to move the trimmer 42 within a plane that is essentially perpendicular to the central beam axis 22 of the pencil beam 20. In another aspect, the driving mechanism 44 can be configured to move the trimmer 42 on curved surface intersecting the central beam axis 22 of the pencil beam 20. In an aspect, the DTC 40 can include a driving controller 46 that is configured to control the driving mechanism 44. In an exemplary aspect, the driving controller 46 can comprise a control interface (not shown) configured to receive a first parameter for the first axis of motion and a second parameter for the second axis of motion that defines the position of the trimmer 42. The system 10 can have a driving controller 46 for each of the driving mechanisms 44 employed, or there can be one driving controller 46 to control all of the driving mechanisms 44. In an aspect, the SS ion therapy system 10 includes a position planning controller 66 configured for defining, for one or more of the spot irradiations, corresponding pre-defined positions for positioning the trimmer 42 during a spot irradiation so as to intercept the pencil beam 20. In an aspect, the position planning controller 66 can be configured to interact with the interface of the driving controller 46. In an aspect, the position planning controller 66 can be a module within the system controller 60. In other aspects, the position planning controller 66 can be a stand-alone controller/computer. In other aspects, the position planning controller 66 can be a controller can be a part of a treatment planning system. In an aspect, the driving controller 46 can be configured to interface with the irradiation controller 62 for receiving a signal indicating a beam on/beam off status. In such an aspect, the driving controller 46 can be configured to allow the motion of the trimmer 42 only when the beam 20 is in an off status, as indicated by the irradiation controller 62. The use of a trimmer 42 according to the invention is illustrated in FIG. 3, showing two spot irradiations of a target 30. As illustrated, a rectangular shaped trimmer 42 is positioned in a pre-defined position to avoid the beam 20 hitting an at-risk organ 70 positioned near the target 30. In an aspect when the particle pencil beam 20 has a Gaussian lateral shape, the beam spot locations on the target 30 are visualized by showing the one sigma beam radius 24, 25 of the two adjacent beam spots. In addition, the two sigma radius 26, 27 and the three sigma radius 28, 29 of the two beams are shown. When the two exemplary spot locations are irradiated, the trimmer 42 will block part of the two sigma 26, 27 and three sigma 28, 29 lateral beam extensions and as a result prohibit the irradiation of the organ at risk 70. In this example, the pre-defined positions of the trimmer 42 for the two beam spot locations are the same. In other words, in this example, the trimmer 42 is maintained in the same position when irradiating the two beam spot locations. In another aspect, the trimmer 42 can be moved in between two spot locations to a different pre-defined location in order to optimize the intercepting effect and spare healthy tissue outside the target boundaries, discussed in more detail below. According to an aspect, as illustrated in FIGS. 4a-d, the SS ion therapy system utilizes a DTC 100 to sharpen the ion beam (not shown). According to an aspect, the DTC 100 is configured to assist the ion therapy source (i.e., an ion source; not shown) to deliver a focused narrow ion beam. In an aspect, the ion therapy source can be selected based upon the ability to produce relatively low-energy ion beams. In an exemplary aspect, the ion therapy source is capable of producing energies ≦160 MeV at the patient surface for proton beams. Such energy levels are required for treating superficial targets but result in increased beam sizes due to the ion beam delivery technology. While a proton therapy source capable of producing energies greater than 160 MeV can be used with the DTC 100, at higher energies, the lateral spread of the proton beam is largely dependent on scattering in the patient and not on the ion beam delivery technology. Therefore, the DTC 100 can be most useful for proton energies <160 MeV where reduction in the lateral spread of the incoming beam will have an impact on the dose distribution in the patient. By operating at these energy levels, the radiological thickness of trimmers 112 (discussed below) can be slightly greater than that of the range of a low energy proton beam, allowing the trimmers 112 to be lightweight compared to traditional collimators, such as the multi-leaf collimators (MLCs) used in photon and ion therapy. However, in other embodiments, other ranges of energy production can be used, which can require trimmers 112 of a greater thickness to be used, requiring more powerful driving mechanisms, discussed in more detail below. In an aspect, the DTC 100 comprises a plurality of trimmers 112. The trimmers 112 can described as rod-like devices that are utilized by the DTC 100 to shape the ion beam employed by the ion therapy source. In an exemplary aspect, the DTC 100 includes four trimmers 112. In the exemplary aspect, the four trimmers 112 comprise a rectangular shape. In other embodiments, the shape of the trimmers 112 can include, but are not limited to, cylindrical, triangular, hexagonal, and the like. However, it is desired that the trimmer 112 have a length that is much greater than the width or height. A longer length is desired so that a trimmer 112 does not need to move along the direction of the length, but only needs to move in one direction. A rectangular shape is desired because it is easy to precisely control a rectangular trimmer 112 to trim an ion spot at a desired location. The height of the trimmer 112 can be dictated by the energy of the ion beam (the trimmer 112 should be of sufficient thickness to completely block the ion beam and stop unwanted ions from reaching the patient). The width of the trimmer 112 can be dictated by the lateral size of the ion beam (the width should be sufficient to completely block the unwanted portion of the ion beam). The length of the trimmer 112 is used to define the useable field size, with the length being much longer such that usable field sizes can be defined to treat large targets. In an exemplary aspect, the cross section of each trimmer 112 can be 2 cm×2 cm. With the mass of each trimmer 112 being highly dependent on the cross section, and the ability to drive the trimmers quickly enough to deliver the DTSS, it is desirable to have a smaller cross sections. In addition, in other embodiments of the present invention, the number of trimmers 112 employed by the DTC 100 can vary as well. However, the number of trimmers 112 should enable the DTC 100 to assist in the shaping the beam of the ion therapy source effectively while keeping the weight of the DTC 100 low enough to enable the DTC 100 to be mounted to the ion therapy source. As in the exemplary aspect illustrated in FIGS. 4a-4d, four trimmers 112 is a logical number because the beam is scanned in a raster pattern and can be intercepted by the trimmers 112 as it arrives at each side of the target. More trimmers 112 could make the DTC 100 more bulky and without improving the dose distribution. Referring back to FIGS. 4a-d, the trimmers 112 are associated with driving mechanisms 114. In an aspect, the driving mechanisms 114 can include linear motors 114. The trimmers 112 can be coupled to the driving mechanisms 114 through connecting rods 116. The DTC 100 can consist of four metal trimmers 112 with rectangular cross-sections, each of which can rapidly move along a path perpendicular to the axis of a narrow, scanned, ion beam. In an aspect, the DTC 100 can have a protruding nose 102 that is small enough to position the trimmers 112 within several centimeters of the patient's skin (see FIG. 4d), even when treating sites such as the head and neck. Such sites can be difficult to access due to the presence of the patient's shoulders. Each trimmer 112 is mounted to a driving mechanism 114, and during the ion therapy delivery process, the trimmers 112 move in synchrony with the scanned ion beam. The trimmers 112 partially block the ion beam at spatial locations where the patient would benefit from beam sharpening, such as at the tumor edges. This increase in beam sharpness results in a concurrent decrease in the radiation dose that spills laterally out of the target tissue and into adjacent normal tissue. In an aspect, the trimmers 112 are comprised of metallic trimmers 112. The trimmers 112 can be comprised of a variety of metals. In an aspect, the trimmers 112 can include brass and other alloys which can comprise of a mixture of metals including, but not limited to, Co, Ni, Cu, Zn, and the like. In an aspect, the metallic trimmers 112 can include other materials shown in FIG. 5a, which plots density versus atomic number. In an aspect, Ti may be used, since it has an atomic number of 22 and a density of 4.5/cm3. In an aspect, titanium alloys may be used. While the composition and dimensions of the trimmers are in relation to the embodiments shown in FIGS. 4a-b, such compositions and dimensions can be applicable to trimmers of other embodiments discussed below as well. In an embodiment, the driving mechanisms 114 can include high performance driving mechanisms 114 configured to rapidly move each trimmer 112. In an exemplary aspect, the driving mechanisms 114 are configured to have 2 g's of acceleration. The driving mechanism 114 can include, but are not limited to, linear motors or belt-driven actuators. In an aspect, motors provided by Automation, Inc. can be utilized as the driving mechanisms 114. The number of driving mechanisms 114 can correspond to the number of trimmers 112 utilized by the DTC 100. For example, in an exemplary embodiment, four linear motors 114 are associated with the four trimmers 112, with each motor 114 configured to move a trimmer 112, allowing for independent control of each trimmer 112. The ends of the driving mechanisms 114 (or the driving mechanism supporting structure or carriage) can be connected to one another, as shown in FIG. 4a-d. The driving mechanisms 114 are connected to the trimmers 112 through connecting rods 116, with the connecting rod 116 being connected at an end of the trimmer 112. In an aspect, the DTC 100 includes a rail system 118 that supports the trimmers 112. The rail system 118 can be connected to a support frame 130. In an aspect, the rail system 118 provides a track/rail 119 on which the trimmers 112 can move. In an exemplary aspect, the trimmers 112 can include rail wheels 113 that engage the rails 119 of the rail system 118. In an exemplary aspect, the rails 119 can be curved, which allows the trimmers 112 to move in a pendulous arc to match the divergence of the ion therapy source (not shown). In an aspect, the DTC 100 can also include a range shifter 120 (see FIGS. 4b-4d). The range shifter 120 is configured to be placed upstream of the patient to reduce the energy, and therefore the penetration depth, of the ion beam. For example, the range shifter 120 can be placed downstream of the ion therapy source and downstream of the spot scanning system discussed above. In an aspect, the range shifter 120 can provide 7.5 g/cm2 of water-equivalent thickness located between the driving mechanisms 114 and the trimmers 112, enabling the range shifter 120 to be as close to the patient as possible. In an aspect, the integrated range shifter 120 is positioned such that the downstream face of the range shifter 120 is as close as possible to the patient without being downstream of the trimmers 112. In another aspect, the integrated range shifter 120 is positioned such that the downstream face of the range shifter 120 is as close as possible to the patient and also downstream of the trimmers 112. By mounting the range shifter 120 in such a position, the in-air penumbra at the plane of the trimmers 112 is minimized, reducing the required width and mass of the trimmers 112 required to block the spreading beam. Minimizing the mass of the trimmers 112 is an important aspect of the design for ensuring rapid dynamic motion of the trimmers 112. The range shifter 120 can also be removed when not needed, reducing the overall weight of the DTC 100 and easing installation of the DTC 100 onto the nozzle of an ion therapy system 150. The range shifter 120 can be supported by a carriage 122. The trimmers 112 can be associated below the range shifter 120 and carriage 122, along with the support rail 118. A support frame 130 can be utilized to contain the other mentioned elements of the DTC 100. While the embodiment of the DTC 100 discussed in reference to FIGS. 4a-d includes a range shifter 120, the DTC 100 does not need to have a range shifter 120. In another aspect, the DTC 100 can supplement or replace the range shifter with one of many possible ridge filters (not shown). A ridge filter broadens the Bragg peaks used for treatment, reducing the number of beam energies required to treat a target. Different ridge filters broaden the Bragg peak to a different extent, and are appropriate for different patients. The use of different ridge filters can decrease treatment times and reduce the susceptibility of the delivered dose distributions to under-dose and overdose-causing interplay effects between the beam scanning pattern, trimmer motion pattern, and internal patient motion. A ridge filter can be placed by replacing the range shifter with a ridge filter, or replacing the range shifter with a combination of a smaller range shifter and a ridge filter. In an aspect, the combination of the trimmers 112, the driving mechanisms 114, the connecting rods 116, the rail system 118, the range shifter 120, along with the support frame 130, form a protruding nose 102 for the DTC 100 that is small enough to position the trimmers 112 within several centimeters of the patient's skin (see FIG. 4d). The configuration allows the DTC 100 to be used even when treating sites such as the head and neck, even with the difficulties to access due to the presence of the patient's shoulders. Referring back to FIGS. 4a-d, the DTC 100 is mounted downstream of the ion therapy source and spot scanning system, just upstream of the patient. In an exemplary aspect, the DTC 100 can be mounted on a nozzle of the spot scanning system. The driving mechanisms 114 are used to rapidly position the trimmers 112 during treatment such that the trimmers 112 track the edge of the target while the SS beam from the ion therapy source is scanned across the patient volume. The DTC 100 is designed such that the trimmers 112 can move rapidly enough to change positions while the ion beam is magnetically scanned across the target, with the trimmers 112 forming a rapidly changing frame that defines the sharp beam edges depending on the position of the ion beam. The configuration of the exemplary aspect minimizes the lateral spread of the beam by being close to the patient as possible. In another embodiment of the present invention, illustrated in FIGS. 6a-b, a DTC 300 can contain a range modulation system 350. The range modulation system 350 enables the rapid modification of ion beam energies, reducing the time necessary to treat a target, without the need of a range shifter. In an exemplary example of the embodiment, the DTC 300 includes a plurality of trimmers 312 connected to motors 314 by connecting rods 316. The DTC 300 can include a rail system 318 to support the trimmers 312 in a similar manner as discussed above. In an aspect, the range modulation system 350 can include of two linearly-traveling wedges 352 that face each other. In an aspect, the wedges 352 can be comprised of a low-atomic number material, including, but not limited to, lucite, graphite, beryllium, and the like, with a small proton scattering cross section. Driving mechanisms 360 connected to the wedges 352 by wedge connectors 354 can control the wedges 352, and can be located in the space between the driving mechanisms 314 controlling the trimmers 312. When the wedges 352 are separated or brought closer together, the amount of range modulating material the ion beam passes through to reach the target is modified. The distance the driving mechanisms 360 are able to translate the wedges 352 of the range modulation system 350 dictates the range over which the ion beam ranges (penetrations) can be modified. In an aspect, to ensure that the DTC 300 is small enough to be moved close to the patient in clinical practice, the DTC 300 can be oriented in a manner such that a collision with the patient would be avoided. In an aspect, the longest part of the DTC 300 can be oriented such that the axial plane of the DTC 300 is perpendicular to the patient's spinal cord, with the shorter part of the DTC 300 being oriented in the longitudinal direction parallel to the spinal cord of the patient. This strategy is especially important when treating head and neck cancers. While not shown, a system controller, similar to those discussed above in relation to FIGS. 1-2, can be utilized in SS ion therapy systems that include the embodiments of the DTCs 100 and 300 illustrated in FIGS. 4a-4d and 6a-b as discussed above. In an aspect, irradiation, SS system, and position planning controllers (or modules) can be utilized to further control the operation of such DTCs 100, 300, including the range modulation system 350 of FIGS. 6a-b. FIG. 7 illustrates another embodiment of a DTC 430 according to an aspect. FIG. 7 illustrates to driving mechanism 434 moving a trimmer 432 to a pre-defined position. The first axis of motion (the X axis) and second axis of motion (the Y axis) of the driving mechanism 434 correspond to two orthogonally superposed translation axes 438, 439 configured as a dual axis stage translation mechanism 434. In this aspect, the trimmer 432 is mounted on the first translation axis 438 of the driving mechanism 434 and is configured for making a translation motion along the first axis (i.e., parallel to the length of the first translation axis 438, shown by the double arrow). The first translation axis 438 is connected to the second translation axis 439 and is configured to translate over the first axis 438 along the second axis direction (parallel to the second translation axis 439, shown by the double arrow). Through this configuration, the trimmer 432 can be positioned to any pre-defined position in the plane defined by the two translation axes 438, 439, with the arrows indicating the direction of motions for the trimmer 432. In another aspect, the trimmer 432 can be mounted on the second translation axis 439. In the aspect illustrated in FIG. 7, the pre-defined positions can be defined by defining a first parameter and a second parameter corresponding to the coordinate positions along the two translation axes. In such aspects, the position planning controller (not shown) is configured for defining, for one or more of said spot irradiations, corresponding pre-defined positions for positioning the trimmer 432. The same can be said for other embodiments of a DTC that include two translation axes. In an aspect, the position planning controller can utilize a display device to visualize the trimmer 432 together with an image of the target area (e.g., a two-dimensional x-ray image). On this image, the spot locations to be irradiated can also be visualized. A user can then use a user input device (e.g., a mouse) to move the trimmer 432 over the screen and position the trimmer at various places, including the spot positions, as well as move the spot positions themselves. A position of the trimmer 432 can be associated with a position of a spot to be irradiated through known means (e.g., selecting the trimmer 432 and spot positions with a mouse). In an aspect, the planning position controller can then calculate the coordinates for the two axes for each of the pre-defined positions selected by the user through the display device and user device. While FIG. 7 illustrates a DTC 430 utilizing only one trimmer 432, FIG. 8 illustrates a similar DTC 430 that utilizes two trimmers 432, 432′ mounted each on their respective driving mechanism 434, 434′. As shown, the first driving mechanism 434 includes two axes of motion 438, 439 being two translation axes X, Y, which are configured for moving the first trimmer 432. This embodiment further comprises a second driving mechanism 434′ with two axes of motion 438′, 439′, which are also two translation axes K, L and which are configured for moving a second trimmer 432′. In this embodiment, the driving mechanism 434, 434′ are configured for moving the two trimmers 432, 432′ in parallel planes. FIG. 9 illustrates another embodiment of the DTC 530 according to aspect of the present invention. The driving mechanism 534 is configured to move a circular trimmer 532 to a pre-defined position, with the first and second axis of motion (X, Y) correspond to two orthogonally superposed translation axes 538, 539 configured as a dual axis stage translation mechanism 534. The trimmer 532 is mounted on the first translation axis 538 and is configured for making a translation motion along the first axis X (i.e., parallel to the length of the first translation axis 538, shown by the double arrow). The first translation axis 538 is connected to the second translation axis 539 and is configured to translate over the first axis 538 along the second axis direction Y (parallel to the second translation axis 539, shown by the double arrow). Through this configuration, the trimmer 532 (and translation axes 538, 539) can be positioned to any pre-defined position, shown by the dashed lines, in the plane defined by the two translation axes 538, 539. In an aspect, an x parameter and a y parameter may be used to place the trimmer 532 at a location on the translation axes X, Y. As discussed above, the trimmer 532 of the present embodiment is configured to have a circular shape. In an exemplary aspect, the trimmer 532 has four circular shaped sides. The circular outer shape defines the cutting edge for cutting part of the pencil beam (not shown), as well as the inner circular shape. However, a portion of the pencil beam can travel through the interior of the inner circular shape of the trimmer 532. By not having an interior portion of the trimmer 532, the weight of the trimmer 532 is reduced. In addition, irradiation can be done to spots that fall within the diameter of the inner circular shape of the trimmer 532. FIG. 10 illustrates another embodiment of the DTC 630 according to an aspect of the present invention, wherein the driving mechanism 634 includes a first axis of motion that is a translation axis 638 for translating the trimmer 632 and the second axis of motion is a rotation axis 639 for rotating the trimmer 632. The rotation axis 639 is essentially perpendicular to the translation axis 638 and the position of the trimmer 632 is defined within a first parameter corresponding to a coordinate position along the translation axis and a second parameter corresponding to a rotation angle with respect to the rotation axis 639. With such an embodiment, the trimmer 632 can be moved on a surface to any position to intercept the pencil beam during a spot irradiation. In the embodiment of FIG. 10, an additional rotation axis can be provided for rotating the trimmer 632 with respect to a rotation axis 637 crossing the trimmer 632. FIG. 11 illustrates another embodiment of a DTC 730 according to an aspect of the present invention. The first axis and second axis (X, Y) of motion of the driving mechanism 734 correspond to two orthogonally superposed translation axes 738, 739 configured as a dual axis stage translation mechanism 734. In addition, the trimmer 732 includes a rotational axis 737. In this aspect, the trimmer 732 is configured for making translation motions along the first axis 738 and second translational axis 739, as well as rotation motions along the rotation axis 737 crossing the trimmer 732. Through this configuration, the trimmer 732 (and translation axes 738, 739 and rotational axis 737) can be positioned to any pre-defined position, shown by the dashed lines, in the plane defined by the two translation axes 738, 739 at a position with the plane defined by the rotational axis 737. FIGS. 12a-b illustrates another further embodiment of a DTC 830 according to another aspect of the present invention. The trimmer 832 is moved by a rotatable driving mechanism 834 comprised of two rotatable concentric rings 835, 836. The trimmer 832 as shown is configured to have a rectangular shape and configured to slide on two points 837, 838 attached each to one of the rings 835, 836. When the rings 835, 836 rotate, the two points 837, 838 will rotate as well, resulting in the movement of the trimmer 832. FIG. 11a illustrates the initial position of the trimmer 832, while FIG. 11b shows another position of the trimmer 832 as the rotatable concentric rings 835, 836 have been rotated. FIG. 13 illustrates an embodiment of a DTC 930 where not only the transverse phase beam can be changed by the trimmer 932, but also the longitudinal beam phase is adjustable as well. The trimmer 932 is mounted to a driving mechanism 934 with a first and second axis (X, Y) of motion that correspond to two orthogonally superposed translation axes 938, 939. As shown, the trimmer 932 is mounted on the first translation axis 938 of the driving mechanism 934 and is configured for making a translation motion along the first axis. The first translation axis 938 is connected to the second translation axis 939 and is configured to translate over the first axis 938 along the second axis direction. Through this configuration, the trimmer 932 can be positioned to any pre-defined position in the plane defined by the two translation axes 938, 939, with the arrows indicating the direction of motions for the trimmer 932. As shown in FIG. 13, the thickness and shape of the trimmer 932 can be configured for changing the energy of the pencil beam 920. For this purpose, the trimmer 932 has a surface 933 that is inclined with respect to the pencil beam 920 such that depending on the relative position of the trimmer 932 with respect to the beam 920, the energy of the beam 920 is more or less reduced. In other words, the trimmer 932 comprises a plane that is inclined with respect to the X, Y plane of motion of the trimmer 932. In addition, the trimmer 932 also comprises a plane (indicated by dashed lines) that is perpendicular to the X, Y moving plane. Depending on the relative position of the pencil beam 920 and this plane, the pencil beam 920 can more or less be intercepted so as to change the lateral shape of the beam 920 and hence modify the transverse beam phase space. In other words, depending on the pre-defined position of the trimmer 932 defined by the coordinates on the motion axis 938, 939, either a longitudinal beam phase space or a transverse beam phase space can be changed. In other embodiments, the DTC can utilize other range modulation systems. For example, in one aspect, the DTC can use a stairstep modulator, similar to that disclosed in EP20080730864. In another embodiment, the range modulation system can include a large water column similar to that shown in FIG. 3 of U.S. Pat. No. 8,129,701 B2. However, in another embodiment, a single water column can be utilized instead of the multiple shown in FIG. 3 of U.S. Pat. No. 8,129,701. Testing Results The ability to control the location of an ion beam using magnetic scanning is an advantageous property of ions that is not possible with photons. This is because photons carry no charge, therefore photon beams are controlled with mechanical collimation systems rather than magnetic fields. In an aspect, the SS method entails the magnetic and/or mechanical scanning of an ion beam over a 3-D Cartesian grid that covers the treatment volume. In an exemplary aspect, the position of a beam spot in depth is controlled by changing the energy of the proton pencil beam by inserting material in the beam, by controlling the beam energy with the proton accelerator, or a combination of both methods. In an aspect, the material can be placed in the beam-line somewhere between the accelerator and the gantry. Common materials may include beryllium and carbon. The number of ions that stop at each position in the target can be controlled by an ion accelerator and beam transport system (i.e., an ion therapy source and its components as discussed above), and can be initially determined by computer optimization (via a system controller) in a treatment planning process, discussed in more detail below. A common measure of the lateral width of an ion beam is sigma (a), which is the standard deviation of the beam's radiation dose profile on a line perpendicular to the direction of proton travel. A description of the a-parameter is provided in FIG. 5c according to an aspect. FIG. 5b illustrates a dose distribution for a single proton beam spot in a head and neck cancer patient. The squares represent the locations of the Bragg peaks for all spots in the axial CAT scan slice shown. The value of the pencil beam sigma in air, σair, depends on the proton delivery technology, and the growth of σ inside the patient is due to multiple Coulomb scattering, a physical process that cannot be modified. FIG. 5c illustrates a Gaussian lateral dose profile of a proton pencil beam in air, showing the definition of σ and the 80%-20% penumbra. A situation for which it is especially important that the radiation dose lateral to the target falls off sharply is intracranial (brain) stereotactic radiosurgery (SRS). In SRS, high radiation doses are delivered to benign lesions, such as acoustic neuromas, and malignant lesions, such as brain metastases, in a single high-dose irradiation session. The brain is highly susceptible to necrosis when small volumes of healthy tissue are exposed to high radiation doses. The dose that can be delivered to the lesion is then limited by the volume of the healthy tissue shell surrounding it, which is dependent upon the volume of the lesion. Ion SS radiosurgery of brain lesions can deliver a lower dose to the tissue shell surrounding the lesion, reducing the risk of healthy brain necrosis relative to photon-based radiosurgery techniques. Such an advantage for ion radiosurgery can only occur if the σ of the pencil beams used for SS is below a certain threshold. In an aspect, σ can be approximately 5 mm. However, σ can vary in other aspects. Examples of photon and proton SS radiosurgery treatment plans for a peripheral brain tumor represented by a clinical target volume (CTV) are shown in FIG. 14. Several different photon and proton SS plans with various radiation dose distributions are shown. The photon irradiation techniques shown are volumetric modulated arc therapy (VMAT) and cone-based radiosurgery, and the proton technique is spot scanning (SS). The quality of the treatment plan degrades as the beam sigma increases, as shown for a single patient in FIG. 14. Since the radiosurgery plans shown in FIG. 14 are for an intracranial brain tumor, the tissue for which the greatest hazard of complications exists is the healthy brain tissue. A normal tissue complication probability (NTCP) for brain tissue necrosis may be calculated for each plan in FIG. 14. For the proton therapy plans, the NTCP increases as the beam sigma increases and greater dose is delivered to the surrounding normal tissues. Since there is a range of NTCP values corresponding to the proton plans, we define “sigma-cross” as the proton pencil beam sigma which yields a proton plan with equal NTCP to that of the better of the two (VMAT or cone-based radiosurgery) photon plans. This value, along with sigma 50% reduction, which represents the beam sigma required to decrease the NTCP by 50%, are plotted in FIG. 15. In order to estimate effectiveness of DTSS at reducing proton pencil beam sigma for intracranial radiosurgery patients, proton beams at that surface of a phantom were simulated using Monte Carlo simulations with the MCNPX code for cases with and without a DTC in place, as shown in FIG. 16. For the conventional case of a proton beam with energy of 127 MeV, an initial sigma of 5 mm, a range shifter thickness of 7.5 g/cm2, and a clinically realistic 5 cm air gap between the downstream range shifter face and the phantom (left side), the sigma in air at the phantom surface was 5.9 mm. With a DTC in place and a 5 cm air gap between the downstream trimmer and the phantom, the sigma in air at the phantom surface was 2.3 mm. These results are summarized in FIG. 17. Sets of photon and proton SS treatment plans such as those in FIG. 14 were generated for 11 patients, and it was determined (FIG. 18) that 8 of 11 (73%) of the patients had NTCP values that could be improved relative to the photon plans when using commercially-available proton SS systems, which would have sigma values of approximately 5.9 mm for the tumor depths considered. If proton pencil beams with σair values of 2.3 mm were used clinically, 100% of the 11 patients, shown in FIG. 18, considered would have a reduced healthy brain NTCP relative to photon radiosurgery techniques. While improvements in σair relative to conventional SS afforded by the DTC could be obtained using existing technology, existing technology consists of either patient-specific brass apertures (i.e., pieces of brass with openings cut out to match the shape of the tumor) or multi-leaf collimators. Since a given brass aperture is shaped only to match the tumor extent for a single plane in the tumor, apertures are not capable of sharpening the 3-dimensional dose distribution to the extent a multi-leaf collimator or the DTC could. In addition, brass apertures need to be manufactured for each patient, and for each beam with which the patient is treated, adding substantial cost of around $500 per custom aperture to the delivery process. Brass apertures also require a construction time, imposing a lower-bound on the time required to plan, prepare for, and deliver a patient's treatment. This is an especially important limitation for SRS, as it is typical for a patient to be treated on the same day their plan is generated with photon SRS. Removing this benefit imposes an impediment to the widespread adoption of ion SRS. MLCs have been proposed as a means to improve SS penumbra. Bues et al (2005) demonstrated that an MLC can be effective at sharpening SS penumbra for low energy proton beams, but found that diminishing returns occurred as the proton beam energy increased. As shown in Table 1, the MLC substantially reduced the 80%-20% penumbra at the depth of the Bragg peak for beam energies of 72 MeV and 118 MeV, but increased the penumbra for the 174 MeV beam. This is because the 20.5 cm range of the 174 MeV proton beam was sufficiently high that multiple Coulomb scattering interactions inside the medium dominated over any improvements in σair provided by the MLC. For shallower depths, multiple Coulomb scattering interactions did not dominate, enabling substantial improvements in penumbra with the use of the MLC. The effective σair value in Table 1 was calculated by scaling the σair value before the MLC by the ratio of the penumbra with-to-without the MLC. Since there is nothing that can be done to prevent multiple Coulomb scattering interactions from occurring between ion beams and patient tissue (FIG. 5b), the advantages of the DTC relative to the collimator-free case are similar to those of the MLC in terms of ability to shape a dose distribution. TABLE 1Penumbra at the location of the Bragg peak for proton beams withoutand with an MLC.1 The penumbra values are taken froma 7 × 7 pattern of equally-weighted beam spots. The distal endsof the MLC leaves are assumed to be 5 cm from the patientsurface. Penumbra values represent the distance between the80%-20% isodose lines.σair beforePenumbraPenumbraEffective σairEnergyRangeMLCw/ow/MLCfrom(MeV)(cm)(mm)MLC (mm)(mm)MLC (mm)724.311.013.03.02.511810.37.29.05.04.017420.55.58.09.06.2 The advantage of utilizing a DTC over a MLC is that the ratio of usable beam area to total area of the face of the DTC is far higher than that of an MLC. Since the penumbra grows geometrically with distance to the patient surface, it is critical that the DTC or MLC is located as close to the patient as possible. The MLC leaves must go somewhere when retracted out of the radiation field, and the housing around an MLC tends to be bulky. This makes MLCs difficult to move to within 10 cm of the patient surface when treating the head and neck region. Two of the smallest available MLCs are the Siemens ModuLeaf and the Radionics MMLC, shown in FIGS. 19a-b, respectively, which have physical field sizes of 7.8 cm×6.5 cm and 6.9 cm×5.4 cm, respectively. The ModuLeaf is also shown in FIG. 20. As shown in FIG. 19a, the percentage of nozzle area through which the proton beam can pass is about 46% for the DTC, which has a physical field size of 15 cm×15 cm, and only 7% for the Siemens ModuLeaf. Thus, even if an existing MLC can be placed close to the patient surface, four junctioned fields (i.e., multiple small fields combined to make one larger field) from the MLCs would be needed to cover the same area as a single DTC field. Although junctioning fields are typically not necessary for intracranial lesions treated with the ModuLeaf, as shown in FIG. 20, larger fields that would require junctioning are expected for many head and neck, esophageal, lung, craniospinal, sarcoma, and liver cancer patients. In addition, commercially available MLCs are optimized for photon therapy rather than proton therapy, which is an important consideration since beam modifying devices for proton therapy are subjected to substantially higher neutron doses than those used in photon therapy. The high neutron doses necessitate the use of electronics that are less sensitive to neutron damage. There are two major enabling principles behind DTC-based DTSS. First, spot scanning dose distributions are only improved by collimation systems when relatively low-energy ion beams are used, which have energies <160 MeV at the patient surface for proton beams. This is because the penumbra at deeper depths from higher energy beams is largely dominated by scatter in the patient. This fact allows the radiological thickness of the trimmers to be slightly greater than that of the range of a low energy proton beam, and lightweight compared to traditional collimators, such as the multi-leaf collimators (MLC) used in photon and ion therapy. Second, with SS, a collimator is necessary at the edge of the target only at the times when the beam is near the edge of the target, and the trimmers can be in motion when the beam is elsewhere, as long as the trimmer motion does not interfere with the scanned beam motion. Modeling of Beamlet Dose Distributions In an aspect, after interacting with the trimmer blades, incoming symmetric proton beamlets (shown in FIG. 21a) can become asymmetric and laterally shift in the beam's eye view, as illustrated in FIG. 21b. In an exemplary aspect, the lateral distribution of an asymmetric trimmed beamlet can still be described using Gaussian parameters, similar to the untrimmed beamlet. This is accomplished by fitting Gaussian functions along each of the four primary lateral axes of the trimmed beamlet, namely X1, X2, Y1, and Y2, as shown in FIG. 21c. With this approach, the lateral profile can then be modeled as follows: O ( x , y , z ) = A ( z ) exp { - [ H ( x - μ x ( z ) ) ( x - μ x ( z ) ) 2 2 σ x 1 2 ( z ) + H ( μ x ( z ) - x ) ( x - μ x ( z ) ) 2 2 σ x 2 2 ( z ) + H ( y - μ y ( z ) ) ( y - μ y ( z ) ) 2 2 σ y 1 2 ( z ) + H ( μ y ( z ) - y ) ( y - μ y ( z ) ) 2 2 σ y 2 2 ( z ) ] } where μx(z), and μy(z) are the positions of maximum dose in the plane of interest and σx1(z), σx2(z), σy1(z), σy2(z) are the sigma values for the four half-Gaussians along each primary axes, centered on (μx(z), μy(z)) at depth z. The Heaviside step function H( . . . ) limits each exponential term to the corresponding half-axis centered at (μx(z), μy(z)). Multiplication by a numerically determined normalization factor A(z) ensures that ∫∫−∞−∞0(x,y,z)dx dy=1 for all z. Such a method can be applied to any asymmetric beamlet, not only those resulting from collimation. In an aspect, after interacting with the trimmer blades, the integral depth dose (IDD) curve of the trimmed beamlet changes from that of an untrimmed beamlet, as illustrated in FIG. 22. By applying a depth dependent correction function, the trimmed beamlet IDD curve can be generated from the untrimmed beamlet IDD. One such correction function takes the form of the equation below:D+(z,R)=D+(0)·(C·z+1)where D+(z,R) represents the depth dependent correction applied to the untrimmed IDD to generate a trimmed IDD, D+(0) is the increase in entrance dose (%) of the trimmed IDD compared to the untrimmed IDD at the surface, and C is a constant parameter that is a function of energy determining the depth dependence of the correction. The equation below describes how the trimmed IDD represented by DT(z,R) may be obtained by addition of the untrimmed integral depth dose curve D(z,R) and the correction described above:DT(z,R)=D(z,R)+D+(z,R) Determining Time-Dependent Trimmer Positions for DTSS Delivery In an aspect, distributing spots in a grid or hexagonal pattern across the target volume and then defining trimmer positions later can be used for placing beam spots. Any DTSS spot placement technique will still produce dose distributions that are superior to those that can be delivered with conventional SS. In another aspect, trimmed spot peak tracing (TSPT) produces superior dose distributions to those achievable with grid or hexagonal spot placement patterns. TSPT is based on the logical conjecture that maximizing the conformity of the dose to the target volume requires that the dose maxima of trimmed spots are positioned on the edge of the target volume. Due to proton scatter off the trimmer and in the target medium, the point of maximum dose in the beam's eye view of a trimmed spot does not occur on the ray along which the scanning magnets are directing the pencil beam upstream of the trimmer. Positioning the point of maximum dose of a trimmed beam spot thus requires that the scanning magnets and trimmers work together. The following is a description of an implementation of the TSPT method according to an aspect. According to an exemplary aspect, as shown in FIGS. 16-17, a single trimmer can reduce the value of σair on one side of the trimmer for a proton pencil beam spot from 5.9 mm to 2.3 mm. The location of the point of maximum dose of the beam spot is also shifted away from the trimmer. FIGS. 21a-b show that an orthogonal set of trimmers can reduce the values of σair on both dimensions of a proton pencil beam spot as a two-dimensional Gaussian. Similarly, trimmers on three or four sides of a pencil beam can reduce the value of σair on each side where a trimmer is placed, and shift the position of the spot peak. By positioning the trimmers at different distances from the center of the incoming spot, the location of the point of maximum dose and 2-D σair value can be varied. According to an aspect, a trimmed pencil beam (i.e., a beam that has been shaped by intercepting trimmers) (TPB) library can be calculated for varying trimmer position combinations, as shown in FIG. 23. These TPBs represent various trimmer positions at various distances from the central axis of the pencil beam of ions to achieve the desired dose distribution. Once the TPB library exists, a method for selecting the appropriate TPB maximum dose location, and, therefore, trimmer configuration, for a given point in the target volume can be defined. FIG. 24 shows the target boundary at an arbitrary energy layer in the beam's eye view. The desired TPB maximum dose points can be positioned at equidistant points on the target boundary, which may, for example, be 5 mm apart. Following the placement of TBP dose maxima on the target boundary, the remaining beam spots can be placed throughout the target volume in a lattice pattern such as that shown in FIG. 24. Alternatively, a fixed spot grid of spot positions may be used with a square, hexagonal, or other pattern, the nearest neighbor spot may be assigned to the target boundary. In such a situation, if scanning magnets are always configured to position the nearest spots to the target border outside the target, a trimmer configuration will exist that could position the point of maximum dose of the TPB closer to or on the target boundary. The desired TPB maximum dose point location is on the target boundary. At each desired TPB maximum dose location, the TSPT algorithm searches the library of i=1, . . . , NTPB trimmed spot kernels for the pencil beam energy, and selects the TPB trimmer configuration that satisfies a search criterion such as: min i TE i where ( 1 ) TE i = Total energy deposited inside target from TPB i Total energy deposited outside target from TPB i ( 2 ) Another possible TPB search criterion is min i MD i where ( 3 ) MD i = Mean dose to target areas above x % isodose line Mean dose to normal tissue area above y % isodose line . ( 4 ) Alternatively, a weighted combination of search TPB criteria can be used as a weighted sum:Ci=(1−ω)TEi+ω·MDi, (5)where w is a scalar weighting factor valued between 0 and 1. A TPB placement strategy according to another aspect is to assign a large number of initial spots with very small inter-spot distance and generate a treatment plan by optimizing the spot weight, which is proportional to the number of ions, to deliver to each spot. In an iterative process, some fraction of the spots with low weights can then be removed, reducing the number of spots required for delivery. If any trimmed spot on the target boundary cannot be created by realistic trimmer positions, it would be replaced with the one with the closest spot shape. According to an aspect, determining the position of each of the four trimmers, as shown in FIGS. 4a-d, necessitates an algorithm that accounts for spot position, spot size, target shape, and the fraction of total spot energy, ε, that the user is willing to accept being delivered to normal tissue outside of the target in the plane being treated. In an aspect, such an algorithm can be implemented by DTSS software, as discussed below. If ε=0, then the trimmers will not allow any spot energy to be deposited outside of the target. This would not be desirable for targets with curved edges (non-rectangles) because the trimmers may have to change position between each spot, dramatically increasing delivery time relative to the case without trimmers. In addition, not allowing any spot energy to fall outside the target could result in trimmer positioning patterns that are too conservative to allow certain regions in the target from receiving a dose, resulting in underdosage of the target. To avoid these problems, options to allow a non-zero fraction of energy from a given beam spot to fall outside the target can be provided. Specifically, the algorithm maximizes ET, the spot energy deposited in the target, under the constraint that ENT, the energy deposited in the normal tissue, should be less than or equal to ε times Etot, the total energy deposited by the spot. In an aspect, the method will define x and y as the orthogonal spatial coordinates of the spots of a given energy in the beam's eye view (BEV) plane at the exit window of the DTC system, as shown in FIG. 25. Tissue types on the plane are defined by the functions AT(x,y) and ANT(x,y), which are valued at unity inside the target tissue and normal tissue, respectively, and zero otherwise. Let D(x,y,xs,ys) be the dose distribution delivered in the BEV plane by the beam spot centered at (xs,ys), which is assumed to be a 2-D Gaussian function for this simplified example: D ( x , y , x s , y s ) = 1 2 π σ x σ y exp [ - 1 2 ( ( x - x s ) 2 σ x 2 + ( y - y s ) 2 σ y 2 ) ] , ( 6 ) where σx and σy define the spot width in the x and y directions, respectively. If the positions of the x and y trimmers are [X1,X2] and [Y1,Y2], respectively, then ET and ENT, are calculated on a given BEV plane as:ET/NT(X1,X2,Y1,Y2)=∫X1X2dx∫Y1Y2dy AT/NT(x,y)D(x,y), (7)and Etot=ET+ENT. The trimmer positions for each spot can be determined by solving the following optimization problem: maximize { X 1 , X 2 , Y 1 , Y 2 } E T subject to : ( a ) E NT ≤ ɛ · E tot , ( b ) X 1 ≤ x s ≤ X 2 , Y 1 ≤ y s ≤ Y 2 ( c ) Δ X m i n ≤ X 2 - X 1 , Δ Y m i n ≤ Y 2 - Y 1 , ( 8 ) where constraint (a) ensures the spot energy deposited in normal tissue does not exceed the user-specified tolerance, constraint (b) ensures no more than half of a beam spot is occluded by any one trimmer blade, and constraint (c) ensures the aperture defined by the trimmers is not below some minimum area, ΔXminΔYmin. If the target is so small that constraint (a) cannot be satisfied without violating constraint (c), then the trimmer positions are defined such that constraints (b) and (c) are satisfied. The optimization problem defined in Equation (8) can be solved with gradient-based optimization techniques using the following derivatives: ∂ E T / NT ∂ X 1 = - ∫ Y 1 Y 2 ⅆ yA T / NT ( X 1 , y ) D ( X 1 , y ) ∂ E T / NT ∂ X 2 = ∫ Y 1 Y 2 ⅆ yA T / NT ( X 2 , y ) D ( X 2 , y ) ∂ E T / NT ∂ Y 1 = - ∫ X 1 X 2 ⅆ xA T / NT ( x , Y 1 ) D ( x , Y 1 ) ∂ E T / NT ∂ Y 2 = ∫ X 1 X 2 ⅆ xA T / NT ( x , Y 2 ) D ( x , Y 2 ) . ( 9 ) The trimmer needs to be in position to intercept the beam when it arrives at its predetermined position. This is accomplished using the trajectory model described in this section. A diagram of the trimmer trajectory model is shown in FIG. 26. As shown, the trimmer trajectory model shows time, trimmer position, and acceleration, but not velocity. Xn is the trimmer position at time Tn, where n is the trimmer travel interval index. Each travel interval is divided into M sub-intervals, and tm,n is the time at the beginning of sub-interval m of travel interval n. The acceleration is applied uniformly over a given sub-interval, and a0,n is the acceleration between times t0,n and t1,n. Suppose the positions that need be visited by a given trimmer edge are given by Xn, where nε[0, N−1] is the position index. Let Tn, Vn, and An be the time, velocity, and acceleration, respectively, of the trimmer when it is at position n. Define ΔXn=Xn+1−Xn and ΔTn=Tn+1−Tn as the trimmer travel interval and travel time, respectively, between positions n and n+1, and define ΔXN-1=ΔTN-1=0. The time, Tn, when the trimmer edge is at position n, and the edge position, Xn can be calculated as: T n = T 0 + ∑ n ′ = 0 n - 1 Δ T n ′ , and X n = X 0 + ∑ n ′ = 0 n - 1 Δ X n ′ . ( 10 ) and the total trimmer travel time for all N positions is TN-1. Divide the travel time ΔTn into integer M sub-intervals of equal length and define the fine-resolution time, tm,n, as: t m , n = T n + Δ T n M m . ( 11 ) Wherein nε[0, M−1] and define am,n as the constant trimmer acceleration between time tm,n and tm+1,n. The trimmer velocity and position at time tm,n are thus: v m , n = V n + Δ T n M ∑ m ′ = 0 m - 1 a m ′ , n , and x m , n = X n + Δ T n M ∑ m ′ = 0 m - 1 v m ′ , n + 1 2 Δ T n 2 M 2 ∑ m ′ = 0 m - 1 a m ′ , n . ( 12 ) respectively, therefore:Tn+1=tM,n=t0,n+1,Vn+1=νM,n=ν0,n+1, and Xn+1=xM,n=x0,n+1, (13) The trimmer travel distance can be expressed as a function of acceleration, velocity, and travel time by substituting νm,n into Xm,n in Equation (12), then setting xm,n to xM,n=Xn+1 using Equation (13) to obtain:ΔXn=Xn+1−Xn=VnΔTn−γnΔTn2. (14)where γ n = 1 M 2 ∑ m = 0 M - 2 ∑ m ′ = 0 m a m ′ , n + 1 2 1 M 2 ∑ m = 0 M - 1 a m , n . ( 15 ) For the case in which the acceleration is a constant An during interval n, am′,n=An for m′ ε [0, M−1], γn=1/2An, and Equation (14) reduces to the familiar kinematic equation. Equation (14) can be solved for ΔTn using the quadratic formula to obtain: Δ T n = - V n ± V n 2 + 4 Δ X n γ n 2 γ n , ( 16 ) Enabling the straight forward calculation of Tn with Equation (10). The trimmer motion optimization problem is that of finding elements, am,n, of the acceleration matrix, a, that minimize the total trimmer travel time TN-1. The problem can be formulated as follows: minimize a T N - 1 subject to : ( a ) V 0 = V N - 1 = 0 ( b ) V n = 0 if sgn ( Δ X n - 1 ) = - sgn ( Δ X n ) for n = 1 , … , N - 2 ( c ) 0 ≤ Δ T n for n = 0 , … , N - 1 ( d ) a mn ≤ A ma x for m = 0 , … , M - 1 and n = 0 , … , N - 1 ( e ) v mn ≤ V ma x for m = 0 , … , M - 1 and n = 0 , … , N - 1. ( f ) V n 2 + 4 Δ X n γ n ≥ 0 ( 17 ) Constraint (a) forces the velocity to be zero for the first and last trimmer positions, and constraint (b) forces the velocity to be zero at positions where the trimmer motion direction change. The sgn(x) function returns the sign of x, and is −1 if x<0, 0 if x=0, and 1 if x>0. Constraint (c) ensures all travel times are non-negative. Constraints (d) and (e) ensure the trimmer acceleration and velocity magnitudes remain below their mechanically-dictated maxima of Amax and Vmax, respectively. Constraint (f) ensures that the derivatives of ΔTn with respect to γn and Vn, do not diverge, and that ΔTn is real. An initial guess for a that satisfies all of the constraints in Equation (17) can be calculated as follows. Let M=2, Vn=0, and a0,n=−a1,n for all n. Then γn=a0,nΔTn/2 and ΔXn=a0,nΔT2n/4=v1,nΔTn/2. If one assigns a0,n=sgn(ΔXn)Amax, then ΔTn=√4ΔXn/a0,n, and if Vmax<ν1,n, then one can assign ν1,n=Vmax, calculate a new ΔTn=|2ΔXn/Vmax| and reassign a0,n=4ΔXn/ΔTn2=Vmax2/ΔXn. The initial guess can be extended to the case of any M that is a multiple by resampling. In the current section, the expression for the gradient of TN-1 with respect to a is provided, and then each component of the expression is derived. The derivative of TN-1 with respect to am,n is calculated as follows: ∂ T N - 1 ∂ a m , n = ∑ n ′ = n N - 1 ∂ Δ T n ′ ∂ a m , n , where ( 18 ) ∂ Δ T n ′ ∂ a m , n = { M - m - 1 / 2 M 2 · ∂ Δ T n ∂ γ n for n ′ = n ∂ Δ T n ′ ∂ V n ′ · ∂ V n ′ ∂ a m , n for n ′ > n . ( 19 ) The components of Equation (19) are the following: ∂ Δ T n ∂ γ n = { ± Δ X n γ n V n 2 + 4 Δ X n γ n - - V n ± V n 2 + 4 Δ X n γ n 2 γ n 2 when γ n ≠ 0 - Δ X n 2 V n 3 when γ n = 0 , ( 20 ) ∂ Δ T n ′ ∂ a m , n = { - 1 ± V n ′ ( V n ′ 2 + 4 Δ X n ′ γ n ′ ) - 1 2 2 γ n ′ when γ n ′ ≠ 0 - Δ X n ′ V n ′ 2 when γ n ′ = 0 , and ( 21 ) ∂ V n ′ ∂ a m , n = { Δ T n M + a _ n ∂ Δ T n ∂ a m , n for n ′ = n + 1 ( 1 + a _ n ′ - 1 ∂ Δ T n ′ - 1 ∂ V n ′ - 1 ) ∂ V n ′ - 1 ∂ a m , n for n ′ > n + 1 , where ( 22 ) a _ n = 1 M ∑ m = 0 M - 1 a m , n ( 23 ) is the average acceleration during interval n. The calculation of Equation (19) is a recursive process, as Equation (22) for the case of n′=n+1 depends on Equation (19) for the case of n′=n, and Equation (22) for the case of n′>n+1 depends on Equation (22) for the case of n′−1. Constraints (a) and (b) have the following derivatives: ∂ Δ V n ′ ∂ a m , n = ∂ Δ v 0 , n ′ ∂ a m , n , where ( 24 ) ∂ Δ v m ′ , n ′ ∂ a m , n = { 0 for n ′ < n ∂ Δ T n ∂ a m , n · 1 M ∑ m ″ = 0 m ′ - 1 a m ″ , n + Δ T n M H ( m ′ - m ) for n ′ = n ∂ V n ′ ∂ a m , n + ∂ Δ T n ′ ∂ a m , n · 1 M ∑ m ″ = 0 m ′ - 1 a m ″ , n for n ′ > n . ( 25 ) Constraint (e) can be rewritten as:|νm,n|=νm,nsgn(νm,n)≦Vmax, (26)thus the derivative of constraint (e) with respect to am,n is: ∂ v m ′ , n ′ ∂ a m , n = ∂ Δ v m ′ , n ′ ∂ a m , n sgn ( v m ′ , n ′ ) + 2 v m ′ , n ′ δ ( v m ′ , n ′ ) = ∂ Δ v m ′ , n ′ ∂ a m , n sgn ( v m ′ , n ′ ) . ( 27 ) The derivative of constraint (f) is: ∂ ∂ a m , n ( V n ′ 2 + 4 Δ X n ′ γ n ′ ) = { 0 for n ′ < n 2 V n ′ ∂ V n ′ ∂ a m , n + { 4 Δ X n ∂ γ n ∂ a m , n 0 for n ′ = n for n ′ > n . ( 28 ) The second partial derivative in Equation (29) can be calculated by rewriting γn in Equation (15) to reveal where the am,n is located in the summations: γ n = 1 M 2 [ ∑ m ′ = 0 m - 1 ∑ m ″ = 0 m ′ a m ″ , n + ∑ m ′ = m M - 2 ( ∑ m ″ = 0 m - 1 a m ″ , n + a m , n + ∑ m ″ = m + 1 m ′ a m ″ , n ) + 1 2 ∑ m ′ = 0 M - 1 a m ′ , n ] . ( 30 ) The first term on the right hand side of Equation (30) is independent of am,n and so are the first and third terms (summations) inside the parentheses, thus then derivatives with respect to am,n vanish and one obtains: ∂ γ n ∂ a m , n = 1 M 2 [ ∑ m ′ = m M - 2 1 + 1 2 ] = M - m - 1 / 2 M 2 . ( 31 ) Equation (19) is obtained by applying the chain rule as follows: ∂ Δ T n ∂ a m , n = ∂ Δ T n ∂ γ n ∂ γ n ∂ a m , n . ( 29 ) The second partial derivative in Equation (29) can be calculated by rewriting γn in Equation (15) to reveal where am,n is located in the summations: γ n = 1 M 2 [ ∑ m ′ = 0 m - 1 ∑ m ″ = 0 m ′ a m ″ , n + ∑ m ′ = m M - 2 ( ∑ m ″ = 0 m - 1 a m ″ , n + a m , n + ∑ m ″ = m + 1 m ′ a m ″ , n ) + 1 2 ∑ m ′ = 0 M - 1 a m ′ , n ] . ( 30 ) The first term on the right hand side of Equation (30) is independent of am,n, and so are the first and third terms (summations) inside the parentheses, thus the derivatives with respect to am,n vanish and one obtains: ∂ γ n ∂ a m , n = 1 M 2 [ ∑ m ′ = m M - 2 1 + 1 2 ] = M - m - 1 / 2 M 2 . ( 31 ) Differentiating Equation (16) with respect to γn and Vn produces Equation (20) and Equation (21), respectively, for the case of a non-zero γn. Applying L'Hôpital's rule to those results, when the “±” is negative, yields Equation (20) and Equation (21) for the case when γn is zero. Equation (22) for the case of n′=n+1 is obtained by setting m=M in Equation (12), thus νm,n=νM,n=Vn+1=Vn′, and differentiating the result with respect to am,n under the recognition that ΔTn is dependent on am,n. Equation (22) for the case of n′>n+1 is obtained using the chain rule: ∂ V n ′ ∂ a m , n = ∂ V n ′ ∂ V n ′ - 1 ∂ V n ′ - 1 ∂ a m , n . ( 32 ) The first partial derivative on the right hand side of Equation is obtained by setting νm,n=νM,n′-1=Vn′ in Equation (12) and then differentiating the result with respect to Vn′-1. The second partial derivative in Equation (32) (as in Equation (22)) is obtained recursively from the evaluation of Equation (22) from the previous n′ value. FIG. 27 is a block diagram illustrating an exemplary operating environment for performing a portion of disclosed methods according to an embodiment of the present invention. This exemplary operating environment is only an example of an operating environment and is not intended to suggest any limitation as to the scope of use or functionality of operating environment architecture. Neither should the operating environment be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment. Further, one skilled in the art will appreciate that the systems and methods disclosed herein can utilize a general-purpose computing device in the form of a computer 1401. The methods discussed above can be performed by the computer 1401. For example, the computer 1401 can perform the duties and responsibilities of the controller 60 discussed above in FIGS. 1-2. Further, the computer 1401 can perform and control the responsibilities of the irradiation controller 62, the SS system controller 64, and the position planning controller 66 discussed above. The components of the computer 1401 can comprise, but are not limited to, one or more processors or processing units 1403, a system memory 1412, and a system bus 1413 that couples various system components including the processor 1403 to the system memory 1412. In the case of multiple processing units 1403, the system can utilize parallel computing. The system bus 1413 represents one or more of several possible types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, such architectures can comprise an Industry Standard Architecture (ISA) bus, a Micro Channel Architecture (MCA) bus, an Enhanced ISA (EISA) bus, a Video Electronics Standards Association (VESA) local bus, an Accelerated Graphics Port (AGP) bus, and a Peripheral Component Interconnects (PCI), a PCI-Express bus, a Personal Computer Memory Card Industry Association (PCMCIA), Universal Serial Bus (USB) and the like. The bus 1413, and all buses specified in this description can also be implemented over a wired or wireless network connection and each of the subsystems, including the processor 1403, a mass storage device 1404, an operating system 1405, DTSS software 1406, DTSS data 1407, a network adapter 1408, system memory 1412, an Input/Output Interface 1410, a display adapter 1409, a display device 1411, and a human machine interface 1402, can be contained within one or more remote computing devices 1414a,b,c at physically separate locations, connected through buses of this form, in effect implementing a fully distributed system. The computer 1401 typically comprises a variety of computer readable media. Exemplary readable media can be any available media that is accessible by the computer 1401 and comprises, for example and not meant to be limiting, both volatile and non-volatile media, removable and non-removable media. The system memory 1412 comprises computer readable media in the form of volatile memory, such as random access memory (RAM), and/or non-volatile memory, such as read only memory (ROM). The system memory 1412 typically contains data such as DTSS data 1407 and/or program modules such as operating system 1405 and DTSS software 1406 (i.e., controlling the various controllers 60 and modules 62, 64, 66 discussed above) that are immediately accessible to and/or are presently operated on by the processing unit 1403. In another aspect, the computer 1401 can also comprise other removable/non-removable, volatile/non-volatile computer storage media. By way of example, FIG. 27 illustrates a mass storage device 1404, which can provide non-volatile storage of computer code, computer readable instructions, data structures, program modules, and other data for the computer 1401. For example and not meant to be limiting, a mass storage device 1404 can be a hard disk, a removable magnetic disk, a removable optical disk, magnetic cassettes or other magnetic storage devices, flash memory cards, CD-ROM, digital versatile disks (DVD) or other optical storage, random access memories (RAM), read only memories (ROM), electrically erasable programmable read-only memory (EEPROM), and the like. Optionally, any number of program modules can be stored on the mass storage device 1404, including by way of example, an operating system 1405 and DTSS software 1406. Each of the operating system 1405 and DTSS software 1406 (or some combination thereof) can comprise elements of the programming and the DTSS software 1406. DTSS data 1407 can also be stored on the mass storage device 1404. DTSS data 1407 can be stored in any of one or more databases known in the art. Examples of such databases include DB2®, Microsoft® Access, Microsoft® SQL Server, Oracle®, mySQL, PostgreSQL, and the like. The databases can be centralized or distributed across multiple systems. In another aspect, the user can enter commands and information into the computer 1401 via an input device (not shown). Examples of such input devices comprise, but are not limited to, a keyboard, pointing device (e.g., a “mouse”), a microphone, a joystick, a scanner, tactile input devices such as gloves, and other body coverings, and the like. These and other input devices can be connected to the processing unit 1403 via a human machine interface 1402 that is coupled to the system bus 1413, but can be connected by other interface and bus structures, such as a parallel port, game port, an IEEE 1394 Port (also known as a Firewire port), a serial port, or a universal serial bus (USB). In yet another aspect, a display device 1411 can also be connected to the system bus 1413 via an interface, such as a display adapter 1409. It is contemplated that the computer 1401 can have more than one display adapter 1409 and the computer 1401 can have more than one display device 1411. For example, a display device can be a monitor, an LCD (Liquid Crystal Display), or a projector. In addition to the display device 1411, other output peripheral devices can comprise components such as speakers (not shown) and a printer (not shown) which can be connected to the computer 1401 via Input/Output Interface 1410. Any step and/or result of the methods can be output in any form to an output device. Such output can be any form of visual representation, including, but not limited to, textual, graphical, animation, audio, tactile, and the like. The computer 1401 can operate in a networked environment using logical connections to one or more remote computing devices 1414a,b,c. By way of example, a remote computing device can be a personal computer, a laptop computer, portable computer, a server, a router, a network computer, a peer device or other common network node, and so on. Logical connections between the computer 1401 and a remote computing device 1414a,b,c can be made via a local area network (LAN) and a general wide area network (WAN). Such network connections can be through a network adapter 1408. A network adapter 1408 can be implemented in both wired and wireless environments. Such networking environments are conventional and commonplace in offices, enterprise-wide computer networks, intranets, and the Internet 1415. According to an aspect, the computer 1401, via the DTSS software 1406 and DTSS data 1407, can control the operation of the SS ion therapy system 10 according to an aspect. In another aspect, the computer 1401 can comprise the controller 60 of the present invention, as well as the various controllers (irradiation controller 62, SS system controller 64, and position planning controller 66 as discussed in reference to FIG. 2). For purposes of illustration, application programs and other executable program components such as the operating system 1405 are illustrated herein as discrete blocks, although it is recognized that such programs and components reside at various times in different storage components of the computing device 1401, and are executed by the data processor(s) of the computer. An implementation of DTSS software 1406 can be stored on or transmitted across some form of computer readable media. Any of the disclosed methods can be performed by computer readable instructions embodied on computer readable media. Computer readable media can be any available media that can be accessed by a computer. By way of example and not meant to be limiting, computer readable media can comprise “computer storage media” and “communications media.” “Computer storage media” comprise volatile and non-volatile, removable and non-removable media implemented in any methods or technology for storage of information such as computer readable instructions, data structures, program modules, or other data. Exemplary computer storage media comprises, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computer. While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention. To the extent necessary to understand or complete the disclosure of the present invention, all publications, patents, and patent applications mentioned herein are expressly incorporated by reference therein to the same extent as though each were individually so incorporated. Having thus described exemplary embodiments of the present invention, those skilled in the art will appreciate that the within disclosures are exemplary only and that various other alternatives, adaptations, and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims. M. Bues, W. D. Newhauser, U. Titt and A. R. Smith, “Therapeutic step and shoot proton beam spotscanning with a multi-leaf collimator: a Monte Carlo study,” Radiation protection dosimetry 115, 164-169 (2005). A. J. Lomax, T. Bortfeld, G. Goitein, J. Debus, C. Dykstra, P. A. Tercier, P. A. Coucke and R. O. Mirimanoff, “A treatment planning inter-comparison of proton and intensity modulated photon radiotherapy,” Radiother Oncol 51, 257-271 (1999). J. D. Fontenot, A. K. Lee and W. D. Newhauser, “Risk of secondary malignant neoplasms from proton therapy and intensity-modulated x-ray therapy for early-stage prostate cancer,” International journal of radiation oncology, biology, physics 74, 616-622 (2009). ICRP, “Recommendations of the International Commission on Radiological Protection: Publication 60,” N0, (1991). E. J. Hall, Radiobiology for the Radiologist, 5 ed. (Lippincott Williams & Wilkins, Philadelphia, Pa., 2000). R. Miralbell, L. Cella, D. Weber and A. Lomax, “Optimizing radiotherapy of orbital and paraorbital tumors: intensity-modulated X-ray beams vs. intensity-modulated proton beams,” International journal of radiation oncology, biology, physics 47, 1111-1119 (2000). R. Miralbell, A. Lomax and M. Russo, “Potential role of proton therapy in the treatment of pediatric medulloblastoma/primitive neuro-ectodermal tumors: spinal theca irradiation,” International journal of radiation oncology, biology, physics 38, 805-811 (1997). R. Miralbell, A. Lomax, L. Cella and U. Schneider, “Potential reduction of the incidence of radiation induced second cancers by using proton beams in the treatment of pediatric tumors,” Int J Radiat Oncol Biol Phys 54, 824-829 (2002). D. C. Weber, A. V. Trofimov, T. F. Delaney and T. Bortfeld, “A treatment planning comparison of intensity modulated photon and proton therapy for paraspinal sarcomas,” International journal of radiation oncology, biology, physics 58, 1596-1606 (2004). R. T. Flynn, S. R. Bowen, S. M. Bentzen, T. Rockwell Mackie and R. Jeraj, “Intensity-modulated x-ray (IMXT) versus proton (IMPT) therapy for theragnostic hypoxia-based dose painting,” Phys Med Biol 53, 4153-4167 (2008). L. Widesott, A. Pierelli, C. Fiorino, I. Dell'oca, S. Broggi, G. M. Cattaneo, N. Di Muzio, F. Fazio, R. Calandrino and M. Schwarz, “Intensity-modulated proton therapy versus helical tomotherapy in nasopharynx cancer: planning comparison and NTCP evaluation,” International journal of radiation oncology, biology, physics 72, 589-596 (2008). D. Thorwarth, M. Soukup and M. Alber, “Dose painting with IMPT, helical tomotherapy and IMXT: A dosimetric comparison,” Radiother Oncol 86, 30-34 (2008). A. J. Lomax, M. Goitein and J. Adams, “Intensity modulation in radiotherapy: photons versus protons in the paranasal sinus,” Radiother Oncol 66, 11-18 (2003). A. Trofimov, P. L. Nguyen, J. J. Coen, K. P. Doppke, R. J. Schneider, J. A. Adams, T. R. Bortfeld, A. L. Zietman, T. F. Delaney and W. U. Shipley, “Radiotherapy treatment of early-stage prostate cancer with IMRT and protons: A treatment planning comparison,” Int J Radiat Oncol Biol Phys (2007). ICRU, “Prescribing, Recording, and Reporting Proton-Beam Therapy, ICRU Report 78,” in J. ICRU, Vol. 7, (Oxford University Press, UK, 2007). A. R. Smith, “Proton therapy,” Phys Med Biol 51, R491-504 (2006). A. J. Lomax, T. Bohringer, A. Bolsi, D. Coray, F. Emert, G. Goitein, M. Jermann, S. Lin, E. Pedroni, H. Rutz, O. Stadelmann, B. Timmermann, J. Verwey and D. C. Weber, “Treatment planning and verification of proton therapy using spot scanning: initial experiences,” Med Phys 31, 3150-3157 (2004). E. Pedroni, R. Bacher, H. Blattmann, T. Bohringer, A. Coray, A. Lomax, S. Lin, G. Munkel, S. Scheib, U. Schneider and A. Tuorovsky, “The 200-MeV proton therapy project at the Paul Scherrer Institute: conceptual design and practical realization,” Med Phys 22, 37-53 (1995). E. Pedroni and H. Enge, “Beam optics design of compact gantry for proton therapy,” Med Biol Eng Comput 33, 271-277 (1995). A. Lomax, “Intensity modulation methods for proton radiotherapy,” Phys Med Biol 44, 185-205 (1999). M. T. Gillin, N. Sahoo, M. Bues, G. Ciangaru, G. Sawakuchi, F. Poenisch, B. Arjomandy, C. Martin, U. Titt, K. Suzuki, A. R. Smith and X. R. Zhu, “Commissioning of the discrete spot scanning proton beam delivery system at the University of Texas M.D. Anderson Cancer Center Proton Therapy Center, Houston,” Med Phys 37, 154-163 (2010). J. Daartz, M. Bangert, M. R. Bussiere, M. Engelsman and H. M. Kooy, “Characterization of a minimultileaf collimator in a proton beamline,” Med Phys 36, 1886-1894 (2009). S. Safai, T. Bortfeld and M. Engelsman, “Comparison between the lateral penumbra of a collimated double-scattered beam and uncollimated scanning beam in proton radiotherapy,” Phys Med Biol 53, 1729-1750 (2008). E. Shaw, C. Scott, L. Souhami, R. Dinapoli, R. Kline, J. Loeffler and N. Farnan, “Single dose radiosurgical treatment of recurrent previously irradiated primary brain tumors and brain metastases: final report of RTOG protocol 90-05,” Int J Radiat Oncol Biol Phys 47, 291-298 (2000). R. A. Siochi, “Leakage reduction for the Siemens Moduleaf,” J Appl Clin Med Phys 10, 2894 (2009). |
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claims | 1. In a nuclear power plant, a system for aligning a nuclear fuel bundle and handling selected fuel rods within the fuel bundle, the fuel bundle residing in a spent fuel pool within the plant, the fuel bundle having one or more water rods and a plurality of fuel rods including full-length fuel rods and part-length fuel rods, the part-length fuel rods having an upper end plug extending vertically within the bundle through a plurality of axially spaced fuel spacers provided between a top end and bottom end of the fuel bundle, each fuel spacer including a plurality of individual cells accommodating corresponding fuel rods and water rods, the system comprising:a fuel prep machine configured to attach to a wall of the spent fuel pool for supporting the fuel bundle thereon,a bundle alignment assembly attached to the fuel prep machine for aligning fuel rods and water rods within the fuel bundle to remove one or both of any twist or bow present in the fuel bundle,wherein the bundle alignment assembly includes a plurality of axially spaced alignment stations configured to be positioned between the top and bottom ends of the fuel bundle for vertically aligning groups of fuel rods and at least one water rod,wherein each alignment station includes a plurality of alignment blade bundles, each blade bundle including a plurality of metal blades rotatable into the fuel bundle from a disengaged position, in which the blades are substantially vertical and disengaged from the fuel bundle, to an engaged position, in which the blades are substantially horizontal and engaged within the fuel bundle, for vertically aligning groups of fuel rods and at least one water rod,a rod grapple tool for extracting selected part-length rods from within the fuel bundle, anda fuel rod guide block slidable onto the top end of the fuel bundle for protecting an uppermost fuel spacer of the fuel bundle, and for aligning fuel rods within individual cells of all the fuel spacers in the fuel bundle. 2. The system of claim 1, wherein the rod grapple tool includes:a gripper at an end of the tool insertable into the fuel bundle for extracting a part-length fuel rod from the bundle, anda protective, removable guide pin inserted within the gripper prior to rod grapple tool insertion, the guide pin having a tapered pin end to prevent damage to the fuel spacers as the rod grapple tool is inserted into the fuel bundle. 3. The system of claim 2, further comprising:a guide pin retrieval tool for, when the rod grapple tool has been inserted into the fuel bundle so that the guide pin and gripper are positionable over a given part-length fuel rod to be extracted, removing the guide pin to permit the gripper to be attached to the upper end plug of the part-length fuel rod without damaging the bundle. 4. The system of claim 3, whereinthe guide pin includes a threaded section above the tapered pin end, andthe guide pin retrieval tool includes an extension element with a tongue attached thereto, the tongue having a threaded opening which fits over the blunt end of the guide pin to mate with the threaded section of the guide pin for releasing the guide pin from the rod grapple tool so as to expose the gripper. 5. The system of claim 4, wherein the guide pin retrieval tool is configured to attach to a handling pole which enables an operator to lower the guide pin retrieval tool in place between the part-length rod grapple tool, the guide pin retrieval tool being insertable down through the rod guide block and through one or more fuel spacers to a position above both the rod grapple tool and a part-length fuel rod to be extracted, so as to remove the guide pin and expose the gripper. 6. The system of claim 1, whereinthe fuel bundle includes an upper tie plate at the top end and a lower tie plate at the bottom end and a generally rectangular channel extending the length of the fuel bundle and surrounding the fuel bundle, upper tie plate and lower tie plate, andthe channel and upper tie plate are removed in the fuel prep machine to expose the fuel bundle top end. 7. The system of claim 1, wherein the fuel rod guide block includes:an upper plate,a lower plate,a plurality of stainless steel tubes extending vertically between the upper and lower plates configured to accept fuel rods as the fuel rod guide block is placed over the fuel rods and water rods of the bundle at the bundle top end, anda pair of side plates attached to the sides of the upper and lower plates by a plurality of fasteners to secure the tubes there between. 8. The system of claim 7, wherein the upper and lower plates include a plurality of openings configured to mirror the locations of the fuel rods and water rods in the fuel bundle so as to align with the tubes, the openings and tubes alignable with the fuel rods and water rods to permit the fuel rod guide block to slide over the fuel bundle. 9. The system of claim 1, wherein the rod grapple tool includes a first end handled by an operator and a second end insertable into the fuel bundle to retrieve a part-length rod, the second end having a protective, removable guide pin which prevents the rod grapple tool from damaging fuel rod spacers as the rod grapple tool is inserted into the bundle. 10. The system of claim 1, wherein the rod grapple tool includes:a lower housing containing a movable gripper rod therein that is extendable from the lower housing, the gripper rod having a proximal end within the lower housing and a distal end terminating in a gripper that is attachable to the end plug of a part-length fuel rod configured to extract the part-length fuel rod from the bundle,a protective, removable guide pin which is attached to the gripper rod distal end so that the gripper is not exposed as the rod grapple tool is inserted into the fuel bundle,an upper housing connected to the lower housing, the upper housing including an activation rod therein which has a first end connected to the proximal end of the gripper rod within the lower housing,a push-pull handle actuatable by an operator and connected to a second end of the activation rod, the push-pull handle having a locked position which prevents activation rod movement and a released position that enables the actuation rod to be pushed forward within the upper housing to move the gripper rod with gripper and guide pin in an extended position. 11. The system of claim 10, wherein the push-pull handle is placed in the released position so that the gripper rod is extended only to remove the guide pin, so as to expose the gripper and to attach the gripper to the part-length fuel rod to be extracted, the push-pull handle being returned to the locked position to remove the part-length fuel rod from the bundle. 12. The system of claim 10, further comprising a guide pin retrieval tool for removing the guide pin to permit the gripper to be attached to the upper end plug of the part-length fuel rod. 13. In a nuclear power plant, a system for removing twist and/or bow in a nuclear fuel bundle to permit inspection and replacement of one or more fuel rods or water rods within the fuel bundle, the fuel bundle having been irradiated in a reactor core and removed to a spent fuel pool within the plant, the system comprising:a fuel prep machine configured to attach to a wall of the spent fuel pool for supporting the fuel bundle thereon, anda bundle alignment assembly attached to the fuel prep machine for aligning fuel rods and water rods within the fuel bundle to remove one or both of any twist or bow within the fuel bundle,wherein the bundle alignment assembly includes a mounting frame, the mounting frame having a plurality of axially spaced alignment stations mounted thereon, each alignment station including a plurality of alignment blade bundles, each blade bundle including a plurality of metal blades rotatable into the fuel bundle from a disengaged position, in which the blades are substantially vertical and disengaged from the fuel bundle, to an engaged position, in which the blades are substantially horizontal and engaged within the fuel bundle, for vertically aligning groups of fuel rods and at least one water rod. 14. The system of claim 13, wherein the fuel prep machine includes:a stanchion with rails formed thereon,a fuel prep carriage for supporting the fuel bundle thereon, the fuel prep carriage connected to the rails and vertically movable along the rails of the stanchion, the fuel prep carriage having an upper rotating fixture and a lower rotating fixture to permit the bundle to be rotated for visual inspection. 15. The system of claim 14, wherein the mounting frame is attached at upper and lower ends to the upper and lower rotating fixtures. 16. The system of claim 15, wherein each alignment blade bundle in a given alignment station is sequentially rotatable into the fuel bundle so as to create a protective grid for vertically aligning a plurality of fuel rods and at least one water rod in the bundle. 17. The system of claim 16, wherein the protective grid formed by the alignment blade bundles are configured to vertically align with the plurality of fuel rods and at least one water rod above each of the fuel spacers in the bundle. 18. The system of claim 16, wherein the protective grid formed by the alignment blade bundles is configured to vertically align the plurality of fuel rods and at least one water rod below each of the fuel spacers in the bundle. 19. The system of claim 16, wherein the protective grid formed by the alignment blade bundles is configured to vertically align the plurality of fuel rods and at least one water rod above and below each of the fuel spacers in the bundle. 20. The system of claim 16, wherein a given alignment station includes three alignment blade bundles, one alignment blade bundle rotatable in a first plane, and the other two blade bundles rotatable in a second plane different from the first to form the grid. 21. The system of claim 20, wherein the one alignment bundle is arranged beneath the other two blade bundles in each alignment station. 22. The system of claim 16, wherein selected blades can be removed from selected blade bundles to align different sections of fuel rods within the bundle. 23. The system of claim 22, wherein different combination of blades of the alignment bundles are rotatable in the engaged position to align one or more fuel rods in at least one of a half cross-section of the bundle, a quarter cross-section of the bundle and an eighth cross-section of the bundle. 24. A fuel rod alignment system for a fuel bundle residing in a spent fuel pool within a nuclear power plant, the fuel bundle having one or more water rods a plurality of fuel rods including full-length rods and part-length rods extending vertically within the bundle through a plurality of axially spaced fuel spacers provided between a top end and a bottom end of the fuel bundle, each fuel spacer including a plurality of individual cells accommodating corresponding fuel rods and water rods, the system comprising:a fuel prep machine configured to attach to a wall of the spent fuel pool for supporting the fuel bundle thereon, anda fuel rod guide block slidable onto the top end of the fuel bundle for protecting an uppermost fuel spacer of the fuel bundle, and for aligning fuel rods within individual cells of all the fuel spacers in the fuel bundle,the fuel prep machine including,a stanchion with rails formed thereon,a fuel prep carriage for supporting the fuel bundle thereon, the fuel prep carriage connected to the rails and vertically movable along the rails of the stanchion, the fuel prep carriage having an upper rotating fixture and a lower rotating fixture to permit the bundle to be rotated for visual inspection,a bundle alignment assembly attached to the fuel prep machine including a plurality of axially spaced alignment stations configured to be positioned between the top and bottom ends of the fuel bundle, wherein the alignment station includes a plurality of alignment blade bundles, each blade bundle including a plurality of metal blades rotatable into the fuel bundle from a disengaged position, in which the blades are substantially vertical and disengaged from the fuel bundle, to an engaged position, in which the blades are substantially horizontal and engaged within the fuel bundle, for vertically aligning groups of fuel rods and at least one water rod. 25. The system of claim 24, whereinthe water rods extend vertically within the fuel bundle from the fuel bundle bottom end to a location above the uppermost fuel spacer of the fuel bundle, with top ends of the water rods being tapered, andthe fuel rod guide block is slidable over the fuel rods and water rods to rest on the tapered top ends of the water rods above the uppermost fuel spacer. 26. The system of claim 24, wherein the fuel rod guide block includes:an upper plate,a lower plate,a plurality of stainless steel tubes extending vertically between the upper and lower plates configured to accept fuel rods as the fuel rod guide block is placed over the fuel rods and water rods of the bundle at the bundle top end, anda pair of side plates attached to sides of the upper and lower plates by a plurality of fasteners to secure the tubes there between. 27. The system of claim 26, wherein the upper and lower plates include a plurality of opening configured to mirror the locations of the fuel rods and water rods in the fuel bundle so as to align with the tubes, the opening and tubes alignable with the fuel rods and water rods to permit the fuel rod guide block to slide over the fuel bundle. 28. The system of claim 26, wherein each side plate includes a plurality of holes therein for facilitating the decontamination of the fuel rod guide once removed from the spent fuel pool. 29. The system of claim 26, wherein the fuel rod guide block further includes:a bail having a generally inverted U-shape with a pair of arms connected to the side plates and an upper horizontal portion attachable to a handling pole for installing the fuel rod guide block on and removing the fuel rod guide block from the top end of the fuel bundle. 30. The system of claim 29, wherein the fuel rod guide block further includes:a pair of bail attachment plates, each bail attachment plate arranged between a side of the tubes facing a corresponding side plate and an inner surface of the corresponding side plate,a pair of bail stops which limit travel of the bail, each bail stop attached to a corresponding bail attachment plate by a plurality of fasteners so as to sandwich its corresponding side plate there between,wherein bottom ends of each of the bail arms are supported by a corresponding bail stop and are attached to a corresponding bail attachment plate by a fastener. |
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063114763 | claims | 1. A solar thermal engine for propelling and powering a craft, the solar thermal engine comprising: a housing having an optical cavity adapted for receiving a beam of concentrated sunlight and converting the beam into ambient thermal energy; a propellant annulus coupled to the housing and selectively operable in a heating mode wherein the propellant annulus transmits at least a first portion of the ambient thermal energy to heat a flow of propellant; a plurality of static power converters coupled to the housing, the static power converters receiving the first portion of the ambient thermal energy when the propellant annulus is not operated in the heating mode, the plurality of static power converters employing the first portion of the ambient thermal energy to generate electrical energy; and an electrical energy storage device coupled to the plurality of static power converters, the electrical energy storage device receiving and storing the electrical energy generated by the plurality of static power converters. a housing having an optical cavity for receiving a beam of concentrated sunlight and converting the beam into ambient thermal energy; a propellant annulus coupled to the housing and operable for selectively heating a flow of propellant, the propellant annulus transmitting at least a first portion of the ambient thermal energy to the flow of propellant when the ambient thermal energy is employed to heat the flow of propellant; a plurality of static power converters for receiving a second portion of the ambient thermal energy and generating electrical energy when a magnitude of the second portion of thermal energy exceeds a predetermined thermal energy threshold; and an electrical energy storage device coupled to the plurality of static power converters, the electrical energy storage device receiving and storing the electrical energy generated by the plurality of static power converters. providing an engine having an optical cavity; directing a beam of concentrated light into the optical cavity; converting the beam of concentrated light into thermal energy; determining if a propellant is to be heated; transmitting at least a first portion of the ambient thermal energy to heat the propellant if the propellant is to be heated; transmitting at least the first portion of the ambient thermal energy to a static power converter to generate electrical energy if the propellant is not to be heated; and storing the electrical energy in an electrical energy storage device. 2. The solar thermal engine of claim 1, wherein a heat exchanger surrounds the optical cavity and is coupled to the propellant annulus, the heat exchanger operable for transferring the at least a first portion of the ambient thermal energy to the propellant annulus. 3. The solar thermal engine of claim 2, wherein the heat exchanger includes a first boundary wall and a second boundary wall that is spaced radially outwardly of the first boundary wall, wherein the propellant annulus is formed between the first and second boundary walls and wherein the propellant annulus is disposed between the first boundary wall and the plurality of static power converters. 4. The solar thermal engine of claim 3, wherein the plurality of static power converters are arranged in a single cylindrical array disposed radially outwardly of the propellant annulus. 5. The solar thermal engine of claim 4, wherein a surface of the single cylindrical array of static power converters shares a common boundary with a heat exchanger coolant passage. 6. The solar thermal engine of claim 3, wherein the plurality of static power converters are arranged in a plurality of cylindrical arrays, each of the plurality of cylindrical arrays being disposed radially outwardly of the propellant annulus. 7. The solar thermal engine of claim 1, wherein the plurality of static power converters are arranged in a plurality of cylindrical arrays disposed within the optical cavity. 8. The solar thermal engine of claim 7, wherein a heat exchanger surrounds the optical cavity and is coupled to the propellant annulus, the heat exchanger operable for transferring the at least a first portion of the ambient thermal energy to the propellant annulus. 9. The solar thermal engine of claim 8, wherein the heat exchanger includes a first boundary wall and a second boundary wall that is spaced radially outwardly of the first boundary wall, wherein the propellant annulus is formed between the first and second boundary walls and wherein the propellant annulus is disposed between the second boundary wall and the plurality of static power converters. 10. The solar thermal engine of claim 1, wherein the electrical energy storage device includes an electrochemical energy storage device. 11. The solar thermal engine of claim 1, wherein the electrical energy storage device includes an electromechanical energy storage device. 12. The solar thermal engine of claim 1, wherein the plurality of static power converters includes a converter selected from a group consisting of alkali metal thermoelectric converters, thermionic converters, thermoelectric power converters and thermophotovoltic converters. 13. The solar thermal engine of claim 1, further including at least one heat pipe condensers for rejecting a remainder portion of the ambient thermal energy from the engine. 14. A solar thermal engine for propelling and powering a craft, the solar thermal engine comprising: 15. The solar thermal engine of claim 14, wherein the electrical energy storage device includes a storage device selected from a group consisting of an electrochemical energy storage device and an electromechanical energy storage device. 16. The solar thermal engine of claim 14, wherein the plurality of static power converters includes a converter selected from a group consisting of alkali metal thermoelectric converters, thermionic converters, thermoelectric power converters and thermophotovoltic converters. 17. A method for propelling and powering a craft, the method comprising the steps of: 18. The method of claim 17, further comprising the step of rejecting the ambient thermal energy not consumed during the steps of heating the propellant and converting the second portion of the ambient thermal energy into electrical energy. 19. The method of claim 17, wherein a storage device selected from a group consisting of an electrochemical energy storage device and an electromechanical energy storage device is employed in the step of storing the electrical energy. 20. The method of claim 17, wherein a converter selected from a group consisting of alkali metal thermoelectric converters, thermionic converters, thermoelectric power converters and thermophotovoltic converters is employed in the step of transmitting at least the first portion of the ambient thermal energy to the static power converter to generate electrical energy. |
050383701 | summary | BACKGROUND OF THE INVENTION The invention relates to an arrangement for generating an X-ray or gamma beam with small cross-section and variable direction, having an X-ray or gamma emitter, from the focus of which a bundle of rays emerges, and a diaphragm arrangement, which cuts out a beam from the bundle of rays and comprises a rotatable hollow-cylindrical first diaphragm body having two mutually offset helical slits on the circumference. Of interest is commonly owned copending application entitled "Device for Forming an X-ray or Gamma Beam of Small Cross-Section and Variable Direction" Ser. No. 400,188 filed Aug. 29,1989 in the name of G. Harding. Arrangements of this type are essentially known from European laid-open patent application 74,021 for medical applications and from German Offenlegungsschrift 3,443,095 corresponding to U.S. Pat. No. 4,750,196 for industrial applications. The diaphragm body of a radiation-absorbing material has in this case the form of a hollow cylinder which is provided on its circumference with two mutually offset helically encircling slits. If a bundle of parallel rays falls onto such a diaphragm body perpendicularly to its cylinder axis, there is always a point at which an X-ray beam passes through the two slits. If the diaphragm body is turned, this point shifts along the axis, so that a periodically moved X-ray beam emerges behind the diaphragm body. This periodically moved X-ray beam can be used for medical or industrial examinations. An X-ray beam with trapezoidal cross-section is defined by the two slits in the diaphragm body. What is desired, however, is a square or a circular cross-section, producing a directionally independent spatial resolution. With the same width of the two slits, the approximation to a square cross-sectional shape is all the better the larger the angle by which the two slits intersect each other. A larger angle of intersection could be achieved by using a diaphragm body with large diameter and small axial length. For many applications, however, a relatively large angle of deflection of the X-ray beam is necessary, which necessitates a corresponding axial length of the diaphragm body; a large diameter is undesirable in many applications due to the associated unit volume. SUMMARY OF THE INVENTION The object of the present invention is to design an arrangement of the type mentioned at the beginning in such a way that a favorable beam cross-section is achieved even in the case of a diaphragm body with small diameter and relatively large axial length. This object is achieved according to the invention by the fact that the slits wind around the diaphragm body in at least one turn each and are shaped in such a way that at least one straight line runs through the slits towards the focus, the position of which line can be varied by turning the diaphragm body. Thus, while in the prior art the two slits extend over an angle at circumference of 180.degree. or have only half a turn, the slits in the invention extend over an angle at circumference of at least 360.degree. or they have at least one turn (one turn corresponds to an angle at circumference of 360.degree..) The projection of the slits onto the axis of rotation or symmetry of the hollow-cylindrical diaphragm bodies therefore forms a considerably larger angle with the axis concerned, so that the X-ray beam cut out with a given slit width has considerably smaller dimensions in the direction of the said axis. With the arrangement according to the invention, as many X-ray beams are generated as there are straight lines which pass through the slits and impinge on the focus. In many applications, however, for example those in which the scattered radiation produced by the X-ray beam is to be measured, one wishes to work just with a single X-ray beam. In a development of the invention it is therefore envisaged that a second diaphragm body which only ever allows through a primary beam is arranged in the bundle of rays, and that the second diaphragm body is arranged and designed in such a way that the primary beam always coincides with one of the straight lines. In a preferred development, it is envisaged that the second diaphragm body has the form of a hollow cylinder, the axis of which lies in the plane containing the axis of symmetry and the focus and the cross-section of which is circular or semicircular and that the second diaphragm body is provided with one slit if of semicircular cross-section or with two helical slits mutually offset by 180.degree. on the circumference if of circular cross-section. If in this case the first diaphragm body is driven faster by a factor of 2n (n is an integer) than the second, an X-ray beam which moves periodically can be cut out. If the diaphragm arrangement is to form a spatially compact unit together with the X-ray or gamma emitter, the diameter of the diaphragm body is no longer negligible in comparison with its distance from the focus, so that an X-ray beam with larger axial distance emerges from the center of the diaphragm body than the beam which enters it. In order to satisfy these geometrical conditions, a further development of the invention envisages that the slits of the first diaphragm body have pitches differing from each other. In that case, the X-ray beams can only ever enter through one slit and emerge through the other slit. In a further development it is envisaged in this case that, of the slits in the first diaphragm body, the one with the greater pitch is narrower than the other one and that on the side of the first diaphragm body facing away from the focus a slit diaphragm is provided, the slit-shaped aperture of which lies in the plane formed by the focus and the axis of symmetry of the first diaphragm body. In this configuration, the dimension of the X-ray beam in the direction of the axis of symmetry is determined by the narrower of the two slits and its direction perpendicular thereto is determined by the aperture in the slit diaphragm. |
055263879 | summary | TECHNICAL FIELD This invention relates to spacers used in a boiling water nuclear reactor (BWR) fuel bundle for maintaining the fuel rods within the fuel bundle in their designed spaced apart relationship. More specifically, the spacer construction in accordance with this invention incorporates improved flow tabs on the peripheral band of the spacer to direct more of the liquid coolant flow toward the outer fuel rods in the bundle rather than merely into the spaces between the fuel rods. BACKGROUND Fuel bundles in boiling water nuclear reactors (BWR's) include an array of upstanding side-by-side fuel rods supported between upper and lower tie plates. Each bundle requires multiple spacers (e.g., seven, axially spaced along the bundle) for the maintenance of the fuel rods in designed spaced apart relationship. The bundle is surrounded between the tie plates by a fuel bundle channel. The lower tie plate is configured to permit the inflow of moderating water coolant while the upper tie plate permits the outflow of both water coolant and generated steam. The surrounding channel confines the flow of coolant to a path around the steam generating fuel rods separate from a water flooded core bypass region surrounding each fuel bundle. Flow tabs are used on the peripheral bands of each spacer to deflect liquid coolant flow from the band to the outer row of fuel rods. This flow redirection deposits water droplets on the fuel rods, increasing the water film thickness and improving the critical power performance of the outer fuel rods. Currently utilized flow tabs consist of simple, planar projections which extend upwardly from the band and which are bent inward at their outer ends. With reference to FIGS. 1 to 3, a conventional fuel assembly 10 comprises a plurality of fuel elements or rods 12 supported between an upper tie plate 14 and a lower tie plate 16. The fuel rods 12 pass through a plurality of fuel rod spacers 18 which provide intermediate support and retain the elongated rods in spaced relation. Each spacer contains a matrix of ferrules F, each adapted to receive and surround a corresponding fuel rod 12. In a typical arrangement, seven such spacers 18 may be located along the approximate 13 foot length of the fuel bundle. Each of the fuel rods 12 includes an elongated tube containing fissile fuel and other materials, such as fertile fuel, burnable poison, inert material or the like, sealed in the tube by upper and lower end plugs 20, 22, respectively. Lower end plugs 22 are formed with extensions for registration and support within openings formed in the lower tie plate 16. At the same time, the upper end plugs 20 are formed with extensions which fit into support openings in the upper tie plate 14. The fuel assembly 10 also includes a thin walled tubular flow channel 24 of substantially square cross section, sized to form a sliding fit over the upper and lower tie plates 14 and 16 as well as spacers 18 so that the channel may be easily mounted to or removed from the fuel bundle. The lower tie plate 16 is formed with a nosepiece 26 adapted to support the fuel assembly 10 in a socket in a core support plate (not shown) in the reactor pressure vessel. The end of this nosepiece is formed with an opening 28 which receives pressurized coolant in an upward flow direction. FIGS. 2 and 3 of the drawings show top and side views, respectively, of the corner region of a conventional spacer 18. Flow tabs 20 are shown extending upwardly from an upper edge 30 of the peripheral band 32 of the spacer, and between adjacent fuel rods 12. Each tab comprises a lower, substantially vertical portion 34 and an upper inwardly bent portion 36. Side edges of each tab are generally inwardly tapered in the upward direction, and both portions 34 and 36 are substantially planar. The bent upper portions 36 of the flow tabs 20 project into the region between each pair of fuel rods 12. The two phase (water and steam) coolant flow is upward, and the steam water mixture flows around the flow tabs while some of the flow is deflected in the direction normal to the flow tab, toward the interior of the spacer. This results in some water being deposited on the adjacent fuel rods 12 and increasing the thickness of the water film. Other representative examples of flow tabs incorporated into fuel bundle spacers may be found in U.S. Pat. Nos. 5,180,548; 5,080,858; 4,879,090; 4,692,302; 4,698,204; 4,683,115 and 4,039,379. SUMMARY OF THE INVENTION The present invention relates to an improved flow tab design which redirects more of the liquid component of the steam water mixture toward the outer fuel rods rather than into the space between the fuel rods, and which offers less resistance generally to the flow of coolant through the channel. In an exemplary embodiment, both the lower and upper portions of the flow tab are provided with secondary bends about vertical and inclined center lines. More specifically, the upper inwardly bent portion has a secondary bend along its inclined center line such that this center line is located downward relative to the outer or side edges of the tab. This shape imparts velocity components to the flow which are parallel to the spacer band and away from the flow tab. As a result, more water droplets are channeled directly to the surfaces of the outer fuel rods. The lower, substantially vertical portion of the flow tab is also formed with a secondary bend about its vertical center line such that the latter is located outwardly of the side edges of the tab, and outwardly of the spacer band itself. This improved lower tab configuration increases the stiffness of the flow tab, and makes it easier to form. In addition, the overall size of the tab relative to conventional tabs as shown in FIGS. 1-3, has been increased to deflect greater amounts of coolant flow. In its broader aspects, the invention relates to a spacer for use with a fuel bundle in a nuclear reactor, the spacer comprising a matrix of ferrules for surrounding individual fuel rods within a bundle; a band surrounding the matrix and defining a peripheral wall of the spacer, the band having an upper edge; a plurality of laterally spaced flow tabs extending upwardly from the upper edge, each flow tab having a substantially vertical portion and an inclined portion; and first means on the inclined portion for imparting velocity components to a flow of coolant along the fuel rods, which components are substantially parallel to the band. In another aspect, the invention relates to a spacer for use with a fuel bundle in a nuclear reactor, the spacer comprising a matrix of ferrules for surrounding individual fuel rods within a bundle; a band surrounding the matrix and defining a peripheral wall of the spacer, the band having an upper edge; and a plurality of laterally spaced flow tabs extending upwardly from the upper edge, each flow tab having a substantially vertical portion joined to the band and an inclined portion joined to the vertical portion and extending upwardly and inwardly relative to the vertical portion, the inclined portion having a first center line located downwardly and inwardly relative to a pair of lateral free edges of the inclined portion. In still another aspect, the invention relates to a spacer for use with a fuel bundle in a nuclear reactor comprising a matrix of ferrules for surrounding individual fuel rods within a bundle; a band surrounding the matrix and defining a peripheral wall of the spacer, the band having an upper edge; and a plurality of laterally spaced flow tabs extending upwardly from the upper edge, each flow tab having a lower substantially vertical portion and an upper inclined portion extending away from the vertical portion, the vertical portion having a vertical crease and the inclined portion having an inclined crease, each located centrally of the tab. It will be appreciated that the improved flow tab configuration in accordance with this invention directs more of the liquid flow directly onto the outer fuel rods and offers less resistance to coolant flow, thereby enhancing overall fuel bundle performance. Other objects and advantages of the invention will become apparent from the detailed description which follows. |
051209730 | summary | TECHNICAL FIELD OF THE INVENTION The invention relates to a method and device for inserting radioactive radiation sources into applicators and for withdrawing the radiation sources, comprising at least one shielded loading and/or storage station for the radiation sources, and a flexible thrust wire guided in a channel and having a coupling adapted to release the radiation source in the radiation position. BACKGROUND OF THE INVENTION AND PRIOR ART A device of this kind is described in European published application No. 0 158 630. It consists of one or more identical modules each comprising a shielded loading and/or storage station for radiation sources, which may not be identical, and a push rod, and offers the possibility of separating the conveying device from a hollow needle in the radiation position by operating a coupling between the radiation source and the push rod that is releasable in the radiation position. The radiation source can be introduced into the hollow needle by the push rod under remote control, and is released and deposited therein. During the treatment the hollow needle can be separated from the push rod so as to give the patient a large measure of freedom of movement. At the end of the treatment the conveying device is again coupled with the hollow needle, so that after engagement of the coupling the individual radiation sources can again be withdrawn individually into the loading and/or storage station. This known device has the disadvantage that a module with a conveying device is required for each radiation source. A further and more serious disadvantage is that in order to leave a radiation source in an applicator the coupling has to be released within the applicator. However, since the space available in hollow radiation needles for interstitial use is very limited, it is difficult to arrange a reliable release mechanism for the coupling in the radiation needle. OBJECT OF THE INVENTION It is therefore an object of the invention to provide a device and a process by means of which it is possible to bring radiation sources from a loading and/or storage station into an applicator, separate them there from the conveying device, leave them there for the duration of the treatment of a patient, and withdraw them again at the end of the treatment by means of the conveying device without operating or controlling the coupling in the region of the applicator. The means for doing this should be of simple construction and easy to use. SUMMARY OF THE INVENTION To this end, the invention consists in providing, in a device of the kind mentioned above, two drives connected respectively to a thrust and a traction wire each guided in a channel, the channels being combined at a fork. In cooperation with a radiation source the traction wire has a releasable coupling effective in the direction of traction and the thrust wire has a releasable coupling effective only in the direction of thrust. A switch is located between the channels leading to the applicators and those leading to the loading and/or storage station on the one hand and the fork on the other hand, and a means for releasing the coupling effective in the direction of traction is located between the switch and the fork. The switch may have a plurality of entrances and exits. The entrances may be connected via channels to the loading and/or storage station and the exits via channels to a corresponding number of applicators. In order to extract a radiation source from a storage channel in the loading and/or storage station and introduce it into one of the applicators, the traction cable having a releasable coupling effective in the direction of traction is first of all advanced by means of one of the two drives via the fork and the appropriately set switch into a storage channel of the loading and/or storage station, is coupled with the radiation source, and withdraws it into the region of the release means for the coupling effective in the direction of traction, which is arranged between the fork and the switch. There, the radiation source and the traction wire are separated, the traction wire is again withdrawn to its end position, and the thrust wire is advanced through the fork until it reaches the radiation source: it then pushes the radiation source through the switch into the applicator. Since there is no connection effective in the direction of traction between this thrust wire and the radiation source, the thrust wire merely serves to move the radiation source forward by pushing and can be withdrawn to its starting position after bringing the radiation source into the applicator, leaving the radiation source in the applicator. It will thus be seen that with two drives, one of which moves the radiation source in the direction of traction and the other in the direction of thrust, and by the provision of a fork and a switch, a very large number of radiation sources can be brought from a loading and/or storage station to a corresponding number of applicators. The applicators can then be separated from the device and remain in the patient. The device does not have to be recoupled with the applicators until the treatment is finished, when the radiation sources are moved successively back to the loading and/or storage station in the manner described. The radiation sources can comprise needle-shaped holders that are filled with radioactive material and have at one end a sleeve with inwardly-facing spring elements which, together with a pin that is located on one end of the traction wire and can be introduced into the sleeve, forms the releasable coupling effective in the direction of traction. Once introduced into the sleeve the pin is held frictionally by the ends of the springs and can be separated in a simple manner by means of a stop cooperating with an end face of the sleeve. For this purpose the greatest diameter of the end of the traction wire with the pin may be less than the diameter of the sleeve, and the stop may consist of a wire duct having an internal diameter greater than the diameter of the end of the traction wire carrying the pin but less than the diameter of the sleeve. Alternatively the radiation sources may consist of needle-shaped holders that are filled with radioactive material and have at one end a sleeve with inwardly-facing resilient hooks which, together with a locking groove on a pin located at one end of the traction wire to engage with the hooks, forms the releasable coupling effective in the direction of traction. In this case a form-locking connection is formed between the hooks and the groove in the pin which cannot come apart as the radiation source is transported through the channels. In this case the means of releasing the coupling effective in the direction of traction may comprise wedge-shaped faces that engage under oblique faces on the hooks, with the greatest diameter of the end of the traction wire carrying the pin being less than the diameter of the sleeve and the internal diameter of a wire duct through the release means being greater than the diameter of the end of the traction wire carrying the pin but less than the diameter of the sleeve. As another possibility, the radiation sources may consist of needle-shaped holders that are filled with radioactive material and consist at one end of magnetic material which, together with an extension, also of magnetic material, at one end of the traction wire, forms the releasable coupling effective in the direction of traction. In this case the release means can also consist of a stop cooperating with an end face of the sleeve, as described above for the first embodiment. |
description | This application claims the benefit of DE 10 2010 025 660.9, filed Jun. 30, 2010. The present embodiments relate to a device and method for irradiating a target volume with a particle beam. Particle therapy is an established way to treat tissue (e.g., malignant tumors). Irradiation methods are used in particle therapy, but may also be employed in non-therapeutic fields such as in research activities (e.g., for product development), or on non-living phantoms, bodies or materials. Irradiation methods may utilize charged particles such as, for example, protons, carbon ions, or other ions. The charged particles are accelerated to high energies, formed into a particle beam, and directed to one or more irradiation rooms by way of a high-energy beam transport system. The particle beam irradiates the object having a target volume in one of the irradiation rooms. In some cases, however, the target volume that is to be irradiated moves. During the irradiation of a patient, respiratory movement may, for example, cause the tumor to move. For research purposes, this type of movement may be simulated using model objects (e.g., phantoms). A “gating” irradiation method is a known way to deal with the possibility that the target volume may move. Such a method monitors the motion of the target volume. The particle beam, with which the target volume is irradiated, operates as a function of the monitoring and is thus dependent on the status of the target volume. When the target volume is located within a suitable or desired region, the particle beam is turned on and may be used to irradiate the target volume. When the target volume is located outside of the suitable or desired region, the particle beam is turned off and may not be used for irradiation purposes. In this way, the particle beam is activated, for irradiation purposes, only when the target volume is located in a suitable region. “Gating” irradiation methods of this type are known, for example, from Tsunashima Y. et al., titled “Efficiency of respiratory-gated delivery of synchrotron-based pulsed proton irradiation”, 2008 Phys. Med. Biol. 53 1947. The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, an accelerator that provides a particle beam capable of quickly and efficiently irradiating a moving target volume may be provided. An irradiation method that enables fast and efficient irradiation of a target volume may also be provided. One embodiment of an accelerator that accelerates a particle beam to an energy for irradiating a target volume is a particle accelerator that operates in phases. The working phases of the accelerator may alternate. During operation, the particles are accelerated by the accelerator in a first working phase. The accelerator may be filled with particles, and the accelerator may accelerate the particles to an irradiation energy provided for the irradiation. When the accelerator is in a second working phase following the first working phase, the accelerated particles are stored or circulated in the accelerator and may be provided and extracted for irradiation purposes. In one embodiment, the accelerator has a control device for controlling the accelerator during the irradiation of the target volume. The control device may operate to interrupt an irradiation of the target volume if the target volume assumes a predetermined state. Following interruption of the irradiation, a residual particle number stored in the accelerator may be compared with a reference value. Operation of the accelerator may be controlled as a function of the result of this comparison. The accelerator may irradiate the target volume using a gating method, in which the irradiation is interrupted when the target volume assumes a predefined state. For example, the irradiation may be interrupted if it is determined that the position of the target volume has changed to such a degree that an irradiation would cause an incorrect dosage. Several gating methods are known. For example, an external surrogate motion signal that provides information about the motion status of the target volume may be recorded. By measuring movement of the abdominal wall, the position of the internally located target volume may be inferred. In other examples, actual movement of the target volume may be monitored directly by using, for example, X-ray photographs, fluoroscopic projections, ultrasound imaging or active, implanted transponders. When the target volume is located outside of a defined spatial region and/or when, in the case of quasi-periodic motion of the target volume, the target volume is situated in a specific phase of the motion cycle, the irradiation process is interrupted. A repeat irradiation of the target volume in a gating method is permitted when the target volume is once again in a further predefined state. This may occur when the target volume reaches a specific location or a specific phase of the motion cycle. Known gating irradiation methods thus apply the particle beam when a so-called gate-on phase is present. Accelerators that are deployed in a particle therapy context may have different, alternating working phases. In the accelerators, the particle beam is applied if the accelerator is in a phase in which particles have already been accelerated to the irradiation energy. The irradiation methods thus apply the particle beam when the accelerator is in the second working phase as explained above. The target volume is irradiated when the second working phase and the gate-on phase are simultaneously present. This poses a problem when all of the particles having the requisite irradiation energy have been consumed and the particle accelerator switches from the second working phase to the first working phase. In such a case, the irradiation is interrupted until both the gate-on phase and second working phase of the accelerator are simultaneously present again. The remaining time of the gate-on phase, in which an irradiation would otherwise be possible, is lost. Time that is lost due to this unfavorable coordination may lengthen an otherwise typical irradiation time in the case of typical movements of a target volume such as a lung by, for example, 5% to 10% of the total irradiation time. In the present embodiments, following an interruption of the irradiation of the target volume that occurs when the target volume assumes a predefined state, the residual particle number remaining in the accelerator may be compared with a reference value. In some embodiments, the comparison may occur immediately following an interruption of the irradiation method. The accelerator may be controlled differently dependending on the result of the comparison. A gate-off phase is measured by the time interval between the time instant at which the beam is interrupted (e.g., caused as a result of the target volume having assumed a predefined state) and the following time instant at which the target volume has assumed a second predefined state, in which irradiation is again appropriate, characterizes the gate-off phase. During the gate-off phase, irradiation is not possible. The length of the gate-off phase is dependent on the amount the target volume actually moves. Advantageously, the accelerator control in the present embodiments may, during the gate-off phase following a gate-on phase, prepare the accelerator for one of the following gate-on phases. The comparison of the residual particle number with the reference value may take place at the beginning (e.g., during the first half) of a gate-off phase. If the residual particle number is less than the reference value, the accelerator may be controlled such that the particle accelerator may be switched from the second working phase to the first working phase. Because the accelerator is once more in the first working phase, particles may again be introduced into and accelerated to the requisite irradiation energy within the accelerator. A sufficiently large number of particles for an irradiation may thus be available once again for irradiation purposes when the accelerator returns to the second working phase of the accelerator. Using the method according to the present embodiments, this advantageously takes place at least partially during a gate-off phase. In one embodiment, the residual particle number stored in the accelerator may be discarded if the residual particle number is less than the reference value. In one embodiment, the reference value used for the comparison may be determined from, for example, a required residual particle number for irradiating a sub-region of the target volume. Accordingly, during one of the following gate-on phases, a sufficiently large number of particles will be present in the accelerator to permit irradiation of the sub-region of the target volume in full. The sub-region of the target volume may be an area that is provided for an irradiation with the same particle energy, such as, for example, an iso-energy layer. The particles stored in the accelerator may be extracted for the purpose of irradiating the sub-region. A method for accelerating a particle beam to an irradiation energy and irradiating a target volume using an accelerator may be performed as follows: (1) the irradiation of the target volume is interrupted if the target volume assumes a predetermined state; (2) following interruption of the irradiation, a remaining or residual particle number stored in the accelerator is compared with a reference value; and (3) the accelerator is controlled as a function of the result of the comparison. The accelerator may be a particle accelerator that operates in a first working phase and a second working phase. In the first working phase, the accelerator accelerates particles to the requisite energy. In the second working phase, the accelerator stores the accelerated particles for irradiation purposes and provides the stored accelerated particles for extraction. The accelerator may be controlled such that the accelerator is switched from the second working phase to the first working phase if the residual particle number is less than the reference value. Depending on the result of the comparison, the residual particle number stored in the accelerator may be discarded. The reference value used for the comparison may be determined from a residual particle number for irradiating a sub-region of the target volume. The sub-region of the target volume may be an area that is provided for irradiation with the same particle energy. The preceding and following description of the individual features, advantages of the features, and effects of the features relate both to the device category and to the method category, without this explicitly being mentioned in each case. The individual features disclosed in the process may also be used in combinations other than those shown. FIG. 1 shows a particle therapy system 10. The particle therapy system 10 is used for irradiating a body arranged on a positioning device with a particle beam 12. The particle beam 12 may consist of charged particles such as, for example, protons, pions, helium ions, carbon ions, or ions of other elements. Tumor-diseased tissue of a patient, for example, may be irradiated as a target volume 14 with the particle beam 12. The particle beam system 10 may also be used, for example, to irradiate a non-living body such as, for example, a water phantom or other type of phantom, or cell cultures for research or maintenance purposes. The objects that form the target volume 14 may be moving bodies. The target volume 14 may be non-visibly located inside a target object 18 and may move quasi-cyclically within the target object 18. The particle therapy system 10 may include an accelerator unit 16 (e.g., a synchrotron) that provides a particle beam 12 with energy for the irradiation. Iso-energy layers and target points that are scanned using a raster scanning method during the irradiation may be, as shown in FIG. 1, located in the target volume 14 that is to be irradiated. A raster scanning method, in which the particle beam 12 is guided from target point to target point without being turned off when a transition is made from one target point to the next, may be used as the scanning method. In other embodiments, other scanning methods may be used. The particle beam 12 in the embodiment shown in FIG. 1 is influenced in a lateral deflection with the aid of scanning magnets 30. The particle beam 12 may, for example, be deflected in a direction that is perpendicular to the beam trajectory direction, such as the x- and y-direction. In other embodiments, other irradiation methods may be used. An alternative irradiation method may, for example, utilize passive beam application. The irradiation system 10 may also include a control device 36 and detectors 34 for monitoring the beam parameters. The control device 36 (e.g., the control system of the irradiation system) controls the individual components of the irradiation system (e.g., the accelerator 16 and the scanning magnets 30). The control device 36 may also be used to turn the particle beam 12 on and off, as desired. The control device 36 collects measurement data such as the data for the detectors 34 for monitoring the beam parameters. The control device may be effected using an irradiation plan 40 that is determined and provided with the aid of an irradiation planning device 38. In order to detect the motion of the target volume 14, a detection device 32 may be provided to record an external surrogate motion signal. The detection device 32 may be, for example, an abdominal belt. A signal waveform may be recorded based on the distension of the detection device. Using the recorded waveform, the characteristic curve of the respiratory cycle of a patient and the position of a tumor moving with the respiration, may be determined. In addition, an analyzer device 46 may be integrated in the control device 36 and may evaluate the surrogate motion signal recorded by the detection device 32. The analyzer device 46 may, for example, determine a gating window with the aid of the surrogate motion signal. In order to detect the motion 24 of the target volume 14, a fluoroscopy device may also be provided. The fluoroscopy device may include a radiation source 20 and a radiation detector 22. The radiation detector 22 may produce continuous or individual X-ray photographs of the target volume 14. In one embodiment, an image evaluation device 42 may be integrated into the control device 36, thus enabling the image data of the fluoroscopy device to be analyzed and compared with other image data. FIG. 2 depicts different working phases of a synchrotron. FIG. 2 shows the particle energy E of the particles in the synchrotron as a function of the time t. A synchrotron is an accelerator that has two different working phases. In a first working phase (bar 51), particles are guided into the synchrotron (act 55) until the synchrotron is filled. In act 57 of the first working phase, the particles guided into the synchrotron are accelerated to a particle energy sufficient for irradiation purposes. In the first working phase, the particles may not be extracted. After the synchrotron is filled with accelerated particles, the particle accelerator may transition to a second working phase (bar 53). In the second working phase, the target volume may be irradiated. The particles circulate or are “stored” in the synchrotron at the energy to which the particles have been accelerated (act 59). The particles may be extracted from the accelerator and directed to irradiate the target volume. As soon as the particles are consumed or a new energy is to be set, the particle accelerator may transition back to the first working phase. FIG. 3 shows the periodic or quasi-periodic motion 61 of a moving target volume. The motion of the target volume may, for example, be caused by a respiratory cycle that raises and lowers the target volume. The motion of the target volume may be subdivided into gate-on phases 63 and gate-off phases 65. During the gate-on phase 63, the position or orientation of the target volume is such that an irradiation may be performed without an appreciably incorrect irradiation of the target volume taking place. During the gate-off phase 65, the irradiation of the target volume should be interrupted, as an irradiation during this phase would lead to a mis-delivery of the dose. The beginning of the gate-on phase 63 or the gate-off phase 65 may be determined using known devices. For example, the detection device 32 or the above-described fluoroscopy device may be used. When the accelerator is in the appropriate working phase (e.g., the second working phase), and the target volume is simultaneously in the gate-on phase, the target volume may be irradiated. The presence of the gate-on phase may be independent of the phase of the accelerator cycle. When the target volume is in the gate-on phase, but the synchrotron is not full of particles, the irradiation is interrupted. Accordingly, no further extraction may take place, and the synchrotron transitions from the second working phase to the first working phase. This transition occurs even though the gate-on phase is still present, because the synchrotron is totally discharged and all the particles are “consumed.” In this situation, the gate-on phase is not effectively utilized, and the remaining time of the gate-on phase is not used. To prevent interruption of the irradiation method, the method shown in FIG. 4 is performed. In this embodiment, an iso-energy layer of the target volume may be irradiated with a predefined dose using the scanning method. The accelerator may be filled completely with particles, and the particles may be accelerated to a predefined energy for the irradiation of the iso-energy layer (act 81). The iso-energy layer may be irradiated during the gate-on phase (act 83). Following termination of the gate-on phase (act 85), a comparison may be performed, in which the residual particle number (N_present) contained or stored in the synchrotron may be compared with the particle number to irradiate the remainder of the iso-energy layer (N_required). If the comparison establishes that the residual particle number is sufficient for irradiating the remaining iso-energy layer (N_required<N_present), the irradiation may continue as soon as the next gate-on phase begins (return to act 83). If the comparison reveals that the residual particle number present in the synchrotron is not sufficient for irradiating the remaining iso-energy layer (N_present<N_required), the residual particle number still present in the synchrotron may be discarded (act 87). The synchrotron may be refilled with particles that are thereupon accelerated to the irradiation energy (return to act 81). The irradiation may continue once the synchrotron returns to the second working phase, and the gate-on phase is simultaneously present (act 83). These acts may be repeated until the iso-energy layer has been irradiated in full. Following these acts, an additional iso-energy layer may then be irradiated. The above-described unfavorable scenario for the irradiation may, therefore, be avoided, or at least minimized, if the information concerning the charge state and/or the fill level of the synchrotron is taken into account in the course of controlling the accelerator (e.g., following termination of each extraction for the accelerator). While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description. |
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abstract | The invention relates to a method for determining a reconstructed image using a particle-optical apparatus. The particle-optical apparatus comprises a particle source for producing a beam of particles, an object plane on which an object to be imaged may be placed, a condenser system for illuminating the object plane with the beam of particles, a projection system for forming an image of the object plane by imaging particles transmitted through the object on an image plane, and a detector for detecting the image, the detector comprising a semiconductor sensor having an array of pixels for providing a plurality of pixel signals from respective pixels of the array in response to particles incident on the detector. |
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abstract | A floating nuclear power reactor includes a self-cooling containment structure and an emergency heat exchange system. The containment structure of the reactor may be flooded upon the temperature or pressure in the containment structure reaching a certain level. The reactor vessel may also be flooded upon the temperature or pressure in the reactor vessel reaching a predetermined level. The reactor includes a heat exchange system and a filtered containment venting system. The reactor also includes a multi-compartment containment structure. Multiple steam by-pass pipes extend to the filtered containment vent chamber. |
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040627268 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to pressure vessels and more particularly to a nuclear reactor pressure vessel nozzle seal. 2. Description of the Prior Art The conventional nuclear reactor pressure vessel comprises a longitudinally disposed cylindrical structure, closed at both ends by a convex base and a domed roof, having reactor coolant inlet and outlet nozzles protruding therethrough. Generally, these nozzles are disposed in a plane transverse to the longitudinal axis of the vessel and angularly separated from each other. Housed within the pressure vessel structure are, among others, the nuclear core, subassemblies and a fluid coolant. Moreover, within the pressure vessel, an annular flange is formed on the inner surface thereof. The flange serves as a means for supporting the reactor core which is suspended from a distribution hoop or shell. The distribution hoop is extended by means of a thermal shield-skirt assembly, which supports the fuel elements in the reactor core and which also serves as a hydraulic guide. In operation, the fluid coolant, in forced circulation, enters the pressure vessel through the inlet nozzles, and flows through the annular hydraulic guide that is formed between the inner surface of the pressure vessel and the skirt. The coolant then rises through the core of the reactor whereupon it is discharged from the vessel through an outlet nozzle which is in fluid communication with the hoop opening through conduit means interposed therebetween. To insure proper circulation, it is imperative that direct communication be prevented between the incoming coolant and the discharging coolant. Toward this end, a leak proof contact between the hoop opening and the pressure vessel outlet nozzle is required. However, although a leak proof contact is necessary to prevent direct fluid communication, structural and differential thermal expansion conditions which can occur between the internal reactor structures and the pressure vessel must be considered. In general, the attendant thermal expansion precludes fixedly joining the conduit means to both the hoop and the pressure vessel wall. Therefore, a leak proof sealing means, either as part of the conduit or in substitution thereof, is required to prevent the commingling of the inlet fluid coolant and the outlet fluid coolant. Further, from a structural consideration it is desirable that the sealing means segregate the fluid coolants without structurally coupling the hoop to the pressure vessel. In the past, a leak proof seal was established by a spring biased contact of a sealing ring or by thermal expansion contact of the conduit. In general, the thermal expansion contact seal consists of carefully and tediously machining the conduit or a ring to be attached thereto to establish a designed clearance or tolerance between the machined conduit or ring face and the pressure vessel nozzle during assembly. The leak-proof condition, however, for this thermal expansion type seal is only achieved at the elevated operating temperatures of the nuclear reactor system when thermal expansion of the hoop and conduit expand to meet the inner wall of the pressure vessel. Moreover, since the pressure vessel also expands during operation, this thermal expansion conduit-seal generally requires a material having a greater thermal expansion coefficient for the hoop and/or the conduit than the expansion coefficient of the pressure vessel, if the leak proof state is to be achieved. The spring contact type seal, moreover, comprises a cylindrically shaped sealing member disposed within and extending from a cylindrical annular cavity concentric therewith. The sealing member is generally machined on one face of its cylindrical shape in order to nestle in close contact with, for example, the pressure vessel wall about the outlet nozzle and thereby prevent leakage therebetween. A spring disposed within the annular cavity interposed between the other face of the cylindrical sealing member and the rear wall of the cavity, or a compression ring, exerts in the axial direction the force necessary to tightly seat the sealing member against the pressure vessel wall. Moreover, to prevent leakage flow from one fluid from traveling through the annulus, between the sealing member and the annular cavity, and across the spring into communication with the other fluid, both the sealing member and the cavity are machined to exact close fitting tolerances such that the sealing member is seated in the cavity with only a very narrow annular gap therebetween. This gap, however, provides a labyrinth-like flow passage for fluid communication and therefore flow leakage is not prevented but merely reduced. Generally, however, this leakage rate is too large and the manufacturing tolerances are too stringent for this type of a seal. Accordingly, there is a need to provide a sealing means which will prevent or at least reduce the leakage flow between the incoming and discharging coolants at all operating conditions without the stringent manufacturing tolerances, or the use of different materials having different thermal coefficients that are characterized by the prior art systems. SUMMARY OF THE INVENTION In accordance with the invention, a reactor pressure vessel-hoop discharge sealing means is provided which eliminates costly machining, removes the thermal expansion determination of the sealing means-pressure vessel clearance, allows a wider selection of materials for the hoop and/or sealing means and establishes a satisfactory leak proof seal in all reactor conditions, operating or during shut down, without structurally coupling the distribution hoop to the pressure vessel. Specifically, a reactor pressure vessel-hoop discharge sealing means that has these features comprises a sealing ring connected to the hoop opening by an impervious expansion bellows. More specifically, the discharge opening seal comprises an annular compression ring member seated in a recess about the hoop opening or a conduit extending therefrom having a sealing ring attached thereto and biased axially therefrom by an expansion bellows weldably connected to both the annular member and the sealing ring. The self actuating bellows seal is designed to insure that the sealing ring will securely contact the pressure vessel in all reactor conditions, operating or not, without structurally coupling the hoop to the pressure vessel. Furthermore, the impervious expansion bellows seal weldably connected to the sealing ring and the annular compression ring provides a boundary across which and around which fluid communication is prevented. Moreover, the machining costs of close tolerance members as found in the prior art thermal expansion and spring type seals are eliminated by this bellows spring system. In addition, this bellows seal design may be remotely assembled by attachment to the hoop prior to the hoop's insertion within the vessel. The various features of novelty which characteristics the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention . |
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053848144 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a pertinent detail of a portion of a reactor core is shown. Control rod drive housing H has fuel support casting C supported thereon. Fuel support casting C includes arm 16 which orients casting C with respect to pin 14 in core plate P. Core plate P divides high pressure lower plenum L from core R, preserving the necessary pressure differential barrier to cause the controlled circulation within the many individual fuel bundles of the reactor. Fuel support casting C includes four apertures 20 onto which four fuel bundles B at their respective lower tie plate assemblies T are placed. Each hollow lower tie plate assembly T is disposed to cause its inlet nozzle N to communicate to one of the apertures 20 of the fuel support casting. Fuel support casting C also includes apertures through which control rods 22 penetrate to the interstices of the four fuel bundles sitting on top of the fuel support casting C. Since the action of the control rods is not important with respect to this invention, further discussion of this aspect of the reactor will not be included. Remembering that only four out of a possible 750 fuel bundles are illustrated, it will be understood that the pressure drop across core plate P is important. Accordingly, a review of the pressure drop within a boiling water nuclear reactor can be instructive. First, and through an orifice (not shown) in the fuel support casting C, an approximate 7 to 8 psi pressure drop occurs at typical 100% power/100% flow operating conditions. This pressure drop is utilized to ensure uniform distribution of bundle coolant flow through the many (up to 750) fuel bundles within a boiling water nuclear reactor. Secondly, at in the lower tie plate of the fuel bundles on each fuel support casting C, approximately 11/2 psi of pressure drop occurs. This pressure drop is a result primarily of the change in flow velocity occurring through this complex geometry structure. Finally, and as the coolant rises and generates steam within the fuel bundle, approximately 10 to 12 psi of pressure drop is incurred. This pressure drop is distributed throughout the length of the fuel bundle--and is important to the operating stability of both the individual fuel bundles and the collective fuel bundles constituting the core of the nuclear reactor. The reader should understand that the summary of pressure drop given above is an over simplification. This is a very complex part of the design and operation of a nuclear reactor. Having said this much, one point must be stressed. Pressure drop within the individual fuel bundles of a boiling water must remain substantially unchanged. Accordingly, if apparatus for preventing debris entrainment into the fuel bundles is going to be utilized, appreciable change in overall fuel bundle pressure drop should be avoided. Having carefully reviewed the requirements for the avoidance of increased pressure drop in debris restricting devices, several further comments can be made. First, any debris catching arrangement should be sufficiently rigid so that the excluding apparatus does not under any circumstance break apart, fail to stop debris, and become the source of further debris itself. For this reason, wire screens are not used. Instead, perforated metal is in all cases utilized in the examples that follow. Second, we have found that it is desirable to restrict pressure drop to a minimum. This can be done by making the velocity of flow through the apertures themselves as low as feasible. A second reason for this limitation is the entrainment of the debris in the flow. Assuming entrainment of debris in the flow, if any possible angle of attack can be realized that will enable debris to pass through an aperture, given sufficient time, passage through the aperture will eventually occur. By maintaining slow velocity at the respective apertures, entrainment of debris is less likely to occur. Further, it has been found that a reorientation of the flow at a rejecting hole to an angle where debris passage is less likely can be achieved. Consequently, flow velocity at restricting apertures is restricted to the minimum possible value. Third, we find that modification of the rod supporting grid--a technique utilized in the prior art--is not satisfactory. Specifically, we prefer to use straining apertures that are as small as possible--down to a dimension of 0.050 of an inch diameter. Unfortunately, the rod supporting grid is a member that must have the required static and dynamic properties to support the fuel rods under all conceivable conditions. Utilizing a matrix of such holes in the rod supporting grid at the pitches required for low pressure drop in the lower tie plate is not practicable. First, since the small apertures would be confined to the plane of the rod supporting grid, a total reduction of flow area will be present that would lead both to unacceptable pressure drop as well as high flow velocities through the individual holes in rod supporting grid. Further, such a matrix of small apertures in the rod supporting grid would reduce the strength of the grid to a level below that required for support of the fuel rods. We have identified the so-called flow volume of the lower tie plate assembly as a primary candidate for the location of debris rejection apparatus--preferably the perforated metal utilized with this construction. In boiling water nuclear reactor fuel bundles at the lower tie plate assembly, there is defined by a peripheral wall W extending between the nozzle N at the lower end and the fuel rod supporting grid G at the upper end, a relatively large flow volume. This flow volume is sufficiently large to accommodate a three dimensional (i.e., non-planar) structure--with one side of the three dimension structure communicated to the nozzle inlet and the other side of the three dimensional structure communicated to the rod supporting grid. At the same time, periphery of the three dimensional supporting structure can be attached to the sides of the lower tie plate assembly--so that all fluids passing through the flow volume of the lower tie plate simply must pass through the restricting apertures of the perforated plate. Only small modification to the lower tie plate assembly is required. The flow volume in the lower tie plate assembly has an additional advantage. Specifically, and if the flow restricting grid has to be confined to a plane extending across the lower tie plate flow volume, the apertures in the plate would define a total flow area less than the plane in which the perforated plate was disposed. Where a perforated plate is utilized to manufacture a three dimensional structure, the area of the available apertures can increase beyond that total area possible when the perforated plate is confined to a flat plane. In fact, where sufficient structure is utilized, the total flow area available in the aggregated holes of the three dimensional structure can approach and even exceed the total cross sectional area across the flow volume of the lower tie plate assembly before the insertion of the debris restricting assembly. In addition a properly designed debris catcher assembly could improve the flow distribution at the inlet to the fuel bundle. Having set forth these considerations, attention can be directed to the embodiments of the invention. Referring to FIG. 2, debris catcher 40 is a separate piece consisting of a short cylinder 42 integral with a hemispherical cap 44. The hemispherical cap has an area approximately twice the are of the lower tie plate assembly inlet throat. Therefore the total flow area through the holes in the cap can be greater than the throat area. By varying the height of the assembly, the flow area through the holes can be adjusted to give an optimum pressure drop through the lower tie plate. The debris catcher of FIG. 2 has a favorable effect on the flow distribution in the flow volume of the lower tie plate assembly. The flow exiting from each hole has a direction normal to the hemispherical cap. The net effect of flow from all of the holes is to distribute the flow uniformly over the area of lower tie plate assembly at the horizontal plane near the rod supporting grid G. This uniform flow results in a uniform flow into the fuel bundle. The debris catcher of this invention requires a modification of the lower tie plate assembly fabrication. Currently the entire assembly T, including the bars 46 of the lower bail, is a single casting which includes a peripheral wall. In order to insert the debris catcher, the bars 46 are omitted from the lower tie plate assembly casting, and are a separate casting. The debris catcher is inserted into the modified lower tie plate assembly casting and is welded in place, and then bars 46 are welded over the nozzle N. Referring to hemispherical cap 44, one disadvantage is present. Specifically, and as to those apertures in the dome, debris entrained in the flow will essentially approach the individual holes of the hemispherical cap 44 directly--that is axially of the axis of each of the holes. This is not preferred. It is better if the overall flow requires a change in direction--in the order of up to 90.degree.--so that the entrained debris and the fluid can have the added forces of momentum separation for separating the usually heavier debris from the less dense coolant/moderator flow. If the flow approaches the screening apertures and then turns in the order of 90.degree., the tendency will be for the debris to be left on the surface of the three dimensional grid construction. This being the case, attention can be devoted to at least some of the following designs. Referring to FIGS. 3A-3C, a three dimensional grid construction is shown having a central inverted cone 50 and a supporting cylinder 60. A separate casting N consists of the bars 46 and a circular ring 48. A lip 62 at the bottom of the cylinder 60 is captured when the casting N is attached to the main casting T. Flow arrows 54, 64 demonstrate with respect to cone 50 and cylinder 60 the general change in direction required for coolant/moderator flow through the three dimensional grid construction disclosed. This has the tendency to cause debris to be deposited on the surface of the perforated plate construction and carried along the surface of the grids to the region 52 where the inverted cone 50 joins the cylinder 60. Referring to FIGS. 4A-4C, a modification of the concept of FIGS. 2 and 3A-3C is shown containing a debris trap. Specifically lower tie plate assembly T in the vicinity of nozzle N is enlarged and fitted with a slightly enlarged cylinder 60'. To the bottom of this is mounted an annulus assembly 70. Annulus assembly 70 gives substantially the same inlet nozzle N dimension as the prior art. The annular volume 72 forms an occluded space which can be used as a debris trap. Specifically, and during prolonged flow an operation, it can be expected that debris will migrate along the surfaces of the three dimensional grid construction to the top of the cylinder 60' and the base of the inverted cone 50. When the flow is reduced or stopped, debris will fall. At least some debris will move into the occluded annular volume 72. Further, and once in annular volume 72, when flow recommences, complete re-entrainment of debris is unlikely. Consequently, once a fuel bundle is removed, to the extent that debris is trapped in annular volume 72, the debris likewise will be removed. Referring to FIGS. 5A-5C, a three dimensional construction featuring an inverted pyramid 80 is utilized having pyramid faces 81-84 fastened to the inside of lower tie plate assembly T adjacent rod supporting grid G. Alteration of the fabrication of assembly T occurs by casting grid G as a separate assembly and joining grid G as by welding at 90. As a possible additional feature, it can be further seen that an annulus 95 has been cast interiorly of flow volume V of lower tie plate assembly T, this annulus being immediately adjacent the base of the inverted pyramid 80. This has the advantage of allowing debris to fall a short distance to the formed debris trap within flow volume V without having the fall of the debris scatter the debris away from the underlying debris catching shadow formed by the annulus 95. Referring to FIGS. 6A-6C, an inverted pyramid construction 80' is illustrated having the discrete sides fabricated from a corrugated construction. This has the advantage of expanding the total area of the grid construction while maintaining the three dimensional grid construction substantially unchanged. Referring to FIGS. 7A and 7B, a three dimensional grid construction is shown wherein a perforated plate 100 is provided with numerous corrugations. The corrugations--like the other three dimensional constructions--expand the effective area as it is disposed across flow volume V of lower tie plate assembly T. FIG. 7C is a detail of the construction. Holes can be placed over the entire surface of the plate, or they can be omitted in regions of sharp bending 110. Using holes over the entire surface provides more flow area and reduces pressure loss. However in regions 110 the general flow direction is the same as-the axis of the holes, so some debris may pass through. When holes are omitted in regions 110, all the flow must make nearly 90.degree. bends. Thus the construction with no holes in the regions of sharp bends is preferred, as shown in FIG. 7C. Thus far, all constructions have shown modification to the lower tie plate assembly T either by introducing the three dimensional grid structure at the nozzle N or under rod supporting grid G. As shown in FIG. 8, the three dimensional grid assembly can be introduced through the lower tie plate assembly T along a side wall 120 into aperture 121. As is shown, grid 100 can be mounted between walls 122 and thereafter inserted in the side walls of the lower tie plate assembly T. The reader will understand that there is the possibility of constructing this invention with a two part tie plate which is bolted together. Referring to FIG. 9, this can be plainly seen. Referring to FIG. 9, a lower tie plate T is shown having a nozzle section N and a rod supporting grid section G. Rod supporting grid section G includes a standard threaded bore 100 for receiving tie rods. Nozzle section N has an underlying threaded bore 102 into which cap screw 101 threads fastening rod supporting grid section G. Thereafter, a tie rod (not shown) is conventionally threaded into rod support grid at that portion of threaded aperture 100 not filled by cap screw 101. As disclosed before, a pyramid shaped three dimensional grid construction 110 with a peripheral flange 115 is fastened between the two tie plate sections. Referring to FIG. 10, substantially the same construction is shown with the rod supporting grid G and the nozzle section N held together with tie rods having an extended end plug 108. Simply stated tie rods R include a lower plug having an extended neck 108 and a lower threaded portion 106. In operation, tapered portion 109 of the lower end plug bears against rod supporting grid section G. At the same time, threaded section 106 threads into threaded bore 104. As before, three dimensional grid 110 is trapped at flange 115 between the confronting portions of the lower tie plate assembly T. It will be realized by those having skill in the art that if tie rods R are removed for inspection, the lower tie plate T as shown in FIG. 10 can become disassembled. For this reason, the embodiment of FIG. 9 is preferred. The reader will understand that the concepts here disclosed will admit of modification. For example, the interior of the lower tie plate volume V can be cast in anticipation of the receipt of the three dimensional grid construction. For example, a boss running along the interior of flow volume V having the profile of grid 100 can receive and seat the three dimensional grid interior of flow volume V. Likewise, other modifications can be made. |
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