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description | This application claims priority to U.S. Provisional Patent Application Ser. No. 62/611,795, filed on Dec. 29, 2017, entitled “Passive Boron Injection System,” and U.S. Provisional Patent Application Ser. No. 62/611,819, filed on Dec. 29, 2017, entitled “Reactor Module (RXM) Without Control Rod Assemblies and Other Systems, Structures and Components.” The entire contents of both previous applications are incorporated by reference herein. This invention was made with Government support under Contract No. DE-NE0000633 awarded by the Department of Energy. The Government has certain rights in this invention. This document relates to systems and methods for controlling a nuclear reaction in a nuclear reactor power system. In nuclear reactors designed with passive operating systems, the laws of physics are employed to ensure that safe operation of the nuclear reactor is maintained during normal operation or even in an emergency condition without operator intervention or supervision, at least for some predefined period of time. In an example implementation, a nuclear power system includes a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel; and a boron injection system positioned in the open volume of the containment vessel and including an amount of boron sufficient to stop the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state. In an aspect combinable with the example implementation, the boron injection system includes a boron container sized to hold or enclose the amount of boron. In another aspect combinable with any of the previous aspects, the boron container includes a openable enclosure that includes a latch actuatable by at least one of a temperature or a pressure. In another aspect combinable with any of the previous aspects, the boron container includes a meltable or dissolvable member that encloses or surrounds the amount of boron. In another aspect combinable with any of the previous aspects, the reactor vessel further includes at least one valve openable to fluidly couple the volume of the reactor vessel with the open volume of the containment vessel. In another aspect combinable with any of the previous aspects, the at least one valve includes a reactor vent valve configured to vent a vaporized primary coolant from the volume of the reactor vessel to the open volume of the containment vessel; and a reactor recirculation valve configured to circulate a mixture of the vented primary coolant and at least a portion of the amount of boron to the reactor core. In another aspect combinable with any of the previous aspects, the amount of boron is in solution with a condensed form of the vented primary coolant. In another aspect combinable with any of the previous aspects, the vaporized primary coolant is at at least one of a pressure or temperature sufficient to actuate the latch to release the amount of boron from the boron container into the open volume, or the vaporized primary coolant is at a temperature sufficient to melt or dissolve the member to release the amount of boron into the open volume. In another aspect combinable with any of the previous aspects, the boron is solid boron in granular form. In another aspect combinable with any of the previous aspects, the reactor vessel excludes control rod assemblies. In another example implementation, a method for controlling a nuclear fission reaction includes operating a nuclear power system to generate a nuclear fission reaction, the nuclear power system including a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate the nuclear fission reaction, a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel, and a boron injection system positioned in the open volume of the containment vessel and including an amount of boron; initiating an emergency operation of the nuclear power system based on a loss of a primary coolant from the volume of the reactor vessel to the open volume of the containment vessel; based on the emergency operation, releasing the amount of boron into the open volume of the containment vessel; circulating the amount of boron from the open volume of the containment vessel to the reactor core; and with the amount of boron, stopping the nuclear fission reaction or maintaining the nuclear fission reaction at a sub-critical state. In an aspect combinable with the example implementation, releasing the amount of boron includes releasing the amount of boron from a boron container positioned in the open volume and sized to hold or enclose the amount of boron. In another aspect combinable with any of the previous aspects, releasing the amount of boron from the boron container includes actuating a latch on the boron by at least one of a temperature or a pressure in the open volume of the containment vessel. In another aspect combinable with any of the previous aspects, releasing the amount of boron from the boron container includes melting or dissolving at least a portion of the boron container based on a temperature in the open volume of the containment vessel. Another aspect combinable with any of the previous aspects further includes, based on the emergency event, opening at least one valve on the reactor vessel to fluidly couple the volume of the reactor vessel with the open volume of the containment vessel. In another aspect combinable with any of the previous aspects, opening at least one valve on the reactor vessel includes opening a reactor vent valve to vent a vaporized primary coolant from the volume of the reactor vessel to the open volume of the containment vessel; and opening a reactor recirculation valve to circulate a mixture of the vented primary coolant and at least a portion of the amount of boron to the reactor core. In another aspect combinable with any of the previous aspects, the amount of boron is in solution with a condensed form of the vented primary coolant. In another aspect combinable with any of the previous aspects, the vaporized primary coolant is at at least one of a pressure or temperature sufficient to actuate the latch to release the amount of boron from the boron container into the open volume, or the vaporized primary coolant is at a temperature sufficient to melt or dissolve the member to release the amount of boron into the open volume. In another aspect combinable with any of the previous aspects, the boron is solid boron in granular form. Another aspect combinable with any of the previous aspects further includes operating the nuclear power system to generate the nuclear fission reaction without any operation of control rod assemblies. In another example implementation, a nuclear power system includes a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a riser positioned above the reactor core; a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the received heat to generate electric power in a power generation system fluidly or thermally coupled to the primary coolant flow path; and a control rod assembly system positioned in the reactor vessel and configured to position a plurality of control rods in only two discrete positions, such that the plurality of control rods are fully withdrawn from the reactor core in a first discrete position of the only two discrete positions and the plurality of control rods are fully inserted into the reactor core in a second discrete position of the only two discrete positions. In an aspect combinable with the example implementation, the control rod assembly is configured to adjust the plurality of control rods from the first discrete position to the second discrete position by at least one of releasing the plurality of control rods to fall to the second discrete position from the first discrete position; or forcibly urging the plurality of control rods from the first discrete position to the second discrete position. In another aspect combinable with any of the previous aspects, the plurality of control rods are sufficient to shut down the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state in the second discrete position. Another aspect combinable with any of the previous aspects further includes a control system communicably coupled to the power generation system and configured to control a power output of the nuclear fission reaction independent of the control rod assembly system during a normal operation of the nuclear power system. In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the power generation system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, the operation of controlling the power generation system to adjust at least one of the turbine inlet steam valve or the feed water pump to adjust the power output of the nuclear fission reaction includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction, or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction; or decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction, or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction. In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the chemical injection system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, the operation of adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction. In another example implementation, a method for controlling a nuclear fission reaction includes operating a nuclear power system to initiate a nuclear fission reaction, the nuclear power system including a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to initiate and maintain the nuclear fission reaction during a normal operation, a riser positioned above the reactor core, and a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; circulating a primary coolant through the primary coolant flow path to receive heat from the nuclear fission reaction; transferring the received heat into a power generation system fluidly or thermally coupled to the primary coolant flow path to generate electric power; and operating a control rod assembly system positioned in the reactor vessel to adjust a position of a plurality of control rods from a first discrete position of only two discrete positions to a second discrete position of the only two discrete positions, such that the plurality of control rods are fully withdrawn from the reactor core in the first discrete position and the plurality of control rods are fully inserted into the reactor core in the second discrete position. In an aspect combinable with the example implementation, adjusting the plurality of control rods from the first discrete position to the second discrete position includes at least one of releasing the plurality of control rods to fall to the second discrete position from the first discrete position; or forcibly urging the plurality of control rods from the first discrete position to the second discrete position. In another aspect combinable with any of the previous aspects, the plurality of control rods are sufficient to shut down the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state in the second discrete position. Another aspect combinable with any of the previous aspects further includes controlling a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation. In another aspect combinable with any of the previous aspects, the nuclear power system further includes a chemical injection system in fluid communication with the primary coolant flow path. Another aspect combinable with any of the previous aspects further includes controlling the power output of the nuclear fission reaction independent of any control rod assemblies by controlling one or more parameters of at least one of the power generation system or the chemical injection system during normal operation. Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, controlling the power generation system to adjust at least one of the turbine inlet steam valve or the feed water pump to adjust the power output of the nuclear fission reaction includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction, or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction; or decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction, or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction. Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction. In another example implementation, a pressurized water reactor (PWR) includes a reactor module that includes a reactor vessel including a volume sized to enclose a reactor core, a riser, and a steam generator, and a containment vessel including a volume sized to enclose the reactor vessel; and a plurality of control rods mounted in the reactor vessel above the reactor core on a control rod manifold, the control rod manifold attached to a control rod actuator operable to release the control rod manifold to drop the plurality of control rods from a first position above the reactor core to a second position within the reactor core. In an aspect combinable with the example implementation, the control rod actuator is inoperable to move the control rod manifold to move the plurality of control rods from the second position to the first position. In another aspect combinable with any of the previous aspects, the plurality of control rods are sufficient to shut down a nuclear fission reaction or maintain the nuclear fission reaction generated by one or more nuclear fuel assemblies in the reactor core at a sub-critical state in the second position. In another example implementation, a nuclear power system includes a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a riser positioned above the reactor core; a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the received heat to generate electric power in a power generation system fluidly or thermally coupled to the primary coolant flow path; and a control system communicably coupled to the power generation system and configured to control a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation. An aspect combinable with the example implementation further includes a chemical injection system in fluid communication with the primary coolant flow path, wherein the control system is communicably coupled to the chemical injection system and configured to control the power output of the nuclear fission reaction independent of any control rod assemblies by controlling one or more parameters of at least one of the power generation system or the chemical injection system during normal operation. In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the power generation system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, the operation of controlling the power generation system to adjust the turbine inlet steam valve includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction; or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction. In another aspect combinable with any of the previous aspects, the operation of controlling the power generation system to adjust the feed water pump includes at least one of decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction; or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction. In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the chemical injection system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, the operation of adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction. In another example implementation, a method for controlling a nuclear fission reaction includes operating a nuclear power system to initiate a nuclear fission reaction, the nuclear power system including a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to initiate and maintain the nuclear fission reaction during a normal operation, a riser positioned above the reactor core, and a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; circulating a primary coolant through the primary coolant flow path to receive heat from the nuclear fission reaction; transferring the received heat into a power generation system fluidly or thermally coupled to the primary coolant flow path to generate electric power; and controlling a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation. In an aspect combinable with the example implementation, the nuclear power system further includes a chemical injection system in fluid communication with the primary coolant flow path. Another aspect combinable with any of the previous aspects further includes controlling the power output of the nuclear fission reaction independent of any control rod assemblies by controlling one or more parameters of at least one of the power generation system or the chemical injection system during normal operation. Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, controlling the power generation system to adjust the turbine inlet steam valve includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction; or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction. In another aspect combinable with any of the previous aspects, controlling the power generation system to adjust the feed water pump includes at least one of decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction; or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction. Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values. In another aspect combinable with any of the previous aspects, adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction. In another example implementation, a pressurized water reactor (PWR) includes a control rod assembly-less reactor module that includes a reactor vessel including a volume sized to enclose a reactor core, a riser, and a steam generator without enclosing a control rod assembly system, and a containment vessel including a volume sized to enclose the reactor vessel; and a power generation system including a steam conduit in fluid communication with the steam generator, a steam turbine-generator, and a steam condenser. In an aspect combinable with the example implementation, the volume of the reactor vessel is less than a volume of a conventional reactor vessel sized to enclose a control rod assembly system. Another aspect combinable with any of the previous aspects further includes a control system communicably coupled to the reactor module and the power generation system, the control system configured to adjust a power output of one or more nuclear fuel assemblies in the reactor core by controlling at least one of a flowrate or pressure of a steam supply to the steam turbine generator or a flowrate or temperature of a feed water circulated from the steam condenser to the steam generator. Another aspect combinable with any of the previous aspects further includes a passive boron injection system electrically decoupled from a Class 1E power source that is electrically coupled to the reactor module. In another aspect combinable with any of the previous aspects, the passive boron injection system is positioned in the volume of the containment vessel and fluidly isolated from the volume of the reactor vessel during normal operation of the reactor module. In another aspect combinable with any of the previous aspects, the passive boron injection system is configured to release an amount of solid boron sufficient to shut down a nuclear fission reaction of the reactor module during an emergency core cooling system (ECCS) event. Various implementations according to the present disclosure may include one, some, or all of the following features. For example, implementations of a nuclear power system according to the present disclosure eliminate control rod assemblies and associated systems in a reactor module, thereby eliminating cost and space associated with installing such systems in the reactor module (e.g., lower material and installation costs in money and time). Further, potential nuisance trips and safety related concerns associated with control rod assemblies need not be accounted for in a nuclear power system with no control rod assemblies and systems. As another example, reactor start-up and shutdown procedures may be more efficiently performed in a nuclear power system that includes no control rod assemblies. As yet another example, operating costs of the reactor module may be reduced for a reactor module with no control rod assemblies compared to convention reactor systems with control rod assemblies. As yet another example, normal operational power output adjustment of the reactor module may more efficiently rely on control of one or more components of a power generation system thermally coupled to the reactor module and/or one or more components of a chemical injection system of a reactor module. The present disclosure also describes implementations of a nuclear power system that includes a binary position control rod assembly system. In some aspects, such a nuclear power system may have lower manufacturing and installation costs in money and time, because the binary position control rod assembly system may include less complex control and installation designs. The present disclosure also describes implementations of a nuclear power system that includes a passive boron injection system. In some aspects, such a system may allow for and facilitate the elimination of control rod assemblies from a reactor module. In some aspects, such a system may allow for and facilitate the use of a binary position control rod assembly system within a reactor module. As another example, such a system may allow for a shutdown of the reactor module (e.g., of the nuclear fission reaction) even with a loss of power (e.g., Class 1E power). As another example, such a system may allow for and facilitate the elimination of active boron systems, including liquid holding tanks, piping, and associated controls, thereby reducing time and cost in manufacturing and commissioning the reactor module. The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. The present disclosure describes systems and methods related to controlling a nuclear reaction in a nuclear power module (e.g., a reactor module (“RXM”)) of a nuclear power system. In some implementations, the systems and methods are associated with a passive boron injection system that may operate to control (e.g., shut down) a nuclear reaction during an emergency operation. The term “boron injection system,” as used herein may utilize boron or other substances that absorb neutrons to reduce or shut down a nuclear fission reaction, such as silver, cadmium, indium, or hafnium. In some implementations, a passive boron injection system according to the present disclosure may operate to ensure that a core of a RXM remains subcritical following an emergency core cooling system (ECCS) initiation. In some aspects, the passive boron injection system may operate even with a loss of Class 1E power to the RXM (and is, therefore, passively operated). In some aspects, the boron injection system does not include conventional holding tanks and piping typically associated with neutron absorption injection systems and further, may not hold the boron (or other material) in solution during non-operation. The present disclosure also describes a nuclear power system, and specifically an implementation of a RXM, that excludes control rod assemblies and their related operational equipment. Thus, in some aspects, a fission reaction in such a RXM may be controlled (e.g., reduced or shut down) with, for example, an active neutron absorption injection system (such as an active boron injection system). In addition or alternatively, the fission reaction in such a RXM may be controlled (e.g., reduced or shut down) by, for example, controlling one or more parameters of a power generation system (e.g., a steam powered turbine power generator) that is fluidly coupled to a primary coolant of the RXM. The present disclosure also describes a nuclear power system, and specifically an implementation of a RXM, that includes a binary position control rod assembly system. For example, in some aspects, a binary position control rod assembly (CRA) system may operationally exist in one (and only one) of two operational states at any moment in time. For example, one of the two operational states may be an “inactive” state in which every control rod assembly of the binary position CRA system is fully withdrawn from a core of the RXM and none of the control rod assemblies affect (i.e., absorb neutrons) an ongoing fission reaction that occurs in the core. The other of the two operational states may be an “active” state in which every control rod assembly of the binary position CRA system is fully inserted into the core of the RXM and all of the control rod assemblies operate to shut down the fission reaction that occurs in the core. FIGS. 1A-1B illustrate example implementations of a nuclear power system 100 that includes a passive boron injection system 200. FIG. 1A illustrates an implementation in which the nuclear power system 100 includes the passive boron injection system 200 but excludes any control rod assembly system. FIG. 1B illustrates an implementation in which the nuclear power system 100 includes the passive boron injection system 200 and includes a conventional control rod assembly system in which one or more control rod assemblies may be incrementally inserted into a core of a nuclear reactor module to incrementally control (e.g., reduce or increase) a power output of the nuclear reactor module. As shown in FIGS. 1A-B, the nuclear power system 100 includes a nuclear reactor module (RXM) 102 and a power generation system 150 that is fluidly coupled to a primary coolant of the RXM 102. In some aspects, the RXM 102 may be a light water reactor, such as a pressurized water reactor (PWR) in which a primary coolant heats, but does not boil within the RXM 102. In other aspects, the RXM 102 may be a boiling water reactor (BWR) or condensing steam generator reactor, in which the primary coolant boils within the RXM 102. The illustrated examples of the RXM 102, however, are of a PWR that relies on natural circulation (e.g., rather than pumped, or forced, circulation) of a primary coolant to heat a secondary working fluid of the power generation system 150 within one or more heat exchangers (as described later). The RXM 102 includes a reactor core 114 (that includes nuclear fuel assemblies 115) mounted in a volume 118 of a reactor vessel 108. Primary coolant 128 (e.g., water) in the reactor vessel 108 surrounds the reactor core 114. The reactor core 114 is further located in a shroud which surround the reactor core 114 about its sides. When the primary coolant 128 is heated by the reactor core 114 as a result of fission events, the primary coolant 128 is directed from the shroud and out of a riser 116 (and, normally, to a level 120 located in an upper portion 122 of the reactor vessel 108). This results in further primary coolant 128 being drawn into and heated by the reactor core 114 which draws yet more primary coolant 128 into the shroud. The primary coolant 128 that emerges from the riser 116 is cooled down and directed towards an annulus (e.g., between the riser 116 and the inside surface of the reactor vessel 108) and then returns to the bottom of the reactor vessel 108 through natural circulation. Thus, a flow path of the primary coolant generally starts at a bottom of the reactor vessel 108, extend upward through the core 114 and then the riser 116, exits the riser 116 near a top of the reactor vessel 108, and extends downward in the annulus between the riser 116 and the inside surface of the reactor vessel 108, back to the bottom of the reactor vessel 108. The reactor core 114 is illustrated as being submerged or immersed in the primary coolant 128, such as water. The reactor vessel 108 houses the coolant 128 and the reactor core 114. A reactor housing (not shown) comprises a shroud in a lower portion and the riser 116 in an upper portion of the reactor housing. The shroud surrounds the reactor core 114 about its sides and serves to direct the coolant 128 (shown as arrows) up through the riser 116 located in the upper half of the reactor vessel 108 as a result of natural circulation of the coolant 128. The reactor vessel 108 is surrounded by a containment vessel 110. The containment vessel 110 is designed so that water or steam from the reactor vessel 108 is not allowed to escape into the surrounding environment. A reactor vent valve 130 is provided to vent steam from the reactor vessel 108 into an upper half of the containment vessel 110, e.g., during an emergency event. A submerged reactor recirculation valve 132 (e.g., located on the reactor vessel 108 below a water line 126 of the primary coolant during an emergency situation) is provided fluidly couple a volume 122 of the reactor vessel 108 with a volume 112 of the containment vessel 110 during an emergency operation (e.g., loss of coolant situation). As shown, the reactor vessel 108 is located or mounted inside the containment vessel 110. An inner surface of the reactor vessel 108 may be exposed to a wet environment including the primary coolant 128, and an outer surface may be exposed to a dry environment such as air. The reactor vessel 108 may be made of stainless steel or carbon steel, may include cladding, and may be supported within the containment vessel 110. The reactor vessel 108 may include a predominately cylindrical shape with ellipsoidal, domed or spherical upper and lower ends. The reactor vessel 108 is normally at operating pressure and temperature. The containment vessel 110 is internally dry and may operate at atmospheric pressure with wall temperatures at or near the temperature of the pool of water 106. The containment vessel 110 is cylindrical in shape, and has spherical, domed, or ellipsoidal upper and lower ends in this example implementation. The entire power module assembly (i.e., containment vessel 110 and enclosed reactor vessel 108) may be submerged in a containment pool of water 106 which serves as an effective heat sink. The pool of water 106 and the containment vessel 110 may further be located below ground in a reactor bay 104. The containment vessel 110 may be welded or otherwise sealed to the environment, such that liquids and gas do not escape from, or enter, the power module assembly. The containment vessel 110 may be supported at any external surface. The containment vessel 110 encapsulates and, in some conditions, cools the reactor core 114. It is relatively small, has a high strength and may be capable of withstanding six or seven times the pressure of conventional containment designs in part due to its smaller overall dimensions. Given a break in the primary cooling system of the power module assembly, no fission products are released into the environment. The containment vessel 110 substantially surrounds the reactor vessel 108 and may provide a dry, voided, or gaseous environment identified as volume 112. Volume 112 may comprise an amount of air or other fill gas such as Argonne or other noble gas. The containment vessel 110 includes an inner surface or inner wall which is adjacent to the volume 112. The volume 112 may include a gas or gases instead of or in addition to air. In one embodiment, the volume 112 is maintained at or below atmospheric pressure, for example as a partial vacuum. Gas or gasses in the containment vessel may be removed such that the reactor vessel 108 is located in a complete or partial vacuum in the volume 112. As shown in FIGS. 1A-1B, the power generation system 150 is fluidly coupled to the RXM 102 at heat exchangers (steam generators) 124 that are located within the reactor vessel 108. Pipes or other conduits fluidly connect the steam generators 124 with a steam flow 152 (on the “high pressure” side of the power generation system 150) and a feed water flow 182 (on the “low pressure” side of the power generation system 150). As shown, a steam inlet valve 154 (with actuator 156) is positioned in the steam flow 152 and upstream of a steam turbine 158. The steam turbine 158 is mechanically coupled to an electric power generator 160 (e.g., based on a flow of high pressure steam 152). Together, the steam inlet valve 154 and steam turbine 158 are on the high pressure side of the power generation system 150. Downstream of the steam turbine 158 (i.e., on the low pressure side of the power generation system 150) is a heat exchanger condenser 162 that receives low pressure steam 164 and a condenser fluid supply 165, while outputting a condenser fluid return 166 (e.g., to one or more cooling towers). A condensed steam flow 168 (e.g., the feed water flow 182) is circulated to and by a pump 170 (which includes a pump motor controller 172). In this example implementation, another heat exchanger 174, which may be operated to either cool or heat the feed water flow 182 to a specified temperature, is fluidly coupled to the pump 170. As shown, heat exchanger 174, in this implementation, receives a fluid supply 178 (e.g., cooling or heating) through a valve 176 (with actuator 176) and outputs a fluid return 180. During normal operation, thermal energy from the fission events in the reactor core 114 causes the coolant 128 to heat. As the coolant 128 heats up, it becomes less dense and tends to rise up through the riser 116. As the coolant 128 temperature reduces, it becomes relatively denser than the heated coolant and is circulated around the outside of the annulus, down to the bottom of the reactor vessel 108 and up through the shroud to once again be heated by the reactor core 114. This natural circulation causes the coolant 128 to cycle through the steam generators 124, transferring heat to a secondary coolant, such as the feed water flow 182 that is pumped (by pump 170) through the steam generators 124. Thus, feed water flow 182 is in thermal communication with (but fluidly isolated from) the primary coolant 128 in this example. As the feed water flow 182 is heated in the steam generators 124, it boils to form steam flow 152 (e.g., at a pressure sufficient to drive the steam turbine 158). Pressure of the steam flow 152 is controlled to the inlet of the steam turbine 158 by the steam valve 154. High pressure steam flow 152 drives the steam turbine 158 to drive the generator 160 to produce electric power. Low pressure steam 164 from the turbine 158 flows to the condenser 162 and is condensed to feed water flow 168/182, where it is pumped back to the steam generators 124. As shown in FIGS. 1A-1B, a control system 999 is communicably coupled to, for example, one or more components of the power generation system 150 and can also be communicably coupled to one or more components of the RXM 102. In some aspects, the control system 999 is configured to perform operations to control the nuclear power system 100 during normal operation as well as an emergency operation (e.g., loss of coolant, etc.). In some aspects, the control system 999 is a mechanical or electro-mechanical system. In other aspects, the control system 999 may be a pneumatic system. In other aspects, the control system 999 may be a microprocessor-based system that uses hardware, firmware, and software to control the nuclear power system 100 (such as shown in FIG. 7). In some aspects, the control system 999 may include a combination of these example systems. The control system 999 may include or be a part of one or more flow control systems implemented throughout the nuclear power system 100. A flow control system can include one or more flow pumps to pump the process streams (e.g., feed water or otherwise), one or more flow pipes through which the process streams are flowed and one or more valves to regulate the flow of streams through the pipes. In some implementations, a flow control system can be operated manually. For example, an operator can set a flow rate for each pump and set valve open or close positions to regulate the flow of the process streams through the pipes in the flow control system. Once the operator has set the flow rates and the valve open or close positions for all flow control systems distributed across the crude oil refining facility, the flow control system can flow the streams within a plant or between plants under constant flow conditions, for example, constant volumetric rate or other flow conditions. To change the flow conditions, the operator can manually operate the flow control system, for example, by changing the pump flow rate or the valve open or close position. In some implementations, a flow control system can be operated automatically. For example, the flow control system can be connected to a computer system to operate the flow control system. The computer system can include a computer-readable medium storing instructions (such as flow control instructions and other instructions) executable by one or more processors to perform operations (such as flow control operations). An operator can set the flow rates and the valve open or close positions for all flow control systems distributed across the crude oil refining facility using the computer system. In such implementations, the operator can manually change the flow conditions by providing inputs through the computer system. Also, in such implementations, the computer system can automatically (that is, without manual intervention) control one or more of the flow control systems, for example, using feedback systems implemented in one or more plants and connected to the computer system. For example, a sensor (such as a pressure sensor, temperature sensor or other sensor) can be connected to a pipe through which a process stream flows. The sensor can monitor and provide a flow condition (such as a pressure, temperature, or other flow condition) of the process stream to the computer system. In response to the flow condition exceeding a threshold (such as a threshold pressure value, a threshold temperature value, or other threshold value), the computer system can automatically perform operations. For example, if the pressure or temperature in the pipe exceeds the threshold pressure value or the threshold temperature value, respectively, the computer system can provide a signal to the pump to decrease a flow rate, a signal to open a valve to relieve the pressure, a signal to shut down process stream flow, or other signals. As shown in FIG. 1A, the passive boron injection system 200 is positioned within the volume 112 of the containment vessel 108. In this example implementation, the passive boron injection system 200 includes a boron container 202 and boron portion 204 mounted within or to the boron container 202. In some aspects, boron portion 204 is a solid boron portion 204 (e.g., in granular form) as used throughout the present disclosure. In alternative aspects, boron portion 204 is in liquid form, with an amount of boron in solution. As previously mentioned, although reference number 200 is called a “boron” injection system in the present disclosure, other neutron absorbing isotopes (e.g., of silver, cadmium, indium, or hafnium) may be included with or substituted for boron in the passive injection system 200 and, in some aspects, “boron” refers to the isotope boron-10. In some aspects, the “passive” system 200 may operate without electrical power, i.e., without Class 1E power being available to the system 200 (illustrated in FIGS. 1A-1B and 2A-2B as reference number 990, electrically coupled to one or more components of the RXM 102 and power generation system 150 but not the passive boron injection system 200). Although a single system 200 is shown, there may be multiple passive boron injection systems 200 positioned in the volume 112. Also, although the system 200 is shown near a top portion of the volume 112, the system 200 may be positioned anywhere in the volume 112. Generally, the passive boron injection system 200 operates to release a specified amount of the solid boron portion 204 (e.g., all or part) into the volume 112 of the containment vessel 110 in response to an emergency event, such as an ECCS event. The solid boron portion 204 (which may be a solid block, solid pieces, or a granular solid) is sufficient in amount and concentration to, when released, shut down a nuclear fission reaction ongoing in the core 114 and/or prevent such a nuclear fission reaction from becoming critical. For example, the amount of boron (e.g., solid, in granular form), would be sufficient to raise a level of boron in the primary coolant 209 in the containment vessel volume 112 (that circulates back into the reactor vessel 108) to about 1,500 to 2,000 parts per million boron. The example boron container 202 may be, for instance, a container with a temperature or pressure responsive opening mechanism 205. The opening mechanism 205, for example, may be a switch, latch, or lock that opens the container 202 at a particular pressure (or temperature) within the volume 112. In some aspects, the particular pressure may be at or near (e.g., just above) a release pressure setpoint of the reactor vent valve 130 (e.g., at or around 1850 psig). The particular temperature may be set below a temperature of high pressure steam that is released by the reactor vent valve 130 during an ECCS event. In some aspects, the container 202 may be made of or comprise a thermoplastic member that contains the solid boron portion 204. As a thermoplastic (or other meltable) member, the container 202 may melt or disintegrate at a particular temperature within the volume 112 to release the solid boron portion 204 into the volume 112. In some aspects, the melting point of the container 202 may be at or near (e.g., just below) a temperature of the primary coolant 128 that is vented or circulated to the volume 112 during an ECCS event. In some aspects, the container 202 may be made of or comprise a water-soluble member that contains the solid boron portion 204. As a water-soluble member, the container 202 may disintegrate upon being submerged in water (or another liquid) within the volume 112 to release the solid boron portion 204 into the volume 112, such as when placed into contact with primary coolant 128 that escapes the reactor vessel 108 into the volume 112 during an ECCS event. FIG. 1B illustrates a similar implementation of the nuclear power system 100 as shown in FIG. 1A, but the system 100 in FIG. 1B includes a control rod assembly system 192 operable to insert one or more control rod assemblies into the core 114 during operation of the RXM 102. Thus, for example, the system 100 in FIG. 1A includes no control rod assemblies at all, while the system 100 in FIG. 1B includes a system that uses control rod assemblies to incrementally control (or shut down) the nuclear fission reaction and, thus, the power output by the RXM 102. In some aspects, the control rod assembly system 192 is a conventional CRA system in which one or more control rod assemblies may be incrementally inserted into and withdrawn from the core 114 to reduce or increase the nuclear fission reaction power output. Alternatively, in some aspects, the control rod assembly system 192 is a binary position CRA system (e.g., as described with reference to FIGS. 3A-3B) in which all of the control rod assemblies are either fully inserted into or fully withdrawn from the core 114 and are not incrementally insertable into the core 114 without being fully inserted (e.g., the CRA system 300 cannot stationarily position control rods at any position other than fully inserted or fully withdrawn). In an example operation of the implementation of nuclear power system 100 shown in FIG. 1A, the RXM 102 (which includes no control rod assemblies) may be controlled during normal operation by, for example, controlling and adjusting one or more components of the power generation system 150 (explained more fully later). Thus, during normal operation, there are no control rod assemblies that adjust or help adjust the power output of the RXM 102. During normal operation, the passive boron injection system 200 located in the volume 112 of the containment vessel 110 is inactive. Once an emergency event occurs, such as an ECCS event, vaporized primary coolant 128 at a pressure greater than the vent pressure of reactor vent valve 130 is vented to the volume 112. Concurrently, due to the emergency event, the primary coolant 128 in the reactor vessel 108 is reduced to level 126. As high pressure/high temperature steam vents to the volume 112 through valve 130, the passive boron injection system 200 is initiated. For example, the container 202 may open due to a rise in pressure in the volume 112 that unlocks or unlatches the container 202, thereby releasing the solid boron portion 204 into the volume 112. Alternatively, the container 202, as a thermoplastic, may melt or disintegrate due to the temperature and/or pressure in the volume 112 of the containment vessel 110, thereby releasing the solid boron portion 204 into the volume 112. Alternatively, the container 202, as a liquid soluble container, may dissolve or disintegrate due to the presence of liquid (e.g., condensed high pressure/high temperature steam that is cooled in the volume 112 by the pool 106) in the volume 112 of the containment vessel 110, thereby releasing the solid boron portion 204 into the volume 112. Once released, the solid boron portion 204 mixes and goes into solution with the liquid primary coolant in the volume 112 of the containment vessel 110. This boron-saturated liquid then returns to the core 114 via the open reactor recirculation valve 132, thereby stopping the nuclear fission reaction and/or maintaining the nuclear fission reaction in a sub-critical state. Thus, an amount of the solid boron portion 204 is sufficient (e.g., in mass and/or concentration) to stop the nuclear fission reaction and/or maintain the nuclear fission reaction in a sub-critical state. In a “sub-critical” state, a nuclear fission reaction cannot be maintained (e.g., is effectively shut down), because a neutron population continues to decrease (more are destroyed than created). In an example operation of the implementation of nuclear power system 100 shown in FIG. 1B, the RXM 102 (which includes no control rod assemblies) may be controlled during normal operation by, for example, controlling and adjusting the control rod assembly system 192 located in the reactor vessel 108. Thus, in some aspects, the power output of the RXM 102 is controlled (at least in part) by conventional control rod assembly insertion into the core 114 to control a level of the nuclear fission reaction during normal operation. However, in some aspects, during an emergency event, such as an ECCS event, the passive boron injection system 200 is initiated (and operates to shut down the reaction or maintain a subcritical reaction) rather than, for example, the control rod assembly system 192. FIGS. 2A-2B illustrate additional example implementations of the nuclear power system 100 (but these examples do not include the passive boron injection system 200). FIG. 2A illustrates an implementation in which the nuclear power system 100 excludes any control rod assembly system but does include a conventional chemical injection system 190 that operates to generally control a power output of the nuclear fission reaction by injecting or removing (as needed, depending on whether power is to be increased or decreased) liquid boron (or other neutron absorbing chemical) directly into the reactor vessel 108. FIG. 2B illustrates an implementation in which the nuclear power system 100 includes a binary position control rod assembly system 300 (e.g., as described with reference to FIGS. 3A-3B) in which all of the control rod assemblies are either fully inserted into or fully withdrawn from the core 114 and are not incrementally insertable into the core 114 without being fully inserted. Thus, in an example operation of the system 100 shown in FIG. 2A, the RXM 102 (which includes no control rod assemblies) may be controlled during normal operation by, for example, controlling and adjusting one or more components of the power generation system 150 (explained more fully later). Thus, during normal operation, there are no control rod assemblies that adjust or help adjust the power output of the RXM 102 of FIG. 2A. During normal operation, the conventional chemical injection system 190 may control (e.g., adjust up or down) the power output of the RXM 102. In an example operation of the system 100 shown in FIG. 2B, the RXM 102 (which includes the binary position control rod assembly system 300) may be controlled during normal operation by, for example, controlling and adjusting one or more components of the power generation system 150 (explained more fully later). Thus, during normal operation, the binary position control rod assembly system 300 does not adjust or help adjust the power output of the RXM 102 of FIG. 2B. During normal operation, the system 300 is inactive. Once an emergency event occurs, such as an ECCS event, the binary position control rod assembly system 300 may operate to shut down the nuclear fission reaction of the RXM 102 or maintain the nuclear fission reaction in a subcritical state by fully inserting one or more control rod assemblies from the system 300 into the core 114 of the RXM 102. FIGS. 3A-3C are schematic illustrations of the binary positioning control rod assembly system 300 (CRA system 300). Generally, the system 300 may operationally exist in one (and only one) of two operational states at any moment in time. For example, one of the two operational states may be an “inactive” state in which every control rod assembly of the binary position CRA system 300 is fully withdrawn from a core 114 of the RXM 102 and none of the control rod assemblies affect (i.e., absorb neutrons) an ongoing fission reaction that occurs in the core 114. In some aspects, the term “fully withdrawn” means that bottom ends of the control rods are completely vertically above (in the case of a CRA system 300 mounted vertically above the core 114) or are completely vertically below (in the case of a CRA system 300 mounted vertically below the core 114) all of the fuel assemblies in the core 114. The other of the two operational states may be an “active” state in which every control rod assembly of the binary position CRA system 300 is fully inserted into the core 114 of the RXM 102 and all of the control rod assemblies operate to shut down the fission reaction that occurs in the core 114. In some aspects, the term “fully inserted” means that the CRA system 300 is in a position in which a manifold of the system 300 is directly adjacent (e.g., on top of) top (or bottom) ends of the fuel assemblies of the core 114. FIG. 3A shows the CRA system 300 (schematically) mounted above the core 114 in the reactor vessel 108. FIG. 3B shows a more detailed schematic illustration of the CRA system 300 in an inactive or fully withdrawn state, in which the CRA system 300 does not affect normal operation of the RXM 102 (and does not affect by reducing or increasing any power output of the RXM 102). FIG. 3C shows a more detailed schematic illustration of the CRA system 300 in an active or fully inserted state, in which the CRA system 300 operates to shut down a nuclear fission reaction of the RXM 102 and/or maintain the nuclear fission reaction of the RXM 102 at a subcritical state. As shown in FIGS. 3B-3C, the illustrated CRA system 300 includes a drive mechanism 308, a drive actuator 310, a drive shaft 302, and a manifold 304. The illustrated CRA system 300, as shown, is illustrated mounted in the reactor vessel 108 and is coupled to control rods 306. Although not specifically shown, there may be multiple (e.g., 16) banks or groups of control rods 306, with each bank or group consisting of multiple (e.g., four) control rods 306 (which each may consist of multiple control rodlets). Thus, reference to operation of control rods 306 may refer to operation (e.g., movement from fully withdrawn to fully inserted) of all control rods 306 or one or more banks of control rods 306. The control rods 306, in FIG. 3B, are illustrated as fully withdrawn from the core 114 (and the control rods 306 are not affecting the nuclear fission reaction in the core 114 in this position). In the illustrated embodiment, the actuator 310 of the drive mechanism 308 is communicably coupled to a control system 312. Generally, the control system 312 may receive information (e.g., temperature, pressure, flux, valve status, pump status, or other information) from one or more sensors of the nuclear reactor system 100 and, based on such information, control the actuator 310 to energize the drive mechanism 308 (e.g., during an ECCS event). In some implementations, the control system 312 may be a main controller (i.e., processor-based electronic device or other electronic controller) of the nuclear reactor system. For example, the main controller may be a master controller communicably coupled to slave controllers at the respective control valves. In some implementations, the control system 312 may be a Proportional-Integral-Derivative (PID) controller, a ASIC (application specific integrated circuit), microprocessor based controller, or any other appropriate controller. In some implementations, the control system 312 may be all or part of a distributed control system. The illustrated drive mechanism 308 is coupled (e.g., threadingly) to the drive shaft 302 and operable, in response to operation of the actuator 310, to adjust a location of the control rods 306 in the reactor vessel 102 by lowering or dropping the manifold 304 on the drive shaft 302. Thus, in some aspects, the drive mechanism 308 may operate simply to drop the control rods 306 into the core (fully inserted) such as in response to an ECCS event. In some aspects, the drive mechanism 308 may not apply a positive force to move the drive shaft 302 and manifold 304 but may simply support these components to oppose a downward force of gravity. For example, the control rods 306 may hang from the manifold 304 under their own weight due to gravity. For insertion, the drive mechanism 308 may simply stop any opposition to a force of gravity acting on the control rods 306, thereby allowing the rods 306 to drop of their own weight into the core 114 (e.g., in the case of rods 306 mounted above the core 114). In the case of rods 306 mounted below the core 114 (not shown in FIGS. 3A-3C), the drive mechanism 308 may, upon an actuation event, apply a positive force opposite to gravity in a bottom mounted drive mechanism (both of which are contemplated by the present disclosure) to drive the control rods 306 up into the core 114 (into a fully inserted position). In some aspects, the actuator 310 and drive mechanism 308 may only operate to release or drop the manifold 304 (and thus the control rods 306) into a fully inserted position in the reactor core 114. Thus, in some aspects, once the control rods 306 are in a fully inserted position (e.g., to stop the nuclear fission reaction during an ECCS event), the actuator 310 and drive mechanism 308 are not able to move the control rods 306 into the fully withdrawn position. In some aspects, in order to reset the control rods 306 to the fully withdrawn position, the RXM 102 must be shut down and the reactor vessel 108 opened in order to move the control rods 306 to the fully withdrawn position. FIG. 4 is a flowchart that describes an example process 400 according to the present disclosure. Process 400, for example, describes steps of an operation in which a passive boron injection system is operated to shut down a nuclear fission reaction during, e.g., an ECCS event, or maintain the nuclear fission reaction in a sub-critical state. In some aspects, process 400 may be implemented by or with the nuclear power system 100 shown in either one of FIGS. 1A-1B. Process 400 begins at step 402, which includes operating a nuclear power system to generate a nuclear fission reaction. For example, as described with reference to FIG. 1A or 1B, the nuclear power system 100 may be operated to generate a nuclear fission reaction in the RXM 102 such that electric power is generated by the power generation system 150. In some aspects, the RXM 102 may operate to generate and manage the nuclear fission reaction without any control rod assembly systems or devices (i.e., no control rod assemblies are positioned or found in the reactor vessel of the RXM 102). In process 400, as shown in FIGS. 1A-1B, a passive boron injection system 200 is positioned in the volume 112 of the containment vessel 110. During normal operation of the RXM 102 (i.e., not an emergency event, SCRAM event, or ECCS event, etc.), there is no fluid communication between the volume 112 and the volume 118. More specifically, no boron from the boron injection system 200 is introduced into the volume 118 during normal operation of the RXM 102. Process 400 may continue at step 404, which includes initiating an emergency operation of the nuclear power system based on a loss of a primary coolant. For example, the RXM 102 may experience an emergency event, such as an ECCS event in which a primary coolant level in the reactor vessel 108 may drop (e.g., to just above the core 114) and a pressure in the reactor vessel 108 exceeds a venting pressure threshold (e.g., thereby releasing vaporized primary coolant 207 to the containment vessel 110 through valve 130 as shown in FIG. 1A). At this event, the nuclear fission reaction may not be controllable and/or may approach a critical state. Process 400 may continue at step 406, which includes initiating a boron injection system based on the emergency operation. For example, based on the reactor vessel 108 venting (e.g., due to pressure build up in the vessel 108) vaporized primary coolant may circulate from the volume 118 of the reactor vessel 108 to the volume 112 of the containment vessel 110. Based on the pressure or temperature of the vented vaporized primary coolant into the volume 112, a boron container that holds the amount of solid boron may open, melt or dissolve (e.g., at least partially). Alternatively, the boron container may be mounted in a position of the volume 112 in which cooled and condensed primary coolant (shown as 209 in FIG. 1A) in the volume (e.g., condensed by heat transfer to the pool 106) contacts the boron container (as a water soluble container) and dissolves the container (e.g., at least partially). Process 400 may continue at step 408, which includes releasing an amount of solid boron from the boron injection system to a volume of a containment vessel. For example, once the boron container opens, or melts, or dissolves (at least partially), the amount of solid boron in the container may be released into the volume 112 of the containment vessel 110 to mix with the primary coolant in the volume 112. As some of the primary coolant that vents as steam condenses in the volume 112 (e.g., condensed by heat transfer to the pool 106), the solid boron mixes with the primary (liquid) coolant (shown as 209) and, e.g., goes into solution. Process 400 may continue at step 410, which includes circulating the released solid boron to a reactor core to shut down the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state. For example, a mixture of the solid boron and condensed primary coolant in the volume 112 circulates back to the reactor core 114 through valve 132 (e.g., which opens also in response to the emergency event, as does valve 130). The amount of solid boron, when in solution with the condensed primary coolant 209, is sufficient to shut down the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state. FIG. 5 is a flowchart that describes an example process 500 according to the present disclosure. Process 500, for example, describes steps of an operation in which a power output of a nuclear power system is controlled during normal operation of the system without any use or presence of any control rod assemblies within a nuclear reactor module of the nuclear power system. In some aspects, process 500 may be implemented by or with the nuclear power system 100 shown in either one of FIG. 1A or 2A. Process 500 begins at step 502, which includes operating a nuclear power system to initiate a nuclear fission reaction. For example, as described with reference to FIG. 1A or 2A, the nuclear power system 100 may be operated to initiate and maintain a nuclear fission reaction in the RXM 102 such that electric power is generated by the power generation system 150. The RXM 102 operates to generate and manage the nuclear fission reaction without any control rod assembly systems or devices (i.e., no control rod assemblies are positioned or found in the reactor vessel of the RXM 102). Process 500 may continue at step 504, which includes circulating a primary coolant through the primary coolant flow path to receive heat from the nuclear fission reaction. For example, primary coolant 128 flows (e.g., naturally, without pumping) from a bottom of the reactor vessel 108, through the core 114 where it receives heat from the initiated nuclear fission reaction, and (as it gains buoyancy due to the heat) through the riser 116 toward the top of the vessel 108. As shown, the vessel 108 is not sized to accommodate any control rod assembly system (e.g., no control rods, no control rod assembly motors). The primary coolant 128 exits the riser 116 at the top of the reactor vessel 108 and travels toward the bottom of the reactor vessel 108 in the annulus between the riser 116 and an interior surface of the vessel 108. Process 500 may continue at step 506, which includes transferring the received heat into a power generation system fluidly or thermally coupled to the primary coolant flow path to generate electric power. For example, as shown in FIGS. 1A and 2A, power generator system 150 is thermally coupled to the RXM 102 through steam generators 124, through which a secondary coolant (i.e., working fluid of the power generator system 150) flows to receive heat from the primary coolant 128 (as it flows through the riser 116 and the annulus). Although FIGS. 1A and 2A illustrate a PWR (e.g., in which a secondary coolant drives the power generation equipment), in some aspects, process 500 may use a BWR in which vaporized primary coolant directly drives the power generation equipment (e.g., the steam turbine 158 coupled to the generator 160). Process 500 may continue at step 508, which includes controlling a power output of the nuclear fission reaction independent of any control rod assemblies during normal operation of the nuclear power system (e.g., exclusive of an emergency event, such as ECCS or otherwise). For example, in some aspects, the power output can be controlled by controlling (e.g., with control system 999) one or more parameters of the power generation system or a chemical control system (e.g., system 190). For instance, in some aspects, the control system 999 may adjust the steam inlet valve 154 open (e.g., to increase power output), which increases a temperature of the primary coolant 128 in the core 114, thereby increasing power output of the nuclear fission reaction. Conversely, in some aspects, the control system 999 may adjust the steam inlet valve 154 closed (e.g., to decrease power output), which decreases the temperature of the primary coolant 128 in the core 114, thereby decreasing power output of the nuclear fission reaction. As another example, in some aspects, the control system 999 may increase the flow rate of the feed water 182 from the pump 170 (e.g., by increasing a speed of the pump 170 through the motor controller 172 as a variable speed drive), which decreases the temperature of the primary coolant 128 in the core 114, thereby decreasing power output of the nuclear fission reaction. Conversely, in some aspects, the control system 999 may decrease the flow rate of the feed water 182 from the pump 170 (e.g., by decreasing the speed of the pump 170 through the motor controller 172), which increases the temperature of the primary coolant 128 in the core 114, thereby increasing power output of the nuclear fission reaction. As another example, in some aspects, the control system 999 may increase a temperature of the feed water 182 (e.g., by adjusting operation of the heat exchanger 174), which decreases the temperature of the primary coolant 128 in the core 114, thereby decreasing power output of the nuclear fission reaction. Conversely, in some aspects, the control system 999 may decrease the temperature of the feed water 182 (e.g., by adjusting operation of the heat exchanger 174), which increases the temperature of the primary coolant 128 in the core 114, thereby increasing power output of the nuclear fission reaction. As another example, the control system 999 may control the chemical injection system 190 to control a power output of the nuclear fission reaction. For example, the control system 999 may control the chemical injection system 190 to release more chemical (e.g., boron or other neutron-absorbing chemical) into the reactor vessel 108 to decrease the power output of the nuclear fission reaction. Conversely, the control system 999 may control the chemical injection system 190 to remove the chemical (e.g., boron or other neutron-absorbing chemical) from the reactor vessel 108 to increase the power output of the nuclear fission reaction. In some aspects, process 400 includes operating the passive boron injection system 200 (shown in FIG. 1A) to shut down the nuclear fission reaction or maintain the reaction in a sub-critical state absent the presence or operation of any control rod assemblies in the RXM 102. FIG. 6 is a flowchart that describes an example process 600 according to the present disclosure. Process 600, for example, describes steps of an operation in which a power output of a nuclear power system is controlled during normal operation of the system without the use of control rod assembly, but with a system that includes a binary position control rod assembly system in which the control rods are positionable (i.e., in a stationary position) in only two discrete positions (e.g., a fully withdrawn position and a fully inserted position). In some aspects, process 600 may be implemented by or with the nuclear power system 100 shown in either one of FIG. 1B or 2B in conjunction with FIGS. 3A-3C. Process 600 begins at step 602, which includes operating a nuclear power system to initiate a nuclear fission reaction. For example, as described with reference to FIG. 1B or 2B, the nuclear power system 100 may be operated to initiate and maintain a nuclear fission reaction in the RXM 102 such that electric power is generated by the power generation system 150. The RXM 102 operates to generate and manage the nuclear fission reaction without any control rod assembly systems or devices (i.e., no control rod assemblies are positioned or found in the reactor vessel of the RXM 102). Process 600 may continue at step 604, which includes circulating a primary coolant through the primary coolant flow path to receive heat from the nuclear fission reaction. For example, primary coolant 128 flows (e.g., naturally, without pumping) from a bottom of the reactor vessel 108, through the core 114 where it receives heat from the initiated nuclear fission reaction, and (as it gains buoyancy due to the heat) through the riser 116 toward the top of the vessel 108. As shown, the vessel 108 is not sized to accommodate any control rod assembly system (e.g., no control rods, no control rod assembly motors). The primary coolant 128 exits the riser 116 at the top of the reactor vessel 108 and travels toward the bottom of the reactor vessel 108 in the annulus between the riser 116 and an interior surface of the vessel 108. Process 600 may continue at step 606, which includes transferring the received heat into a power generation system fluidly or thermally coupled to the primary coolant flow path to generate electric power. For example, as shown in FIGS. 1B and 2B, power generator system 150 is thermally coupled to the RXM 102 through steam generators 124, which a secondary coolant (i.e., working fluid of the power generator system 150) flows to receive heat from the primary coolant 128 (as it flows through the riser 116 and the annulus). Although FIGS. 1B and 2B illustrate a PWR (e.g., in which a secondary coolant drives the power generation equipment), in some aspects, process 600 may use a BWR in which vaporized primary coolant directly drives the power generation equipment (e.g., the steam turbine 158 coupled to the generator 160). Process 600 may continue at step 608, which includes operating a control rod assembly system positioned in the reactor vessel to adjust a position of a plurality of control rods from a fully withdrawn first discrete position to a fully inserted second discrete position. For example, with reference to FIGS. 3A-3C, the binary position CRA system 300 is operable to position the control rods 306 in only two positions. The first position, shown in FIG. 3B, is when the control rods 306 are fully withdrawn from the reactor core 114. As shown in that figure, the control rods 306 are held stationary above the core 114 such that the control rods 306 exert no or insubstantial effect on the nuclear fission reaction generated by the fuel assemblies 115 in the core 114. The second position, shown in FIG. 3C, is when the control rods 306 are fully inserted into the reactor core 114. As shown in that figure, the control rods 306 (having been moved or dropped from the first position) are positioned adjacent the nuclear fuel assemblies 115 in the core 114. In the second position, for example, the control rods 306 shutdown or maintain the nuclear fission reaction generated by the fuel assemblies 115 in the core 114 at a sub-critical state. FIG. 7 is a schematic diagram of a control system (or controller) 700 of all or part of a nuclear power system, such as the control system 999 shown in FIGS. 1A-1B and 2A-2B or the control rod assembly controller 312 shown schematically in FIGS. 3B-3C. The system 700 can be used for the operations described in association with any of the computer-implemented methods described previously. The system 700 is intended to include various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. The system 700 can also include mobile devices, such as personal digital assistants, cellular telephones, smartphones, and other similar computing devices. Additionally the system can include portable storage media, such as, Universal Serial Bus (USB) flash drives. For example, the USB flash drives may store operating systems and other applications. The USB flash drives can include input/output components, such as a wireless transmitter or USB connector that may be inserted into a USB port of another computing device. The system 700 includes a processor 710, a memory 720, a storage device 730, and an input/output device 740. Each of the components 710, 720, 730, and 740 are interconnected using a system bus 750. The processor 710 is capable of processing instructions for execution within the system 700. The processor may be designed using any of a number of architectures. For example, the processor 710 may be a CISC (Complex Instruction Set Computers) processor, a RISC (Reduced Instruction Set Computer) processor, or a MISC (Minimal Instruction Set Computer) processor. In one implementation, the processor 710 is a single-threaded processor. In another implementation, the processor 710 is a multi-threaded processor. The processor 710 is capable of processing instructions stored in the memory 720 or on the storage device 730 to display graphical information for a user interface on the input/output device 740. The memory 720 stores information within the system 700. In one implementation, the memory 720 is a computer-readable medium. In one implementation, the memory 720 is a volatile memory unit. In another implementation, the memory 720 is a non-volatile memory unit. The storage device 730 is capable of providing mass storage for the system 700. In one implementation, the storage device 730 is a computer-readable medium. In various different implementations, the storage device 730 may be a floppy disk device, a hard disk device, an optical disk device, or a tape device. The input/output device 740 provides input/output operations for the system 700. In one implementation, the input/output device 740 includes a keyboard and/or pointing device. In another implementation, the input/output device 740 includes a display unit for displaying graphical user interfaces. The features described can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. Additionally, such activities can be implemented via touchscreen flat-panel displays and other appropriate mechanisms. The features can be implemented in a control system that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), peer-to-peer networks (having ad-hoc or static members), grid computing infrastructures, and the Internet. While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of what is described. For example, the steps of the exemplary flow charts in FIGS. 4-6 may be performed in other orders, some steps may be removed, and other steps may be added. Accordingly, other embodiments are within the scope of the following claims. |
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abstract | A fuel assembly for a nuclear reactor having an upstream minor portion defining an upstream end, a main portion, and a downstream minor portion defining a downstream end. Fuel rods extend in a flow interspace permitting a flow of coolant through the fuel assembly in contact with the fuel rods. Two elongated tubes form a respective internal passage extending in parallel with the fuel rods and enclosing a stream of the coolant. Each elongated tube having a bottom, an inlet at the upstream minor portion and an outlet at the downstream minor portion. Each elongated tube having an inlet pipe having an inlet end and an outlet end in the internal passage at a distance from the bottom, thereby forming a space in the internal passage between the outlet end and the bottom. |
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abstract | Embodiments herein disclose a shielding curtain that is configured to block through passage of electromagnetic radiation. The shielding curtain may be a flap portion of a larger shielding curtain or a single, unitary body that includes a single mounting bead and a plurality of flaps. The shielding curtain is formed of a polymer material that has a uniformly dispersed particulate material. Electromagnetic radiation emitted by an inspection system is blocked by the uniformly dispersed particulate material. |
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claims | 1. A method of adjusting the illumination in a plane that is illuminated by an illumination system, wherein the illumination system comprises a first raster element and a second raster element, and wherein the position of the first raster element relative to the second raster element is changed in such a way that a predetermined illumination is achieved in said plane. 2. The method of claim 1, wherein the fist raster element is offset in a first plane relative to the second raster element and/or the second raster element is offset in a second plane relative to the first raster element. 3. The method of claim 1, wherein the second raster element is put into a tilted position relative to the first raster element. 4. An optical device for an illumination system for a microlithographic projection exposure apparatus, comprising a first raster element which receives light of a light source, wherein the first raster element produces a light source image of the light source on a second raster element, wherein the light source image is of a magnitude and the second raster element is of a width that is larger than the magnitude of the light source image, and wherein the first raster element can be changed in its position relative to the second raster element. 5. The optical device of claim 4, wherein the first raster element is part of a multitude of first raster elements, wherein said multitude of first raster elements forms a first optical element, in particular a first faceted optical element. 6. The optical device of claim 4, wherein the second raster element is part of a multitude of second raster elements, wherein said multitude of second raster elements forms a second optical element, in particular a second faceted optical element. 7. The optical device of claim 5, wherein the first optical element is arranged in a first plane and the first optical element is configured to be movable in the first plane, so that by moving the first optical element the position of the first raster element is changed in relation to the second raster element. 8. The optical device of claim 6, wherein the second optical element is arranged in a second plane and the second optical element is configured to be movable in the second plane, so that by moving the second optical element the position of the first raster element is changed in relation to the second raster element. 9. The optical device of claim 5, wherein a first multitude of first raster elements are arranged in a first column and a second multitude of first raster element are arranged in a second column, and the first raster elements in the first column have a first multitude of first limits and the raster elements in the second column have a second multitude of second limits, and wherein the first column is moved in relation to the second column in a direction along the column, so that the first limits have an offset in relation to the second limits. 10. The optical device of claim 4, wherein the first raster element is configured in a reflective design as a first raster mirror element. 11. The optical device of claim 10, wherein the second raster element is configured in a reflective design as a second raster mirror element. 12. The optical device of claim 11, wherein the second raster element is arranged to be tiltable relative to a plane. 13. The optical device of claim 4, wherein the first raster element has substantially the shape of a field to be illuminated. 14. An illumination system for use in microlithography, comprising the optical device of claim 4, wherein a field in a field plane is illuminated. 15. The illumination system of claim 14, further comprising a mirror and/or lens device that is arranged so that it follows the optical device in the light path from the light source to the field plane. 16. The illumination system of claim 14, further comprising a field aperture stop. 17. The illumination system of claim 14, wherein the optical device is of a refractive design. 18. The illumination system of claim 14, wherein the optical device is of a reflective design. 19. An illumination system for use in microlithography, comprising a first optical element serving to form a multitude of light source images of a light source on a pupil raster element of a second optical element, wherein devices are provided by which the position of the light source images on said pupil raster element can be changed. |
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claims | 1. A method of trapping ion beams within a chamber comprising the steps ofcreating a field reversed configuration magnetic field about a rotating plasma within a chamber, including generating an azimuthal electric field within the chamber causing acceleration of plasma electrons and ions,generating an ion beam comprising a plurality of ions,neutralizing the ion beam with a plurality of electrons,injecting the ion beam into the chamber,draining an electric polarization from the ion beam, andtrapping the ion beam in an orbit within the chamber. 2. The method of claim 1 further comprising the step of electrically polarizing the neutralized ion beam. 3. The method of claim 2 wherein the step of electrically polarizing the neutralized ion beam includes passing the neutralized ion beam through a unidirectional magnetic field. 4. The method of claim 1 where in the step of creating a field reversed configuration magnetic field includes the steps ofgenerating a magnetic guide field within the chamber,injecting plasma into the chamber along field lines of the guide field,creating the azimuthal electric field within the chamber causing the plasma to rotate and form a poloidal magnetic self-field surrounding the plasma,increasing the rotational energy of the plasma to increase the magnitude of the self-field to a level that overcomes the magnitude of the guide field, andjoining field lines of the guide field and the self-field. 5. The method of claim 4 wherein the step of creating the guide field includes energizing a plurality of field coils and mirror coils extending about the chamber. 6. The method of claim 4 further comprising the step of increasing the magnitude of the guide field to maintain the rotating plasma at a predetermined radial size. 7. The method of claim 4 wherein the step of creating the azimuthal electric field includes the step of energizing a betatron flux coil within the chamber and increasing current running through the coil. 8. The method of claim 7 wherein the step of increasing the rotational energy of the rotating plasma includes increasing the rate of change of the current running through the coil. 9. The method of claim 8 further comprising the step of increasing the rate of change of the current running through the flux coil to accelerate the rotating plasma to fusion relevant conditions. 10. The method of claim 9 further comprising the step of creating an electrostatic well within the chamber. 11. The method of claim 10 further comprising the step of tuning the electrostatic well. 12. The method of claim 11 wherein the step of tuning the electrostatic well includes manipulating the magnitude of the guide field. 13. The method of claim 1 wherein the injected ion beam has fusion level energy. 14. The method of claim 1 wherein the injected ion beam orbits in a betatron orbit. 15. The method of claim 1 wherein the step of draining an electric polarization from the ion beam includes the step of contacting the ion beam to a plasma layer contained within the field reversed configuration magnetic field. 16. The method of claim 1 wherein the step of injecting the ion beam into the chamber includes injecting the ion beam orthogonal to a principal axis of the chamber and at a radial position from the principle axis where a plasma layer is contained with the field reversed configuration magnetic field. 17. The method of claim 15 wherein the step of trapping the beam includes exerting a Lorentz force due to the field reversed configuration magnetic field on the ion beam to bend the ion beam into a betatron orbit. 18. The method of claim 10 further comprising the steps of magnetically confining ions within the field reversed configuration magnetic field and electrostatically confining electrons within the electrostatic well. 19. The method of claim 18 further comprising the step of forming fusion product ions. 20. The method of claim 19 further comprising the step of exiting the fusion product ions from the field reversed configuration magnetic field in an annular beam. 21. A method of trapping ion beams within a chamber comprising the steps ofinjecting a neutralized ion beam into a field reversed configuration (FRC) magnetic field formed around a rotating plasma within a chamber, wherein formation of the FRC includes generating an azimuthal electric field within the chamber causing acceleration of plasma ions and electrons, andtrapping the neutralized ion beam in an orbit within the chamber. 22. The method of claim 21 further comprising the steps ofneutralizing the ion beam with a plurality of electrons and electrically polarizing the neutralized ion beam. 23. The method of claim 22 further comprising the steps ofdrifting the polarized and neutralize ion beam undeflected through the field reversed configuration magnetic field into contact with a plasma contained within field reversed configuration magnetic field, anddepolarizing the ion beam. 24. The method of claim 23 wherein the steps of depolarizing the ion beam includes the steps of contacting the ion beam with the plasma within the field reversed configuration magnetic field and draining the electric polarization from the ion beam. 25. The method of claim 21 wherein the step of injecting the ion beam includes injecting the ion beam orthogonal to a principal axis of the chamber and at a radial position from the principle axis where a plasma is contained with the field reversed configuration magnetic field. 26. The method of claim 24 wherein the step of trapping the beam includes exerting a Lorentz force due to the field reversed configuration magnetic field on the ion beam to bend the ion beam into a betatron orbit. 27. The method of claim 21 further comprising the steps ofcreating a magnetic guide field with axially extending field lines within a chamber,rotating a plasma comprising charged particles of electrons and ions within the chamber by applying ponderomotive forces from an azimuthal electric field to the charged particles,forming a magnetic poloidal self field surrounding the rotating plasma due to the current carried by the rotating plasma, andincreasing the rotational energy of the plasma to increase the magnitude of the self-field to a level that overcomes the magnitude of the guide field causing field reversal. 28. The method of claim 27 wherein applying pondermotive forces includes creating a azimuthal electric field by increasing current running through a betatron flux coil concentric with a principle axis of the chamber. 29. A method of trapping ion beams within a chamber comprising the steps ofmaintaining a magnetic field with field reversed topology formed about a rotating plasma within a chamber, including generating an azimuthal electric field within the chamber causing acceleration of plasma ions and electrons,injecting a neutralized ion beam into a chamber, andtrapping the ion beam in an orbit within the chamber. 30. The method of claim 29 wherein the neutralized beam is polarized. 31. The method of claim 30 further comprising the step of depolarizing the ion beam. 32. The method of claim 29 wherein the step of injecting the ion beam into the chamber includes injecting the ion beam orthogonal to a principal axis of the chamber and at a radial position from the principle axis where a rotating plasma layer is contained with the field reversed configuration magnetic field. 33. A method of trapping particle beams within a chamber comprising the steps ofmaintaining a magnetic field with field reversed topology formed about a rotating plasma within a chamber, including generating an azimuthal electric field within the chamber causing acceleration of plasma ions and electrons,injecting a particle beam into a chamber, andtrapping the particle beam in an orbit within the chamber. 34. The method of claim 33 wherein the particle beam is an ion beam. 35. The method of claim 34 wherein the step of injecting the ion beam into the chamber includes injecting the ion beam orthogonal to a principal axis of the chamber and at a radial position from the principle axis where a rotating plasma layer is contained with the field reversed configuration magnetic field. |
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048775754 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS It is well known that the concept of reactivity is most readily applicable in a nuclear reactor core under the condition that the fractional rate of change of neutron population is identically the same in all regions of the core or, equivalently, that the shape of the neutron flux distribution is static. The present invention instead of accepting a single signal believed to be representative of neutron flux level in the core and passing the information in that signal through a single "solver" of the point kinetics equations, accepts two or more such input signals and processes the information carried by the respective signals through identical, but independent, "solvers" of the point kinetics equations. The output reactivity values generated by the several "solvers" are then compared and when all of the independent reactivity values agree within a preset tolerance, the average of all the independent values is accepted as a valid measure of the instantaneous core reactivity. A minimum acceptable set of input signals to be processed by the reactivity computer of the present invention consists of the signals generated by the top section and the bottom section of a single long ion chamber, provided that only symmetric perturbations in the radial neutron flux distribution occur as the measurement progresses. Signals generated by one or more movable incore detectors or by suitable fixed incore detectors temporarily or permanently positioned in appropriate locations within the reactor core would be highly desirable supplements to this minimum acceptable set of input signals. In the event that non-symmetric perturbations to the core neutron flux distribution are involved in the measurements being performed such as would result from a single control rod withdrawal or insertion or an N-1 worth test, signals from all available long ion chamber sections would constitute a minimum acceptable input signal set. The present invention also requires that boron dilution between rod movements be done at a constant rate for maintaining a very nearly just critical configuration in the reactor at zero power level. The present invention also accepts the instantaneous reactivity values determined by the methodology mentioned above to be valid and continuously, within the unavoidable discrete time step character of digital processing, generates a linear fit in time to the current set of acceptable instantaneous reactivity values and subjects the fit so generated to a statistical test of acceptability. When enough valid data have been collected and processed, as indicated by acceptance on statistical grounds of the fit of the reactivity value variation versus time, a set of values of current time, reactivity and rate of change of reactivity, i.e., slope of the fit, is recorded. Using this set of values, the fit of reactivity versus time is extrapolated back in time t the time of the most recent earlier set of values and the change in reactivity associated with the most recent control bank movement is evaluated and reported to the user. When a sufficient number of acceptable reactivity values have been produced or when an acceptable fit to the current reactivity variation has been obtained, a signal, which may be in the form of an activated indicator light, can be transmitted to the reactor operator to inform him that data collection and processing at the current rod position has been completed and that he may adjust control bank position and continue on with the measurement process. A simplified block diagram of the system of the present invention is illustrated in FIG. 2. At least two neutron detectors 20 detect the neutron flux produced in the reactor core and produce electrical current signals proportional to the flux detected. The current signals are processed by a conventional signal conditioning unit 22 and supplied to a reactivity computer 24 as analog values. The reactivity computer 24 can include the same conventional digital reactivity computer that determines reactivity from a single channel neutron detector. A suitable pair of single channel digital reactivity computer that can be connected to a personal computer, such as an IBM PC-AT, to form the reactivity computer 24 for a two neutron detector system can be obtained from Westinghouse. The reactivity computer 24 determines the reactivity in the core for different regions by averaging typically ten samples for each detector taken over a period of approximately 10 milliseconds, solves the known point kinetics equations, and displays these instantaneous reactivities on a strip chart recorder type display 26. When the reactivities produced by the plural neutron detectors remain coincident for a long enough time to satisfy a statistical test of "goodness" such as The Standard Error of Estimate Test, the reactivity computer 24 signals an operator via display 28 that the currently measured reactivity is valid or correct, thereby allowing the operator to move the control rods by the next step increment. After rod movement, the reactivity computer 24 determines the control rod worth based on the coincident reactivity values and provides the operator with a differential control rod worth for the previous control rod movement. FIG. 3 illustrates a typical reactivity trace produced by upper and lower neutron detectors provided exterior to the nuclear reactor core. The substantially vertical line 40 indicates the reactivity change that occurs during control rod movement from, for example, the 180 step position to the 190 step position. Once the control rods have been moved the reactivity trace 42 produced by the lower neutron detector. diverges from the trace 44 produced by the upper detector. During the period of reactivity change between control rod movements the reactivity is increasing because of the reduction of neutron absorbers (boron) in the coolant. During a period of constant dilution the traces of the detectors should be straight, and before the operator is allowed to move the control rods a second time, the rate of reactivity change must stabilize into substantially a straight line. The portions 46 in FIG. 3 indicate diverging reactivities measured by the upper and lower neutron detectors after the reactivity traces have crossed. The regions 46, where the reactivity traces 42 and 44 are not coincident and do not provide a substantially straight trace, are inappropriate for determining core reactivity and thus control rod worth. The regions 48 identified in FIG. 3 are regions where core reactivity is valid because the traces are coincident and straight. This general area of FIG. 3 is illustrated substantially enlarged in FIG. 4. The present invention compares the instantaneous reactivities of the lower 42 and upper 44 detectors looking for the first point of coincidence 50 that can be identified. Coincidence occurs when the reactivity values are within 0.5% of the largest expected step reactivity change during measurements. After coincidence begins, the present invention requires that coincidence be maintained for a time period T sufficient to allow a statistical fit to be made. When coincidence has continued for the time period T, the operator can be signaled indicating that control rod movement can be performed. A least squares fit to the coincidence reactivity 52 values occurring during the time period T is performed to produce a straight line 54 and the corresponding slope intercept form equation for the straight line 54. The computer then determines the intersection 56 of the straight line 54 and vertical line 58. The vertical line 58 passes through the point where reactivity equals zero during control rod movement. Control rod worth is then determined by the reactivity difference between point 56 and a point 60 where the previous fitted straight line intersects the vertical line 58. The control rod worth for the control rod movement associated with vertical line 58 is then provided to the operator on display 28. The process described above is illustrated by the flowchart of FIG. 5. A suitable language for the corresponding digital computer program is PASCAL. The process starts 70 by setting 72 and 74. a first fit flag to off and an operator signal flag to on. The first fit flag is set when a new measurement cycle is started. The on operator flag tells the operator the control rods can be moved. A control rod movement by the operator causes the reactivity and the flux distribution in the core to change abruptly. After setting the flag, the reactivity computer 24 takes 10 samples 76 of the flux values produced by each neutron detector along with other parameters necessary to determine reactivity such as time and control rod position. If the control rods were not moved in the last time step 78, the computer 24 averages the values, calculates 80 the reactivities associated with each flux detector, stores the calculated reactivity values and outputs the values to the strip chart recorder. If the control rods were moved in the last time step, the first fit flag is set 82 and the operator signal flag is turned 84 off. A commonly used reference for calculating reactivity,,as in step 80, is A. F. Henry's paper. "The Application of Reactor Kinetics to the Analysis of Experiments", Nuclear Science and Engineering: 3, 52-70 (1958). In this paper Henry derives the well known reactor kinetics equations which appear as equation 6 in the paper. Equation 6 requires that the conditions of equation 5 there,in be satisfied before the simplification of equation 6 will be valid. Equation 5 essentially requires that the reactor settle down to a steady rate of change state before reactivity can be measured. This settling down period is typically from 2 to 4 minutes after control rod movement. When the settling down has occurred, the coincidence between detector reactivity values begins. It is conventional to make measurements of core reactivity under conditions in which the source term Q of the Henry equations is a negligible contributor to the neutron balance and in a situation where the time derivative term dT(t)/dt very quickly becomes of negligible consequence after a perturbation in the core properties. With these two simplifications equation 6 of the Henry paper will produce: ##EQU1## and subsequently ##EQU2## It is of course impractical to measure the actual value of the amplitude function T(t) of a large nuclear reactor. Hence, the assumption is routinely made that the response signal from a suitably located neutron detector is proportional to the value of the amplitude function at any given time. Thus, EQU T(t)=.mu.DR(t) (6) where DR(t) is the magnitude of the detector response signal and the equations actually solved are ##EQU3## where EQU C.sub.i (t)=.LAMBDA..mu.C.sub.i (t) (9) In this final form the equation set is commonly referred to as the "point kinetics" equations. Continuous, online evaluation of the reactivity of a large nuclear reactor core and of changes in the reactivity resulting from externally produced changes in core properties can be accomplished readily by solving the set of simultaneous linear and differential equations discussed above. Once the reactivities are determined by the point kinetics equations, a determination is made 86 concerning whether the reactivities are equal, that is, the reactivities are considered equal when they are all within a preselected variance of each other. This is done for all reactivities produced, by comparing each reactivity with all other determined reactivities if more than two neutron detectors are used in the comparisons. If the reactivities are not equal 86, the process cycles back to sample the measurement parameters again. If the reactivities are within the preselected variance, the average reactivity is produced 88. The average is then used with the previously stored average reactivities to perform a least squares fit 90 versus time. If the rate of change is approximately zero 92 the process is stopped 94. If the rate of change is not approximately equal to zero, a statistical check 96 of the fit of the values using the Standard Error of Estimate Test is performed 96. If the fit is not acceptable 98, a new set of parameters is obtained and the process is repeated. If the fit is acceptable, the fit parameters, core conditions and time are stored 100. If the first fit flag is not on 102, the fit variables are initialized 104 and a new set of parameters are sampled. This allows the process to produce a new fit if the operator does not promptly move the control rods. If a new fit is obtained it is used for future differential worth calculations. If the fit flag is on, the intersections and differences are determined 106 in accordance with the procedures described with respect of FIG. 4. The differences are then used to compute 108 the differential rod worth which is output to the operator after which the operator signal flag is turned on 110. The first fit flag is also turned on 112 after which the process returns to obtain new sample parameters. Once the operator has the last control rod worth for the insertion steps, the operator compares these values to a chart produced by the core designer for the latest fuel loading. The comparison will show whether the design values are accurate. It is possible, though not desirable for safety reasons, to allow the reactivity computer 24 to initiate control rod movement when the period for coincidence has been detected, rather than wait for the operator to move the rods. This would further improve the efficiency of the control rod worth test. It is also possible to vary the time period required for coincidence before reactivity values are validated by setting tighter or less restrictive statistical criteria of "goodness". A further improvement in the present invention would be to calculate boron balance (or worth) and measure reactor temperature, and provide these values as outputs along with reactivity and control rod worth. The many features and advantages of the invention are apparent from the detailed specification and thus it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. |
claims | 1. A method for producing a solution including a radionuclide, the method comprising:(a) bombarding a target solution comprising an aqueous solution of a nitrate salt of a metal in the presence of dilute nitric acid in a target cavity of a solution target with protons to produce a solution including a radionuclide, wherein the radionuclide is 68Ga,wherein the target cavity is cooled with a coolant during the bombardment. 2. The method of claim 1, wherein the target solution is bombarded with protons in the target cavity of the solution target operating as a closed system. 3. The method of claim 2, wherein the solution target has a volume capacity of two milliliters or less. 4. The method of claim 2, wherein the target cavity is defined by a generally conical wall and a target window foil. 5. The method of claim 1, wherein the target solution comprises 68Zn-enriched zinc nitrate. 6. The method of claim 1 wherein the concentration of nitric acid in the target solution is 0.1 M to 2 M. 7. The method of claim 1, wherein step (a) comprises bombarding the target solution with a particle beam having an energy of 15 MeV or less. 8. The method of claim 1, further comprising:(b) passing the solution including the radionuclide through a column including a sorbent to adsorb the radionuclide on the sorbent; and(c) eluting the radionuclide off the sorbent. 9. The method of claim 8, wherein the sorbent comprises a hydroxamate resin. 10. The method of claim 8, wherein step (c) comprises eluting the radionuclide off the sorbent using a phosphate. 11. The method of claim 8, wherein the radionuclidic purity of the radionuclide is greater than 99% after step (c). 12. The method of claim 8, further comprising:(d) passing the eluted radionuclide through a second column including a sorbent. 13. The method of claim 8, wherein step (c) comprises eluting the radionuclide off the sorbent at a pH of 3.5 to 7. |
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description | The present application claims priority of Patent Application No. 10 2010 056 337.4, filed Dec. 27, 2010 in Germany, entitled “PARTICLE BEAM SYSTEM AND SPECTROSCOPY METHOD”, the content of which is hereby incorporated by reference in its entirety. The invention relates to transmission electron microscopes (TEMs) and to methods of operating transmission electron microscopes. The invention in particular relates to transmission electron microscopes and methods of operating transmission electron microscopes for performing spectroscopic measurements of a sample, such as recording energy loss spectra that are representative of energy losses experienced by electrons while interacting with the sample. Energy loss spectra are suitable for detecting elementary excitations of a sample, such as excitation of surface plasmons in the sample, for example. To this end, for example a monochromatic electron beam can be directed onto the sample, resulting in excitations of the sample and a reduction of the kinetic energy of electrons of the beam by an amount corresponding to the energy of the excitation. If an energy spectrum of the electron beam subsequent to its interaction with the sample is recorded, the recorded energy spectrum contains information relating to the excitation energies. The articles J. Nelayah, L. Gu, W. Sigle, C. T. Koch, I. Pastoriza-Santos, L. M. Liz-Marzán, and P. A. van Aken, “Direct imaging of surface plasmon resonances on single triangular silver nanoprisms at optical wavelength using low-loss EFTEM imaging”, Opt. Lett. 34, 1003-1005 (2009) and Wilfried Sigle, Jaysen Nelayah, Christoph T. Koch, and Peter A. van Aken, “Electron energy losses in Ag nanoholes—from localized surface plasmon resonances to rings of fire,” Opt. Lett. 34, 2150-2152 (2009) describe applications of this method. It is an object of the present invention to propose a particle beam system and a spectroscopy method which can be used to record energy loss spectra with a higher degree of accuracy. According to embodiments, a particle beam system comprises a high-voltage source for providing a high voltage at a high-voltage output of the high-voltage source and providing a control signal, which is indicative of a deviation of the provided high voltage from a reference voltage or of a temporal change or fluctuation of the high voltage, at a controller output of the high-voltage source, an acceleration electrode, which is electrically connected to the high-voltage output, for accelerating the particles in a particle beam to a kinetic energy that corresponds to the high voltage, a focusing lens, which is arranged in the beam path of the particle beam downstream of the acceleration electrode, for focusing the beam onto a location of a sample, an energy-dispersive component, which is arranged in the beam path of the particle beam downstream of the sample and is configured to deflect particles of different kinetic energies differently, a detector, which is arranged in the beam path downstream of the energy-dispersive component, and a controller, which is connected to the controller output of the high-voltage source and is configured to effect, in dependence on the control signal provided by the high-voltage source, changes in operating parameters of the energy-dispersive component or of other particle-optical components arranged in the beam path of the particle beam or to correct intensities detected by the spatially resolving detector with respect to the energy. The inventor has recognized that instabilities in a high-voltage source providing an acceleration voltage for a particle beam that is used for the measurement are the cause of a limit on the resolution that can be achieved when measuring energy loss spectra. It is therefore conceivable to better stabilize high-voltage sources used for providing the acceleration voltage. In conventional high-voltage sources for particle beam systems, however, considerable measures for stabilizing said high-voltage sources are employed already, which incur substantial costs and cannot satisfactorily prevent still remaining instabilities, in particular drifting and low-frequency noise. In order to achieve the abovementioned object it is proposed therefore to accept a certain instability of the high-voltage source and to detect changes in the high voltage or deviations of the provided high voltage from a reference voltage and to undertake correction measures at another point in the beam path of the particle beam before or after interaction with the sample. According to an exemplary embodiment, the particle beam system comprises a beam deflector, which is arranged in the beam path between the energy-dispersive component and the spatially resolving detector. The beam deflector can provide an adjustable electric or magnetic field that has a deflecting effect on the particle beam or adjustably deflect the particle beam in another way. The beam deflector is controlled by the controller in dependence on the control signal provided by the high-voltage source. In particular, the deflection angle for the particle beam produced by the beam deflector is increased or decreased here if the deviation of the high voltage provided by the high-voltage source from the setpoint voltage increases or decreases. With this measure it is possible to improve the quality of the energy loss spectrum detected by the spatially resolving detector. Without the controller actuating the beam deflector, a relative increase in the high voltage provided by the high-voltage source would, for example, result in a relative increase in the kinetic energy of the particles in the beam. However, independently of their kinetic energy, the particles experience equal energy losses at the sample that corresponds to the energies of the excitations in the sample. An energy spectrum that is recorded using the spatially resolving detector downstream of the energy-dispersive component is thus shifted to higher energies owing to the relative increase in the high voltage, without changing its relative form that is defined by the unchanging energy losses. A high voltage that varies while the spectrum is recorded using the spatially resolving detector thus results in smearing of the recorded spectrum. Owing to the beam deflector, which is arranged between the energy-dispersive component and the spatially resolving detector, being actuated as explained above, it is possible, after appropriate calibration, to entirely avoid the spectrum shifting to higher or lower energies, with the result that a stable energy loss spectrum can be recorded. According to a further exemplary embodiment, the particle beam system comprises an actuator, which is configured to displace the detector in a direction transverse to the beam path or an incidence direction of the particles on the detector. The actuator is controlled by the controller in dependence on the control signal provided by the high-voltage source. Similar to the case where the previously described beam deflector is used, it is possible, by actuating the actuator to displace the detector, to compensate for shifts, caused by changes in the high voltage, in the energy spectrum, which is recorded using the detector, such that the same energy loss spectra can be recorded for different high voltages. According to a still further exemplary embodiment, the particle beam system comprises a high-voltage source for providing a high voltage at a high-voltage output and for providing a control signal, which is indicative of a deviation of the provided high voltage from a reference voltage, at a controller output, an acceleration electrode, which is electrically connected to the high-voltage output, for accelerating the particles in a particle beam to a kinetic energy that corresponds to the high voltage, a focusing lens, which is arranged in the beam path of the particle beam downstream of the acceleration electrode, for focusing the beam onto a sample, a monochromator, which is arranged in the beam path of the particle beam upstream of the focusing lens and is configured to allow only those particles of the particle beam to pass whose kinetic energy is within an adjustable energy interval, a detector, which is arranged in the beam path of the particle beam system downstream of the sample, for detecting particle beam intensities, and a controller, which is connected to the controller output of the high-voltage source and is configured to control the monochromator such that a central energy of the energy interval changes in dependence on the control signal provided by the high-voltage source. According to a still further exemplary embodiment, the particle beam system comprises a high-voltage source for providing a high voltage at a high-voltage output and providing a control signal, which is indicative of a deviation of the provided high voltage from a reference voltage, at a controller output, an acceleration electrode, which is electrically connected to the high-voltage output, for accelerating the particles in a particle beam to a kinetic energy that corresponds to the high voltage, a focusing lens, which is arranged in a beam path of the particle beam system downstream of the acceleration electrode, for focusing the beam onto a sample, an energy-dispersive component, which is arranged in the beam path downstream of the sample and is configured to deflect particles of different kinetic energies differently, a detector, which is arranged in the beam path downstream of the energy-dispersive component, and a controller, which is connected to the controller output of the high-voltage source and is configured to control the energy-dispersive component such that a dispersion by the energy-dispersive component changes in dependence on the control signal provided by the high-voltage source. Similar to the case where the previously described beam deflector, which is arranged in the beam path of the particle beam system downstream of the energy-dispersive component, is used, it is possible, by controlling the energy-dispersive component itself, to compensate for changes, caused by changes in the high voltage, in an energy spectrum of the particle beams, which is recorded with the aid of the detector, such that the same energy loss spectra can be recorded for different high voltages. According to a still further exemplary embodiment, the particle beam system comprises a high-voltage source for providing a high voltage at a high-voltage output and providing a control signal, which is indicative of a deviation of the provided high voltage from a reference voltage, at a controller output, an acceleration electrode, which is electrically connected to the high-voltage output, for accelerating the particles in a particle beam to a kinetic energy that corresponds to the high voltage, a focusing lens, which is arranged in a beam path of the particle beam system downstream of the acceleration electrode, for focusing the beam onto an object plane, a detector, which is arranged in the beam path downstream of the object plane, and a controller, which is configured to record, with the aid of the detector, energy spectra of the particles contained in the particle beam downstream of the object plane. A plurality of energy spectra are successively recorded and manipulated here by shifting each of the energy spectra in the direction of the energy by an amount that is determined in dependence on the control signal provided by the high-voltage source. The spectra thus manipulated are then added up to a total spectrum. It is possible in this manner to compensate for changes, caused by changes in the high voltage, in the spectra measured with respect to the energy thereof such that the individual measured spectra are in each case representative of identical energy loss spectra which can be superposed in order to increase a statistical significance of the spectra. In the exemplary embodiments described below, components that are alike in function and structure are designated as far as possible by alike reference numerals. Therefore, to understand the features of the individual components of a specific embodiment, the descriptions of other embodiments and of the summary of the invention should be referred to. FIG. 1 schematically shows a particle beam system 1 suitable for recording energy loss spectra. The particle beam system 1 is a transmission electron microscope (TEM) comprising a particle beam source 3 having an emitter 5, an extractor electrode 6 and a plurality of other electrodes 7 for generating an electron beam 9. The electron beam source can be, for example, a Schottky field emission source, which for example generates a beam current of 100 pA with an energy width of 0.7 eV. The particle beam system 1 may comprise a monochromator 11, which is configured to allow only those electrons of the particle beam to pass whose kinetic energy is within an adjustable energy interval. To this end, the monochromator comprises a plurality of electrodes (not shown in FIG. 1) in order to guide the electron beam 9 in the illustrated Q-shaped path. An aperture plate 12 is arranged in the beam path, wherein only particles of the beam whose kinetic energy is within the set energy interval may traverse an aperture of the plate 12. One example of a suitable monochromator is described in the patent specification U.S. Pat. No. 6,770,878 B2, the disclosure of which is incorporated in its entirety in the present application. With a suitable monochromator it is possible to limit the width of the energy interval for example to 50 meV. The monochromator 11 is merely optional in the particle beam system and can be omitted if an energy width of the electron beam provided by the electron source 3 is already less than or equal to an energy width desired for the examination to be carried out. A plurality of acceleration electrodes 13 are arranged in the beam path of the particle beam system 1 downstream of the monochromator for accelerating the electrons of the electron beam 9 to a kinetic energy of, for example, 200 keV, while their energies before traversing the acceleration electrodes 13 was, for example, 4 keV. In the illustrated example, the monochromator 11 is arranged between the electron source 3 and the acceleration electrodes 13, with the result that comparatively small deflection fields are necessary to guide the electron beam on a curved path required for monochromatization. However, it is also possible to arrange a monochromator in the beam path downstream of the acceleration electrodes 13 and to monochromatize the electron beam of high kinetic energy. After acceleration, the electron beam 9 traverses a condenser system 15 and is then focused at an object plane 19 by a single-field condenser objective lens 17. A sample to be examined is arranged in the object plane 19 which is traversed by the particle beam 9. A beam deflector 16 may be provided in the beam path upstream of the object plane 19 in order to scan the beam over the object plane 19 and direct it onto selected locations of a sample. Depending on the design of the system and in particular of the condenser lens, the electron beam in the sample plane can have diameters that are smaller than 0.2 nm, for example. The kinetic energy of the electrons of the beam 9 that are traversing the sample plane 19 is defined by a voltage difference between an area surrounding the sample plane 19 and the emitter 5 of the electron source. Typically the sample arranged in the object plane 19 is kept at ground potential and the emitter 5 at high-voltage potential. However, it is also possible to deviate from this. In any case a high-voltage source 21 is necessary in order to provide the necessary high potential difference between the emitter 5 and the sample. In the exemplary embodiment illustrated, a high-voltage output 23 of the high-voltage source 21 is electrically connected to the emitter 5 so as to keep the latter at a high electric potential with respect to earth. The high-voltage source 21 further comprises a control input 25 in order to be supplied with a control signal which is indicative of a reference voltage for the high voltage to be provided at the high-voltage output 23. This control signal is generated by and supplied from a controller 27 via an output 29 of the controller 27. The controller 27 further comprises an output 31 for controlling the monochromator 11 and for setting a central energy of the interval of kinetic energies which are allowed to traverse the monochromator 11. Here, the electric potentials to be applied to the electrodes 6, 7, the components of the monochromator 11 and the acceleration electrodes 13 are high-voltage potentials which can be generated by separate high-voltage sources or using the high-voltage source 21 together with auxiliary circuits such as voltage dividers and/or low-voltage sources. The monochromator 11 in that case is for example not connected directly to the output 31 of the controller 27 but to a suitable auxiliary circuit, such as a voltage divider, that is connected to the high-voltage source, for generating the voltages suitable for controlling the monochromator 11. The electrons of the electron beam 9, which are directed onto the sample, interact with the sample and can excite said sample, in which case individual electrons lose an amount of energy that corresponds to the excitation energy of an excitation of the sample. Therefore it is of interest to determine the energy spectrum of the electrons of the electron beam after interaction with the sample to obtain information relating to the possible excitations of the sample. To this end, the particle beam system 1 comprises a projection system 35, which comprises one or more electron-optical lenses and is arranged in the beam path downstream of the objective lens 17. Arranged in the beam path downstream of the projective system 35 is an energy-dispersive electron-optical component 37, which provides different deflection angles for particles of different kinetic energies, such that a spatially resolved energy spectrum of the beam 9 is produced in a spectrum plane 39 in the beam path downstream of the energy-dispersive component 37. The energy-dispersive component 37 can be configured as is described, for example, in U.S. Pat. Nos. 4,740,704 and 6,384,412, wherein the disclosure of these documents is incorporated in its entirety in the present application. The spectrum plane 39 is imaged onto a spatially resolving detector 43 using a further projection system 41, which may comprise one or more electron-optical lenses. The spatially resolving detector 43 can be configured, for example, as a line detector which is oriented such that particles of different energies are incident on the detector at different locations due to the dispersion by the energy-dispersive component 37. By spatially resolved detection of intensities of the incident particles it is thus possible to detect the intensities in an energy-resolved manner, i.e. to measure the energy spectrum of the electron beam 9 subsequent to its interaction with the sample. Line 47 in FIG. 2 schematically illustrates such an energy spectrum as can be recorded by the detector 43 if the high voltage provided by the high-voltage source 21 corresponds exactly to the reference voltage and a given sample is arranged in the object plane 19. Line 49 in FIG. 2 schematically represents a spectrum, recorded using the detector 43, as is formed for the same sample where however the high voltage provided by the high-voltage source 21 is greater than the reference voltage. This results in a higher kinetic energy of the electrons travelling through the sample and, owing to the dispersion by the energy-dispersive component 37, in a shift of the spectrum detected using the detector 43 to the left in the illustration of FIG. 2. If the high-voltage source 21 is not sufficiently stable and the high voltage provided is subject to noise, this results in the spectrum in the illustration of FIG. 2 to being persistently displaced to and fro during the measurement using the detector 43 due to the dispersion by the energy-dispersive component 37. The spectrum finally obtained by integration is correspondingly smeared and thus prevents obtaining of certain information contained in the energy distribution of the electrons. Since even conventional high-voltage sources of complex design are not sufficiently stable for high-resolution energy loss measurements, the particle beam system 1 has various options for compensating for fluctuations of the high-voltage source 21. A temporal fluctuation of the high voltage provided at the output 23 of the high-voltage source 21 is determined in said high-voltage source 21 itself and provided, as an electric signal, at the control output 51 of the high-voltage source 21. The control output 51 is connected to an input 53 of the controller 27. The controller 27 can thus, via the input 53, read a signal that is indicative of the fluctuation in the high voltage provided or the deviation of the high voltage provided at the high-voltage output 23 from the reference voltage. A first possibility of compensating for the fluctuations in the high voltage during the recording of energy loss spectra uses a beam deflector 55, which is arranged in the beam path downstream of the energy-dispersive component 37 and upstream of the detector 43. The beam deflector 55 can generate a magnetic and/or an electric field that deflects the electron beam 9. The beam deflector 55 is controlled by the controller 27, which provides a control signal at its output 57 for the deflector 55 which is determined by the controller 27 in dependence on the control signal of the high voltage. For example, the control signal can be determined such that a change in the deflection angle provided by the deflector 55 for the beam is proportional to a deviation of the provided high voltage from the reference voltage. The controller 27 here produces, in dependence on the control signal of the high-voltage source, a change in the deflection signal such that the deflection produced by the deflector 55 compensates for that shift of the electron spectrum on the detector which corresponds to the energy deviation of the electrons from the reference energy, caused by the deviation of the high voltage from the setpoint voltage, and to the shift of the electron spectrum on the detector, caused therefrom due to the dispersion by the energy-dispersive component 37. By controlling the deflector 55 in dependence on the deviation of the provided high voltage from the reference voltage it is possible to largely avoid the shift of the spectra due to the deviation of the high voltage, explained previously in conjunction with FIG. 2. A second possibility of avoiding such shifts, which can be used alternatively to or complementary with the previously described first possibility, is controlling of the monochromator 11 in dependence on the deviation of the provided high voltage from the reference voltage. Here the controller 27 controls, via its output 31, the monochromator 11 such that the central energy of the interval of kinetic energies of the electrons, which are allowed to pass through the monochromator 11, is increased or decreased if the high voltage provided decreases or increases, respectively, due to the determined temporal fluctuations. A third possibility for avoiding the deterioration of the detected energy spectra due to the deviation of the provided high voltage from the reference voltage, which can be used alternatively or in addition to one or both of the possibilities described previously, involves the energy-dispersive component 37 being controlled by the controller 27 via an output 61 thereof in dependence on the fluctuation of the high voltage provided or in dependence on the deviation of the provided high voltage from the reference voltage. This may achieve an effect similar to that of the deflector 55 and results in a shift of a spectrum of electrons impacting the detector 43 due to changes in the high voltage does not take place, or takes place only to a very limited extent. A fourth possibility of avoiding the smearing of the measured spectrum due to fluctuations of the high voltage, which can be used alternatively to or in combination with one or more of the possibilities described previously, involves the controller 27 reading in quick succession a plurality of spatially resolved intensity spectra from the detector 43 via a data line 42. To this end, the detector can be a CMOS sensor, for example, which allows a particularly quick reading operation. The controller reads the intensity values, which were detected in a spatially resolved manner by the detector 43, together with a value of the control signal, which is representative of the current deviation of the provided high voltage from the reference voltage. In dependence on this deviation, each spectrum that is read from the detector 43 is corrected by shifting the respective measured values towards higher or lower energies, wherein the value of the shift is determined in dependence on the respective deviation of the provided high voltage from the setpoint voltage. Thus each of the read spectra is corrected with respect to the deviation of the provided high voltage from the reference voltage such that in the end the plurality of spectra can be added up to obtain a total spectrum of high statistical significance that is not smeared due to the fluctuations of the provided high voltage. A fifth possibility for avoiding the smearing of the measured spectrum due to fluctuations of the high voltage, which can be used alternatively to or in combination with one or more of the possibilities described previously, involves an actuator 60, which may for example include an electric motor or piezo actuator, being actuated by the controller 27 via an output 58 thereof, wherein the actuator 60 is configured to displace the spatially resolving detector 43 transversely to an incidence direction of the beam 9 on the detector in a lateral direction illustrated by an arrow 62. This can achieve an effect similar to that of the previously described deflector 55 and results in a shift of the spectrum of electrons incident on the detector 43 due to changes in the high voltage taking place to a comparatively limited extent. FIG. 3 is a schematic diagram of an exemplary embodiment of a high-voltage source 21. The high-voltage source 21 provides a high voltage of for example 200 kV between the connections 23 and 24. Here, the connection 24 may be connected to an internal ground of the high-voltage source 21, which in turn is connected to a ground of the particle beam system 1. The high-voltage source 21 further comprises the control input 25 for setting the reference value of the high voltage to be provided between the connections 23 and 24, wherein a signal, which is representative of the instantaneous deviation of the high voltage provided between the connections 23 and 24 from their reference value, is output at the control output 51. The high-voltage source 21 comprises an alternating voltage generator 81, which generates an alternating voltage with a given voltage amplitude. This alternating voltage is transformed in a transformer 83 into an alternating voltage with a higher voltage amplitude. On the basis of this alternating voltage with higher voltage amplitude, a high-voltage converter 85, such as a Cockroft-Walton generator for example, generates a rectified high voltage, which is smoothed by one or more filter resistors 87 and filter capacitors 89, such that the smoothed high voltage is available at the connection 23. The magnitude of the high voltage is determined via an amplitude controller 91, which controls the voltage amplitude of the alternating voltage generator 81. To this end, a voltage signal is supplied to the amplitude controller 91 via a measurement resistor 93, which voltage signal is indicative of the magnitude of the high voltage provided between the connections 23 and 24, wherein, in the amplitude controller 91, this supplied voltage is compared with the voltage supplied to the high-voltage source 21 via the connection 25 and, in dependence on this comparison, the voltage amplitude of the alternating voltage generator is increased or decreased. The controller 27 can thus control the magnitude of the high voltage provided between the connections 23 and 24 via the connection 25. A load current measurement instrument 95 is provided for measuring the current flowing between the connections 23 and 24. A capacitive voltage divider having capacitors 97 and 98 is provided between the connectors 23 and 24, wherein an amplifier 99 amplifies the voltage present between the capacitors 97 and 98 and provides a signal corresponding to the amplified voltage at the output 51 such that a signal is output via the output 51 to the controller 27 of the particle beam system 1, which signal corresponds to the instantaneous temporal change in the high voltage provided between the connections 23 and 24 and thus to the deviation thereof from its reference value. In the previously explained exemplary embodiments, the detector 43 is a linear detector detecting an energy spectrum of the electron beam which is incident on it. However, it is likewise possible to detect an energy spectrum with a non-spatially resolving detector, by moving this detector or an aperture associated therewith, which is arranged in the beam path downstream of the energy-dispersive component 37, transversely to the beam direction, and the intensities detected by the detector are recorded in dependence on the position of the aperture or the detector, respectively. It is furthermore possible for a two-dimensionally resolving detector to be used to detect the energy spectrum. In the previously explained exemplary embodiments, the particle beam system is a transmission electron microscope. However, the present disclosure is not limited thereto. In further possible exemplary embodiments, the particle beam system can be a transmission ion microscope. One example of this is a gas field ion microscope, in which an ion beam is generated by ionizing gas atoms in an electrostatic field of an emission peak. The object is then irradiated with an ion beam, wherein ions transmitted through the object can lose energy, with the result that their energy loss spectrum, too, can be detected. If the particle beam apparatus is an ion microscope, the objective lens can be a magnetic lens, an electrostatic lens or a combination of a magnetic lens and an electrostatic lens. In the previously explained exemplary embodiments, the particle beam system has a monochromator arranged in the beam path upstream of the objective lens. This does not necessarily have to be the case. In other exemplary embodiments, no monochromator is provided between the particle source and the object. In particular, a monochromator is not necessary where an energy width of the particle beam produced by the particle source is sufficiently small for desired examination. This can be the case in particular for cooled ion sources or electron sources. While the invention has been described with respect to certain exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention set forth herein are intended to be illustrative and not limiting in any way. Various changes may be made without departing from the spirit and scope of the present invention as defined in the following claims. |
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description | The U.S. Government has rights in this invention pursuant to Contract No. DE-AC02-06CH11357 between the U.S. Department of Energy and UChicago Argonne, LLC, representing Argonne National Laboratory. 1. Field of the Invention This invention relates to purification of scandium and more specifically, this invention relates to the isolation and purification of medical radioisotopes from irradiated targets. 2. Background of the Invention Radioisotopes play important roles in numerous areas ranging from medical treatments to national security and basic research. Some examples include investigations of structures and reactions involving atomic nuclei, Mossbauer spectroscopy, radio-thermoelectric generation and other nuclear batteries, nuclear device detection, nuclear non-proliferation, cancer diagnosis and therapies. Radionuclide production technology for medical applications has been pursued since the early 1900s both commercially and in nuclear science centers. The ionizing nature of the emissions of certain radioactive isotopes can be used to destroy malignant biological tissues. The unpredictable and fast-acting properties of tumors and infectious diseases demand that radionuclide therapies employ a wide arsenal of radioisotopes of differing radioactive emissions. Many medical radioisotopes are now in routine production and are used in day-to-day medical procedures, with production centers currently seeking FDA approval for additional radioisotopes. Despite these advancements, research is accelerating around the world to improve the existing production methodologies as well as to develop novel radionuclides for new medical applications. For more than 40 years, the National Nuclear Security Administration (NNSA) has targeted the conversion of world-wide research reactors from highly-enriched uranium (HEU) to low-enriched uranium. This is problematic inasmuch as these HEU reactors are a pivotal source of medical radioisotopes such that the conversion of these reactors may curtail isotope availability. Although high specific activity (HSA) radioisotopes are important in nearly all aspects of radiochemical work, most radionuclides produced in nuclear reactors have low specific activity due to the inherently limited production reaction pathways, (n,γ) that only change the mass number and not the atomic number and thus not the identity of the element. Specific activity refers to the radioactivity of a given radioisotope per unit mass, usually per mass of the ground state of the element of interest present in the sample. In order to achieve HSA radioisotopes, the product of nuclear reactions must be chemically different and separable from the target material. These are the keys to producing HSA radioisotopes. In the medical sense, HSA radioisotopes are essential for radioisotope therapy or radioimmunotherapies (RIT). Here HSA radioisotopes are bound to specific sites that are coordinated to targeting vectors that seek markers expressed on/in cancer tissues. Low specific activity radioisotopes will not work for these applications as the nonradioactive target material (or non-useful isotope) will compete for the binding site meant for the radioisotope. Fewer agents with the desired cancer fighting payload (radioisotope) make it to the cancer site, thus decreasing the effectiveness of the therapy. Separation of desired radioisotope from the target material is of paramount importance for medical applications as well as for radiological source preparation, and nuclear fuel reprocessing. Technologies described herein for the chemical separation of radioisotopes from target materials can also be useful for industrial applications such as the isolation of pure products from ores and mineral deposits and visa versa. Radionuclides with ionizing beta emissions, several day half-lives, and appropriate gamma emissions are potential candidates for radioimmunotherapy. Scandium-47 is an emerging combined therapeutic and diagnostic (theragnostic) medical isotope that can be used for targeted radionuclide therapies in the treatment of a variety of tumors and rheumatoid arthritis. Sc-47 is a β emitter of moderate radiation energies (max. 439 and 600 keV) with a 3.35 day half-life. In addition, Sc-47 emits a γ-ray of 159 keV, which is suitable for Single Photon Emission Computed Tomography (SPECT). Methods researched for the production of high-specific activity Sc-47 include nuclear activation of enriched titanium targets by fast-neutron reactors, high-energy proton accelerators, or electron accelerators. Carrier free (HSA) Sc-47 can be produced in a nuclear reaction either from Ti-47 (n,p) or from Ca-46 (n,γ). State of the art scandium isolation and purification protocols require complex and time-consuming separation avenues. Lengthy steps with columns and metal complexing agents are often required. Multiple solvent extraction steps using multiple ion exchange columns are employed in state of the art methods. Also, these processes are long, in excess of 8-12 hours. These long processing times are particularly troublesome inasmuch as the desired radio-isotope is decaying with time and therefore lost over extending processing times. Given these shortcomings in scandium isolation and purification protocols, the availability of scandium is potentially very expensive and uncertain. Therefore, while Sc-47 has very desirable half-life of 3.35 days, the medical community is forced to use less viable alternatives. A need exists in the art for a system and method for economically isolating and purifying Sc-47. The system and method should integrate several element harvesting procedures in as few steps as possible and omit excessively hazardous or complex reagents so as to render product as quickly as possible. Furthermore, the system and method should eliminate or at least minimize secondary waste streams, and provide the option of recycling the target material. An object of the invention is to provide a process and a system to isolate and purify medical grade isotopes that overcomes many of the drawbacks of the prior art. The invention can facilitate the separation of any divalent cations (e.g., the alkaline earths such as Ca(II), Sr(II) Ba(II), and Ra(II)) and trivalent cations (e.g., Y-90, the lanthanides, Lu-177, Sm-153, Er-169, Tb-161, Gd-159, Pr-143, Pm-149, Dr-165, Ho-166, Pr-142, Ac-225), and Group 4 elements Ti, Zr, Hf, Th, from other materials. Another object of the invention is to provide a process and system for isolating and purifying Sc-47 from irradiated titanium targets. A feature of the invention is that a single resin bed is utilized to isolate and purify the scandium, whereby only sulfuric acid is required as the vehicle to transport and adsorb the scandium to the resin. An advantage of the invention is that radiopharmaceutically pure (e.g. greater than about 95 percent) Sc-47 is generated in less than 3 hours. Still another object of the present invention is to provide a process for isolating and purifying carrier free Sc-47 such that no additional agents need be added to aid in isolation and purification. A feature of the invention is that sulfuric acid is utilized in the separation step of the protocol. An advantage of the process is that no evaporations or multiple complexing agents are required, thereby streamlining the process. Briefly, the invention provides a method for isolating isotopes from homogeneous or heterogeneous bulk material, the method comprising dissolving the material to create a solution; contacting the solution with a resin so as to retain isotopes on the resin and generate an eluent containing titanium; contacting the isotope-containing resin with acid of a first concentration to remove impurities (e.g., iron, aluminum, any residual titanium and other ions) from the resin; and contacting the isotope-containing resin with an acid of a second concentration to remove purified isotope from the resin. The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. All numeric values are herein assumed to be modified by the term “about”, whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one skilled in the art would consider equivalent to the recited value (e.g., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. The recitation of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. The invention provides a method and system for isolating and purifying +2, +3, and +4 oxidation state moieties from other materials. For example, the invention provides a facile method for isolating and purifying hard trivalent oxidation state moieties, including, but not limited to Sc-47, Lu-177, Y-90, and Ac-225. (“Hard” ions have small ionic radii and large positive ionic charges.) A salient feature of the invention is loading separation resins with a liquid phase mixture of isotopes, wherein in the liquid phase contains bisulfate and/or sulfate anions. Any amount of bisulfate facilitates loading. Concentrations of between about 0 to about 2.5 M sodium bisulfate are suitable. Embodiments of the invention include solely sulfuric acid as the dissolution agent in the isotope liquid phase. Other embodiments include mixtures of sulfuric acid with other acids (such as: hydrofluoric acid/sulfuric acid, nitric acid/sulfuric acid, hydrochloric acid/sulfuric acid, etc.) in the isotope liquor. Generally, the sulfuric is the primary component of any acid mixture. For example, the sulfuric acid is in excess to the hydrofluoric acid. That hydrofluoric acid can be used in the invented resin system is counterintuitive inasmuch as the acid's strong anion stymies DGA complexing with the target radioisotopes. However, surprisingly and unexpectedly, the inventors found that sulfate anions, and particularly bisulfate anions, facilitate adsorption of target radioisotopes (e.g., Sc-47) to resins, whether the anions are combined with other mineral acids or presented neat as H2SO4. As such, HF can be used to readily dissolve the target and the sulfate and/or bisulfate can be used to aid in the retention of the isotope to the resin. The limiting reagent in this complexation is the bisulfate. The final product of the invention is a high purity (above 95 percent) yield of radioisotopes for medical and other applications. Purity relates to the specific activity. High specific activity is extremely important in chelation chemistry, discussed below in relation to the production of medical isotopes. Radioisotopes produced via the invention are in pico- and nano-gram quantities. Therefore, chelators are generally in great excess compared to the radioisotope and any impurities in the process eluent. After chelation, a targeting vector (e.g., an antibody specific for a cancer) is complexed with the chelated radioisotope. If there are any impurities, the chelator may bind those impurities and the drug will be less effective. Furthermore, if there are impurities, the impurities will compete for the binding sites and thus not all of the radioactive (or useful) component will be utilized. The presence of other radioisotopes can also introduce radiation uncertainties which could reduce the quality of gamma images, diminish the accuracy of therapeutic ionizations, or provide unnecessary additional radiation dose to the patient and medical staff. An embodiment of the invention provides a method and system for isolating medical radioisotopes from irradiated feedstock. One such radioisotope is scandium 47. Scandium has a hard trivalent (+3) oxidation state. This provides an important chelation advantage. The chelated construct is combined with antibodies for targeted application to neoplasms and other cancerous tissues. It also has desirable radiations, e.g., beta and gamma emissions, for therapy and diagnositics, respectively. Recently, electron linacs have become capable of producing photons with sufficient energy and flux for radioisotope production. The electron linac may provide a cheaper method, than nuclear reactors, for producing radioisotopes with higher specific activity and increased yields. FIG. 1 depicts a method, designated as numeral 10, for isolating and purifying medical radioisotopes from activated targets. These targets are generally homogeneous and heterogeneous bulk material such as elemental metal or metal alloy, metal oxide cladding, ore, etc., that have been irradiated. The targets may also be mixtures of solid and liquid phases. The targets are “activated” when nuclear radiation treatment produces the radioisotopes of interest within the target. For example, the targets are first subjected to irradiation from photons (converted electrons) and electrons produced from electron accelerators to generate trivalent and divalent moieties such as Sc-47, Lu-177, Y-90, Ac-225, and other medically relevant radioisotopes. In the case of Sc-47 production, Ti-48 is bombarded with photons produced from electrons striking a convertor. The photon ejects a neutron from the titanium atom, thereby transmuting the higher weight titanium into the lower weight Sc-47. Then, the titanium-oxide targets 12 are contacted with an acid 14, which is preferably heated to above 70° C. but below the boiling point of water or about 100° C., so as to dissolve. This solubilizes 16 the nuclear products within those targets. Water 18 is added to decrease the viscosity of the solution, thereby creating a relatively more free-flowing solution 20. Notwithstanding, the initial loading of the resin is with a liquid phase of about 5 M or higher in acid concentration (e.g., about −0.5 to about −1 pH). This free flowing solution 20 is preferable in facilitating the next step which is permeating a resin 22 with the solution so as to begin the separation process. The resin may be confined as in a column, or free flowing. The analyte of interest is retained on the column such that the diluent 24 comprises mainly titanium. In an embodiment of the invention, a single cation exchange resin column or bed is utilized throughout the process. In an embodiment of the invention, a salient feature to this part of the protocol is that only sulfuric acid is used as the loading acid (i.e., the carrier vehicle for transporting and adsorbing the targeted isotope to the resin). Surprisingly and unexpectedly, the inventors found that sulfuric acid synergizes the trapping (adsorption) of target radioisotopes onto DGA resins. Overall, this simplifies the overall process and purification chemistry downstream. The resin is then subjected to nitric acid 26 of between about 5 and about 8 M) so as to begin extraction of impurities 28a (e.g., iron, aluminum, alloys, etc.) from the scandium-containing resin. A second impurity-releasing wash is utilized using mild (about 5 M to about 8 M) hydrochloric acid 30. This creates a second impurities-ladened diluent 28b and removes any residual nitric acid remaining from the first wash. However, if the final product is desirable in HNO3, no HCl wash is required. Rather, a second wash using dilute HNO3 (0.1 M) can be utilized after the initial 5-8 M HNO3 wash. Impurities are washed away in the following order: The resin is first loaded with H2SO4 to remove extra Titanium, the resin is then permeated with HNO3 to remove iron and other impurities the resin and HCl is then added to the resin to remove the HNO3 to get the resin media into HCl form so that the final product is solely in HCl, in those instances where the isotope is to be supplied in HCl. The now heavily scandium-ladened resin 32 is permeated with relatively dilute acid 34 (such as 0.1 M hydrochloric acid) to generate diluent comprising mainly solubilized scandium 36. This renders the resulting resin 38 suitable for recycling 40. Optionally, the resin is regenerated with sulfuric acid (e.g., at about a 4 to about 10 M, and preferably from about 5 to about 7 M concentration) before recycling back to the beginning of the process. The resulting, eluted scandium 36 is subjected to filtration 42 such as by contacting the eluted scandium 36 with a sterile filter to provide pure (e.g., greater than 95 percent) scandium 47 diluent 44. A salient feature of the invented process and system is the use of titanium as the target, sulfate-rich sulfuric acid to solubilize the scandium, and DGA for purifying the scandium. Another salient feature of the invented method and system is the use of diglycolamide based resins, (e.g., N,N,N′,N′-tetra-n-octyldiglycolamide (DGA Resin, Normal) or N,N,N′,N′-tetrakis-2-éthylhexyldiglycolamide (DGA Resin, Branched)), such as those commercially available from Eichrom Technologies (Lisle, Ill.). In an embodiment of the invention, the resin comprises a diglycoamide having the following structural formula: wherein R is an alkyl selected from the group consisting of normal or branched derivatives of DGA and combinations thereof. The resin works by solvating cations with an inorganic counter-ion in the solubilized titanium liquor. Concentrations of the acid extracting vehicles will vary at various steps of the process. For example, the titanium target solubilization step 14 requires sulfuric acids at concentration above about 2 M, and preferably between about 4 M and about 8 M. It is noteworthy that the titanium removal steps require only sulfuric acid (and not other mineral acid solutions, for example nitric acid). This single acid paradigm for titanium solubilization and removal minimizes the overall time and effort for processing the scandium. However, mixtures of sulfuric acid and other acids also can be used. For example, hydrofluoric acid can be used to dissolve the titanium target to create a solution. Then, the titanium-containing hydrofluoric acid solution is diluted with sulfuric acid to facilitate loading of the resin. Alternatively, the column can be loaded with titanium-containing hydrofluoric acid which is first diluted with another mineral acid of 5 M concentration or higher. (Such mineral acid being HCl or HNO3.) Surprisingly, and unexpectedly, the inventors found that resin sorption of the isotopes of interest is more efficient in at least acidic conditions (e.g., approximately greater or equal to 5 M acid concentrations). Similarly, the impurity extraction steps 28a, 28b, post-titanium removal, require relatively concentrated nitric acid (e.g., above about 3 M and below about 8 M) and hydrochloric acid (e.g., above about 3 M and below about 8 M), respectively. No evaporations or multiple resin beds are required to perform the invented method and system. Aside from the initial heating of the titanium dissolving sulfuric acid, the process can be done at any temperature and pressure. For example, temperatures between 0 C and 100 C are acceptable. As for pressures, ambient, negative or positive pressures are also acceptable. Generally, pressures between about 10 mTorr to about 6000 Torr are used. For example, pressure can be applied to the resin as a force flow method, whereby the loaded solution is forced through the resin. Alternatively, a negative pressure is applied to the resin at its downstream end so as to pull the load solution through. So let us say that we can go from. In summary, the invented process comprises: irradiating a sample so as to transmute portions of that sample to a target isotope; dissolving the sample so as to create a liquid containing the target isotope; purifying the isotope by contacting the liquid to an ion exchange media; recycling the exchange media; and repeating the process. Titanium dioxide was combined with sulfuric acid and ammonium sulfate such that approximately 10 times more ammonium sulfate by weight was present than the titanium dioxide. (The sulfate expedites dissolution of titanium dioxide.) This entire mixture was heated for about 1 to about 2 hours at above 70° C. After dissolution, the solubilized target mixture is permeated through a DGA column. Preferably, the mixture is first cooled to allow direct handling, e.g., to below approximately 70° C. This permeation results in the targeted isotope (e.g., Sc-47) to be retained by the column while the titanium is washed out as eluent. Any additional titanium is removed from the resin via a 5 M sulfuric acid wash of the same resin bed. The resin bed is then stripped of any other impurities by washing it with nitric acid and or hydrochloric acid. Concentrations of these acids can be above about 3 M and below about 10 M. As little as about 5-10 milliliters (mL) of wash solution will facilitate impurities removal. Approximately 0.1M HCl is utilized to dislodge the scandium-47 from the finally washed resin. Optionally, the eluent is subjected to filtering. For example, 5 micron sterile syringe filters are suitable. Sulfuric acid solutions were prepared over a concentration range of 2-8 M from reagent-grade concentrated sulfuric acid and deionized water. Hydrochloric acid solutions were prepared over a concentration range of 0.05-1.5 M from reagent-grade concentrated hydrochloric acid and deionized water. Hydrofluoric acid solutions were prepared over a concentration range of 0.1-28 M from optima-grade hydrofluoric acid H2SO4—HF solutions were prepared over a hydrofluoric acid concentration range of 0.1-28 M (5 M H2SO4 with varying concentrations of HF) from reagent-grade sulfuric acid, optima-grade hydrofluoric acid, and deionized water. The prepared acid solutions were titrated with 1.0 N sodium hydroxide solution. The 46Sc solution (used as a long-lived tracer for reduction to practice) was prepared in-house and had an activity range of 6,030-6,480 cpm. The stable scandium stock solution was obtained from 10,000 μg/mL scandium in dilute nitric acid standard reference material solution. The titanium stock solution was obtained from 10,018±46 μg/mL titanium in 0.5% (v/v) HNO3 / trace HF standard reference material solution. The yttrium-88 stock solution was prepared from dilution of a 50 mg/mL YCl3.H2O in 0.1 M HCl solution and had an activity range of 22,000-26,500 cpm. The batch method was utilized at standard temperature and pressure (25° C., 1 atm) to assess the potential performance of titanium, yttrium, and scandium on a chromatography column. While 47Sc is the isotope of interest for medical applications, the batch study portion of this investigation was conducted using the 46Sc radioisotope (Eγ1=1.12 MeV, Eγ2=0.889 MeV, t1/2 =83 days) because it has a longer half-life than 47Sc, making its supply more reliable. The 88Y radioisotope (Eγ=1.060 MeV, t1/2=103.6 days) was also used as a homolog in this study for its easily-detected radioactive decay mode and its commercial availability. Activities for both the 46Sc and 88Y studies were separately determined with a Nal gamma-ray spectrometer. Each element was treated with its own batch study. In the investigation, a small amount of resin (0.1 g for natTi, 0.01 g for natSc, 46Sc, and 88Y) was added to a clean 15 mL polypropylene centrifuge tube using an analytical balance for each acid concentration studied (in triplicate). An aliquot of prepared acid solution (2 mL for natTi and 1 mL for natSc, 46Sc, and 88Y) and 100 μL of element stock solution were added. Additionally, an aliquot of acid solution and 100 μL of elemental stock solution were added to a clean 15 mL centrifuge tube as a laboratory control (sans resin), and an aliquot of acid was added to a clean scintillation vial to obtain background concentrations and activities. For each acid concentration (2-8 M H2SO4 in 1 M increments, 0.05-1.5 M HCl in 0.1 M increments, 0.1-28 M HF over the [0.1, 1, 7.2, 14.4, 28.8] M range, and 5 M H2SO4—HF for HF concentrations of [0.1, 1, 2, 5, 10] M), these five samples were prepared and placed on a gyratory shaker (New Brunswick Scientific Co., Inc., Model G2) operating at 350 rpm to allow for sorption of the elements onto the resin. After one hour of shaking, each sample was extracted from the centrifuge tube with a sterile 3 mL syringe/needle combination (BD Medical). The needle was removed and a 0.2 μm 13 mm PTFE syringe filter (Whatman, Pall Gelman Acrodisc) was affixed to the syringe boor. The solution was forced through the filter into either a clean 15 mL centrifuge tube (natTi, natSc) or a clean scintillation vial (46Sc, 88Y ). Samples containing titanium and cold scandium were submitted to the Argonne Analytical Chemistry Laboratory for ICP-MS analysis for titanium and scandium concentrations. Samples containing radioactive scandium and yttrium were counted using Nal scintillation gamma-ray spectroscopy for three hours for 46Sc in H2SO4 solutions, ten minutes for 46Sc in HCl solutions, five hours for 88Y in H2SO4 solutions, and sixty seconds for 88Y in HCl solutions. The results obtained for the uptake of 46Sc on the resin in H2SO4 solutions are summarized in Table I. One indication of a favorable separation is a high dry-weight distribution ratio, Dw, of the chemical component of greatest interest, and a low Dw for other species present. The distribution ratio is proportional to the retention of a chemical species on a chromatographic column resin bed. The distribution ratio is calculated using Equation 1, where A0 is the total activity of the solution loaded onto the resin, As is the activity of the solution withdrawn from the resin after mixing, w is the mass (in grams) of resin, and V is the total volume (in mL) of solution mixed with resin. The A0 and the As values should take into consideration any background activity present in the prepared acid solutions. D W = A 0 - A s w A s V Equation 1 ) Table 1 shows that the distribution ratio for 46Sc increases with the acidity of the H2SO4 solutions over the 2-6 M concentration range with a maximum value of 48,466.5 mL/g in 6 M H2SO4 and an average activity of 2 cpm. The activity of a 100 μL aliquot of the scandium stock solution in 1 mL of deionized water was determined to be 670±2 cpm. The filtration system experienced approximately 10% retention of the total activity, determined by calculating the percent difference between the filtered laboratory control solution and the unfiltered stock solution aliquot in deionized water. TABLE 146Sc, 88Y, and natTi Dw on resin in H2SO4 systems[H2SO4] (M) 46 Sc D w ( mL g ) 88 Y D w ( mL g ) nat Ti D w ( mL g ) 2.03518.776.80.53.031490.73913.50.33.9956,590.8>10,0000.14.964>10,000>10,0000.25.951>10,000>10,0000.87.871>10,000>10,0000.4 FIG. 2 demonstrates the affinity of 46Sc and its homolog, 88Y, for the resin in H2SO4 while titanium is not retained. Surprisingly and unexpectedly, the inventors found that temperature had relatively no effect on resin performance or isotope yield, particularly in the continuous production protocol. As such, generally, the invention can be conducted at between approximately 15 ° C. and approximately 100 ° C. As noted supra, a myriad of radiation sources are available to generate the target radioisotopes. A preferred route is via a LINAC. The following is one such protocol: A “clam shell” target station was attached at the end of a beam line of the Argonne National Laboratory 50 MeV/30 kW electron LINAC. A water cooled tungsten convertor was used to convert the incident electrons to photons. The convertor consisted of three tungsten disks 0.08″ thick and spaced 0.04″ apart. Two natural Ti foils (2″×4″×0.035″ 99.7%) and 10 g of natural TiO2 (Sigma Aldrich, >99% A.C.S. grade, ˜2″×2″×0.125″) were irradiated using this target station. The Ti foils were placed ˜0.1875″ and 0.625″ behind the convertor. The foils were cooled with compressed air forced through a coil submerged in ice water. The TiO2 was ˜1.375″ from the convertor and was in contact with a water-cooled plate. The foils were wrapped in high-grade aluminum foil for containment and the TiO2 was doubly wrapped with the same foil. The three targets were irradiated with an electron beam energy of 35 MeV at 2 kW and a frequency of 22 Hz providing an average current of 56 μA. The beam was on target for three hours. All samples were counted with an HPGe detector (Table 1) after retrieval the following day. The titanium plates were scanned by a gamma scanner to verify the beam position and size. The TiO2 target was portioned and dissolved, pursuant to the protocol disclosed supra. In summary, a 50 MeV/30 kW electron LINAC was suitable for production of scandium in useful quantities. The yield is expected to increase linearly with increased power and irradiation time. These experiments confirmed the production of all expected radioscandium radioisotopes from a natural TiO2 target. It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. The present methods can involve any or all of the steps or conditions discussed above in various combinations, as desired. Accordingly, it will be readily apparent to the skilled artisan that in some of the disclosed methods certain steps can be deleted or additional steps performed without affecting the viability of the methods. As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” “more than” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. In the same manner, all ratios disclosed herein also include all subratios falling within the broader ratio. One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the present invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Accordingly, for all purposes, the present invention encompasses not only the main group, but also the main group absent one or more of the group members. The present invention also envisages the explicit exclusion of one or more of any of the group members in the claimed invention. |
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abstract | In a method of determining an operating margin to a given operating limit in a nuclear reactor, operational plant data from an on-line nuclear reactor plant is accessed, and reactor operation is simulated off-line using the operational plant data to generate predicted dependent variable data representative of the given operating limit. The predicted dependent variable data is normalized for evaluation with normalized historical dependent variable data from stored operating cycles of plants having a similar plant configuration to the on-line plant. A time-dependent average bias and a time-dependent uncertainty value for the predicted dependent variable data are determined using the normalized historical dependent variable data, and a risk-tolerance level for the on-line plant is obtained. An operating margin to the given operating limit is determined based on the determined time time-dependent average bias value and time-dependent uncertainty value so as to satisfy the risk-tolerance level of the evaluated plant. |
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abstract | A fuel assembly, which linearizes change of an infinite multiplication factor of a fuel and flattens excess reactivity while increasing average fissile plutonium enrichment of a MOX fuel, and a reactor are provided. The fuel assembly includes first fuel rods containing Pu and not containing burnable poison, a second fuel rod containing uranium and burnable poison and not containing Pu, a water rod, and a channel box accommodating the first and second fuel rods and the water rod in a bundle. The second fuel rod is disposed on an outermost periphery and/or adjacent to the water rod, of a fuel rod array in a horizontal section, and N2<N1 (N2 is a positive integer or zero) is satisfied where the number of second fuel rods arranged on the outermost periphery is N1 and the number of second fuel rods arranged adjacent to the water rod is N2. |
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039403106 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The field of this invention is nuclear reactors which use a coolant fluid under pressure, such as light water (H.sub.2 O). 2. Description of the Prior Art U.S. Pat. No. 3,462,345 to Felix S. Jabsen discloses a nuclear reactor in which several fuel elements and individual control rods are provided in the reactor vessel. The individual control rods are longitudinally adjustable in the region of the fuel elements and are movable hydraulically in the guide tubes of the fuel elements, using the reactor coolant and a pump arranges outside the reactor vessel. For the purpose of moving the control rods hydraulically in the guide tubes, the pump generates suction or low pressure in a space provided at the cover of the reactor vessel by means of a suction line which leads from the lid of the reactor vessel to the pump. The pressure line is also connected to the lower part of the reactor vessel. The problem with this arrangement disclosed in the U.S. Pat. No. 3,462,345 is that if a break occurs in a suction line, this would cause a withdrawal of the control rods from the guide tubes, thereby jeopardizing the safety of the nuclear reactor. SUMMARY OF THE INVENTION The object of this invention is to provide an arrangement for the hydraulic operation of control rods within the reactor vessel such that withdrawal of the control rods is prevented in event of trouble, such as a break in the pressure line carrying the reactor coolant, thereby avoiding damage to the nuclear reactor. The nuclear reactor of this invention uses a coolant fluid under pressure and comprises: a reactor pressure vessel; a core disposed within the reactor pressure vessel; one or more fuel elements disposed within the reactor vessel; one or more control rods disposed adjacent to the fuel elements within the reactor vessel; one or more guide tubes, each guide tube having a control rod disposed longitudinally therein, the control rods being movable hydraulically within the guide tubes; a pump disposed outside of the reactor vessel for maintaining the coolant fluid under pressure; and a pressure line carrying coolant fluid under pressure from the pump to the reactor vessel. The high pressure end of the pressure line is connected to the lower end of each guide tube, thereby generating high pressure at the lower end within the guide tube for operating the control rod within the guide tube to support the control rod and move the control rod out of the guide tubes and away from the core, with the result that in the event of a break in the pressure line and a loss of pressure, the control rods are inserted further into the guide tube. Thus, the arrangement of this invention utilizes high pressure, rather than low or a suction pressure, to support the control rods. A high pressure control valve is located outside the reactor vessel at a point accessible for maintenance and is used to control the control rods of the fuel elements. Several high pressure control valves may also be used to control the control rods within the reactor vessel so that not all control rods of the fuel elements are moved at the same time. A flow control connector is brought through the lid of the reactor vessel in a pressure tight manner and a flexible connection is provided between the high pressure control valve and the flow control connector. If more than one high pressure control valve is used, the plurality of valves may be distributed on the outside periphery of the flow control connector so that a compact, space-saving design is achieved. Inside the reactor vessel, the pressure line branches into a plurality of feed lines. These feed lines from several fuel elements lead into one flow control connector. A guide adapter is used between the flow control connector and the guide tubes of the fuel element or elements, with a flexible connection between the guide adapter and the guide tubes. The purpose of this design is to compensate for manufacturing and installation tolerances and to avoid harmful forces in assembly. The feed lines are flexibly coupled to each other. In order to obtain an indication of the position of the control rods within the guide tubes, the pressure exerted by the coolant being fed to the lower end of the guide tube is measured and then the pressure loss over the length of the upper guide tube is measured. |
048759457 | summary | BACKGROUND OF THE INVENTION The present invention relates to a process for cleaning the exhaust gas from a fusion reactor of exhaust gas components containing heavy hydrogen, the heavy hydrogen exhaust gas components comprising tritium and/or deuterium in their elemental forms and impurities which contain tritium and/or deuterium in chemically bound form, wherein the tritium and/or deuterium is released from its chemically bound form, and the released tritium and/or deuterium and the elemental heavy hydrogen are separated from the exhaust gas and returned into the fuel cycle. The exhaust gas from the fuel cycle of a fusion reactor consists essentially of non-reacted fuel, tritium and deuterium in their elemental forms and, in addition helium, the "ash" from nuclear fusion reaction, it contains quite a number of other impurities whose concentrations attain only a few percent and which, partly, contain heavy hydrogen chemically bound to them. The majority of these impurities are carbon monoxide and hydrocarbons, such as methane. In addition, ammonia, carbon dioxide and water vapor usually occur at lower concentrations in the exhaust gas. On account of its content of elemental and chemically bound heavy hydrogen (tritium and deuterium), this exhaust gas cannot be stacked directly to the atmosphere because the heavy hydrogen (tritium and deuterium) fraction must be separated beforehand. It is furthermore desirable to recycle tritium and deuterium into the fusion process. Various techniques have been proposed for cleaning the exhaust gas of a fusion reactor. Processes and an apparatus for decontaminating exhaust gas of tritium and/or deuterium have been suggested by Kerr et al, "Fuel Cleanup System for the Tritium Systems Test Assembly: Design and Experiments", Proceedings of Tritium Technology in Fission, Fusion and Isotopic Application, Dayton, Ohio, Apr. 29, 1980, at pages 115 to 118. According to one process described by Kerr et al, the exhaust gas containing the impurities is first passed through an intermediate container, that is, a variable volume surge tank which is used to remove flow fluctuations and provide a constant feed pressure. The exhaust gas is then passed to a first catalytic reactor in which any free oxygen is reduced and combined with hydrogen at 450.degree. K. to form water. The exhaust gas is then sent to a molecular sieve bed at 75.degree. K. in which all impurities are adsorptively removed and are thus separated out from the exhaust gas. When the capacity of the molecular sieve bed is exhausted, it is heated to 400.degree. K. to desorb the impurities which are then sent to a second catalytic reactor in the form of an oxygen-supplying packed bed operating at 800.degree. K. where the impurities (e.g., ammonia and hydrocarbons) are oxidized into tritium- and/or deuterium-containing water and into tritium- and/or deuterium-free compounds, namely into CO.sub.2, N.sub.2 and Ar. The tritium- and/or deuterium-containing water then is frozen out at 160.degree. K., and thereafter the frozen water is periodically vaporized. The vapors are fed into a hot uranium metal bed which acts as a getter and which at 750.degree. K. transforms (reduces) the water into D- and/or T-containing hydrogen and stable UO.sub.2. In lieu of the reduction by means of the uranium metal bed, Kerr et al state that the reduction can also be carried out with the aid of an electrolytic cell when such a cell becomes available. Kerr et al also describe a process based on hot uranium metal getters. In this process, the exhaust gas, after leaving the variable volume surge tank, enters a primary uranium bed operating at 1170.degree. K. In this bed, impurities are removed by chemical reactions that form uranium oxides, carbides, and nitrides. The inert argon, with traces of the other impurities, passes through the primary uranium bed and is sent to a molecular sieve bed as in the above-described process. The regenerated argon, with a small amount of tritium, is sent from the molecular sieve bed to a titanium bed, at 500.degree. K., which collects DT and passes on an argon stream containing only tenths of a ppm of DT. Kerr et al state that a disadvantage of this process is that operating temperatures of 1170.degree. K. cause permeation and material problems. Kerr et al also describe the use of palladium diffusers, and state that they have numerous disadvantages including the need for elevated pressures, reported brittle failures during temperature cycling, reported poisoning by ammonia and methane, and the fact that they can not produce an impurity stream free of hydrogen isotopes. P. Dinner et al, "Tritium System Concepts for the Next European Torus Project", Fusion Technology, Volume 8, No. 2, Part 2, pages 2228-2235, September 1985 (2nd Meeting on Tritium Technol., Dayton, Ohio, 1985) use for the purpose of cleaning the exhaust gas of a fusion reactor a combination of a high-temperature getter and a palladium/silver membrane. The drawback associated with this process and the process of Kerr et al that employ getter beds is that the getter bed must be operated at high temperatures (up to 900.degree. C.). Both material problems and problems resulting from losses due to permeation of tritium may occur during the processes of Kerr et al and Dinner et al. The replacement of the getter bed, which is necessary periodically, gives rise to safety problems due to the fine pyrophoric dust released and the fact that the getter bed must be disposed of as radioactive waste. Another means of cleaning the exhaust gas of a fusion reactor according to P. Dinner et al, (talk during the 2nd Meeting on Tritium Technol., Dayton, Ohio, 1985) consists in a combination of high-temperature getter, oxygen releasing fixed bed for catalytic oxidation. The associated drawback is that the separated tritium is obtained as water whose radiotoxicity is greater by orders of magnitude compared to gaseous tritium, that the process requires a great number of process steps, and that the oxygen releasing fixed bed has to be operated at 500.degree. C. At this temperature level there is the danger that the catalyst sinters and becomes ineffective and that an explosion might be caused by an uncontrolled release of oxygen. In DE-OS 36 06 316 and in DE-OS 36 06 317, processes are described for cleaning the exhaust gas from fusion reactors wherein an oxygen releasing fixed bed, a metal bed as the "getter," and a palladium or palladium-silver membrane are used. DE-OS 36 06 317 further discloses the use of a Ni-catalyst. These processes are subject to the drawbacks which are associated with the operation of the oxygen releasing fixed bed. SUMMARY OF THE INVENTION Thus, it is an object of the present invention to provide a simple process comprising few process steps by which the exhaust gas of fusion reactors can be cleaned up. Another object of the present invention is to provide a process which can be operated at temperatures not much higher than 450.degree. C. and without addition of oxygen, neither by direct oxygen supply nor by use of an oxygen releasing fixed bed. A further object of the present invention is to provide a process which employs process components that comprise materials not consumed during the process, i.e., which exert a catalyzing effect, so as to keep the operating expenditure and the amount of waste arising in a plant working on this process low. A still further object of the present invention is to provide a process in which the separated elemental tritium and deuterium are produced in highly pure form because this implies a minimum of radiotoxicity and because in the elemental form they can be recycled into the fusion process. Additional objects and advantages of the present invention will be set forth in part in the description which follows and in part will be obvious from the description or can be learned by practice of the invention. The objects and advantages are achieved by means of the processes, instrumentalities and combinations particularly pointed out in the appended claims. To achieve the foregoing objects and in accordance with its purpose, the present invention provides a process for cleaning an exhaust gas from a fusion reactor of exhaust gas components containing heavy hydrogen, the heavy hydrogen components of the exhaust gas being (i) at least one elemental heavy hydrogen isotope selected from deuterium and tritium and (ii) at least one impurities containing the heavy hydrogen isotope deuterium and/or tritium in chemically bound form, the impurities being at least hydrocarbon and water vapor, the exhaust gas further containing carbon monoxide as an impurity, wherein the heavy hydrogen is released from its chemically bound form, and the released heavy hydrogen and the at least one elemental heavy hydrogen isotope are separated from the exhaust gas and returned into the fuel cycle, comprising: (a) bringing the exhaust gas into a palladium/silver permeator operating at a temperature of less than 450.degree. C. to decompose into its elements any ammonia in the exhaust gas and to separate the exhaust gas into a first stream containing a major fraction of the elemental heavy hydrogen (i) and elemental heavy hydrogen formed by any ammonia decomposition and a residual gas stream containing the impurities, (b) adding carbon monoxide to the residual gas stream if the carbon monoxide/water ratio is less than 1.5 to bring the carbon monoxide/water ratio of the residual gas stream to .gtoreq.1.5, (c) reacting the water vapor in the residual gas stream with the carbon monoxide at a carbon monoxide/water ratio of .gtoreq.1.5 at 150.degree. to 200.degree. C. on a CuO/Cr.sub.2 O.sub.3 /ZnO catalyst, to produce quantitatively hydrogen and carbon dioxide, (d) passing the resulting gas stream from step (c) into a palladium/silver permeator containing a nickel/aluminum oxide-bulk catalyst, or into a nickel catalyst bed followed by a palladium/silver permeator, in order to split up the hydrocarbon into its elements and to separate the hydrogen in its elemental form from the remaining gas to form a decontaminated residual gas stream which does not contain any hydrogen and a hydrogen gas stream which contains elemental hydrogen, and (e) combining the hydrogen gas stream containing elemental hydrogen separated in step (d) with the first stream containing the major fraction of hydrogen separated in step (a). The decontaminated residual gas stream which does not contain any hydrogen (neither elemental nor bound) can be released into the atmosphere or can be recycled into the CuO/Cr.sub.2 O.sub.3 /ZnO catalyst in step (c). It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, but are not restrictive of the invention. |
description | The present invention concerns the field of production of high grade radionuclides, suitable in particular for medical use. More specifically, it relates to a process for producing high grade lead 212, as well as an apparatus specially designed for conducting said process automatically. Radionuclides have been shown to be promising candidates in the medical field, such as in imaging and radiotherapy, notably radioimmunotherapy for the treatment of cancers. In particular, lead 212 has been the subject of intensive developments in these applications and the production of high purity lead 212 has thus become a prerequisite. In this context, several processes have been developed. As illustrated in FIG. 1, which represents the radioactive decay chain of uranium 232 and thorium 232, lead 212 belongs to the thorium 232/uranium 232 radioactive family of which it is a daughter product. It is also a daughter product of radium 224 which, in this chain, falls between thorium 232/uranium 232 and lead 212. Back in the 80's, U.S. Pat. No. 4,663,129 suggested a process for producing lead 212 from radium 224, where only one system is used to generate lead 212 from radium 224, followed by elution of bismuth 212 and lead 212 by conducting a series of acid digestions with various acid elution solutions. However, this part of the process is not self-contained and requires the intervention of an operator. Further, in effect, this process does not allow achieving a purity of more than 99.5%, which is no longer sufficient considering the current medical requirements. Further, in this process, radium 224 is obtained from thorium 228 on a basic anion exchange column. WO03/086569 discloses a system where the parent radionuclide is eluted from the extraction medium whereas the daughter radionuclide is retained by the system. U.S. Pat. No. 6,787,042 discloses a process where a daughter radioisotope solution obtained from a generator loaded with the parent isotope is transferred to a separate extracting medium to purify the daughter from the parent radioisotope. More recently, WO2013/174949 discloses a method for producing high purity lead 212 from radium 224 where radium 224 is bound to a cation exchange resin and a aqueous solution A1 of lead 212 is eluted therefrom and further purified through a chromatography column which is first washed with an acid solution A2 and then eluted with a third A3 solution, with a pH gradient. However, the purity of the final product still needs to be improved. In particular, this process involves high volumes of a plurality of solutions which may introduce further potential impurities in the final product. There is thus still a need to provide a process for producing radionuclides, such as lead 212, which achieves a high level of purity, may be easily automated, and/or may be implemented without contaminating the operating staff. It would also be desirable to have available an apparatus that makes it possible to implement this method in an automated manner and in a closed system. These goals and others may be achieved by the present invention. A method for producing lead 212 for medical use is provided, as well as an apparatus specially designed for automated implementation in a closed system of this method. A process for producing a daughter radionuclide from a parent radionuclide is provided comprising the steps of: a) loading the parent radionuclide on a first solid medium contained in a generator and onto which the parent radionuclide is bound and whereby the daughter radionuclide is formed by radioactive decay of the parent radionuclide; b) eluting this medium with a A0 solution so as to recover a A1 solution comprising the daughter radionuclide; c) optionally adjusting the pH of the A1 solution so as to obtain a A1′ solution, d) loading this A1 or A1′ solution onto the head of a second solid medium contained in a chromatography column; e) first washing said second solid medium with a A2 solution; f) second washing said second solid medium with a A2′ solution; g) eluting the daughter radionuclides with a A3 solution,characterized in that in the chromatography column the first washing step is conducted from head to tail of the column and the second washing step and the second eluting step are conducted from tail to head of the column. The process of the invention may include one or more preliminary steps so as to provide the desired parent radionuclide, for instance to obtain the parent radionuclide from the radionuclide available as starting product (“the source radionuclide”) when the parent radionuclide is downstream the source radionuclide in the decay chain. This may be achieved by generating the desired parent radionuclide from a source radionuclide in a generator, where the source radionuclide is retained and from which the parent radionuclide can be eluted. Thus, once extracted from the generator, the daughter radionuclide is subjected to a liquid chromatography on a column, with a unique combination of backward second washing and eluting steps, whereas the loading and first washing steps are conducted frontward. This makes it possible to eliminate very efficiently both radiological and chemical impurities, which are extracted from the generator jointly with the daughter radionuclide, and to achieve a high chemical and bacteriological purity through the steps on the chromatography column. According to the process, the daughter radionuclide can be obtained with improved radiological, chemical and bacteriological grades. In particular the process herein differs from that of WO2013/17949 in that a further second washing step is introduced and said second washing step and the elution step are conducted in an inverted way, that is from tail to head of the column, by contrast to the washing and eluting steps disclosed in WO2013/174949. It was found unexpectedly that the combinations of these distinctive features allowed smaller amounts of the washing and eluting A2′ and A3 solutions, thus shortening the duration of the purification and introducing less potential contaminants, thus increasing the purity of the daughter radionuclide eventually obtained. Another advantage is that the column may be repetitively used without changing the resins, as the side products are discarded according to the process. Still further, the process leads to products concentrated in the daughter radionuclide. It has been also hypothesized that the better efficacy could also be associated in particular with the avoidance of possible clogging within of the column. Moreover, as the liquid chromatography on a column is a technique that can be automated and coupled to the production from the generator, which is itself a technique that can be automated, this means the process offers a method that can be implemented in an automated mode. In addition, as the liquid chromatography on a column and the production of radionuclide in a generator are techniques based on the circulation of liquid media through solid media, they can both be implemented in a closed system. As used herein: The terms “radionuclide”, “radioisotope” are used interchangeably and refer to a nuclide that is radioactive, subject to undergoing radioactive decay. “Radioactive decay” also known as nuclear decay or radioactivity, is the process by which a nucleus of an unstable atom loses energy by emitting ionizing radiation, resulting in the formation of a new nuclide together with the emission of ray(s). A “parent radionuclide” is a species which undergoes radioactive decay and leads to the formation of a “daughter radionuclide”. A “daughter radionuclide” is a species that is formed following radioactive decay of a parent radionuclide. A parent radionuclide and a daughter radionuclide may be adjacent ((ie) the parent's decay leads directly to its daughter), or not (there is one or more species between the parent and the daughter radionuclide in the decay chain). In other words, the expression “parent radionuclide” encompasses all species located in successive ranks upstream the daughter radionuclide in the decay chain, whereas a parent radionuclide may give rise to one or more daughter radionuclides in successive ranks downstream the decay chain. “Radiotherapy” refers to any therapy using ionizing radiation, generally as part of cancer treatment to control or kill malignant cells. It includes both curative and adjuvant therapy. “Radioimmunotherapy” (RIT) refers to any therapy where an antibody is associated with a radionuclide to deliver cytotoxic radiation to a target cell. In cancer therapy, an antibody with specificity for a tumor-associated antigen is used to deliver a lethal dose of radiation to the tumor cells. The ability for the antibody to specifically bind to a tumor-associated antigen increases the dose delivered to the tumor cells while decreasing the dose to normal tissues. Generally, radioimmunotherapy involves the administration of a product where the radionuclide is bound to the antibody through a chelating agent. “Purity” refers to chemical, radiological and/or bacteriological purity. The terms “radiological purity” refer for a radionuclide to the purity this radionuclide presents with regard to the radioelements from which it originates by radioactive decay, as well as with regard to the other radionuclides which are not part of its radioactive decay chain, and not to the purity it presents with regard to the radionuclides which it generates itself through its own radioactive decay. The radiological impurities include the radionuclides likely to be present in the radioisotope generator, starting with the latter, whereas the chemical impurities include the organic degradation products resulting from radiolysis of the solid media present in the generator or the chromatography column, as well as the organic and mineral contaminants likely to be introduced into these media, for example by the solutions that are used to prepare and extract the daughter radionuclide or adventitious metals naturally present in the environment, in air or in the solution bags. According to an embodiment, the parent and daughter radionuclides belong to the radioactive decay chain of thorium 232 and/or uranium 232 or from artificial sources. They may be in particular chosen from thorium, radium, lead and bismuth isotopes, more specifically among thorium 228, radium 224 and lead 212 and their mixtures. According to an embodiment, the daughter radionuclide is lead 212. According to an embodiment, the parent radionuclide is chosen from radium 224. In case where radium 224 (the parent radionuclide) is not used as the starting product (the “source radionuclide”), thorium 228 may be used instead as a source radionuclide. The process then comprises a preliminary step comprising generating radium 224 from thorium 228 in a generator. According to an embodiment, such generator comprises as solid medium DGA (marketed by Triskem). It may be eluted by an acidic solution, such as HCl solution, to recover radium 224 which in turns may be used as the parent radionuclide in step a). According to an embodiment, the process of the invention may further comprise any additional step to clean the system, such as steps to empty the system and/or to remove any clogging that may have formed in the solid medium. Generally, such cleaning steps may be conducted in a fashion so as to maintain the sterility and purity of the system. Air-flushing is preferred. According to an embodiment, the process of the invention comprises the step: h) air-flushing the second solid medium. Generally, this step may be conducted with sterile filtered air, such as air filtered through a 0.2 μm filter. The production of the daughter radionuclide from the parent radionuclide in the generator and its extraction from this generator can be carried out, in a manner known per se. According to an embodiment, the first solid medium may be chosen from any solid media that can retain the parent radionuclide but that do not retain the daughter radionuclide. According to an embodiment, the first solid medium can be a cation exchange resin that can retain the parent radionuclide but that does not retain the daughter radionuclide. As an illustration, one can cite the resin sold by the company BIO-RAD under the reference AG™ MP50 and which consists of a macroporous matrix of polystyrene/divinylbenzene onto which sulphonic groups —SO3H are grafted. Such resin is generally appropriate to produce lead 212 from radium 224. According to an embodiment, the solution comprising the parent radionuclide is an aqueous acid solution. The acid may be chosen from hydrochloric or nitric acid. The concentration is adjusted so as to achieve a pH range where the parent radionuclide may be retained on the first solid medium. Generally, this solution may contain from 1 to 3 moles/L, more specifically 2 moles/L of hydrochloric or nitric acid. Preferably, the solution comprising the parent radionuclide has a radiological purity greater than or equal to 99.5%. Following the loading, the first solid medium may be washed by using a further solution, such as an aqueous acid solution. This solution may generally comprise from 0.01 to 2 moles/L, more particularly 0.01 mole/L of hydrochloric or nitric acid. The parent radionuclide produces the daughter radionuclide by radioactive decay in the generator. The daughter radionuclide is then eluted through the resin by using an A0 solution. According to an embodiment, the A0 solution is an aqueous acid solution. The pH is generally adjusted so that the parent radionuclide is retained in the solid medium and the daughter radionuclide is released from the solid medium. According to an embodiment, the A0 solution may be an aqueous solution containing from 1.5 to 2.5 moles/L and, in particular 2 moles/L of hydrochloric or nitric acid. Following the elution, an A1 solution comprising the eluted daughter radionuclide is obtained at the tail of the column. According to an embodiment, the A2 and A2′ solutions are similar. According to an embodiment, the generation of the daughter radionuclide in the generator may comprise the following steps: loading the cation exchange resin with an acid aqueous solution containing the parent radionuclide, washing the resin with an aqueous acid solution, leaving the parent radionuclide to produce the daughter radionuclide by radioactive decay; and eluting the resin with an aqueous acid solution A0 so as to obtain a A1 solution. In accordance with an embodiment of the invention, the loading of the stationary phase with the aqueous solution A1 may be carried out without altering the pH of this solution when it is extracted from the parent radionuclide generator. According to an alternative embodiment, it is also possible to alter the pH of the A1 solution, such as before it is loaded onto the second solid medium present in the chromatography column, so as to increase the retention of the daughter radionuclide by decreasing (by addition of a strong acid) or increasing (by dilution with water and/or addition of a strong base) the pH of the aqueous A1 solution of this stationary phase. An A1′ solution is thus obtained. According to an embodiment, the second solid medium is a stationary phase contained in a column. Generally, the second solid medium selectively retains the daughter radionuclide present in the A1 or A1′ solutions, even when contacted with A2 or A2′ solution. In other words, it retains the daughter radionuclide present in the A1 and A1′ aqueous solutions but does not retain, or practically does not retain, the radiological and chemical impurities also present in the A1, A1′, A2, A2′ solutions or in the medium. According to a further embodiment, the second solid medium releases said daughter radionuclide when contacted with the A3 solution. According to an embodiment, the chromatography is advantageously carried out using the second solid medium in a stationary phase which includes an ether crown as the extractant and, in particular, a dicyclohexano-18-crown-6 or a dibenzo-18-crown-6 whose cyclohexyl or benzyl groups are substituted by one or more C1 to C12 alkyl groups, with a straight or branched chain. In particular, a stationary phase may be used which comprises 4,4′(5′)-di-tert-butylcyclohexano-18-crown-6 as the extractant, such a stationary phase presenting the advantage of selectively retaining over 99% of the daughter radionuclide present in an aqueous solution containing from 1.5 to 2.5 moles/L of a strong acid, which typically corresponds to the types of aqueous solutions that may be used to extract a daughter radionuclide from a parent radionuclide, such as lead 212 from a radium 224 generator. This type of stationary phase is available in bottles or also packaged in ready-to-use columns or cartridges for chromatography, from the company TRISKEM International under the commercial name “Pb resin”. In accordance with embodiments of the invention, the chromatography is a liquid chromatography. The liquid chromatography on a column may be chosen from various types of chromatography, such as an extraction chromatography or a partition chromatography, in other words a chromatography which is based on the distribution of the elements that are to be separated between an organic phase, or extractant, and an aqueous phase, the extractant being bound to an inert support and forming with it the stationary phase, whereas the aqueous phase represents the mobile phase. It is also possible to purify the daughter radionuclide extracted from the generator by liquid chromatography on a column other than extraction chromatography, for example, cation exchange chromatography. Whatever the type of liquid chromatography chosen and the type of stationary phase used, the purification of the daughter radionuclide on the liquid chromatography on a column generally comprises: loading the stationary phase with the aqueous solution A1 or A1′, to allow the daughter radionuclide present in this solution to be retained by the stationary phase; washing the stationary phase with an aqueous solution A2, backward washing with a A2′ solution, Said washing being carried out to eliminate from the stationary phase the radiological and chemical impurities it contains but without releasing the radionuclide; backward eluting the daughter radionuclide from the stationary phase with an aqueous solution A3, to recover the daughter radionuclide in the form of an aqueous solution, wherein the backward washing and backward eluting steps are conducted from tail to head of the column whereas the loading and first washing step are conducted from the head of the column. Generally, the conditions under which these three steps are carried out and, particularly, the pH values of aqueous phases A1, A1′, A2 and A3, are suitably chosen as a function of the stationary phase used and/or the nature of the daughter radionuclide. Thus, for example, in the case where the liquid chromatography on a column is carried out using the previously mentioned “Pb resin” as the stationary phase: the aqueous solution A1 or A1′ advantageously has an acidity corresponding to that of an aqueous solution of a strong acid having a molar concentration ranging from 1.5 to 2.5 and, preferably equal to 2, and corresponds, for example, to an aqueous solution containing from 1.5 to 2.5 moles/L and, more particularly, 2 moles/L of hydrochloric or nitric acid, preferably hydrochloric acid; the aqueous A2 and A2′ solution, identical or different advantageously have an acidity corresponding to that of an aqueous solution of a strong acid of molar concentration ranging from 0.1 to 0.5 and, preferably, equal to 0.5, and corresponds, for example, to an aqueous solution containing from 0.1 to 0.5 mole/L and, more particularly, 0.5 mole/L of hydrochloric or nitric acid; the aqueous solution A3 advantageously has a pH ranging from 5 to 9 and corresponds, for example, to an aqueous solution of ammonium acetate which preferably contains 0.15 to 1 mole/L and, more particularly, 0.4 mole/L of ammonium acetate. Generally, the backward elution comprises two stages: a first and a second elution fractions. The first elution fraction aims at increasing the pH and does not contain or contains only few daughter radionuclides. The second elution fraction actually elutes the daughter radionuclide and is enriched in the daughter radionuclide. The first fraction may thus be discarded and the second fraction may be collected. According to a preferred embodiment, the process of the invention may be conducted to produce lead 212 from radium 224 comprising the following steps: a) loading radium 224 on a cation exchange resin contained in a generator; b) eluting with a 2 N hydrochlorid acid solution so as to recover an A1 solution comprising lead 212; c) loading said A1 solution on the stationary phase at the head of a liquid chromatography column; d) washing the column from the head to tail with a A2 solution of 0.1 N hydrochlorid acid; e) washing from the tail to head of the column with the same A2 solution; f) eluting from the tail to the head of the column with a A3 solution of 0.4 N ammonium acetate to recover lead 212; g) air flushing. According to a further object, the present invention also provides lead 212 obtainable by the method of the invention. The so obtained lead 212 has generally a radiological purity of more than 99.95%. As an illustration, lead 212 may be obtained with a purity of more than 99.99%. According to an embodiment, the method may also comprise a bacteriological purification of the daughter radionuclide, which is preferably carried out after the liquid chromatography on the column, for example by circulating the aqueous solution having been used to elute the daughter radionuclide through a pore filter, e.g. a 0.2 μm pore filter. According to an embodiment, lead 212 may be obtained with a chemical purity within the following specifications: Ag, As, Bi, Cd, Cu, Hg, Mo, Pb, Sb, Sn<2 ppm (ie)<2 mg/L Pb<0.2 ppm (ie)<200 μg/L Fe<0.3 ppm (ie)<300 μg/L Th<10 ppb (ie)<10 μg/L. Preferably, the whole process is implemented within a closed system or circuit, that is to say in practice in an apparatus allowing all the aqueous solutions used or produced, from the aqueous solution used for extracting the daughter radionuclide from the generator to the aqueous solution containing the daughter radionuclide eluted from the chromatography column, to circulate in a circuit that is totally isolated from the surrounding environment and, notably, from the ambient air and the potential pollutants contained therein, which contributes to obtaining the daughter radionuclide of very high chemical purity. Further, the process can be automated, without intervening staff and consequential human errors that may occur. Apparatus An apparatus is also provided for the automated production of a daughter radionuclide from a parent radionuclide using a generator comprising a solid medium onto which the parent nuclide is fixed and whereby the daughter nuclide is formed by radioactive decay of the parent nuclide, the apparatus comprising a configurable fluid circuit comprising: a chromatography column having a head port and a tail port, at least one connection port for connecting the generator to the fluid circuit, at least one inlet port for connecting fluid sources to the fluid circuit, at least one valve controlled by an electronic control unit for selectively connecting the chromatography column, the connection port and the inlet port(s) in various configurations, wherein the fluid circuit comprises a first elution configuration for circulating an A1 solution exiting the generator and containing the daughter radionuclide, through the chromatography column from head port to tail port for loading the chromatography column with the daughter radionuclide, and at least one configuration for circulating a fluid through the chromatography column from tail port to head port. According to an embodiment, the fluid circuit in the first elution configuration is configured for circulating an A0 solution from an inlet port and through the generator and for circulating the A1 solution exiting the generator through the chromatography column from head port to tail port. According to an embodiment, the fluid circuit comprises a first washing configuration for circulating an A2 washing solution from an inlet port through the chromatography column from head port to tail port. According to an embodiment, the fluid circuit comprises a second washing configuration for circulating an A2′ washing solution from an inlet port through the chromatography column from tail port to head port. According to an embodiment, the fluid circuit comprises a second elution configuration for circulating an A3 elution solution from an inlet port through the chromatography column from tail port to head port. According to an embodiment, the fluid circuit comprises a flushing configuration for circulating air through the fluid circuit for flushing the fluid circuit with air. According to an embodiment, the electronic control unit is configured for controlling the valve(s) for configuring the fluid circuit in the first elution configuration, the first washing configuration, the second washing configuration and the second elution configuration. According to an embodiment, the electronic control unit is configured for controlling the valve(s) for configuring the fluid circuit in the flushing configuration. According to an embodiment the fluid circuit comprises an outlet port for collecting a solution recovered from the head of the chromatography column and/or a waste outlet port for collecting waste by-products recovered from the tail port and/or the head port of the chromatography column. According to an embodiment the fluid circuit comprises a distribution valve arranged and configured for directing fluid selectively to a head port of the chromatography column for a circulation of the fluid through the chromatography column from the head port to the tail port or to the tail port of the chromatography column for a circulation of the fluid through the chromatography column from tail port to head port. According to an embodiment the fluid circuit comprises a head valve at the head port of the chromatography column and a tail valve at the tail port of the chromatography column, the distribution valve being arranged and configured for directing fluid selectively to the head valve or to the tail valve. According to an embodiment the fluid circuit comprises two connection ports, including an inlet connection port for connection to an inlet of the generator and an outlet connection port for connection to an outlet of the generator. According to another aspect, an automated apparatus is provided comprising a fluid circuit comprising a chromatography column and at least one valve controlled by an electronic control unit, the fluid circuit having various configurations depending on the valve actuation, wherein the fluid circuit comprises at least one configuration for circulating a fluid through the chromatography column in a first direction, from head to tail, and at least one configuration for circulating a fluid through the chromatography column in a second direction opposed to the first direction, from tail to head. The apparatus 20 of FIGS. 2-6 is configured for the automated production of a daughter radionuclide from a parent radionuclide using a generator 22 comprising the first solid medium onto which the parent radionuclide is fixed and whereby the daughter radionuclide is formed by radioactive decay of the parent radionuclide. In a known manner, the generator 22 comprises a container containing a first solid medium previously loaded with the parent radionuclide, the container allowing circulation of a solution through the container in contact with the solid medium. The generator 22 has ports for fluid connection of the container to a fluid circuit. In one embodiment, the first solid medium is loaded with radium 224 for the production of lead 212 by radioactive decay of this radium. The radium preferably has a radiological purity greater than or equal to 99.5%. The apparatus 20 comprises a fluid circuit 24 comprising a chromatography column 26, generator connection ports 28A, 28B for connecting the generator 22 to the fluid circuit 24, solution inlet ports 30A, 30B, 30C, 30D for connecting solution sources S0, S2, S3, S4 to the fluid circuit 24, and automatically actuated valves 32, 34, 36, 38, 40, 42 controlled by an electronic control unit 44. The fluid lines are illustrated in continuous lines and the control lines connecting the control unit 44 to the components of the fluid circuit 24 are illustrated as dashed lines. The fluid circuit 24 comprises two connection ports 28A, 28B, including an inlet connection port 28A for connection to an inlet of the generator 22 and an outlet connection port 28B for connection to an outlet of the generator 22. The apparatus 20 also comprises a product outlet port 46 for receiving a solution containing the daughter radionuclide and a waste outlet port 48 for receiving waste by-products. The apparatus comprises fluid lines fluidly connecting the chromatography column 26, the connection ports 28A, 28B, the inlet ports 30A, 30B, 30C, 30D, the valves 32, 34, 36, 38, 40, 42, and the outlet ports 46, 48. The chromatography column 26 is provided for purifying, by a liquid chromatography, the daughter radionuclide extracted from the generator 22, from the radiological and chemical impurities which are extracted from this generator jointly with the daughter radionuclide. This chromatography column 26 can be either a column that has been previously prepared, conditioned and calibrated, or a commercially available ready-to-use column. In all cases, the chromatography column 26 contains the second solid medium, such as an extraction chromatography stationary phase, which is capable of retaining the daughter radionuclide under certain conditions and also capable of releasing the daughter radionuclide by elution under other conditions. The chromatography column 26 comprises a head port 26A and a tail port 26B to connect the chromatography column 26 to the fluid circuit 24 of the apparatus 20. In a preferred embodiment suited to the use of the apparatus 20 in a nuclear medicine department, the sources S0, S2, S3, S4 are syringes or bags filled with a predetermined amount of appropriate fluids which are to be used during the operation of the apparatus 20. Preferably each source is suited to use in nuclear medicine: it has no rubber or silicon grease. Preferably, all the material in contact with the fluids are compatible with the acids used. In embodiment illustrated on FIG. 2, a first source S0 contains the A0 solution, a second source S2 contains the A2 solution also used as the A2′ solution, a third source S3 contains the A3 solution and a fourth source S4 contains filtered air. The fluid circuit 24 comprises at least one electronically controlled pump arranged for circulating the fluids from the inlet ports 30A, 30B, 30C, 30D and through the fluid circuit 24 in the various configurations. Each pump is controlled by the control unit 44. The fluid circuit 24 of the apparatus 20 of FIG. 2 comprises a first pump 50 and a second pump 52. The fluid circuit 24 is configurable for selectively connecting the chromatography column 26, the connection ports 28A, 28B, the inlet ports 30A, 30B, 30C, 30D, the outlet ports 46, 48 and the pumps 50, 52 according to various configurations. More specifically, the valves 32, 34, 36, 38, 40, 42 are arranged and controlled for selectively connecting the chromatography column 26, the connection ports 28A, 28B and the inlet ports 30A, 30B, 30C, 30D, the outlet ports 46, 48 and the pumps 50, 52 according to different configurations. The fluid circuit 24 comprises a source selection valve 32 fluidly connected to the inlet ports 30A, 30B, 30D and to an inlet of first pump 50. The inlet ports 30A, 30B, 30D are respectively connected to the first source S0, the second source S2 and the fourth source S4. The selection valve 32 is configured for directing fluid from selectively one of the first source S0, the second source S2 and the fourth source S4 to the inlet of the first pump 50. The inlet of the second pump 52 is connected to the third source S3. The fluid circuit 24 comprises a by-pass valve 34 fluidly connected to the outlet of the first pump 50, to the second pump 52, to the inlet connection port 28A and to a distribution valve 36 of the fluid circuit 24. The by-pass valve 34 is configured for selectively directing fluid from the first pump 50 to the inlet connection port 28A, from the first pump to the distribution valve 36 or from the second pump 52 to the distribution valve 36. The distribution valve 36 is fluidly connected to the by-pass valve 34, to the outlet connection port 28B, to a head valve 38 and a tail valve 40 of the fluid circuit 24. The distribution valve 36 is configured for selectively directing fluid form the by-pass valve 34 to the head valve 38 or from the by-pass valve 34 to the tail valve 40 or from the outlet connection port 28B to the head valve 38. The head valve 38 is fluidly connected to the distribution valve 36, to a head port 26A of chromatography column 26 and to an outlet valve 42. The head valve 38 is configured for selectively receiving fluid from the distribution valve 36 and providing the fluid to the head port 26A or receiving fluid from the head port 26A and providing the fluid to the outlet valve 42 or receiving fluid from the distribution valve 36 and providing the fluid to the outlet valve 42. The tail valve 40 is connected to the distribution valve 36, to a tail port 26B of the chromatography column 26 and to the outlet valve 42. The tail valve 40 is configured for selectively receiving fluid from the distribution valve 36 and providing the fluid to the tail port 26B or receiving fluid from the tail port 26B and providing the fluid to the outlet valve 42. The outlet valve 42 is connected to the head valve 38, to the tail valve 40, to the product outlet port 46 and to the waste outlet port 48. The outlet valve 42 is configured for receiving fluid selectively from the head valve 38 or the tail valve 40 and providing the fluid selectively to the product outlet port 46 or to the waste outlet port 48. A product flask 49 is connected to the product outlet port 46. Preferably, a filter 49A is placed at the entrance to the product flask 49 to complete the chemical purification of daughter radionuclide by a bacteriological purification. The filter 49A has for example a pore size or pore diameter of 0.2 μm. A waste receptacle 51 is connected to the waste outlet port 48 for collecting waste by-product solutions from the fluid circuit 24, generated during operation of the apparatus 20. The different configurations of the fluid circuit 24 are illustrated in FIGS. 2-6, in which the bold fluid lines are the fluid lines in which the fluid circulates and the thin fluid lines are the fluid lines in which no fluid circulates. In a first elution configuration (FIG. 2), the fluid circuit 24 is configured for circulating the A0 solution from the inlet port 30A and through the generator 22 to recover the A1 solution containing the daughter radionuclide and for circulating the A1 solution from the generator 22 through the chromatography column 26 frontward from head to tail. In the first elution configuration, the valves 32, 34, 36, 38, 40, 42 are controlled such that the A0 solution flows from the first source S0 successively through the valve 32, through the first pump 50, through the by-pass valve 34 and through the generator 22, and the A1 solution exiting the generator 22 flows through the distribution valve 36, through the head valve 38, through the chromatography column 26 from head port 26A to tail port 26B, through the tail valve 40, through the outlet valve 42 and to the waste outlet port 48. In a frontward washing configuration (FIG. 3), the fluid circuit 24 is configured for circulating the A2 solution from the second source S2 through the chromatography column 26 from head port 26A to tail port 26B. In the frontward washing configuration, the valves 32, 34, 36, 38, 40, 42 are controlled such that the A2 solution flows from the second source S2 successively through the valve 32, through the first pump 50, through the by-pass valve 34, through the distribution valve 36, through the head valve 38, through the chromatography column 26 from head port 26A to tail port 26B, through the tail valve 40, through the outlet valve 42 and to the waste outlet port 48. In the frontward washing configuration, the generator 22 is by-passed. In a backward washing configuration (FIG. 4), the fluid circuit 24 is configured for circulating the A2′ solution through the chromatography column 26 from tail port 26B to head port 26A. The A2′ solution is here the same as the A2 solution and is circulated from the second source S2. In the backward washing configuration, the valves 32, 34, 36, 38, 40, 42 are controlled such that the A2′ solution flows from the second source S2 successively through the valve 32, through the first pump 50, through the by-pass valve 34, through the distribution valve 36, through the tail valve 40, through the chromatography column 26 from tail port 26B to head port 26A, through the head valve 38, through the outlet valve 42 and to the waste outlet port 48. In the backward washing configuration, the generator 22 is by-passed. In a second elution configuration (FIG. 5), the fluid circuit 24 is configured for circulating the A3 solution from the third source S3 through the chromatography column 26 from tail port 26B to head port 26A. In the second elution configuration, the valves 32, 34, 36, 38, 40, 42 are controlled such that the A3 solution flows from the third source S3 successively through the second pump 52, through the by-pass valve 34, through the distribution valve 36, through the tail valve 40, through the chromatography column 26 from tail port 26B to head port 26A, through the head valve 38, through the outlet valve 42. In the second elution configuration, the generator 22 is by-passed. In the second elution configuration, the outlet valve 42 is controlled to flow the fluid selectively to the product outlet port 46 or the waste outlet port 48. Preferably, in a first phase (not shown), the outlet valve 42 is controlled to flow the fluid to the waste outlet port 48 and then, in a subsequent second phase, the outlet valve 42 is controlled to flow the fluid to the product outlet port 46 (FIG. 5). The first phase allows to discard the first elution fraction which aims at increasing the pH and does not contain or contain only few daughter radionuclide, whereas the second phase allows to collect the second elution fraction which actually elutes the daughter radionuclide and is enriched in the daughter radionuclide. In an alternative, the first phase is omitted and the outlet valve 42 is controlled to flow the fluid to the product outlet port 46 permanently during the second elution configuration. In a flushing configuration (FIG. 6), the fluid circuit 24 is configured for circulating air from the fourth source S4 to the product outlet 46 and/or to the waste product outlet 48 for flushing the fluid circuit 24 with air. In the flushing configuration, the valves 32, 34, 36, 38, 40, 42 are controlled such that the air flows from the fourth source S4 to the product outlet port 46 with passing successively through the valve 32, the pump 50, the by-pass valve 34, the distribution valve 36, the head valve 38 and the outlet valve 42. The outlet valve 42 is controlled for directing air sequentially to one of the product outlet 46 and the waste product outlet 48 and then to the other, for flushing the corresponding fluid lines. In the flushing configuration, the generator 22 and the chromatography column 26 are by-passed. As illustrated on FIGS. 2-6, the apparatus 20 comprises a sealed enclosure 54 defining a chamber 56 containing the fluid circuit 24. The inlet ports 30A, 30B, 30C, 30D, the connection ports 28A, 28B and the outlet ports 46, 48 allow to connect respectively sources S1, S2, S3, S4, the generator 22 and the product and waste receptacles 49, 51 to the fluid circuit 24 from outside the enclosure 54. FIGS. 7-11, in which same or similar parts use same references, illustrate another apparatus 20 configured for the automated production of a daughter radionuclide from a parent radionuclide using a generator 22 comprising a solid medium onto which the parent nuclide is fixed and whereby the daughter nuclide is formed by radioactive decay of the parent nuclide. The apparatus 20 of FIGS. 7-11 uses fewer valves than the apparatus of FIGS. 2-6. The fluid circuit 24 of the apparatus 20 of FIGS. 7-11 comprises an inlet valve 32 fluidly connected to the inlet ports 30A, 30B, 30C, 30D and an outlet connected to the inlet of a pump 60. The inlet valve 32 is configured for directing fluid from selectively one of the inlet ports 30A, 30B, 30C, 30D to the inlet of the pump 60. The fluid circuit 24 comprises a distribution valve 62 fluidly connected to the outlet of the pump 60 and to the inlet connection port 28A, the head valve 38 and the tail valve 40. The distribution valve 62 is configured for connecting the outlet of the pump 60 to selectively one of the inlet connection port 28A, the head valve 38 and the tail valve 40. The outlet connection port 28B is fluidly connected to the fluid line connecting the distribution valve 62 to the head valve 38. Fluid exiting the generator 22 is injected into the fluid line connecting the distribution valve 62 to the head valve 38. The head valve 38 is fluidly connected to the distribution valve 62, to a head port 26A, to the product outlet port 46 and to the waste outlet port 48. The head valve 38 is configured for selectively directing fluid from the distribution valve 62 to the head port 26A or directing fluid from the head port 26A to the outlet port 46 or directing fluid from the head port 26A to the outlet port 48. The tail valve 40 is connected to the distribution valve 62, to a tail port 26B, to the outlet port 46 and to the outlet port 48. The tail valve 40 is configured for selectively directing fluid from the distribution valve 62 to tail port 26B, directing fluid from the tail port 26B to the outlet port 46 or directing fluid from the tail port 26B to the outlet port 48. The apparatus 20 of FIGS. 7-11 allows configurations functionally similar to that of the apparatus of FIGS. 2-6, namely a first elution configuration, a frontward washing configuration, a backward washing configuration, a second elution configuration and a flushing configuration. In the first elution configuration (FIG. 7), the valves 32, 62, 38, 40 are controlled such that the A0 solution flows from the first source S0 successively through the selection valve 32, through the pump 60, through the distribution valve 62 and through the generator 22, the A1 solution exiting the generator 22 circulating through the head valve 38, through the chromatography column 26 from head port 26A to tail port 26B, through the tail valve 40 and to the waste outlet port 48. In the first washing configuration (FIG. 8), the valves 32, 62, 40, 38 are controlled such that the A2 solution flows from the second source S2 successively through the selection valve 32, through the pump 60, through the distribution valve 62, through the head valve 38, through the chromatography column 26 from head port 26A to tail port 26B, through the tail valve 40 and to the waste outlet port 48. In the second washing configuration (FIG. 9), the valves 32, 62, 40, 38 are controlled such that the A2′ solution (which is here the same as the A2 solution) flows from the second source S2 successively through the selection valve 32, through the pump 60, through the distribution valve 62, through the tail valve 40, through the chromatography column 26 from tail port 26B to head port 26A, through the head valve 38 and to the waste outlet port 48 (see arrows and references A2′). In the second elution configuration (FIG. 10), the valves 32, 62, 40, 38 are controlled such that the A3 solution flows from the third source S3 successively through the selection valve 32, through the pump 60, through the distribution valve 62, through the tail valve 40, through the chromatography column 26 from tail port 26B to head port 26A and through the head valve 38 (see arrows and references A3). In the second elution configuration, the head valve 38 is controlled to flow the fluid selectively to the product outlet port 46 or the waste outlet port 48. Preferably, in a first phase (not shown), the head valve 38 is controlled to flow the fluid to the waste outlet port 48 and then, in a subsequent second phase, the head valve 38 is controlled to flow the fluid to the product outlet port 46 (FIG. 10). In an alternative, the first phase is omitted and the head valve 38 is controlled to flow the fluid to the product outlet port 46 permanently during the second elution configuration. In the flushing configuration (FIG. 11), the valves 32, 62, 40, 38 are controlled such that the air flows from the fourth source S4 successively through the selection valve 32, through the pump 60, through the distribution valve 62 and through the tail valve 40. The tail valve 40 is controlled for directing air sequentially to one of the product outlet port 46 and the waste outlet port 48 and then to the other for flushing the fluid circuit 24 with air. The apparatus of FIGS. 7-11 allows reducing the number of valves and thus makes the apparatus easier and more economical to manufacture. Advantageously, the ports are provided with a color code for avoiding an operator to make any mistake upon connecting the S0, S2, S3, S4 sources, the generator 22 and the receptacles 49, 51 to the fluid circuit 24. In one embodiment, the pumps 50, 52 and 60 are syringe-pumps controllable to retrieve from a source a predetermined amount of fluid and to inject said determined amount into the fluid circuit 24. In the embodiments of FIGS. 2-6 and 7-11, the enclosure 54 prevents access to fluid circuit 24. The enclosure comprises a lockable access device such as a door to allow access to the chamber 56. This makes it possible to prevent any non-qualified persons from accessing the fluid circuit 24 of the apparatus 20, particularly the components having some radiological activity, or the components whose functioning can be damaged. In the embodiments of FIGS. 2-6 and 7-11, the generator 22 is located outside the enclosure 54 and is removably connectable to the fluid circuit 24 via the connection ports 28A, 28B. This allows replacing the generator 22 by another similar generator. Indeed, due to the lifetime of the parent radionuclide, the generator can only be used for a limited period of time. For example, the radium 224 has a half-life time of 3.66 days. In a similar manner, the chromatography column 26 can be disconnected from the fluid circuit 24 for replacement by another similar column. The general dimensions of the various components of the apparatus 20 are relatively small, which makes it possible to arrange them in an enclosure 54 which is also small in size. The apparatus 20 can therefore be a portable apparatus that can be used close to the area of usage of the daughter radionuclide, e.g. the lead 212. The apparatus 20 has several inlet ports 30A, 30B, 30C, 30D to which the different sources S0, S2, S3, S4 of fluids are connected to the apparatus 20. Preferably, each source S0, S2, S3, S4 is associated with a respective inlet port 30A, 30B, 30C, 30D. In order to avoid any reversal between the sources S0, S2, S3, S4, the apparatus 20 comprises so-called failsafe features allowing an operator to correctly connect each source S0, S2, S3, S4 to the corresponding inlet port 30A, 30B, 30C, 30D. According to an embodiment, the failsafe features are visual features, e.g. a color coding. Each source S0, S2, S3, S4 has a color code and the corresponding inlet port 30A, 30B, 30C, 30D has the same color code. Alternatively or optionally, each source S0, S2, S3, S4 and the corresponding inlet port 30A, 30B, 30C, 30D has complementary fool proofing shapes such that each source S0, S2, S3, S4 is connectable only to the corresponding inlet port 30A, 30B, 30C, 30D. In this way it becomes impossible to connect a source to an inlet port with which it is not associated, thus preventing any human error. Each apparatus of FIGS. 2-6 and 7-11 makes it possible to implement the method of the invention in an automated manner. The valves 32, 34, 36, 38, 40, 42; 32, 62, 38, 40 and the pumps 50, 52, 60 are automatically controlled by the control unit 44 for implementing the method of the invention. In operation, the daughter radionuclide is produced in the generator 22 by radioactive decay of the parent radionuclide and the daughter radionuclide is retained on the first solid medium. The control unit 44 is configured for successively operating the first elution configuration, the frontward washing configuration, the backward washing method and the second elution method, and, optionally, the purging method. Extraction of the Daughter Radionuclide (FIG. 2 or 7) The apparatus 20 is configured in the first elution configuration. The A0 solution is circulated through the generator 22 and the A1 solution containing the daughter solution exits the generator 22. Loading to the Chromatography Column (FIG. 2 or 7) The apparatus 20 still being in the first elution configuration, the A1 solution exiting the generator 22 is circulated through the chromatography column 26 from head to tail. The daughter radionuclide is retained by the second solid medium contained in the chromatography column 26. Frontward Washing of the Chromatography Column (FIG. 3 or 8) The apparatus 20 is configured in the first washing configuration. The A2 solution is circulated through the chromatography column 26 from head to tail. The A2 solution removes radiological and chemical impurities from the second solid medium while the daughter radionuclide is retained by the second solid medium. Backward Washing of the Chromatography Column (FIG. 4 or 9) The apparatus 20 is configured in the backward washing configuration. The A2′ solution is circulated through the chromatography column 26 from tail to head. The A2′ solution removes radiological and chemical impurities from the second solid medium while the daughter radionuclide is retained by the second solid medium. Second Elution of the Chromatography Column (FIG. 5 or 10) The apparatus 20 is configured in the second elution configuration. The A3 solution is circulated through the chromatography column 26 from tail to head. The A3 solution removes the daughter radionuclide from the second solid medium and is collected in a collecting device, e.g. in the product flask 49. Preferably, in a first phase of the second elution, the fluid flows to the waste outlet port 48 and then, in a subsequent second phase of the second elution, the fluid flows to the product outlet port 46. The first phase allows discarding the first elution fraction which aims at increasing the pH and does not contain or contain only few daughter radionuclide, whereas the second phase allows to collect the second elution fraction which actually elutes the daughter radionuclide and is enriched in the daughter radionuclide. In an alternative, the first phase is omitted and the fluid flows to the product outlet port 46. Purging of the Apparatus (FIG. 6 or 11) The apparatus 20 is configured in the flushing configuration. The purified air is circulated from the source S4 to product receptacle 49 and/or the waste receptacle 51 to flush components of the fluid circuit 24. The following examples are given as an illustration of an embodiment of the invention, for non-limiting purposes. Lead 212 was produced with an apparatus similar to the one that has just been described and by a process comprising the following steps: A radium 224 generator containing 400 mg of a cation exchange resin (company BIO-RAD—reference AG™ MP50) as the solid medium was used. The resin was initially loaded with 30 mL of a solution containing 173 MBq of radium 224 of radiological purity greater than 99.5% (such as that determined by γ spectrometry). The system without the generator was loaded with 2 mL of a 2N HCl solution at the loading rate of 1 mL/min. The generator was then eluted with 5 mL of a 2N HCl solution at the elution rate of 0.5 mL/min. The resulting solution was then loaded on the head of the chromatography column. A ready-to-use chromatography column containing 80±10 mg of “Pb resin” (company TRISKEM International) as the stationary phase was washed with 1 mL of a 0.1N HCl solution at the washing rate of 0.5 mL/min. It was then washed in a backward fashion with 1 mL of a 0.1N HCl solution at the washing rate of 0.5 mL/min. 0.5 mL of an aqueous solution containing 0.4 mol/L of ammonium acetate (pH 6.5) was used to load the system (loading rate: 0.5 mL/min). 1 mL of an aqueous solution containing 0.4 mol/L of ammonium acetate (pH 6.5) was used to elute the Pb column in a backward fashion (elution rate: 0.25 mL/min) to elute the lead 212 from the stationary phase of the chromatography column and recover it at the head of the column. The system was then flushed with sterile air (0.2 μm filter) (1 mL at 1 mL/min). Radium 224 was left to generate lead 212 for 19 h and 82 MBq of lead 212 were obtained. After a second delay of 24h, the system yielded 80 MBq of lead 212. A third cycle after another 24 h lead to 64 MBq of lead 212. The lead 212 obtained exhibited a radiological purity of more than 99.95%, generally about 99.995%. The grade is such that even radium 224 was not detectable after 1 week. Its chemical purity was characterized by the presence, in the lead 212 elution solution, of: less than 25 ppb (parts per billion) of lead (other than lead 212) and manganese; less than 2 ppb of cobalt, copper, molybdenum, cadmium, thorium, tungsten and mercury; less than 2 ppm of vanadium, iron and zinc. Its bacteriological purity was characterized by sterility and less than 0.5 endotoxin unit/mL; and this in less than 20 minutes between the start of the extraction of lead 212 from the radium 224 generator and the end of the filling of the flask 46 with purified lead 212. Lead 212 was produced with an apparatus similar to the one that has just been described and by a process comprising the following steps: A radium 224 generator containing 400 mg of a cation exchange resin (company BIO-RAD—reference AG™ MP50) as the solid medium was used. The resin was initially loaded with 24 mL of a solution containing 169 MBq of radium 224 of radiological purity greater than 99.5% (such as that determined by γ spectrometry). The system without the generator was loaded with 2 mL of a 2N HCl solution at the loading rate of 1 mL/min. The generator was then eluted with 5 mL of a 2N HCl solution at the elution rate of 0.5 mL/min. The resulting solution was then loaded on the head of the chromatography column. A ready-to-use chromatography column containing 80±10 mg of “Pb resin” (company TRISKEM International) as the stationary phase was washed with 1 mL of a 0.1N HCl solution at the washing rate of 0.5 mL/min. It was then washed in a backward fashion with 1 mL of a 0.1N HCl solution at the washing rate of 0.5 mL/min. 0.5 mL of an aqueous solution containing 0.4 mol/L of ammonium acetate (pH 6.5) was used to load the system (loading rate: 0.5 mL/min). 1 mL of an aqueous solution containing 0.4 mol/L of ammonium acetate (pH 6.5) was used to elute the Pb column in a backward fashion (elution rate: 0.25 mL/min) to elute the lead 212 from the stationary phase of the chromatography column and recover it at the head of the column. The system was then flushed with sterile air (0.2 μm filter) (1 mL at 1 mL/min). Radium 224 was left to generate lead 212 for 20 h and 81 MBq of lead 212 were obtained, After a second delay of 21 h, the system yielded 71 MBq of lead 212. A third cycle after another 9 h lead to 40 MBq of lead 212. The lead 212 obtained exhibited a radiological purity of more than 99.95%, generally about 99.995%. The grade is such that even radium 224 was not detectable after 1 week. Its chemical purity was characterized by the presence, in the lead 212 elution solution, of: less than 17 ppb (parts per billion) of lead (other than lead 212) and manganese; less than 2 ppb of cobalt, tungsten, thorium and mercury; less than 0.1 ppm of copper, molybdenum, iron and cadmium; less than 3 ppm of vanadium and zinc. Its bacteriological purity was characterized by sterility and less than 0.5 endotoxin unit/mL; and this in less than 20 minutes between the start of the extraction of lead 212 from the radium 224 generator and the end of the filling of the flask 46 with purified lead 212. |
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abstract | The present invention provides systems, methods and devices for storing and/or disposing of hazardous waste material. In some embodiments, the waste material includes nuclear waste such as calcined material. In certain embodiments, the device includes a container having a container body, a filling port configured to couple with a filling nozzle and a filling plug, and an evacuation port having a filter. The evacuation port is configured to couple with an evacuation nozzle and an evacuation plug. In certain embodiments, the method includes (a) adding hazardous waste material via a filling nozzle coupled to a filling port of a container, the container including an evacuation port, (b) evacuating the container during adding of the hazardous waste material via an evacuation nozzle coupled to an evacuation port of the container, (c) sealing the filling port, (d) heating the container, and (e) sealing the evacuation port. |
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summary | ||
description | FIG. 2 shows a preferred embodiment of a canister for the containment of a radioactive item according to the invention. Canister 101 comprises substantially tubular body 124, interior 128, a first, preferably closed, end 125, and second end 140. Interior 128 is adapted by size and geometric configuration to receive a radioactive item such as an nuclear reactor pressure vessel for storage, transportation, and disposal. Preferably interior 128 is large enough for such radioactive item to be disposed within the canister without difficulty, and to allow the addition of a stabilizer, as described herein, yet simultaneously as small as practicable, in order to reduce the size and weight of the completed package and to ease transportation and handling. Thus length width 134 and length 135 of the canister and in particular the canister interior are large enough to accommodate the item to be contained, but not larger than necessary for the purposes described herein. The selection of suitable dimensions and geometry will not trouble the designer of ordinary skill once he or she has been made familiar with disclosure. For most RPVs substantially circular cross sections will serve satisfactorily, and facilitate easy and inexpensive fabrication and employment of the canister. Body 124 of canister 101 further comprises integral sacrificial fenders 126 located adjacent each end of the canister. Sacrificial fenders 126 are comprised of extensions of body 124 of the canister beyond the end caps or closures of the canister, that is, beyond those portions of the canister actually used for containing the radioactive item, and are adapted to absorb or dissipate shocks administered to the completed containment package by deforming under contact loads. The mechanics of such fenders and their role in attenuating or absorbing shocks are well understood and will be plain to those of skill in the art, given the disclosure herein. The canister 101 shown in FIG. 2 further comprises lid or other closure means 108, which is adapted for attachment of a portion of the item to be contained. Lid or closure 108 can comprise a simple end plate, as shown, or might take the form of a cap-type enclosure sized to encompass the entire end of the canister, or any other suitable means for closing the canister. In the embodiment depicted in FIG. 2 closure 108 is adapted for the attachment of a portion of the contained device by means of holes 141, which are sized and positioned to accept attachment fittings present on the item to be contained, for example, the head attachment posts in a PWR pressure vessel. Preferably any portions of items to be attached to the exterior of the canister are not highly radioactive, or are sealable in their own right. Lid or top plate 108 further comprises optional fill and vent ports 160 and 161. Central ports 160 are provided for optional filling of the interior of the RPV body with grout or other sealant; peripheral ports 161 for filling the gap between the canister interior and the RPV exterior. Canister 101 in FIG. 2 further comprises optional secondary circumferential shield 130. Secondary shields are advantageously employed to provide additional containment of relatively highly radioactive portions of any contained items, such as some of the internal structures in a PWR pressure vessel. Preferably circumferential shields are employed in conjunction with cap or lid-type shields such as shields 122 and 142 shown in FIG. 5. A particular advantage of using substantially cylindrical canisters of the type shown in FIG. 2 is that secondary shields are relatively simple to fabricate and install, and provide substantial structural reinforcement as well. In the case of cicumferential shields, open-ended cylinders of nearly the same size as the canister body may be employed, and may be disposed around the inner or outer surfaces of the canister, at any axial position along the canister that may be desired. Cap or lid type shields may be fabricated from flat plate material merely by trimming them to size, and may be placed at any axial location within the canister or covering one or both ends of the canister. In either case it is often suitable, as will be understood by those having ordinary familiarity with the art of radiation shielding, that the same materials as those employed in fabricating the canister body may be used in fabricating secondary shield structures, with substantial savings in cost. Cap or lid shields are particularly useful for providing ALARA (As Low As Reasonably Achievable) shields during stacking of internal parts, external fittings, and/or insulation inside an RPV as described herein, as an added shield against radiation for workers. Canisters or containment vessels according to the invention and as shown in FIG. 2 are substantially easier and less expensive to fabricate than prior art containment vessels. This is in large part due to their simplified construction, as described. They are also economical to use, especially during the containment and removal of decommissioned RPV""s, because they may easily be separated into sections, moved into place for containment of the RPV or other item, and reassembled easily. For example, the containment canister shown in FIG. 2 may be cut anywhere along the length of its body into two or more sections merely by cutting the container, as for example by means of any conventional metal cutting methods, along a circumference such as that shown by reference numeral 138 in FIG. 2, the location of which may be varied anywhere along the body of the canister, such that two sections 136 and 137 result. In such cases reassembly is accomplished merely by replacing second section 137 back in place adjacent to first section 136 and reattaching, as for example by welding. The use of secondary radiation shield 130 also facilitates the use of the canister in this fashion, as it can be used as a doubler or structural reinforcement as well as an additional radiation shield. Canister 101 may be fabricated economically and easily by rolling or otherwise forming tubular body 124 by conventional means from sheet or plate metal, and welding or otherwise attaching a bottom plate at closed end 125 and lid or closure plate 108. Integral fenders 126 are easily formed in such processes by placing the end closures at a suitable distance from the ends of the body structure, leaving the fenders protruding or extending from the body. Provision of optional fillet 143, which is also readily formed by rolling or other conventional means, is particularly beneficial, as it permits provision of integral fenders 126 as described, in such fashion that fenders 126 are able to perform their function with full efficiency, while optionally permitting the canister weight and the weight of any of its contents to be transferred directly to the floor or other surface on which canister 101 and any contents are placed, without passing through and possibly harming the fenders or reducing their capacity to absorb or dissipate shocks. Optionally fenders 126 are of sufficient depth to allow them to provide protection not only to the containment package as a whole, and in particular to the packaged radioactive item, but also to any additional items, such as removed reactor vessel pressure head, which may be attached to the exterior of the canister. An early part of the process for containing a radioactive item according to the invention is preparing the radioactive item for packing. Generally this comprises removing at least one external fitting from the item, and optionally portions of the internals of the item as well. A process of preparing the item for packing is shown in FIGS. 3 and 4. FIG. 3 is a cutaway schematic elevation of an intact radioactive item, specifically a PWR pressure vessel, prior to being processed for containment according to the invention. Reactor pressure vessel (RPV) 102 comprises body 114 and head 115, internals 117, and a number of external fittings 103, including water nozzles 144 and control structures 145. Head 115 is joined to body 114 at flange 146 by means of attachments 132, and insulation 116 is in place around exterior 105 of the RPV. Internals 117 comprise upper internals 147 and lower internals 148. In FIG. 4 the RPV of FIG. 3 has been at least partially processed for containment according to the invention. External fittings 103 have been trimmed so that non-removed portions 104 of the fittings are substantially flush with external surface 105 of body 114. In particular, non-removed portions 104 of the external fittings do not protrude past the outer circumference of flange 146. Moreover, internals portions 148 including the central portion of the core barrel and the core baffle assembly have been removed from interior 109 of the RPV, and upper internals 147 have been stacked on top of support plate 142, which preferably serves also as a secondary radiation shield. Portions 149 of core barrel 151 (FIG. 3) are also disposed within the RPV. Additional portions 119 of the upper internals and insulation 116 removed from the exterior of the RPV are also placed in otherwise vacant space within the RPV body. A secondary support structure and ALARA shield 122 is placed atop internals 117, 147, and removed portions of external fittings 103 are placed thereupon. Additional insulation 116 taken from the exterior of the RPV body is placed atop fittings 103. Penetrations 120 of RPV body 114 have been stopped by means of plugs 121. As described herein, it is beneficial during at least the first portions of this process to leave the reactor coolant fluid or other liquid in the RPV, to serve as a radiation shield for those working on the containment process. Preferably this is accomplished by leaving water or other liquid in the RPV body to at least the level of 123 in FIG. 4 until the more highly-radioactive components of the core have been removed and all penetrations 120, for example, have been plugged; at this point it is advantageous to drain the fluid, install secondary supports and shield structures such as 142 and 122, and proceed with packaging. FIG. 5 is a schematic view of a radioactive item being disposed within a canister in accordance with the invention. Presented is one scenario of placing RPV 102 within canister 101. This scenario can be altered to accommodate plant specific and unique conditions. Internal shields 130 are welded to lower section 136 and upper section 137 of the canister during manufacturing. Lower section 136 of canister 101 has been placed atop transfer cart 160 with a removal frame and trunnions 139. Transfer cart 160 with lower section 136 has initially been placed in position 161 near RPV installation point 152. Head 115 of RPV 102 has been removed and lifting device 163 attached to RPV body 114. RPV 102 has been disconnected from the remainder of the plant of which it formed part by disconnecting external fittings 103, including piping 144, and penetrations 120 in RPV body 114 have been sealed. RPV external surfaces 105 are sealed with paint or other suitable substance to immobilize surface contaminants. RPV body 114 has been removed from RPV installation 152 and raised, whereupon transfer cart 160 with lower section 136 has been moved into loading position 169, and RPV body 114 has been disposed within section 136 of the canister. Canister 101 and RPV body 114 are ready for a stabilizer to be introduced in gap 106 between the RPV body 114 and the interior wall of canister 101. After gap 106 has been filled to a level sufficient to allow the stabilizer to support RPV body 114 and the stabilizer allowed time to set sufficiently, or RPV body 114 otherwise sufficiently supported, upper section 137 of canister 101 is placed over the RPV body and reattached to lower section 136 by welding or other suitable means. RPV studs 185 are installed through top plate 108 of upper section 137 into the flange of RPV body 114. Spray metalizing is used to seal openings between between RPV studs 185 and attachment penetrations 141 (FIG. 2) through upper section 137. Head 115 is placed atop external surface 127 of the canister, and fixed thereto, preferably by means of head attachments 132 threaded onto RPV studs 185. If necessary, the completed containment package will be turned about its upright longitudinal axis by pivoting the package with trunnions 139 on the removable frame on lower section 136. The package may then be removed from the plant housing and made ready for shipment by removing the frame with trunnions 139. It may be seen that division of canister 101 into two or more sections provides a number of benefits, such as a reduction in clearance height requirements to place RPV body 102 within the canister. This is especially beneficial in the limited workspaces of most nuclear plant installations. FIG. 6 is a cutaway schematic view of a radioactive item packaged in accordance with the invention. In addition to elements shown in other Figures, stabilizer 107 is shown substantially filling gap 106 between canister 101 and RPV 102. RPV head is in place atop lid 108 of the canister, and attached by means of RPV head-body attachments 132, which, together with stabilzer 107, further comprise the sole attachment between the RPV body and the containment canister. Optionally the entire interior of the RPV body is filled with stabilizer 107, to further immobilize contaminants and stored components. A containment package for a PWR pressure vessel is described. This example corresponds to plans for disposal of the Connecticut Yankee PWR. A containment canister according to the invention and as shown generally in FIG. 2, including top and bottom plates and fillet, is fabricated from three-inch thick structural carbon steel. Secondary shielding of two-inch thick carbon steel is placed within the canister body so as to shield the most highly radioactive portions of the completed package. The canister is fabricated in two sections, with the weld seam located behind the secondary shielding on rejoining. Rejoining is accomplished by full penetration weld. The canister, including integral fenders, 35xe2x80x2 3xe2x80x3 feet in length, 17xe2x80x2 10xe2x80x3 diameter, and weighs 190 tons empty. The completed package, with stabilizing grout and externally-attached RPV head, weighs 800 tons. The height of the package, with head attached, is 39xe2x80x2 7xe2x80x3. The head and RPV body are attached to each other, and to the canister, by means of the approximately twelve (12) head closure studs present on the reactor in service, which pass through canister lid and into upper flange of the RPV body. The canister provides containment shielding equivalent to DOT Industrial Package type 2, analyzed to withstand a 1 foot horizontal drop and a 1 foot drop with 2 feet of slap-down at either end. Ninety-nine point eight (99.8) percent of the radioactive material present is intrinsically contained within RPV activated metals themselves; remaining 0.2% is affixed to metal surfaces and is immobilized by grout or epoxy. A method for placing and sealing a PWR pressure within a containment vessel is described. The RPV is disconnected from external piping, controls, and the like, and the head is removed, as described and as shown generally in FIGS. 2-6. Highly radioactive portions of the internals are removed for separate containment and storage. Segmented internals, including particularly upper internal components, are placed inside the RPV body as described. Nominal 30 pcf low-density cellular concrete (LDCC) is placed inside the RPV body to seal and immobilize remaining and relocated internals. The RPV body is lifted over and lowered into position within the canister lower section, with a gap between the RPV and the canister interior. Nominal 70 pcf LDCC is poured into the gap to a sufficient depth to support the RPV after curing, and is allowed to cure. The lifting rig used to position the RPV is removed. Removed portions of the RPV nozzles are placed inside the RPV, atop an ALARA plate. RPV head closure guide studs (ref. 132 in FIG. 6) are installed in some of the RPV head attachment stud holes. The canister upper section is lifted and lowered into place over the guide studs, so that it rests upon the RPV head flange. RPV hold down studs are installed using remaining RPV head attachment stud holes. The canister upper and lower sections are welded together. Openings between the canister top plate and the RPV hold down and guide studs are sealed with metalizing spray. Nominal 70 pcf LDCC is pumped into remaining voids between the canister and the RPV body through peripheral fill ports opened in the top of the canister. Nominal 30 pcf LDCC is pumped into remaining voids inside the RPV body through center fill ports opened in the canister top plate. Fill and vent ports in the canister top plate are plugged and sealed. The RPV head is placed on top of the canister and the guide studs already in place. The guide studs are cut flush with the top of the RPV head flange. All LDCC is allowed to complete curing. The package is rigged for removal from the assembly location by the attachment of lugs and/or other structures to the canister exterior. The package is lifted and turned to a substantially horizontal position, secured to transport conveyance, and transported to a disposal site. Preferred embodiments of the various structures disclosed herein are fabricated from any materials having sufficient strength, durability, corrosion resistance, and radioactive shielding qualities to serve the purposes described for such structures. Suitable materials are known, and have been identified herein where appropriate; but any materials having suitable qualities will serve. While the invention has been described and illustrated in connection with preferred embodiments, many variations and modifications as will be evident to those skilled in this art may be made without departing from the spirit and scope of the invention, and the invention is thus not to be limited to the precise details of methodology or construction set forth above as such variations and modification are intended to be included within the scope of the invention. |
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054593662 | claims | 1. A battery for an electroscope comprising: an evacuated battery chamber having a support disposed therein and being light transmissive therethrough; a substantially open-ended hollow member connected to the support and being light transmissive therethrough; and an isotopic source material carried by the hollow member and emitting charged particles across an annular evacuated gap onto the wall of the evacuated battery chamber. a first electrode having a hollow, substantially cylindrical form; a second electrode having a hollow, substantially cylindrical form and being arranged coaxially with respect to the first electrode; an isotopic source material carried by one of the first and second electrodes; and a chamber containing the one electrode carrying the isotopic source material, and being formed at least partially by first and second substantially, spaced apart light transmissive members disposed at opposite axial ends of the chamber. 2. A battery according to claim 1, wherein the source material is tritium coated on a surface of the hollow member. 3. A battery according to claim 1, wherein the hollow member is cylindrical and substantially coaxial with the evacuated battery chamber. 4. A battery for an electroscope comprising: 5. A battery according to claim 4, wherein the first electrode is supported in electrical isolation from the second electrode by one of the first and second transparent members. 6. battery according to claim 4, wherein the source material is tritium coated on an outer surface of an inner one of the first and second electrodes. 7. A battery according to claim 4, wherein the chamber is evacuated. |
abstract | An electron-beam metrology system includes a specimen stage to mount a specimen on which a device pattern is formed, electron optics to radiate the device pattern with an electron-beam, a secondary electron detector to detect a secondary electron generated by the radiation of the electron-beam, and an information processing system to analyze a signal obtained from the secondary electron detector. A standard reference for metrology is held on the specimen stage, and the standard reference includes a first grating unit pattern including an array of gratings having pitch sizes which are verified by an optical method, and a second grating unit pattern including an array of gratings having pitch sizes which are smaller than the pitch sizes of the first grating unit pattern. |
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054815860 | claims | 1. An automatic position control system for use in an x-ray machine, comprising an x-ray source including a beam limiting device which produces a narrow x-ray beam, a sensor which senses the position of said narrow x-ray beam, a mechanical sweep system which moves said narrow beam and said sensor in the same direction, a feedback control circuit which receives a signal from said sensor and a reference signal and generates an error signal, said error signal being inputted to said mechanical sweep system to adjust the position of said narrow x-ray beam, such that said narrow x-ray beam is centered on said sensor. a servo positioning motor which moves said beam limiting device, a motor controller which controls said servo-positioning motor, and a sensor positioning motor which moves said-sensor. a first element separated by a gas from a second element, said first element comprising a plurality of photodiodes connected in series separated by resistors, and a first and a second terminal each terminated by a terminating resistor. a source of a narrow beam of radiation which scans across an object to be imaged, a sensor for said narrow beam of radiation which moves in the same direction as said narrow beam, said sensor generating an output signal which indicates the position of the beam relative to a specific location on the sensor, and a control circuit which receives said signal from said sensor and outputs a control signal to regulate the position of the beam relative to said sensor to cause said beam to become aligned with the specific location on the sensor. a first element separated by a gas from a second element, said first element comprising a plurality of photodiodes connected in series separated by resistors, and a first and a second terminal each terminated by a terminating resistor. 2. An automatic position control system of claim 1 wherein said mechanical sweep system comprises 3. The automatic exposure control system of claim 2 wherein said feedback control circuit comprises a first electronic circuit which compares said signal from said sensor and said reference signal and outputs an error signal to said motor controller which outputs a signal to said servo-positioning motor. 4. An automatic position control system of claim 1 wherein said sensor is an ionization chamber comprising 5. An automatic position control system of claim 1 wherein said sensor comprises 6. The automatic exposure control system of claim 1 further comprising a second electronic circuit which inputs signals to said motor controller and said sensor positioning motor. 7. The system of claim 1, wherein said x-ray machine is a mammography machine. 8. An imaging system comprising 9. The system of claim 8 wherein said radiation is x-radiation. 10. The system of claim 8 wherein said control circuit comprise a comparator for comparing said sensor signal with a reference signal and outputting an error signal. 11. The system of claim 10 further comprising a controller which controls the position of the beam in response to said error signal. 12. The system of claim 8 wherein said sensor comprises 13. The system of claim 8 wherein said sensor comprises |
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abstract | A rotation apparatus is usable with a control drum in a nuclear environment. The control drum is situated on a shaft that is rotatable about a horizontal axis of rotation, and the control drum includes an absorber portion and a reflector portion. The rotation apparatus includes a rotation mechanism that is structured to apply to the shaft in an operational position a force that biases the shaft to rotate toward a shutdown position, with the force being resisted by a motor to retain the shaft in the operational position when the motor is powered. The force is not resisted when the motor is unpowered. The rotation apparatus further includes a rotation management system that controls the rotation of the shaft. |
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054855004 | claims | 1. A digital X-ray imaging system comprising: X-ray generator means including an X-ray tube; X-ray generator controlling means for controlling said X-ray generator means; X-ray detecting means for detecting an X-ray transmitted through a subject, said X-ray detecting means having an X-ray grid for shielding a scattered X-ray; signal processing means for acquiring signals from said X-ray detecting means and processing the signals to obtain a digital X-ray images of said X-ray transmitted subject through said subject; display means for displaying an image of said subject obtained by said signal processing means; position changing means for changing a relative position between said X-ray detecting means, said subject and said X-ray tube by moving one of said X-ray detecting means and said X-ray tube; position change controlling means for controlling said position changing means; and imaging-sequence controlling means for controlling said position change controlling means and said X-ray generator controlling means; wherein said imaging-sequence controlling means controls to set a plurality of imaging view fields, to set each of a plurality of regions of interest of said subject to generally a central area of an X-ray detecting plane of said X-ray generating means, said X-ray detecting plane being an incident plane of said transmitted X-ray through said subject, and to set at least one imaging view field to contain an intermediate region between said plurality of regions of interest, and said signal processing means corrects a sensitivity non-uniformity, caused by said X-ray generator means and said X-ray detecting means, of each of said digital X-ray images of said plurality of imaging view fields, and joins together a plurality of said digital X-ray images of said plurality of imaging view fields. wherein, the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject being performed by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table, and the geometric distortion correction for each pixel position of said digital X-ray image being performed by using said corresponding position relation table. wherein the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject being performed by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table, and the geometric distortion correction for each pixel position of said digital X-ray image being performed by using said corresponding position relation table, and wherein in joining together said plurality of X-ray digital images of said plurality of imaging view fields, joining points whereat said plurality of X-ray digital images are joined together are determined, coordinate systems for said plurality of digital X-ray images are unified, and an obtained joined image is subjected to the density correction near the joined area. wherein a marker is added to said subject, said plurality of imaging view fields are imaged, and the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject being performed by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table, and the geometric distortion correction for each pixel position of said digital X-ray image being performed by using said corresponding position relation table, and wherein in joining together said plurality of X-ray digital images of the imaging view fields by referring to said marker contained in common in said plurality of X-ray digital images, joining points whereat said plurality of X-ray digital images are joined together are determined, coordinate systems for said plurality of digital X-ray images are unified, and an obtained joined image is subjected to the density correction near the joined area. wherein the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject being performed by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table, and the geometric distortion correction for each pixel position of said digital X-ray image being performed by using said corresponding position relation table, and wherein in joining together said plurality of X-ray digital images of the imaging view fields, joining points whereat said plurality of X-ray digital images are joined together are determined, coordinate systems for said plurality of digital X-ray images are unified, and an obtained joined image is subjected to the density correction near the joined area. controlling to set a plurality of imaging view fields of said subject in order to divisionally image target imaging regions of said subject a plurality of times; changing a relative position between said X-ray detecting means and said subject; controlling to set each of said plurality of imaging view fields by setting each of regions of interest of said subject to generally a central area of an X-ray detecting plane of said X-ray detecting means, said X-ray detecting plane being an incident plane of said transmitted X-ray, and by setting at least one imaging view field to contain an intermediate region between said plurality of regions of interest; correcting the sensitivity non-uniformity and geometric distortion, caused by said X-ray generator means and said X-ray detecting means, of each of said digital X-ray images of said plurality of imaging view fields; obtaining a digital X-ray image by joining together at least two of said digital X-ray images of said plurality of imaging view fields; and displaying at least said joined digital X-ray image. X-ray generator means; X-ray generator controlling means for controlling said X-ray generator means; X-ray detecting means for detecting an X-ray transmitted through a subject, said X-ray detecting means having an X-ray grid for shielding a scattered X-ray; signal processing means for acquiring an output signal from said X-ray detecting means and processing the signal to obtain a digital X-ray image of said X-ray transmitted through said subject; display means for displaying an image of said subject obtained by said signal processing means; position changing means for changing a relative position between said X-ray detecting means and said subject; position change controlling means for controlling said position changing means; and imaging-sequence controlling means for controlling same position change controlling means and said X-ray generator controlling means, wherein said imaging-sequence controlling means controls to set a plurality of imaging view fields, to set each of a plurality of regions of interest of said subject to generally a central area of an X-ray detecting plane of said X-ray detecting means, said X-ray detecting plane being an incident plane of said transmitted X-ray, and to set at least one imaging view field to contain an intermediate region between said plurality of regions of interest, said signal processing means corrects the sensitivity non-uniformity and geometric distortion, caused by said X-ray generator means and said X-ray detecting means, of each of said digital X-ray images of said plurality of imaging view fields, and joins together at least two said digital X-ray images of said plurality of imaging view fields, and said display means displays at least said joined digital X-ray image. X-ray generator means; X-ray generator controlling means for controlling said X-ray generator means; X-ray detecting means for detecting an X-ray transmitted through a subject, said X-ray detecting means having an X-ray grid for shielding a scattered X-ray; signal processing means for acquiring an output signal from said X-ray detecting means and processing the signal to obtain a digital X-ray image of said X-ray transmitted through said subject; display means for displaying an image of said subject obtained by said signal processing means; position changing means for changing a relative position between said X-ray detecting means and said subject; position change controlling means for controlling said position changing means; and imaging-sequence controlling means for controlling same position change controlling means and said X-ray generator controlling means, wherein said imaging-sequence controlling means controls to set a plurality of imaging view fields, to set each of a plurality of regions of interest of said subject to generally a central area of an X-ray detecting plane of said X-ray detecting means, said X-ray detecting plane being an incident plane of said transmitted X-ray, and to set at least one imaging view field to contain an intermediate region between said plurality of regions of interest, said position changing means moves said X-ray detecting means while maintaining constant the distance between said X-ray generator means and said subject and the distance between said X-ray generator means and the center of the X-ray detecting plane of said X-ray detecting means, and while setting the X-ray detecting plane perpendicular to a line passing through the center of the X-ray detecting plane and an X-ray emitting position of said X-ray generator means, said signal processing means corrects the sensitivity non-uniformity and geometric distortion, caused by said X-ray generator means and said X-ray detecting means, of each of said digital X-ray images of said plurality of imaging view fields, and joins together at least two said digital X-ray images of said plurality of imaging view fields, and said display means displays at least said joined digital X-ray image. controlling to set a plurality of imaging view fields of said subject in order to divisionally image target imaging regions of said subject a plurality of times; changing a relative position between said X-ray detecting means and said subject by moving one of said X-ray detecting means and said X-ray tube; controlling to set each of said plurality of imaging view fields by setting each of regions of interest of said subject to generally a central area of an X-ray detecting plane of said X-ray detecting means, said X-ray detecting plane being an incident plane of said transmitted X-ray, and by setting at least one imaging view field to contain an intermediate region between said plurality of region of interest; correcting a sensitivity non-uniformity and geometric distortion of said plurality of digital X-ray images caused by said X-ray generator means and said X-ray detecting means; obtaining a digital X-ray image by joining together at least two of said digital X-ray images of said plurality of imaging view fields; and displaying at least said joined digital X-ray image. a pre-process step of generating a sensitivity non-uniformity correction factor table used for correcting sensitivity non-uniformity caused by said X-ray generator means and said X-ray detecting means and a corresponding position relation table used for correcting geometric distortion caused by said X-ray generator means and said X-ray detecting means, prior to imaging said subject; a post-process step of correcting digital X-ray image data of said subject obtained by imaging the view field of said subject; and a step of subjecting data of a plurality of digital X-ray images obtained by imaging a plurality of imaging view fields to the sensitivity non-uniformity correction and geometric distortion correction. generating said sensitivity non-uniformity correction factor table from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction; and generating said corresponding position relation table from said digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations. generating said sensitivity non-uniformity correction factor table from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction; generating said corresponding position relation table from digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations; performing the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table; and performing the geometric distortion correction for each pixel position of said digital X-ray image data by using said corresponding position relation table. generating said sensitivity non-uniformity correction factor table from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction; generating said corresponding position relation table from digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations; performing the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table; performing the geometric distortion correction for each pixel position of said digital X-ray image data by using said corresponding position relation table; and in joining together said plurality of X-ray digital images of said plurality of imaging view fields, determining joining points whereat said plurality of X-ray digital images are joined together, unifying coordinate systems for said plurality of digital X-ray images, and subjecting an obtained joined image to the density correction near the joined area. generating said sensitivity non-uniformity correction factor table from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction; generating said corresponding position relation table from digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations; adding a marker to said subject and imaging said plurality of imaging view fields; performing the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table; performing the geometric distortion correction for each pixel position of said digital X-ray image data by using said corresponding position relation table; and in joining together said plurality of X-ray digital images of the imaging view fields by referring to said marker contained in common in said plurality of X-ray digital images, determining joining points whereat said plurality of X-ray digital images are joined together, unifying coordinate systems for said plurality of digital X-ray images, and subjecting an obtained joined image to the density correction near the joined area. generating said sensitivity non-uniformity correction factor table from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction; generating said corresponding position relation table by imaging said subject with a marker chart placed on said subject, said marker chart having a plurality of elements with predetermined transmittances and position relations, and by measuring said geometric distortions of the obtained digital X-ray image from the position relations between predetermined elements of said marker chart; performing the sensitivity non-uniformity correction for said digital X-ray image data obtained by imaging the view field of said subject by obtaining a sensitivity non-uniformity correction factor at each pixel position of said digital X-ray image from said sensitivity non-uniformity correction factor table; performing the geometric distortion correction for each pixel position of said digital X-ray image data by using said corresponding position relation table; and in joining together said plurality of X-ray digital images of the imaging view fields, determining joining points whereat said plurality of X-ray digital images are joined, unifying coordinate systems for said plurality of digital X-ray images, and subjecting an obtained joined image to the density correction near the joined area. X-ray generator means including an X-ray tube; X-ray generator controlling means for controlling said X-ray generator means; X-ray detecting means for detecting an X-ray transmitted through a subject, said X-ray detecting means having an X-ray grid for shielding a scattered X-ray; signal processing means for acquiring signals from said X-ray detecting means and processing the signals to obtain digital X-ray images of said X-ray transmitted subject through said subject; display means for displaying an image of said subject obtained by said signal processing means; position changing means for changing a relative position between said X-ray detecting means and said subject and a relative position between said X-ray detecting means and said X-ray generator means by moving said X-ray detecting means; position change controlling means for controlling said position changing means; and imaging-sequence controlling means for controlling said position change controlling means and said X-ray generator controlling means; wherein said imaging-sequence controlling means controls to set a plurality of imaging view fields, to set each of a plurality of regions of interest of said subject to generally a central area of an X-ray detecting plane of said X-ray generating means, said X-ray detecting plane being an incident plane of said transmitted X-ray through said subject, and to set at least one imaging view field to contain an intermediate region between said plurality of regions of interest. moving said X-ray detecting means to set an imaging view field by changing a relative position between said X-ray detecting means and said subject, while maintaining constant the distance between said X-ray generator means and said subject and the distance between said X-ray generator means and the center of the X-ray detecting plane of said X-ray detecting means, and while setting the X-ray detecting plane perpendicular to a line passing through the center of the X-ray detecting plane and an X-ray emitting position of said X-ray generator means; controlling to set each of said plurality of imaging view fields by setting each of regions of interest of said subject to generally a central area of an X-ray detecting plane of said X-ray detecting means, said X-ray detecting plane being an incident plane of said transmitted X-ray, and by setting at least one imaging view field to contain an intermediate region between said plurality of regions of interest; correcting the sensitivity non-uniformity and geometric distortion, caused by said X-ray generator means and said X-ray detecting means, of each of said digital X-ray images of said plurality of imaging view fields; obtaining a digital X-ray image by joining together at least two of said digital X-ray images of said plurality of imaging view fields; and displaying at least said joined digital X-ray image. 2. A digital X-ray imaging system according to claim 1, wherein said display means displays at least a digital X-ray image obtained by joining together at least two of said digital X-ray images of said imaging view fields. 3. A digital X-ray imaging system according to claim 1, wherein said regions of interest are the right and left lungs of said subject, generally near the center of each lung is set to the central area of the said X-ray detecting plane, and said subject is imaged two times. 4. A digital X-ray imaging system according to claim 1, wherein said signal processing means further corrects geometric distortion, caused by said X-ray generator means and said X-ray detecting means, of each of said digital X-ray images of said plurality of imaging view fields. 5. A digital X-ray imaging system according to claim 1, wherein the X-ray detecting plane of said X-ray detecting means moves on a straight trajectory in a plane containing said X-ray detecting plane, while imaging said plurality of imaging view fields. 6. A digital X-ray imaging system according to claim 1, wherein the X-ray detecting plane of said X-ray detecting means moves on a circular trajectory in a plane containing said X-ray detecting plane, while imaging said plurality of imaging view fields. 7. A digital X-ray imaging system according to claim 1, wherein said X-ray generator means and said subject are disposed at predetermined positions, and said position changing means moves said X-ray detecting means while maintaining constant the distance between said X-ray generator means and said subject and the distance between said X-ray generator means and the center of the X-ray detecting plane of said X-ray detecting means, and while setting the X-ray detecting plane perpendicular to a line passing through the center of the X-ray detecting plane and an X-ray emitting position of said X-ray generator means. 8. A digital X-ray imaging system according to claim 7, wherein said position changing means further includes rotating means for rotating said X-ray detecting means placed on a stage having a rotation axis. 9. A digital X-ray imaging system according to claim 7, wherein said position changing means further includes rotating means for rotating said X-ray detecting means placed on a stage having a rotation axis, and parallel position changing means for parallel by moving said X-ray detecting means. 10. A digital X-ray imaging system according to claim 1, wherein said position changing means moves said subject while imaging said plurality of imaging view fields. 11. A digital X-ray imaging system according to claim 1, wherein said position changing means continuously changes the relative position between said X-ray detecting means and said subject during the X-ray exposure for imaging said subject. 12. A digital X-ray imaging system according to claim 1, wherein an area providing a grid function of said X-ray grid has an area covering the X-ray detecting plane of said X-ray detecting means, and a longitudinal direction of an X-ray absorbing plate constituting said X-ray grid is perpendicular to a scanning line direction of an image pickup tube of an imaging device of a television camera constituting said X-ray detecting means. 13. A digital X-ray imaging system according to claim 1, wherein said position changing means moves said X-ray detecting means in a direction defining a straight trajectory, and said X-ray tube has an X-ray slit, and an opening of said X-ray slit moves in the direction same as the direction of movement of said X-ray detecting means. 14. A digital X-ray imaging system according to claim 1, wherein said X-ray tube has an X-ray slit, and in imaging each of said plurality of imaging view fields, said position changing means moves said X-ray tube and said X-ray slit by making the directions of said X-ray tube and said X-ray slit toward said X-ray detecting means coincide with each other. 15. A digital X-ray imaging system according to claim 1, wherein said X-ray detecting means includes an X-ray image intensifier, a television camera, and an optical system coupling said X-ray image intensifier and said television camera. 16. A digital X-ray imaging system according to claim 15, wherein said position changing means moves said X-ray detecting means in a direction defining a straight trajectory, and an image pickup tube is used as an imaging device of said television camera, and a scanning line direction of said image pickup tube is parallel to the direction of movement of said X-ray detecting means. 17. A digital X-ray imaging system according to claim 15, wherein said position changing means moves said X-ray detecting means in a direction defining a straight trajectory, and a CCD device is used as an imaging device element of said television camera, and the pixel disposal of said CCD device is parallel to the direction of moving said X-ray detecting means. 18. A digital X-ray imaging system according to claim 1, wherein the imaging view field of an X-ray image intensifier constituting said X-ray detecting means has a size covering one lung and mediastinum of said subject, and a joined image containing both the lungs and mediastinum of said subject is formed by two radiographic exposures of the right lung and mediastinum and the left lung and mediastinum. 19. A digital X-ray imaging system according to claim 18, wherein said position changing means moves said X-ray detecting means in a direction defining a straight trajectory, and the X-ray incident plane of said X-ray image intensifier has a shape of a circle, a distance of movement of said X-ray detecting means required for said two radiographic exposures is about 1/2 of the diameter of said circle, and said joined image has a view field of a square having the side length of about .sqroot.3/2 the diameter of said circle. 20. A digital X-ray imaging system according to claim 1, wherein said signal processing means executes a pre-process for generating a sensitivity non-uniformity correction factor table used for correcting sensitivity non-uniformity caused by said X-ray generator means and said x-ray detecting means and a corresponding position relation table used for correcting geometric distortion caused by said X-ray generator means and said X-ray detecting means, prior to imaging said subject, and executes a post-process for correcting digital X-ray image data of said subject obtained by imaging the view field of said subject, wherein data of a plurality of digital X-ray images obtained by imaging a plurality of imaging view fields being subjected to the sensitivity non-uniformity correction and geometric distortion correction to join together said plurality of digital X-ray images. 21. A digital X-ray imaging system according to claim 20, wherein said sensitivity non-uniformity correction factor table is generated from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction, and said corresponding position relation table is generated from digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations. 22. A digital X-ray imaging system according to claim 20, wherein said sensitivity non-uniformity correction factor table is generated from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction, and said corresponding position relation table is generated from digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations, and 23. A digital X-ray imaging system according to claim 20, wherein said sensitivity non-uniformity correction factor table is generated from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction, and said corresponding position relation table is generated from digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations, 24. A digital X-ray imaging system according to claim 20, wherein said sensitivity non-uniformity correction factor table is generated from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction, and said corresponding position relation table is generated from digital X-ray image data obtained by imaging a chart having a plurality of elements with known position relations, 25. A digital X-ray imaging system according to claim 20, wherein said sensitivity non-uniformity correction factor table is generated from digital X-ray image data obtained by imaging a chart having a uniform X-ray transmittance in one direction, and said corresponding position relation table is generated by imaging said subject with a marker chart placed on said subject, said marker chart having a plurality of elements with predetermined transmittances and position relations, and by measuring said geometric distortions of the obtained digital X-ray image from the position relations between predetermined elements of said marker chart, 26. An X-ray imaging method of radiating an X-ray from X-ray generator means to a subject, passing an X-ray transmitted through said subject through an X-ray grid for shielding a scattered X-ray, detecting said X-ray passed through said X-ray grid by X-ray detecting means, acquiring a signal detected by said X-ray detecting means and processing a digital signal representing said X-ray transmitted through said subject, and obtaining a digital X-ray image, comprising the steps of: 27. A digital X-ray imaging system comprising: 28. A digital X-ray imaging system comprising: 29. An X-ray imaging method of radiating an X-ray from X-ray generator means including an X-ray tube to a subject, passing an X-ray transmitted through said subject through an X-ray grid for shielding a scattered X-ray, detecting said X-ray passed through said X-ray grid by X-ray detecting means, acquiring a signal detected by said X-ray detecting means and processing a digital signal representing said X-ray transmitted through said subject, and obtaining a digital X-ray image, comprising the steps of: 30. A digital X-ray imaging method according to claim 29, wherein said step of changing the relative position includes moving said X-ray detecting means which includes a step of moving said X-ray detecting plane of said X-ray detecting means on a straight trajectory in a plane containing said X-ray detecting plane, while imaging said plurality of imaging view fields. 31. A digital X-ray imaging method according to claim 29, wherein said step of moving said X-ray detecting means includes a step of moving said X-ray detecting plane of said X-ray detecting means on a circular trajectory in a plane containing said X-ray detecting plane, while imaging said plurality of imaging view fields. 32. A digital X-ray imaging method according to claim 29, wherein said step of changing the relative position includes moving said X-ray detecting means which includes a step of moving said X-ray detecting means while maintaining constant the distance between said X-ray generator means and said subject and the distance between said X-ray generator means and the center of the X-ray detecting plane of said X-ray detecting means, and while setting the X-ray detecting plane perpendicular to a line passing through the center of the X-ray detecting plane and an X-ray emitting position of said X-ray generator means. 33. A digital X-ray imaging method according to claim 32, wherein said step of moving said X-ray detecting means includes a step of rotating said X-ray detecting means placed on a stage having a rotation axis. 34. A digital X-ray imaging method according to claim 32, wherein said step of moving said X-ray detecting means includes a step of moving said X-ray detecting means placed on a stage having a rotation axis, and a step of parallel moving said X-ray detecting means. 35. A digital X-ray imaging method according to claim 29, further comprising: 36. A digital X-ray imaging method according to claim 35, further comprising the steps of: 37. A digital X-ray imaging method according to claim 35, further comprising the steps of: 38. A digital X-ray imaging method according to claim 35, further comprising the steps of: 39. A digital X-ray imaging method according to claim 35, further comprising the steps of: 40. A digital X-ray imaging method according to claim 35, further comprising the steps of: 41. A digital X-ray imaging system comprising: 42. A digital X-ray imaging system according to claim 41, wherein said signal processing means corrects a sensitivity non-uniformity and geometric distortion, caused by said X-ray generator means and said X-ray detecting means, of each of said digital X-ray images of said plurality of imaging view fields, and joins together a plurality of said digital X-ray images of said plurality of imaging view fields. 43. A digital X-ray imaging system according to claim 41, wherein the X-ray detecting plane of said X-ray detecting means moves on a circular trajectory in a plane containing said X-ray detecting plane, while imaging said plurality of imaging view fields. 44. A digital X-ray imaging system according to claim 41, wherein said X-ray generator means and said subject are disposed at predetermined positions, and said position changing means moves said X-ray detecting means while maintaining constant the distance between said X-ray generator means and said subject and the distance between said X-ray generator means and the center of the X-ray detecting plane of said X-ray detecting means, and while setting the X-ray detecting plane perpendicular to a line passing through the center of the X-ray detecting plane and an X-ray emitting position of said X-ray generator means. 45. A digital X-ray imaging system according to claim 44, wherein said position changing means further includes rotating means for rotating said X-ray detecting means placed on a stage having a rotation axis. 46. A digital X-ray imaging system according to claim 44, wherein said position changing means further includes rotating means for rotating said X-ray detecting means placed on a stage having a rotation axis, and parallel position changing means for parallelly moving said X-ray detecting means. 47. An X-ray imaging method of radiating an X-ray from X-ray generator means to a subject, passing an X-ray transmitted through said subject through an X-ray grid for shielding a scattered X-ray, detecting said X-ray passed through said X-ray grid by X-ray detecting means, acquiring a signal detected by said X-ray detecting means and processing a digital signal representing said X-ray transmitted through said subject, and obtaining a digital X-ray image, comprising the steps of: |
claims | 1. A device for protecting a subject against exposure to electromagnetic radiation emitted from a remote source, the device comprising:a) a housing;b) a solenoid operably connected to a driver, said solenoid capable of generating incident radiation; andc) a polymer comprising:i. a polar matrix,ii. an oxydated hydrocarbon emulsifier,iii. a galvanic salt,iv. a dye or stain, andv. a polysaccharide;wherein upon exposure to said incident radiation, said polymer emits random electromagnetic oscillation frequencies that counter adverse effects associated with the subject's exposure to the electromagnetic radiation. 2. The device according to claim 1, wherein said solenoid comprises a two frequency mode that generates two carrier frequencies of incident radiation. 3. The device according to claim 1, wherein said solenoid comprises a two frequency mode that generates two carrier frequencies of incident radiation, wherein said carrier frequencies are higher than said oscillation frequencies. 4. The device according to claim 1, wherein said driver is a Microprocessor controlled drive circuit. 5. The device according to claim 1, wherein said polymer is housed within an inner cylinder, further wherein said solenoid is positioned around the circumference of said inner cylinder. 6. The device according to claim 1, wherein said remote source is selected from the group consisting of a computer, a computer peripheral, a cellular telephone, a personal communications device, a television, an audio system and a household appliances. 7. The device according to claim 1, wherein said remote source is selected from the group consisting of any intentional and/or unintentional sources of electromagnetic radiation with Effective Radiation Power (ERP) limited in compliance with FCC Regulations. 8. A method of protecting a subject against exposure to electromagnetic radiation emitted from a remote source, the method comprising providing the device according to claim 1 within an effective radius of the subject and driving said solenoid. |
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043303684 | summary | The present invention relates generally to cable handling systems and more particularly to a system for use in a specific type of nuclear reactor, for example one which utilizes an assembly of rotatable plugs such as a liquid metal fast breeder reactor (LMFBR). A typical reactor of the type just recited has many operating components located within a sealed vessel. These components include an inner core, and, with respect to the present invention, an upper internal structure or instrument tree as it is also called and an internal fuel hoist for carrying fuel assemblies into and out of the core. The vessel itself includes an assembly of rotatably mounted, horizontal plugs serving to perform certain position related functions within the vessel including moving the hoist between various operating points therein. The reactor also requires power, instrumentation and service connections between an internal location within the vessel, specifically the instrument tree, and an external location, whereby to interconnect certain components within the vessel to certain remote, external components. In an actual reactor of the type to which the present invention is especially suitable, specifically the LMFBR referred to above, the assembly of plugs, also referred to above, includes three horizontally extending, circular plugs mounted for rotation about their respective vertical axes. These plugs include an outermost plug which is the largest of the three, an intermediate plug mounted eccentrically within the outer plug and an inner plug mounted eccentrically within the intermediate plug. The internal fuel hoist is mounted to and extends down from the underside of the inner circular plug. In this way, by rotating the three plugs alone or in different combinations with one another, either clockwise or counterclockwise, the hoist can be moved both rectilinearly and/or curvilinearly between various points within the reactor vessel. However, at the same time it must be remembered that the reactor also includes power, instrumentation and service connections between components within the vessel, specifically the instrument tree and external components, as stated previously, and this has heretofore been greatly complicated by plug rotation. A common way of alleviating the complication just recited has been to actually disconnect the various connections (actually electrical and/or tubular fluid carrying cables) between the internal and external components during rotation of the plugs. In order to do this in a reliable manner, it is absolutely necessary to make sure that all cables are completely connected or unconnected, whichever the case may be, and this is quite time consuming and hence costly. Accordingly, there have been proposals in the past to maintain the connections between the internal and external components during rotation of the plugs, thereby eliminating this latter time consuming and hence costly drawback. One proposal has been to use a cable support system that sits on the rotatable plugs and spans the annulus between adjacent plugs. This system uses commercially available hardware including a cable containing a rolling chain belt mechanism which rests on the plugs and spans the annulus between the plugs, thereby greatly congesting the area over the reactor vessel and complicating the rotating plug seal replacement. As will be seen hereinafter, the present invention eliminates the time consuming and costly problem of connecting and disconnecting cables between internal and external reactor components by providing a cable handling system which allows the cables to remain connected during rotation of the various plugs. However, the cable handling system of the present invention is one which does not congest the area over the rotatable plugs or cause problems related to seal replacement. In addition, as will be seen hereinafter, this system is relatively uncomplicated in design, reliable in use, and, in a preferred embodiment, uses commercially available cable containing rotating belt equipment as part of the main support. Aero-trak by Aero-Motive Manufacturing Company and Powertrak by Gleason, division of Maysteel Corporation are two commercially available rolling belt devices useable in the present invention. In view of the foregoing, one object of the present invention is to provide a cable handling system for use in a nuclear reactor of the general type described above and specifically a system which does not require disconnecting the otherwise connected internal and external components of the reactor during rotation of its plug assembly. Another object of the present invention is to provide a cable handling system which does not greatly congest the area of the reactor directly above its plug assembly and which does not complicate seal replacement to any significant degree. Still another object of the present invention is to provide a cable handling system which is relatively uncomplicated in design and reliable in use. As will be seen hereinafter, the cable handling system disclosed herein includes a vertically extending drum tower fixedly mounted to and extending up from the topside of one of the rotating plugs, specifically from the center point on the previously recited intermediate plug in a preferred embodiment and carrying a cylindrical drum at its top. In this system, a first section of power, instrumentation and service cables (including electric and fluid cables) extend between certain components within the vessel, for example, the previously recited instrument tree, and a fixed terminal box at the base of the drum or tower. This section then passes up the tower to a fixed drum point at the top of the tower. A second section of the cables (and a section of the aforementioned rolling belt) is between the point on the drum and a remote, external point such that the distance between the two points varies, depending upon the way in which the plug and drum move. In this regard, the second cable section must be of sufficient configuration to compensate for this change in distance as the plugs rotate. Moreover, in order to compensate for plug rotation, the overall cable handling system includes cable support means (the rolling belt mechanism described) for supporting it for movement with the drum and for causing a segment to wrap around or unwrap from the drum, depending upon the way in which the latter and its supporting plug rotate. As will be seen hereinafter, for the majority (normally about 5/6th) of the fuel handling operations within the reactor core, the remote end of the rolling belt mechanism stays in one location. Rotation and relative movement is compensated by rolling on and off the drum and/or by axial movement of the radial loop. For the remaining portion, (about 1/6th) of the operation within the core, the fuel hoist tower will hit the rolling belt mechanism unless the latter is moved. For these operations a carriage is provided to move tangentially to one side or another of a center line moving the mechanism with it to allow the fuel hoist to reach the center line from either side, i.e., as a result of clockwise or counter-clockwise rotation of the plugs. |
051827638 | claims | 1. An X-ray exposure apparatus, comprising: an X-ray source; and an illumination system for illuminating a mask pattern with X-rays from said X-ray source to expose a wafer to the mask pattern; wherein said illumination system includes a reflection mirror for reflecting the X-rays from said X-ray source to produce a reflection beam and a driving device for swinging said reflection mirror; wherein said reflection mirror has a reflection surface disposed so that the X-rays are grazingly inputted thereto; wherein said reflection surface has a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam; wherein each layer of said multilayered film of said reflection mirror has a thickness which gradually increases with an increase in a distance from said radiation beam in a plane of incidence of the X-rays; and wherein said driving device swings said reflection mirror so as to shift a position and an angle of incidence of the X-rays upon said reflection mirror in the plane of incidence, to thereby scanningly deflect the reflection beam to scan the mask pattern with the deflected reflection beam. said movable mirror has a multilayered film effective to provide an increased relative reflectivity of a predetermined wavelength of the reflection beam, wherein each layer of said multilayered film has a thickness which changes with position so as to substantially avoid a shift of said wavelength with the shift in the angle of incidence of the radiation beam. a radiation source; a reflection mirror for reflecting a radiation beam from said radiation source to produce a reflection beam, said reflection mirror having a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam, wherein a layer of said multilayered film has a thickness which gradually increases with an increase in a distance from said radiation source in a plane of incidence of the radiation beam; and a driving device for swinging said reflection mirror so as to shift a position and an angle of incidence of the radiation beam upon said reflection mirror, in the plane of incidence of the radiation beam, to thereby scanningly deflect the reflection beam. an X-ray source; and an illumination system for illuminating a mask pattern with X-rays from said X-ray source to expose a wafer to the mask pattern; wherein said illumination system includes a reflection mirror for reflecting the X-rays from said X-ray source to produce a reflection beam and a driving device for swinging said reflection mirror; wherein said reflection mirror has a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam; wherein each layer of said multilayered film of said reflection mirror has a thickness which gradually increases with an increase in a distance from said X-ray source in a plane of incidence of the X-rays; and wherein said driving device swings said reflection mirror so as to shift a position and an angle of incidence of the X-rays upon said reflection mirror in the plane of incidence, to thereby scanningly deflect the reflection beam to scan the mask pattern with the deflected reflection beam. a radiation source; a reflection mirror for reflecting a radiation beam from said radiation source to produce a reflection beam, said reflection mirror being disposed so that the radiation beam is grazingly inputted thereto, and said reflection mirror having a multilayered film effective to provide an increased relative reflectivity with respect to a predetermined wavelength of the reflection beam, wherein each layer of said multilayered film has a thickness which increases with an increase in a distance from said radiation source in a plane of incidence of the radiation beam; and a driving device for swinging said reflection mirror so as to shift a position and an angle of incidence of the radiation beam upon said reflection mirror, in the plane of incidence of the radiation beam, to thereby scanningly deflect the reflection beam. mask holding means for holding the mask; wafer holding means for holding the wafer; and an illumination system for illuminating a circuit pattern of the mask with the radiation beam from said radiation source to thereby expose the wafer to the circuit pattern of the mask with the radiation beam, said illumination system comprising a scanning mirror for reflecting the radiation beam to the mask, said scanning mirror having a multilayered film formed thereon and being movable to change the position and angle of incidence of the radiation beam upon said scanning mirror, wherein said multilayered film of said scanning mirror provides increased reflectivity to a portion of the radiation beam having a particular wavelength and wherein each layer of said multilayered film has a thickness which changes with the position thereon so as to substantially compensate for a change in the particular wavelength resulting from a change in the angle of incidence of the radiation beam. mask holding means for holding the mask; wafer holding means for holding the wafer; and an illumination system for illuminating a circuit pattern of the mask with the radiation beam from said X-ray source to thereby expose the wafer to the circuit pattern of the mask with the radiation beam, said illumination system comprising a scanning mirror for reflecting the radiation beam to the mask, said scanning mirror having a multilayered film formed thereon and being movable along a plane of incidence of the radiation beam to change the position and angle of incidence of the radiation beam upon said scanning mirror, wherein said multilayered film of said scanning mirror provides an increased reflectivity to a portion of the radiation beam having a particular wavelength and wherein each layer of said multilayered film has a thickness which gradually increases along the plane of incidence and in a direction from said X-ray source to the mask so as to substantially compensate for any change in the particular wavelength resulting from a change in the angle of incidence of the radiation beam. moving the scanning mirror to change the position and angle of incidence of the radiation beam upon the scanning mirror; providing a multilayered film on the scanning mirror for increased reflectivity with respect to a particular wavelength component of the radiation beam; and providing each layer of the multilayered film with a thickness which changes with the position thereon so as to substantially compensate for any change in the particular wavelength resulting from a change in the angle of incidence of the radiation beam. 2. A reflection device including a movable mirror for reflecting a received radiation beam to produce a reflection beam, wherein said movable mirror is so moved that, with respect to a plane of incidence of the radiation beam, a position and an angle of incidence of the radiation beam are shifted with the movement of said movable mirror, characterized in that: 3. A scanning system, comprising: 4. A scanning system according to claim 3, wherein said reflection mirror is disposed so that the radiation beam from said radiation source is grazingly inputted to said reflection mirror. 5. A scanning system according to claim 3, wherein said reflection mirror has a flat reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 6. A scanning system according to claim 4, wherein said reflection mirror has a flat reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 7. A scanning system according to claim 3, wherein said reflection mirror has a convex reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 8. A scanning system according to claim 4, wherein said reflection mirror has a convex reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 9. A scanning system according to claim 3, wherein said reflection mirror has a convex reflection surface and wherein said driving device oscillatingly moves said reflection mirror rectilinearly in a direction traversing the radiation beam. 10. A scanning system according to claim 4, wherein said reflection mirror has a convex reflection surface and wherein said driving device oscillatingly moves said reflection mirror rectilinearly in a direction traversing the radiation beam. 11. An X-ray exposure apparatus, comprising: 12. An apparatus according to claim 11, wherein said reflection mirror is disposed so that the X-rays from said X-ray source are grazingly inputted to said reflection mirror. 13. An apparatus according to claim 11, wherein said reflection mirror has a flat reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 14. An apparatus according to claim 12, wherein said reflection mirror has a flat reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 15. An apparatus according to claim 11, wherein said reflection mirror has a convex reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 16. An apparatus according to claim 12, wherein said reflection mirror has a convex reflection surface and wherein said driving device rotationally moves said reflection mirror through a rotational shaft spaced from said reflection surface. 17. An exposure apparatus according to claim 11, wherein said reflection mirror has a convex reflection surface and wherein said driving device oscillatingly moves said reflection mirror rectilinearly in a direction traversing the X-rays. 18. An exposure apparatus according to claim 12, wherein said reflection mirror has a convex reflection surface and wherein said driving device oscillatingly moves said reflection mirror rectilinearly in a direction traversing the X-rays. 19. A scanning system, comprising: 20. An exposure apparatus for exposing a wafer to a mask with a radiation beam from a radiation source, said apparatus comprising: 21. An apparatus according to claim 20, wherein said radiation source comprises an X-ray source. 22. An apparatus according to claim 21, wherein said scanning mirror has a flat reflection surface for reflecting the radiation beam, and wherein said scanning mirror is swingingly movable to change the position and angle of incidence of the radiation beam upon the flat reflection surface. 23. An apparatus according to claim 21, wherein said scanning mirror has a reflection surface of convex shape for reflecting the radiation beam, and wherein said scanning mirror is swingingly movable to change the position and angle of incidence of the radiation beam upon the reflection surface. 24. An apparatus according to claim 21, wherein said scanning mirror has a reflection surface of convex shape for reflecting the radiation beam, and wherein said scanning mirror is rectilinearly movable to change the position and angle of incidence of the radiation beam upon the flat reflection surface. 25. An apparatus according to claim 20, wherein the radiation beam from said radiation source is projected obliquely upon said scanning mirror and wherein said scanning mirror is movable along a plane of incidence of the radiation beam. 26. An X-ray exposure apparatus for exposing a wafer to a mask with a radiation beam from an X-ray source, said apparatus comprising: 27. An apparatus according to claim 26, wherein said scanning mirror has a flat reflection surface for reflecting the radiation beam, and wherein said scanning mirror is swingingly movable to change the position and angle of incidence of the radiation beam upon the flat reflection surface. 28. An apparatus according to claim 26, wherein said scanning mirror has a reflection surface of convex shape for reflecting the radiation beam, and wherein said scanning mirror is swingingly movable to change the position and angle of incidence of the radiation beam upon the reflection surface. 29. An apparatus according to claim 26, wherein said scanning mirror has a reflection surface of convex shape for reflecting the radiation beam, and wherein said scanning mirror is rectilinearly movable to change the position and angle of incidence of the radiation beam upon the flat reflection surface. 30. In a semiconductor device manufacturing method wherein a mask is scanningly illuminated with a radiation beam emanating from a radiation source and reflected by a scanning mirror to print a circuit pattern of the mask on a wafer with the radiation beam, the improvement comprising: 31. A method according to claim 30, further comprising providing the scanning mirror with a flat reflection surface. 32. A method according to claim 30, further comprising providing the scanning mirror with a reflection surface of convex shape. |
06236698& | abstract | A nuclear reactor instrumentation system including a plurality of in core nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core. The income nuclear instrumentation assemblies each include a fixed type neutron detector assembly having a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly having a plurality of fixed type gamma ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors. A power range detector signal processing device is operatively connected to the fixed type neutron detector assemblies through signal cables. A gamma thermometer signal processing device is operatively connected to the fixed type gamma thermometer assembly of the in core nuclear instrumentation assembly through a signal cable. |
054835712 | abstract | A method for the x-ray inspection of materials making use of the Moire effect is described. The Moire effect results when two patterns are superimposed, a third pattern is produced. Any change in either of the first two patterns creates a change in the third. Moire inspection is common with visible light, this invention allows the technique to be extended to locations inaccessible to visual inspection. A first pattern of high radio contrast material is attached to or included in the sample. X-rays are projected through the sample. A second pattern is imposed at the observation point, either before or after the formation of the x-ray image. The two patterns interact to create a third, Moire, pattern. As the material is stressed the Moire pattern changes, the degree of change indicating the degree of stress. |
048760617 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite of FIGS. 1A And 1B (referred to hereinafter as FIG. 1) is an elevational view, partly in cross-section, of a pressurized water reactor 10 comprising a pressure vessel 12 including an upper dome, or head assembly, 12a, cylindrical sidewalls 12b, and a bottom closure 12c comprising the base of the reactor 10. Plural radially oriented inlet nozzles 11 and outlet nozzles 13 (only one (1) of each appearing in FIG. 1) are formed in the sidewall 12b, adjacent the upper, annular end surface 12d of the sidewall 12b. Whereas the cylindrical sidewall 12b may be integrally joined, as by welding, to the bottom closure 12c, the head assembly 12a is removably received on the upper, annular end surface 12d of the sidewall 12b and secured thereto. The sidewall 12b further defines an inner, generally annular mounting ledge 12e for supporting various internal structures as later described. Within the bottom closure 12c, as schematically indicated, is so-called bottom-mounted instrumentation 14. The lower barrel assembly 16 comprises a generally cylindrical sidewall 17, affixed at its lower end to a lower core plate 18, which is received on mounting support 18b, as generally schematically illustrated. The cylindrical sidewall 17 extends substantially throughout the axial height of the vessel 12 and includes an annular mounting ring 17a at the upper end thereof which is received on the annular mounting ledge 12e thereby to support the assembly 16 within the vessel 12. As will be rendered more apparent hereafter, the sidewall 17 is solid in the vicinity of the inlet nozzles 11, but includes an aperture 17b having a nozzle ring 17c mounted therein which is aligned with and closely adjacent to the outlet nozzle 13, for each such nozzle. An upper core plate 19 is supported on a mounting support 17d affixed to the interior surface of the cylindrical sidewall 17 at a position approximately one-half the axial height thereof. Fuel rod assemblies 20 are positioned in generally vertically oriented, parallel axial relationship within the lower barrel assembly 16 by bottom mounts 22 carried by the lower core plate 18 and by pinlike mounts 23 carried by, and extending through, the upper core plate 19. Flow holes 18a and 19a (only two of which are shown in each instance) are provided in predetermined patterns, extending substantially throughout the areas of the lower and upper core plates 18 and 19, respectively. The flow holes 18a permit passage of a reactor coolant fluid into the lower barrel assembly 16 in heat exchange relationship with the fuel rod assemblies 20, which comprise the reactor core, and the flow holes 19a permit passage of the core output flow into the inner barrel assembly 24. A neutron reflector and shield 21 is mounted interiorly of the cylindrical sidewalls 17, in conventional fashion. The inner barrel assembly 24 includes a cylindrical sidewall 26 which is integrally joined at its lower edge to the upper core plate, 19. The sidewall 26 has secured to its upper, open end, an annular mounting ring 26a which is received on an annular hold-down spring 27 and supported along with the mounting ring 17a on the mounting ledge 12e. The sidewall 26 further includes an aperture 26b aligned with the aperture 17b and the output nozzle 13. Within the inner barrel assembly 24, and densely packed within the cylindrical sidewall 26, are positioned a plurality of rod guides in closely spaced, parallel axial relationship; for simplicity of illustration, only two such rod guides are shown in FIG. 1, namely rod guide 28 housing a cluster 30 of radiation control rods (RCC) and a rod guide 32 housing a cluster 34 of water displacement rods (WDRC). The rods of each RCC cluster 30 and of each WDRC cluster 34 are mounted individually to respectively corresponding spiders 100 and 120. Mounting means 36 and 37 are provided at the respective upper and lower ends of the RCC rod guide 28 and, correspondingly, mounting means 38 and 39 are provided at the respective upper and lower ends of the WDRC rod guide 32. The lower end mounting means 37 and 39 rigidly mount the respective rod guides 28 and 32 to the upper core plate 19, as illustrated for the RCC rod guide mounting means by bolt 37'. The upper mounting means 36 and 38 mount the respective rod guides 28 and 32 to a calandria assembly 50, and particularly to a lower calandria plate 52. The calandria assembly 50, in more detail, comprises a generally cylindrical, flanged shell 150 formed of a composite of the flange 50a, an upper connecting cylinder 152 which is welded at its upper and lower edges to the flange 50a and to the upper calandria plate 54, respectively, and a lower connecting cylinder, or skirt, 154 which is welded at its upper and lower edges to the upper and lower calandria plates 54 and 52, respectively. The lower connecting cylinder, or skirt, 154 includes an opening 154a aligned with each of the outlet nozzles 13 such that the axial core outlet flow received within the calandria 52 through the openings 52a in the lower calandria plate 52 may turn through 90.degree. and exit radially from within the calandria 52 through the opening 154a to the outlet nozzle 13. The annular flange 50a is received on the flange 26a to support the calandria assembly 50 on the mounting ledge 12e. Plural, parallel axial calandria tubes 56 and 57 are positioned in alignment with corresponding apertures in the lower and upper calandria plates 53 and 54, to which the calandria tubes 56 and 57 are mounted at their respective, opposite ends. Extending upwardly beyond the upper calandria plate 54 and, more particularly, within the head assembly 12a of the vessel 12, there are provided plural flow shrouds 60 and 61 respectively aligned with and connected to the plural calandria tubes 56 and 57. A corresponding plurality of head extensions 62 and 63 is aligned with the plurality of flow shrouds 60, 61, the respective lower ends 62a and 63a being flared, or bell-shaped, so as to facilitate assembly procedures and, particularly, to guide the drive rods (not shown in FIG. 1) into the head extensions 62, 63 as the head assembly 12a is lowered onto the mating annular end surface 12d of the vessel sidewall 12b. The flared ends 62a, 63a also receive therein the corresponding upper ends 60a, 61a of the flow shrouds 60, 61 in the completed assembly, as seen in FIG. 1. The head extensions 62, 63 pass through the upper wall portion of the head assembly 12a and are sealed thereto. Control rod cluster (RCC) displacement mechanisms 64 and water displacement rod cluster (WDRC) displacement mechanisms 66 are associated with the respective head extensions 62, 63 flow shrouds 60, 61 and calandria tubes 56, 57 which, in turn, are associated with respective clusters of radiation control rods 30 and water displacement rods 34. The RCC displacement mechanisms (CRDM's) 64 may be of well known type, as are and have been employed with conventional reactor vessels. The displacement mechanisms (DRDM's) 66 for the water displacement rod clusters (WDRC's) 34 may be in accordance with the disclosure of U.S. Pat. No. 4,439,054-Veronesi, assigned to the common assignee hereof. The respective drive rods (not shown in FIGS. 1A and 1B) associated with the CRDM's 64 and the DRDM's 66 are structurally and functionally the equivalent of elongated, rigid rods extending from the respective CRDM's 64 and DRDM's 66 to the respective clusters of radiation control rods (RCC's) 30 and water displacement rods (WDRC's) 34, and are connected at their lower ends to the spiders 100 and 120 Apertures 58 and 59 in the lower calandria plate accommodate the corresponding drive rods. The CRDM's and DRDM's 64 and 66 thus function through the corresponding drive rods to control the respective vertical positions of, and particularly, selectively to lower and/or raise, the RCC's 30 and the WDRC's 34 through corresponding openings (not shown) provided therefore in the upper core plate 19, telescopingly into or out of surrounding relationship with the respectively associated fuel rod assemblies 20. In this regard, the interior height D.sub.1 of the lower barrel assembly 16 is approximately 178 inches, and the active length D.sub.2 of the fuel rod assemblies 20 is approximately 153 inches. The interior, axial height D.sub.3 is approximately 176 inches, and the extent of travel, D.sub.4, of the rod clusters 30 and 34 is approximately 149 inches. It follows that the extent of travel of the corresponding CRDM and DRDM drive rods is likewise approximately 149 inches. While the particular control function is not relevant to the present invention, insofar as the specific control over the reaction within the core is effected by the selective positioning of the respective rod clusters 30 and 34, it is believed that those skilled in the art will appreciate that moderation or control of the reaction is accomplished in accordance with the extent to which the control rod clusters 30 are inserted into or withdrawn from the core and with the effective water displacement which is achieved by selective positioning of the water displacement rod clusters 34. The flow of the reactor coolant fluid, or water, through the vessel 10 proceeds, generally, radially inwardly through a plurality of inlet nozzles 11, one of which is seen in FIG. 1, and downwardly through the annular chamber 15 which is defined by the generally cylindrical interior surface of the cylindrical side wall 12b of the vessel 12 and the generally cylindrical exterior surface of the sidewall 17 of the lower barrel assembly 16. The flow then reverses direction and passes axially upwardly through flow holes 18a in the lower core plate 18 and into the lower barrel assembly 16, from which it exits through a plurality of flow holes 19a in the upper core plate 19 to pass into the inner barrel assembly 24, continuing in parallel axial flow therethrough and finally exiting upwardly through flow holes 52a in the lower calandria plate 52. Thus, parallel axial flow conditions are maintained through both the lower and inner barrel assemblies 16 and 24. Within the calandria 50, the flow in general turns through 90.degree. to exit radially from a plurality of outlet nozzles 13 (one of which is shown in FIG. 1). The inlet coolant flow also proceeds into the interior region of the head assembly 12a through perimeter bypass passageways in the mounting flanges received on the ledge 12e. Particularly, a plurality of holes 170, angularly spaced and at a common radius, are formed in the flange 17a and provide axially-directed flow paths from the annular chamber 15 into the annular space 172 intermediate the spring 27 and the interior surfaces of the sidewalls of the vessel 12; further, a plurality of aligned holes 174 and 176 extend through the flanges 26a and 50a, the holes 174 being angularly oriented, to complete the flow paths from the annular space 172 to the interior of the head assembly 12a. The flow of coolant proceeds from the head region through annular downcomer flow paths defined interiorly of certain of the flow shrouds 60, 61 and calandria tubes 56, 57, as later described, from which the head coolant flow exits into the top region of the inner barrel assembly 24, just below the lower calandria plate 52, to mix with the core outlet flow and pass through the calandria 50, exiting from the outlet nozzles 13. FIG. 2 is a bottom plan view of the resiliently loaded, top end lateral support in accordance with the present invention, taken along the line 2--2 in FIG. 1 and thus showing, in crosssection, an upper end portion of a WDRC rod guide 32 and a bottom plan view of the associated top end lateral support 38. The resiliently loaded, top end lateral support 38 furthermore will be described with concurrent reference to FIGS. 3 and 4, which respectively comprise simplified, or schematic, cross-sectional elevational views taken along the line 3--3 in FIG. 2 and respectively showing the lateral support of the invention in the engaged and disengaged relationships, as between the calandria bottom plate 52 and the lateral support 38 of a WDRC rod guide 32. It will be understood that the lateral support 38 of the present invention, in each of its various embodiments disclosed herein, is not restricted for use with the WDRC rod guides 32 but instead may be employed with the top end support 36 of an RCC rod guide 28. The WDRC rod guide 32, throughout substantially its entire axial length, comprises a relatively thin metal sidewall 70 of generally square cross-sectional configuration which carries, at its upper extremity, a reinforced, generally coaxial sleeve 72 having an outer, generally square cross-sectional configuration corresponding to the outer perimeter of the thin sidewall 70. The sleeve 72 is permanently joined, such as by welding, at its bottom end to the top end of the thin sidewall 70 at their respective, common outer perimeters. The sleeve 72 is machined to define a generally cylindrical interior sidewall 72' and, further, to define arcuate recesses 72" which are in alignment with the outer portion of respectively corresponding openings 52a in the lower calandria plate 52 so as to maintain non-obstructed flow holes 100. In accordance with the invention, a cylindrical mount 80 having a central aperture 81 therethrough is positioned on the lower calandria plate 52 with the aperture 81 thereof in alignment with a corresponding aperture 59 in the lower calandria plate 52. The mount 80 furthermore includes an annular extension 82 which is received in a corresponding annular recess 59a in the lower surface of the lower calandria plate 52, which affords lateral locking of the cylindrical mount 80 to the lower calandria plate 52. Bolts 83 (FIG. 2) are received through suitable countersunk bores 84 and threaded holes (not shown) provided in the lower calandria plate 52, for securing the cylindrical mount 80 to the latter. Preferably, the mount 80 is machined to define mounting segments 85 of reduced vertical thickness in which the countersunk bores 84 are formed. There are thus defined integral, equiangularly spaced arms 86, each arm 86 further being defined by a pair of vertical sidewalls 87a, 87b. Pivotal links 88, shown schematically in FIG. 2, and which may have any of various configurations as illustrated hereinafter, are pivotally secured at their first ends in corresponding mounting sockets 90 in the integral arms 86 and are releasably engaged at their opposite, free ends in receiving sockets 92 formed in the upper, inner portions of the sleeve 72. As best seen in FIG. 3, each of the mounting sockets 90 includes an open channel portion 90a and a socket portion 90b corresponding in configuration and dimensions to that of the first end 88a of the link 88. Particularly, the first end 88a and the socket portion 90b have mating, generally cylindrical surfaces, the socket portion 90b encompassing an arc greater than 180.degree. so as to retain the first end 88a of the pivotal link 88 therein while permitting limited pivotal movement of the link 88 through an arc, or angle, defined by the channel 90a. With reference to FIG. 2, it will be understood that the socket portion 90b is machined through the full width of the corresponding integral arm 86 and thus is open, or accessible, at the sidewalls 87a and 87b to permit sliding the first end 88a of the pivotal link 88 into the socket portion 90b. Further, an annular groove 89 is formed in the surface of the socket portion 90b, midway of the axial length thereof, and a hole 91a is formed so as to extend through the integral arm 86, perpendicular to the axis of rotation of the first end 88a of the pivotal link 88 and so as to intersect the annular groove 89, and a pin 91b is inserted through the hole and passes tangentially through the annular groove 89 for axially locking the first end 88a within the mounting socket 90, while permitting free pivotal movement thereof. The receiving sockets 92 likewise have a mating configuration with respect to the second, free ends 88b of the corresponding links 88, but surround the latter through an angular extent of less than 180.degree. such that the second, free ends 88b are releasably engaged thereby. The links 88 are of sufficient width (in the plane of FIG. 2) and thickness (in the plane of FIG. 3) so as to afford sufficient strength and stability so as to maintain a relative non-rotational and centered relationship between the cylindrical mount 80 and the sleeve 72, as now more fully described FIG. 3, as before noted, illustrates the installed position of the calandria 50, and more particularly the lower calandria plate 52, with respect to the sleeve 72 of a representative WDRC rod guide 32 FIG. 4, on the other hand, indicates an interim step in the installation of the calandria assembly 50, and more particularly of the lower calandria plate 52 relative to the sleeve 72, the arrow A indicating the direction of movement for installation of the calandria 50. In the position shown in FIG. 4, the links 88 have pivoted downwardly by force of gravity, to the extent permitted by the channels 90a of the mounting sockets 90, to disengaged positions at which the second, free ends 88b of the links 88 have rotated axially inwardly to retracted positions in alignment with the ledges 94. As the calandria 50 is lowered further in the direction of arrow A, the links 88 engage the aligned ledges 94 and are rotated, or pivoted, upwardly thereby in the direction indicated by arrows B and thus move radially outwardly, travelling along the ledges 94, toward the receiving sockets 92. In the fully installed position of the calandria 50, shown in FIG. 3, the respective axes of the link ends 88a and 88b and of the sockets 90 and 92 are in substantially a common horizontal plane. The links 88 preferably are bowed upwardly in a central portion 88c, intermediate the ends 88a and 88b; further, they are of sufficient flexibility in a radial direction as to be compressed in the fully installed position of FIG. 3, and thereby loading of the sleeve 72 relative to the fixed mount to prevent lateral motion of the sleeve 72 and its associated rod guide. On the other hand, vertical motion due to axial growth and axially directed vibrations is accommodated by the pivoting movement of the links 88 which remains, even in the engaged position of FIG. 3. It will be appreciated that removal of the calandria is equally simple, merely requiring that the calandria 50 be lifted. This causes the links to pivot, or rotate downwardly relative to the cylindrical mount 80 by force of gravity, whereby the second, free ends 88b thereof move radially inwardly, thereby being released from the engaged positions within the receiving sockets 92, to the disengaged and retracted positions shown in FIG. 4. Several alternative embodiments of the pivotal links are possible, and all thereof fall within the scope of the invention. Examples thereof are set forth in the following FIGS. 5 through 8, each of which comprises a fragmentary and simplified, cross-sectional elevational view; in each of FIGS. 5 through 7, the engaged position of the links, as in FIG. 3 hereof, is shown in solid lines and the disengaged or retracted position of the links, as in FIG. 4, is shown in phantom lines. Corresponding elements in the successive FIGS. 5 through 8 are identified by corresponding, but respectively succeeding "100's" digits, i.e., "100," "200,". In FIG. 5, accordingly, the cylindrical mount 180 is attached to the lower calandria plate 52 with the respective central apertures 181 and 159 thereof in alignment. An annular extension 182 of the mount 180 is received in an annular recess 159a. The link 188 includes a first end 188a pivotally mounted within the socket portion 190b of mounting socket 190. The link 188 of FIG. 5 differs from the link 88 of FIGS. 3 and 4, in that the central portion 188c thereof is "U-shaped", thereby to afford the required lateral resiliency. This configuration permits the legs 188d and 188e to assume a flat profile, as contrasted to the bowed profile of the central portion 88c of the links 88 of FIG. 3. As also is apparent in FIG. 5, the cylindrical mount 180 may be of substantially the same outer diameter as the interior diameter of the sleeve 172, such that the respective, contiguous cylindrical surfaces 180a and 172a thereof are in close proximity. The flat configuration of the link 188 facilitates this configuration of the cylindrical mount 180 Should transverse, or lateral, forces exceed the resilient loading force of the links 188, the surface 180a of the cylindrical mount 180 serves as an abutment stop, against excessive, or extreme, lateral displacement of the sleeve 172 Conversely, these surfaces 180a and 172a are normally separated and in spaced, concentric relationship due to the resilient loading force of the links 188, such that abrasion and wear concerns are effectively eliminated. As also seen in FIG. 5, the sleeve 172 includes a ledge 194 and a receiving socket 192 in which the free end 188b of the illustrative link 188 is received, in its engaged position. The disengaged position of link 188 is illustrated in phantom lines in FIG. 5, the free end 188b being shown as resting on the ledge 194 of the sleeve 172. The embodiment of FIG. 5 has the same functional operation with regard to the pivotal movement of the link 188 between the engaged and disengaged positions and correspondingly during installation or removal of the calandria assembly, as described in relation to FIGS. 3 and 4. FIG. 6 illustrates a third embodiment of the present invention which affords the same functional characteristics as the previously discussed embodiments, but in which the link 288 is formed of a flexible material which permits the pivotal action described for the links of the prior embodiments. More particularly, the first end 288a of the link 288 is clamped securely to the cylindrical mount 280 by a bolt 283 which commonly secures, therefore, both the link 288 and the mount 280 to the lower calandria plate 52. The second, free end 288b similarly is received on the ledge 294 of the sleeve 272 during installation of the calandria 50. As that installation continues, the link 288 is caused to flex in the region adjacent the mount 280 to a more generally horizontal orientation in the completely installed position of the calandria 50, and in which position the free end 288b is received in the receiving socket 292 in accordance with the solid line positions of those elements. During removal of the calandria 50, the link 288 returns to its normal, downwardly pivoted and radially retracted position shown in phantom lines. FIG. 7 illustrates yet another embodiment of the present invention, which combines several features of the embodiments of FIGS. 3, 4 and 5. Specifically, the cylindrical mount 380 is secured to the lower calandria plate 52 with the respective central apertures 381 and 359 thereof in alignment, an annular extension 382 being received in a mating annular recess 359a in the lower calandria plate 52. The cylindrical mount 380, as in the case of FIG. 5, is of sufficient radial extent so as to dispose its outer cylindrical surface 380a immediately adjacent the inner cylindrical surface 372a of the sleeve 372, thereby to function as a rigid abutment limiting the extent of lateral movement of the sleeve 372 and its associated rod guide Link 388 may correspond substantially to link 88 of FIGS. 3 and 4, the cylindrical mount 380 being configured to afford sufficient clearance to accommodate the bowed central portion of link 388 in the installed position shown in solid lines, link 388 being under compression in that installed position as before described. The first and second ends 388a and 388b of the link 388 correspondingly are pivotally mounted in the socket portion 390b of the mounting socket 390 and releasably received and engaged in the receiving socket 392. In the downwardly pivoted position of link 388, as shown in dotted lines, the has rotated downwardly and inwardly and the free end 388b thereof has engaged ledge 394. Lip 390a of the socket 390 limits the extent of the downward, rotary or pivotal movement of the link 388. Yet another embodiment of the invention is shown in FIG. 8 which combines features of the structures of FIGS. 5 and 7 and an alternative structural provision to flexibly restrain relative lateral movement between the mount 480 and the associated sleeve 472. Again, the cylindrical mount 80 is secured to the calandria 52 with the respective central apertures 481 and 459 in alignment. Likewise, an annular extension 482a is received in the annular recess 459a. Similarly to FIGS. 5 and 7, the cylindrical mount 480 extends radially outwardly a sufficient distance so as to dispose its outer cylindrical surface 480a in close proximity to the inner cylindrical surface 472a of the sleeve 472. Link 488 is pivotally mounted at its first end 488a in the corresponding mounting socket 490b, for limited pivotal movement as defined by the channel 490a. The second, free end 488b is releasably received and engaged in the corresponding socket 492 of the sleeve 472 in the engaged position of link 88, as shown in solid lines, and travels along the ledge 494 during the installation and removal of the calandria assembly 50. Due to the relatively flat or generally straight, radial configuration of the link 488, link 488 offers little if any resiliency in the lateral, or radial direction. Instead, to provide the desired lateral, resilient loading in the embodiment of FIG. 8, a portion of the sleeve 472 is cut along a top horizontal line shown at 473, and downwardly along two slots extending from the horizontal slot 473 to an integral, resilient hinge 474, and the exterior surface therebetween is machined to a planar surface 476, thereby to define an integral leaf spring 475. The spring 475 is slightly, resiliently deflected by the relatively rigid link 488 when pivoted to the installed position of the calandria 50 as illustrated in FIG. 8. Although not shown in FIG. 8, it readily will be appreciated that upon removal of the calandria 50, link 488 pivots downwardly relatively to the cylindrical mount 480 to the extent permitted by channel 490a of the mounting socket 490 and the second, free end 488b thereof thereupon is withdrawn from socket 492 and moved radially inwardly along the ledge 494, permitting the leaf spring portion 475 to resiliently return to its normal, aligned position with the remainder of the sleeve 472. As in the case of the embodiments of FIGS. 5 and 7, the closely spaced, adjacent surfaces 480a of the cylindrical mount 480 and 472a of the sleeve 472 are protected from abrasion during normal operation by the resilient lateral loading afforded through engagement of the links 488 with the leaf springs 475, but serve under excessive lateral loads as a rigid abutment, limiting any excessive lateral movement of the sleeve 472. Numerous modifications and adaptations of the lateral support of the invention will be apparent to those of skill in the art, and thus it is intended by the appended claims to encompass all such modifications and adaptations which fall within the true spirit and scope of the invention. |
description | This Application is a divisional of application Ser. No. 11/781,043, filed Jul. 20, 2007, which application claims the benefit and priority under 35 U.S.C. 119(e) from U.S. Provisional Application No. 60/820,064, filed Jul. 21, 2006 and entitled “Lithography Aware Leakage and Timing Analysis,” the entire disclosure of which is hereby incorporated by reference for all purposes. The present invention relates to the field of electronic design automation. More specifically, the present invention relates to electronic design automation including lithography aware leakage and timing analysis. Leakage has become a primary concern in the consumption of power in semiconductor chips. Timing also is a concern because it drives the capability of the circuitry to make the calculations rapidly enough to meet customer's requirements. Historically power and timing were deterministically calculated often considering worst case analysis. Over time it has become obvious that deterministic calculation results in insufficient yield, especially as each individual circuit component is considered from a worst case perspective. Instead, statistical analysis may be used, realizing that a range of operation distribution exists for which most of the distribution well meets customer requirements. This statistical analysis has come to be used on both timing analysis and more recently on leakage analysis. Leakage is a function of the overall transistor gate width in a given circuit. Low threshold voltage FETs have significantly higher leakage and correspondingly higher performance. For multi-threshold voltage processes there are typically two levels. A low threshold (VT) device for high performance and a normal threshold device for lower power and lower performance. By selectively utilizing low threshold devices only where needed, the performance requirement is met while keeping the power consumption relatively low. One method to approximate leakage current which will be utilized by the chip is by totaling the cumulative FET gate width for each threshold device. There are systematic variations and random variations which affect timing and power. An example of a systematic variation would be lithography defocus since this is a controllable parameter that affects the entire chip. A random variation would be due to a change in the number of dopant molecules since these can vary on a transistor by transistor basis. These variations impact the overall design and can be used statistically to tune the design to meet timing and leakage requirements. Accordingly, what is desired are improved methods and apparatus for solving the problems discussed above. Additionally, what is desired are improved methods and apparatus for reducing some of the drawbacks discussed above. The present invention relates to providing electronic design automation with lithographic aware leakage and timing analysis. In various embodiments, a method for performing leakage calculations includes receiving information specifying an integrated circuit. A neighborhood of shapes associated with the integrated circuit is determined. Leakage information associated with the integrated circuit is generated based on the neighborhood of shapes. Determining the neighborhood of shapes may include determining a first set of spacings to a boundary of a first cell from an internal shape. A second set of spacings may be determined from the boundary of the first cell to a shape of a second cell. A lithography process may be characterized using the first and second set of spacings. In some embodiments, characterizing the lithography process may include characterizing effective transistor channel lengths as a function of the first and second set of spacings. A mapping may be generated from the first and second set of spacings to the lithography process. A mapping may be generated from the first and second set of spacings to leakage. Leakage of the first cell may be calculated based on the first and second set of spacing. The internal shape may include a polysilicon transistor shape. The internal shape may also include a wiring shape. In one embodiment, a computer program product is stored on a computer readable medium for performing leakage calculations. The computer program product includes code for receiving information specifying an integrated circuit, code for determining a neighborhood of shapes associated with the integrated circuit, and code for generating leakage information associated with the integrated circuit based on the neighborhood of shapes. In a further embodiment, a system for performing leakage calculations includes a processor and a memory. The memory is coupled to the processor and stores a set of instructions which when executed by the processor cause the processor to receive information specifying an integrated circuit, determine a neighborhood of shapes associated with the integrated circuit, and generate leakage information associated with the integrated circuit based on the neighborhood of shapes. In various embodiments, a method for performing delay calculations includes receiving information specifying an integrated circuit. A neighborhood of shapes associated with the integrated circuit is determined. Delay information associated with the integrated circuit is generated based on the neighborhood of shapes. Determining the neighborhood of shapes may include determining a first set of spacings to a boundary of a first cell from an internal shape. A second set of spacings may be determined from the boundary of the first cell to a shape of a second cell. A lithography process may be characterized using the first and second set of spacings. In some embodiments, characterizing the lithography process may include characterizing effective transistor channel lengths as a function of the first and second set of spacings. A mapping may be generated from the first and second set of spacings to the lithography process. A mapping may be generated from the first and second set of spacings to delay. Delay of the first cell may be calculated based on the first and second set of spacing. The internal shape may include a polysilicon transistor shape. The internal shape may also include a wiring shape. In one embodiment, a computer program product is stored on a computer readable medium for performing delay calculations. The computer program product includes code for receiving information specifying an integrated circuit, code for determining a neighborhood of shapes associated with the integrated circuit, and code for generating delay information associated with the integrated circuit based on the neighborhood of shapes. In a further embodiment, a system for performing delay calculations includes a processor and a memory. The memory is coupled to the processor and stores a set of instructions which when executed by the processor cause the processor to receive information specifying an integrated circuit, determine a neighborhood of shapes associated with the integrated circuit, and generate delay information associated with the integrated circuit based on the neighborhood of shapes. In various embodiments, a method for calculating neighborhood spacings includes receiving information specifying a plurality of cells. A first set of spacings from a first shape associated with a first cell to a boundary associated with the first cell is determined. A second set of spacings from the boundary to a second shape associated with a second cell is determined. A neighborhood of shapes is generated based on the first and second set of spacings. In one embodiment, a computer program product is stored on a computer readable medium for calculating neighborhood spacings. The computer program product includes code for receiving information specifying a plurality of cells, code for determining a first set of spacings from a first shape associated with a first cell to a boundary associated with the first cell, code for determining a second set of spacings from the boundary to a second shape associated with a second cell, and code for generating a neighborhood of shapes based on the first and second set of spacings. In various embodiments, a method for determining circuit performance includes receiving information specifying an integrated circuit. A neighborhood of shapes of a plurality of cells associated with the integrated circuit is determined. A first set of spacings to a boundary of at least one of the cells from an internal shape is determined. A second set of spacings from the boundary the cell to a shape associated with at least one of the plurality of cells is determined. A lithography process is characterized using the first and second set of spacings. A mapping is generated from the first and second set of spacings to leakage. Leakage of the cells is calculated based on the first and second set of spacings. A mapping is generated from the first and second set of spacings to delay. Delay of the cells is calculated based on the first and second set of spacings. Performance information associated with the integrated circuit is generated based on electrical connections between the cells and the calculated delays and leakages of the cells. In one embodiment, a computer program product is stored on a computer readable medium for determining circuit performance. The computer program product includes code for receiving information specifying an integrated circuit, code for determining a neighborhood of shapes of a plurality of cells associated with the integrated circuit, code for determining a first set of spacings to a boundary of at least one of the cells from an internal shape, code for determining a second set of spacings from the boundary the cell to a shape of at least one of the plurality of cells, code for characterizing a lithography process using the first and second set of spacings, code for generating a mapping from the first and second set of spacings to leakage, code for calculating leakage of the cells based on the first and second set of spacings, code for generatings a mapping from the first and second set of spacings to delay, code for calculating delay of the cells based on the first and second set of spacings, and code for generating performance information associated with the integrated circuit based on electrical connections between the cells and the calculated delays and leakages of the cells. The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. The figures and the following description relate to preferred embodiments of the present invention by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of the claimed invention. Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein. In general, Optical Proximity Correction (OPC) is a step in the manufacturing process that semiconductor manufactures employ to improve the quality of high-performance integrated circuit designs such as microprocessors. The overall lithography process involves projecting a circuit design from a mask, through a complex lens system that reduces the image onto a wafer that will later be divided into individual chips. These circuits contain tiny metal and polysilicon lines on the order of 100 nm in width, in some cases smaller than the wavelength of the light used to print them. Several problems arise from the small size of these features and the finite size and inherent limitations of the imaging system. First, the high frequency components required to reproduce the sharp edges in polygon features may fall outside the lens. Secondly, stray light entering the opening from one shape may find its way into another shape in close proximity, leading to a complex interaction of the electric fields of adjacent polygons. Thus, the final shapes will have rounded corners and may bulge towards adjacent shapes, possibly shorting together and rendering the chip defective if the situation is bad enough. Optical Proximity Correction (OPC) is the process of modifying the polygons that are drawn by the designers to compensate for the non-ideal properties of the lithography process. Given the shapes desired on the wafer, the mask is modified to improve the reproduction of the critical geometry. This is done by dividing polygon edges into small segments, moving the segments around, and by adding additional small polygons to strategic locations in the layout. The addition of OPC features to the mask layout allows for tighter design rules and significantly improves process reliability and yield. The following figures demonstrate the use of and results of OPC. FIG. 1 illustrates a view of an original desired shape of an exemplary portion of a circuit under design. This shape normally has significant shortening on its ends and rounding of its corners during fabrication. OPC adds dumbbell shapes to prevent foreshortening and narrows or widens pieces to result in the proper final shapes. FIG. 2 illustrates a view of a desired shape (dotted line) with optical proximity correction of the exemplary portion of the circuit under design of FIG. 1. The solid line formed by the outline of the shapes indicates the OPC shape to accomplish the desired final shape. FIG. 3 illustrates a view of the desired shape of FIG. 2 including a final fabricated semiconductor shape. A line 301 indicates the final fabricated shape. Without using OPC, the final shape would have looked much worse and would not have approximated the original desired shape. In various embodiments, systems and methods provide electronic design simulation using the neighborhood environment of cells of the design to determine the impact on both leakage and timing. The disclosed concept utilizes knowledge both about the individual cells and about the neighborhood around the cells and the resulting impact on the fabricated semiconductors. As discussed above, Optical proximity correction (OPC) considers the on chip shapes and the immediately adjacent shapes and corrects them to have the final fabricated shape more closely reflect the original design intent. OPC, however, is insufficient to account for defocus associated with having multiple shapes adjacent to one another. As an example, wires with different spacings have different defocus sensitivities. Likewise, effective channel lengths (Leff) depend on the number and closeness of other nearby channels. In various embodiments, an electronic design automation (EDA) system identifies distances within individual cells. The distance between a specific cell and its neighbor, along with information on that neighbor, is then factored into the leakage and timing analysis. FIG. 4 illustrates a view of a circuit under design with lithography characterization and spacing definition. A cell outline is used for a place and route (P&R) boundary 402. As illustrative examples, shapes 404-1 and 404-2 of corresponding transistors are near the boundary 402 of the cell. Because cells are typically assembled in a horizontally adjacent fashion, only this direction is described. However, the present invention is not limited to one dimension, and may include, for example, two dimensional adjacency calculations. Spacings {s} are determined. As an example of the spacing, a spacing s_ur denotes the upper-right space between polysilicon shape 406-1 defining transistor channels in the boundary 402 and adjacent polysilicon shape 408-1. Similarly, spacings s_lr, s_ul, and s_ll denote lower-right, upper-left, and lower-left spacings respectively. For clarity only two transistors 404 are shown, but the spacings s_ul and s_ll are spacings between two transistors and two polysilicon shapes that are not shown. In a two dimensional analysis, spacings for the right and left top and right and left bottom may be determined. Although the description is directed to transistors and polysilicon transistor channel shapes, the analysis may be applied to other elements, such as wiring shape. To determine the information described in FIG. 4, the distances {b} within a cell, to nearby cell boundaries 402 are also determined. FIG. 5 illustrates a view of a circuit under design showing boundary distances to the boundary 402 from within a cell. For instance, the distance b_ur denotes the distance from within the cell to the upper-right boundary, again for polysilicon shapes. Similarly distances b_lr, b_ul, and b_ll denote lower-right, upper-left, and lower-left distances respectively. This information is collected for all cells in the library. FIG. 6 illustrates a flow chart of a methodology of simulating a circuit under test using neighboring cells. The processing depicted in FIG. 6 may be performed by software modules (e.g., instructions or code) executed by a processor of a computer system, by hardware modules of the computer system, or combinations thereof. Once the internal spacings {b} and the spacings {s} to neighboring cells, for a specific design, are considered, the appropriate delay and leakage may be calculated, based on a given defocus. The methodology of this calculation is now described. Steps 602, 604, 606 and 608 are pre-characterization steps. The EDA system derives correspondence between transistor locations and transistor names in a golden netlist (step 602) as described below in conjunction with FIG. 7. This is a layout versus schematic (LVS) process. The EDA system performs a lithography simulation process using a boundary distance spacing (step 604) as described below in conjunction with FIG. 8. One example would be the characterization of effective channel lengths as a function of spacings. The EDA system characterizes boundary distances (step 606) as described below in conjunction with FIG. 9. In one embodiment delay or leakage is characterized as a function of the effective channel lengths. The EDA system then maps spacing to effective channel length and finally to delay and leakage (step 608) as described below in conjunction with FIG. 10. Step 610 is a timing and leakage analysis step. The EDA system computes timing and leakage given the channel lengths determined based on the placed cells and spacings (step 610). The steps 602, 604, 606 and 608 are now described in conjunction with FIGS. 7, 8, 9, and 10, respectively. FIG. 7 illustrates a flow chart of the deriving step 602. The result of this process is a transistor look up table that identifies location on a per cell basis. The EDA system imports a graphic design system file, such as a GDSII file, of a standard library (step 702), and imports the golden netlist for all cells as well (step 704). The EDA system determines correspondence between a transistor by name and the transistor's location in the cell (step 706). The EDA system forms a look up table (LUT) describing the locations of the transistors on a per cell basis (step 708). This transistor location look up table is used for all cells for OPC (block 710). FIG. 8 illustrates a flow chart of a lithography simulation methodology of the step 604. The resulting output is a new look up table describing the spacings based on the lithographic simulation for each cell. The EDA system runs a lithographic simulation for all transistors as a function of the spacing {s} for each cell (block 802). One embodiment characterizes the effective channel lengths versus spacing for all cells. The EDA system forms a look up table from the spacings {s} run in the lithographic simulation (block 804). The lithographic simulation look up table is formed for all cells (block 806). FIG. 9 illustrates a flow chart of the boundary distance characterization step 606 of FIG. 6. One embodiment determines the spacing from the transistor channels to the boundary of the cell. The resulting output is an enhancement to the look up table where boundary distances are included for each cell. Using the LUT from step 806, the EDA system performs a design rule check (DRC) to determine the distances {b} that represent the distances of the boundary transistors 406 to the P&R boundary 402 (step 902). The EDA system inserts the distances {b} into the lithographic simulation look up table generated in step 806 (step 904) to form an enhanced lithographic simulation look up table for all cells (step 906). FIG. 10 illustrates a flow chart of a standard cell characterization step 608 of FIG. 6. The resulting output is a library (lib) file with the delay or leakage information incorporated. The EDA system determines the Leff (step 1005) based on the spacing {s} to the surrounding structures. The change in delay or the change in leakage based on a change in Leff is determined (step 1010). The delay or leakage for each cell based on each transistor in each cell is determined based on each transistors Leff (step 1002). These Leff values are those determined based on the spacing {s}. A library file with the delay and leakage information (step 1004) is generated. The calculation of step 1002 may be accomplished by either direct calculation, where all of the combinations of four spacings are traversed. Alternatively the calculation can be accomplished by relating the spacings to effective channel lengths and then in turn relating them to leakage or delay. By example the direct delay calculation can be represented as follows:D=f(s_ul,s_ll,s_ur,s_lr)Another embodiment has the delay related to the effective channel lengths as follows:D=f(g(s))The terms in this equation indicate that the delay “D” is a function of the effective channel length “g”, which is in turn a function of the spacing “s” between channels. For two dimensional analyses, the spacing {s} and distances {b} include distances from the top and bottom of the cell. The width of channels and interconnections are also accounted for in the analysis because of the impact of the side of a channel or interconnection to neighboring devices. FIG. 11 is a simplified block diagram of a computer system 1100 that may incorporate embodiments of the present invention. FIG. 11 is merely illustrative of an embodiment incorporating the present invention and does not limit the scope of the invention as recited in the claims. One of ordinary skill in the art would recognize other variations, modifications, and alternatives. In one embodiment, computer system 1100 typically includes a monitor 1110, a computer 1120, user output devices 1130, user input devices 1140, communications interface 1150, and the like. As shown in FIG. 11, computer 1120 may include a processor(s) 1160 that communicates with a number of peripheral devices via a bus subsystem 1190. These peripheral devices may include user output devices 1130, user input devices 1140, communications interface 1150, and a storage subsystem, such as random access memory (RAM) 1170 and disk drive 1180. User input devices 1130 include all possible types of devices and mechanisms for inputting information to computer system 1120. These may include a keyboard, a keypad, a touch screen incorporated into the display, audio input devices such as voice recognition systems, microphones, and other types of input devices. In various embodiments, user input devices 1130 are typically embodied as a computer mouse, a trackball, a track pad, a joystick, wireless remote, drawing tablet, voice command system, eye tracking system, and the like. User input devices 1130 typically allow a user to select objects, icons, text and the like that appear on the monitor 1110 via a command such as a click of a button or the like. User output devices 1140 include all possible types of devices and mechanisms for outputting information from computer 1120. These may include a display (e.g., monitor 1110), non-visual displays such as audio output devices, etc. Communications interface 1150 provides an interface to other communication networks and devices. Communications interface 1150 may serve as an interface for receiving data from and transmitting data to other systems. Embodiments of communications interface 1150 typically include an Ethernet card, a modem (telephone, satellite, cable, ISDN), (asynchronous) digital subscriber line (DSL) unit, FireWire interface, USB interface, and the like. For example, communications interface 1150 may be coupled to a computer network, to a FireWire bus, or the like. In other embodiments, communications interfaces 1150 may be physically integrated on the motherboard of computer 1120, and may be a software program, such as soft DSL, or the like. In various embodiments, computer system 1100 may also include software that enables communications over a network such as the HTTP, TCP/IP, RTP/RTSP protocols, and the like. In alternative embodiments of the present invention, other communications software and transfer protocols may also be used, for example IPX, UDP or the like. In some embodiment, computer 1120 includes one or more Xeon microprocessors from Intel as processor(s) 1160. Further, one embodiment, computer 1120 includes a UNIX-based operating system. RAM 1170 and disk drive 1180 are examples of tangible media configured to store data such as embodiments of the present invention, including executable computer code, human readable code, or the like. Other types of tangible media include floppy disks, removable hard disks, optical storage media such as CD-ROMS, DVDs and bar codes, semiconductor memories such as flash memories, read-only-memories (ROMS), battery-backed volatile memories, networked storage devices, and the like. RAM 1170 and disk drive 1180 may be configured to store the basic programming and data constructs that provide the functionality of the present invention. Software code modules and instructions that provide the functionality of the present invention may be stored in RAM 1170 and disk drive 1180. These software modules may be executed by processor(s) 1160. RAM 1170 and disk drive 1180 may also provide a repository for storing data used in accordance with the present invention. RAM 1170 and disk drive 1180 may include a number of memories including a main random access memory (RAM) for storage of instructions and data during program execution and a read only memory (ROM) in which fixed instructions are stored. RAM 1170 and disk drive 1180 may include a file storage subsystem providing persistent (non-volatile) storage for program and data files. RAM 1170 and disk drive 1180 may also include removable storage systems, such as removable flash memory. Bus subsystem 1190 provides a mechanism for letting the various components and subsystems of computer 1120 communicate with each other as intended. Although bus subsystem 1190 is shown schematically as a single bus, alternative embodiments of the bus subsystem may utilize multiple busses. FIG. 11 is representative of a computer system capable of embodying the present invention. It will be readily apparent to one of ordinary skill in the art that many other hardware and software configurations are suitable for use with the present invention. For example, the computer may be a desktop, portable, rack-mounted or tablet configuration. Additionally, the computer may be a series of networked computers. Further, the use of other micro processors are contemplated, such as Pentium™ or Itanium™ microprocessors; Opteron™ or AthlonXP™ microprocessors from Advanced Micro Devices, Inc; and the like. Further, other types of operating systems are contemplated, such as Windows®, WindowsXP®, WindowsNT®, or the like from Microsoft Corporation, Solaris from Sun Microsystems, LINUX, UNIX, and the like. In still other embodiments, the techniques described above may be implemented upon a chip or an auxiliary processing board. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims. In addition, the technique and system of the present invention is suitable for use with a wide variety of EDA tools and methodologies for programming a device. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the pending claims along with their full scope or equivalents. The present invention can be implemented in the form of control logic in software or hardware or a combination of both. The control logic may be stored in an information storage medium as a plurality of instructions adapted to direct an information-processing device to perform a set of steps disclosed in embodiments of the present invention. Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will appreciate other ways and/or methods to implement the present invention. The embodiments discussed herein are illustrative of one or more examples of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications or adaptations of the methods and/or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the scope of the present invention. Hence, the present descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated. The above description is illustrative but not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of the disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the pending claims along with their full scope or equivalents. |
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description | 1. Field of the Invention The present invention relates to a liquid radioactive waste treatment system which evaporates a liquid radioactive waste in a natural environment, and more particularly, to a liquid radioactive waste treatment system in which solar heat is used, outside air is drawn in and circulated, and a liquid waste is in contact with the outside air and evaporated. 2. Description of Related Art Radioactive waste is divided into solid, liquid, and gaseous radioactive waste. Not as much research on liquid radioactive waste management has been carrying out as research on radioactive solid waste management. Liquid radioactive waste is generated by nuclear power generation or radioactive isotope use. The generated liquid waste is required to be safely processed and managed to prevent the waste from harming humans. Also, an evaporation process is required for volume reduction. As an amount of liquid waste increases, a need for processing accumulated liquid waste increases. Also, a liquid radioactive waste treatment standard is compounded due to an increase in industrial waste water. The transportation and processing of the liquid waste is more difficult than with solid waste. As one of the methods of managing liquid radioactive waste, a method which evaporates and concentrates liquid radioactive waste by mainly using steam, or processes liquid radioactive waste using an ion exchange resin has been proposed. However, an energy consumption efficiency and process efficiency of such method are low, which is uneconomical. Accordingly, a system which has a high energy consumption efficiency and process efficiency is required. Also, the other method of managing liquid radioactive waste which flows liquid radioactive waste and absorbs liquids of liquid waste by using an evaporation fabric has been proposed. However, the evaporation fabric using fabrics is exposed to direct sunlight, and thus an evaporation fabric life is shortened, and a great amount of solid waste may be generated. When the evaporation fabric is vertically installed, a period of time for contacting the liquid waste with air is short, and thereby causing a low evaporation efficiency. Also, liquid waste may not be evenly absorbed in the evaporation fabric, and a channeling phenomenon may occur and thus, evaporation surface area may be reduced. The present invention provides a liquid radioactive waste treatment system which uses solar heat, and thereby improving an energy consumption efficiency and performance efficiency. The present invention also provides a liquid radioactive waste treatment system which may process a great amount of liquid radioactive waste, be advantageous for maintenance and repair, and be semi-permanently used, with a simple and small-sized structure. The present invention also provides a liquid radioactive waste treatment system which increases a period of time for liquid to contact with air and solar heat, and thereby may improve an evaporation efficiency and rapidly process a great amount of liquid radioactive waste. The present invention also provides a liquid radioactive waste treatment system which may prevent a channeling phenomenon. According to an aspect of the present invention, there is provided a liquid radioactive waste treatment system includes a housing, an evaporation unit, and a liquid waste dispersing unit. In this instance, the housing comprises an external wall, the wall being able to be penetrated by sunlight and being comprised of a transparent material. The evaporation unit comprises an evaporation plate having an uneven surface on which the liquid waste flows. The liquid waste dispersing unit is located above the evaporation plate and disperses the liquid waste. Also, a plurality of evaporation plates is provided, and each of the evaporation plates is stacked to be spaced apart from each other by a predetermined distance. Also, a guide plate is perpendicularly attached to the evaporation plate at each side of the evaporation plate in order to prevent the liquid waste from leaking. The evaporation plate is positioned to be inclined at a predetermined angle, and a lower end of the evaporation plate is formed to be inclined into a single direction, to enable the liquid waste flow in the direction. The evaporation plate is preferably made of a stainless steel. Also, an inlet fan and an exhaust fan are mounted on the external wall of the housing. Air which is flowed inside of the housing from the inlet fan, passes over the evaporation plate, and is discharged to an outside of the housing via the exhaust fan after monitoring system. Such airflow improves an evaporation efficiency. A heat collector plate may be further mounted on an upper wall of the housing and stores solar heat. The liquid waste which passes the evaporation plate may move to the heat collector plate, be heated, and move to the evaporation plate again to circulate. Also, according to another aspect of the present invention, there is provided a liquid radioactive waste treatment system, the system including: a housing which is covered with a glass; an evaporation module where an evaporation plate, having an uneven surface in the housing, and a guide plate, which is perpendicularly attached to the evaporation plate at each side of the evaporation plate, are stacked, and each of the evaporation plates are spaced apart from each other by a predetermined distance; and a liquid waste dispersing unit, which comprises a plurality of evaporation modules, is located above the plurality of evaporation modules, and disperses the liquid waste. The liquid radioactive waste treatment system has a high energy consumption efficiency and may be semi-permanently used by using solar heat. Also, in the liquid radioactive waste treatment system, a period of time for contacting with the solar heat and air increases, and thereby may have a high evaporation efficiency, and may rapidly process a great amount of liquid waste. Also, a channeling phenomenon may be prevented. Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. FIG. 1 is a perspective view illustrating a liquid radioactive waste treatment system according to an embodiment of the present invention. FIG. 2 is a perspective view illustrating a flow of air. FIG. 3 is a perspective view illustrating an evaporation plate. As illustrated in FIGS. 1, 2 and 3, the liquid radioactive waste treatment system according to an embodiment of the present invention includes a housing 100, an evaporation unit 200, and a liquid waste dispersing unit 300. The housing 100 includes an external wall 130, and an interior space for the evaporation unit 200 and the liquid waste dispersing unit 300. The external wall 130 of the housing 100 may be penetrated by sunlight and made of a glass. However, the external wall 130 may not be limited to glass. A frame, which is not illustrated is formed in the housing 100. Also, a glass, and the like may be installed between the frames. An inlet fan 110 is mounted on a side of the housing 100 in order to draw air into the housing 100. An exhaust fan 120 is mounted on upper wall of the housing 100 in order to discharge the air which is in the housing 100. The air which is drawn from the inlet fan 110 passes an evaporation plate 211, and then is discharged to an outside of the housing 100 via the exhaust fan 120. When a portion of a side of the housing 100 is open, a liquid waste may be evaporated on the evaporation plate 211 through natural convection. However, forced convection may be performed by installing the inlet fan 110 and the exhaust fan 120 according to an embodiment of the present invention may improve an evaporation efficiency. However, it is preferable that natural convection and forced convection are combined to provide even greater improvement of the evaporation efficiency, which is described in detail with reference to FIG. 2. The evaporation unit 200 includes an evaporation module 210 including the evaporation plate 211. Four evaporation modules 210 are provided on each side, right and left, and thus, eight evaporation modules 210 are provided in total. Each of the evaporation modules 210 includes a plurality of evaporation plates 211, and the each of the evaporation plates 211 is stacked to be spaced apart from each other by a predetermined distance. Also, the evaporation plates 211 have an uneven surface, i.e. the evaporation plate 211 is corrugated. Specifically, the evaporation plate 211 is a medium for evaporation which plays an essential role in the evaporation, and increases a distance where the liquid waste flows, due to the uneven surface. Also, the evaporation plate 211 increases the period of time for contacting the liquid waste with the evaporation plate 211 due to the uneven surface. As an example, each of the evaporation modules 210 may be comprised of twenty five evaporation plates 211, and each of the twenty five evaporation plates 211 may be spaced apart from each other by 5 cm. Also, when four evaporation modules 210 are provided at each side, right and left, two hundred evaporation plates 211 may be provided in total. The evaporation plate 211 is positioned to be inclined at a predetermined angle so that the liquid waste may smoothly flow. The evaporation plate 211 may be made of a stainless steel (SUS). The stainless steel refers to a corrosion resistant steel which has a higher corrosion resistance than a iron. The uneven surface of the evaporation plate 211 is illustrated in FIG. 3. As illustrated, the evaporation plate 211 is perpendicularly corrugated. A guide plate 212, which has a predetermined height, is perpendicularly attached to the evaporation plate 211 at each side of the evaporation plate 211. Also, a connection bar 213, which is horizontally extended, is attached between each of the guide plates 212. The evaporation plate 211 is provided between two of the guide plates 212, and protruded from the plurality of connection bars 213. The evaporation plate 211 is integrally formed to be located under the connection bar 213, at a portion where the connection bar 213 is formed, and the evaporation plate 211 and the connection bar 213 are integrally formed. The guide plate 212 is combined with the evaporation plate 211 by welding. The guide plate 212 prevents the liquid waste from leaking into a left or right direction, and supports the evaporation plate 211. In order to improve the evaporation efficiency, the liquid waste is required to stay on the evaporation plate 211 for a longer period of time. For this, forty three evaporation plates 211 may be provided for each evaporation module 210, and inclined by about 45°. Also, a protrusion height of the stainless steel corrugation may be about 30 mm. In this instance, the stainless steel is about 1 m×4 m, and a thickness of the stainless steel is about 0.5 mm. Also, the guide plate 212 may be formed to have a length of about 2.5 m and a height of about 50 mm. FIG. 4 is a front view illustrating a flow of liquid waste on an evaporation plate. As illustrated in FIG. 4, the liquid waste regularly flows down to a subsequent space on the evaporation plate 211, after filling a higher space on the evaporation plate 211. Accordingly, a channeling phenomenon may be prevented, i.e. the liquid waste flows in a single direction. Also, a lower end of the evaporation plate 211 is formed to be inclined into a single direction, to enable the liquid waste to flow in the same direction. The liquid waste which is discharged at the lower end of the evaporation plate 211 may be collected in a separate vessel. FIG. 5 is a side view illustrating a liquid waste dispersing unit. As illustrated in FIG. 5, the liquid waste dispersing unit 300 branches off from a main pipe 310 to a branch pipe 320. The branch pipe 320 carries the liquid waste to an upper end of an evaporation plate 211. When dispersing the liquid waste, the liquid waste flows on the evaporation plate 211, and evaporation begins. An operation of evaporation on the evaporation plate 211 has been described above. FIG. 6 is a perspective view illustrating a liquid radioactive waste treatment system according to another embodiment of the present invention. As illustrated in FIG. 6, a heat collector plate 400 is mounted on an upper wall of the housing 100. The heat collector plate 400 may store the solar heat, and stored solar heat may raise an internal temperature of the housing 100. Also, the stored solar heat may raise a temperature of liquid waste through the evaporation plate 211 or the liquid waste dispersing unit 300 since the stored solar heat may be contacted with the evaporation plate 211 or the liquid waste dispersing unit 300. The liquid waste which passes the evaporation plate 211 is collected in a separate vessel, moves to the heat collector plate 400 via a separate tube which is not illustrated, and is heated in the heat collector plate 400. The heated liquid waste in the separate tube raises the internal temperature of the housing 100, which is similar in principle to a boiler. When the temperature of liquid waste is raised by 1° C., an evaporation loss increases by 0.02 l per unit area (m2) per one hour. Thus, according to experimental results, when forming a heat collector plate 400 with an area of about 3200 m2 in total, the evaporation loss increases by about 64 l per hour. Also, when water with a temperature of about 20° C. is heated to a temperature of about 50° C., i.e. a temperature increase of about 30° C., the evaporation loss increases by about 1900 l per hour. Also, a comparison experiment with a conventional evaporation fabric is described. When a liquid waste is evaporated by using the conventional evaporation fabric, at an airflow rate of about 2 m/sec between the evaporation fabrics, the liquid waste is evaporated at a rate of about 1.25 l/hr·m2. However, when using a corrugated evaporation plate, the liquid waste is evaporated at a rate of about 2.0 l/hr·m2. Accordingly, when the corrugated evaporation plate is used, the evaporation loss increases by about 1.5 times. Thus, when considering a total operational cost including a treatment cost for 15 years, about a billion Korean won is saved. The present invention may not be limited to a liquid radioactive waste treatment, and may be applied to a general industrial liquid waste treatment. According to the present invention, a liquid radioactive waste treatment system uses solar heat, and thereby may improve an energy consumption efficiency and manufacturing efficiency. Also, according to the present invention, a liquid radioactive waste treatment system may process a great amount of liquid radioactive waste, be advantageous for maintenance and repair, and be semi-permanently used, with a simple and small-sized structure. Also, according to the present invention, a liquid radioactive waste treatment system increases a period of time for contacting with air and solar heat, and thereby may improve an evaporation efficiency and rapidly process a great amount of liquid radioactive waste. Also, according to the present invention, a liquid radioactive waste treatment system may prevent a channeling phenomenon. Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents. |
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claims | 1. A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:a frame comprising a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure; anda plurality of elongated fuel elements supported by the frame, each of said plurality of fuel elements comprising fissile material, wherein as viewed in a cross section that is perpendicular to an axial direction of the fuel assembly, the plurality of fuel elements are arranged into a mixed grid pattern that comprises a first grid pattern and a second grid pattern, the second grid pattern being different from the first grid pattern, wherein:each of the plurality of fuel elements has a common circumscribed diameter;the first grid pattern comprises a pattern of square rows and columns;the centerline-to-centerline distance between the rows and columns equals the common circumscribed diameter;the second grid pattern comprises a pattern of equilateral triangles; anda length of each side of each triangle equals the common circumscribed diameter. 2. The fuel assembly of claim 1, wherein:the plurality of fuel elements includes non-overlapping first, second, and third subsets, each subset including a plurality of the fuel elements,the plurality of fuel elements of the first subset are disposed within respective grid positions defined by the first grid pattern,the plurality of fuel elements of the second subset are disposed within respective grid positions defined by the second grid pattern,the plurality of fuel elements of the third subset are disposed within respective overlapping grid positions, the overlapping grid positions falling within both the first grid pattern and the second grid pattern. 3. The fuel assembly of claim 1, further comprising additional fuel elements supported by the frame, wherein the additional fuel elements are not disposed within any of the grid positions defined by the first or second grid pattern. 4. The fuel assembly of claim 1, wherein: each of the plurality of fuel elements comprises: a fuel kernel comprising fuel material disposed in a matrix of metal non-fuel material, the fuel material comprising fissile material, and a cladding surrounding the fuel kernel, each of the fuel elements has a multi-lobed profile that forms spiral ribs. 5. A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:a frame comprising a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure; anda plurality of elongated fuel elements supported by the frame, each of said plurality of fuel elements comprising fissile material, wherein as viewed in a cross section that is perpendicular to an axial direction of the fuel assembly, the plurality of fuel elements are arranged into a mixed grid pattern that comprises a first grid pattern and a second grid pattern, the second grid pattern being different from the first grid pattern, each elongated fuel element defining a fuel element cross-section perpendicular to the axial direction of the fuel assembly, wherein each elongated fuel element directly contacts at least one adjacent fuel element, and wherein:the frame comprises a shroud surrounding the plurality of fuel elements such that all of the plurality of fuel elements are disposed inside the shroud;the shroud comprises a first sidewall, a second sidewall, and a third sidewall, wherein the first and second sidewalls meet at a first corner and the second and third sidewalls meet at a second corner; andthe fuel assembly comprises a first corner structure disposed inside the shroud adjacent the first corner and in contact with the first sidewall and the second sidewall and a second corner structure disposed inside the shroud adjacent the second corner and in contact with the second sidewall and the third sidewall, wherein each of the first and second corner structures define a corner structure cross-section perpendicular to the axial direction of the fuel assembly that is different from each fuel element cross-section, wherein the first and second corner structures are separate. 6. The fuel assembly of claim 5, wherein at least one of the first corner structure and the second corner structure comprises a burnable poison. 7. The fuel assembly of claim 6, wherein at least one of the first corner structure and the second corner structure abuts at least one of the plurality of elongated fuel elements. 8. The fuel assembly of claim 5, wherein each of the plurality of fuel elements has a common circumscribed diameter. 9. The fuel assembly of claim 5, wherein:the first grid pattern comprises a pattern of square rows and columns,the centerline-to-centerline distance between the rows and columns equals the common circumscribed diameter,the second grid pattern comprises a pattern of equilateral triangles, anda length of each side of each triangle equals the common circumscribed diameter. 10. The fuel assembly of claim 5, wherein at least one of the first corner structure and the second corner structure defines an inner contour that is partially-cylindrical and abuts one of the plurality of elongated fuel elements. 11. The fuel assembly of claim 10, wherein the inner contour defines an arc of between about 90 degrees and about 310 degrees. 12. The fuel assembly of claim 10, wherein the inner contour defines an arc of between about 150 degrees and about 310 degrees. 13. The fuel assembly of claim 5, wherein at least one of the first corner structure and the second corner structure abuts three adjacent elongated fuel elements of said plurality of elongated fuel elements. 14. The fuel assembly of claim 5, wherein at least one of the first corner structure and the second corner structure comprises a tubular structure. 15. The fuel assembly of claim 14, wherein at least one of the first corner structure and the second corner structure abuts the shroud and one of the plurality of elongated fuel elements. 16. The fuel assembly of claim 14, wherein at least one of the first corner structure and the second corner structure further comprises a material helically wrapped around the tubular structure. 17. The fuel assembly of claim 5, wherein at least one of the first corner structure and the second corner structure defines three concave, partially-cylindrically shaped surfaces, each of which abuts one of the plurality of elongated fuel elements. 18. The fuel assembly of claim 5, wherein at least one of the first corner structure and the second corner structure comprises one or more of: a burnable poison, steel, alloys or ceramics of zirconium, and/or uranium, and/or plutonium, and/or thorium. 19. The fuel assembly of claim 5, wherein at least one of the first corner structure and the second corner structure is attached to the shroud. 20. A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:a frame comprising a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure; anda plurality of elongated fuel elements supported by the frame, each of said plurality of fuel elements comprising fissile material, wherein as viewed in a cross section that is perpendicular to an axial direction of the fuel assembly, the plurality of fuel elements are arranged into a mixed grid pattern that comprises a first grid pattern and a second grid pattern, the second grid pattern being different from the first grid pattern, wherein:the frame comprises a shroud having a first planar sidewall and a second planar sidewall connected by a corner region, wherein all of the plurality of fuel elements are disposed inside the shroud;the fuel assembly comprises a corner structure comprising a burnable poison, wherein the corner structure is located outside of the shroud and extends over the corner region of the shroud from the first planar sidewall to the second planar sidewall. 21. The fuel assembly of claim 20, wherein the corner structure is attached to the shroud. 22. A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:a frame comprising a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure; anda plurality of elongated fuel elements supported by the frame, each of said plurality of fuel elements comprising fissile material, wherein as viewed in a cross section that is perpendicular to an axial direction of the fuel assembly, the plurality of fuel elements are arranged into a mixed grid pattern that comprises a first grid pattern and a second grid pattern, the second grid pattern being different from the first grid pattern, wherein:the frame comprises a shroud such that all of the plurality of fuel elements are disposed inside the shroud, wherein the shroud comprises a first sidewall and a second sidewall separate from one another; andthe fuel assembly comprises a corner structure joining the first sidewall to the second sidewall at a corner of the shroud, wherein the corner structure comprises a burnable poison. 23. The fuel assembly of claim 22, wherein the corner structure is attached to the shroud. 24. A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:a frame comprising a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure; anda plurality of elongated fuel elements supported by the frame, each of said plurality of fuel elements comprising fissile material, wherein as viewed in a cross section that is perpendicular to an axial direction of the fuel assembly, the plurality of fuel elements are arranged into a mixed grid pattern that comprises a first grid pattern and a second grid pattern, the second grid pattern being different from the first grid pattern, wherein:the frame comprises a shroud such that all of the plurality of fuel elements are disposed inside the shroud; andthe fuel assembly comprises four corner structures each comprising a burnable poison, wherein the shroud comprises four separate plates joined by said four corner structures. |
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description | The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor for carrying out the invention. Various modifications, however, will remain readily apparent to those skilled in the art. Turning now to the drawings and, with particular attention to FIG. 1, a radiation therapy device 10 pursuant to embodiments of the present invention is shown. According to one embodiment of the present invention, radiation therapy device 10 includes a beam shielding device (not shown) within a treatment head 24, a control unit in a housing 30 and a treatment unit 32. An accessory tray 25 is mounted to an exterior of treatment head 24. Accessory tray 25, in one embodiment, is configured to receive and securely hold attachments used during the course of treatment planning and treatment (such as, for example, reticles, wedges, or the like). Radiation therapy device 10 includes a gantry 26 which can be swiveled around a horizontal axis of rotation 20 in the course of a therapeutic treatment. Treatment head 24 is fastened to a projection of the gantry 26. A linear accelerator (not shown) is located inside gantry 26 to generate the high energy radiation required for the therapy. The axis of the radiation bundle emitted from the linear accelerator and the gantry 26 is designated by beam path 12. Electron, photon or any other detectable radiation can be used for the therapy. Embodiments of the present invention permit the controlled delivery of both primary electron and primary photon beams to a treatment zone 18 during the course of a prescribed treatment. During a course of treatment, the radiation beam is trained on treatment zone 18 of an object 22, for example, a patient who is to be treated and whose tumor lies at the isocenter of the gantry rotation. The plates or leaves of the beam shielding device within the treatment head 24 are substantially impervious to the emitted radiation. The collimator leaves or plates are mounted between the radiation source and the patient in order to delimit (conform) the field. Areas of the body, for example, healthy tissue, are therefore subject to as little radiation as possible and preferably to none at all. The plates or leaves are movable such that the distribution of radiation over the field need not be uniform (one region can be given a higher dose than another). Furthermore, the gantry can be rotated so as to allow different beam angles and radiation distributions without having to move the patient. According to one embodiment of the present invention, several beam shaping devices are used to shape radiation beams directed toward treatment zone 18. In one embodiment, a photon collimator and an electron collimator are provided. Each of these collimators, as will be described further below, may be separately controlled and positioned to shape beams directed at treatment zone 18. According to one embodiment, the photon collimator (not shown in FIG. 1) is contained within treatment head 24 and the electron collimator (not shown in FIG. 1) is removably mounted on accessory tray 25. Radiation therapy device 10 also includes a central treatment processing or control unit 32 which is typically located apart from radiation therapy device 10. Radiation therapy device 10 is normally located in a different room to protect the therapist from radiation. Treatment unit 32 includes a processor 40 in communication with an operator console 42 (including one or more visual display units or monitors) and an input device such as a keyboard 44. Data can be input also through data carriers such as data storage devices or a verification and recording or automatic setup system. More than one control unit 32, processor 40, and/or operator console 42 may be provided to control radiation therapy device 10. Treatment processing unit 32 is typically operated by a therapist who administers actual delivery of radiation treatment as prescribed by an oncologist. Therapist operates treatment processing unit 32 by using keyboard 44 or other input device. The therapist enters data defining the radiation dose to be delivered to the patient, for example, according to the prescription of the oncologist. The program can also be input via another input device, such as a data storage device. Various data can be displayed before and during the treatment on the screen of operator console 42. Embodiments of the present invention permit the delivery of both primary electron and primary photon beams to treatment zone 18 during the course of a prescribed treatment. Embodiments of the present invention permit the creation and control of both photon and electron radiation beams which closely match the shape and size of treatment zone 18. Referring now to FIG. 2, a block diagram is shown depicting portions of a radiation therapy device 10 and treatment unit 32 according to one embodiment of the present invention. In particular, treatment delivery elements of a radiation therapy device are shown, which may be configured in radiation therapy device 10 and treatment unit 32 as depicted in FIG. 1. The treatment delivery elements include a computer 40, operatively coupled to an operator console 42 for receiving operator control inputs and for displaying treatment data to an operator. Operator console 42 is typically operated by a radiation therapist who administers the delivery of a radiation treatment as prescribed by an oncologist. Using operator console 42, the radiation therapist enters data that defines the radiation to be delivered to a patient. Mass storage device 46 stores data used and generated during the operation of the radiation therapy device including, for example, treatment data as defined by an oncologist for a particular patient. This treatment data is generated, for example, using a treatment planning system 60 which may include manual and computerized inputs to determine a beam shape prior to treatment of a patient. Treatment planning system 60 is typically used to define and simulate a beam shape required to deliver an appropriate therapeutic dose of radiation to treatment zone 18. Data defining the beam shape and treatment are stored, e.g., in mass storage device 46 for use by computer 40 in delivering treatment. According to one embodiment of the present invention, treatment planning may include activities which occur prior to the delivery of the treatment, such as the generation of treatment data defining a photon treatment, an electron treatment, and/or a mixed beam treatment. Embodiments of the present invention permit the use of mixed beam treatments without the need for extended disruptions to install electron applicators or other shielding devices. Further, embodiments of the present invention permit field shaping of electron beams during a treatment in a device which also permits field shaping of photon beams during a treatment. Although a single computer 40 is depicted in FIG. 2, those skilled in the art will appreciate that the functions described herein may be accomplished using one or more computing devices operating together or independently. Those skilled in the art will also appreciate that any suitable general purpose or specially programmed computer may be used to achieve the functionality described herein. Computer 40 is also operatively coupled to various control units including, for example, a gantry control 44 and a table control 48. In operation, computer 40 directs the movement of gantry 26 via gantry control 44 and the movement of table 16 via table control 48. These devices are controlled by computer 40 to place a patient in a proper position to receive treatment from the radiation therapy device. In some embodiments, gantry 26 and/or table 16 may be repositioned during treatment to deliver a prescribed dose of radiation. Computer 40 is also operatively coupled to a dose control unit 50 which includes a dosimetry controller and which is designed to control a beam source 52 to generate a desired beam achieving desired isodose curves. Beam source 52 may be one or more of, for example, an electron and/or photon beam source. Beam source 52 may be used to generate radiation beams in any of a number of ways well-known to those skilled in the art. For example, beam source 52 may include a dose control unit 50 used to control a trigger system generating injector trigger signals fed to an electron gun in a linear accelerator (not shown) to produce en electron beam as output. Beam source 52 is typically used to generate a beam of therapeutic radiation directed along an axis (as shown in FIG. 1 as item 12) toward treatment zone 18 on patient 22. According to one embodiment of the invention, the beam generated by beam source 52 is shaped using one or more collimator assemblies, depending on the type of beam generated. For example, in one embodiment, a photon beam produced by beam source 52 is shaped by manipulating a photon collimator 64, while an electron beam produced by beam source 52 is shaped by manipulating an electron collimator 62. According to one embodiment, photon collimator 64 and electron collimator 62 are multi-leaf collimators having a plurality of individually-movable radiation blocking leaves. The leaves of each such collimator are individually driven by a drive unit 58, 59 and are positioned under the control of electron collimator control 54, photon collimator control 55 and sensor(s) 56 and 57. Drive units 58, 59 move the leaves of each collimator in and out of the treatment field to create a desired field shape for each type of beam. In one embodiment, where an electron beam is to be generated and primary electrons are to be used in a treatment, photon collimator control 55 operates to retract individual leaves of photon collimator 64, while electron collimator control 54 operates to position individual leaves of electron collimator 62 across the path of the electron beam to generate a desired electron field shape at the isocenter. Similarly, in one embodiment, where a photon beam is to be generated and primary photons are to be used in a treatment, electron collimator control 54 operates to retract individual leaves of electron collimator 62 while photon collimator control 55 operates to position individual leaves of photon collimator 64 across the path of the photon beam to generate a desired photon beam field shape at the isocenter. In other embodiments, both collimators 62, 64 may be controlled in concert during the course of a treatment to generate a desired field shape at the isocenter. Referring now to FIG. 3, a perspective view of portions of radiation therapy device 10 is shown. In particular, FIG. 3 depicts portions of treatment head 24 as well as elements along a beam path 12. According to one embodiment of the present invention, treatment head 24 includes an accessory tray 25 or other mounting device positioned between treatment head 24 and treatment area 18. Components of a photon collimator (item 64 of FIG. 2) are shown as collimator blocks 90, 92 in FIG. 3. Collimator blocks 90, 92 are positioned within treatment head 24 and may include a number of individual elements or xe2x80x9cleavesxe2x80x9d which may be independently controlled to create a desired field shape at the isocenter. Any of a number of known collimators and shaping devices may be used as photon collimator (item 64 of FIG. 2) in conjunction with embodiments of the present invention. According to one embodiment of the present invention, a separate electron collimator 62 is provided. According to one embodiment of the present invention, components of electron collimator 62 are removably mounted on accessory tray 25, allowing electron collimator 62 to be quickly installed and removed by radiation therapists or other technicians in order to add or remove electron field shaping capabilities to a radiation therapy device. According to one embodiment, individual leaf beds consisting of a number of individual collimator leaves 70a-n are mounted on accessory tray 25 such that they can be moved in a direction 72 across beam path 12. In one embodiment, the individual leaves 70a-n are formed of radiation attenuating materials. For example, brass or tungsten are currently preferred materials, although other materials with similar radiation attenuating characteristics may be used. In one embodiment, individual leaves 70a-n have a width of approximately 1-2 cm. Those skilled in the art will recognize that other shapes and sizes of individual leaves 70a-n may be selected to produce different field shapes at treatment zone 18. Collimator drives 58a-n and other control circuitry are also removably mounted on accessory tray 25. In one embodiment, collimator drives 58a-n and other control circuitry are mounted on an exterior surface of accessory tray, away from beam path 12, providing greater durability and length of service for the electrical components used to operate electron collimator 62. According to one embodiment of the present invention, a container 80 (such as a balloon or the like) filled with helium is positioned along a portion of beam path 12 to reduce the amount of free air along beam path 12. In one embodiment, container 80 is removably mounted to accessory tray 25. By replacing some of the air in the air column with helium (or another gas having a low density), the penumbra of the electron beam is reduced, allowing greater control over the shape and effect of the beam at the isocenter. In particular, use of helium along beam path 12 maintains the electron beam spread at a clinically acceptable level by decreasing the number of scattering interactions the electrons experience before they reach treatment zone 18. In operation, a shaped electron field may be delivered to treatment zone 18 by retracting leaves of photon collimator blocks 90, 92, passing the electron beam through helium-filled container 80, and selectively shaping the beam by manipulating electron collimator 62. Multiple fields can thus be delivered to treatment zone 18 during the course of a treatment without manual intervention. Further, embodiments of the present invention support mixed beam treatments by selectively switching between electron and photon beams. According to embodiments of the present invention, manual intervention and equipment set-up is reduced or eliminated. Applicants have found that mounting components of electron collimator 62 on accessory tray 25 provides several desirable benefits. For example, during most types of treatments, electron collimator 62 provides sufficient patient clearance in all gantry and table positions. Further, electronic components, such as collimator drives 58a-n, will enjoy greater longevity because they are positioned away from beam path 12. Additionally, greater accuracy is provided during treatment because the overall swing weight of treatment head 24 and accessory tray 25 are minimized. The inventive configuration also enjoys the advantage of allowing ready removal and replacement of components. Accessory tray 25, in some embodiments, includes one or more accessory slots (not shown) into which components of electron collimator 62 may fit. In some embodiments, components of electron collimator 62 are installed by simply inserting the components into one or more accessory slots of accessory tray 25. As a result, for treatments that require greater clearance (e.g., such as photon treatments of breast cancer, etc.), components of electron collimator 62 may be readily removed, and then re-installed as needed. Placement of components of electron collimator 62 on accessory tray 25 also serves to reduce the electron penumbra at the isocenter, providing greater accuracy in the delivery of electron treatments. Those skilled in the art will recognize that the electron penumbra can be reduced further by positioning components of electron collimator 62 closer to the isocenter; however, this increases problems with collision. In some embodiments, additional collision detection and avoidance components may be utilized in radiation therapy device 10 to reduce collisions and to allow closer positioning of components of electron collimator 62. Referring now to FIG. 4, details regarding the construction of electron collimator 62 are shown. FIG. 4 is a beams eye view of electron collimator 62, showing the placement of container 80 in relation to components of electron collimator 62. In one embodiment, electron collimator 62 includes a plurality of individual collimator drives 58a-n each coupled to drive individual leaves 70a-n of the collimator. As depicted, individual leaves 70a-n may be positioned using collimator drives 58a-n to generate a desired collimator shape, thereby producing a desired electron field shape at the treatment area on a patient. Those skilled in the art will appreciate that various adaptations and modifications of the just described preferred embodiments can be configured without departing from the scope and spirit of the invention. Although a preferred embodiment utilizing removable electron collimator components has been described, in one embodiment, the electron collimator components may be mounted in a manner that does not facilitate ready removal. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein. |
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abstract | Disclosed are an installation case for a radiation device, an oil-cooling circulation system and an X-ray generator which belong to the technical field of X-ray generator. This disclosure aims to solve the technical problems existing in the conventional X-ray generator, that is, the conventional X-ray generator provides bad sealing, the weight of the case body of the conventional X-ray generator is heavy, and the leakage dose of the X-ray in the conventional X-ray generator is large. The installation case for a radiation device according to this disclosure comprising a case body and a collimator fixedly connected with the case body, the collimator being provided with a beam exit aperture and the case body being provided with a beam exit opening, the installation case for a radiation device further comprises a shielding device provided within the case body, the collimator and the shielding device are integrally formed, or the collimator and the shielding device are two separate parts and are fixedly connected with each other; each layer of the shielding device is provided with a ray exit aperture, and the ray exit aperture, the beam exit aperture and the beam exit opening are coaxial. The X-ray generator according to this disclosure comprises the oil-cooling circulation system according to this disclosure. The installation case for a radiation device according to the disclosure provides improved sealing and ray leakage-proof performance. |
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abstract | Apparatus for interrupting and/or scanning a beam of penetrating radiation, such as for purposes of inspecting contents of a container. A source, such as an x-ray tube, generates a fan beam of radiation effectively emanating from a source axis, with the width of the fan beam collimated by a width collimator, such as a clamshell collimator. An angular collimator, stationary during the course of scanning, limits the extent of the scan, and a multi-aperture unit, such as a hoop, or a nested pair of hoops, is rotated about a central axis, and structured in such a manner that the total beam fluence incident on a target is conserved for different fields of view of the beam on the target. The central axis of hoop rotation need not coincide with the source axis. |
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description | This application claims the benefit of Korean Patent Application No. 10-2014-0192561, filed on Dec. 29, 2014, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. Field One or more exemplary embodiments relate to a method and system for improving control of a steam generator level for preventing oscillation of the steam generator level in a nuclear power plant, and more particularly, to a system and method of preventing oscillation of a steam generator level and resultant shutdown of a nuclear reactor, which may be caused when a high-level priority control function is frequently and repeatedly turned on/off as the steam generator level is excessively increased, by improving a feedwater control system in the nuclear power plant. Description of the Related Art A nuclear power plant consists of 100 or more systems respectively having individual functions. The systems are largely classified into a nuclear steam supply system (NSSS) that is based on a nuclear reactor, a turbine-generator system which is supplied with steam to operate a generator so as to produce electricity, and other subordinate facilities. A nuclear power plant with a pressurized water reactor (PWR), which is currently mainly used as a nuclear power plant in Korea, consists of a primary system that is based on a nuclear reactor, a secondary system that includes a turbine, a steam generator, an electric generator, and a condenser, an engineered safeguard system that is to prepare for accidents, a power transmission and supply system, an instrumentation and control system, and other subsidiary systems. Hot water generated by a nuclear reactor circulates through a heat-transfer pipe included in a steam generator, which is connected to the nuclear reactor through a coolant pipe, so as to transfer heat to feedwater flowing into the steam generator through another pipe, and then, returns to the reactor. A level of the feedwater in the steam generator should be appropriately maintained so that the steam generator easily performs this function. A nuclear power plant generates a signal for shutdown of a nuclear reactor according to an increase or a decrease in a steam generator level so as to ensure safety. However, if a transient event occurs in a nuclear power plant, since a shutdown margin of a nuclear reactor having a low steam generator level is relatively less than a shutdown margin of a nuclear reactor having a high steam generator level in a feedwater control system, there is a high possibility of shutdown of a nuclear reactor when a steam generator level is high. Accordingly, a feedwater control system in the related art has a high-level override (HLO) function such that, if a steam generator level is equal to or higher than 85%, as shown in FIG. 1, all feedwater control valves are closed and a main feedwater pump is operated at a lowest speed by setting an output value of a feedwater control system to “0”. The HLO function is performed so that a high-level priority control mode is executed if a steam generator level is 85%, and then, deactivated if the steam generator level reaches 80%. However, in a feedwater control system in a related art, if a signal for controlling a steam generator level is drastically switched to an output signal from a proportional integral controller when a high-level priority control mode is deactivated due to recovery of a steam generator level, since a high-level priority control function is frequently turned on/off as the steam generator level is changed, the steam generator level may oscillate. Thus, shutdown of a nuclear reactor having a high steam generator level may occur. Accordingly, a method of controlling a steam generator level to prevent oscillation of a steam generator level while a high-level priority control function is being performed is needed. One or more exemplary embodiments include a system and method of preventing drastic oscillation of a steam generator level which may occur when a high-level priority control mode is deactivated. One or more exemplary embodiments include a non-transitory computer-readable recording storage medium having recorded thereon a computer program which, when executed by a computer, performs the method. Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. According to one or more exemplary embodiments, a steam generator level control system configured to prevent oscillation of a steam generator level at a nuclear power plant includes: a comparator configured to compare a steam generator level with a predetermined level-set value; a proportional integral control output unit configured to generate a proportional integral control value by using an output from the comparator; a high-level priority control signal generator configured to output a signal instructing to enter a high-level priority control mode if the steam generator level is equal to or greater than first criteria, and output a signal deactivating the high-level priority control mode if the steam generator level is equal to or less than second criteria; and a high-level priority control signal receiver configured to control a control signal using a value of the proportional integral control output unit to be transmitted to a main feedwater pump and a feedwater control valve in a normal mode, obstruct a control signal using a value of the proportional integral control output unit in the high-level priority control mode, and control a predetermined output value to be transmitted to the main feedwater pump and the feedwater control valve, wherein the proportional integral control output unit controls to output a value obtained when the proportional integral control value is reduced for a certain time period after the high-level priority control mode is deactivated. The proportional integral control output unit may include: a proportional integral controller configured to generate a proportional integral control value by using an output from the comparator; and an output reducer configured to control the proportional integral controller to reduce the proportional integral control value for a certain time period if a high-level priority control mode is deactivated according to a signal from the high-level priority control signal generator. The proportional integral control output unit may include: a proportional integral controller configured to generate a proportional integral control value by using an output from the comparator; and an output reducer configured to receive the proportional integral control value, and reduce the proportional integral control value for a certain time period after a high-level priority control mode is deactivated according to a signal from the high-level priority control signal generator and output the reduced proportional integral control value to the high-level priority control signal receiver. The output reducer may reduce the proportional integral control value at a certain rate or in correspondence with a certain value. In detail, the output reducer may reduce the proportional integral control value to half the proportional integral control value. The output reducer may reduce the proportional integral control value for a predetermined time period, or until the steam generator level is reduced to a value equal to or less than a predetermined value after the high-level priority control mode is deactivated, or until the proportional integral control value is reduced to a value equal to or less than a predetermined value after the high-level priority control mode is deactivated. The steam generator level control system may further include: a main feedwater pump speed controller configured to receive an output from the high-level priority control signal receiver and control a speed of the main feedwater pump; and a feedwater control valve opening controller configured to receive an output from the high-level priority control signal receiver and control a degree of opening the feedwater control pump. According to one or more exemplary embodiments, a steam generator level control system configured to prevent oscillation of a steam generator level at a nuclear power plant includes: a comparator configured to compare a steam generator level with a predetermined level-set value; a proportional integral control output unit configured to generate a proportional integral control value by using an output from the comparator; a high-level priority control signal generator configured to output a signal instructing to enter a high-level priority control mode if the steam generator level is equal to or greater than first criteria, and output a signal deactivating the high-level priority control mode if the steam generator level is equal to or less than second criteria; and a high-level priority control signal receiver configured to control a control signal using a value of the proportional integral control output unit to be transmitted to a main feedwater pump and a feedwater control valve in a normal mode, obstruct a control signal using a value of the proportional integral control output unit in the high-level priority control mode, and control a predetermined output value to be transmitted to the main feedwater pump and the feedwater control valve, wherein the high-level priority control signal generator receives a proportional integral control value from the proportional integral control output unit, and controls a signal instructing to enter the high-level priority control mode not to be output until the proportional integral control value is reduced to a value equal to or less than a predetermined value after the high-level priority control mode is deactivated. According to one or more exemplary embodiments, a non-transitory computer-readable recording storage medium having recorded thereon a computer program, when executed by a computer, performs the method. Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the exemplary embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items The description, provided hereinafter, merely illustrates principles of the inventive concept. Therefore, those skilled in the art may implement the principles of the inventive concept and invent a wide variety of devices that are included in the concept and scope of the inventive concept, though not dearly described or illustrated herein. In addition, it is to be understood that all conditional terms and embodiments, listed herein, are intended only for the purpose of helping to understand the concept of the inventive concept, and are clearly not limited to the embodiment and states that are particularly enumerated herein. In addition, it may be understood that a detailed description that provides particular embodiments as well as the principles, perspectives, and embodiments of the inventive concept are intended to include structural and functional equivalents of the particular embodiments as well as the principles, perspectives, and embodiments of the inventive concept. Additionally, it may be understood that such equivalents include not only known equivalents but also equivalents that will be developed in the future, that is, all elements that are invented to perform the same functions regardless of structures. Therefore, functions of various elements shown in the drawing that includes a processor or a functional block which is shown to have a concept similar to the processor may be provided by using not only dedicated hardware but also hardware with a capability to run appropriate software. If provided by the processor, the functions may be provided by a single dedicated processor, a single shared processor, or a plurality of individual processors, and some of the functions may be shared by such processors. In addition, terms such as a processor, control, or terms that have a concept similar thereto shall not be interpreted to exclusively quote hardware with a capability to run software, and shall be understood to implicitly include digital signal processor (DSP) hardware, read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile memory without limitation, as well as other well-known hardware. A purpose, advantages, and features of the inventive concept will become apparent from the following detailed description. In the description of the inventive concept, certain detailed explanations of well-known technology are omitted when it is deemed that they may unnecessarily obscure the essence of the inventive concept. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of components, but do not preclude the presence or addition of one or more other components, unless otherwise specified. Hereinafter, the inventive concept will be described in detail by explaining embodiments of the inventive concept with reference to the attached drawings. A general configuration of a steam generator level control system is described with reference to FIG. 1. A comparator 2 compares a steam generator level value 1 of a steam generator, which is measured by a steam generator level measuring sensor included in the steam generator, to a level-set value. Then, a resultant value of the comparing is input to a proportional integral controller 3. The steam generator level value 1 of the steam generator is input to a high-level priority control signal generator 4. If the steam generator level value 1 is equal to or greater than a predetermined value, for example, 85%, a signal instructing to enter a high-level priority control mode (a high-level priority control signal) is generated. If a high-level priority control signal is generated by the high-level priority control signal generator 4, a high-level priority control signal receiver 5 prevents outputting of an output signal from the proportional integral controller 3, and controls a predetermined value to be output to a main feedwater pump speed controller 6 and a feedwater control valve opening controller 7 so that an output value of a flow rate requiring signal from a feedwater control system is 0. In other words, the high-level priority control signal receiver 5 controls a signal commanding to close a feedwater control valve to be output to the feedwater control valve opening controller 7, and controls a signal instructing to operate a main feedwater pump at a lowest speed to be output to the main feedwater pump speed controller 6. Additionally, if a high-level priority control mode is deactivated, the high-level priority control signal receiver 5 controls an output to be transmitted from the proportional integral controller 3 to the main feedwater pump speed controller 6 and the feedwater control valve opening controller 7. FIG. 2 is a block diagram of a configuration obtained by improving the configuration shown in FIG. 1, according to an exemplary embodiment. According to an exemplary embodiment, referring to FIG. 2, similarly to the configuration shown in FIG. 1, a steam generator level control system includes a comparator 120, a proportional integral control output unit 130, a high-level priority control signal generator 140, a high-level priority control signal receiver 150, a main feedwater pump speed controller 160, and a feedwater control valve opening controller 170. According to an exemplary embodiment, the steam generator level control system is different from the steam generator level control system in the related art, shown in FIG. 1, in that a high-level priority control signal is transmitted to the proportional integral control output unit 130 as well as the high-level priority control signal receiver 150, and that the proportional integral control output unit 130 reduces an output value of the proportional integral controller 3 according to the high-level priority control signal. Hereinafter, each element is described. The comparator 120 receives a value of a steam-generator level from a sensor for measuring the steam-generator level, and outputs a resultant value obtained by comparing the value of the steam-generator level to a predetermined level-set value. The high-level priority control signal generator 140 receives the value of the steam-generator level. Then, the high-level priority control signal generator 140 outputs a high-level priority control signal if the value of the steam-generator level is equal to or greater than a first predetermined value, and outputs a signal deactivating a high-level priority control mode (a high-level priority control deactivating signal) if the value of the steam-generator level is equal to or less than a second predetermined value. The outputting of a high-level priority control deactivating signal may be performed by using a method of transmitting a signal other than a high-level priority control signal, or by using a method of repeatedly outputting a high-level priority control signal until a value of a steam generator level becomes equal to or greater than a first value, and then, reaches a second value, and stopping the outputting of the high-level priority level control signal if the value of the steam generator level becomes equal to or less than the second value. Generally, the first value is a value obtained when a steam generator level becomes 85%, and a second value is a value obtained when the steam generator level becomes 80%. In other words, the first value and the second value may vary with characteristics of a nuclear power plant system. Both the first value and the second value may be changed by a facility manager with respect to the high-level priority control signal generator 140 and may be pre-stored. The high-level priority control signal receiver 150 receives an output signal from the high-level priority control signal generator 140. If the high-level priority control signal receiver 150 receives a high-level priority control signal, the high-level priority control signal receiver 150 obstructs an output of a value received from the proportional integral control output unit 130, and outputs predetermined information. Here, the predetermined information is information instructing an output value of a flow rate requiring signal from a feedwater control system to be 0. The predetermined information instructs the feedwater pump opening controller 170 to close a feedwater valve and instructs the main feedwater pump speed controller 160 to operate a main feedwater pump at a lowest speed. Additionally, if a high-level priority control signal is not received or a high-level priority control deactivating signal is received, the high-level priority control signal receiver 150 controls to output a signal that was output from the proportional integral control output unit 130. The main feedwater pump speed controller 160 receives a signal from the high-level priority control signal receiver 150 and outputs a signal for controlling a speed of the main feedwater pump. The feedwater control valve opening controller 170 receives a signal from the high-level priority control signal receiver 150 and outputs a signal for controlling a degree of opening the feedwater control valve. In other words, in a normal mode, the main feedwater pump speed controller 160 and the feedwater control valve opening controller 170 control a speed of the main feedwater pump and a degree of opening the feedwater control valve according to a value output to the proportional integral control output unit 130. In a high-level priority control mode, the high-level priority control signal receiver 150 obstructs an output from the proportional integral control output unit 130, and controls a speed of the main feedwater pump and a degree of opening the feedwater control valve according to additional information. A function of controlling a speed of the main feedwater pump according to a received signal, which is performed by the main feedwater speed controller 160, and a function of controlling a degree of opening the main control valve, which is performed by the feedwater control valve opening controller 170, are well-known technology. Thus, a description thereof is not provided here. The proportional integral control output unit 130 outputs a proportional integral control value that is generated in response to an output signal from the comparator 120 that is employed as an input value. The proportional integral control output unit 130 changes an output proportional integral control value, according to a signal from the high-level priority control signal generator 140. The proportional integral control output unit 130 includes a proportional integral controller 131 and an output reducer 132 to perform such a function. The proportional integral controller 131 performs a same function as that of the proportional integral controller 3 included in the steam-generator level control system in the related art, which is described above. In other words, the proportional integral controller 131 outputs a proportional integral control value generated in response to an output signal from the comparator 120 that is employed as an input value. The output reducer 132 controls the proportional integral controller 131 to output an output value of the proportional integral controller 131 without having to change the output value, or controls the proportional integral controller 131 to reduce an output value of the proportional integral controller 131 and output the reduced output value to the high-level priority control signal receiver 150, according to a signal from the high-level priority control signal generator 140. In detail, if a high-level control signal is generated, and thus, the steam generator level control system operates in a high-level priority control mode, and then, the high-level priority control mode is deactivated, the output reducer 132 controls the proportional integral controller 131 to reduce an output from the proportional integral controller 131 and output the reduced output to the high-level priority control signal receiver 150. This may prevent a phenomenon in which, after a high-level priority control mode is deactivated, the steam generator level control system returns to the high-level priority control mode as a feedwater speed is drastically increased, that is, a phenomenon in which a steam generator level oscillates repeatedly from a high level to a normal level. The proportional integral controller 131 and the output reducer 132 may be disposed as shown in FIG. 3 or 4. As shown in FIG. 3, the output reducer 132 may be connected to both to the high-level priority control signal generator 140 and the proportional integral controller 131, so that the output reducer 132 receives a signal from the high-level priority control signal generator 140 and outputs a signal, which is to control an output from the proportional integral controller 131, to the proportional integral controller 131, and thus, an output from the proportional integral controller 131 is controlled by the output reducer 132 after the output reducer 132 has received a signal from the high-level priority control signal generator 140. As another method, as shown in FIG. 4, the output reducer 132 may be disposed at a rear end of the proportional integral controller 131, so that the output reducer 132 receives a value output to the proportional integral controller 131, and reduces a proportional integral control value received according to an output signal from the high-level priority control signal generator 140 and outputs the reduced proportional integral control value. A time period for which the output reducer 132 reduces an output from the proportional integral controller 131 may be determined by time, a steam generator level, or an output value of the proportional integral controller 131 (a proportional integral control value). As an example of reducing an output from the proportional integral controller 131 with reference to time, if a high-level priority control mode is deactivated, the output reducer 132 may reduce an output value of the proportional integral controller 131 during a time period which is preset by a system operator. In this case, an output value may be reduced at a predetermined rate with reference to the output value or reduced in correspondence with a predetermined value. A reduction rate may be 50%. Additionally, an output value may be reduced at a constant rate or in correspondence with a constant value during a time period for which the output value is reduced, or a reduction rate or a reduced value may be gradually decreased. As an example of reducing an output from the proportional integral controller 131 with reference to a steam generator level, even if a high-level priority control mode is deactivated as a steam generator level is decreased, an output from the proportional integral controller 131 may be reduced until before the steam generator level becomes equal to or less than a predetermined value. For example, assuming that a high-level priority control mode is activated when a steam generator level is 85%, and that the high-level priority control mode is deactivated when the steam generator level is 80%, even when the steam generator level is equal to or less than 80%, if the steam generator level is equal to or less than 75%, an output from the proportional integral controller 131 may be reduced. In this case, an output from the proportional integral controller 131 may be reduced at a constant rate or in correspondence with a constant value until before the steam generator level becomes equal to or less than a predetermined value. Alternately, a reduced rate or value may be decreased as the steam generator level is reduced. A purpose an exemplary embodiment is to prevent oscillation of a steam generator level which may occur after a high-level priority mode is deactivated. According to an exemplary embodiment, the output reducer 132 reduces an output from the proportional integral controller 131 for a certain time period right after a high-level priority control mode is deactivated. Accordingly, in the above-described example, an output from the proportional integral controller 131 is not reduced simply because a steam generator level is equal to or greater than 75%, and an output from the proportional integral controller 131 is reduced if a steam generator level is equal to or greater than 75% in a time period when a set condition is met after a high-level priority control mode is deactivated. FIG. 5 is a block diagram of a configuration of a steam generator level control system according to another exemplary embodiment. According to exemplary embodiments described with reference to FIGS. 2 through 4, an output from the proportional integral controller 131 is reduced after a high-level priority control mode is deactivated. However, according to another exemplary embodiment described with reference to FIG. 5, oscillation of a steam generator level is prevented by using a method of setting a dead band, the setting being performed by the high-level priority control signal generator 140. In detail, the steam generator level control system, shown in FIG. 5, includes the comparator 120, the proportional integral control output unit 130, the high-level priority control signal generator 140, the high-level priority control signal receiver 150, the main feedwater pump speed controller 160, and the feedwater control valve opening controller 170. The proportional integral control output unit 130 outputs a proportional integral control value, as described with reference to FIG. 2. The high-level priority control signal generator 140 receives an input of an output value of the proportional integral controller 131, and then, controls the high-level priority control signal receiver 150 not to output a high-level priority control signal for a certain time period after a high-level priority control mode is deactivated until an output value of the proportional integral control output unit 130 is reduced sufficiently. The time period may be a fixed time period, or may be changed according to an output value of the proportional integral control output unit 130. If the time period may be changed, the time period may be determined as a time period until an output value of the proportional integral control output unit 130 is reduced to a value equal to or less than a predetermined value. A range of an output value of the proportional integral control output unit 130, in which a high-level priority control signal is not output, may be determined by a system operator or developer. FIG. 6 is a graph showing a comparison between a result of controlling a steam generator level according to an exemplary embodiment and a result of controlling a steam generator level in the related art. FIG. 6 shows a comparison between a result of the controlling according an exemplary embodiment described with reference to FIG. 2 and a result described with reference to FIG. 1. As shown in FIG. 6, according to an exemplary embodiment, it may be understood that oscillation of a steam generator level is remarkably decreased after a high-level priority control signal is generated. According to an exemplary embodiment, oscillation of a steam generator level, which may be caused by frequently turning a high-level priority control signal ON/OFF, may be prevented by controlling an output value of a proportional integral controller included in a feedwater control system when the steam generator level control system enters a high-level priority control mode due to a high steam generator level. Thus, a sudden shutdown of a nuclear reactor which may be caused by the oscillation of a steam generator level may be prevented in advance. The inventive concept can also be embodied as computer-readable codes on a computer-readable recording medium. The computer-readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer-readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer-readable recording medium can also be distributed over network coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. It should be understood that exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments. While one or more exemplary embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inventive concept as defined by the following claims. |
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054616565 | claims | 1. A method for sterilizing water comprising: (a) forming a flow passageway for passing water through a defined area; (b) providing a non radioactive source for producing X-rays inside the flow passageway; (c) generating X-rays inside the flow passageway at a first intensity; (d) passing water through the flow passageway and the X-rays at a first rate sufficient to sterilize the water. (e) cladding the flow passageway with a material for containing X-rays. (a) forming a flow passageway for passing the material through a defined area; (b) providing a non radioactive source for producing X-rays inside the flow passageway; (c) generating X-rays inside the flow passageway at a first intensity; and (d) passing the material in a flow through the flow passageway and the X-rays at a first rate sufficient to sterilize the material. (e) cladding the flow passageway with a second material for containing X-rays. 2. The method as in claim 1 further comprising: 3. The method as in claim 1 wherein step (b) further comprises providing an X-ray source having a vacuumated dielectric chamber containing a gas that produces an ECR plasma in an applied resonant magnetic field. 4. The method as in claim 1 wherein step (b) further comprises providing an ECR-X source. 5. The method as in claim 1 wherein step (b) further comprises providing more than one non radioactive X-ray source spaced apart, each source having a vacuumated dielectric chamber containing a gas that produces an ECR plasma in an applied resonant magnetic field and generating X-rays at an intensity so that the water flowing at a second rate is cumulatively exposed to X-rays sufficient to sterilize the water. 6. The method as in claim 5 wherein each non radioactive X-ray source is an ECR-X source. 7. The method as in claim 1 wherein steps (a) and (b) further comprise bending the flow passageway on opposite sides of the X-ray source and cladding the flow passageway between and about the bends with a material for containing X-rays so that X-rays generated by the source inside the flow passageway are confined within the flow passageway. 8. The method as in claims 3, 4, 5 or 6 wherein step (c) further comprises energizing each X-ray source with from 200 to 500 watts of microwave power. 9. A method for sterilizing a flowable material comprising: 10. The method as in claim 9 further comprising: 11. The method as in claim 9 wherein step (b) further comprises providing an X-ray source having a vacuumated chamber containing a gas that produces an ECR plasma in an applied resonant magnetic field. 12. The method as in claim 9 wherein step (b) further comprises providing an ECR-X source. 13. The method as in claim 9 wherein step (b) further comprises providing more than one non radioactive X-ray source spaced apart, each source having a vacuumated chamber containing a gas that produces an ECR plasma in an applied resonant magnetic field and generating X-rays at an intensity so that the material flowing at a second rate is cumulatively exposed to X-rays sufficient to sterilize the material. 14. The method as in claim 13 wherein each non radioactive X-ray source is an ECR-X source. 15. The method as in claim 9 wherein steps (a) and (b) further comprise bending the flow passageway on opposite sides of the X-ray source and cladding the flow passageway between and about the bends with a material for containing X-rays so that X-rays generated by the source inside the flow passageway are confined within the flow passageway. 16. The method as in claims 11, 12, 13 or 14 wherein step (c) further comprises energizing each X-ray source with from 200 to 500 watts of microwave power. |
claims | 1. Spent nuclear fuel transfer cask having motor-driven lids that slide toward and away from each other, the spent nuclear fuel transfer cask comprising:a transfer container having a space for accommodating a canister storing spent nuclear fuel;a neutron shielding body disposed around an outer circumference of the transfer container to shield neutrons; andan opening/closing portion coupled to a lower portion of the transfer container to open and close the lower portion of the transfer container,wherein the opening/closing portion comprisesa support portion that has a first through-hole communicating with the transfer container and supports the transfer container, wherein a lower portion of the transfer container is placed on the support portion;a base plate that is arranged below the support portion at a certain interval and has a second through-hole through which the canister to be taken out passes; anda lid assembly that includes a first lid portion sliding between the support portion and the base plate to open and close part of the first through-hole, and a second lid portion sliding between the support portion and the base plate to open and close a remaining portion of the first through-hole, andwherein the first lid portion includes a first lid and a first motor for sliding the first lid, and the second lid portion includes a second lid and a second motor for sliding the second lid,the spent nuclear fuel transfer cask further comprising,a first support frame coupled to the outside of the first lid; anda second support frame coupled to the outside of the second lid,wherein the first and second motors are coupled to the support portion,a first motor shaft of the first motor and a second motor shaft of the second motor protrude downward through the support portion,the outside of the first support frame is engaged with the first motor shaft,the outside of the second support frame is engaged with the second motor shaft, andwhen the first and second motors rotate, the first and second support frames slide to open and close the first through-hole. 2. The spent nuclear fuel transfer cask of claim 1, wherein a protrusion portion is formed at an end of the first lid, a placement portion on which the protrusion portion is placed is formed in the second lid, and the protrusion portion is placed on the placement portion of a step shape to close the first through-hole. 3. The spent nuclear fuel transfer cask of claim 1, wherein a guide rail for guiding the first and second support frames when the first and second support frames are slid is coupled to the base plate. 4. The spent nuclear fuel transfer cask of claim 1, whereinthe first and second lids are formed in a semicircular shape, respectively,the first support frame includes a pair of first side frames arranged to face each other in a sliding direction of the first lid and a first connection frame connecting the pair of first side frames to each other, and when the pair of first side frames and the first connection frame are arranged outside the first lid, an arc portion of the first lid, the pair of first side frames, and the first connection frame are spaced apart from each other to form an empty space, andthe second support frame includes a pair of second side frames arranged to face each other in a sliding direction of the second lid and a second connection frame connecting the pair of second side frames to each other, and when the second side frame and the second connection frame are arranged outside the second lid, an arc portion of the second lid, the pair of second side frames, and the second connection frame are spaced apart from each other to form an empty space. 5. Spent nuclear fuel transfer cask having motor-driven lids that slide toward and away from each other, the spent nuclear fuel transfer cask comprising:a transfer container having a space for accommodating a canister storing spent nuclear fuel;a neutron shielding body disposed around an outer circumference of the transfer container to shield neutrons; andan opening/closing portion coupled to a lower portion of the transfer container to open and close the lower portion of the transfer container,wherein the opening/closing portion comprisesa support portion that has a first through-hole communicating with the transfer container and supports the transfer container, wherein a lower portion of the transfer container is placed on the support portion;a base plate that is arranged below the support portion at a certain interval and has a second through-hole through which the canister to be taken out passes; anda lid assembly that includes a first lid portion sliding between the support portion and the base plate to open and close part of the first through-hole, and a second lid portion sliding between the support portion and the base plate to open and close a remaining portion of the first through-hole, andwherein the first lid portion includes a first lid and a first motor for sliding the first lid, andthe second lid portion includes a second lid and a second motor for sliding the second lid,wherein a lower side of the base plate is coupled to a fitting plate that includes an insertion portion protruding downward and is inserted to an upper side of the canister. 6. Spent nuclear fuel transfer cask having motor-driven lids that slide toward and away from each other, the spent nuclear fuel transfer cask comprising:a transfer container having a space for accommodating a canister storing spent nuclear fuel;a neutron shielding body disposed around an outer circumference of the transfer container to shield neutrons; andan opening/closing portion coupled to a lower portion of the transfer container to open and close the lower portion of the transfer container,wherein the opening/closing portion comprisesa support portion that has a first through-hole communicating with the transfer container and supports the transfer container, wherein a lower portion of the transfer container is placed on the support portion;a base plate that is arranged below the support portion at a certain interval and has a second through-hole through which the canister to be taken out passes; anda lid assembly that includes a first lid portion sliding between the support portion and the base plate to open and close part of the first through-hole, and a second lid portion sliding between the support portion and the base plate to open and close a remaining portion of the first through-hole, andwherein the first lid portion includes a first lid and a first motor for sliding the first lid, and the second lid portion includes a second lid and a second motor for sliding the second lid,wherein a first guide groove extending in one direction is formed in a lower surface of the first lid,a second guide groove extending in one direction is formed in a lower surface of the second lid, andthe base plate includes a first stopper that is inserted into the first guide groove and is caught on an end of the first guide groove when the first lid is opened, and a second stopper that is inserted into the second guide groove and is caught on an end of the second guide groove when the second lid is opened. |
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abstract | An X-ray analysis instrument, in particular, an X-ray diffractometer (21), has an X-ray source (22; SC) that emits an X-ray beam (23), an X-ray optics (24), in particular a multi-layer X-ray mirror, and a collimator mechanism (BM), wherein the collimator mechanism (BM) forms an aperture window (2, 2′) with an aperture opening (3, 3′) through which at least part (26) of the X-ray beam (23) passes. The collimator mechanism (BM) comprises means for gradual movement of the aperture window (2, 2′) in at least one direction (A/B, x, y) transversely to the X-ray beam (23), the aperture opening (3, 3′) is at least as large as the cross-section (32) of the X-ray beam (23) at the location of the aperture window (2, 2′), and the path of movement (VWx, VWy) of the aperture window (2, 2′), which is accessible by the collimator mechanism (BM), in the at least one direction (A/B, x, y) is at least twice as large as the extension (RSx, RSy) of the X-ray beam (23) at the location of the aperture window (2, 2′) in this direction (A/B, x, y). The X-ray analysis instrument offers a wider scope of beam conditioning possibilities. |
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description | This application is the U.S. national phase of International Application No. PCT/GB2007/003435, filed 11 Sep. 2007, which designated the U.S. and claims priority to Great Britain Application No. 0617943.6, filed 12 Sep. 2006, the entire contents of each of which are hereby incorporated by reference. The present invention relates to a method and apparatus for accelerating charged particles and a method and apparatus for producing electromagnetic radiation using accelerated charged particles. It has been known for some 25 years that the huge electric fields formed in the charge density wave that trails an intense laser pulse propagating through a plasma (ionized gas) could be used to accelerate charged particles in a distance which is one-thousand times smaller than that required with a conventional accelerator for comparable output energies. Laser-driven plasma accelerators, also known as wake-field accelerators, could therefore form the basis of a new class of very compact accelerator with dimensions of only a few centimeters (excluding the driving laser), and able to generate particle beams with energies equal to those delivered by conventional machines some tens or hundreds of meters long. A further advantage is that the output beam, usually electrons but other charged particles are also possible, from a plasma accelerator is comprised of pulses of much shorter duration (femtoseconds) than possible with a conventional accelerator (which typically delivers bunches several picoseconds long). Laser-driven plasma accelerators could therefore replace the conventional accelerators used to power radiation sources, such as synchrotrons, to form a compact source of short pulses of charged particles and tunable radiation. However, there are practical difficulties associated with injecting charged particle bunches to be accelerated into the plasma accelerator, which can limit the quality of the accelerator output. For example, where bunches of charged particles are generated separately and transported to the plasma accelerator, it is very difficult to avoid the bunches becoming less well defined spatially (i.e. spreading out) during the transport phase. This and other limitations in the precision with which the injection process can be carried out can cause fluctuations in the output energy of the accelerator (“jitter”) and/or undesirable energy spread within the output charged particle bunches. Undulators may be used to derive electromagnetic radiation from accelerated charged particle beams and thereby form a radiation source. Such undulators are based on arrays of permanent magnets arranged so that their magnetic fields periodically deflect a charged particle beam passing through them. The transverse motion thus imparted to the charged particle beam produces so-called undulator or wiggler synchrotron radiation, which forms the basis of modern synchrotron sources. Undulators are also used in free-electron laser x-ray sources to produce intense coherent x-ray radiation. X-ray free-electron laser undulators are usually between 20 and 150 meters long and have many thousands of periods. Generally, strong magnetic fields are required to deflect the charged particle beam, which makes it difficult to miniaturize the permanent magnets and produce a compact undulator. It is an object of the present invention to provide an improved compact undulator for a radiation source. It is a further object of the invention to improve charged particle injection in plasma accelerators. According to an aspect of the invention, there is provided a method of producing electromagnetic radiation, comprising: forming a plasma channel in a capillary; firing a laser pulse through the plasma channel; arranging for a group of charged particles to be injected into a plasma density wake of the laser pulse so as to be accelerated by the wake; and arranging the plasma channel and the firing of the laser pulse such that the wake of the laser pulse exerts a transverse force on the injected group of charged particles that varies periodically as the laser pulse propagates along the channel length, the resulting transverse acceleration of the group of charged particles causing emission of said electromagnetic radiation. According to a further aspect of the invention, there is provided an electromagnetic radiation source, comprising: a capillary suitable for creating a plasma channel; a laser source arranged to fire a laser pulse through the plasma channel; and means for injecting a group of charged particles into a plasma density wake of the laser pulse so that the group is accelerated by the wake, wherein the laser source and channel are arranged so that in use the wake of the laser pulse exerts a transverse force on the injected group of charged particles that varies periodically as the laser pulse propagates along the channel length, the resulting transverse acceleration of the bunch of charged particles causing emission of said electromagnetic radiation. According to the above, the wake behind a laser pulse in the channel, which may be defined as the disturbance in the plasma charge density caused by passing of the laser pulse, may be used as an undulator to produce electromagnetic radiation, and in particular to produce a short high frequency radiation pulse. The spatial period between undulations (which may vary along the capillary according to the desired output frequency or range of frequencies to take into account acceleration or deceleration of the charged particles) in embodiments of such a system may be substantially shorter than 1 mm to produce X-ray radiation, in contrast to dimensions of 1 cm or longer for a comparable permanent magnet type undulator. This means, for example, that a 1000 period undulator with a periodicity of 100 microns can be made only 10 cm long, which reduces the cost and size of the undulator considerably. Conventional undulators can cost several £100 k/meter and need to be housed in large specially constructed buildings with thick layers of concrete radiation shielding. A plasma undulator such as that discussed could be added to a laser-driven accelerator (plasma accelerator) at virtually no extra cost. The frequency of the output radiation depends on the velocity of the charged particles. The closer to the speed of light the higher the frequency. In the charged particle frame of reference the undulator period is Doppler shifted and appears to have a shorter period (by a factor equal to the relativistic Lorentz contraction factor γ). The charged particles will radiate light with this period (i.e. Doppler shifted frequency). However, from an observer in the laboratory frame the frequency is again Doppler shifted to a high frequency. It can be said that the radiation is thus double Doppler shifted—once into the charged particle frame and then again back into the laboratory frame. In practice, therefore, the frequency (and therefore wavelength) of the output radiation depends predominantly on the spatial period of the undulator (λu) and the energy (E) of the charged particles, which may be parameterized by the Lorentz factor γ in E=γmec2, me being the rest mass of the charged particle. In these terms, the output wavelength is approximately given by λ=λu/2γ2. However, there are correction terms which depend on the strength of the transverse deflection force. The term “undulator” is understood in the field to encompass means to induce oscillation in one-dimension (e.g. a transverse oscillation in combination with translational motion) and also periodic motion in three-dimensions, such as helical motion in a magnetic field. For very strong deflection forces, the emitted radiation is sometimes called wiggler radiation and many high harmonics of the fundamental frequency are produced extending the spectral range of the synchrotron source. A further useful aspect of the above embodiment is that it makes possible the production of ultra-short duration radiation pulses, potentially shorter than 10 fs, which is not easy to achieve using other tunable light sources. Moreover, this technique provides the basis for generating widely tunable femtosecond pulses of X-rays, which is difficult/impossible to do any other known way. The short duration of the radiation pulses is possible because the plasma charge density can be made to vary on a very short length scale—typically a few tens of microns. This sets the wave period of the plasma charge density wake which the charged particles “surf down”, and the surfer, which is the charged particle group or bunch being accelerated, must be shorter than the wave period otherwise it will straddle more than one plasma wave and parts of the charged particle bunch will be accelerated and parts will be decelerated. The plasma density wave period thus essentially fixes the bunch length, which in turn limits the duration of the radiation pulse. The ability to produce femtosecond scale pulses in this way would be of value to scientists wishing to carry out time-resolved studies of the structure of matter, for example, by allowing such studies to be carried out on unprecedented time scales and providing the basis for making X-ray “movies” of the structure of matter evolving on its natural time scales, e.g. in chemical reactions etc. The transverse force from the wake may stem from a corresponding deflection of the wake caused by deflection of the laser pulse. The plasma channel and the firing of the laser pulse can be arranged to do this in several ways. One option is to fire the laser pulse into the channel off-axis (i.e. a special arrangement of the firing of the laser pulse rather than of the channel, which can simply be straight in this embodiment), which causes a periodic transverse deflection of the laser pulse (via “mode beating”). This phenomenon can be visualized via the analogy of a toboggan or bobsleigh rattling down a snow channel or a marble rolling along a horizontal U-shaped gutter. Following the marble analogy, if the marble is rolled along the bottom of the gutter, in a direction parallel to the axis of the gutter, it will continue to roll undeflected. However, if the marble is either started to one side, or pushed in a direction which makes an angle with the axis of the gutter, or both, it will undergo periodic transverse motion (due to a gravity-induced transverse restoring force arising from the U-shape of the gutter). In a plasma channel, the transverse charge density gradient, which is what makes the plasma channel “channel” the laser pulse, provides the transverse restoring force for the laser beam. “Off-axis” injection of the laser pulse may therefore comprise firing the laser pulse in a direction parallel to a longitudinal central axis of the channel (or capillary) but starting from a point radically spaced from the axis, or it may comprise firing the laser pulse in an oblique direction relative to the axis but starting from a point on the axis, or a mixture of both. A second option, which may be applied separately or in conjunction with the first option, is to provide a channel having a shape, induced by the shape of the capillary, that causes the periodic transverse deflection of the laser pulse and wake (i.e. a special arrangement of the channel or capillary rather than of the firing of the laser pulse, which may be carried out normally). Suitable shapes may include undulations of substantially sinusoidal longitudinal cross-section or localized deviations in cross-section that are separated longitudinally along the channel. Both options can be implemented at relatively low cost and can be used together to produce a finely controlled radiation source. Other possibilities include helix-type shapes or square-wave patterns. More generally, any shape in which there are periodic variations in the transverse position of the axis of the channel, or in the cross-section of the channel, or both, might be suitable. Further, as discussed below, it may prove useful to vary the period of the pattern with position along the channel. This may be useful, for example, for controlling the position of the accelerated charged particle bunch in the wake (for example, to keep the bunch at the same position in the wake), to vary the spectrum of the output radiation or to maintain coherence of radiation emitted from one undulator period to the next. The above-described periodic plasma channels can be created by forming capillaries which have periodic variations in the position of their axis or in their cross-section. The capillaries can be precision machined for this purpose using laser micromachining or other etching methods in a substrate such as sapphire, for example. The step of arranging for a group of charged particles to be injected into a wake of the laser pulse may comprise producing a group of charged particles externally of the capillary and injecting them into the capillary from the outside. This approach has the advantage that a large number of charged particles can be introduced into the channel relatively easily. Additionally or alternatively, the injected group of charged particles may originate from the plasma itself and be extracted by the wake of the laser pulse. This approach obviates the need for a separate source of charged particles and also avoids problems associated with transporting the charged particles from a separate charged particle generating system to the capillary, thereby potentially producing more controlled charged particle injection. Various methods may be used for promoting injection of charged particles from the plasma. For example, density variations in the plasma can be induced which promote charged particle injection; these can be achieved by means of deviations in the profile of the capillary (see below) and/or by using additional laser pulses (i.e. in addition to the laser pulse used to accelerate charged particles trapped in its wake). The plasma formed in the capillary may be arranged to have a transverse density profile that favours focussing of the laser pulse towards a central axis of the capillary (i.e. the plasma forms a channel for guiding the laser pulse). This helps keep the intensity of the laser pulse high over a long distance, thus enabling more effective acceleration of charged particles in the wake of the laser pulse. The focussing effect is also what makes it possible to induce the laser pulse to undergo periodic variations: the forces which focus the laser towards the centre of the channel are the same ones that would force the laser pulse to execute periodic motion in the periodic plasma channel. The transverse density profile may, for example, be characterized by having a falling density from the walls of the channel towards the axis of the channel. Such a plasma density profile may be created where the plasma is formed by firing a discharge through a gas contained in the capillary, heat transfer to walls of the capillary causing the plasma to have a higher temperature near the central axis of the capillary compared with the temperature near the walls of the capillary. A means for injecting a group of charged particles into the channel may be provided in the form of a longitudinally localized deviation in the cross-section of the capillary that, in use, causes a corresponding deviation in the plasma density, said deviation in the plasma density being such as to cause injection of a group of charged particles from the plasma into a wake of the laser pulse in the region of the deviation in the channel so that the group is accelerated by the wake. This arrangement allows highly controlled charged particle injection which can reduce the energy spread of an accelerated charged particle bunch as well as reduce jitter in the average energy of the charged particle bunch. According to a further aspect of the invention, there is provided an apparatus for accelerating charged particles, comprising: a capillary suitable for forming a plasma channel; and a laser source arranged to fire a laser pulse through the plasma channel, wherein said capillary has a longitudinally localized deviation in its cross-section that, in use, causes a corresponding deviation in the plasma density, said deviation in the plasma density being such as to cause injection of a group of charged particles from the plasma into a wake of the laser pulse in the region of the deviation in the capillary so that the group is accelerated by the wake. According to a further aspect of the invention, there is provided a method of accelerating charged particles, comprising: forming a plasma channel in a capillary; and firing a laser pulse through the plasma, wherein said capillary has a longitudinally localized deviation in its cross-section that causes a corresponding deviation in the plasma density, said deviation in the plasma density being such as to cause injection of a group of charged particles from the plasma into a wake of the laser pulse in the region of the deviation in the capillary so that the group is accelerated by the wake. Here, charged particles are injected into the wake of the laser pulse in the sense that they are subsequently swept along by the wake, moving longitudinally away from their original positions in the plasma along the length of the channel, accelerating during this trajectory due to the electric fields within the wake so as to emerge at high energy later on in the channel (at the end of the channel, for example). These injected charged particles will stay within the wake at roughly the same distance behind the laser pulse during much of the remaining trajectory of the laser pulse in the channel. Charged particles from the plasma that are not injected into the wake may be disturbed by the laser pulse as it passes, and this may include some element of longitudinal acceleration, but such charged particles will not normally be carried along significantly with the wake: they will tend to return towards their starting positions after the laser pulse has passed. This latter case is what often happens when the laser pulse is propagating through a uniform plasma, although some injection of charged particles may nevertheless occur (for example, the wake itself will tend to act on the laser pulse even in a nominally uniform plasma, which can cause the laser pulse to distort and cause injection; furthermore, when the laser intensity is very high—high enough to cause charged particles to travel close to the speed of light—some charged particles will be spontaneously trapped in/injected into the wake). However, the dynamics of the displaced charged particles changes when the longitudinal density of the plasma is non-uniform (as may be induced by the deviations in the capillary structure, for example) and can be such as to promote the desired entrapment of the charged particles in the wake of the laser pulse. This latter point may be understood more clearly via the surfer analogy again. Injection of charged particles into the plasma wave such that they are accelerated basically consists of preparing the charged particles to catch the wave (i.e. improving their chances of being swept along with the wave), which can be viewed as analogous to the way a surfer might paddle in the direction of an arriving wave in the sea in order to “catch” it as it passes. Just as the surfer paddles in the direction of the wave, the idea in the plasma channel is that by locally changing the form of the capillary in which the plasma channel is formed it should be possible locally to change the longitudinal density of the plasma (i.e. in the direction the wave will travel), thus causing local longitudinal gradients in the plasma density which have been shown to promote charged particle injection. According to this approach, charged particles are injected in a controlled way into a precise part of the plasma wave, right at the point they will start to be accelerated, and acceleration can be maintained over a long distance since the laser pulse will be focussed by the channel. This approach may therefore produce a stable charged particle beam both in terms of output energy fluctuations (i.e. “jitter”) and energy spread of the output charged particle bunches. The position of the deviation in the capillary may be used to determine a final energy for the accelerated group of charged particles because it can determine the length over which the charged particles are accelerated. The output energy of the accelerator system can therefore easily be controlled by adjusting the separation between a point of injection of the charged particles to be accelerated and an output. For example, the capillary may comprise at least one further longitudinally localized deviation in its cross-section that, in use, causes at least one corresponding further deviation in the plasma density, each said further deviation in the plasma density being such as to cause injection of a further group of charged particles from the plasma into the wake of the laser pulse in the region of the further deviation in the channel so that each further group is accelerated by the wake. The plurality of localized deviations in such an arrangement can therefore be used to inject charged particles bunches that are to be accelerated to different energies, the positions of the respective longitudinal deviations determining the final energies. A high intensity laser pulse fired through a plasma (an ionized gas) displaces charged particles as it propagates through the plasma in a similar way to a boat pushing its way through water. Like the displaced water particles in the boat analogy, the displaced charged particles also tend to return roughly (not necessarily exactly) towards their starting positions after the laser pulse has passed due to Coulomb forces, and enter into a kind of oscillatory motion in the wake of the laser pulse. Displacement of the charged particles in the wake of the laser pulse is associated with enormous electric fields. Longitudinal components of these electric fields can be used to accelerate charged particles along the direction of the laser pulse. In particular, it is possible to inject charged particles into the wake in such a way that they effectively surf along behind the laser pulse, remaining in a region of the wake that has an accelerating longitudinal electric field component over some distance. Injecting bunches of charged particles into a wake in this way is the principle of operation of a laser-driven plasma accelerator. A practical problem that has been encountered is maintaining the intensity of the driving laser pulse over distances of more than a millimeter or so, which has limited the output energy of laser-driven accelerators to a few hundred MeV (106 electron volts). However, recent developments have shown that a plasma waveguide can be used to keep the laser pulse focused over several centimeters, increasing the output of the accelerator to the GeV level. This is the same sort of energy routinely used in synchrotron facilities, but generated in an accelerator only a few cm long. FIGS. 1A and 1B illustrate one way in which a plasma waveguide can be created according to an embodiment of the invention. A capillary 2 (shown side on in FIG. 1A and end on in FIG. 1B), which may be a few centimeters long and a few hundred micrometers in diameter, is filled with a suitable gas (hydrogen, for example). An electric discharge is then fired through the capillary 2, which ionizes the gas and produces the plasma channel. The discharge naturally produces a plasma that is hotter than the walls of the capillary and thermal conduction between the plasma and the walls causes a temperature gradient between a longitudinal axis of the capillary 2 and the walls of the capillary 2. The plasma is hotter near the axis of the capillary 2 than near the walls. The temperature gradient causes a density gradient in the plasma with the plasma having a lower density near the axis than near the walls. The effect of this density gradient is to keep the laser pulse focussed near the axis of the capillary (i.e. to “guide” the laser pulse down the plasma channel thus formed) by means of refraction (the light will tend to bend away from the higher density region towards the lower density region). Any diffractive effects tending to cause radial divergence of the laser pulse will thus tend to be compensated by the refractive properties of the plasma channel. This continual focussing of the laser pulse is indicated schematically by arrows 4 in FIG. 1B (and also FIG. 2B—see below) and is the basic principle of one type of plasma channel or waveguide. FIGS. 2A and 2B show corresponding views of the plasma-filled capillary 2 of FIGS. 1A and 1B after a laser pulse 6 has been fired down the capillary 2. Charged particles are injected from device 10 into the wake 8 of the laser pulse 6 as the laser pulse 6 passes an injection point in the capillary 2 so as to be accelerated by the wake as described above. Charged particle injection can be achieved either by injecting an externally produced charged particle beam from a conventional accelerator (as shown), or through “all-optical” injection, promoted, for example, via a density gradient induced by longitudinal structure in the capillary 2. Successfully injected charged particles are displaced by the passing laser pulse and made to oscillate at the correct phase and phase velocity to be captured by the wake and accelerated to high energies (the latter method is described in more detail below). Accelerated bunches of charged particles can be used to produce high frequency radiation such as X-rays, which can be useful in many applications. As discussed above, this conversion process may be carried out by passing the accelerated charged particles through an undulator consisting of an array of permanent magnets configured to cause the charged particle beam to undergo periodic transverse displacements as it passes between them. However, the array of permanent magnets is expensive, inflexible and frequency-limited. FIGS. 3 and 4 show undulators according to an embodiment of the present invention, in which the wake of a laser pulse applies an undulating force on charged particles being accelerated within it. One way in which this can be achieved is by bending or otherwise forming the capillary 2 into an undulating shape as shown in FIG. 3, which causes a periodic variation in the plasma channel formed in the capillary that in turn will force the laser pulse and its wake, to undulate (i.e. be displaced periodically in a transverse direction) as it propagates through the waveguide (indicated schematically by arrows 12). The undulating plasma wake exerts a periodically changing transverse force on charged particles injected into the wake. Various channel shapes may be used to promote the undulating motion of the wake. These may include discrete disturbances or “bumps” 14, as shown in FIG. 3, or may comprise a continuous sectional profile, for example having a substantially sinudoidal sectional form (not shown). A further alternative would be helical, which could be used to produce circularly polarized light, which would be of great advantage for some applications. Generally speaking, the main function of the periodically varying channel is to cause the laser to follow a similar path and therefore, through the strong transverse forces of the wake, to guide the charged particle bunch also along a similar path (much in the same way as a toboggan would follow a periodically winding snow track, extending the previously used analogy) Similar undulation of the plasma wake can be achieved by introducing the laser pulse into the waveguide channel slightly off-axis, as illustrated in FIG. 4 (arrow 18 representing a laser pulse and dotted line 16 representing a longitudinal axis of the channel 2). The effect is to produce mode beating of the laser pulse, which effectively causes the laser pulse to be periodically deflected away from the axis 16 as it propagates down the channel 2. A combination of the arrangements of FIGS. 3 and 4 may also be used to fine tune the transverse motion of the charged particle bunches. Whichever of the two above approaches are adopted, the transverse acceleration of the charged particles in the channel 2 produces electromagnetic radiation, in the same way as a charged particle beam in an undulator insertion device in a synchrotron storage ring (which undulator would typically employ an array of permanent magnets, for example, to drive the transverse accelerations of the charged particles). FIG. 5 shows a generalised apparatus for carrying out the above method. A capillary 2 is provided into which a gas can be introduced. A discharge circuit 34 is provided for passing an electric discharge through the gas in order to form a plasma channel within the capillary. Specific details of such an arrangement can be found in the article Investigation of a hydrogen plasma waveguide, D. J. Spence and S. M. Hooker, Phys. Rev. E 63, 015401 (R), herein incorporated in its entirety by reference. In this example, the capillary 2 has a diameter of order 200 μm (more generally, it is envisaged that a range of capillary diameters from about 10 μm to 500 μm might be useful) and a length of several centimeters, and may comprise a hollow tube or be formed by laser-machining ‘u-shaped’ channels/grooves into the surface of two plates and bringing the plates together to form a capillary. Further details of how plasma channels may be created, including the method of laser machining of the capillaries and gas inlets etc. can be found in Radiation sources based on laser-plasma interactions, D. A. Jaroszynski, et al., Phil. Trans. R. Soc. A, Vol. 364, No. 1840/Mar. 15, 2006, pages—689-710-, herein incorporated in its entirety by reference. Suitable materials for the tube or plates are alumina or sapphire, or other high-temperature materials. Hydrogen gas is introduced into the capillary 2, via holes with a diameter of order 100 μm which are laser-machined near each end, so that the density of hydrogen is constant between these gas injection points. An alternative arrangement would be to inject gas at different pressures at each end of the capillary 2. This would set up a flow of gas along the capillary 2 which would give a small longitudinal gradient in the plasma density; such gradients may be useful for “phase-matching” the acceleration, although they would not be sufficient to induce charged particle injection. Electrodes 36 located at each end of the capillary enable a discharge pulse to be struck through the capillary 2 by the discharge circuit 34, thereby ionizing the gas within. The discharge pulse is driven by a capacitor with a capacitance of order 2 nF, charged to an initial voltage of around 20 kV. The resulting discharge current has a peak of several hundred amperes and a half-period of order 200 ns. Laser source 32 is configured to introduce a laser pulse into the channel 2 (either on- or off-axis) once the plasma has been established. In practice, this can be done using a mirror or lens to focus the laser beam into the desired part of the capillary 2. Charged particle source 10 is provided to inject the charged particles to be accelerated by the wake of the laser pulse into the capillary 2. Alternatively and/or additionally, the charged particles may be injected from the plasma itself by providing localized deviations in the cross-section of the capillary 2 (see below). An undulator section 30 may be provided at the output end of the channel 2 for applying transverse periodic motion to the charged particle beam in order to produce radiation (for example X-rays). The charged particles may continue to be accelerated as they propagate through the undulator section 30 so that the spatial separation between undulations may have to increase (taking into account relativistic effects, of course) moving from left to right along the undulator section 30 if the frequency of the radiation which is generated is to be kept constant in the laboratory frame of reference. The important point is that the double Doppler shift will change as the charged particles reach higher energy, which will tend to shift the radiation frequency upwards. This effect can be compensated by increasing the “undulator” periodicity so that the output radiation frequency remains constant. There may also be applications where it would be useful to allow changes in the generated frequency as the charged particles propagate through the undulator. For example, this might allow broad bandwidth radiation to be generated which could subsequently be compressed to generate very short duration pulses. Thus, manipulation of the undulator period (either with a constant or varying period) can be used to control the detailed properties of the spectrum of the output radiation. Although the accelerating portion of the channel 2 and the undulating section 30 are shown as separate elements in the embodiment of FIG. 5, they may also be combined into a single channel. According to an embodiment of the invention, injection of charged particles into the wake of the laser pulse is achieved by promoting acceleration of charged particles from the plasma itself. This may be achieved by creating a deviation in the cross-section of the capillary 2. The deviation in the cross-section of the capillary 2, which is localized in the sense of being of short spatial extent along a longitudinal axis of the waveguide (i.e. along the direction of propagation of the laser pulse), causes a corresponding localized deviation in the density of the plasma. This localized density deviation promotes joining of a large number of charged particles (a “bunch”) into the wake of the passing laser pulse (such that they are accelerated and stay in the wake as it moves down the capillary 2) and the acceleration of charged particles thus injected can be maintained over a long distance since the laser pulse will be channelled by the plasma channel formed in capillary 2 (for example, due to the refractive effects of the temperature induced radial density gradient in the plasma). The technique allows a high level of control of properties of the output charged particle beam such as output energy fluctuations (i.e. “jitter”) and energy spread of the output charged particle bunches. The deviation in the cross-section of the capillary 2 can take a number of different forms. For example, the deviations may be localized in the sense that the length of capillary over which the cross-sectional shape of the capillary changes is small in comparison with the length of the capillary 2. The effect of this arrangement is to cause a spatially sharp or sudden change in the plasma density in the region of the deviation. The form of the capillary may be identical either side of the deviation or may be different (for example, when the deviation is a step-change in the cross-sectional area of the capillary). FIG. 6 shows an example arrangement. Gas to be ionized to produce the plasma in capillary 2 is introduced via gas inlet pipes 22 and 24 formed in substrate 48 (the direction of gas flow being indicated by arrows 23) and leaves the capillary 2 via gas outlets 26 and 28 (the direction of gas flow being indicated by arrows 27). The gas flow may be provided and controlled by means of a gas flow controller 50. The localized deviation in this example comprises a localized increase 20 in the cross-sectional area of the capillary 2. For the particular example shown, the diameter 42 of the capillary 2 is 210 microns and the diameter 40 of the localized increase 20 is 420 microns. However, the diameters and/or length of the localized deviation may be varied to achieve optimal charged particle injection. This arrangement leads to a sharp change in the longitudinal (also referred to as “axial”) density of the plasma channel formed in the capillary 2 through a combination of changes in the heat flow to the wall of the capillary 2 and changes to the way the gas flows through the capillary 2 linked to the localized deviation 20. FIG. 7 shows an alternative embodiment including a similar arrangement of gas inlets 22/24, outlets 26/28, gas flow 23/27 and capillary 2 as FIG. 6 (the same reference numerals have been used to represent analogous features). However, in this embodiment, the localized deviation comprises an additional section of capillary 21 extending laterally away from the capillary 2 down which the laser pulse will propagate in use. In the example shown, the additional section of capillary 21 extends away from the capillary 2 in two directions (up and down in FIG. 7), but it is also conceivable that the additional section 21 will only extend away in a single direction. When the electrical discharge is fired down the capillary 2, plasma is forced up into this additional capillary 21 which leads to the required sharp localized change in the longitudinal density of the plasma. FIG. 8 shows a further embodiment, which makes use of a different flow pattern for the gas to be ionized. In this example, only a single gas inlet 22 is provided with two gas outlets 26 and 28 in order to produce a steady flow of gas to be ionized in the capillary 2. The localized deviation consists in this case of a step-change 44 in the cross-sectional area of the capillary 2. In effect, the capillary 2 is made up of two sections, a first with a smaller diameter 42 (of 210 microns in the particular example given) and a second with a larger diameter 46 (of 460 microns in the particular example given). Gas is made to flow continuously over the step-change 44 before the electrical discharge is fired, thereby establishing an initial gas density that varies along the axis of the capillary 2 (which is not the case in the embodiments of FIGS. 6 and 7). When the electrical discharge is fired, the variation in initial gas density translates to a corresponding variation in the longitudinal density of the plasma. Other shapes of localized deviation may also be suitable, for example deviations with a tapered profile (i.e. comprising a continuously changing cross-section over a short (localized) length of the capillary 2), or deviations with a helically varying cross-section (or other azimuthally non-uniform deviation). Generally speaking, the deviations should be such as to perturb the plasma density in the region of the deviation in such a way as to promote the injection of charged particles into the wake of a laser pulse passing through the channel 2. Bunches of charged particles carried along in the wake of a laser pulse in the capillary 2 are subjected to electrical forces that increase the energy of the bunch. Normally, the capillary 2 will be arranged such that bunches of charged particles are accelerated continuously from an injection point (where the charged particles are injected) to an output point (where the charged particles escape the capillary 2). The output energy of a charged particle bunch in such an arrangement will therefore depend, for a given laser pulse, on the distance between the injection and output points. A capillary 2 can be configured to output bunches of charged particles with different output energies by controlling the point in the channel at which the charged particles are injected into the wake of the laser pulse. Charged particle bunches inserted into the wake early in its trajectory through the capillary 2 will be accelerated more than charged particles injected into the wake later on. FIG. 9 show schematically how a capillary 2 might be configured to output charged particle bunches with three different energies, corresponding to each of the three longitudinally localized deviations 20, which promote charged particle injection at each of the points A, B and C. For laser pulses travelling from left to right in the figure, charged particles injected at point A will have the highest energy, following next by charged particles injected at point B, with charged particles injected at point C having the lowest energy. The above discussion assumes that the injected charged particles are accelerated over their entire trajectory along the capillary 2, which it is envisaged will be the normal arrangement. However, this may not always be the case, depending on how far the charged particles are made to travel down the capillary 2. If no countermeasures are taken, for example, the accelerated charged particles (which quickly reach speeds near to the speed of light in vacuum) will eventually overtake the laser pulse which is propagating at a slower speed through the plasma (or at least advance relative to the laser pulse to a point in the wake which is no longer in an accelerating electric field), a phenomenon known as “dephasing” that will interrupt acceleration of the charged particle bunch. As mentioned above, the problem of de-phasing may be tackled by establishing a plasma density in the capillary that changes gradually in the longitudinal direction (as opposed to the sharp localized change that is needed for injection of charged particles into the wake of the laser pulse). Such a gradual change may take place over a significant portion of the trajectory of the laser pulse, for example, which will generally mean over a distance considerably (i.e. many times) longer than the spatial period of undulations in a capillary radiation source or the longitudinal extent of the localized deviations in an injector. FIG. 10 shows an example of how this might be achieved over section of uniform capillary 2, with gas being input via inlet 22 and output via outlets 26 and 28. In the arrangement shown, the density of gas before the electrical discharge is fired may be estimated theoretically. In particular, for the majority of the capillary 2, assuming the flow is viscous, laminar and incompressible, the pressure variation within the capillary may be written as: P ( z ) = P ( z g ) z z g where z is the distance from the gas outlet 26 or 28 and zg is the distance from the gas inlet 22 to the gas outlet 26 or 28. P(zg) is the initial pressure at the gas inlet 22. This arrangement therefore produces a gas density that changes gradually over an extended region of the capillary 2 which, when the electrical discharge is fired, with produce a plasma channel with a plasma density that also varies gradually along the length of the capillary 2. In the example shown in FIG. 10, the gas inlet 22 is located in the centre of the capillary 2 but other arrangements are possible that will still permit a gradually changing plasma density to be formed. A further possible variation would be to add further gas inlets along the length of the capillary 2, which would make it possible to control the longitudinal profile of the initial gas density, and hence the longitudinal plasma density once the discharge has fired, more precisely. Both gradually increasing plasma densities (i.e. increasing along the direction of propagation of the laser pulse) and gradually decreasing plasma densities may be useful for improving the performance of laser-driven plasma accelerators. For example, gradually increasing plasma densities would generally be effective for overcoming dephasing, while gradually decreasing plasma densities would generally be effective for reducing the energy spread of a bunch of accelerated charged particles. In the above examples, the charged particles in question will usually be electrons and/or positrons, but other charged particles may also be used. |
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abstract | In order to achieve high throughput in a SEM-type defect-reviewing apparatus and method for automatically acquiring images of review defects present on samples, including: a cell comparison step subdivided into the steps of (a) providing a defect detection success ratio or defect detection success map due to at least a cell comparison scheme for each wafer or each chip, (b) selecting a review sequence of either the cell comparison scheme or a die comparison scheme on the basis of the provided defect detection success ratio or defect detection success map, (c) if the cell comparison scheme is selected, judging whether detection of the review defect is possible by executing the cell comparison scheme; and a die comparison step in which die comparison is performed if the judgment result indicates that the detection of the review defect is impossible, or if the die comparison scheme is selected in the selection step. |
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054669430 | claims | 1. A device for testing an object comprising: a housing providing a test chamber therein; first means for retaining said object within said test chamber; second means positioned within said test chamber for generating and transmitting uniform electromagnetic radiation to said object; and third means disposed within said test chamber in thermal communication with said second means for varying the temperature thereof. a housing providing a test chamber therein; an evacuated test dewar for retaining said object within said test chamber; a uniform infrared radiating source positioned within said test chamber for generating and transmitting uniform electromagnetic radiation to said object; and a thermoelectric cooler disposed within said test chamber in thermal communication with said radiating source for varying the temperature thereof. 2. The testing device of claim 1 wherein said first means is a test dewar under vacuum. 3. The testing device of claim 1 wherein said object under test is a focal plane array. 4. The testing device of claim 1 further including a platform for retaining said object within said first means. 5. The testing device of claim 4 wherein said platform is a cold finger. 6. The testing device of claim 1 wherein said second means comprises a uniform infrared radiating source. 7. The testing device of claim 6 wherein said uniform infrared radiating source is fashioned from copper and includes a painted surface. 8. The testing device of claim 1 wherein said third means comprises a thermoelectric cooler. 9. The testing device of claim 8 wherein said thermoelectric-cooler is a two stage thermoelectric cooler. 10. The testing device of claim 1 wherein said first means further includes a radiation shield having an aperture formed therein for admitting said uniform electromagnetic radiation. 11. The testing device of claim 10 wherein said radiation shield is comprised of aluminum. 12. The testing device of claim 1 further including a blackbody housing for enclosing said second means. 13. The testing device of claim 1 further including a heat sink for cooling said third means. 14. The testing device of claim 13 further including a cooling fan for cooling said heat sink. 15. The testing device of claim 14 further including a shroud for enclosing said cooling fan. 16. The testing device of claim 1 further including a hermetically sealed connector for providing access to said second means. 17. The testing device of claim 1 wherein said second means simulates typical terrestrial background radiation levels over a temperature range of from -40.degree. C. to +80.degree. C. 18. A device for testing an object comprising: |
039490262 | abstract | A graphite jacket for a fuel element for nuclear reactors is made by placing a dry mixture of graphite and a powdered thermosetting resin in a mold without application of pressure and heating said mixture to thermoset said resin and then subjecting to a coking treatment. The coked jacket is then filled with a mixture of fissile particles and graphite and the complete assembly is closed and treated with a gaseous hydrocarbon at an elevated temperature to deposit pyrolytic carbon. |
description | The present invention relates generally to methods and means for accurately controlling the output stability of a generator that controls an electronic radiation source when used in a high temperature environment, such as within the domain of oil and gas well logging. Well or borehole logging is the practice of making an accurate record, known as a well log, of the geologic formations through which a borehole creates a path or conduit. Well logging activities are performed during all phases of an oil and gas well's development; drilling and evaluation, completion, production and abandonment. The oil and gas industry logs rock and fluid properties to find hydrocarbon-bearing strata in the formations intersected by the borehole. The logging procedure consists of lowering a tool on the end of a wireline into the well to measure the properties of the formation. An interpretation of these measurements is then made to locate and quantify potential zones containing hydrocarbons and at which depths these zones exist. Logging is usually performed as the logging tools are pulled out of the hole. This data is recorded in real-time via a data connection to the surface logging unit or using a memory unit aboard the tool to create either a printed record or electronic presentation called a well log which is then provided to the client. Well logging is performed at various intervals during the drilling of the well and when the total depth is drilled. Density logging is the practice of using a specific well logging tool to determine the bulk density of the formation along the length of a wellbore. The bulk density is the overall density of a rock including the density of the minerals forming the rock and the fluid enclosed in the pores within the rock. A radioactive isotope-based source, usually Cesium 137 (137Cs), applied to the wall of the borehole emits gamma rays into the formation so these gamma rays may be thought of as high velocity particles which collide with the electrons of the atoms that compose the formation. At each collision the gamma rays lose some of their energy -to the electrons, and then continues with diminished energy. This type of interaction is known as Compton scattering. A proportion of the scattered gamma rays reach detectors located at fixed distances from the source, and is counted as an indication of formation density. In oilfield operations isotopes can be lost into the well as a result of the breakage of the logging tool at the risk of being irretrievable. Such events can lead to the closure of the well or measures taken to ensure that radioactive material cannot circulate or permeate out of the well. Indeed, direct contamination and the risk to oilfield workers of dangerous levels of exposure are not uncommon. Although comprehensive control measures are in place, the risk associated with the use of highly radioactive isotopes during oilfield operations will always be present. As is the nature of radioactive materials, the half-life of the material also determines its useful lifetime. Although density logging tools are calibrated to take into account the reduction in activity of an isotope, the useful life of the isotope is somewhat short-lived. A 137Cs source will produce only one-half of its initial gamma-ray output after a period of 30 years. Consequently, isotope-based sources require periodic replacement, and the older isotopes disposed of. Disposal requirements include precautions similar to that of normal nuclear waste, such as that produced as a waste product at nuclear power stations. The typical regulatory limit for the amount of 137Cs which may be used during a logging operation is a maximum of 1.3 Curie. During density logging operations, a certain number of photons per second are required to enter into the detectors to ensure a high enough statistic for the purposes of data quality consistency and interpretation. As a result, density logging operations are normally performed such that the tool is moved at a rate of 1,800 feet per hour to ensure sufficient photons enter the detectors at any particular depth to offer a data resolution acceptable to the client (typically a repeatability to 0.01 g/cc density). In a 15,000 ft long well, this can translate to just over 8 hours of logging time, bottom to surface (or at least 2 hours in the zone of the reservoir). Operations cannot currently be performed faster as the speed of logging relates to an acquisition speed proportional to the output of the gamma-source. For safety reasons, the amount of 137Cs used is capped, with a resultant cap in the minimum amount of time required to perform a log. Various means have been published purporting to mitigate this issue by using x-ray sources as a substitute for gamma-ray sources. By changing the source from a chemical source, with its known output rate, for an x-ray tube, the output of which is dependent upon a number of factors, e.g., input set voltage, input frequency, number of multiplier stages, the designed peak-peak voltage for each multiplier stage, the capacitance of the ladder, the temperature of the generator, etc., introduces variations into the output of the generator that imperil the ability to achieve the statistical ability required to achieve a repeatability of 0.01 g/cc density. In some cases, prior art discloses methods to monitor the output radiation of x-ray tubes, and to use the changes in resultant radiation output levels as input modify the input voltage of the generator. However, modification of x-ray output after it has already been produced would not help correct the log data that would already have been detrimentally affected by the changes in x-ray energy/output. A resistor-based feedback loop may be implemented such that the output potential of the multiplier can be monitored. As the capacitance of the capacitors in the multiplier reduces with ambient temperature, the natural hail ionic frequency of the multiplier will increase as a function of temperature. If the input frequency of the ladder is fixed (which is typical), then the result will be a reduction in the efficiency of the multiplier with increase in ambient temperature, and the output voltage of the generator will reduce. With the exception of NP0, which exhibits a low capacitance per unit volume (and therefore very large in comparison to equivalent value capacitor materials), the majority of capacitor materials that are useful within a downhole tool tend to exhibit a variable capacitance with respect to environmental temperature. Within high-temperature environments the capacitance can degrade to such an extent that efficiency of the high-voltage ladder will degrade such that thermal-run-away and failure can be expected. None of the prior art teaches of practical methods that can be employed to ensure that the output stability of the x-ray tube remains good enough to perform the critical measurement, while compensating for variations in temperature typical in a tool that is being logged in a borehole. In addition, none of the prior art deals with the effects of temperature on the generator electronics as a separable error input to the control scheme, thereby permitting temperature effects to be controlled independently of other issues affecting the output stability of the generator. For example, U.S. Pat. No. 3,327,199 to Gardner et al. discloses a DC to DC high voltage power supply system including a transistor chopper DC to AC inverter type circuit and a high voltage output transformer that includes an extra secondary winding, hereinafter referred to as a tertiary winding, which generates a feedback voltage which is proportional to the high voltage output. A passing element, for example, a transistor, is located between the DC input voltage and the DC to AC inverter circuit and is controlled by the voltage generated by the tertiary winding to provide a highly regulated DC input voltage to said inverter circuit. The DC voltage appearing across a tertiary winding rectifier circuit is coupled to a filter circuit comprising capacitors in combination with a temperature compensating resistance. U.S. Pat. No. 5,023,768 to Collier discloses a high voltage, high power DC power supply that includes a single turn primary winding driven through a resonating capacitor by an AC source having a frequency in excess of about 100 kHz. The primary winding includes a pair of concentric cylindrical metal walls having opposite ends electrically connected to each other. A volume between the walls includes plural secondary winding assemblies, having different axial positions along the walls. Each of the assemblies includes an annular magnetic core surrounding the interior wall, a winding on the core and a voltage-doubling rectifier. DC voltages developed across each secondary winding assembly by the rectifier are added together to provide the high voltage, high power output. U.S. Pat. No. 5,400,385 to Blake et al. discloses a supply for a high bias voltage in an X-ray imaging system has an inverter and a voltage multiplier that produce an alternating output voltage in response to control signals. A voltage sensor produces a signal indicating a magnitude of the output voltage. A circuit determines a difference between the sensor signal and a reference signal that specifies a desired magnitude for the output voltage and that difference is integrated to produce an error signal. The error signal preferably is summed with a precondition signal that is an approximation of a nominal value for the signal sum and the summation producing a resultant signal. Another summation device arithmetically combines the resultant signal and the sensor signal with a signal corresponding to a one-hundred percent duty cycle of the inverter operation in order to produce a duty cycle command. An inverter driver generates the inverter control signals-that have frequencies defined by the resultant signal and have duty cycles defined by the duty cycle command. A unique state machine is described which generates those control signals. U.S. Pat. No. 4,641,330 to Herwig et al. discloses of a high voltage supply circuit for an x-ray tube includes a high voltage transformer having a primary side driven by voltage pulses generated by a drive circuit. The drive circuit includes sub-circuits for controlling the pulse repetition frequency, which is selected as equal to a parallel resonant frequency of a high voltage generator connected to the secondary side of the transformer, for the purpose of saving energy. The drive circuit also includes a sub-circuit for controlling the pulse duration, with the filament voltage in the x-ray tube being regulated by this pulse duration. U.S. Pat. No. 7,564,948 to Wraight et al. discloses of an x-ray source being used as a replacement for a chemical source during density logging along with various means of arranging the apparatus and associated power-supply, also teaches of the means of filtering the primary beam from the x-ray source such that a filtered dual-peak spectrum can be detected by a reference detector which is then used to directly control (feedback) the x-ray tube voltage and current for stability purposes. However, the patent discloses only a compact x-ray device (bipolar) with a grid, a power supply in the form of a Cockcroft-Walton rolled up into a cylinder between two Teflon cylinders in order to save space, and the aforementioned filtered reference detector method. Finally, U.S. Pat. No. 8,481,919 to Teague teaches a means of creating and controlling the electrical power necessary, by serially stepping up the DC reference and creating high potential field control surfaces, to control either a bipolar or unipolar x-ray tube for the purposes of replacing chemical sources in reservoir logging. The reference also teaches one or more moveable/manipulatable beam hardening filters and rotating light-house collimation on the source, the use of gaseous insulators including SF6 as an electrical insulator in a downhole x-ray generator. However, the reference does not disclose a method of using the increased output of the x-ray device to enable longer offset detectors to enable analysis of the non-invaded zone of the formation. It also fails to teach of a method to increase the permissible count rate within a detector volume by doubling the number of PMTs for a given detector volume. A control mechanism for a high-voltage generator for supplying voltage and current to an electronic radiation source in high-temperature environments is provided, the control mechanism including at least one voltage feedback loop for monitoring the output of the generator; at least one environmental temperature monitor; a control bus; and at least one control processor. A method of controlling a high-voltage generator that powers an electronic radiation source in high-temperature environments is also provided, the method including at least: measuring the output voltage of the generator; measuring the temperature within the generator's environment, using a control mechanism to modify an associated driving frequency, and using a control mechanism to modify an associated driving pulse-train, such that the change in properties of the electronic components of the generator as a result of changes in environmental temperature are characterized and the generator's driving signals modified to maintain optimally efficient input parameters for a specific environmental temperature. The methods and means described herein enable the efficient and stable use of ultra-high voltage generators and electronic radiation sources within the high-temperature environment of a borehole. A control mechanism for a high-voltage generator that powers an electronic radiation source in high-temperature environments is provided, the tool including at least a voltage feedback loop for monitoring the output of the generator, a temperature monitor, a control bus and a control processor. With reference now to the attached Figures, FIG. 1 illustrates the relationship between the percentage change in capacitance [101] of four different types of capacitor materials and environmental temperature in degrees Celsius [102]. With the exception of NP0 [103], which exhibits a low capacitance per unit volume, the majority of capacitor materials that are useful within a downhole tool tend to exhibit a variable capacitance with respect to environmental temperature [102]. Within high-temperature environments, typically above 85 degrees Celsius, the capacitance [101] can degrade to such an extent that efficiency of the high-voltage ladder will degrade such that thermal-run-away and failure can be expected. FIG. 2 illustrates a high-voltage ladder [201], driving a unipolar electronic radiation source [202] based upon a multistage Greinacher multiplier (Cockcroft-Walton), may be driven by an alternative current waveform [204] that has been generated by a H-bridge circuit [203]. A resistor-based feedback loop [205] may be implemented such that the output potential of the multiplier can be monitored. As the capacitance of the capacitors [206] in the multiplier reduces with ambient temperature, the natural harmonic frequency of the multiplier will generally increase as a function of temperature. If the input frequency of the ladder is fixed (which is typical), then the result will be a reduction in the efficiency of the multiplier with increase in ambient temperature, and the output voltage of the generator will reduce. If a control processor [207] is implemented to control the operating frequency of the driver, the ambient temperature can be monitored [208] and used as an input into the control algorithm. In such a scheme, the drive frequency of the multiplier can be made to increase to match the increasing natural frequency of the multiplier as a function of ambient temperature. The whole generator can be characterized to ascertain the most optimum (efficient) frequency of the ladder as a function of temperature, and that data used to shape the control algorithm, the result being that multiplier efficiency and output voltage remain constant even into high ambient temperature regimes. FIG. 3 illustrates a typical H-bridge configured driver using Field Effect Transistors (FETs). The HV in direct-current potential [303] will define the output Peak-peak voltage of the H-bridge into the transformer [306] and consequently, determine the output voltage of multiplier compared to a reference potential [305], such as ground. A processor [207] can be configured such to produce Pulse Width Modulation (PMW) signals to inputs [301, 302] on either side of the H-bridge to control the frequency and duty cycle of the output waveform. The frequency of the output waveform can be the result of an algorithm that uses temperature gauges as an input to determine the optimum resonant frequency for multiplier as a function of ambient temperature. FIG. 4 illustrates a bipolar x-ray source tube [401]. A bi-polar configured electronic source tube does not possess a grounded anode or cathode. As such, the negative [402] and positive [403] generators work together to determine the overall tube potential [411], which is a combination of the output of each multiplier [409, 410]. As the effective load on each multiplier changes as a function of the operating point of the other pole's operating set-point, the potential for chaotic behavior to arise is possible, unless the setpoint for the output of each generator is monitored accurately. One of the two generators' controllers [406, 407] can act as the overall system ‘master’ and the other as the ‘slave’. In this manner, each controller would be responsible of maintaining its own set-point [409, 410] but the control master would ensure that the overall tube potential remains constant by issuing set-point modification instructions over a communications bus [408] between the two generator controllers [406, 407]. FIG. 5 illustrates an alternative schematic representation of the bipolar configured drive system. As a single pole's generator may contain tens or hundreds of stages, each doubling or tripling the DC potential of the multiplier, it is obvious that controlling the multiplier though modification of the DC input potential to the H-bridge [511, 512] would result in the significant amplification of an variation (or error) in the DC level of the input. In that respect, input DC level modification isn't an optimum control mechanism if very high output potential accuracy is desired. As the responsiveness (or time-base) of the generator is a function of length, capacitance, and operating frequency, it is possible that any output potential feedback or monitoring loop [504, 505] could produce a time-delay into the control system [507, 508]. If correctly filtered, the feedback loop potential can be used for accurate control of the output. As the change in multiplier output as a function of temperature (and therefore, efficiency change) is a separate control dimension to the feedback loop, it would make little sense to attempt to control temperature effects and general output instabilities by real-time control of the DC input level to the multiplier. By characterizing the temperature coefficients of the generator as a separate control dimension, and short-term variations in the output feedback loop can be corrected for directly (as a single dimensional change) by monitoring the environmental temperature [509, 510] and correcting the drive-pulse-chain input parameters from the control processors [507, 508]. The setpoint of each is communicated over the communications bus [506] which links the two generators. FIG. 6 illustrates three examples of control drive-train inputs shown as high-voltage potential [604] in, referencing ground potential [605], as a function of time [606] in milliseconds. In the first example, a standard control pulse [601] exhibits a 33% duty cycle; the FET being controlled is outputting 33% of the time in a cyclic function. The second example [602] illustrates the effect of increasing the output frequency of the controlling PWM signal, here the duty cycle remains at 33%, however the frequency has been doubled. The third example [603] illustrates one possible embodiment of a modification (or modulation) of the ‘pulse-train’. In this example the duty cycle remains at 33%, but every 3rd pulse is skipped such that, for a short period of time, the amount of pulses (and therefore, energy) being delivered into the multiplier is reduced such that the output of the generator will decrease temporarily as a function of the percentage of skipped pulses in the pulse-train over the time period of the total number of pulses at the set operating frequency. The time taken for this control input to reach the output is dependent upon the number of stages in the multiplier and the operating frequency of the multiplier—typically, the time-based of the generator would be operating frequency divided by the number of discrete multiplier stages. In one embodiment, a high-voltage ladder driving a x-ray tube based upon a multistage Greinacher multiplier (Cockcroft-Walton) is driven by an alternative current waveform that has been generated by a H-bridge circuit consisting Field Effect Transistors (FETs). A resistor-based feedback loop is configured such that the output potential of the multiplier can be monitored directly, and the resultant signal fed (comparator) into a microprocessor. The direct-current input potential (for the FETs) will define the output Peak-peak voltage of the H-bridge into the transformer and consequently, determine the output voltage of multiplier. The input potential to the FETs can be controlled by the controller to make large modifications to the output of the generator, such as a ‘start-up’ where the output of the generator may be required to change from 0 kV to 300 kV, for example. A processor can be configured such to produce Pulse Width Modulation (PMW) signals to either side of the H-bridge to control the frequency and duty cycle of the output waveform. The frequency of the output waveform is the result of an algorithm that uses temperature gauges as an input to determine the optimum resonant frequency for multiplier as a function of ambient temperature. Said processor is equipped with firmware that controls the input voltage, frequency, duty-cycle and pulse-train configuration of the FET-based H-bridge. As the capacitance value of the capacitors in the multiplier reduces with ambient temperature, the natural harmonic frequency of the multiplier will increase as a function of ambient temperature. As the processor is configured such to control the operating frequency of the H-bridge, the ambient temperature can be monitored and used as an input into a control algorithm. In this embodiment, the drive frequency of the multiplier can be made to increase to match the increasing natural frequency of the multiplier as a function of ambient temperature. The whole generator can be characterized to ascertain the most optimum (efficient) frequency of the ladder as a function of temperature, and that data used to shape the control algorithm. The result being that multiplier efficiency and output voltage remain constant even into high ambient temperature regimes. In a further embodiment, a bipolar x-ray tube does not include a grounded anode (as the anode is connected to a second ‘positive’ generator). The negative and positive generators work together to determine the overall tube potential, which is essentially the combined output of the multipliers. As the effective load on each multiplier changes as a function of the operating point of the other pole's operating set-point, the potential for chaotic behavior is possible, unless the setpoint for the output of each generator is monitored accurately. Therefore, one of the two generators' controllers acts as the overall system ‘master’ and the other as the ‘slave.’ In this manner, each controller is responsible of maintaining its own set-point but the master ensures that the overall tube potential remains constant by issuing set-point modification instructions over a communications bus that links the two controllers. In yet another embodiment, a standard control pulse exhibiting a specific duty cycle, i.e., the FET being controlled is outputting a specific percentage of the time in a cyclic function. The output frequency of the PWM signal controlling the ladder may be adjusted by algorithm to compensate for temperature effects in the generator, while the duty cycle remains constant. The firmware in the controller(s) is configured such to affect a modification (or modulation) of the ‘pulse-train’. In another embodiment, the duty-cycle remains at constant but every 25th pulse is skipped such that, for a short period of time, the amount of pulses (and therefore, energy) being delivered into the multiplier is reduced such that the output of the generator decreases temporarily as a function of the percentage of skipped pulses in the pulse-train over the time period of the total number of pulses at the set operating frequency. The time taken for this control input to reach the output is dependent upon the number of stages in the multiplier and the operating frequency of the multiplier—typically, the time-base of the generator is the operating frequency divided by the number of discrete multiplier stages. In another embodiment, the control algorithm of the processor would determine what short-term changes would need to be made to the output of the multiplier, and effect real-time changes to the pulse train, such as changing from 100/100 equal pulses to 98/100 (where in 1 in 50 are skipped), or where 96/100 equal pulses (1 in 25 skipped) and then reverting to the original set-point as necessary to ensure a highly accurate output stability—changes of a few volts. In the example embodiments, such stability in operation permits an electronic radiation source to exhibit statistical output stability similar to a chemical source, thereby enabling their use within downhole logging tools where the statistical repeatability of the measurement is paramount. In such cases, high logging speeds are achieved without forsaking statistical repeatability/accuracy over the mission time (or log time) of the logging tool as a function of temperature, which typically varies with depth and mission time. In the example embodiments, the output of the generator feeding the electronic radiation source remains constant as a function of ambient temperature, regardless of the choice of capacitance substrate in the generator. In the example embodiments, discrete modification of the pulse-train permits very precise control of the generator output. In the example embodiments, very accurate digital control by direct quantization of the energy entering the multiplier permits a high-speed control mechanism that is characterizable, such that control of two inter-linked generators (in the case of a bipolar tube) is achievable with a high degree of output stability. In a further example embodiment, the electronic radiation source controlled by the method is an electronic x-ray source. In yet another embodiment, the electronic radiation source controlled by the method is an electronic pulsed-neutron generator source. The foregoing specification is provided only for illustrative purposes, and is not intended to describe all possible aspects of the present invention. While the invention has herein been shown and described in detail with respect to several exemplary embodiments, those of ordinary skill in the art will appreciate that minor changes to the description, and various other modifications, omissions and additions may also be made without departing from the spirit or scope thereof. |
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abstract | An X-ray fluorescence measuring system and related measuring methods are disclosed, the system using X-ray energy at a level of less than 80 KeV may be directed toward a material, such as coal. The energy fluoresced may be detected (10) and used to measure the elemental composition of the material, including trace elements. The material may be moving or stationary. |
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053902211 | abstract | In a boiling water nuclear reactor fuel bundle, a debris catching arrangement is disclosed for incorporation within the flow plenum up stream or below the rod supporting grid of the lower tie plate assembly. The device is preferably placed within the lower tie plate flow plenum between the fuel bundle inlet and the rod supporting grid structure supporting the fuel rods; alternate placement can include any inlet channel upstream of the fuel rods including the fuel support casting. The disclosed debris catching designs include strainer structures defining spatially separated straining or obstructing layers imparting to the fluid in the plenum a circuitous flow path. This circuitous flow path causes the two phase separation of the heavier debris from the lighter transporting water by flow direction change with the debris directed and detoured to a trapping structure. Further, a strainer structure is provided in the plenum that does not constitute a continuum of fine structure across the strained plenum which might become clogged to the extend that overall flow is restricted. The strainer structure is positioned so that eventual trapping of the debris occurs upon cessation of flow so that with removal of the plenum from the reactor, such as removal of the fuel bundle, the debris is likewise removed. Embodiments are disclosed which include swirling deflection, cone deflection, and strainer structure deflection of debris. |
052788768 | abstract | A head for closing a nuclear reactor pressure vessel shell includes an arcuate dome having an integral head flange which includes a mating surface for sealingly mating with the shell upon assembly therewith. The head flange includes an internal passage extending therethrough with a first port being disposed on the head mating surface. A vent line includes a proximal end disposed in flow communication with the head internal passage, and a distal end disposed in flow communication with the inside of the dome for channeling a fluid therethrough. The vent line is fixedly joined to the dome and is carried therewith when the head is assembled to and disassembled from the shell. |
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claims | 1. A system to position a filter in an imaging system, comprising:a plate defining an aperture through the plate;a filter frame having at least a first filter holding portion operable to move relative to the aperture;a movement system configured to move the filter frame relative to the aperture, the movement system having:a motor;a single rail extending between a first end and a second end and positioned relative to the aperture, wherein the single rail extends along a first side of the filter frame;a shaft configured to be rotated by the motor, wherein the shaft extends along a second side of the filter frame opposed to the first side; anda connection member coupling the shaft to the filter frame, wherein the connection member is operable to move the filter frame relative to the rail when the shaft is rotated by the motor. 2. The system of claim 1, further comprising:a position determining assembly coupled to the shaft and operable to sense a rotation of the shaft. 3. The system of claim 2, wherein the position determining assembly further comprises:a position determination module connected to the sensor;a communications link;an input portion operable to be sensed by the sensor;wherein the input portion is axially fixed to the shaft. 4. The system of claim 1, further comprising:a filter member carried by the filter frame at the first filter holding portion;wherein the filter member includes a plurality of slots extending therethrough operable to be precisely positioned relative to the aperture. 5. The system of claim 1, further comprising:a bushing having a first engaging surface and a second engaging surface;wherein the first engaging surface extends at an angle relative to the second engaging surface;wherein the first engaging surface engages a first surface of the filter frame and the second engaging surface engages a second surface of the filter frame. 6. The system of claim 1, further comprising:a processor;wherein the position determining module is operable to generate an index pulse when the filter frame is at a home position;wherein the index pulse is transmitted as an index signal to the processor;wherein the processor is operable to determine that the at least first filter holding portion is at a home position based on the index signal. 7. The system of claim 6, wherein the processor is further operable to receive a position signal from the position determining module;wherein the processor is operable to execute instructions to determine a position of the at least a first filter holding portion relative to the aperture. 8. The system of claim 1, wherein the shaft includes a first thread and the connection member includes a second thread, the second thread engaging the first thread to enable the connection member to move relative to the shaft when the shaft is rotated by the motor. 9. The system of claim 1, wherein the connection member has (i) threads to engage threads on the shaft and (ii) a filter frame connection. 10. A system to position a filter in an imaging system, comprising:a plate defining an aperture through the plate;a single rail extending between a first end and a second end and fixed relative to the mounting plate;a motor;a shaft configured to be rotated by the motor;a connection member configured to engage the shaft, wherein the connection member is operable to move relative to the rail when the shaft is rotated by the motor;a filter frame having at least a first filter holding portion; anda position determining module;wherein the position determining module includes a sensor operable to sense a rotation of the shaft. 11. The system of claim 10, further comprising:a position determination system comprising at least the position determining module and an input portion;wherein the input portion is fixed to the shaft. 12. The system of claim 10, wherein the single rail is on an opposite side of the filter frame from the shaft;wherein the filter frame is moveably connected to the shaft through the connection member and the single rail;wherein the single rail is only one rail. 13. The system of claim 12, wherein the shaft rotates relative to the single rail, but is linearly fixed relative to the single rail. 14. The system of claim 10, further comprising:a bushing having a first engaging surface and a second engaging surface;wherein the first engaging surface extends at an angle relative to the second engaging surface;wherein the first engaging surface engages a first surface of the filter frame and the second engaging surface engages a second surface of the filter frame. 15. The system of claim 10, wherein the positioning determining module is spaced away from the motor and fixedly connected to the shaft. 16. The system of claim 10, further comprising:a filter member having at least a first through slot, a second through slot, and a third through slot;wherein the first through slot, the second through slot, and the third through slot are spaced apart and configured to be positioned over the aperture with the rotation of the shaft. 17. The system of claim 10, wherein the shaft includes a first thread and the connection member includes a second thread, the second thread engaging the first thread to enable the connection member to move relative to the shaft when the shaft is rotated by the motor. 18. A method of positioning a filter in an imaging system, comprising:operating a motor system to rotate a shaft;engaging and moving a connection member that is fixed to a frame member by engaging the shaft with the connection member;moving the frame member along a rail fixed relative to the shaft;sensing a position of the frame member based on rotation of the shaft; andpositioning the frame member relative to an aperture. 19. The method of claim 18, further comprising:operating a control system to select a filter to filer an imaging beam;transmitting a selected filter position;wherein operating the motor system to rotate the shaft includes rotating the shaft to move the frame member to a selected position. 20. The method of claim 18, further comprising:movably fixing the frame member so only a single rail member. |
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claims | 1. A process for producing selected isotopic daughter products from parent materials characterized by the steps of:binding said parent material upon a SAMMS sorbent material configured to selectively bind said parent material over said isotopic daughter product,generating said selected isotopic daughter products from the parent material while the parent material is bound to the SAMMS sorbent material; andeluting said selected isotopic daughter products from the SAMMS sorbent material. 2. The process of claim 1 further comprising the step of passing an eluent formed by said elution step through a second sorbent material to remove a preselected material from said eluent. 3. The process of claim 2 further comprising the step of passing said eluent through a third sorbent material after passage through said second sorbent material. 4. The process of claim 1 wherein said parent material comprises Mo-99, and said daughter product comprises Tc-99m. 5. The process of claim 4 wherein said sorbent comprises a Cu-EDA-SAMMS material. 6. The process of claim 4 wherein said sorbent comprises a thiol SAMMS material, 7. The process of claim 4 wherein said sorbent comprises a metal capped thiol-SAMMS material. 8. The process of claim 1 wherein said binding, generating and eluting steps each take place at a different pH. 9. The process of claim 8 wherein said binding step takes place at a lower pH than said generating step, and said eluting step takes place at a higher pH than said generating step. 10. The process of claim 8 wherein said eluting step has a higher pH than either said binding step or said generating step. 11. The process of claim 4 wherein the Mo-99 is produced by Mo98 (n,γ)Mo99. 12. The process of claim 4 wherein the Mo-99 is produced by Mo100(γ,n)Mo99. 13. The process of claim 11 wherein the irradiated Mo-99 has a specific activity greater than 100 millicuries Mo99/gram of molybdenum. 14. The process of claim 4, wherein said parent material comprises molybdenum and Mo-99 where the specific activity of the Mo-99 is less 5,000 curie Mo99/gram of molybdenum. 15. The process of claim 4 further comprising the step of concentrating the Tc-99m to at least 25 millicurie/mL by passing said eluent through a secondary column that will bind pertechnetate and provide subsequent small volume elution of Tc-99m. |
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claims | 1. A passive cooling system for a spent fuel pool in a nuclear power plant, to provide cooling in the absence of onsite and offsite power, the spent fuel pool having an inner wall and an outer wall, the system comprising:a gap formed between the inner wall and the outer wall of the spent fuel pool, the outer wall being spaced a distance from the inner wall forming the gap substantially along a periphery of the spent fuel pool, wherein the gap is substantially filled with air;a heat sink comprising a mass of earth located outside of the outer wall of the spent fuel pool;one or more thermal conductive members having a first end directly connected to the outer wall and a second end directly connected to the heat sink, said one or more members structured to transport heat from the gap to the heat sink; anda water supply system, comprising:a water source;at least one discharge header having a first end connected to the water source and a second end connected to the gap; anda valve located within the at least one discharge header, wherein the valve is configured to switch between a normal position in which it is closed, preventing a flow of water from the water source to the gap and an activated position in which the valve is open, allowing a flow of water through the discharge header and into the gap, wherein in the activated position, the gap is at least partially filled with water that conducts heat generated in the spent fuel pool through the gap to the one or more conductive members that transport the heat to the heat sink. 2. The passive cooling system of claim 1 further comprising one or more conductive cooling fins attached to the second end of the one or more members to enhance transport of the heat from the members to the heat sink. 3. The passive cooling system of claim 1 wherein the nuclear power plant contains a pressurized water reactor. 4. The passive cooling system of claim 1 wherein the inner wall of the spent fuel pool is formed by a spent fuel pool liner. 5. The passive cooling system of claim 1 wherein the outer wall of the spent fuel pool is formed by a concrete wall. 6. The passive cooling system of claim 1 wherein the gap is continuous along the periphery of the spent fuel pool. 7. The passive cooling system of claim 1 wherein the gap is partitioned into a plurality of channels. 8. The passive cooling system of claim 7 wherein each of said plurality of channels has a discharge header located therein. 9. The passive cooling system of claim 1 wherein the at least one discharge header is located at the top or near the top of the gap. 10. The passive cooling system of claim 1 wherein the valve is configured to activate in response to a loss of offsite power event with or without availability of emergency diesels operable to supply AC electrical power to active spent fuel pool cooling pumps. 11. The passive cooling system of claim 1 wherein the valve is configured to activate in response to a station blackout when all backup sources of DC electrical power are exhausted. 12. The passive cooling system of claim 1, wherein the first end of the one or more thermal conductive members penetrates through the outer wall of the spent fuel pool. |
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abstract | An optical integrator used in an illumination optical system for illuminating an illumination target surface on the basis of light from a light source has a first fly's eye optical system having a plurality of first optical elements arranged in parallel at a position optically conjugate with the illumination target surface in an optical path between the light source and the illumination target surface, and a second fly's eye optical system having a plurality of second optical elements arranged in parallel so as to correspond to the plurality of first optical elements in an optical path between the first fly's eye optical system and the illumination target surface. At least one first optical element out of the plurality of first optical elements, and another first optical element different from the at least one first optical element have their respective postures different from each other about an optical axis of the illumination optical system or about an axis parallel to the optical axis. |
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claims | 1. A particle therapy apparatus comprising:a stationary particle beam generator configured to output a particle beam having a first energy;an energy degrader for reducing an energy of the particle beam from the first energy to a second energy, such that an energy spread of the particle beam output by the energy degrader is increased with respect to an energy spread of the particle beam output by the particle beam generator; anda rotatable gantry configured to receive the particle beam having the first or the second energy in a direction substantially along a rotation axis of the rotatable gantry, the rotatable gantry including:a beam optic system having a plurality of dipole magnets including a first dipole magnet and a last dipole magnet and configured to bend the received particle beam along a beam path to a target,wherein the beam optic system is configured to have a first position along the beam path where a nominal dispersion at the first position is larger than a nominal beam size at the first position, and wherein the first position is located downstream of the first dipole magnet and upstream of the last dipole magnet; andan energy spread limiting device, installed at the first position, to limit the energy spread of the particle beam having the second energy to a selected maximum energy spread. 2. The particle therapy apparatus according to claim 1, wherein the energy spread limiting device includes a momentum analyzing slit. 3. The particle therapy apparatus according to claim 1, wherein the energy spread limiting device includes a momentum analyzing aperture. 4. The particle therapy apparatus according to claim 1, wherein the energy spread limiting device includes a momentum analyzing collimator. 5. The particle therapy apparatus according to claim 1, wherein the particle beam generator is a cyclotron. 6. The particle therapy apparatus according to claim 1, wherein the first energy of the particle beam is between 230 MeV and 250 MeV. 7. The particle therapy apparatus according to claim 1, wherein the particle beam is a proton beam, and the second energy is between 70 MeV and 250 MeV. 8. The particle therapy apparatus according to claim 1, wherein the rotatable gantry is configured to rotate at least 180 degrees. 9. The particle therapy apparatus according to claim 1, wherein:the nominal dispersion is a transversal displacement of a particle having a momentum differing by 1% of an average momentum of all particles of the beam, andthe nominal beam size being is a one sigma beam size value of a mono energetic particle beam having the average momentum. 10. The particle therapy apparatus according to claim 1, where the nominal dispersion at the first position is between 1 cm and 3 cm and the nominal beam size at the first position is between 0.2 cm and 1 cm. 11. The particle therapy apparatus according to claim 1, wherein the beam optic system further comprises a plurality of quadrupole magnets configured to perform at least one of focusing or defocusing the particle beam and wherein the first position is located after at least one quadrupole magnet of the plurality of quadrupole magnets. 12. The particle therapy apparatus according to claim 11, further comprising a controller configured to set the magnetic fields of at least one of one or more of the plurality of dipole magnets or of one or more of the quadrupole magnets of the beam optic system such that the particle beam having the second energy has the nominal dispersion larger than the nominal beam size at the first position. 13. The particle therapy apparatus according to claim 12, wherein the energy spread limiting device has an opening through which at least a portion of the beam passes, and wherein the controller is configured to control the energy spread limiting device based, at least in part, on a calibration curve defining the opening of the energy spread limiting device as a function of an energy spread of the particle beam at an input of the energy spread limiting device. 14. A particle therapy apparatus comprising:a stationary particle beam generator configured to output a particle beam having a first energy;an energy degrader configured for receiving the particle beam having the first energy and for reducing an energy of the particle beam from the first energy to a second energy, such that an energy spread of the particle beam output by the energy degrader is increased with respect to an energy spread of the particle beam output by the particle beam generator; anda rotatable gantry configured to receive the particle beam having the first or the second energy in a direction substantially along a rotation axis of the gantry, and wherein the gantry includes:a plurality of dipole magnets including a first dipole magnet and a last dipole magnet configured to bend the particle beam having the second energy along a beam path to a target, andan energy spread limiting structure located in the beam path between the first dipole magnet and the last dipole magnet, at a first position where a nominal dispersion of the particle beam having the second energy is larger than a nominal beam size of the particle beam having the second energy, and having a spacing to limit an energy spread of the particle beam having the second energy to a selected maximum energy spread. 15. The particle therapy apparatus according to claim 14, wherein:the nominal dispersion is a transversal displacement of a particle having a momentum differing by 1% of an average momentum of all particles of the beam, andthe nominal beam size is a one sigma beam size value of a mono-energetic particle beam having the average momentum. 16. The particle therapy apparatus according to claim 14, wherein the energy spread limiting structure includes a momentum analyzing slit. 17. The particle therapy apparatus according to claim 14, wherein the energy spread limiting structure includes a momentum analyzing aperture. 18. The particle therapy apparatus according to claim 14, wherein the energy spread limiting structure includes a momentum analyzing collimator. 19. The particle therapy apparatus according to claim 14, wherein the energy spread limiting structure is part of the gantry. 20. The particle therapy apparatus according to claim 14, wherein the particle beam generator is a cyclotron. 21. The particle therapy apparatus according to claim 14, wherein the first energy of the particle beam is between 230 MeV and 250 MeV. 22. The particle therapy apparatus according to claim 14, wherein the particle beam is a proton beam, and the second energy is between 70 MeV and 250 MeV. 23. The particle therapy apparatus according to claim 14, wherein the rotatable gantry is configured to rotate at least 180 degrees. 24. The particle therapy apparatus according to claim 14, further comprising a controller configured to set the magnetic fields of one or more of the plurality of dipole magnets. 25. The particle therapy apparatus according to claim 24, wherein the controller is configured to adjust magnetic strengths of one or more of the plurality of dipole magnets such that the particle beam having the second energy has the nominal dispersion larger than the nominal beam size at the first position. 26. The particle therapy apparatus according to claim 14, wherein the nominal dispersion at the first position is between 1 cm and 3 cm and wherein the nominal beam size at the first position is between 0.2 cm and 1 cm. 27. A particle therapy apparatus comprising:a stationary particle beam generator configured to output a particle beam having a first energy;an energy degrader for reducing an energy of the particle beam from the first energy to a second energy, such that an energy spread of the particle beam output by the energy degrader is increased with respect to an energy spread of the particle beam output by the particle beam generator; anda rotatable gantry configured to receive the particle beam having the first or the second energy in a direction substantially along a rotation axis of the rotatable gantry, the rotatable gantry including:a beam optic system having a plurality of dipole magnets including a first dipole magnet and a last dipole magnet and configured to bend the received particle beam along a beam path to a target,wherein the beam optic system is configured to have a first position along the beam path where a nominal dispersion of the beam having the second energy is larger than a nominal beam size of the beam having the second energy, and wherein the first position is located downstream of the first dipole magnet and upstream of the last dipole magnet; andan energy spread limiting device, installed at the first position, to limit the energy spread of the particle beam having the second energy to a selected maximum energy spread. |
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044908369 | description | The FIGURE illustrates a schematic cross-sectional view of a shut-off valve construction in accordance with the invention. Referring to the drawing, the shut-off valve has a housing 1 which is provided with an inlet spigot 2, an outlet spigot 3, a spherical valve chamber 4, a valve seat 5, a spigot 6 and a flange 7 about the spigot 6. In addition, the valve has a cover 10 mounted on the flange 7 of the housing 1 and which cooperates with the housing 1 to form a housing system. The cover 10 includes a flange 11 which abuts the flange 7 of the housing and a wall 12 with which defines a cylinder within the valve chamber 4. As indicated, the wall 12 extends coaxially with the flange 11 and defines a cylindrical space 15. The valve also has a valve stem 22 which has a mushroom-shaped lid 24 at one end and a piston 20 at the opposite end. This piston 20 is slidably disposed in the cylinder 12 to move axially within the cylinder space 15. As indicated, the piston 20 divides the cylinder space 15 into two chambers 36, 37. The upper chamber 36 as viewed, is of cylindrical shape while the lower chamber 27 is of annular shape. The mushroom-shaped lid 24 includes a conical seat 25 for seating against the valve seat 5 at the outlet spigot. A cylindrical guide 26 has a flange 27 connected by bolts to the endface of the wall 12 in order to guide the valve stem 22. This guide 26 is also provided with a back seat 30 which cooperates with an appropriately machined shoulder 32 on the lid 24. The valve stem 22 also has a blind bore 34 at the side facing the cover 10 which contains a compression spring 35. As shown, the spring 35 has one end abutting the base of the bore 34 and an opposite end abutting the cover 10 at the top end face of the cylinder space 15. Hereinafter, the cylinder space above the piston 20, including the space in the bore 34, is called the "first chamber" 36 while the annular space between the underside of the piston 20 and the end face of the guide 26 is called the "second chamber" 37. A duct 38 extends through the cover 10 from the first chamber 36 with one branch communicating via a fixed throttle means 45 in the cover 10 with a connecting line 46 outside the cover 10. This connecting line 46 contains a closing valve 47 and passes through a wall 59, for example, a wall of a containment vessel of a nuclear reactor plant, to a low pressure chamber 50 located outside the wall 59. The throttle means 45 has a fixed aperture cross-section. To insure redundance, the throttle means 45 has two through-apertures since it is unlikely that two parallel openings will be simultaneously clogged. Depending upon the analysis of possible faults, a single throttle aperture can be provided, if required, downstream of a screen having a larger total aperture cross-section. The duct 38 also connects via a transverse bore 40 to two chambers of two control valves 42, 43. Each control valve 42, 43 has an axially movable valve component 52 which is disposed in a chamber and which has a turned portion of quadrant cross-section at the end face outside a central flat sealing surface and a blind bore at the opposite end. Each blind bore contains a compression spring which bears against the end faces of the control valve chambers and which face away from each other. As indicated, the chambers of the control valves 42, 43 face away from each other and are connected via ducts 54, 55 to a connecting line 57 extending from the cover 10. The connecting line 57 contains a closing valve 58 adjacent to and within the wall 59 and passes through the wall 59 to a change-over valve 60. The change-over valve 60 has two spigots to connect the line 57 to a source of high pressure medium (not shown) or to the low pressure chamber 50. A further duct 63 is disposed in the cover 10 and extends from the valve chamber 4. As indicated, the duct 63 contains a non-return valve 64 and connects via short connecting lines 61, 62 with the respective contoured end faces of the valve components 52 of the control valves 42, 43. When these control valves 42, 43 are open, the duct 63 is able to communicate with the first chamber 36 via the transverse bore 40 and duct 38. A further duct 65 is also provided in the cover 10 to communicate with the second chamber 37 at the bottom end. This duct 65 leads to a connecting line 68 outside the cover 10 which line 68, in turn, extends through the wall 59 to the low pressure chamber 50 and contains a closing valve 69 adjacent to and within the wall 59. A change over valve 70 is also disposed in the line 68 to connect the line 68 to the low pressure chamber 50 or to a line 72 which supplies an external medium at high pressure. A further external-medium connecting line 75 extends from the line 72 through the wall 59 via a closing valve 73 disposed outside the wall 59 and a non-return valve 77 within and adjacent the wall 59. The connecting line 75 communicates via a pair of non-return valves 79 within the cover 10 with the transverse bore 40 of the duct 38. During normal operation, the shut-off valve is open, as viewed, and a hot pressure medium flows through via the spigots 2, 3. The shut-off valve remains in this position because, when the closing valve 58 is open, the connecting line 57 is filled with high pressure medium from the pressure medium source (not shown) via the change over valve 60 which is in the position shown. This pressure medium, assisted by the springs in the blind bores of the valves 42, 43, holds the valve components 52 in the closing position. As a result, the cylinder chamber 36 is connected to the low pressure chamber 50 and is relieved of pressure via the throttle means 45 and the open closing valve 47. The second chamber 37 is similarly connected to the low pressure chamber 50 and is relieved of pressure via the open closing valve 69 and the change over valve 70. The pressure of the medium in the valve chamber 4 acts on the cross-section inside the back seat 30 and maintains the shut off valve open against the force of the spring 35 and the weight of the entire movable lid system formed by the lid 24, the piston 20 and the stem 22. If the valve is to be closed, the change over valve 60 is moved 90.degree. clockwise from the illustrated position so that the connecting line 57 discharges to the low pressure chamber 50. Under the action of the pressure medium supplied through the duct 63 from the valve chamber 4, the valve components 52 move into the open position. At the same time, the medium from the valve chamber 4 flows from the duct 63 through the transverse bore 40, duct 38, throttle means 45 and closing valve 47 into a low pressure chamber 50. Another stream of medium also flows into the first chamber 36. If the flow cross-sections of the lines, valves and throttle means 45 are suitably adapted to one another, the pressure building up in the chamber 36 is near the pressure in the valve chamber 4. Since the piston 20 has a greater outside diameter than the back seat 30 under the above mentioned pressure conditions, the lid 24 moves into a closing position whereupon the medium from the second chamber 37 is conveyed through the duct 65, connecting line 68 and open valve 69 into the low pressure chamber 50. In order to reduce the loss of medium via the throttle means 45 and discharge line 46 into the low pressure chamber 50, the valve 47 can be closed at the same time as the change over valve 60 is switched over to the low pressure chamber 50. If, after being closed by the pressure medium, the shut-off valve is to be again opened, the change over valve 60 is switched over to the illustrated position in order to supply external medium to the line 57. If the closing valve 47 has been closed, the valve 47 is now reopened. Since the pressure of the foreign medium in the connecting line 57 is higher than in the valve chamber 4, the two control valve components 52 move into the closing positions. Since a medium is now flowing from the duct 38 through the throttle means 45 and connecting line 46 to the low pressure chamber 50, whereas no pressure medium flows through the control valves 42, 43, the first chamber 36 is relieved of pressure. If the pressure down stream of the shut-off valve is high enough compared with the low pressure in the chamber 50, the shut-off valve opens immediately. If this is not the case, the plug of the change-over valve 70 is rotated 90.degree. counter-clockwise, as viewed. In this way, the external medium flows into the second chamber 37 via the open closing valve 69. As a result of the additional action of the external medium pressure in the second chamber 37, the shut-off valve now moves into the open position. Depending on the conditions to be fulfilled by the shut-off valve, the diameters of back seat 30, piston 20 and stem 22 will be dimensioned in dependence on the diameter of valve seat 5 and the cross-section of the spring 35. As a result of the aforementioned operations, the shut-off valve can be opened even if there is no pressure at the shut-off valve. If the shut-off valve has to be closed when not under pressure and if the force of the spring 35, increased by the dead weight of the movable lid system, is insufficient to move the lid 24 when the valve 69 is open and valve 70 is in the illustrated position, the external medium can be introduced into the first chamber 36 via the connecting line 75, valve 73, valve 77 and the pair of non-return valves 79. The shut-off valve is so constructed that if the control line 57 breaks, the shut-off valve moves into the closed position as required, e.g. in the case of isolating valves of nuclear reactor plants. The non-return valve 77 and closing valves 69, 47 and 58 are disposed so that if a pipe breaks, any contaminated medium is prevented from escaping through the lines 68, 46, 75, 57 through the safety-vessel wall 59. An additional safety logic circuit acting on the closure valves can be used for this purpose for example. The low-pressure chamber 50 can, for example, be the condenser of a steam turbine plant. In addition to providing two apertures in the throttle means 45, redundance may also be obtained by providing a pair of non-return valves in parallel instead of the non-return valve 64. The throttle means 45 is adapted to prevent pressure medium from escaping too quickly from the duct 38 if the connecting line 46 leaks and the shut-off valve has to be moved into the closing position. The throttle cross-section must be dimensioned accordingly. As a result, even if all the connecting lines break, the shut-off valve will occupy the closed position required for safety purposes. If the springs in the control valves 42, 43 are suitably dimensioned and valve components 52 or a throttle aperture parallel thereto have sufficient radial clearance, the change-over valve 60 can be omitted and the control line 57 can be connected to the chamber 50 directly via the valve 58. As a result, when the valve 58 is closed, the pressure in the duct 63 builds up in the connecting line 57 due to leakage at the valve components 52. If the control line 57 is relieved from pressure by opening valve 58, the control valves 42, 43 open. Under the action of the springs disposed in the blind bores of the valve components 52 the valves 42, 43 close, if the valve 58 opens. The closing valve 58 is very important from the safety standpoint. It may therefore be advantageous to associate the valve 58 with a redundant valve in parallel. Of note, the closing valves 47, 48 and 69 and the non-return valve 77 can be disposed on the outside of the safety-vessel wall 59 so that they are always accessible and open to inspection. The invention thus provides a shut-off valve which can be readily fabricated in a factory and which is reliable in use. The invention provides a shut-off valve of simple construction which can be made at small costs without reducing reliability. To this end, the construction of the valve is simplified by disposing the closing valves in the connecting lines, by providing the throttle means with a fixed flow cross-section in a duct within the housing cover and by giving the duct associated with the second chamber a fixed minimum cross-section. |
claims | 1. An x-ray system for exciting a sample under x-ray analysis, comprising:a curved, point-to-point focusing monochromating optic for redirecting and focusing a monochromatic x-ray beam from an x-ray source towards a first focal point;a second, convergent-beam-to-point focusing optic positioned within, and receiving, the monochromatic x-ray beam, and directing a focused x-ray beam towards a second focal point on the sample; anda detector positioned near the sample to collect radiation from the sample as a result of the focused x-ray beam;wherein the curved monochromating optic produces a beam spot size at the first focal point larger than a beam spot size produced by the second optic at the second focal point, wherein a beam spot size on the sample is thereby reduced using the second optic;wherein the second optic is positioned within the monochromatic x-ray beam, before the first focal point, thereby receiving the monochromatic x-ray beam as it converges toward the first focal point. 2. The x-ray system of claim 1, wherein the curved monochromating optic comprises an optical surface, the optical surface being doubly-curved. 3. The x-ray system of claim 2, wherein the monochromating optic is a doubly curved crystal optic. 4. The x-ray system of claim 2, wherein the monochromating optic is a doubly curved multilayer optic. 5. The x-ray system of claim 2, wherein the second optic is a polycapillary optic. 6. The x-ray system of claim 2, wherein the second optic is a monocapillary optic. 7. The x-ray system of claim 1, wherein the at least one curved monochromating optic comprises a plurality of doubly-curved optical crystals or a plurality of doubly-curved multilayer optics. 8. The x-ray system of claim 1, wherein the second focal point on the sample is positioned between the second optic and the first focal point. 9. The x-ray system of claim 1,wherein the x-ray source comprises an electron-bombardment-type x-ray tube. 10. The x-ray system of claim 9, wherein the x-ray tube is a low power x-ray tube of less than 100 watts. 11. The x-ray system of claim 1, further comprising:a controller for monitoring and/or controlling the position of the sample, the second focal point, and/or the detector to provide an accurate indication of the location of the second focal point on the sample. |
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050420593 | description | DETAILED DESCRIPTION OF THE INVENTION It is known that when polymers are pyrolyzed, they are carbonized in their original form. This is a good procedure of fabricating a carbonaceous material with a large area and good flexibility. However, the carbonaceous material obtained by the above procedure has, in most cases, a structure which is completely different from that of graphite. Polyphenylene oxadiazole which has been set forth before is a material which is exceptionally converted into graphite of good properties. We have made studies on a number of polymer materials including POD so as to obtain graphite films which have better rocking and reflectivity characteristics than the known graphite film obtained from POD. According to one embodiment of the invention, there is provided a radiation optical element which comprises a graphite film obtained by thermally treating a specific type of polymer at a temperature of not lower than 2800.degree. C. under a pressure of not lower than 4 kg/cm.sup.2. The starting polymer materials useful in the present invention include, for example, polyphenylene oxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzooxazole, polybenzobisoxazole, polypyromellitimide, polyphenylene-isophthalamide, polyphenylene-benzoimidazole, polyphenylene-bisimidazole, polythiazole and poly-p-phenylene-vinylene. In view of the characteristic properties and the ease in graphitization, polyphenylene oxadiazole and polypyromellitimide are preferred. These polymers are now commercially available and include polymers of isomers of the respective monomers. For instance, polythiazole used herein includes polymers of 1,2 and/or 1,3-isomer. These polymers are subjected to the thermal treatment or pyrolysis in the form of a film or sheet preferably having a thickness of from 1 to 400 micrometers, preferably from 4 to 200 micrometers in order to facilitate graphitization efficiently although the film having a thickness outside the above range may be used. The thermal treatment or pyrolysis should be effected at a temperature of not lower than 2800.degree. C. under a pressure of not lower than 4 kg/cm.sup.2. Higher temperature and high pressures are conductive to better rocking and reflectivity characteristics. In view of economy and ease in handling, the upper limit of the temperature is preferably 3600.degree. C. and the upper limit of the pressure is preferably about 500 kg/cm.sup.2. Depending upon the type of polymer and the thickness of polymer film, the time required to complete graphitization of the film is usually from 10 to 180 minutes. A longer time may be used but further merits cannot be expected. The thermal treatment should be effected in vacuum or in a gas inert to the polymer used or the graphitization reaction. Such an inert gas may be argon, helium, nitrogen and the like. The resultant graphite films exhibit better rocking and reflectivity characteristics as will be particularly described in examples. As will become apparent from Example 1 appearing hereinafter, the pyrolysis under a pressure not lower than 4 kg/cm.sup.2 can provide a graphite film of polyphenylene oxadiazole whose characteristic properties including a rocking characteristic and a reflection efficiency are greatly improved over those of the known graphite film of polyphenylene oxadiazole. This is considered to result from the difference in pyrolyzing conditions. The graphite film obtained in this embodiment may be used, as it is, as a radiation optical element if desired. However, it is preferred to provide the graphite film on a suitable support as is particularly shown in FIGS. 2 and 3. In FIG. 2, there is shown a radiation optical element E including a flat smooth support 1 and a graphite film 2 formed on one side of the support 1. This element E may be used as an X-ray monochromator. The element E of FIG. 3 includes a curved smooth support 1' and a graphite film 2' formed on the inner side of the support 1' as viewed in the figure. This element serves as a kind of convergent lens. The support in these embodiments may take any forms if required and may be cylindrically or arbitrarily curved or flat. The support is usually made of glass, metals, ceramics and the like. The graphite film is attached to a flat or curved support by means of an adhesive which does not adversely influence the element and particularly the graphite film. Examples of such adhesives include epoxide compounds, cyanoacrylates, and the like. The graphite films set forth above have good rocking and reflectivity characteristics and can be fabricated in a desired size with good flexibility. Accordingly, the graphite film products obtained by the above procedures can be applied as various optical elements including not only the lens and monochromater as shown in FIGS. 2 and 3, but also analyzers and filters. In practical applications, a graphite film having a thickness of several to several tens micrometers are suitable for X-rays with a wavelength of approximately several to about 8 or 9 angstroms. For X-rays with a shorter wavelength, the graphite should favorably be in the form of a sheet or block having a thickness of not less than 0.5 mm. Moreover, for monochromaters or filters, for neutron rays, 2 mm to 50 mm thick graphite blocks are necessary. In order to obtain a graphite sheet or block of a desired thickness, a plurality of polymer films each having 1 to 400 micrometers are stacked and thermally treated (a) at a temperature up to 2800.degree. C. at a pressure of not higher than 20 kg/cm.sup.2 and then (b) at a temperature of not lower than 2800.degree. C. at a pressure not lower than 20 kg/cm.sup.2. Alternatively, a plurality of graphite films may be pressed at a temperature not lower than 2800.degree. C. at a pressure not lower than 20 kg/cm.sup.2, thereby obtaining a block of a desired thickness. In the former case, the thermal treatment (a) is effected at a heating rate of several to several tens degree/minute. The treatment (b) is conducted over 10 to 180 minutes. The pressures in the respective steps (a) and (b) may be constant for each step. Preferably, the pressure within a defined range is continuously varied and kept at a maximum level and returned to an initial level, followed by repeating this cycle. For instance, the pressure up to 20 kg/cm.sup.2 at temperatures lower than 2800.degree. is imposed so that the pressure gradually increases from 0 to 20 kg/cm.sup.2 in a given time. When it reaches a maximum level, the pressure is maintained for a given time and is subsequently returned to an initial level. This is repeated several to several tens times. Over 2800.degree. C., the pressure imposed is gradually varied from 20 kg/cm.sup.2 to an intended level in the same manner as set forth above. This is advantageous in that wrinkles as will be produced, more or less, during the thermal treatment can be substantially removed. If a curved sheet is necessary, the thermal treatment may be effected in a mold capable of causing a desired curve of the sheet to be formed. Graphite has a lattice distance of 3.354 angstroms and cannot thus be used as an optical element for soft X-rays as stated before. As a diffraction grating for a wavelength of soft X-rays, there are known thin films of organic compounds such as EDDT, ADP or KAP or multi-layered thin films which are obtained by alternately depositing carbon and tungsten, or silicon and nickel. However, with the organic compounds, thermal stability and reflection intensity are not satisfactory. On the other hand, the multi-layered films are very complicated in the fabrication procedure, coupled with another disadvantage that they cannot be applied to X-rays having a wavelength of not higher than 20 angstroms. More particularly, there is not known any film serving as a diffraction grating which exhibits good characteristics and are capable of being applied for soft X-rays having a wavelength of from about 10 to 20 angstroms. According to another embodiment of the invention, the above problem can be solved by provision of a graphite film which is interacted with a metal halide to form a film of a metal halide-intercalated graphite compound where the metal halide is intercalated inbetween layer lattices of the graphite. The intercalation of a metal halide into graphite involves two types including a first stage intercalation wherein the metal halide is included in an individual space between any adjacent lattice layers of graphite. Another type includes a second stage intercalation wherein the metal halide is intercalated in every third space between lattice layers of graphite. The intercalation used herein means both types of intercalations. The starting graphite film may be one which is obtained in the first embodiment. More particularly, a film or sheet of a polymer which is selected from those defined with respect to the first embodiment and including polyphenylene oxadiazole is subjected to thermal treatment at a temperature of not lower than 2800.degree. C. either at a normal pressure or at a pressure of not lower than 4 kg/cm.sup.2 in vacuum or in an inert gas. The intercalated graphite compound film using a metal halide is generally obtained by a gas phase method, a solvent method or an electrolytic method. In the practice of the invention, the intercalated film is obtained either by a procedure wherein a graphite film and a metal halide are heated in a stream of a halogen such as Cl, Br, I or F at a temperature of from 200.degree. to 500.degree. C. for a time of from 5 to 10 days for the first stage intercalation and for a time of from 1 to 4 days for the second stage intercalation, or by a procedure wherein a graphite film and a metal halide are placed in a sealed glass and heated in vacuum under conditions indicated above. If the halogen stream is used, the halogen used should be a halogen of the metal halide used. For the first stage intercalation, a longer time is necessary. The metal halides used to react with the graphite include, for example, BCl.sub.3, MgCl.sub.2, AlCl.sub.3, ScCl.sub.3, TiCl.sub.4, CrCl.sub.3, MnCl.sub.2, FeCl.sub.3, CoCl.sub.2, NiCl.sub.2, CuCl.sub.2, ZnCl.sub.2, GaCl.sub.3, YCl.sub.3, NbCl.sub.5, MoCl.sub.5, RhCl.sub.3, PdCl.sub.2, CdCl.sub.2, RuCl.sub.3, ZrCl.sub.4, InCl.sub.3, HfCl.sub.4, TaCl.sub.5, WCl.sub.6, ReCl.sub.4, OsCl.sub.4, PtCl.sub.4, AuCl.sub.3, HgCl.sub.2, TlCl.sub.3, BiCl.sub.4, ICl, IBr, FeCl.sub.2, BF.sub.3, AlBr.sub.3, SiF.sub.4, TiF.sub.4, FeBr.sub.3, CuBr.sub.2, PF.sub.6, GaBr.sub.3, NbF.sub.5, MoF.sub.6, CdBr.sub.2, TaF.sub.6, WF.sub.6, OsF.sub.3, AuBr.sub.3, TlBr.sub.3, and mixtures thereof. Of these, NiCl.sub.2 and CuCl.sub.2 are preferred. Aside from the metal halides, alkali metals such as Na or K may be used to form an intercalated graphite compound. However, these intercalated compounds are unstable and are not suitable for the purposes of the invention. The film of the intercalated graphite compound obtained in this manner has a high reflection efficiency for soft X-rays, a lattice distance larger than that of the graphite film, and high resistances to heat and moisture. In addition, the intercalated compound film is so high in flexibility that it can be bonded to a curved or flat support or substrate without breakage. For this purpose, an adhesive such as epoxide compounds, pitches and the like may be used. Thus, this film can be applied as an optical element such as a lens, monochromater, analyzer or filter similar to the graphite film of the first embodiment. Moreover, the films of the intercalated graphite compound are readily self-bonded by pressing to form a block or sheet of a desired thickness. The self-bonding property of the intercalated graphite compound film may be utilized in combination with graphite films in a further embodiment of the invention to make a thick film whose properties are predominant of those of the graphite films. The graphite film set forth before with respect to the first embodiment may, in some cases, involve a difficulty in making a thick film because of the generation of gases during the thermal treatment of polymer film. If a thick polymer film is pyrolyzed in order to obtain a thick graphite film, gases generated in the vicinity of or near the film surface may readily escape to outside. However, the gases generated around the inner portion of the film are difficult to escape and may be included in the inside. As the pyrolysis proceeds further, the gases increase in amount, which may eventually lead to cracking of the entirety of the film. Further, formation of a block or sheet of graphite films by pressing requires relatively severe thermal treating conditions as set out before. For obtaining a thick sheet of block having graphite properties, adhesiveness of the films of the intercalated graphite compound can be conveniently utilized. This is described with reference to FIGS. 4 and 5. In FIG. 4, there is shown an optical element E which includes graphite films 10 and intercalated graphite compound films 12 which are superposed or stacked alternately and pressed. FIG. 5 shows an optical element E which includes graphite films 10' and intercalated graphite compound films 12' sandwiched between the graphite films 10' as shown. If a desired number of graphite films and intercalated graphite compound films in number sufficient to be alternately superposed with the graphite films so that the graphite films are formed as an outermost layer on opposite sides, or if a desired number of intercalated graphite compound films are sandwiched between graphite films, a desired thickness can be readily obtained. The superposed or sandwiched films are appropriately bonded by pressing generally at a pressure of not less than 4 kg/cm.sup.2. In view of the ease in fabrication, the starting graphite and intercalated graphite compound films are conveniently both in the thickness of from 4 to 200 micrometers. The superposed or sandwiched block or sheet may be used as it is or after deposition on a curved or non-curved support through an adhesive as used in the first embodiment. If deposition is made on a curved support, it is convenient to subject the block and the support to press molding using a mold of a desired form. By this, a radiation optical element having a desired radius of curvature in conformity with the radius of the curved support is obtained. As will become apparent from examples, the reflectivity of the block or sheet is predominantly influenced by the reflectivity of the graphite films, not of the intercalated graphite compound films. In addition, such a sheet or block has a plane distance, d, of 3.353 angstroms and is coincident with that of a graphite single crystal. The graphite films or blocks, intercalated graphite compound films or blocks, and combinations of the graphite films and intercalated graphite compound films have been described hereinabove. Typical examples of applications of the radiation optical elements using these films or combinations are described with reference to FIGS. 6 and 7 wherein like reference numerals indicate like parts. FIG. 6 schematically shows an application of a radiation optical element to a convergent lens system for X-rays. In the figure, the system S includes a convergent lens 20 having a curved substrate 22 and a graphite film 24 bonded to the inner surface of the curved substrate 22. Indicated by 26 is a plate made, for example, of molybdenum having a hole 28 with a diameter of about 1 mm through which a radiation 30 such as a CuK.alpha. line is passed. The radiation is reflected at the convergent lens 20 and focussed on a photographic plate 32. In this manner, a fine X-ray pattern is obtained. Instead of the graphite film, the intercalated graphite compound film or the combination of the graphite and intercalated graphite compound films may be likewise used. FIG. 7 schematically shows an X-ray monochromater system using the film or sheet of the invention. In the figure, the monochromater is indicated as M and includes a convergent lens 20 having a curved substrate 22 and a graphite film 24 and a monochromater 34 for X-rays having a flat glass substrate 36 and a graphite film 38 formed on one side of the substrate 36. Reference numerals 26, 26' are respectively, plates having small holes 28, 28' and reference numeral 40 indicates a counter. In operation, when an X-ray 42 is incident on the monochromater, it reflects and passes through the hole 28 of the plate 26 on the convergent lens 24. The converged ray is passed through the small hole 28' of the plate 26' and focussed into the counter 10. It will be noted that when the angle of incidence of the X-ray 42 passed to the X-ray monochromater 34 is changed, the wavelength of the X-ray passing through the small hole 28 changes. The present invention is more particularly described by way of examples. In examples, the lattice constant, rate of graphitization, electric conductivity and rocking characteristic were measured by the following methods. (1) Lattice Constant (Co) A sample was subjected to measurement of an X-ray diffraction pattern using an X-ray diffractometer, PW-1051, by Philips and an Cuk .alpha. line. The constant was calculated from the equation of .lambda.=2d sin .theta.(2d=Co) using a diffraction line at (002) in the vicinity of 2 .theta.=26.degree.-27.degree.. In the equation n=2 and .lambda. is a wavelength of the X-ray used. (2) Rate of Graphitization The rate was calculated from the following equation using a plane distance, d, EQU d.sub.002 =3.354g+3.44(1-g) where g=1 means complete graphite and g=0 means amorphous carbon. (3) Electric Conductivity (S/cm) A sample was provided with four-terminal electrodes using a silver paste and a gold wire wherein a constant current was passed from the outer electrodes to detect a voltage drop at the inner electrodes. The width, length and thickness of the sample were determined through microscopic observation, from which the electric conductivity was calculated. (4) Rocking Characteristic An X-ray diffractometer TU-200B made by Rigaku Denki Co., Ltd. was used to measure a rocking characteristic at a peak of the graphite (002) line. The rocking characteristic was indicated as a half-value width of the resultant absorption. EXAMPLE 1 Films of polyphenylene oxadiazole (POD), polybenzothiazole (PBT), polybenzobisthiazole (PBBT), polybenzooxazole (PBO), polybenzobisoxazole (PBBO), polypyromellitimide (PI), polyphenylene isophthalamide (PA), polyphenylene benzoimidazole (PPBI), polyphenylene benzobisimidazole (PBBI), polythiazole (PT) and poly-p-phenylene vinylene were pyrolyzed at a temperature of 2800.degree. C. at a pressure of 20 kg/cm.sup.2 for 1 hour in argon. The resultant graphite films were subjected to measurement a lattice constant, a rate of graphitization and a rocking characteristic. For comparison, a film of polyphenylene oxadiazole (POD) was similarly pyrolyzed at 2800.degree. C. at a normal pressure to obtain a graphite film. This film was also measured similar to the above graphite films of the invention. Moreover, a reflection efficiency of the graphite films of the invention was determined using a CuK .alpha. line in relation to the reflection efficiency of the graphite film of the polyphenylene oxadiazole for comparison. The results are shown in Table 1 below. TABLE 1 ______________________________________ Rocking Lattice Rate of Graphi- Character- Type of Constant tization istic Reflection Polymer (.ANG.) (%) (.degree.) Efficiency ______________________________________ POD 6.708 100 6.9 1.0 for Comp. POD 6.708 100 1.2 1.5 PBT 6.708 100 0.9 1.67 PBBT 6.710 98 1.0 1.74 PBO 6.710 98 0.7 1.71 PBBO 6.711 97 0.9 1.64 PI 6.709 99 0.8 1.89 6.710 98 0.8 1.64 PPBI 6.709 99 0.7 1.74 PBBI 6.710 98 0.8 1.80 PT 6.712 97 1.0 1.81 PPV 6.709 99 0.7 1.97 ______________________________________ The graphite film of POD for comparison has a graphitization rate of 100, but other graphite films have a graphitization rate of 100 to 97% and are thus equal or slightly inferior to the comparison film. However, the rocking characteristic of the films of the invention ranges from 1.5.degree. to 1.97.degree., which is better than 6.9.degree. of the comparative POD graphite film. In addition, the reflection efficiency is higher by 1.5 to 1.97 times than that of the POD graphite film. Thus, the graphite films of the invention are better in the characteristics as an X-ray optical element than the known POD graphite film. EXAMPLE 2 A film of a polybenzothiazole was pyrolyzed at a temperature of 2800.degree. C. under a pressure of 20 kg/cm.sup.2 for 1 hour in argon obtain a graphite film. The resultant film had a size of 5 cm.times.10 cm and a thickness of 30 micrometers. This film was bonded to a curved substrate made of Cu through an epoxide adhesive as shown in FIG. 3 to make a convergent lens. This lens was used in a X-ray lens system as shown in FIG. 6 in which the plate 26 was made of molybdenum with the hole 28 having a diameter of 1 mm. When a CuK .alpha. line 30 was passed through the hole 28, it was reflected at the film 24 of the convergent lens 20 and converged toward a photographic plate 32 located at a focussing point. An image formed on the plate 32 was a single line with a length of 1 mm and a width of about 13 micrometers, thus being good in convergence. When passing twice through the convergent lens 20, a fine X-ray pattern with a width of 1 micrometer or below could be obtained. EXAMPLE 3 Two films of polypyromellitimide each having a thickness of 25 micrometers were pyrolyzed at 3000.degree. C. at a normal pressure for 1 hour to obtain 15 micrometer thick graphite films each with a size of 5 cm.times.5 cm. One of the films was bonded to a smooth flat glass substrate through an epoxide adhesive. Another film was used to make a convergent lens as in Example 3. These optical elements were used to assemble an X-ray monochromater system as shown in FIG. 7 wherein the plates 26, 26' were each made of molybdenum. When an X-ray 42 from a Cu target was passed, a characteristic X-ray of CuK .alpha. was observed intensely at 13.288.degree.. The line width was found to be 0.18.degree.. When compared with a similar system using a natural graphite single crystal, the line width was reduced form 0.3.degree. to 0.18.degree., thus revealing the high performance of the graphite of the invention. EXAMPLE 4 10 micrometer thick PA films were each placed between quartz plates and heated at a rate of 20.degree. C. minute in a nitrogen gas and thermally treated at 1000.degree. C. for 1 hour. This film was sandwiched between graphite substrates and heated from room temperature at a rate of 10.degree. C./minute and treated at a temperature of 2800.degree. C. for 1 hour, followed by cooling at a rate of 20.degree. C./minute. Four graphite films were hot pressed using a high temperature hot press made by Chuugai Furnace Ind. Co., Ltd. under different conditions. The resultant sheets were subjected to measurements of the lattice constant, rate of graphitization, electric conductivity and rocking characteristics with the following results. TABLE 2 ______________________________________ Rate of Electric Rocking Hot Press Conditions Lattice Graphi- Conduc- Character- Temp. Pressure Const. tization tivity istic (.degree.C.) (kg/cm.sup.2) .ANG. % S/cm .degree. ______________________________________ 1600 40 6.710 99 14000 7.4 1600 100 6.710 99 15000 7.1 2800 40 6.708 100 19000 0.42 2800 100 6.708 100 19000 0.28 ______________________________________ As will be apparent from the above results, higher temperatures and higher pressures are effective in improving the rocking characteristic. The pressing under conditions of 2800.degree. C. and 100 hours results in a rocking value of 0.28.degree.. When the pressing time is prolonged to 2 hours under the above conditions, the value reaches 0.26.degree.. EXAMPLE 5 The PA films treated at 2800.degree. C. in the same manner as in Example 4 were hot pressed under conditions of 2800.degree. C. 40 kg/cm.sup.2. For the pressing, 10, 20, 80 and 200 graphite films were, respectively, used to obtain 38 micrometers, 110 micrometers, 380 micrometers and 1 mm. The physical properties including the rocking characteristic were similar to those of Example 4 of the invention. EXAMPLE 6 20 films of each of PI, POD and PA, each having a thickness of 25 micrometers thermally treated and graphitized at a temperature between 1000.degree. and 2000.degree. C. under a pressure of 10 kg/cm.sup.2, at a temperature between 2000.degree. and 2800.degree. C. under a pressure of 20 kg/cm.sup.2 and at a temperature of 3000.degree. C. under a pressure of 40 kg/cm.sup.2, thereby obtaining graphite blocks. The characteristics of the blocks are shown in Table 3 below. TABLE 3 ______________________________________ Rate of Electric Rocking Lattice Graphi- Conduc- Character- Const. tization tivity istic Polymer Film .ANG. % S/cm .degree. ______________________________________ PI 6.708 100 20000 0.18 POD 6.708 100 18500 1.1 6.708 100 19000 1.0 ______________________________________ EXAMPLE 7 This example illustrates an intercalated graphite compound film. A 20 micrometer thick graphite film obtained by pyrolyzing a film of polyphenylene oxadiazole at 3000.degree. C. at a normal pressure for 1 hour in Ar and 2 g of CuCl.sub.2 were placed in a glass tube and sealed under vacuum, followed by reaction at 500.degree. C. for 7 days. As a result, a first-stage CuCl.sub.2 -graphite intercalation compound film was obtained. This film was subjected to measurements of a position of reflection line, lattice distance, reflectivity and plane index with respect to the CuK .alpha. line (1.5418 angstroms). The reflectivity was measured by the use of an ordinary diffractometer and expressed as a ratio of a reflection intensity from plane (00 l) of the graphite intercalation compound to the strength of an incident X-ray. The lattice distance was calculated from the Bragg equation using a reflection angle (2.theta.) at the plane (00 l) for the CuK .alpha. line. The results are shown in Table 4 below. TABLE 4 ______________________________________ Lattice Distance Reflectivity 2.theta. (.degree.) (.ANG.) (%) Plane Index ______________________________________ CuCl.sub.2 - 9.408 9.400 0.95 (001) Graphite Intercala- 18.881 4.700 2.1 (002) tion Compound Film 28.486 3.133 0.37 (003) ______________________________________ The reflection lines are those corresponding to planes (001), (002) and (003) of the graphite intercalated compound. The reflectivity was about 2% at the highest plane (002) and about 1% at (001). The half-value widths of the respective lines were each below 0.2.degree.. Thus, the film was found to have satisfactory characteristics as an X-ray optical element. EXAMPLE 8 A 10 micrometer thick graphite film obtained by pyrolyzing a film of polyphenylene phthalamide at 3000.degree. C. at a normal pressure for 1 hour was placed in a glass tube and sealed under vacuum along with 2 g of FeCl.sub.3, followed by reaction at 300.degree. C. for 5 days to obtain a first-stage FeCl.sub.3 -graphite intercalation compound film. This film was subjected to measurements in the same manner as in Example 7. The results are shown in Table 5 below. TABLE 5 ______________________________________ Lattice Distance Reflectivity 2.theta. (.degree.) (.ANG.) (%) Plane Index ______________________________________ FeCl.sub.3 - 9.440 9.368 0.87 (001) Graphite Intercalated 18.920 4.690 2.00 (002) Compound Film 28.609 3.120 0.33 (003) ______________________________________ The reflection lines are those corresponding to planes (001), (002) and (003) of the graphite intercalation compound. The reflectivity was about 2% at the highest plane (002) and about 0.87% at (001). The half-value widths of the respective lines were all below 0.2.degree.. Thus, this film was found to have satisfactory characteristics for use as an X-ray optical element. EXAMPLE 9 A 25 micrometer thick graphite film obtained by pyrolyzing a film of polypyromellitimide at 3000.degree. C. at a normal pressure for 1 hours in vacuum and 2 g of TaCl.sub.5 were placed in thionyl chloride and reacted at 60.degree.C. for 10 days while passing an argon gas, thereby obtaining a second-stage TaCl.sub.5 -graphite intercalation compound film. This film was subjected to measurements in the same manner as in Example 7. The results are shown in Table 6 below. TABLE 6 ______________________________________ Lattice Distance Reflectivity 2.theta. (.degree.) (.ANG.) (%) Plane Index ______________________________________ TaCl.sub.5 - 6.882 12.844 0.63 (001) Graphite Intercalated 13.797 6.418 0.58 (002) Compound Film 20.754 4.280 1.61 (003) 27.790 3.210 1.54 (004) ______________________________________ The reflection lines are those corresponding to planes (001), (002), (003) and (004) of the graphite intercalation compound. The reflectivity was about 1.5% at the highest planes (003) and (004) and 0.6% at (001). The half-value widths of the respective lines were all below 0.3.degree.. Thus, the film was satisfactory for use as an X-ray optical element. EXAMPLE 10 20 micrometer thick graphite films obtained by pyrolyzing films of polyphenylene oxadiazole and 4 g of CuCl.sub.2 were sealingly placed in a glass tube under vacuum and reacted at 500.degree. C. for 7 days to obtain first-stage CuCl.sub.2 -graphite intercalation compound films. Seventy five films were superposed and pressed under a pressure of 50 kg/cm.sup.2 to obtain an about 3 mm thick graphite intercalation compound block. This block was subjected to measurement of a tensile shearing stress by the use of a tensile tester, revealing that the adhesion strength of the block was 1 kg/cm.sup.2. The block was subjected to measurements of the position of the reflection line, lattice distance, reflectivity and plane index in the same manner as in Example 7. The results are shown in Table 7 below. TABLE 7 ______________________________________ Lattice Distance Reflectivity 2.theta. (.degree.) (.ANG.) (%) Plane Index ______________________________________ CuCl.sub.2 - 9.408 9.400 1.51 (001) Graphite Intercalated 18.881 4.700 3.5 (002) Compound Block 28.486 3.133 0.64 (003) ______________________________________ The reflection lines are those corresponding to the planes (001), (002) and (003). The plane distance was the same as that of a single graphite intercalation compound film. The reflectivity was about 3.5% at (002) and about 1.5% at (001), which were higher than those of the single graphite intercalation compound film. The half-value widths of the respective lines were all 0.25.degree. and were thus inferior to the values of the single film. Nevertheless, the block was sufficient for use as an X-ray optical element. EXAMPLE 11 This example illustrates application of a graphite intercalation compound block as a convergent lens as shown in FIG. 6. One hundred and fifty graphite films intercalated with CuCl.sub.2, each having a size of 5 cm.times.10 cm and a thickness of 20 micrometers, were superposed and press molded to have a curvature coinciding with a curved support thereby forming a a lens having a 3 mm thick block on the support. The graphite used was made from polypyromellitimide. Substantially in the same manner as in Example 2, a CuK .alpha. line was passed through a Mo plate 28 with a diameter of 1 mm toward the lens fabricated above as 20 and focussed on a photographic plate 32 to form an image of a single line with a 1 mm and a width of about 15 micrometers on the plate 32. When the converging system was arranged to allow the line to converge twice, there was obtained a fine pattern with a width of not larger than 1 micrometer. EXAMPLE 12 The general procedure of Example 3 was repeated except that an X-ray monochromater was made as follows. One hundred and fifty CuCl.sub.2 -graphite intercalation compound films were superposed and pressed at a pressure of 20 kg/cm.sup.2 to obtain an about 3 mm thick block with a size of 5 cm.times.5 cm and this block was bonded to a glass substrate. The graphite used was obtained from polypyromellitimide. When an X-ray from a Cu target was passed, a characteristic X-ray of CuK .alpha. was intensely observed at .theta.=4.704.degree.. The line width was 0.2.degree.. As will be apparent from the above, when the graphite intercalation compound was used as a radiation optical element, a plane distance of about 10 .ANG. can be attained which would be difficult when using known multi-layered films. This means that there can be obtained a radiation optical element for soft X-rays with a wavelength of about 10 angstroms. EXAMPLE 13 50 polyphenylene oxadiazole films were pyrolyzed at a temperature of 3000.degree. C. for 30 minutes to obtain graphite films each having a thickness of 20 micrometers. On the other hand, 40 micrometer thick graphite films were obtained from 49 polyphenylene oxadiazole films under conditions as used above. These graphite films were intercalated with CuCl.sub.2 to obtain forty nine first-stage CuCl.sub.2 -graphite intercalation compound films. The intercalated graphite films were, one by one, inserted inbetween the graphite films for alternate superposition, followed by pressing at a pressure of 50 kg/cm.sup.2, thereby obtaining a superposed graphite block having a thickness of about 3 mm. This block was subjected to measurement of reflection line positions for CuK .alpha. (1.5418 angstroms), relative intensities to a reflection intensity at plane (002) of the graphite plate taken as 100, and plane indexes. The results are shown in Table 8 below. TABLE 8 ______________________________________ 2.theta. (.degree.) Relative Intensity Plane Index ______________________________________ Graphite 26.576 100 (002) 54.734 5.2 (004) 87.187 0.6 (006) CuCl.sub.2 - 9.408 0.95 (001) Graphite Intercalated 18.881 2.1 (002) Compound 28.486 0.37 (003) ______________________________________ The reflection lines are those corresponding to planes (001), (002) and (003) of the graphite intercalation compound and those corresponding to planes (002), (004) and (006) of the graphite. The reflection intensity is predominantly intense for the line corresponding to plane (002) of the graphite. The reflection angle (2.theta.) of the graphite was 26.576.degree. with a plane distance, d, of 3.354 .ANG., coinciding with those of a graphite single crystal. The half-value width was 0.2.degree. and thus, the graphite plate has satisfactory characteristics as an X-ray optical element. EXAMPLE 14 Example 13 was repeated thereby making a graphite block. This block was press molded using a cylindrical tool having such a curvature as a curved substrate. The molded block was bonded to the curved substrate to make a converging lens. This lens was applied to a system as shown in FIG. 6. When a CuK .alpha. line 30 was passed through the hole 28 of the molybdenum plate 26 and focussed through the lens 20 on the photographic plate 32. A single line image was obtained with a length of 1 mm and a width of about 15 micrometers. Thus, the lens had good convergence. When the CuK .alpha. line 30 was passed twice through the lens 20, a fine pattern with a width of 1 micrometer or below could be obtained. EXAMPLE 15 In the same manner as in Example 14 an about 3 mm thick superposed block was made and attached to a flat glass substrate to make an X-ray monochromater. This monochromater was assembled in a system as shown in FIG. 7. When the angle .theta. of the incidence of the X-ray 42 was changed, the wavelength of the X-ray 42 passing through the hole 28 of the Mo plate could be changed. After the passage though the hole 28, the X-ray was directed toward a convergent lens as used in Example 12 at which it was changed in direction to pass through the hole 28' and focussed into the counter 40. When an X-ray from a Cu target was passed, a characteristic X-ray of CuK.alpha. was intensely observed at .theta. =13.288.degree.. The line width was 0.2.degree.. When comparing with the case where a natural graphite single crystal, the line width was reduced from 0.3.degree. to 0.2.degree.. Thus, the superposed graphite plate was confirmed to have good properties. EXAMPLE 16 Polyphenylene oxadiazole films were thermally treated at 3000.degree. C. for 30 minutes in vacuum to obtain 20 micrometers thick graphite films. Part of the graphite films was used to make a first-stage CuCl.sub.2 -graphite intercalation compound films each with a thickness of 40 micrometers. The graphite films and the intercalation compound films were superposed as shown in FIG. 5 in such a way that 25 intercalation compound films were placed on one graphite film. Three layers of the above combination were superposed so that upper and lower films were the graphite films and pressed at a pressure of 50 kg/cm.sup.2, thereby obtaining an about 3 mm thick graphite block serving as a radiation optical element. This block was subjected to measurements of reflection line positions, lattice distance, reflectivity and plane index. The results are shown in Table 9 below. TABLE 9 ______________________________________ Lattice Distance Reflectivity 2.theta. (.degree.) (.ANG.) (%) Plane Index ______________________________________ Graphite 26.576 3.354 4.18 (002) 54.734 1.677 0.20 (004) 87.187 1.118 0.03 (006) CuCl.sub.2 - 9.408 9.400 1.51 (001) Graphite Intercala- 18.881 4.700 3.5 (002) tion Compound Film 28.486 3.133 0.64 (003) ______________________________________ The reflection lines are those corresponding to planes (001), (002) and (003) of the graphite intercalation compound and those corresponding to planes (002), (004) and (006) corresponding to the graphite. The reflectivity at the line corresponding to plane (002) of the graphite films and the reflectivity at the line corresponding to plane (002) of the intercalation compound films are substantially the same. The reflection angle (2.theta.) at plane (002) of the graphite films is 26.576.degree. with a plane distance, d, of 3.354 .ANG., coinciding with those of a graphite single crystal. The plane distance calculated from the lines of the intercalation compound is substantially the same as that of a single film. The half-value width was 0.2.degree. for the (002) line of the graphite, and 0.3.degree. for the (001) line and 0.27.degree. for the (002) line of the intercalation compound. Thus, the block obtained in this example was satisfactory in the characteristics for use as an X-ray optical element. In the above examples 13 to 16, graphite films obtained from polyphenylene oxadiazole are described. It should be noted when graphite films obtained from other polymer films indicated in Tables 1 and 2 and graphite intercalation compound films made of graphite films made from polyimide and metal halides are used, similar results are obtained. Moreover, application of the elements to X-rays has been described, the elements are also applicable as a monochromater, analyzer, lens or film for neutron spectroscopy. |
abstract | Embodiments of the present disclosure are directed to systems, components, and methods for transferring canisters containing radioactive material, for example, from a container assembly using a transfer assembly to a horizontal storage module (HSM). Systems in accordance with various embodiments of the present disclosure include, for example, a vertical to horizontal (VTH) transfer station for a canister and method of transfer, a horizontal to horizontal (HTH) transfer station for a canister and methods of transfer, a transport wagon system for transporting a canister to a horizontal storage module (HSM), and an HSM system for long-term storage of a canister. |
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048517020 | claims | 1. A radiation shield suitable for preventing radiation or radioisotopes from reaching or contacting a person using a vessel containing a radioactive solution, said shield comprising: a radiopaque container having a top and a bottom opening; and means for supporting said vessel within said container without said means blocking said top or bottom opening, wherein said container reduces emission of said radiation through the sides of said vessel. providing a radiation shield having a radiopaque container with a top and bottom opening; and means for supporting said vessel within said container without blocking said top or bottom openings, wherein said container reduces emission of said radiation through the sides of said vessel; placing said vessel within said radiopaque container; and transporting said vessel from a first position to a second position by holding said container without touching said vessel. 2. The radiation shield of claim 1 wherein said radiopaque container comprises means to permit incubation liquid to directly enter the bottom opening of said container and surround that portion of said vessel containing said radioactive solution. 3. The radiation shield of claim 1 wherein said container is a sleeve that fits over said vessel. 4. The radiation shield of claim 3 wherein said sleeve has a substantially flat bottom surface for allowing said sleeve to rest in a free-standing position on a flat surface. 5. The radiation shield of claim 3 wherein said container is sized and shaped to hold a microtube having a lid and comprises a ridge or dimples formed along said top opening to elevate the lid of the microtube from the sleeve to facilitate access to the lid. 6. The radiation shield of claim 3 wherein said sleeve comprises a flange for allowing suspension of said sleeve in a rack, wherein liquid may enter the bottom opening of said sleeve and surround that portion of said vessel containing said radioactive solution. 7. The radiation shield of claim 1 wherein said radiopaque container comprises an incubation rack for supporting a plurality of vessels and a radiopaque shield formed along the perimeter of said rack. 8. The radiation shield of claim 7 further comprising a radiopaque cover for shielding radiation emanating through said top opening. 9. The radiation shield of claim 1 wherein said radiopaque container comprises a block of radiopaque material having a plurality of bores. 10. The radiation shield of claim 1 wherein said container is transparent. 11. The radiation shield of claim 1 wherein said container is fabricated using acrylic, polycarbonate or other subtantially radiopaque plastic material. 12. A method for preventing radiation or radioisotopes from reaching or contacting a person using a vessel containing a radioactive solution, said method comprising the steps of: 13. The method of claim 12 further comprising the step of placing said radiopaque container comprising said vessel within an incubation liquid whereby said vessel is caused to attain the temperature of said liquid. |
052271250 | summary | FIELD OF THE INVENTION The present invention relates to a tool for handling a cluster of rods of consumable poison, used particularly in a fuel building of a nuclear power station, for example of the PWR type, in order to carry out handling operations on clusters of rods of consumable poison. The tool is used especially during the first refuelling of the nuclear reactor and makes it possible to extract under water the clusters of rods of consumable poison inserted in the fuel assemblies or into cells of spent-fuel storage racks equipped with adaptors. The tool is attached to a winch of a platform displaceable in the fuel building and comprises a head for gripping the cluster, connected to the end of a handling member displaceable slidably in a tool body between an active position, in which the head and at least part of the member project from the body in order to grip the cluster, and a retracted position, in which the member, the gripping head and part of the cluster extend within the body for the displacement of the cluster. Moreover, the tool comprises combs for guiding the rods, provided at the corresponding end of the body and displaceable by raising between a retracted position, in which they extend substantially along the wall of the body, and an active position, in which they extend substantially perpendicularly to the wall in order to guide the rods when these extend at least partially within the body. BACKGROUND OF THE INVENTION In the prior art, the displacement of these combs between the retracted and active positions is effected by means of an operating linkage actuable, for example, by a user. However, such a linkage has a relatively complex structure, its bulky and risks jamming of the combs. SUMMARY OF THE INVENTION The object of the invention is to solve these problems by providing a handling tool of simple structure and reduced bulk in which the displacement of the combs between the active and retracted positions is carried out in a highly reliable way and without the risk of jamming. To this end, the subject of the invention is a handling tool of the type described above, comprising elastic means for stressing the combs into the active position and means for retracting the combs counter to the stress of the elastic means, displaceable between an active position of retraction of the combs and a retracted position of release of the combs by the gripping head and/or the handling member during their displacement between their active position and their position retracted within the body . |
039473210 | summary | This invention relates to neutronic reactors, and particularly to a control and shim rod shield room for a reactor. As is more fully described in the copending application of Robert M. Evans Ser. No. 649,407 filed Feb. 21, 1946, in which is disclosed a neutronic reactor with which the present invention finds particular adaptation, it is necessary for control of the operation of the reactor to provide control and shim rods of neutron absorbing material which can be inserted into the reactor preferably from one lateral face, and withdrawn therefrom partially or fully as dictated by the activity of the reactor. For this purpose, suitable passages are provided in the reactor and control and shim rods are mounted for movement into and out of the passages. For further more detailed discussion of the nuclear physics and physical characteristics of neutronic reactors, particularly control and shim rods, reference is made to the copending application of Fermi and Szilard, Ser. No. 568,904, filed Dec. 19, 1944, now U.S. Pat. No. 2,708,656. However, the rods are highly radioactive when they are withdrawn from the passages due to the high degree of neutron bombardment to which they have been subjected while in the active portion of the reactor and a problem is presented of safeguarding personnel from the radiations from the withdrawn rods and from the open ends of the passages leading into the reactor. One of the principal objects of the present invention is to provide novel simple and effective means of shielding control and shim rods when they are in their withdrawn position. Another object is to shield personnel from radiations from the control and shim rod passages into a reactor when the rods are fully removed for servicing or repairs. |
053717686 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a typical fuel bundle B having the spacer of this invention is illustrated. The fuel bundle includes lower tie plate L having nose piece N. A plurality of full length fuel rods R extend from lower tie plate L to upper tie plate U. In the usual embodiment, one or more of the fuel rods R is a part length fuel rod R.sub.p. These fuel bundles are surrounded by a channel C extending from lower tie plate L at least to the vicinity of upper tie plate U. As is known in the prior art, the bands of the spacers can include flow tabs T. (See FIGS. 1 and 2). The reader will understand that the fuel bundle B is shown only for a portion of its length. Specifically, the fuel bundle is sectioned at surrounding channel C so that the spacers S.sub.1, S.sub.2, and S.sub.3 can be seen. The reader will understand that the invention here is especially applicable to spacers S.sub.2 and S.sub.3. Referring to the perspective view of FIG. 2, the construction of a spacer S.sub.2 and S.sub.3 without the placement of the fuel rods within the spacer is illustrated. The spacer is a two level spacer including preferably lower ferrule layer F and upper swirl vane layer V. Lower ferrule layer F includes conventional side-by-side ferrules 14 having shortened height and annular walls of minimum thickness. Normally, such ferrule spacers have heights in the order of 1.2 inches. The preferred spacer of this invention has a preferred height in the order of one-half to three-quarters of the normal value. That is to say, the ferrule height is held to a limit of 0.9 inch or less. A similar modification has been made to the thickness of the spacer. Normally, ferrule spacers have wall thickness in the order of 0.020 inches. In the construction here utilized, the wall thickness of the material of the ferrule is reduced below 0.020 inches--preferably in the range of 0.015 inches. These reductions in material dimensions are required for designs which normally have a high inherent bundle pressure drop. The remainder of the construction of the ferrule layer F is conventional. The spacer is surrounded by band 16 and includes stops 18 and loop springs 20 interior of the ferrules (See FIG. 3B). Vane portion V is just as easily understood. Referring to FIG. 4A, a material which is preferably Zircalloy is shown with generally "I" shaped upstanding metal cut out sections connected at the bottom by continuous band 42. At the top, sections 40 have an interrupted band 44. Centrally of the generally "I" shaped bands are central tabs 46. The width of sections 40 is generally the minimum width of the subchannel region 48 formed between adjacent ferrules 14 (See FIG. 3D). This minimum width is utilized so that when the respective members 40 are twisted, the resulting twisted structure only overlies the subchannel region at 48. Continuous arm 42 includes tabs 43. Tabs 43 are spaced for keying to the tops of the assembled ferrules 14. These tabs 43 may conveniently serve as points of attachment. Preferably, vanes 30 include at least 90.degree. twists from top to bottom. As here shown, the channels include the illustrated 180.degree. twists. Such twisting enables arms 44 to form a grid parallel to continuous arm 42 at the bottom with arms 46 being joined at 90.degree. to form a continuous interval. Preferably continuous arm 42 is fastened to the top of ferrule array F. Returning to FIG. 2, the paths along which the swirl vanes V are attached is shown. Preferably, a row R.sub.1 of vanes V is placed between the first and second rows of fuel rods. Likewise, a row R.sub.2 of vanes V is placed between the second and third row of fuel rods. It will be observed that the matrix illustrated is a 10 by 10 array of fuel rods having water rods W.sub.1 and W.sub.2 each displacing four fuel rods from the matrix. In this event, partial rows R.sub.3 of swirl vanes V can be used between the fuel rods of the third and fourth rows. Having set forth the construction of spacers S.sub.2 and S.sub.3, the operation of the spacer can now be set forth. It will be understood that when a reactor operates under normal power loads--in excess of 80% of available power--the upper two phase region of bundle B constitutes a region where rods R must be provided with a desired liquid film coating for the generation of steam. This will be the region where spacers S.sub.2 and S.sub.3 will be located. It will further be understood, that spacer S.sub.1 is not a candidate for this spacer construction. Simply stated, nuclear loading of fuel rods R is designed so that at the top end of the active fuel region, fuel rods R do not have the heat output that threatens the "dryout" conditions on the surfaces of the fuel rod cladding. It has been set forth that the spacer construction of spacers S.sub.2 and S.sub.3 has minimized the pressure drop effect of adding swirl vanes to an existing spacer design. This minimized pressure drop is at least due to not decreasing the flow area through the axial length of the spacer. Therefore, the more mobile, lower density steam will tend to avoid the region in favor of the higher density, less mobile liquid water. Regarding ferrule layer F, it will be understood that the interstitial volume between each ferrule 14 and each fuel rod R is an area of relatively high flow resistance. Regarding the vane layer V, it will be understood that the high velocity flow exiting from the subchannels between the spacer ferrules will immediately impact upon the swirl vanes. There the liquid (being the higher density fluid component) will be centrifugally thrust toward the surrounding fuel rods while vapor will continue relatively unobstructed through the vane region. At the same time, the subchannel region 48 between ferrules 14 will define a flow path of relatively low resistance. Thus, steam vapor passing the level of ferrule layer F can in large measure be bypassed to flow in subchannel region 48. It will be understood that it is preferred to place vane layer V overlying ferrule layer F. There is a reason for this order. Specifically, it is the function of swirl vanes 40 to permit steam to rise directly upwardly along vanes 40. At the same time, water particles will be centrifugally impelled from vanes 40 to surrounding fuel rods. Presuming vane layer V was below ferrule layer F, such impelling of water to and toward fuel rods R would cause water to contact directly the ferrules 14 and not the rods R. This does not appear to be as desirable as permitting impelled water to impact otherwise unobstructed fuel rods R--as where vane layer V overlies ferrule layer F. |
047598964 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings where similar features of the invention are designated by the same reference numerals among the various figures of the drawings. FIG. 1 illustrates a type of pressurized light water nuclear reactor 10 to which the present invention may be adapted. The invention, however, is not to be limited to such a reactor 10 which is being described primarily for purposes of description and explanation of the invention. A pressure vessel 11 houses a nuclear core 12 which is structurally supported therein by a set of components which are often referred to as the reactor internals (not completely shown). The nuclear core typically comprises a plurality of fuel assemblies 14, square in cross section, and stacked side by side in a parallel array. The nuclear core 12 has a resulting shape which approximates that of a right circular cylinder with the periphery being irregular or stepped when viewed in cross section due to the square configuration of the fuel assemblies 14. This may be partially seen in FIG. 2. The reactor internals include a core barrel 15 which separates the reactor coolant flow entering the pressure vessel 11 (through nozzle 16) from the reactor coolant exiting the pressure vessel 11 (through nozzle 17). In this manner, the reactor coolant flow may be directed down the outside of core barrel 15, turn 180.degree. and flow up through the nuclear core 12. The reactor internals also serve to make the transition from the irregular shape of the core periphery to the circular shape of the core barrel 15. Typically, vertical stainless steel plates 18 are positioned against the irregular core pheriphery. The vertical plates are supported by a plurality of horizontally positioned former plates 19 which are bolted to the vertical plates 18. The former plates 19 are in turn, bolted to the core barrel 15. The space between the horizontal former plates 19 is filled with water which flows in the same direction through the nuclear core 12. Since this flow is core bypass flow, it is desirable to maintain the flow at a minimum value yet sufficient to cool the former plates 19, vertical plates 18 and core barrel 15. Pressure vessel 20 is typically made from steel plates which are welded together in the axial and/or circumferential directions as represented by the axis A--A and/or B--B in FIG. 1 which respectively represent the centerlines of such welds. It is to be understood that the locations of such welds are not necessarily fixed relative to the nuclear core 12. However, once a reactor is fitted with a nuclear core, then the location of the pressure vessel welds are fixed relative to that core and any other core later loaded into that pressure vessel throughout the lifetime of that reactor. Viewed differently, for any given reactor, the orientation of the irregular core periphery is fixed relative to the welds (A--A or B--B) joining the plates making up the pressure vessel. In the example shown in the drawings, horizontal weld 21 is located approximately at core midplane and vertical weld 22 is located opposite the corner 23 of fuel assembly 14". As illustrated, welds 21 and 22 are thus exposed to the most severe fast flux condition. In actual practice this may not be the case; there may be only one weld or such welds may be exposed to the least severe fast flux condition. It is necessary that the location of the actual welds of a pressure vessel be determined relative to the core location and orientation and relative to the power and fast neutron flux distribution (horizontal and vertical) output by a particular core. Still referring to FIG. 2, irregular line C--C in combination with plates 18 circumscribe an arbitrary area of the core 25 which for purposes of providing an example for the description of the invention is to be deemed to materially contribute to the fast neutron flux to which weld 22 is exposed. As can be seen, area 25 encompasses parts of fuel assemblies 14', 14", 14'", and 14"". Appropriate nuclear calculations are required to be performed to determine the actual contribution to the fast neutron flux from each fuel rod in the peripheral core area and to determine the amount of displacer rods and/or nuclear poisoning needed to reduce the fast flux at the welds of the pressure vessel 11 to an acceptable level. For further description of the invention, it will be assumed that the calculations show that core peripheral area 25 described by line C--C needs to be provided with displacer rods and/or poisoned and/or provided with nuclear reflective material. The displacer rods which may comprise solid or sealed hollow tubes fit within openings within the fuel assemblies which contain a nuclear moderator (in the described reactor 10, the moderator comprises the light water reactor coolant.) By displacing the moderator within area 25, less moderating of the fast neutrons (produced by the fissioning of the nuclear fuel) occurs, which causes less fission to occur and, therefore, causes less fast neutrons to be produced. In this manner, weld 22 is exposed to less fast neutrons. If a nuclear poison rod is used, it will have the beneficial effect of the displacer rods and absorb some of the slow or moderated neutrons which are available for fissioning; and, thereby, additionally reduce the production of the fast neutrons which additionally reduces the number of fast neutrons which would be absorbed by weld 22. The nuclear poison would also absorb some of the fast neutrons to which the weld 22 would be otherwise exposed. If a reflector rod is used, it will provide the beneficial effect of the displacer rod and will reflect some neutrons back into the core and away from weld 22. Any of the techniques or a combination of such techniques may be employed with equal effectiveness consistent with and as constrained by the aforementioned nuclear calculations. FIG. 3 illustrates, in the lower portion thereof, a partial cross section of the core 12 including core area 25 taken along the grids 29 of fuel assemblies 14', 14", 14'" and 14"". Grids 29 typically are positioned at various locations along the length of fuel assembly 14 and serve to space and support a plurality of parallel arranged fuel rods 26 and control rod guide thimbles 27 at appropriate distances from each other so as to allow the reactor coolant to circulate in heat transfer relationship with fuel rods 26. Such grids 29 are well known in the art. As can be seen, guide thimbles 27 comprise hollow tubes which are attached to grid 29 and are spaced or distributed over the cross section thereof. Fuel assemblies 14 are thus comprised of fuel rods 26, guide thimbles 27 and grids 29. Guide thimbles 27 serve to guide the movement of control rods which fit within guide tubes 27. Control rods primarily serve to control the power output of the nuclear reactor 10, and are well known in the art. Typically, control rods comprise pellets of a nuclear absorbing material stacked end on end within hollow tubes and sealed at the ends. A plurality of such tubes are then attached to a central hub which is connected to a control rod drive mechanism. Since any fuel assembly 14 may be placed at any location within core 12, it is common practice to have each fuel assembly 14 equipped with the same number of guide tubes 27 and that they be positioned at the same location within the fuel assembly. In this manner, the position and operation of the control rod assemblies are not constrained by any fuel assembly 14; and, as explained, any fuel assembly 14 can be placed anywhere in the core 12. Typically, control rod assemblies are not located at the core pheriphery, but the fuel assemblies 14 at the core periphery are equipped with guide tubes 27. Hence, the guide tubes 27 in the fuel assemblies 14 at the core periphery are not used. The centermost opening 33 in fuel assembly 14 is typically provided for purposes of instrumentation and accordingly, is not available for one of the rods of the present invention. The dots 28 in FIG. 2 within core area 25 represent the location of unused guide tubes 27 in fuel assemblies 14. Referring again to FIG. 3, a displacer/absorber/reflector rod assembly 30 is shown therein. Displacer/absorber/reflector rod assembly 30 comprises a plurality of displacer/absorber/reflector rods 31 arranged parallel to each other and attached to hub 32. The arrangement of displacer/absorber/reflector rods 31 on assembly 30 coincides with the location of guide tubes 27 in core area 25. Thus, each of rods 31 fit within guide tubes 27 of core area 25. Rods 31 may comprise a displacer rod in the form of a hollow sealed tube made, for example, from zirconium alloy or stainless steel. Or, rods 31 may comprise a displacer/reflector rod made, for example, from a solid material such as stainless steel, or any other suitable reflector material, or may comprise a sealed hollow tube filled with a reflector material such as zirconia, or any other suitable reflector material. Or, rods 31 may comprise a displacer/absorber rod made as conventional control rod absorber rods are made and using the same materials: for example, boron carbide, cadmium-indium-silver, hafnium, etc. Or, rods 31 may comprise a combination of such displacer rods containing absorbing materials and reflecting materials appropriately positioned along the length of rod 31. Such absorbing and/or reflecting materials may extend the full length of rods 31. Or rods 31 may comprise a portion of reflector and/or absorber material appropriately located between particular core axial positions with the remainder of the rod 31 being substantially nonabsorbing and/or nonreflecting. Or, rods 31 may have any desired length. In essence, rod assembly 30 may be precisely tailored in its makeup as determined by the nuclear calculations previously mentioned. The various combinations are limitless. Also. any core area may be provided with one or more rod assemblies 30. The displacer/absorber/reflector rod assembly 30 may be positioned within its designed area 25 during core loadings or reloadings and simply left there during subsequent reactor operation. Rod assembly 30 may be conventionally sandwiched between the core upper and lower support plates (not shown) so as to retain the same in its assembled position during reactor operation. In carrying out the method of the invention, the following procedure may be used. The relationship of the core 12 relative to the horizontal B--B and/or vertical A--A welds on the pressure vessel 11 are documented. Calculations and/or measurements of the fast neutron flux (greater than one million electron volts or other agreed upon value) are ascertained at the location of the welds. Using whatever criteria is desired, by which the value of the neutron flux is to be reduced, calculations are made which determine the size and location of the core peripheral area which is to be provided with one or more rod assemblies 30 and to determine whether reflection and/or absorption is required in addition to the displacer rod effect and over what length and at what axial location. Based on such calculations, the precisely tailored rod assemblies are fabricated and loaded into position at the desired core location. The reactor is thereafter normally operated at rated power. Measurements may be made during reactor operation to verify the design and placement of the displacer/absorber/reflector rods and if any changes are deemed warranted, they may be carried out as per the above-described procedure. While the invention has been described, disclosed, illustrated and shown in certain terms or certain embodiments or modifications which it has assumed in practice, the scope of the invention is not intended to be nor should it be deemed to be limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended. |
summary | ||
claims | 1. A breathable material for protection against electromagnetic radiation, the breathable material consisting of a single layer, the single layer comprising:a) a base material comprising pores, wherein the pores are entirely filled with an inorganic filler and a breathability agent;b) said inorganic filler comprising at least one radiation shielding agent selected from the group consisting of bismuth, bismuth compound, and a combination thereof;c) said breathability agent comprising a hydrophilic polymer gel of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS),d) wherein the breathable material for protection against electromagnetic radiation comprises a water vapor transport rate ranging from about 100 g/m2/day to about 1871 g/m2/day, and wherein the breathable material for protection against electromagnetic radiation is effective against radiation ranging from x-rays to gamma rays. 2. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said base material comprises at least one member selected from the group consisting of track-etched polymeric membrane, microporous membrane, polymer sheet, porous polymer sheet, inorganic membrane, inorganic fabric, organic fabric, and a combination thereof. 3. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said base material comprises at least one member selected from the group consisting of polyester, nylon, aramid, cotton, and a combination thereof. 4. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said base material comprises a woven or non-woven material. 5. An article comprising the breathable material for protection against electromagnetic radiation of claim 1. 6. A suit, blanket, tent, glove, boot, mask, covering, an article or structure mimicking a naturally occurring article or structure, or an article of clothing comprising the breathable material for protection against electromagnetic radiation of claim 1. 7. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said inorganic filler further comprises at least one metal selected from the group consisting of lead, platinum, gold, copper, tin, antimony, silver, and a combination thereof. 8. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said inorganic filler further comprises at least one metal oxide selected from the group consisting of bismuth oxide, boron oxide, lead oxide, iron oxide, chrome oxide, titanium oxide, silicon oxide, aluminum oxide, and a combination thereof. 9. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said inorganic filler comprises nanoparticles, microparticles, nanowires, nanotubes, nanoscrolls, or nanoflakes, or a combination thereof. 10. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said inorganic filler comprises crystalline material, amorphous material, or a combination thereof. 11. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said inorganic filler comprises gel, particulate material, powder, liquid, or a combination thereof. 12. The breathable material for protection against electromagnetic radiation of claim 1, further comprising:a) a breathability enhancing agent comprising a hydrophilic inorganic material. 13. The breathable material for protection against electromagnetic radiation of claim 12, wherein:a) the hydrophilic inorganic compound comprises magnesium hydroxide. 14. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) the pores have an average diameter of about 10 nm to about 5 micron. 15. The breathable material for protection against electromagnetic radiation of claim 1, wherein:a) said inorganic filler further comprises at least one inorganic agent selected from the group consisting of lead oxide, iron oxide, chrome oxide, titania, alumina, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, silver, silver compound, calcium oxide, calcium hydroxide, aluminum oxide, tin, tin compound, antimony, antimony compound, tungsten, tungsten compound, boron, boron compound, silicon, silicon compound, lead, lead compound, platinum, platinum compound, gold, gold compound, copper, copper compound, uranium, uranium compound, and a combination thereof. |
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description | The embodiments of the present invention will now be explained with reference to the drawings. FIG. 1 shows one embodiment of the invention. In FIG. 1, the current pulse signals output from a neutron detector 1 are converted and amplified into voltage pulse signals at a pre-amplifier 2 before being input to a pulse count rate measurement unit 3. The current pulse signals output from the neutron detector 1 are negative. The voltage pulse signals (negative neutron signals) output from the pre-amplifier 2 is input to a negative pulse height discriminator 8 that constitutes the pulse count rate measurement unit 3. The negative pulse height discriminator 8 is provided with a negative discrimination level Ln for measuring the negative pulse count of the neutron signals. When the voltage pulse signal is smaller (greater in absolute value) than the negative discrimination level Ln, the negative pulse height discriminator 8 outputs a pulse signal to add to a negative pulse counter 9. In a positive pulse height discriminator 18, the positive discrimination level Lp is set by a positive discrimination level setting circuit 5 for measuring the positive pulses caused by excessive extrinsic electric noises. The discriminator 18 outputs a pulse signal when the noise pulse signal exceeds the positive discrimination level Lp to add to a positive pulse counter 19. The discrimination level setting circuits 4 and 5 for negative pulse count measurement and positive pulse count measurement each sets the negative or positive pulse height discrimination level Ln or Lp as shown in FIG. 3(b). The pulse count of the negative pulse counter 9 is provided to a display device 11, a trip circuit 12a, and a pulse count rate correction circuit 22. Further, the output of the pulse count rate correction circuit 22 is provided to the display device 11 and a trip circuit 12b. The pulse count of the positive pulse counter 19 is provided to the display device 11, the pulse count rate correction circuit 22 and a count rate anomaly detection circuit 24, and the output of the count rate anomaly detection circuit 24 is provided to the display device 11. The output of the trip circuits 12a and 12b are provided to the display device 11. Next, the operation mentioned above is explained with reference to the flowchart of FIG. 2. The current pulse signal shown in FIG. 3(a) output from the neutron detector 1 for detecting the neutron flux density is converted and amplified into a voltage pulse signal by the pre-amplifier 2 before being input to a negative pulse height discriminator 8 constituting the pulse count unit 3. The negative pulse height discriminator 8 outputs a pulse signal when the voltage pulse signal is smaller (greater in absolute value) than the negative discrimination level Ln to add to the negative pulse counter 9. On the other hand, the positive pulse height discriminator 18 provides a pulse signal to the positive pulse counter 19 that counts the pulses when the noise pulse signal exceeds the positive discrimination level Lp. In step S1 of the pulse count unit 3, the negative pulse counter 9 counts the number of negative pulses, and in step S2, the positive pulse counter 19 carries out the count-rate process of the positive pulses. In step S3, the count rate anomaly detection circuit 24 compares the counted value of the positive pulses counted by the positive pulse counter 19 with a preset value. If the counted value does not reach the preset value, the procedure advances to step 5, and if the counted value is equal to or greater than the preset value, the procedure advances to step 4. In step S4, the count rate anomaly detection circuit 24 displays the count rate anomaly on the display device. Normally, when no electric noise exists, there is no count rate anomaly displayed on the display device 11, but when electric noise pulses exceeding a certain level is mixed in, the count rate anomaly is displayed on the display device 11. In step S5, the pulse count rate correction circuit 22 inputs the negative pulse count rate of the negative pulse counter 9 and the positive pulse count rate of the positive pulse counter 19, and computes xe2x80x9cnegative pulse countxe2x80x94positive pulse countxe2x80x9d to correct the measured value, and thereafter in step S6, the corrected measured value (count rate) is displayed as the measured value on the display device 11. In step S7, the trip circuit 12 compares the corrected measured value with the trip preset value, and if the corrected measured value has not reached the trip preset value the procedure is terminated, and if the corrected measured value is equal to or greater than the trip preset value, the procedure advances to step 8. In step 8, the trip circuit 12 displays on the display device 11 that trip output exists. This is how the neutron measurement is performed, but normally, there exists no excessive extrinsic electric noise, so only the negative neutron pulses are counted by the negative pulse counter 9. If excessive extrinsic electric noise is generated and the negative pulse counter 9 counts the neutron pulses and the electric noise pulses, not only the negative pulse count rate but also the positive pulse count rate measured by the positive pulse counter 19 is displayed simultaneously on the display device 11. Further, the count rate anomaly detection circuit 25 compares the positive pulse count rate with the preset value, and when the positive pulse count rate exceeds the preset value, it displays a count rate anomaly detection result on the display device 11. By looking at the display device 11, the operator can determine easily that the increase in negative pulse count rate is caused by the electric noise. Thereafter, when the electric noise disappears and the decrease in negative pulse count rate is displayed on the display device 11, the decrease in the positive pulse count rate measured by the positive pulse counter 19 is simultaneously displayed on the screen. Further, since the positive pulse count rate becomes smaller than the preset value, the count rate anomaly detection circuit 24 clears the count rate anomaly detection result and outputs the result to the display device 11, so it is shown on the display that the state is normal. According to these operations, it could easily be judged that the decrease in the negative pulse count rate is caused by the disappearance of the electric noise. As explained above, even if excessive extrinsic electric noise with shorter intervals than the signal pulse width is mixed into the pulse signals continuously, the present invention detects and displays the occurrence of the electric noise by counting the positive pulses, and moreover, detects and displays the variation of the positive pulse count rate simultaneously when detecting and displaying the variation of the negative pulse count rate accompanying the occurrence and disappearance of the extrinsic electric noise. Accordingly, the present invention enables the operator to confirm the status of the system easily and to determine that the fluctuation of the counted value is caused by electric noises. Next, the function of correcting the pulse count rate according to the present invention is explained. The negative pulse height discrimination level Ln and the positive pulse height discrimination level Lp are set in advance as shown in FIG. 3(b) so that the negative pulse count and the positive pulse count of the extrinsic electric noises are equal when no neutron signal exists. The pulse count rate correction circuit 22 carries out an operation to subtract the positive pulse count from the negative pulse count. Thereby, even when electric noise is superposed continuously over the neutron pulse signals with smaller intervals than the signal pulse width as shown in FIG. 3(c), the pulse count rate correction circuit 22 is capable of computing the corrected count rate excluding the fluctuation of the pulse count rate caused by the influence of the electric noises. This corrected count rate is displayed on the display device 11. Moreover, a trip circuit 12a and a trip circuit 12b are provided to correspond to the count rate before the correction and the count rate after the correction, and the trip output status is displayed on the display device 11, thereby enabling the operator to understand the status related to the electric noise more accurately. As explained above, even if excessive extrinsic electric noise having a shorter interval than the signal pulse width is mixed into the pulses, the present invention enables to measure the pulse count rate stably without being influenced by the noise. Accordingly, the present invention improves the reliability of the neutron flux measurement. FIGS. 4(a) through (c) show examples of the screen displaying the negative pulse count rate together with the positive pulse count rate and the corrected pulse count rate according to the present invention. FIG. 4(a) is a display screen example of the display device 11 showing the case where no noise exists in the input signal and no trip output of the xe2x80x9chighxe2x80x9d count rate exists. FIG. 4(b) is a display screen example of the display device 11 showing the case where the negative pulse count rate is increased since noise signals are mixed into the input signal, but the function to correct the pulse count rate enables to compute the correct count rate, so no high count rate trip output exists. FIG. 4(c) shows the displayed screen example of the display device 11 showing the case where no noise signal exists in the input signal, but the actual count rate exceeds the trip value, so therefore a high count rate trip is output. The measurement is performed as mentioned, and the counting of positive noise pulse signals are performed simultaneously when counting the negative pulse signals output from the neutron detector, and the positive pulse count per unit time is subtracted from the negative pulse count per unit time so as to measure the neutrons. In other words, the negative pulse count rate computed by subtracting the positive pulse count rate (noise pulses) from a negative pulse count rate that is the sum of the noise pulses and the neutron flux detection pulses counted within a measurement cycle of a unit time is set as the neutron measurement value. According to the present invention, the noise pulses detected in both positive and negative polarities are cancelled so that the count of the negative pulse signals corresponding to the detection pulse signals of the neutron flux is obtained for neutron measurement. Therefore, the neutrons can be measured with high accuracy without being influenced by the number of noise pulses that are mixed in per unit time. |
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claims | 1. A fast spectrum molten salt reactor comprising:one or more heat exchangers;an unmoderated nuclear reactor core configured to contain a volume of molten fuel salt of sufficient size to establish criticality due to the production of fast neutrons within the volume;a primary coolant system configured to circulate a molten fuel salt-coolant mixture between the unmoderated nuclear reactor core and the one or more heat exchangers; anda molten fuel salt exchange system, the molten fuel salt exchange system being configured to reduce reactivity of the fast spectrum molten salt reactor by replacing a selected volume of the molten fuel salt-coolant mixture with a selected volume of feed material when a parameter indicative of reactivity of the molten salt reactor indicates that the reactivity has increased above an upper threshold defining a maximum reactivity,wherein the molten fuel salt exchange system is fluidically coupled to the nuclear reactor core and configured to exchange the selected volume of the molten fuel salt-coolant mixture with the selected volume of feed material containing a mixture of a selected fertile material and a carrier salt,wherein the feed material does not contain any fissile material,wherein the molten fuel salt exchange system is configured to control a composition of UCl3—UCl4—NaCl as a whole in a fast spectrum fission reaction by exchanging the feed material with the selected volume of the molten fuel salt-coolant mixture in the nuclear reactor core. 2. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a feed-fuel supply unit configured to transfer the feed material into the molten fuel salt-coolant mixture circulating through the nuclear reactor core. 3. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a feed-fuel supply unit configured to transfer the selected volume of the feed material into the molten fuel salt-coolant mixture circulating through the nuclear reactor core. 4. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a feed-fuel supply unit configured to transfer a selected composition of the feed material into the nuclear reactor core. 5. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a used-fuel transfer unit configured to transfer the selected volume of the molten fuel salt-coolant mixture as used-fuel from the nuclear reactor core. 6. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to transfer concurrently the selected volume of the molten fuel salt from the nuclear reactor core and the feed material into the nuclear reactor core. 7. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to control the reactivity of the fast spectrum molten salt reactor by exchanging the feed material with the selected volume of the molten fuel salt-coolant mixture in the nuclear reactor core. 8. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to control the composition of the molten fuel salt-coolant mixture in the nuclear fission reaction by exchanging the feed material with the selected volume of the molten fuel salt-coolant mixture in the nuclear reactor core. 9. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system is configured to exchange repeatedly the selected volume of the molten fuel salt-coolant mixture with the selected volume of the feed material to maintain the parameter indicative of reactivity of the molten salt reactor within a selected range of nominal reactivity over time. 10. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system further includes a volumetric displacement control system having one or more volumetric displacement assemblies insertable into the nuclear reactor core, each volumetric displacement assembly being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core. 11. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system includes a volumetric displacement control system having one or more volumetric displacement bodies insertable into the nuclear reactor core, each volumetric displacement body being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core. 12. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system further includes a volumetric displacement control system having one or more volumetric displacement bodies insertable into the nuclear reactor core, each volumetric displacement body being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core, the volumetric displacement control system further having a molten fuel salt spill-over system configured to transport the molten fuel salt-coolant mixture that is displaced by the volumetric displacement body above a tolerated fill level of the nuclear reactor core. 13. The fast spectrum molten salt reactor of claim 1 wherein the molten fuel salt exchange system further includes a volumetric displacement control system having one or more volumetric displacement bodies insertable into the nuclear reactor core, each volumetric displacement body being configured to volumetrically displace at least some of the molten fuel salt-coolant mixture from the nuclear reactor core when inserted into the nuclear reactor core, one or more volumetric displacement bodies being insertable at multiple insertion depths into the nuclear reactor core to maintain the parameter indicative of reactivity of the molten salt reactor within a selected range of nominal reactivity over time. 14. The fast spectrum molten salt reactor of claim 12, wherein the spill-over system includes a reservoir configured to receive the molten fuel salt-coolant mixture that is displaced by the volumetric displacement body above a tolerated fill level of the nuclear reactor core. 15. The fast spectrum molten salt reactor of claim 1, wherein the molten fuel salt exchange system removes molten fuel salt directly from the nuclear reactor core. 16. The fast spectrum molten salt reactor of claim 1, wherein the molten fuel salt exchange system delivers feed material directly into the nuclear reactor core. 17. The fast spectrum molten salt reactor of claim 1, further comprising:one or more reactivity parameter sensors configured to monitor the reactivity of the fast spectrum molten salt reactor. 18. The fast spectrum molten salt nuclear reactor of claim 17, wherein the one or more reactivity parameter sensors are selected from a fission detector, a neutron flux monitor, a neutron fluence sensor, a fission product sensor, a temperature sensor, a pressure sensor or a power sensor. 19. The fast spectrum molten salt reactor of claim 1, further comprising:a reactor containment vessel that encloses the one or more heat exchangers and the unmoderated nuclear reactor core. 20. The fast spectrum molten salt reactor of claim 1, further comprising:a feed material source containing feed material. |
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abstract | A treatment of a heater tube intended to be used in a pressurizer of the primary cooling system of a nuclear reactor. In particular, the heater tube comprises a heater housed in a substantially cylindrical sheath. The material of which this sheath is made is a work-hardened austenitic stainless steel. In particular, the external surface of the sheath is liable to undergo a stress corrosion during use of the heatertube. The method includes a heat treatment step, preferably using induction heating, in which the external surface of the sheath is heat-treated so as to recrystallize the material of the sheath at least on the surface thereof. |
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description | 1. Field The embodiments described herein relate generally to linear accelerators. More particularly, the described embodiments relate to linear accelerators providing multiple operating modes. 2. Description A linear accelerator produces electrons or photons having particular energies. In one common application, a linear accelerator produces a radiation beam used for medical radiation treatment. The beam may be directed toward a target area of a patient in order to destroy cells within the target area by causing ionizations within the cells or other radiation-induced cell damage. Radiation treatment plans are designed to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. However, designers of a treatment plan assume that relevant portions of a patient will be in a particular position relative to a linear accelerator during delivery of the treatment radiation. If the relevant portions are not positioned exactly as required by the treatment plan, the goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved. More specifically, errors in positioning the patient can cause the delivery of low radiation doses to tumors and high radiation doses to sensitive healthy tissue. The potential for misdelivery increases with increased positioning errors. Conventional imaging systems may be used to determine a patient position prior to treatment according to a particular radiation treatment plan. For example, a radiation beam is emitted by a linear accelerator, passes through a volume of the patient and is received by an imaging system. The imaging system generates a two-dimensional portal image of the patient volume, which can be used to determine whether the patient is in a position dictated by the particular treatment plan. The foregoing imaging systems may be both ineffective and inefficient. For example, the radiation beam generated by a linear accelerator for imaging may deliver a dose rate that is significantly less than a dose rate used for radiation treatment, but other characteristics of the beam may be unsuitable for imaging. Moreover, no efficient systems exist for changing these characteristics such that the resulting beam is suitable for imaging. In order to address the foregoing, some embodiments provide a system, method, apparatus, and means to receive a first instruction to enter an imaging mode, and, in response to the first instruction, automatically perform at least one of: reducing a focal spot size of a radiation beam, moving a flattening filter out of a path of the radiation beam, replacing a first target for photon emission with a second target for photon emission, or moving a scatter-reducing filter into the path of the radiation beam. Embodiments may further include reception of a second instruction to enter a first radiation treatment mode, and, in response to the second instruction, automatic performance at least one of: increase of a focal spot size of the radiation beam, movement of the flattening filter into the path of the radiation beam, replacement of the second target with the first target, or movement of the scatter-reducing filter out of the path of the radiation beam. According to some aspects, the second instruction comprises an instruction to enter a photon radiation treatment mode, a third instruction is received to enter an electron radiation treatment mode, and, in response to the third instruction, the first target or the second target is automatically moved out of the path of the radiation beam so that neither the first target or the second target is in the path of the radiation beam. Some embodiments include an input device to receive a first instruction to enter an imaging mode, and a second instruction to enter a first radiation treatment mode, and an accelerator waveguide to emit a radiation beam. Also included in these embodiments is at least one of a first device to reduce a focal spot size of a radiation beam in response to the first instruction, and to increase a focal spot size of the radiation beam in response to the second instruction, a second device to move a flattening filter out of a path of the radiation beam in response to the first instruction, and to move the flattening filter into the path of the radiation beam in response to the second instruction, a third device to replace a first target for photon emission with a second target for photon emission in response to the first instruction, and to replace the second target with the first target in response to the second instruction, or a fourth device to move a scatter-reducing filter into the path of the radiation beam in response to the first instruction, and to move the scatter-reducing filter out of the path of the radiation beam in response to the second instruction. The appended claims are not limited to the disclosed embodiments, however, as those in the art can readily adapt the descriptions herein to create other embodiments and applications. The following description is provided to enable a person in the art to make and use some embodiments and sets forth the best mode contemplated by the inventors for carrying out some embodiments. Various modifications, however, will remain readily apparent to those in the art. FIG. 1 is a perspective view of system 1 according to some embodiments. Shown are linear accelerator 10, operator console 20, beam object 30, imaging device 40 and table 50. System 1 may be used to generate radiation for imaging and/or for medical radiation treatment. In this regard, beam object 30 comprises a patient positioned to receive treatment radiation according to a radiation treatment plan. System 1 may be employed in other applications according to some embodiments. In one example according to some embodiments, a first instruction to enter an imaging mode is received, and, in response to the first instruction, at least one of the following is automatically performed: reducing a focal spot size of a radiation beam, moving a flattening filter out of a path of the radiation beam, replacing a first target for photon emission with a second target for photon emission, or moving a scatter-reducing filter into the path of the radiation beam. Embodiments may further include reception of a second instruction to enter a first radiation treatment mode, and, in response to the second instruction, automatic performance at least one of: increase of a focal spot size of the radiation beam, movement of the flattening filter into the path of the radiation beam, replacement of the second target with the first target, or movement of the scatter-reducing filter out of the path of the radiation beam. Linear accelerator 10 may deliver a radiation beam from treatment head 101 toward a volume of object 30 that is located at an isocenter of accelerator 10. According to some embodiments, the radiation beam may comprise photon or electron radiation having various energies. Various implementations of treatment head 101 according to some embodiments are described below. Imaging device 40 may comprise any system to acquire an image based on received photon radiation (i.e., X-rays) and/or electron radiation. Imaging device 40 acquires images that are used before, during and after radiation treatment. For example, imaging device 40 may be used to acquire images for diagnosis, verification and recordation of a patient position, and verification and recordation of an internal patient portal to which treatment radiation is delivered. As described above, the effectiveness of radiation treatment often depends on the quality of the acquired images. In some embodiments, imaging device 40 is a flat-panel imaging device using a scintillator layer and solid-state amorphous silicon photodiodes deployed in a two-dimensional array. The RID1640, offered by Perkin-Elmer®, Inc. of Fremont, Calif., is one suitable device. In other embodiments, imaging device 40 converts X-rays to electrical charge without requiring a scintillator layer. In such imaging devices, X-rays are absorbed directly by an array of amorphous selenium photoconductors. The photoconductors convert the X-rays directly to stored electrical charge that comprises an acquired image of a radiation field. Imaging device 40 may also comprise a CCD or tube-based camera. Such an imaging device may include a light-proof housing within which are disposed a scintillator, a mirror, and a camera. Imaging device 40 may be attached to gantry 102 in any manner, including via extendible and retractable housing 401. Gantry 102 is rotatable around an axis before, during and after emission of the radiation beam. Rotation of gantry 102 may cause treatment head 101 and imaging device 40 to rotate around the isocenter such that the isocenter remains located between treatment head 101 and imaging device 40 during the rotation. Table 50 supports object 30 during radiation therapy. Table 50 is adjustable to ensure, along with rotation of gantry 102, that a volume of interest is positioned between treatment head 101 and imaging device 40. Table 50 may also be used to support devices used for acquisition of correction images, other calibration tasks and/or beam verification. Operator console 20 includes input device 201 for receiving instructions from an operator and output device 202, which may be a monitor for presenting operational parameters of linear accelerator 10 and/or interfaces for receiving instructions. Such instructions may include an instruction to enter an imaging mode and an instruction to enter a treatment mode. Output device 202 may also present images acquired by imaging device 40 to verify patient positioning prior to radiation treatment. Input device 201 and output device 204 are coupled to processor 203 and storage 204. Processor 203 executes program code according to some embodiments. The program code may be executable to control system 1 to operate as described herein. The program code may be stored in storage 204, which may comprise one or more storage media of identical or different types, including but not limited to a fixed disk, a floppy disk, a CD-ROM, a DVD-ROM, a Zip™ disk, a magnetic tape, and a signal. Storage 204 may, for example, store a software application to provide radiation treatment, radiation treatment plans, portal images, and other data used to perform radiation treatment. The other data may include sets of hard-coded parameters for various elements of system 1, or “soft pots”, that are associated with various functions of system 1. For example, one set of soft pots may be associated with an imaging mode, another set of soft pots may be associated with an X-ray treatment mode, and while another set of soft pots may be associated with an electron treatment mode. Operator console 20 may be located apart from linear accelerator 10, such as in a different room, in order to protect its operator from radiation. For example, accelerator 10 may be located in a heavily shielded room, such as a concrete vault, which shields the operator from radiation generated by accelerator 10. Each of the devices shown in FIG. 1 may include less or more elements than those shown. In addition, embodiments are not limited to the devices shown in FIG. 1. FIG. 2 is a block diagram of system 1 showing internal elements of linear accelerator 10, operator console 20, and imaging device 40 according to some embodiments. Embodiments may differ from that shown in FIG. 2 and/or from that shown in FIG. 1. Linear accelerator 10 of FIG. 2 includes electron source 103 for injecting electrons into accelerator waveguide 104. Source 103 may comprise an electron gun including a heater, a cathode (thermionic or other type), a control grid (or diode gun), a focus electrode, an anode, and other elements. An injector current sourced by particle source 103 may be controlled by injector pulses received from injector 105. Injector 105 may, in turn, receive trigger signals from trigger control 106 and control the amplitude of the injector pulses by a control grid bias voltage applied to source 103. Accelerator waveguide 104 includes cavities that are designed and fabricated so that electric currents flowing on their surfaces generate electric fields that are suitable to accelerate the electrons. The oscillation of these electric fields within each cavity is delayed with respect to an upstream cavity so that an electron is further accelerated as it arrives at each cavity. The oscillating electric fields within the cavities of accelerator waveguide 104 are produced in part by an oscillating electromagnetic wave received by accelerator waveguide 104 from RF power source 107. Trigger control 106 may control RF power source 107 to generate an electromagnetic wave having a selected power and/or pulse rate. RF power source 107 may comprise any suitable currently- or hereafter-known pulsed power source. In some embodiments, RF power source 107 comprises a magnetron. RF power source 107 comprises a klystron and an RF driver in some embodiments. Accelerator waveguide 104 may output beam 108 to bending envelope 109. Beam 108 includes a stream of electron bunches having various energies and bending envelope 109 may comprise an evacuated magnet to bend beam 108 approximately two hundred seventy degrees. Bending envelope 109 may also focus beam 108 and select one or more energies for output. Bending envelope 109 may select an energy by establishing a magnetic field that will allow only electrons of a selected energy (or of a range of energies surrounding the selected energy) to turn two hundred seventy degrees and exit through window 110. Other bending angles and/or systems to select energies may be used. Window 110 may comprise two metal foils with water flowing therebetween for cooling. Beam 108 enters treatment head 101 after passing through window 110. Treatment head 101 may comprise any number and arrangement of elements according to some embodiments. Treatment head 101 of FIG. 2 includes control unit 111 which may receive control signals from operator console 20. Control unit 111 is coupled to beam focuser 112, target housing 113 including hi-Z target 114 and low-Z target 115, flattening filter 116, and other elements 117. The depiction of treatment head 101 in FIG. 2 is not intended to indicate relative sizes or spatial relationships of the elements located therein, although some embodiments may be thus reflected. The couplings between control unit 111 and each of elements 112 through 117 may comprise mechanical and/or electrical couplings. One or more elements may reside between control unit 111 and an element to which it is shown coupled in FIG. 2. In some embodiments, control unit 111 comprises one or more separate elements, each of which is coupled to one or more of elements 112 through 117. One or more of elements 112 through 117 may be controlled directly by operator console 20 and/or by another device according to some embodiments. The elements of treatment head 101 may be configured based on an operating mode of system 1. For example, the elements may be configured in a first arrangement if an instruction is received to enter a treatment mode, and the elements may be configured in a second arrangement if an instruction is received to enter an imaging mode. FIG. 2 illustrates an arrangement used in a treatment mode according to some embodiments. Beam focuser 112 may comprise any suitable system to receive beam 108 and to change a focal spot size thereof. The focal spot size may refer to the profile of the beam at a location where photon emission occurs within one of targets 113 and 114. Generally, a smaller focal spot may be suitable for imaging while a larger focal spot may be suitable for delivering treatment. In some embodiments, beam focuser 112 comprises deflector plates disposed adjacent to a path of beam 108. Control unit 111 may energize the deflector plates during emission of beam 108 in order to create a desired focal spot size. Beam focuser 112 may be used to increase the focal spot size for treatment in a case that the focal spot size would be unsuitably small in the absence of beam focuser 112. Alternatively, beam focuser 112 may be used to reduce the focal spot size for imaging in a case that the focal spot size would be unsuitably large in the absence of beam focuser 112. Treatment head 111 may include mechanical elements to move beam focuser 112 out of the path of beam 108 if a selected operating mode does not require beam focusing. Target housing 113 includes hi-Z (i.e., high atomic weight) target 114, which may comprise Gold, Tungsten, or another suitable material. Upon receiving electron beam 108, such a target may generate photons having an energy spectrum suitable for radiation treatment. Low-Z (i.e., low atomic weight) target 115 may comprise Carbon, Aluminum, or another suitable material. Such a target may generate photons having an energy spectrum suitable for imaging in response to receipt of electron beam 108. The terms hi-Z and low-Z as used herein are not intended to indicate particular atomic weights, but only a relationship of the atomic weight of target 114 to the atomic weight of target 115. Target housing 113 may comprise any suitable system to selectively place target 114 or target 115 in the path of beam 108. Such placement may be controlled by control unit 111. Target 114 is shown placed in the path because system 1 is in an X-ray treatment mode according to some embodiments. Flattening filter 116 may comprise any one or more elements to improve a profile of beam 108 for treatment. In this regard, an intensity of X-ray beam 108 at beam object 30 may be highest at the center of the radiation field and may significantly decrease toward the edges of the field. Flattening filter 116 may therefore be used to provide a more even intensity distribution. Control unit 111 may be coupled to flattening filter 116 so as to selectively place flattening filter in the path of beam 108 for a treatment mode. Flattening filter 116 may, however, increase an amount of radiation scattering, and therefore may not be suitable for an imaging mode of operation. Control unit 111 may therefore also be coupled to flattening filter 116 so as to selectively move flattening filter 116 out of the path of beam 108 for an imaging mode. Other elements 117 may include shield blocks, dosimetry chambers, collimator plates, accessory trays and any other treatment, imaging, calibration, and verification devices as are known in the art. One or more of other elements 117 may be electrically and/or mechanically coupled to control unit 111, operator console 20, and/or to one or more other devices. For example, dosimetry chambers of other elements 117 may transmit dosimetric information directly to operator console 20. In another example, collimator plates of elements 117 may be driven to desired positions by a motor that is controlled by operator console 20. Operator console 20 of FIG. 2 may control an injector current produced by particle source 103, and/or an amount of power generated by RF power source 107. Such control may include control of trigger control 106 to control injector 105 or RF power source 107, respectively. Operator console 20 may also control imaging device 40 to acquire an image, and may control one or more elements of treatment head 101 via control unit 111. Examples of the latter control according to some embodiments are provided below. FIG. 3 is a flow diagram of process steps 60 according to some embodiments. Process steps 60 may be executed by one or more elements of linear accelerator 10, operator console 20, treatment head 101, control unit 111, and other devices. Accordingly, process steps 60 may be embodied in hardware and/or software. Process steps 60 will be described below with respect to the above-described elements, however it will be understood that process steps 60 may be implemented and executed differently than as described below. Prior to step 61, an operator may use input device 201 of operator console 20 to initiate operation of system 1. In response, processor 203 may execute program code of a system control application stored in storage 204. FIG. 4 is an outward view of a user interface that is presented by output device 202 in some embodiments due to execution of the program code. Interface 80 may be used by an operator to input instructions to system 1. Conversely, system 1 may receive the instructions via interface 80. Embodiments may utilize one or more interfaces that share zero or more features with interface 80. In the illustrated embodiment, field 81 indicates a status of system 1. As shown, the status indicates that system 1 is being programmed. Fields 82 through 86 indicate keys of input device 201 that may be used to instruct system 1 to enter a selected operational mode. For example, function keys F1, F2, F3 and F4 (not shown) may be used to issue instructions to enter a low-energy photon radiation treatment mode, a high-energy photon radiation treatment mode, an electron radiation treatment mode, and an imaging mode, respectively. The selected mode is displayed in field 87, with other details of the mode shown in fields 88 and 89. Fields 90 indicate a position of gantry 102 and a configuration of collimator plates of elements 117, while fields 91 through 93 identify accessories mounted in each of three accessory trays of elements 117. Fields 95 are reserved for presenting preset and actual values of dose (MON1 and MON2), beam on time (Time) and dose rate (MU/Min). At step 61, the operator selects one of function keys F1 through F4 of input device 201. It will initially be assumed that function key F4 is selected. FIG. 5 shows interface 80 after selection of function key F4 according to some embodiments. Fields 87 and 89 are automatically filled, while the operator may complete field 88 and the top row of fields 95 directly or using sub-interfaces of interface 80. Selection of function key F4 causes the labels of fields 82 through 86 to change. According to the new labels, function keys F2, F3 and F4 may be used to control collimator plates of elements 117, and function key F1 may be used to access a sub-interface for specifying a desired dose. After completing all required fields of interface 80 and of any sub-interfaces, an operator places system 1 into a Ready mode by pressing an Accept key of input device 201. According to the present example, detection of the pressing of the Accept key comprises receiving an instruction to enter a mode. Flow therefore proceeds to step 62 after the Accept key is pressed. System 1 determines whether an imaging mode or a treatment mode has been selected at step 62. Continuing with the present example, a focal spot size of a radiation beam is reduced at 63 because an imaging mode has been selected. As described above, the focal spot size may be reduced by any suitable system to receive beam 108 and to change a focal spot size thereof. In some embodiments of step 63, control unit 111 energizes deflector plates of beam focuser 112 such that beam 108 will create a desired focal spot size on a target when beam 108 is generated. In this regard, step 63 may be performed prior to generation of beam 108. A flattening filter is then moved out of a path of the radiation beam at step 64. FIG. 6 is a block diagram of system according to some embodiments. As shown, flattening filter 116 has been moved from the position shown in FIG. 2 to a position out of the path of beam 108. Any suitable mechanism may be employed to move flattening filter 116 at step 64. Next, at step 65, a first target is replaced with a second target. FIG. 6 also shows target 115 occupying the position in the path of beam 108 that was occupied by target 114 in FIG. 2. In the illustrated embodiment, target 114 may be replaced by target 115 by moving housing 113 as shown. Any suitable systems for switching targets 114 and 115 may be employed. A scatter-reducing filter is moved into the path of the radiation beam at 66. FIG. 6 shows scatter-reducing filter 118 in the path of radiation beam 108. Scatter radiation is believed to decrease image quality; therefore introduction of a scatter-reducing filter may increase image quality. The embodiment of FIG. 2 does not include a scatter-reducing filter. An image is then acquired by imaging device 40 at step 67. According to some embodiments of step 67, linear accelerator 10 is controlled to emit beam 108 toward treatment head 101 at a specified energy and dose rate. Beam 108 is focused by beam focuser 112 to reduce a focal spot size thereof, and impacts target 115 to generate a divergent photon beam having an energy spectrum suitable for imaging. The photon beam passes through scatter-reducing filter 118, other elements 117, and beam object 30 before impacting imaging device 40. Imaging device 40 therefore acquires the image based on the photon beam as attenuated by beam object 30. In some embodiments, operator console 20 updates the lower row of fields 95 of interface 80 in real time during acquisition of the image. Steps 63 through 66 may be performed under the control of control unit 111 in response to signals received from operator console 20. For example, operator console 20 may transmit a set of instructions and/or parameters associated with an imaging mode to control unit 111 after step 62. The set may be stored among one or more soft pots of storage 204. In this regard, step 61 may comprise reception of the set of instructions and/or parameters by control unit 111 (or by another one or more elements for controlling elements of treatment head 101). More generally, steps 61 and 62 may be performed by any element of system 1, may be performed at several times by different elements of system 1, and may be performed at any time prior to step 67. Step 63 through 66 can also occur at any time before step 67. Some embodiments include performance of only one, two, or three of steps 63 through 66. The steps of 63 through 66 that are performed may occur in any order relative to one another. Two or more of steps 63 through 66 may be performed simultaneously. FIG. 7 is a block diagram of system 1 prior to step 67 according to some embodiments of process steps 60. FIG. 7 is intended to illustrate some of the above-mentioned possible variations of process steps 60. As shown, beam focuser 112 is positioned outside of the path of radiation beam 108. Beam focuser 112 according to the illustrated embodiment comprises a device that increases a focal spot size of beam 108, therefore beam focuser 112 is moved out of the path in order to reduce the focal spot size at step 63. The FIG. 7 embodiment reflects the completion of steps 64 and 65 as described below. However, step 66 is not performed with respect to the FIG. 7 embodiment because system 1 of FIG. 7 does not include a scatter-reducing filter. FIG. 8 is a block diagram of system 1 prior to step 67 according to still other embodiments of process steps 60. As shown, beam focuser 112 is positioned in and flattening filter 116 is moved out of the path of radiation beam 108 to operate as described with respect to step 63, step 64, and FIG. 6. The FIG. 8 embodiment includes only a single hi-Z target 114 and therefore does not perform step 65 of process steps 60. Moreover, system 1 of FIG. 8 does not include a scatter-reducing filter, and therefore step 66 is not performed with respect to the FIG. 8 embodiment. Flow returns to step 61 after step 67. It will now be assumed that an instruction to enter a treatment mode is received at step 61. The instruction may be received in response to operator selection of function keys F1 through F3 during presentation of interface 80 of FIG. 4. FIG. 9 illustrates interface 80 after selection of function key F2 (X-FIX-L) according to some embodiments. Function key F2 is associated with low-energy X-ray treatment, therefore fields 87 and 89 are automatically filled to indicate such treatment. The operator may complete field 88 and the top row of fields 95 using sub-interfaces associated with the new labels of fields 82 through 86. As described above, an operator may place system 1 into a Ready mode by pressing an Accept key of input device 201 after completing all required fields of interface 80 and of any sub-interfaces. Detection of the depressed Accept key may also comprise receiving an instruction to enter a mode at step 61. Next, at step 62, it is determined that system 1 has been instructed to enter a treatment mode. Accordingly, flow continues to step 68 to increase a focal spot size of a radiation beam. The focal spot size may be increased by deactivating or removing a beam focuser otherwise operable to reduce the focal spot size, or by placing a beam focuser for increasing the focal spot size in the path of the beam. FIG. 2 illustrates the former scenario, with beam focuser 112 being deactivated at step 68. FIG. 2 also illustrates flattening filter 116 having been moved into the path of beam 108 at step 69, and replacement of target 115 with target 114 at step 70. Some embodiments of process steps 60 further include movement of a scatter-reducing filter out of the path of the radiation beam at step 71. The embodiment of FIG. 2 does not include a scatter-reducing filter. System 1 executes radiation treatment at step 72. According to some embodiments of step 72, linear accelerator 10 is controlled to emit beam 108 toward treatment head 101 at a specified energy and dose rate suitable for radiation treatment. The specified energy may be substantially identical to the energy used to acquire the image at step 67, and the dose rate may be significantly larger. Beam 108 then impacts target 114 to generate a divergent photon beam having an energy spectrum suitable for treatment. The photon beam passes other elements 117 and beam object 30 to deliver a radiation dose to a target volume of beam object 30. In some embodiments, operator console 20 updates the lower row of fields 95 of interface 80 as shown in FIG. 9 during treatment. As described with respect to steps 63 through 66, steps 68 through 71 may be performed under the control of control unit 111 in response to signals received from operator console 20. Such control may include transmission of a set of instructions and/or parameters associated with radiation treatment to control unit 111 after step 62. The set may be stored among one or more soft pots of storage 204. Some embodiments such as that shown in FIG. 2 include performance of only one, two, or three of steps 68 through 71. The steps of 68 through 71 that are performed may occur in any order relative to one another. Two or more of steps 68 through 71 may be performed simultaneously. According to some embodiments, dosimetric characteristics of beam 108 may be changed in response to an instruction to enter an imaging mode and/or in response to an instruction to enter a treatment mode. For example, in response to an instruction to enter an imaging mode, RF power source 107 and/or bending envelope 109 may be controlled as described in commonly-assigned, co-pending Application Ser. No. (Attorney Docket No. 2005P00148US), entitled Megavoltage Imaging System, such that beam 108 possesses characteristics suitable for imaging. The several embodiments described herein are solely for the purpose of illustration. Therefore, persons in the art will recognize from this description that other embodiments may be practiced with various modifications and alterations. |
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abstract | The invention concerns a method for irradiating a target with a beam approaching target points, involving the following steps: Measuring at least one of the parameters relating to the position of the beam and the intensity of the beam, changing the beam as a function of the at least one measured parameter, particularly as a function of a variance relating to the at least one measured parameter. The method is characterized in that the at least one measured parameter is measured at the most once per target point. Furthermore, the invention concerns a device for irradiating a target in accordance with the invention-based method and a control system for controlling such a device. |
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description | The present invention relates to a charging device of aerosol particles using an X-ray source for generating a soft X-ray. Recent nanotechnology is given attention regarding nanophase material since the nanophase material has a property better than a conventional material. In the nanotechnology, manufacturing, generation, transportation, deposition, and measurement of nanoparticles are essential. Charging particles or obtaining an equilibrium charged state is an effective method for controlling the nanoparticles in transportation or deposition processes. For example, the nanotechnology is used in crystal film formation by electrostatic deposition of charged colloid nanoparticles, and synthesis of two component system nanoparticles by attachment of nanosize aerosols each charged to opposite polarities. Charging of nanoparticles is indispensable in measurement of nanoparticles using static electricity such as, nanocluster DMA and particle beam mass analyzer. Particles are normally charged as a result of impact between the gas ion and the particles. The charging state of the particles can be divided into unipolar charge and bipolar charge in accordance with the charged state. A bipolar charging device using radiation is usually used. A radiation source includes radioactive substances such as americium (241Am), krypton (85Kr), polonium (210Po) and the like. FIG. 1 is a cross sectional view showing one example of a conventional bipolar charging device using radiation. In FIG. 1, an inlet duct 2 for introducing aerosols, and a outlet duct 3 for exhausting the aerosols are provided on both ends of a cylindrical chamber 1. A radiation source 4 such as americium (241Am) is arranged at an intermediate part of the chamber 1. Rectifying plates 5, 6 for rectifying the aerosols passing through the chamber are arranged on the left and the right. The rectifying plates 5, 6 include a plurality of fine openings, are used for rectifying the aerosols, and are arranged in the vicinity of the inlet duct 2 and the outlet duct 3, as shown in the figure. By arranging the radiation source 4 within the chamber 1 and introducing the aerosols into the chamber 1, the fine particles of the aerosols are charged by a large amount of positive and negative ions, and the equilibrium charging state can be obtained when the average charged amount is substantially zero. Further, a charging device for generating unipolar charged ions is recently given attention for its wide range of applications. The conventional unipolar charging device, as shown in FIG. 2, includes a chamber 11 configured with a cylindrical part 12 made of resin for side surfaces, and with electrodes 13, 14 for upper and lower surfaces thereof. Voltage is applied between the upper and lower electrodes 13, 14 from a high voltage power source 15, and an ammeter 16 for measuring minute current is connected therebetween. A radiation source 17 of americium (241Am) is arranged on the electrode 14 at the lower surface of the chamber 11. If the height of the chamber is for example, 90 mm, α ray only reaches to about 40 mm due to its range; thus, bipolar ions are generated at the lower part of the chamber. As an electric field is generated, ions of desired polarity move towards the upper part of the chamber 1. Therefore, when aerosols are flowed through the inlet duct 18, the unipolar particles are discharged from the outlet duct 19, thereby achieving unipolar charging. The charging device using corona discharge is capable of generating unipolar or bipolar high concentration ions, and is thus widely used. According to this method, when direct current or alternating current voltage of high voltage is applied to the electrode, unipolar or bipolar ions can be generated in the vicinity of the electrode. However, in the conventional device for charging the aerosol particles using radiation, the half-life of the radioactive substance is long and thus has a problem in terms of safety. For example, americium requires 432.2 years, and krypton (85Kr) requires 10.72 years. Thus, management over a long period time is difficult. Further, polonium (210Po) has a short half-life of 138 days, and thus has a problem in that the line source must be changed every few months. Further, the conventional unipolar charging device using radiation has small generation number of ions, and has losses inside the charging device or inside a piping, and thus has a disadvantage of being difficult to use unipolar charged nanoparticles for various applications. It also has a disadvantage in that a charging operation can not be stopped when necessary. Additionally, the charging device using corona discharge generates ozone, causes corrosion of electrodes during discharge, and generates particulate substances by the gas phase reaction at a strong electrical magnetic field, and thus has a disadvantage of polluting air. The corona discharge also has a disadvantage of generating current noise. The present invention aims to provide a charging device of aerosol particles that is safe and easy to handle in place of the conventional charging device using radiation source or corona discharge. According to a first aspect of the present invention, a aerosol particle charging device comprises a chamber, an inlet duct which flows gas including aerosol particles to be processed into the chamber, a outlet duct which exhausts the processed aerosols from the chamber, and an X-ray emitting section which is arranged facing the chamber and emits an X-ray having a main wavelength within a range of 0.13 nm to 2 nm. In this aerosol particle charging device, the X-ray emitting section may include a power switch for controlling emission and stop of the X-ray. According to a second aspect of the present invention, a aerosol particle charging device comprises a chamber, an X-ray emitting section which is arranged facing one region of the chamber and emits an X-ray having a main wavelength within a range of 0.13 nm to 2 nm, an electric field generation section which includes electrode plates arranged on both surfaces facing each other of the chamber and generates an electric field from an irradiating section to a non-irradiating section of the X-ray within the chamber, an inlet duct which is arranged in the X-ray non-irradiating section of the chamber and flows gas including aerosol particles to be processed into the chamber, and a outlet duct which is arranged at a position facing the inlet duct of the X-ray non-irradiating section of the chamber and exhausts the processed aerosols from the chamber. In this aerosol particle charging device, the X-ray emitting section may include a power switch for controlling emission and stop of the X-ray. FIG. 3 is a cross sectional view showing a configuration of a charging device of aerosol particles according to a first embodiment of the present invention. In the figure, a chamber 21 is a brass cylindrical container having an inner diameter d1 of 40 mm. An X-ray emitting section 22 is arranged at an opening at a side of the chamber 21. The X-ray emitting section 22 emits X-rays from the middle of a left end of the cylindrical chamber. An inlet duct 23 for introducing the aerosols is arranged at an upper part of the chamber 21. A outlet duct 24 for exhausting the bipolar charged aerosols is arranged at the middle of the other end of the chamber. A rectifying plate 25 having a plurality of openings for rectification is arranged in the vicinity of the outlet duct 24. Here, a distance from the X-ray emitting section 22 to the rectifying plate 25 is 90 mm. The X-ray emitting section 22 is an X-ray source for generating a soft X-ray of 0.13 to 2 nm, and emits the X-ray at a solid angle of 120° from a window made of beryllium. Such X-ray emitting section is disclosed in, for example, Japanese Patent No. 2951477. The ions are generated across the entire emission range on a steady basis by the emission of the X-ray. If the numbers of positive and negative ions generated at the same time are unbalanced, unbalance also occurs in the charged state of the particles by one of the ions. However, according to the X-ray emitting section used in the present invention, an equivalent amount of positive and negative ions are simultaneously generated since weak X-ray is constantly irradiated. Therefore, the aerosols are neutralized without unbalance in the charging polarity. Further, ozone, electromagnetic noise, powder dust or the like does not occur. The X-ray emitting section 22 includes a power switch 22a. Emission and stop of the X-ray can be controlled by turning the power switch 22a on and off. An operation result of the aerosol particle charging device of this embodiment will now be explained using the drawings. FIG. 4 shows a ratio of the particles of relatively low concentration each having an aerosol diameter of 10 nm, 20 nm and 30 nm charged while retained in a region irradiated by the X-ray. In the figure, ▴ is a charging ratio of when a retention time is 3.2 seconds and Δ is when a retention time is 0.5 seconds in this embodiment. Moreover, ● is a case where a retention time is 3.2 seconds, and ◯ is of when it is 0.5 seconds in the conventional charging device using americium as the radiation source. As seen from the figure, a charging phenomenon of the charging device using the X-ray source is a charging process similar to the conventional device using the radiation source. FIG. 5 shows the number concentration of charged particles with respect to time retained in the chamber. A solid line is for the aerosol particle charging device using the soft X-ray according to this embodiment, and a broken line is for the conventional charging device using americium as the radiation source. A curve A is when a particle diameter is 30 nm, curve B is when a particle diameter is 50 nm, and curve C is when a particle diameter is 100 nm. As shown in the figure, in the charging device using the X-ray source, the particle number concentration reaches a peak at around 1.2 seconds regardless of the particle diameter. On the other hand, in the charging device using americium, the peak is at around 2.6 seconds. Therefore, the particles can be charged within a time shorter than the conventional device. Thus, the retention time of the particles in the chamber becomes short, and a sufficient charging can be performed to a flow of large flow rate. The present invention is thus easy to handle and generates ions at a high concentration compared to the conventional charging device using radiation source or corona discharge. Further, bipolar ions are simultaneously generated, and thus aerosols can be neutralized. If the power switch is arranged at the X-ray emitting section, switching can be easily performed by turning the power switch on and off, and thus has effects of being able to stop the generation of X-rays during non-operation, or to check the difference of the charging effect. For example, during an emergency or in a time of disaster of when using or storing the charging device, the radiation source may be exposed thereby causing external or internal explosion in the worst case of an emergency, disaster and the like in the charging device using the radiation source, but in the present device, safety is ensured due to a current break (automatic circuit including power switch or electric power failure). That is, safety can be ensured in handling and storage, and the X-ray can be irradiated only when necessary. An unipolar aerosol particle charging device according to a second embodiment of the present invention will now be explained. FIG. 6 is a cross sectional view showing the aerosol particle charging device of this embodiment. Similar to the conventional example mentioned above, in this embodiment, the chamber 31 is formed by a cylindrical part 32 made of resin and electrodes 33, 34 made of metal such as stainless steel for the upper surface and the lower surface. A direct current high-voltage power source 35 is connected between the upper and lower electrodes 33, 34, and an ammeter 36 is connected to the electrode 33 of the upper surface. An inlet duct 37 and a outlet duct 38 are arranged on the upper part of the chamber 31 at positions facing each other. In this embodiment, an X-ray emitting section 39 for releasing soft X-ray is arranged at substantially the middle of the chamber 31 in place of the radiation source of americium as mentioned above. The X-ray emitting section 39 is the same as that of the first embodiment mentioned above. The upper half of the opening of the X-ray emitting section 39 is covered by a side wall of the cylindrical part 32 as shown in the figure. The upper part of the opening may be covered by a shielding plate instead of the side wall. As such, the upper half of the X-ray beam is shielded, and the X-ray can be irradiated to only the lower half of the chamber 31, thereby generating positive and negative bipolar ions at the lower half of the chamber 31 by the X-ray. Further, the positive and negative ions can be separated by applying direct current high voltage to the upper and lower electrodes 33, 34 of the chamber 31. For example, if the electrode 33 is positive, the negative ions move towards the upper part of the chamber 31, and when the electrode 33 is negative, the positive ions move towards the upper part of the chamber 31. Therefore, when the aerosols are introduced from the inlet duct 37, the aerosols charged unipolar by the unipolar ion at the upper part of the chamber can be exhausted from the outlet duct 38. Thus, the unipolar charged aerosols can be exhausted by irradiating the X-ray to about ½ of the region of the chamber 31, and arranging the inlet duct and the outlet duct at the non-irradiated part not irradiated by the X-ray so as to face each other. The X-ray emitting section 39 in this embodiment also includes a power switch 39a. Emission and stop of the X-ray can be controlled by turning the power switch 39a on and off. FIGS. 7 and 8 show results of measurement of ion current of when the same electric field is generated and the chamber is closed to measure ion generation concentration of the unipolar charging device according to this embodiment and the conventional example. In FIG. 7, ◯ shows a generation property of the positive ions of the charging device using the X-ray of this embodiment, and ● shows a property of the negative ions of this embodiment of the X-ray. Herein, ▪ shows a positive and negative ion generation property of the conventional unipolar charging device using americium as the radiation source. As shown in the figure, in the conventional unipolar charging device, 14 nA is obtained when the voltage is about 5 kV and is substantially saturated, but in the unipolar charging device of this embodiment, the current increases in accordance with the applied voltage, and the ion generation number is thus considered to be high. FIG. 8 shows the ion number concentration with respect to the applied voltage, where ◯ is the positive ion generation property, and ● is the negative ion generation property of this embodiment. Herein, □ shows the generation property of the positive polarity ion, and ▪ shows the generation property of the negative ion of the conventional device using americium as the radiation source. The difference of the positive and negative number concentration is based on the difference in the ion mobility, and in either case, the number concentration of this embodiment is high. In the unipolar charging device using americium, the peak is within a range of 0.5 to 1 KV, whereas in the X-ray charging device, the peak is between 2.5 to 3 KV. FIGS. 9 and 10 show a charging ratio of when the particles ionize when the shown voltage is applied with respect to the particle diameter of the aerosol fine particles. FIG. 9 is for the positive ion, where ◯ and □ show a charging ratio with respect to a particle diameter of when 2.5 KV and 1.0 KV is applied, respectively, in the unipolar charging device of this embodiment. On the other hand, ● and ▪ show a charging ratio with respect to a particle diameter of when 0.5 KV and 3.0 KV is applied, respectively, in the conventional charging device using americium. FIG. 10 shows a generation property of the negative ion, where ◯ and ● in the figure are measurement values of the charging device of when 2.5 KV and 0.5 KV are applied using the X-ray and the americium, respectively, and the solid line and the broken line show the theoretical values. As apparent from the figures, in the charging device according to this embodiment, the charging ratio increases with increase in particle diameter regardless of polarity, similar to the conventional example, and has a high charging ratio with respect to the conventional example. Thus, by using the X-ray, the unipolar charging particles can be generated at high concentration and in a short period of time. Further, the unipolar ions can be easily generated, and thus fine particles in electrostatic coating and air cleaner can be removed. The nanoparticles of high concentration are generated, and nanoparticle charging become possible and thus can be applied to manufacturing electronic application elements and the like. When the X-ray emitting section includes the power switch, switching can be easily performed by turning on and off the power switch, and thus has effects of being able to stop the generation of X-rays during non-operation, or to check the difference of the charging effect. For example during an emergency or in a time of disaster of when using or storing the charging device, the radiation source may be exposed thereby causing external or internal explosion in the worst case of an emergency, disaster and the like in the charging device using the radiation source, but in the present device, safety is ensured due to a current break (automatic circuit including power switch or electric power failure). That is, safety in handling and storage is ensured and the X-ray is irradiated only when necessary. In this embodiment, X-ray is irradiated to a region of about ½ of the cylindrical chamber, and the inlet duct and the outlet duct are arranged at the upper part of the chamber acting as the non-irradiated part of the X-ray, but of course, the irradiating region of the X-ray is not limited to ½, and the shape of the chamber may not necessarily be a cylinder. According to the present invention, the handling can be simplified and the ions can be generated at high concentration compared to the conventional charging device using the radiation source or the corona discharge. The bipolar ions are simultaneously generated, and thus the aerosols can be neutralized. Since the unipolar ions can be easily generated, the removal of fine particles in electrostatic coating and air washer becomes possible. The nanoparticles of high concentration can be generated, and nanoparticle charging becomes possible and thus can be applied to manufacturing of electronic application elements and the like. |
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053894731 | summary | BACKGROUND OF THE INVENTION The present invention relates to methods of producing X-ray grids. It is known to produce X-ray grids by mechanically glueing alternating X-ray transmitting and X-ray non transmitting layers. However, the mechanical process of their manufacture is difficult. Also, an X-ray grid is known which is composed of a monolithic panel with openings and a coating which is composed of an X-ray absorbing material. The monolithic panel is composed of a light sensitive glass and is exposed by a light beam passing through a mask which corresponds to a pattern of the X-ray grid. This method has certain limitations with respect to thickness of the panel and a relatively low accuracy of the finished grid due to distortions of the light beam at the edges of the mask and openings. Finally, in accordance with another method an X-ray grid is produced from a light-sensitive glass which is exposed through a thin shaping device or mask so that various areas of the panel are exposed with different intensities, and then the image produced by the exposure is developed by heating, and the panel is etched in an aqueous solution of hydrofluoric acid, so that a grate is produced by forming of openings which are made in the exposed areas and separated by partitions in non-exposed areas. The thusly produced panels are glued together as layers so that the axes of the openings coincide with each other, and a grid of the desired thickness is produced. The glass can be an X-ray absorbing glass, or its inner walls of the openings can be covered with an X-ray absorbing coating. In this method in order to produce a finished X-ray grid, several thin dispersing grates are assembled to form a grid, and each layer must have openings aligned with the openings of the neighboring layers. This method requires assembling of the layers so that a great numbers of openings can be aligned with each other and directed to a common focal point of the grid. For example, with the optimal number of strips 30 per cm, the number of openings in the cellular grid per 1 cm.sup.2 is 900; and with the efficient area of the grid 340.times.420 mm the number of openings in each layer of the grid is 1 398 600. It is evident that it is difficult to manufacture such panels having such great number of openings with high accuracy with exact coincidence of the openings and the partitions, or actually practically impossible. Utilization of electromagnetic radiation with a relatively great wavelength which is commensurate with the wavelength of the ultraviolet region of the spectrum leads to distortions of the formed image through the thickness of the exposed panel due to refraction, reflection and dispersion in the exposed glass of the rays which form the image, and the absolute value of the distortion increases with the increase of the thickness of the exposed panel. When the flat shaping device is utilized, substantial distortion of the formed images of elements of an X-ray grid does not permit obtaining of a non-distorted three-dimensional image of the grid in the panels of the substantial thickness, for example when it is necessary to provide the grid ratio of 6, 8, 12, etc. This is why it was necessary to make a composite grid. This method also cannot be used for making parallel X-ray grids, since it involves the use of only a pointed radiation source. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a new method of producing X-ray grids, which is more efficient and increases grid quality since it makes possible producing the openings of the grid in a monolithic panel of a required thickness. In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method of producing an X-ray grid, in accordance with which a panel or plate of a photosensitive material is exposed through a mask and then developed to produce a hidden image and etched, wherein in accordance with the new features of the present invention the photosensitive material is a photosensitive glass with a differential of solubility not less than 25, and the-exposure is performed with a radiation having a wavelength which is shorter than a wavelength of an ultraviolet radiation, for example by X-ray radiation or gamma radiation. When the method is performed in accordance with the present invention, X-ray grids can be produced with much higher output and much higher quality than in accordance with previously known methods. The novel features of the present invention will be best understood from the following description of preferred embodiments. |
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description | This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. P2003-67559, filed on Mar. 13, 2003, the entire contents of which is hereby incorporated herein by reference. 1. Field of the Invention The present invention relates to a collimator which is used in a radiotherapy apparatus and controls a radiation field by a plurality of collimating leaves. The present invention also relates to a method of positioning a plurality of collimating leaves of the collimator. 2. Discussion of the Background It is important to reduce X-ray exposure to an object such as a patient when a radiotherapy apparatus or an X-ray diagnosis apparatus is used. Many types of techniques are presented for accomplishing the X-ray exposure reduction. One well-known technique is the use of a collimator. The collimator narrows a radiation field by reducing its aperture size. The aperture size is controllable by adjusting positions of aperture blades in intercrossing (X-Y) directions. The aperture blades are typically made of an X-ray non-transmission material such as lead or tungsten. In one example of the collimator, a lamp is provided at a position corresponding to an X-ray radiator. A shade resulting from the lamp light through the controlled aperture of the collimator is used for adjusting and determining an actual radiation field. In other words, a desired radiation field is obtained by controlling the aperture so that the shade is identical to the desired radiation field. This technique is disclosed, for example, in Japanese Patent Application Disclosure PH3-44768. In many cases, however, a multileaf collimator is used for a radiotherapy apparatus. The multileaf collimator includes an arrangement of a plurality of collimating leaves formed in a mutually contiguous manner. The collimating leaves perform a function similar to that of the aperture blades. Instead of a pair of aperture blades, a pair of collimating members each of which include a plurality of collimating leaves are used in one direction for controlling the aperture so as to help form the shape of the aperture more appropriately to the shape of a tumor. If, however, the above-mentioned lamp is used to adjust a plurality of collimating leaves, it is not easy to obtain sufficient accuracy in terms of position adjustment. The position adjustment is usually performed at a position of the isocenter within a light emission field of the lamp. The required accuracy at the isocenter is, for example, one millimeter error. Meanwhile, a position of the collimating leaf is typically detected to the precision of 0.1 millimeter. Therefore, the detection error (i.e., incorrect detection result) of the collimating leaf position may lead to an error expansion at the isocenter. In other words, a slight detection error may result in an error beyond the required accuracy at the isocenter. Consequently, a high accuracy in the position detection is required for the collimating leaves. According to a first aspect of the present invention, there is provided a collimating device for controlling the radiation field of an X-ray radiated from an X-ray radiator. The device includes a plurality of first collimating leaves, a plurality of second collimating leaves, a beam generator, a detector, a memory, and a controller. The plurality of second collimating leaves oppose the first collimating leaves. The beam generator is configured to generate a beam which emanates between the first plurality of collimating leaves and the second plurality of collimating leaves. The detector is configured to detect the beam. The memory is configured to store position information of each leaf of the first and second plurality of collimating leaves when each leaf is determined to intersect the beam based on the detection. The controller is configured to position each leaf based on the position information so as to control the radiation field. According to a second aspect of the present invention, there is provided a collimating device for controlling a radiation field of an X-ray radiated from an X-ray radiator. The device includes a plurality of first collimating leaves, a plurality of second collimating leaves, a beam generator, a detector, a memory, and a controller. The plurality of second collimating leaves oppose the first collimating leaves. The beam generator is configured to generate at least first and second beams. The first beam intersects the first plurality of collimating leaves. The second beam intersects the second plurality of collimating leaves. The detector is configured to detect the first and second beams. The memory is configured to store first position information of each leaf of the first plurality of collimating leaves when each leaf is determined to intersect the first beam based on the detection. The memory is also configured to store second position information of each leaf of the second plurality of collimating leaves when each leaf is determined to intersect the second beam based on the detection. The controller is configured to position the each leaf of the first plurality of collimating leaves based on the first position information and each leaf of the second plurality of collimating leaves based on the second position information so as to control the radiation field. According to a third aspect of the present invention, there is provided a radiotherapy apparatus for radiating an X-ray and concentrating the X-ray towards a predetermined part of an object. The apparatus includes an X-ray radiator and a collimator. The X-ray radiator is configured to radiate the X-ray. The collimator is configured to control a radiation field of the X-ray radiated by the X-ray radiator. The collimator includes a plurality of first collimating leaves, a plurality of second collimating leaves, a beam generator, a detector, a memory, and a controller. The plurality of second collimating leaves oppose the first collimating leaves. The beam generator is configured to generate a beam. The beam emanates between the first plurality of collimating leaves and the second plurality of collimating leaves. The detector is configured to detect the beam. The memory is configured to store position information of each leaf of the first and second plurality of collimating leaves when each leaf is determined to intersect the beam based on the detection. The controller is configured to position each leaf based on the position information. According to a fourth aspect of the present invention, there is provided a method of positioning collimating leaves for use in a collimator which controls a radiation field of an X-ray radiated from an X-ray radiator. The collimating leaves include a plurality of first collimating leaves and a plurality of second collimating leaves opposing the first collimating leaves. The method begins by generating a beam which emanates between the first plurality of collimating leaves and the second plurality of collimating leaves. The method continues by detecting the beam and storing position information of each leaf of the first and second plurality of collimating leaves when each leaf is determined to intersect the beam based on the detection. The method further continues by positioning each leaf based on the position information so as to control the radiation field. According to a fifth aspect of the present invention, there is provided a method of positioning collimating leaves for use in a collimator which controls a radiation field of an X-ray radiated from an X-ray radiator. The collimating leaves include a plurality of first collimating leaves and a plurality of second collimating leaves opposing the first collimating leaves. The method begins by generating at least first and second beams. The first beam intersects the first plurality of collimating leaves and the second beam intersects the second plurality of collimating leaves. The method continues by detecting the first and second beams and storing first position information of each leaf of the first plurality of collimating leaves when each first collimating leaf is determined to intersect the first beam based on the detection and second position information of each leaf of the second plurality of collimating leaves when each second collimating leaf is determined to intersect the second beam based on the detection. The method further continues by positioning each first collimating leaf based on the first position information and each second collimating leaf based on the second position information so as to control the radiation field. Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is an illustration showing an example of a situation when a radiotherapy apparatus is used according to the first embodiment of the present invention. As shown in FIG. 1, a radiotherapy apparatus includes a radiation apparatus 10, a patient couch 20, and a controller 30. The radiation apparatus is used for radiating an X-ray towards an object such as a patient P. The patient couch 20 is used for positioning the patient P so that the radiated X-ray is exposed to a tumor of the patient P. The controller 30 is used for organically controlling units and apparatuses of the radiotherapy apparatus including the radiation apparatus 10 and the patient couch 20. The radiation apparatus 10 includes a fixed gantry 11, a rotation gantry 12, a radiation head 13, and a collimator 14. The fixed gantry 11 is fixed on the floor. The rotation gantry 12 is rotatablly supported by the fixed gantry 1.1 The radiation head 13 includes an X-ray radiator and is provided in a body extended from one end of the rotation gantry 12. The collimator 14 is incorporated in the radiation head 13. The rotation gantry 12 is nearly 360 degrees rotatable around a horizontal axis H of the fixed gantry 11. The collimator 14 is rotatable around an X-ray axis I radiated from the radiation head 13. An intersection of the axes I and H is called an isocenter IC. The isocenter is, for example, determined at a position one meter from the X-ray radiator. The rotation gantry 12 can be used at a predetermined fixed position in the radiation and/or configured to rotate so as to enable various types of radiations, such as, for example, a rotation radiation, a pendulum radiation, and an intermittent radiation. The patient couch 20 is rotatable along an arc centered on the axis I in a direction G within a predetermined angle range. The patient couch 20 includes an upper mechanism 21, a table 22, an elevator mechanism 23, and a bottom mechanism 24. The upper mechanism 21 supports the table 22 where the patient Plies. The upper mechanism 21 has a mechanism for moving the table 22 in directions e (i.e., head-foot directions of the patient P) and directions f (i.e., right-left directions of the patient P). The upper mechanism 21 is supported by the elevator mechanism 23. The elevator mechanism 23 may be formed by link mechanics and be configured to move up and down in direction d, as shown. Accordingly, the elevator mechanism 23 raises and lowers the upper mechanism 21 and the table 22 within a predetermined range. This elevator mechanism 23 is supported by the bottom mechanism 24. The bottom mechanism 24 has a rotation mechanism which rotates the elevator mechanism 23 around an axis positioned by a distance L from the axis I in directions F. The upper mechanism 21 and the table 22 rotate with the elevator mechanism 23 when the bottom mechanism 24 is rotated by a predetermined angle. For the radiotherapy practice, a medical staff such as a doctor D operates an operation unit (to be described in FIG. 13) connected to the controller 30 so as to position the patient P and determine the radiation field by the collimator 14. In the radiotherapy practice, it is important to concentrate the radiation to a treated area or part such as a malignant tumor so as to avoid unnecessary X-ray exposure to normal tissues. The collimator 14 is used to control the radiation (field) to a limited area for the above purpose. The collimator 14 will be described with reference to FIGS. 2 to 6. FIG. 2 is an illustration showing an exemplary configuration of the collimator 14 viewed from a first direction according to the first embodiment of the present invention. The collimator typically includes a first pair of collimating members 140A and 140B, and a second pair of collimating members 141A and 141B. The first pair may be perpendicular to the second pair. The first pair is placed at a first distance from an X-ray source S. The X-ray source S is part of the X-ray radiator. The second pair is placed at a second distance from the X-ray source S. The first distance may be shorter than the second distance. The collimating members 140A and 140B may have, but are not limited to, an arc shape along a circular arc centered about the X-ray source S. The collimating members 140A and 140B may move along the circular arc (i.e., along direction X). The collimating members 140A and 140B may be opposed to each other and provided at symmetrical positions in relation to the axis I. The collimating member 140A may be a conventional aperture blade made of a heavy metal such as lead or tungsten, and move towards and away from the collimating member 140B. The collimating member 140A is driven by a driver 142A through a gear 144A. Similarly, the collimating member 140B may be a conventional aperture blade made of a heavy metal such as lead or tungsten, and move towards and away from the collimating member 140A. The collimating member 140B is driven by a driver 142B through a gear 144B. Therefore, the positions of the first pair of collimating members 140A and 140B are controlled so as to narrow or reduce the radiation field of the X-ray radiated from the X-ray source S in the direction X. Each of the collimating members 140A and 140B is independently controlled. The positions of the second pair of collimating members 141A and 141B are controlled so as to further narrow or reduce the radiation field of the X-ray radiated from the X-ray source S in different directions. The collimating member 141A includes a plurality of collimating leaves 141A1 to 141An. Similarly, the collimating member 141B includes a plurality of collimating leaves 141B1 to 141Bn. FIG. 3 is an illustration showing an exemplary configuration of the collimator 14 viewed from a second direction according to the first embodiment of the present invention. Since FIG. 3 shows a view from a direction perpendicular to the view shown in FIG. 2, FIG. 3 shows only one collimating leaf 141A1 as an example of the collimating member 141A. Similarly, only one collimating leaf 141B1 is shown as an example of the collimating member 141B. Therefore, the following explanation regarding the collimating leaf 141A1 also applies to collimating leaves 141A2 to 141An. The following explanation regarding the collimating leaf 141B1 also applies to collimating leaves 141B2 to 141Bn. As shown in FIG.3, the collimating leaves 141A1 and 141B1 may have, but are not limited to, an arc shape along a circular arc centered about the X-ray source S. The collimating leaves 141A1 and 141B1 may move along the circular arc (i.e., along directions Y). The collimating leaves 141A1 and 141B1 may be opposed to each other and be provided at symmetrical positions against the axis I. The collimating leaf 141A1 moves towards and away from the collimating leaf 141B1. The collimating leaf 141A1 is driven by a driver 143A1 through a driving gear 143a. Similarly, the collimating leaf 141B1 moves towards and away from the collimating leaf 141A1. The collimating leaf 141B1 is driven by a driver 143B1 through a driving gear 145B1. Therefore, the positions of the second pair of collimating members 141A and 141B are controlled so as to further narrow or reduce the radiation field in the directions Y, which has already been narrowed by the first pair of collimating members 140A and 140B. The position of each of the collimating leaves 141A1 and 141B1 are independently controlled. Further, the positions of each of the collimating leaves 141A1 to 141An are independently controlled and the positions of each of the collimating leaves 141B1 to 141Bn are also independently controlled. Therefore, as shown in FIG. 4, by controlling the position of each of the collimating leaves 141A1 to 141An and 141B1 to 141Bn, it is possible to adjust an aperture U to a shape of a malignant tumor T. The collimating leaves 141A1 to 141An and 141B1 to 141Bn will be described in detail below. FIG. 5 is an illustration showing an exemplary configuration of the collimator 14 viewed from a third direction according to the first embodiment of the present invention. FIG. 5 shows a view from a top or a bottom of the collimator 14 along the axis I. The first pair of collimating members 140A and 140B is shown by chain double-dashed lines. The collimating leaves 141A1 to 141An are arranged in a mutually contiguous manner. As the collimating leaf 141A1 has been described as connected to the driver 143A1, the collimating leaves 141A1 to 141An are connected to drivers 143A1 to 143An, respectively. Accordingly, the collimating leaves 141A1 to 141An are independently driven by the drivers 143A1 to 143An, respectively. Similarly, the collimating leaves 141B1 to 141Bn are arranged in a mutually contiguous manner. As the collimating leaf 141B1 has been described as connected to the driver 143B1, the collimating leaves 141B1 to 141Bn are connected to drivers 143B1 to 143Bn, respectively. Accordingly, the collimating leaves 141B1 to 141Bn are independently driven by the drivers 143B1 to 143Bn, respectively. FIG. 6 is an illustration showing an example of the driver 143A1 according to the first embodiment of the present invention. The following explanation of the driver 143A1 also applies to the drivers 143A2 to 143An and 143B1 to 143Bn. FIG. 6 shows a relationship between the driver 143A1 and the collimating leaf 141A1. As shown in FIG. 6, the collimating leaf 141A1 is formed of a sector with an arc along a bottom edge 141a. The side far from the collimating leaf 141B1 (not shown in FIG. 6) is formed of a wedge. This side may alternatively be flat. The other side of the collimating leaf 141A1 by which the radiation is collimated is flat. The bottom edge 141a has gear teeth so as to engage with the driving gear 143a. The driving gear 143a is fixed at one end of a shaft 143b. The shaft 143b is driven by a motor 143c through a warm gear 143d and the other gears. Accordingly, the shaft 143b rotates in accordance with the motor 143c. The driver 143A1 also includes a potentiometer 143e and an encoder 143f. The potentiometer 143e and the encoder 143f are used to detect position information of the collimating leaf 141A1. Outputs of the potentiometer 143e and the encoder 143f are supplied to the controller 30. The controller 30 controls the motor 143c based on the supplied outputs, allowing the collimating leaf 141A1 to be positioned appropriately. Next, a control technique of the collimator 14 will be described below. Regarding the first pair of collimating members 140A and 140B, the collimating member 140A is moved away from the collimating member 140B along the direction X. There is a stopper (or a holder) to hold the collimating member 140A at a position furthest from the collimating member 140B. A position control determination of the collimating member 140A is performed based on the held position. Similarly, the collimating member 140B is moved away from the collimating member 140A along the direction X. There is a stopper (or a holder) to hold the collimating member 140B at a position furthest from the collimating member 140A. A position control determination of the collimating member 140B is performed based on the held position. The controller 30 controls the drivers 142A and 142B so as to move the collimating members 140A and 140B to appropriate positions. Accordingly, the collimator 14 adjusts its aperture with a preferred width along the X direction. The relationship between the collimating member 140A (140B) and the driver 142A (142B) is similar to that between the collimating leaf 141A1 and the driver 143A1. Regarding the second pair of collimating members 141A and 141B, it is necessary to accurately control the position of each collimating leaf along the Y direction so as to obtain a preferred radiation field through the aperture of the collimator 14. Although there is a technique of positioning each collimating leaf in a manner similar to the first pair of the collimating members 140A and 140B, it is not preferable since each collimating leaf may be transformed due to an impact shock caused when the collimating leaf is held by the stopper. Therefore, according to the first embodiment of the present invention, a reference position (or position information) of each collimating leaf is accurately determined without any impact shock to each collimating leaf. Accordingly, the position of each collimating leaf of the collimating leaves 141A1 to 141An and 141B1 to 141Bn is controlled based on the position information so as to obtain a desired aperture (or a desired radiation field on the patient P). In other words, the controller 30 controls the distance each collimating leaf is moved based on the position information. As shown in FIG. 5, the collimator 14 includes a laser beam generator 41 and a laser beam receiver 42 so as to determine the reference position. The laser beam receiver 42 includes a function as a detector for detecting a received laser beam. The laser beam generator 41 and the laser beam receiver 42 are opposed to each other so that a laser beam 40 generated from the laser beam generator 41 emanates between the collimating members 141A and 141B. The laser beam 40 also intersects the axis I. One example is that the laser beam 40 runs in a direction perpendicular to the direction Y. In other words, an incident angle of the laser beam 40 between the collimating members 141A and 141B is 90 degrees in relation to the direction Y. Another example is that the laser beam direction may not be perpendicular to the direction Y. The incident angle is, for example, 85 degrees in relation to the direction Y. In another example above, position information of each collimating leaf is compensated based on the incident angle and a position along the direction X in the collimating member 141A or 141B. The compensated position information is used as the reference position. The laser beam generator 41 and the laser beam receiver 42 are placed, for example, at positions shown in FIG. 7 as part of the collimator 14. The collimator 14 is supported in the radiation head 13. Prior to the laser beam generation, the collimating leaves 141A1 to 141An are moved away from the collimating leaves 141B1 to 141Bn along the direction Y. There are stoppers (or holders) to hold the collimating leaves 141A1 to 141An at positions furthest from the collimating leaves 141B1 to 141Bn. Similarly, the collimating leaves 141B1 to 141Bn are moved away from the collimating leaves 141A1 to 141An along the direction Y. There are stoppers (or holders) to hold the collimating leaves 141B1 to 141Bn at positions furthest from the collimating leaves 141B1 to 141Bn. After the holding of the collimating leaves 141A1 to 141An and 141B1 to 141Bn, each collimating leaf is individually moved towards the laser beam 40. For example, the collimating leaf 141A1 is moved towards the laser beam 40 (i.e., towards the collimating leaf 141B1). When the collimating leaf 141A1 intersects the laser beam 40 at the first position, the first position is detected by the potentiometer 143e or the encoder 143f as the reference position of the collimating leaf 141A1. The detected reference position is stored as the position information of the collimating leaf 141A1 in a memory of the controller 30. After the detection regarding the collimating leaf 141A1, the collimating leaf 141A1 is moved back to the position of the stopper. In response, the collimating leaf 141A2 is moved towards the laser beam 40 (i.e., towards the collimating leaf 141B2)1. When the collimating leaf 141A2 intersects the laser beam 40 at the second position, the second position is detected by the potentiometer 143e or the encoder 143f as the reference position of the collimating leaf 141A2. The detected reference position is stored as the position information of the collimating leaf 141A2 in a memory of the controller 30. A similar detection is repeated for the rest of the collimating leaves (i.e., the collimating leaves 141A3 to 141An and 141B1 to 141Bn). In the above case, the intersection may be determined when the laser beam receiver 42 detects the received laser beam 40 at a predetermined percentage which can be detected without any intersection of the collimating leaf 141A1, as shown in FIG. 8. For example, the predetermined percentage may be 50 percent. As a modification, the collimating leaf may first be moved to a position where the laser beam is completely blocked, and then moved back to a position where the laser beam is half blocked. As described above, when the laser beam 40 does not emanate between the collimating members 141A and 141B in a direction perpendicular to the direction Y as shown in FIG. 9, the detected reference position (position information) maybe compensated in accordance with the incident angle of the laser beam 40. Further, as shown in FIG. 10, when a gear mechanism is used to move a collimating leaf, the relationship between positions of the collimating leaf and the shaft 143b is changed due to a gear engagement in the gear rotation. Therefore, the reference position may also be compensated in accordance with a rotation direction of the shaft 143b (i.e., a moving direction of the collimating leaf), taking the gear engagement into consideration. In this case, for example, two types of compensated position information may be prepared, one for a first direction (e.g., left) and one for a second direction (e.g., right). This compensation may also take a rotation amount or angle of the shaft into consideration since the above relationship between positions of the collimating leaf and the shaft 143b is kept until the shaft 143b is rotated by a certain angle. Similar compensation may also be applied to a rotation of the rotation gantry 12. In other words, the position information may be compensated in accordance with the rotation angle of the rotation gantry 12 and the compensated position information may be used to position the collimating leaves 141A1 to 141An and 141B1 to 141Bn in accordance with a rotation angle used in a radiotherapy. The laser beam 40 generated by the laser beam generator 41 is not necessarily received by the laser beam receiver 42 directly. As shown in FIG. 11, after having passed through the collimating members 141A and 141B, the laser beam 40 generated by the laser beam generator 41 may be reflected by one or more mirrors 100 (reflectors), and then be received by the laser beam receiver 42. Another example is shown in FIG. 12. The laser beam 40 generated by the laser beam generator 41 may be reflected by one or more mirrors 110 (reflectors) before passing through the collimating members 141A and 141B, and then be received by the laser beam receiver 42. Instead of the laser beam generator 41 and the laser beam receiver 42, a photo-sensing system may be used for the same purpose. Basic operations of determining the reference position of each collimating leaf and positioning each collimating leaf will be described with reference to FIGS. 12 and 13. FIG. 13 is a block diagram showing an exemplary configuration of a collimator control apparatus according to the first embodiment of the present invention. FIG. 14 is a flowchart showing an example of a flow of the reference position determination and the collimating leaf positioning according to the first embodiment of the present invention. As shown in FIG. 13, the controller 30 controls various components of the radiotherapy apparatus and is connected to an operation unit 31. The operation unit 31 is used to input various types of information and to instruct various operations. The controller 30 includes a memory 32, a central processing unit (CPU) 33, a radiation field determination unit 34, and a calculation unit 35. The memory 32 stores the position information as described above. The CPU 33 operates as a host controller. The radiation field determination unit 34 determines an aperture of the collimator 14 so as to control the radiation field of an X-ray radiated by the X-ray source S. The calculation unit 35 calculates a movement distance of the collimating leaves 141A1 to 141An and 141B1 to 141Bn. The controller 30 also calculates a movement distance of the collimating members 140A and 140B. The controller 30 further includes one or more processors for controls of, for example, a radiation, the rotation gantry 12, and the patient couch 20. Since, however, these processors do not directly relate to explanations of the collimator 14 according to the first embodiment, explanations of these controls are omitted herein. The doctor D operates the operation unit 31 so as to instruct the reference position determination for each collimating leaf of the collimating members 141A and 141B. In response to the instruction, the CPU 33 activates (or renders operative) the laser beam generator 41 and the laser beam receiver 42 so that the laser beam is generated (step 1). The CPU 33 also drives the motor 143c so as to move all the collimating leaves 141A1 to 141An and 141B1 to 141Bn backward (step 2). That is, the collimating leaves 141A1 to 141An are moved away from the collimating leaves 141B1 to 141Bn and held by the stoppers. Also, the collimating leaves 141B1 to 141Bn are moved away from the collimating leaves 141A1 to 141An and held by the stoppers. The processing order of steps 1 and 2 may also be reversed. An operator who operates the operation unit 31 so as to instruct the reference position determination is not limited to the doctor D but may be any other permitted person. The collimating leaf 141A1 is moved from the position held by the stopper towards the collimating leaf 141B1. The collimating leaf 141A1 is stopped at a position where the collimating leaf 141A1 intersects the laser beam 40. For example, the received laser beam may be 50 percent in strength of the laser beam received without any intersection. The position is detected by the potentiometer 143e or the encoder 143f as a reference position of the collimating leaf 141A1. The detected reference position is stored as position information of the collimating leaf 141A1 in the memory 32 (step 3). After the detection and the storage, the collimating leaf 141A1 is moved back to the position of the stopper (step 4). In step 5, it is determined whether reference positions are detected for all the collimating leaves 141A1 to 141An and 141B1 to 141Bn. Therefore, the operations in steps 3 and 4 are performed individually for each of the collimating leaves 141A1 to 141An and 141B1 to 141Bn. When the reference position is detected and stored as position information for each of the collimating leaves 141A1 to 141An and 141B1 to 141Bn, the operation of the laser beam generator 41 and the laser beam receiver 42 are terminated (step 6). The calculation unit 35 then calculates a distance of how much each of the collimating leaves 141A1 to 141An and 141B1 to 141Bn should be moved so as to form an aperture corresponding to a radiation field designated for a particular radiotherapy (step 7). The calculated distance is a distance from the reference position. Based on the calculated distance for each of the collimating leaves 141A1 to 141An and 141B1 to 141Bn, each collimating leaf is positioned by driving the motor 143c (step 8). In addition, the calculation unit 30 also calculates the distance to move each of the collimating members 140A and 140B to form the designated radiation field. Accordingly, all the collimating leaves 141A1 to 141An of the collimating member 141A and 141B1 to 141Bn of the collimating member 141B and the collimating members 140A and 140B are positioned, respectively, to form the aperture corresponding to the radiation field appropriate for the shape of a tumor. The operations in steps 1 to 6 are not limited to being performed just prior to an actual radiotherapy. The operations may, for example, be performed any time the radiotherapy apparatus is powered. In other words, the laser beam generator 41 can be activated in response to the power supply to the radiotherapy apparatus without the doctor D's instruction. Also, the operations may alternatively be performed at predetermined intervals, for example, every three months or during other predetermined intervals. These calibrations are effective to correct deviance that might occur due to the use of the device (or the several times of use). The operations in steps 1 to 6 may, for example, take only three minutes. The position information (the reference position) and/or the calculated distance may be displayed in a display provided in or connected to the radiotherapy apparatus. As explained above, according to the first embodiment of the present invention, the reference position (position information) of each collimating leaf is accurately determined without any impact shock to each collimating leaf. Accordingly, the position of each collimating leaf of the collimating leaves 141A1 to 141An and 141B1 to 141Bn is controlled based on the position information. This makes it possible to easily and accurately obtain a desired aperture corresponding to the radiation field which is appropriate for the shape of a tumor. In addition, since the reference position of each collimating leaf can automatically be detected, it is possible to accurately and quickly adjust positioning of a plurality of collimating leaves. Therefore, the X-ray exposure to the patient P can be highly reduced, and a preferred radiotherapy can be conducted to the patient P. A medical staff's work can also be reduced. (Second Embodiment) The first embodiment has described the collimating leaf position detection with one laser beam. In the second embodiment, various types of collimating leaf position detections using a plurality of laser beams will be described with reference to FIGS. 14 to 22. FIG. 15 is an illustration showing the first example of the collimating leaf position detection with two laser beams according to the second embodiment of the present invention. As shown in FIG. 15, a laser beam 401 generated from a laser beam generator 411 is received by a laser beam receiver 421. The laser beam 401 may be used to detect a position of each collimating leaf of the collimating member 141A. Similarly, the laser beam 402 generated from a laser beam generator 412 is received by a laser beam receiver 422. The laser beam 402 may be used to detect a position of each collimating leaf of the collimating member 141B. In this configuration, it may be possible to perform the detection for both of the collimating members 141A and 141B at the same time. FIG. 16 is an illustration showing the second example of the collimating leaf position detection with two laser beams according to the second embodiment of the present invention. As shown in FIG. 16, both the laser beams 401 and 402 are generated from a laser beam generator 410. The laser beam 401 is reflected by a mirror 120 or any other type of reflector and received by the laser beam receiver 421. The laser beam 402 is reflected by a mirror 130 or any other type of reflector and received by the laser beam receiver 422. Similarly to FIG. 15, the laser beam 401 reflected by the mirror 120 may be used to detect a position of each collimating leaf of the collimating member 141A. The laser beam 402 reflected by the mirror 130 may be used to detect a position of each collimating leaf of the collimating member 141B. If the laser beam generator 410 is capable of generating the laser beam 402 while the laser beam 401 is generated, it may be possible to perform the detection for both of the collimating members 141A and 141B at the same time. According to the configuration shown in FIG. 16, only one laser beam generator is required for the detection with two laser beams. The placement relationship among the laser beam generator 410 and the mirrors 120 and 130 can be arranged according to necessity. Instead of the use of only one laser beam generator 410, only one laser beam receiver may be used with reflectors such as mirrors. Or alternatively, only one laser beam generator may be used with only one laser beam receiver for two laser beams, using reflectors at both ends. FIG. 17 is an illustration showing the third example of the collimating leaf position detection with two laser beams according to the second embodiment of the present invention. As shown in FIG. 17, a laser beam 403 generated from a laser beam generator 413 is received by a laser beam receiver 423. The laser beam 403 may be used to detect a position of each collimating leaf of the collimating member 141A. In this example, the side furthest from the collimating member 141B intersects the laser beam 403. Similarly, the laser beam 404 generated from a laser beam generator 414 is received by a laser beam receiver 424. The laser beam 404 may be used to detect a position of each collimating leaf of the collimating member 141B. The side furthest from the collimating member 141A intersects the laser beam 404. Also in this configuration, it may be possible to perform the detection for both of the collimating members 141A and 141B at the same time. FIG. 18 is an illustration showing an example of the collimating leaf position detection with three laser beams according to the second embodiment of the present invention. As shown in FIG. 18, the laser beams 40, 403, and 404 are generated from respective laser beam generators 41, 413, and 414. The generated laser beams 40, 403, and 404 are received by the respective laser beam receivers 42, 421, and 424. As shown in FIG. 19, a pair of the laser beam generator 413 and the laser beam receiver 423 is placed where the laser beam 403 intersects the side of the collimating member 141A furthest from the collimating member 141B when the collimating member 141A is moved furthest from the collimating member 141B. Position information detected at this position may be used when the collimating leaf of the collimating member 141A is moved and positioned against the collimating member 141B. Similarly, although not shown in FIG. 19, the laser beam generator 414 and the laser beam receiver 424 pair is placed where the laser beam 404 intersects one side of the collimating member 141B which is further from the collimating member 141A when the collimating member 141B is moved furthest from the collimating member 141A. Position information detected at this position regarding each collimating leaf may be used when the collimating leaf of the collimating member 141B is moved against the collimating member 141A. Such a use of position information may be advantageous when the gear engagement is changed in accordance with the moving direction of each collimating leaf, as shown in FIG. 10. When each collimating leaf of the collimating member 141A is moved towards the collimating member 141B, other position information may be used. As shown in FIG. 20, the laser beam generator 41 and the laser beam receiver 42 pair is placed where the laser beam 40 runs through the axis I. As described in the first embodiment, position information detected when each collimating leaf of the collimating member 141A is moved to intersect the laser beam 40 with one side close to the collimating member 141B may be used when the collimating leaf of the collimating member 141A is moved towards the collimating member 141B. Similarly, although not shown in FIG. 20, position information detected when each collimating leaf of the collimating member 141B is moved to intersect the laser beam 40 with one side close to the collimating member 141A may be used when the collimating leaf of the collimating member 141B is moved towards the collimating member 141A. Such a use of position information may be advantageous when the gear engagement is changed in accordance with the moving direction of each collimating leaf, as shown in FIG. 10. FIG. 21 is an illustration showing an example of the collimating leaf position detection with four laser beams according to the second embodiment of the present invention. As shown in FIG. 21, the laser beams 401 to 404 are generated from laser beam generators 411 to 414. The generated laser beams 401 to 404 are received by the laser beam receivers 421 to 424. In this configuration, the laser beam generator 413 and the laser beam receiver 423 pair can be placed anywhere one side of each collimating leaf of the collimating member 141A can intersect the laser beam 403. The one side is a side furthest from the collimating member 141B. One example of the placement is where the one side intersects the laser beam 403 when the collimating member 141A is moved furthest from the collimating member 141B, as shown in FIG. 19. Position information detected at this position regarding each collimating leaf may be used when the collimating leaf of the collimating member 141A is moved and positioned against the collimating member 141B. Similarly, the laser beam generator 414 and the laser beam receiver 424 can be placed anywhere one side of each collimating leaf of the collimating member 141B can intersect the laser beam 404. The one side is a side furthest from the collimating member 141A. One example of the placement is where the one side intersects the laser beam 404 when the collimating member 141B is moved furthest from the collimating member 141B. Position information detected at this position regarding each collimating leaf may be used when the collimating leaf of the collimating member 141B is moved and positioned against the collimating member 141A. Still in FIG. 21, the laser beam generator 411 and the laser beam receiver 421 pair can be placed between the collimating members 141A and 141B. For example, position information detected when each collimating leaf of the collimating member 141A is moved to intersect the laser beam 401 with one side closest to the collimating member 141B may be used when the collimating leaf of the collimating member 141A is moved and positioned towards the collimating member 141B. Similarly, the laser beam generator 412 and the laser beam receiver 422 pair can also be placed between the collimating members 141A and 141B. For example, position information detected when each collimating leaf of the collimating member 141B is moved to intersect the laser beam 402 with one side closest to the collimating member 141A may be used when the collimating leaf of the collimating member 141B is moved and positioned towards the collimating member 141A. Although it depends on where the pair for the laser beam 401 and the pair for the laser beam 402 are placed, one of the pairs, for example the pair of the laser beam generator 412 and the laser beam receiver 422 for the laser beam 402, as shown in FIG. 22, can be placed where the laser beam 402 intersects one side closest to the collimating member 141B when each collimating leaf of the collimating member 141A is moved closest to the collimating member 141B. Position information detected at this position may be used when the collimating leaf of the collimating member 141A is moved and positioned towards the collimating member 141B. Similarly, although not shown in FIG. 22, one of the pairs, for example the pair of the laser beam generator 411 and the laser beam receiver 421 for the laser beam 401, can be placed where the laser beam 401 intersects one side closest to the collimating member 141A when each collimating leaf of the collimating member 141B is moved closest to the collimating member 141A. Position information detected at this position may be used when the collimating leaf of the collimating member 141B is moved and positioned towards the collimating member 141A. Such a use of position information may be advantageous when the gear engagement is changed in accordance with the moving direction of each collimating leaf, as shown in. FIG. 10. FIG. 23 is an illustration showing an example of the collimating leaf position detection with four laser beams for each collimating leaf according to the second embodiment of the present invention. As shown in FIG. 23, laser beams 405 to 407 generated from laser beam generators 415 to 417 are received by laser beam receivers 425 to 427, respectively. The laser beams 406 to 407 emanate between the collimating members 141A and 141B. In addition, the laser beam generator 41 and the laser beam receiver 42 pair can be placed so that the laser beam 40 runs through the axis I and between the collimating members 141A and 141B. These laser beams 40 and 405 to 407 may be used to a plurality of reference positions for each collimating leaf of the collimating member 141A. For example, an interval between adjacent laser beams may be the same. The laser beam 407 may run where each collimating leaf of the collimating member 141A is moved closest to the collimating member 141B. Also for example, the laser beam 405 may run where each collimating leaf of the collimating member 141A is moved furthest from the collimating member 141B. The laser beam 40 does not have to run through the axis I. Although not shown in FIG. 23, a similar detection technique can be applied to the position detection of each collimating leaf of the collimating member 141B. The technique shown in FIG. 23 may realize more accurate detection. According to the embodiments of the present invention, the shape of each collimating leaf is not limited to an arc but can be any possible shape. Also the moving direction of each collimating leaf is not limited to a direction along a circular arc centered about an X-ray source but can be any direction, for example, a horizontal direction. In the above embodiments of the present invention, the collimating members 140A and 140B have not been described as including a plurality of collimating leaves. When, however, each of the collimating members 140A and 140B includes a plurality of collimating leaves, the above embodiments of the present invention can also be applied to positioning of such collimating leaves. The embodiments of the present invention described above are examples described only for making it easier to understand the present invention, and are not described for the limitation of the present invention. Consequently, each component and element disclosed in the embodiments of the present invention may be redesigned or modified to its equivalent within a scope of the present invention. Furthermore, any possible combination of such components and elements may be included in a scope of the present invention as long as an advantage similar to those obtained according to the above disclosure in the embodiments of the present invention is obtained. Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. |
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summary | ||
abstract | A container for confining nuclear waste, including a sleeve of longitudinal axis closed at a first longitudinal end by a base and a second longitudinal free end via which the container is designed to be loaded, a plug configured to close the second longitudinal free end tightly, a flange fixed on the inner face of the sleeve to the side of the second longitudinal free end, the plug having at least one external diameter substantially equal to at least one internal diameter of the flange, the plug configured to be welded on the flange such that the welding zone is offset radially towards an interior of the container, relative to an inner face of the sleeve. |
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claims | 1. An in-core-monitor-guide-tube supporting apparatus configured to be disposed in a reactor vessel, the apparatus comprising:a plurality of in-core monitor guide tubes configured to guide a plurality of in-core neutron monitors that measure neutrons in the reactor vessel, and comprising upper tie-plate fixing sections and lower tie-plate fixing sections projecting in a radial direction of the in-core monitor guide tubes;a plurality of control-rod guide tubes being cylindrical in shape, and configured to function as guide tubes in each of which a control rod is driven;a core support plate, wherein each of the plurality of control-rod guide tubes has first and second ends opposite to each other, and the second end is located closer to the core support plate than the first end;a plurality of control-rod-guide-tube fixing sections formed by flanges being substantially rectangular in shape when viewed in an axial direction of the control-rod guide tube, wherein the plurality of control-rod-guide-tube fixing sections are fixed to the second ends of the control-rod guide tubes, and are detachably fixed to an upper surface of the core support plate with bolts without being in direct contact with a lower surface of the core support plate such that each of the control-rod guide tubes is removable in the axial direction of the control-rod guide tube together with the corresponding control-rod-guide-tube fixing section;a plurality of tie plates including an upper tie plate fixed to the upper tie-plate fixing sections of the in-core monitor guide tubes and a lower tie plate fixed to the lower tie-plate fixing sections of the in-core monitor guide tubes, wherein a thickness direction of the tie plates is an axial direction of the in-core monitor guide tubes, wherein a plurality of monitor-guide-tube through-holes and control-rod-guide-tube through-holes are formed in the tie plates in positions corresponding to the in-core monitor guide tubes and the control-rod guide tubes, wherein the control-rod-guide-tube through-holes are formed such that not only the control-rod guide tubes but also the control-rod-guide-tube fixing sections can pass through the control-rod-guide-tube through-holes;an upper-tie-plate rib formed from the upper tie plate towards the core support plate;an upper-tie-plate flange connected to an end in a direction of the core support plate of the upper-tie-plate rib;a lower-tie-plate rib formed from the lower tie plate towards the upper-tie-plate; anda lower-tie-plate flange connected to an end in the top cover direction of the lower-tie-plate rib, connected to the upper-tie-plate flange and fixed to the core support plate. 2. The in-core-monitor-guide-tube supporting apparatus according to claim 1, wherein each of the in-core monitor guide tubes are cylindrical in shape. |
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abstract | A storage/transport container for radioactive material is made by first subdividing a chamber formed between an inner shell and an outer shell into first and second compartments by means of a foraminous partition having a predetermined maximum mesh size. Then an aggregate of a predetermined minimum particle size greater than the predetermined maximum mesh size is introduced into one of the compartments and a suspension of cement and water is introduced into the first compartment such that the aggregate remains in the one compartment and the cement and water flow through the partition into the second compartment. Normally the aggregate and the suspension are both introduced into the same compartment. |
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062367005 | abstract | Downcommer coupling apparatus and methods for replacing a core spray line downcommer pipe coupled to a shroud T-box are described. In one embodiment, the coupling apparatus includes a wedge flange, a wedge, a wedge housing, a pipe seal, a cylindrical pipe, an elbow, a lower flange, and a shroud seal. The downcommer pipe is connected to the coupling apparatus by extending the pipe through the wedge flange, the wedge, and the wedge housing. The wedge has a plurality of flexible thinned segments that extend into the wedge housing to secure the downcommer pipe to the wedge housing. Wedge flange bolts extend through the wedge flange, the wedge, and the wedge housing to rigidly secure the downcommer pipe to the coupling apparatus. Dowel bolts extend through the wedge housing and the downcommer pipe to provide vertical and torsional load transfer from the downcommer pipe to the coupling apparatus. The lower flange is configured to receive the shroud T-box. In one embodiment two lower flange bolts extend through the shroud and into the nutbar to secure the coupling apparatus to the shroud. A third lower flange bolt extends through the shroud and secures the clamp to the t-box. The clamp prevents axial movement of the T-box. |
048428124 | claims | 1. A method for decreasing the rate of deposition of colloidal corrosion products from a nuclear reactor coolant onto an internal reactor surface in contact with the coolant and having surface characteristics that attract such products said method comprising: providing a batch of particles that are suspensible in said coolant and which have active surfaces that possess surface characteristics that attract said corrosion products; and suspending said particles in said coolant whereby said corrosion products deposit on the surfaces of the particles. providing a batch of particles that are suspensible in said coolant and which have surface characteristics that attract said corrosion products; suspending said particles in said coolant whereby said corrosion products deposit on the surfaces of said particles; and removing said particles and the corrosion products deposited thereon from said coolant. 2. A method as set forth in claim 1 wherein said reactor surface and said active particle surfaces comprise zirconium dioxide. 3. A method as set forth in claim 2 wherein said particles are of zirconium oxide. 4. A method as set forth in claim 3 wherein said forming step comprises oxidizing a zirconium metal sponge. 5. A method as set forth in claim 3 wherein said forming step comprises oxidizing a zirconium salt. 6. A method as set forth in claim 3 wherein said forming step comprises oxidizing a zirconium hydride. 7. A method as set forth in claim 2 wherein said forming step comprises vacuum sputtering zirconium oxide onto a particulate substrate. 8. A method as set forth in claim 7 wherein said particulate substrate comprises a material having magnetic susceptibility. 9. A method as set forth in claim 8 wherein said material comprises magnetite. 10. A method as set forth in claim 1 wherein the total surface area of said active surfaces is larger than the area of said reactor surface. 11. A method as set forth in claim 10 wherein the surface area of the active surfaces is at least 20 times larger than the area of said reactor surface. 12. A method for removing colloidal corrosion products from a nuclear reactor coolant comprising: 13. A method as set forth in claim 12 wherein said particles have magnetic susceptibility and said removing step comprises magnetically attracting said particles. 14. A method as set forth in claim 12 wherein said particles have acquired magnetic susceptibility as a result of agglomeration of said corrosion products thereon and said removing step comprises magnetically attracting said composite particles and corrosion products. 15. A method as set forth in claim 12 wheren said removing step comprises filtering said coolant. 16. A method as set forth in claim 13 wherein said removing step comprises filtering said coolant. 17. A method as set forth in claim 14 wherein said removing step comprises filtering said coolant. |
summary | ||
054815797 | description | BEST MODE FOR CARRYING OUT THE INVENTION Referring now to FIG. 1, a representative example of a fuel assembly is shown generally at 10. The assembly includes a plurality of fuel rods 12 forming a bundle. The rods 12 are connected at their upper ends to an upper tie plate 14 and are supported at their lower ends by a lower tie plate grid, generally designated 16, which forms part of a lower tie plate assembly, generally designated 18. Spacers 20 are arranged at a plurality of vertically spaced locations to maintain lateral spacing of the fuel rods 12 relative to one another. The fuel bundle is disposed within a fuel bundle channel 22 whereby coolant water introduced through the bottom nozzle or inlet opening of the tie plate assembly 18 flows upwardly through a flow volume defined by a peripheral wall 24 of the lower tie plate assembly 18, through the lower tie plate grid 16, and then along and about the fuel rods 12 enclosed by the channel 22. As illustrated in FIG. 1, many of the fuel rods 12 are omitted so that water rods 26 and 28 may be seen. The water rods 26 and 28 have lower end plugs which are seated in the lower tie plate grid 16 by any suitable means, such as a threaded connection (not shown). The fuel rods include both full length rods 12 extending between the lower tie plate grid 16 and the upper tie plate 14, and partial length rods 30. The partial length rods 30 extend from the lower tie plate grid 16 to a spacer 20' shown just below the upper ends of the partial length rods 30 in FIG. 1. The spacers 20 located above the partial length rods are provided with enlarged apertures overlying each of the partial length rods. Likewise the upper tie plate 14 includes enlarged apertures overlying each partial length rod. The partial length rods are set forth in both function and purpose in a patent application entitled Two-Phase Pressure Drop Reduction, BWR Assembly Design filed Apr. 4, 1988, No. 176,975, owned by the common Assignee herein. FIG. 2 illustrates a conventional arrangement of fuel rod bosses 32, as viewed from the underside of the upper tie plate 14. In addition to the fuel rod bosses 32, the upper tie plate also provides a pair of diagonally related bosses 34 and 36 for receiving the end plugs of the water rods 28 and 30, respectively. Referring now to FIG. 3, the lower side of an upper tie plate 14' in accordance with this invention includes conventional bosses 32' for the fuel rods, and an enlarged double boss 38 for receiving the end plugs 68 of a pair of water rods 44, 46 (see FIG. 5, 8B) in accordance with this invention. This double boss 38 includes substantially cylindrical boss portions 48 and 50, associated through holes 48A, 50A, respectively, and a connecting web portion 52. The double boss 38 is connected to the other fuel rod bosses 32' in the upper tie plate by a series of relatively narrow webs 54, but it will be appreciated that the double boss extends downwardly below the plane defined by the lowermost edges of fuel rod bosses 32', as seen for example in FIG. 4A. With specific reference to FIGS. 4A and 4B, the double boss 38 includes a center post 56 extending upwardly from a hole 58 at the center point of the web 52, aligned with and laterally between the water rod boss centers 60 and 62. The center post 56 may be assigned for threaded engagement with the upper tie plate. The thickened web 52 also includes a projection 64 extending forwardly of the double boss 38 and formed with a hole 66 on a vertical center axis which is located forwardly of and parallel to the hole 58 and also parallel to the axes of the water rod boss centers 60, 62. Projection 64 extends axially only a relatively small portion of the height of the double boss 38, as best seen in FIG. 4A. As also seen in FIG. 4A the center post 56 is provided with an enlarged diameter removable cap 66. Turning now to FIGS. 5A and 5B, the upper end of a water rod 46 is shown to include an end plug 68 having an upper end formed with a recessed portion or cut-out 70, the shape of which, in plan, is shown in FIG. 5B and the axial extent of which is defined by horizontal shoulders 72, 74. The end plug 68, upon assembly of the upper tie plate 14, will be received in boss hole 50A, for example, and will project above the double boss 38 for cooperation with a latching bar as described further below. Water rod 44 is identical to rod 46 and similar reference numerals are used for the end plug, cut-out, etc. FIGS. 6A through 6C illustrate a latching bar 76 in accordance with a preferred embodiment of the invention, for use with the double boss 38 and water rods 44, 46. The latching bar 76 may be envisioned as a section cut from the center of a cylinder having an upper part 78 of one (smaller) diameter and a lower part 80 of a second (larger) diameter. Thus, the latching bar 76 is formed by flat sides 82 and 84, and curved ends 86, 88 on one side and similarly curved opposite ends 90, 92 on the opposite side. The lower part 80 may be considered as having oppositely extending lower ends 88 and 92. The bar is formed with a vertically extending central through bore 94, having an upper portion 96 with a first relatively larger diameter, and a lower portion 98 with a second, relatively smaller diameter (see FIG. 6C). The latching bar 76 is also formed with a forwardly extending projection 100 (similar to the projection 64) formed with a hole 102, the center line or axis of which is parallel to and forward of the center axis of bore 94. Hole 102 is also located midway between the curved ends 86, 90. The lower surface 104 of the latching bar 76 is provided with a centrally located, elongated rib 106, extending between flat sides 82, 84 and across the center hole 94. Turning now to FIG. 7A, a locking pin 108 is shown which includes a main, cylindrical body portion 110, with an annular groove 112 located between the ends of the pin. The lower end of the pin has an enlarged diameter portion 114, tapering to a rounded point 116. The upper end of the pin has an enlarged, removable head or cap 118. The annular groove 112 is sized to receive a split compression ring 120, shown in FIG. 7B. In a normal assembly procedure, the center post 56 is secured in the hole 58 in the tie plate 14' and the latching bar 76 is then located on the center post, such that the latter extends upwardly through the hole 94. The cap 66 is then reattached to the post 56, thereby securing the latching bar 76 to the tie plate 14'. Locking pin 108 is seated within the hole 102, and it should be noted that cap 118 must be removed so that the pin 108 can be inserted through the hole 102 from below, with enlarged lower end 114 serving as a stop. Once the upper end of the cap protrudes above the upper surface of the latching bar, with ring 120 located as shown in FIG. 8A, cap 118 may be refastened to the pin 108. To install the upper tie plate 14' and to lock the latter to the water rods 44, 46, and with reference also to FIGS. 8A, 8B and 9A, 9B, the upper tie plate 14' is lowered onto the fuel rod bundle including the pair of water rods 44, 46 with respective cut-outs 70 facing each other as best seen in FIG. 8A. A pair of coil springs 122, 124 are seated on horizontal shoulders 123, 125, respectively, at the interface between end plugs 68 and water rods 44, 46. The upper tie plate 14' is moved downwardly over the fuel rods and water rods 44, 46, against the bias of springs 122, 124, and with the end plugs 68 extending upwardly through the boss holes 48A and 50A. Note the angular orientation of the latch bar 76 (in FIGS. 8A and 8B) which is an unlocked assembly position. With reference now to FIGS. 9A and 9B, it will be appreciated that the latch bar 76 can be rotated from the orientation shown in FIGS. 8A and 8B to the orientation shown in FIGS. 9A and 9B such that the lower ends 88, 92 of the latch bar 76 lie within the cut-outs 70 of the end plugs 68. When so located, and upon release of downward pressure on the upper tie plate 14', the coil springs 122, 124 will exert an upward bias on the upper tie plate 14', at the same time biasing the enlarged lower end portion 80 of the latch bar 76 into engagement with shoulders 72', 74' of the cut-outs 70. The upper tie plate 14' is thus secured to the water rods 44, 46 which, in turn, are rigidly secured to the lower tie plate. The locking pin 108 is then pushed downwardly into the aligned hole 102, radially compressing the ring 120 until the ring passes completely through the hole 102, and then springs outwardly below the projection 100 as illustrated in FIG. 9A. Enlarged lower end 114 is now seated within hole 66 in the projection 64. Ring 120 thus prevents accidental detachment of the pin 108, while the pin 108 itself prevents rotation of the locking bar 76 relative to the boss 38 and thus prevents accidental unlocking of the water rods 44, 46 vis-a-vis the upper tie plate 14'. An important feature of the invention is the inclusion of the elongated rib 106 along the lower surface 104 of the latching bar 76. It will be appreciated that the latching bar is thus able to rock back and forth, to the left and to the right as viewed m FIG. 9A and 9B, as it rests on the upper surface of the double boss 38 of the upper tie plate 14'. This rocking action is also facilitated by reason of the fact that the center post 56 has a smaller diameter than bores 96, 98 through the latch bar 76. As a result, radiation growth (in the axial direction) of the respective water rods 44, 46 call occur with equal distribution of the lifting load between the two water rods. In other words, the rocking action of the latch bar 76 distributes the lifting load equally between the two water rods 44, 46 and compensates for unequal initial lengths and unequal changes in length caused by irradiation growth during service. With reference now to FIGS. 10A through 10C, a modified latch bar 106 is shown which is similar in all respects to the latch bar 76, with the few differences noted below To avoid unnecessary duplicative description, only those few differences will be described in detail. The latch bar includes an extended upper portion 128, with a forwardly extending projection 130 at the upper end thereof, including through hole 132. Lower portion 134 is formed with a forwardly extending projection 136 and associated through hole 138, in vertical alignment with through hole 132. The relatively short axial extents of projection 130 and 136 leaves a relatively substantial axial space therebetween, the purpose for which will be described below. With reference to FIGS. 11A-11C, a locking pin 140 for use with latch 126 is shown to include an enlarged head 142 and a shank 144, partially threaded at 146. A threaded nut or ting 148 is adapted for threaded attachment to the shank. The locking pin 140 is initially inserted through the hole 132, at which point coil spring 150 is slipped over the shank 144 followed by threaded attachment of the ring 148. The lower end of shank 144 is then passed through the hole 138 of projection 136 in this way, the locking pin Coy reason of spring 150 acting between projection 130 and ring 148) is biased downwardly. In this alternative embodiment, and with reference also to FIGS. 12A and 12B, after the latch bar 106 is rotated into the locked position against the biasing forces of springs 122, 124, and with the locking pin 140 held in a raised position, the pin is released and allowed to move downwardly into the aligned hole 66 in the projection 64 of the double boss 38. With the pin 140 resiliently urged into the double boss 38, any relative rotation between latching bar 126 and boss 38 is prevented while, at the same time, the biasing force of spring 150 prevents accidental separation of the pin 140. With reference now to FIGS. 13A through 13C, a third alternative latch bar construction 156 is disclosed wherein, in place of a forward projection (of the type shown at 100 in FIG. 6A and at 130 and 136 in FIG. 10A), a pair of horizontal stops 158 and 160 extend laterally from the flat face 162 of a lower enlarged portion 164 of the latch bar. In this embodiment, a spring finger locking pin 166 (FIG. 14) may be inserted into an elongated hole (not shown) in the projection 168 formed in the modified double boss 170 of the upper tie plate 172 This is done, of course, only after the latch bar 156 is rotated to the locking position shown in FIGS. 15A and 15B. Then, when the locking pin 166 is inserted into the upper tie plate 172, it will extend vertically between the stops 158 and 160, which prevents any significant rotation and thus unlocking of the latch bar 156. Locking pin 166 is formed with resilient spring fingers 174, 176 with enlarged ends 178, 180 which protrude from the projection 168 when fully inserted (see FIG. 15A), thereby preventing accidental removal of the pin by a simple lifting or sliding movement. In other words, spring fingers 174, 176 must be squeezed together before the enlarged ends 178, 180 can pass through the projection 168 in a disassembly direction. With reference now to FIGS. 16A-16D, another latch bar is shown at 182. The bar 182 includes an upstanding center portion 184, counterbored at 186 to a shoulder 188, with the bore continuing at a reduced diameter through the remaining thickness of the bar. A pair of laterally extending, generally horseshoe-shaped hooks 190, 192 extend laterally away from the center portion 184, with the hooks 190, 192 having rounded water rod engagement surfaces facing in opposite directions. With specific reference to FIG. 16A, it may be seen that the water rods 194, 196 are formed with annular grooves or cut-outs 196, 198 which are simply reduced diameter portions with beveled entry surfaces 200, 202, respectively. With the latch bar in place on the upper tie plate 204, the former is rotated into the locking position shown in FIG. 16A, and bolt 206 and associated coil spring 208 are employed to secure the latch bar to the tie plate. Insofar as the bolt 206 is threaded into the tie plate 204, and not the latch bar itself, spring biased axial movement of the bar relative to the bolt 204 is permitted to facilitate rotation of the latch bar 182 into the locked position. FIG. 16D illustrates a variation of the latch bar 182. Specifically, the latch bar 208 is formed with squared water tube engagement surfaces within oppositely facing hooks 210, 212 for use with water rods having a square cross-section 214 in the cut-out or grooved portions. This arrangement provides for even greater locking surface area as between the latch bar 208 and the associated water rods. This arrangement also provides for locked angular orientation of the water rods. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. |
048030406 | claims | 1. In a nuclear reactor having a core comprised of a plurality of cladded fuel elements, a coolant having a primary flow through the core over said cladded fuel elements, said fuel elements including fissionable fuel which emits delayed-neutrons (DN) as part of a nuclear chain reaction, a breached fuel element diagnostic apparatus comprising: monitoring means for measuring the coolant primary flow rate and reactor power and generating output signals in response thereto; delayed-neutron monitoring system (DNMS) means for measuring the equivalent recoil area (ERA) of a breach in the cladding of said fuel elements and for continuously monitoring the DN age and DN activity and generating output signals in response thereto, said DN age comprising the sum of a transit time, T.sub.tr, and hold-up time, T.sub.h ; operability validation means for testing the operability of the components of said DNMS means and generating output signals indicating the operability of said components; and a knowledge system comprising a factual knowledge base, a judgment knowledge base and means for said judgmental knowledge base to access said factual knowledge base, said judgmental knowledge base receiving, as input signals, the output signals from said monitoring means, DNMS means and operability validation means, said judgmental knowledge base comprising means for determining the operability of said reactor from a predetermined combination of judgmental knowledge base input signals, said predetermined combination accounting for a nonconstant DN age, and generating output signals in response thereto. a loop flow circuit; a pump for conveying coolant flow from said core through said loop flow circuit and back to said core; at least three separate DN activity detectors proximate to said loop flow circuit; and ERA evaluating means responsive to said DN activity detectors for generating output signals indicating the ERA of a breached fuel element and the DN age. pump testing means for testing the operability of said pump; loop flow measuring means for measuring the flow through said loop flow circuit; thermocouple means for measuring the temperature of the coolant in said monitoring loop; and means for testing the operability of said DN activity detectors. voltage measuring means for measuring the pump voltage; and current measuring means for measuring the pump current. (a) an alarm status in response to input signals indicating: (i) decreasing DN activity and stationary DN age and nondecreasing reactor power, or (ii) decreasing DN activity and increasing DN age and nonincreasing T.sub.h and nonconsistant primary flow rate; (b) said reactor should be scrammed in response to input signals indicating: (i) decreasing DN activity and nonincreasing T.sub.h and no malfunction in the DNMS; (c) said reactor should be manually shut down in response to input signals indicating; (i) increasing DN activity and stationary DN age and nonincreasing reactor power and the ERA is above a predetermined limit, or (ii) increasing DN activity and decreasing DN age and the ERA is above a predetermined limit, or (iii) decreasing DN activity and increasing DN age and increasing T.sub.h and the ERA is above a predetermined limit, or (iv) decreasing DN activity and increasing DN age and nonincreasing T.sub.h and nonconsistent primary flow rate and a malfunction in said DNMS; (d) said reactor should continue to operate in response to input signals indicating: (i) stationary DN activity, or (ii) increasing DN activity and stationary DN age and increasing reactor power, or (iii) increasing DN activity and stationary DN age and nonincreasing reactor power and the ERA is below a predetermined limit, or (iv) increasing DN activity and decreasing DN age and the ERA is below a predetermined limit, or (v) decreasing DN activity and increasing DN age and increasing T.sub.h, and the ERA is below a predetermined limit, or (vi) decreasing DN activity and increasing DN age and nonincreasing T.sub.h and consistently changing primary flow rate, or (vii) decreasing DN activity and stationary DN age and decreasing reactor power. monitoring changes in DN activity with DN activity detecting means and generating an output signal in response thereto; continuously monitoring changes in the, age of DN with DN age monitoring means and generating an output signal in response thereto, said DN age comprising the sum of a transit time, T.sub.tr, and a hold up time T.sub.h ; measuring the equivalent recoil area (ERA) of a breach in the cladding of said fuel elements with ERA measuring mean and generating an output signal in response thereto; testing the operability of said DN activity monitoring means, said DN age monitoring means and said ERA measuring means with operability validation means and generating output signals indicating the operability thereof; measuring the power of said reactor and generating an output signal in response thereto; measuring the primary coolant flow rate and generating an output signal in response thereto; determining and indicating the status of said reactor including whether said reactor should be scrammed, manually shut down, continue to operate or whether an alarm status should be set from predetermined combinations of output signals, said predetermined combination accounting for a nonconstant DN age. determining the operability of said pump; measuring the coolant flow in said loop flow circuit; measuring the temperature of the coolant in said loop flow circuit; and testing the operability of said DN activity detectors. measuring the voltage of said pump; and measuring the current of said pump. indicating an alarm status in response to output signals indicating: (i) decreasing DN activity and stationary DN age and nondecreasing reactor power, or (ii) decreasing DN activity and increasing DN age and nonincreasing T.sub.h and nonconsistent primary flow rate; indicating said reactor should be scrammed in response to output signals indicating: (i) decreasing DN activity and nonincreasing T.sub.h and nonmalfunction in said multiple detector DN monitoring loop; indicating said reactor should be manually shut down in response to output signals indicating: (i) increasing DN activity and stationary DN age and nonincreasing reactor power and the ERA is above a predetermined value, or (ii) increasing DN activity and decreasing DN age and the ERA is above a predetermined limit, or (iii) decreasing DN activity and increasing DN age and increasing T.sub.h and the ERA is above a predetermined limit, or (iv) decreasing DN activity and increasing DN age and nonincreasing T.sub.h and nonconsistent primary flow rate and a malfunction in said multiple detector DN monitoring loop; indicating said reactor should continue to operate in response to output signals indicating: (i) stationary DN activity, or (ii) increasing DN activity and stationary DN age and increasing reactor power, or (iii) increasing DN activity and stationary DN age and nonincreasing reactor power and the ERA is below a predetermined limit, or (iv) increasing DN activity and decreasing DN age and the ERA is below a predetermined limit, or (v) decreasing DN activty and increasing DN age and increasing T.sub.h and the ERA is below a predetermined limit, or (vi) decreasing DN activity and increasing DN age and nonincreasing T.sub.h and consistently changing primary flow rate, or (viii) decreasing DN activity and stationary DN age and decreasing reactor power. 2. The apparatus of claim 1 wherein said judgmental knowledge base output signals indicate whether said reactor should continue to operate, be manually shut down, be scrammed, or whether an alarm status should be set and further comprising display means, responsive to said knowledge system output signal, for translating said signals into conventional human readable form. 3. The apparatus of claim 2 further comprising at least one audible alarm responsive to said knowledge system output signals, said alarm indicating the occurence of predetermined reactor conditions. 4. The apparatus of claim 3 wherein said DNMS is a multiple detector DN monitoring loop comprising: 5. The apparatus of claim 4 wherein said operability validation means comprises: 6. The apparatus of claim 5 wherein said pump is an electromagnetically driven pump and wherein said pump testing means comprises: 7. The apparatus of claim 6 further comprising interactive terminal means communicating with said knowledge system for allowing a human operator to query the status of components of said reactor for operability validation. 8. The apparatus of claim 6 wherein said judgmental knowledge base generates an output signal indicating: 9. In a nuclear reactor having a core comprised of a plurality of cladded fuel elements, a coolant having a primary flow over said cladded fuel elements said elements including fissionable fuel which emits delayed neutrons (DN) as part of a nuclear chain reaction a method of diagnosing the status of said reactor, when said reactor has a breached fuel element, comprising the steps of: 10. The method of claim 9 wherein said DN activity detecting means, said DN age monitoring means and said ERA measuring means define a multiple detector DN monitoring loop comprising a loop flow circuit; a pump for conveying coolant flow from said core through said loop flow circuit and back to said core; at least three separate DN activity detectors proximate to said loop flow circuit; and ERA evaluating means responsive to said DN activity detectors for generating output signals indicating the ERA of a breached fuel element and the DN age wherein the step of testing the operability of said DN activity monitoring means, and said ERA measuring means comprises: 11. The method of claim 10 wherein said pump is an electromagnetically driven pump and wherein the step of determining the operability of said pump comprises: 12. The method of claim 11 wherein the step of determining and indicating the status of said reactor comprises: 13. The method of claim 12 further comprising displaying said reactor status in human readable form. 14. The method of claim 13 further comprising sounding audible alarms indicating predetermined reactor conditions. 15. The method of claim 14 further comprising the step of communicating with said knowledge system to query the status of components of said reactor. |
claims | 1. A nuclear power plant having a nuclear reactor, comprising: a first steam supply system connected between the nuclear reactor and a steam turbine, a second steam supply system branched from the first steam supply system and connected downstream of the steam turbine, a first valve in the first steam supply system for adjusting steam pressure to the steam turbine, a second valve in the second steam supply system for adjusting branched steam pressure, a first controller that generates a first control signal for the first valve and a second control signal for the second valve, and a second controller that generates a third control signal for the second valve, the third control signal having priority over the second control signal; and two controlling valves operating independently from one another, wherein said second valve is configured to be operated by at least one of said two controlling valves. 2. A nuclear power plant, according to claim 1 , wherein each of said two controlling valves are controlled by a different control signal. claim 1 3. A nuclear power plant, according to claim 1 , wherein said two controlling valves comprise a servo valve and a fast acting solenoid valve. claim 1 4. A nuclear power plant, according to claim 3 , wherein said servo valve is controlled by said second control signal and wherein said fast acting solenoid valve is controlled by said third control signal. claim 3 5. A nuclear power plant, according to claim 3 , wherein said fast acting solenoid valve controls operation of said second valve when said servo valve is malfunctioning. claim 3 6. The nuclear power plant according to claim 1 , wherein the third control signal is generated if the second valve is closed and the pressure in the steam turbine decreases. claim 1 7. The nuclear power plant according to claim 1 , wherein the third control signal includes an opening signal for the second valve. claim 1 8. The nuclear power plant according to claim 7 , wherein the third signal is generated if the second valve is closed within a predetermined time period after receiving the second signal. claim 7 9. The nuclear power plant according to claim 7 , wherein the third signal is released if the second valve is opened within a predetermined time period after receiving the third signal. claim 7 10. The nuclear power plant according to claim 1 , wherein the second valve is multiplexed, and each second valve accepts the second signal and the third signal. claim 1 11. The nuclear power plant according to claim 7 , wherein the third signal is released if the steam pressure from the nuclear reactor is a predetermined value. claim 7 12. The nuclear power plant according to claim 6 , wherein the third signal is generated only once. claim 6 13. The nuclear power plant according to claim 1 , wherein the third control signal is generated at least when the plant is not in regular operating mode. claim 1 14. The nuclear power plant according to claim 1 , wherein the third control signal acts to avoid that both the first valve and the second valve are closed. claim 1 |
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abstract | A self-regulating inherently safe apparatus for generating neutrons is described herein that includes a reaction chamber that sustains neutron generation when filled with a liquid fissionable material and an expansion chamber that dampens neutron generation from the liquid fissionable material in response to expansion of the liquid fissionable material into the expansion chamber. Consequently, the apparatus may substantially dampen neutron generation for operating temperatures above a nominal operating temperature without requiring active or external control and inherently limit neutron generation to a maximum desired output power. Also described herein is a self-regulating system and corresponding method for extracting energy from fissionable material that includes a neutron generator that generates neutrons from a liquid fissionable material and a sub-critical collection of fissionable material that generates a non-sustaining plurality of fission events from neutrons received from the neutron generator. |
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RE0347086 | summary | BACKGROUND OF THE INVENTION This invention relates to scanning microscopes used for imaging the topography of surfaces and, more particularly, to a scanning ion conductance microscope comprising, a reservoir holding a sample to be scanned therein; a micropipette having a tip communicating with a shaft; an electrolyte solution disposed within the reservoir covering the sample and disposed within the tip and shaft of the micropipette; a first microelectrode disposed in the shaft in electrical contact with the electrolyte therein; a second microelectrode disposed in the reservoir in electrical contact with the electrolyte therein; scanning means for scanning the tip of the micropipette over a top surface of the sample in a scanning pattern; voltage means for applying a voltage across the first and second microelectrodes; current means for measuring the current flowing between the first and second microelectrodes and for supplying an indication of the current at an output thereof; and, control logic means having an output connected to the scanning means and an input connected to the output of the current means for causing the scanning means to set the height of the tip at a desired distance above the top surface and for outputting data of interest related to the top surface as it is scanned. The family of scanning probe microscopes that have been introduced to the scientific community of recent years is broadening the frontiers of microscopy. As typified by the greatly simplified general example of FIG. 1, these microscopes scan a sharp probe 10 over the surface 12 of a sample 14 to obtain surface contours, in some cases actually down to the atomic sale. The probe 10 may be affixed to a scanning mechanism and moved in a scan pattern over the surface 12 or alternately (and equally effectively because of the small sizes involved) the probe 10 may be stationary with the sample 14 mounted on a scanning mechanism that moves the surface 12 across the probe 10 in a scanning pattern. The point 16 of the probe 10 rides over the surface 12 as the probe is moved across it as indicated by the arrow 18. As the point 16 follows the topography of the surface 12, the probe 10 moves up and down as indicated by the bi-directional arrow 20. This up and down movement of the probe 10 is sensed to develop a signal which is indicative of the z directional component of the 3-dimensional surface 12. The use of a piezoelectrically driven tube to affect the x-, y-, and z-directional movements employed in the scanning process is generally accepted in such devices and such well known equipment is preferred for use in the scanning aspects of this invention as well. Various methods are employed to sense the vertical movement of the probe 10. Where the sample 14 is of an electrically conductive material and the scanning is conducted in a non-conductive environment such as air, current flow between the probe point 16 and the surface 12 can be employed to control the vertical position of the probe 10. The vertical control signal then supplies the z-directional component. For non-conducting materials it is more common to measure the vertical deflection of the probe 10 directly in order to develop the z-directional component. While the contact type of scanning probe microscope as described above works well in certain environments, in other environments it is virtually worthless. This is particularly true where the sample is of a soft material which cannot be subjected to the contacting probe described above. While the biasing force of the probe against the surface of the sample in such prior art apparatus is exceedingly small, it is still there and the probe itself is quite sharp in order to follow the contours demanded of it. Accordingly for example, if a soft membrane is contact scanned, it is torn by the probe. Additionally, despite their various attributes, such prior art scanning microscopes can only supply a visualization of the surface topography. They cannot show, for example, ion flow capabilities of and through the surface under examination. Wherefore, it is an object of the present invention to provide a non-contacting scanning microscope which can be used to display an indication of the surface topography of materials which cannot be scanned with a contacting probe. It is another object of the present invention to provide a scanning microscope which can be used to display an indication of ion flow capabilities of and through a surface under examination. Other objects and benefits of this invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it. SUMMARY The foregoing objects have been achieved in the scanning ion conductance microscope capable of providing both topographic and ion conductance information about a sample of the present invention comprising, a reservoir holding a sample to be scanned therein; a micropipette having a tip communicating with a shaft; an electrolyte solution disposed within the reservoir covering the sample and disposed within the tip and shaft of the micropipette; a first microelectrode disposed in the shaft in electrical contact with the electrolyte therein; a second microelectrode disposed in the reservoir in electrical contact with the electrolyte therein; scanning means for scanning the tip of the micropipette over a top surface of the sample in a scanning pattern; voltage means for applying a voltage across the first and second microelectrodes; current means for measuring the current flowing between the first and second microelectrodes and for supplying an indication of the current at an output thereof; control logic means having an output connected to the scanning means and an input connected to the output of the current means for causing the scanning means to set the height of the tip at a desired distance above the top surface and for outputting data of interest related to the top surface as it is scanned; feedback means connected between the scanning means and the control logic means for providing the control logic means with an indication of a z-directional component of the position of the tip of the micropipette; and wherein, the control logic means includes first logic for causing the scanning means to position the tip of the micropipette at a distance above the top surface which will maintain the ion conductance between the first and second electrodes at a constant value which will cause the tip to follow the top surface in close non-contacting proximity thereto whereby the data of interest output by the control logic means reflects the topology of the top surface; and, the control logic means includes second logic for causing the scanning means to scan the tip of the micropipette in a plane parallel and close adjacent above the top surface whereby the data of interest output by the control logic means reflects the ion conductance of the top surface at the positions of the tip. In an alternate embodiment, there are a plurality of the micropipettes disposed to form a multi-barrel scanning head and a plurality of the first microelectrodes are disposed in respective ones of the micropipettes. Each of the microelectrodes is specific to a different ion whereby when the second logic of the control logic causes the scanning means to scan the tip of the micropipette in a plane parallel and close adjacent above the top surface, the data of interest output by the control logic means reflects the ion conductance of the top surface at the positions of the tip of each of the micropipettes. |
055442048 | claims | 1. A process for the automatic stabilization of the reactivity of a neutron chain reaction of a nuclear reactor having a core containing a main body of fissionable fuel and which is fixed in position in a core vessel, said main body of fissionable fuel generating a neutron-flux zone between two horizontal planes providing said, said process comprising the steps of: (a) providing a tubular chamber extending through said neutron-flux zone, said tubular chamber being closed on each end by sieves and containing fissionable fuel particles constituting a minor body of fissionable fuel, said tubular chamber having an upper end substantially at an upper one of said planes and a lower end extending below a lower one of said planes; (b) entraining said fissionable fuel particles of said minor body of fissionable fuel upwardly in said tubular chamber in a coolant flow from a location in said chamber below said zone into said zone, said coolant flow passing into said chamber through one of said sieves at said lower end and out of said chamber through another of said sieves at said upper end; (c) providing at said location below said zone and said lower one of said planes a space in said chamber for accumulation of said fissionable fuel particles out of said neutron-flux zone, said coolant flow maintaining said fissionable fuel particles of said minor body of fissionable fuel in said zone; and (d) automatically causing said fissionable fuel particles of said minor body of fissionable fuel to collect by gravity in said space upon a failure of upward entrainment of said fissionable fuel particles of said minor body of fissionable fuel in said coolant flow, thereby reducing the reactivity of said chain reaction, said space and the fissionable fuel particles of said minor body of fissionable fuel collected therein in step (d) being dimensioned to influence said reactivity by substantially 0.5% to 1%. 2. The process defined in claim 1 wherein said fissionable fuel particles of said minor body of fissionable fuel are coated nuclear fuel particles, said coolant flow is a stream of coolant branched from a main coolant stream of said nuclear reactor and passes through said chamber in a direction opposite an action of gravity on said particles in said chamber, and said coolant flow is discharged from a top of said chamber upon sieving of said particles therefrom. 3. The process defined in claim 2 wherein said particles of said minor body of fissionable fuel are formed by nuclear fuel of a greater enrichment than nuclear fuel of said main body. |
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039327485 | claims | 1. A method of determining the distance between an area under fire and the muzzle of the weapon by means of autoradiography of the irradiated firing residues on this area, comprising (a) firing at several carrier areas from various distances, (b) subsequently activating the carrier areas by neutron irradiation, (c) subsequently contacting the carrier areas with a film sensitive to nuclear radiation, (d) developing the film, (e) preparing an autoradiograph of a firing trace to be investigated by following steps (b) through (d), (f) comparing the series of autoradiographs produced after development on the film with the autoradiograph produced of the firing trace to be investigated. 2. Method as claimed in claim 1, wherein the carrier areas are made of the same material as the area under fire. 3. Method as claimed in claim 1, wherein the firing residues are transmitted from the carrier areas and the area under fire after activation onto to a new carrier from which the autoradiographs are made. 4. Method as claimed in claim 3, wherein the area with the firing residues is contacted with an adhesive foil under pressure, subsequently area and foil are separated from each other and the adhesive side of the foil is covered with another foil. 5. Method as claimed in claim 4, wherein the distance standard used for evaluation of the autoradiographs is the total density measured together with the number of particles by means of image analyzers. |
044141777 | description | BEST MODE FOR CARRYING OUT THE INVENTION The drawing illustrates a single length of tubing in the system. It is to be understood that the system will normally consist of a multiplicity of such tubes. Each would monitor a different sensing elevation within a reactor vessel. The length of small diameter metal tubing 10 within the pressurized vessel has an open end 11 at the sensing location where the condition of coolant is to be monitored. The tubing is brought out of the vessel to its exterior. This will be typically accomplished by a welded vessel penetration through a wall section 12. The portion of the length of tubing 10 exterior to the vessel walls 12 is shown as being wrapped in insulation 13, which prevents cooling of the liquid. The exterior or outer end of the length of tubing 10 is closed, and while liquid and/or gaseous coolant might enter it, no coolant flows through the length of tubing. As generally illustrated in the drawings, the tubing would lead to an insulated housing 14 which mounts a pressure transducer 15 capable of producing signals as a function of the pressure sensed within housing 14. The transducer 15 is operably connected to the interior of the length of tubing 10, and pressure sensed by it will be identical to the pressure at the open end 11, less the static head difference, which can be electronically compensated. The thermocouple leads 16 are preferably brought from the interior of the vessel through the interior of the length of tubing 10. The leads 16 and leads 17 from the pressure transducer 15 are preferably directed to temperature and pressure readout devices shown respectively at 18 and 20. The sensed signals are fed to an analyzer 21, which might be a microprocessor programmed to compare the magnitude of each signal to known values representing saturated temperatures of the coolant at the measured pressures. Any desirable output can be obtained from the analyzer 21. As an example, it might be provided with annunciators 22, 23, and 24 which respectively signal normal coolant conditions, abnormal void fraction conditions, and low liquid level. During normal use of the reactor with the coolant pumps operable, the appratus would provide constant measuring of temperature and pressure within the vessel interior. When either the temperature or pressure measured by the apparatus exceeds the programmed limits, the system will annunciate to indicate a possible condition of two-phase flow. If the analyzer determines that superheated steam exists at the open end 11 of the length of tubing 10, the annunciator 24 would indicate that liquid level has dropped below the elevation of the open end 11. This system is also capable of sensing liquid level by placing the open ends 11 of a number of lengths of tubing 10 at incremental elevations within the vessel to be monitored. If the primary reactor coolant pumps are turned off, the void fraction flow that commonly occurs within the reactor vessel will separate. As the liquid coolant level falls below the open end 11 of each length of tubing 10 the sensed temperature and pressure values for that individual length of tubing 11 will become superheated steam. This will be recognized by the analyzer 21 and indicated by annunciator 24. By relating this condition to the known elevation of the open end 11, liquid level can be accurately determined. Practical utilization of this system in a reactor core requires space availability, as well as physical access into the vessel and associated piping. Current design of boiling water and pressurized water reactors have sufficient vertical space in their cores for ten to eighteen sensing lines comprising lengths of tubing as generally discussed. It appears practical to transition such lines out of the vessel through the existing borate injection standpipe or other possible locations, such as flange fittings. When designing the apparatus, it is necessary to assure an adequately prompt response to void fractions caused by rapidly dropping pressure because of voiding in the length of tubing 10. Since the system is designed for detection of small and medium break loss of coolant accidents, there should not be a rapid drop in coolant loop pressure. However, if these were to occur, the pressure transducer 15 would reduce erratic and dropping pressure readings. The analyzer 21 can be programmed to activate the appropriate annunciator when such conditions occur. The problem of response time could be eliminated completely by sizing the interior of the length of tubing 10 sufficiently large to preclude slug-flow effects. In other words, the inside diameter of the tubing would be sufficiently larger that the surface tension of the liquid fluid within the length of tubing would be insignificant and not impede fluid flow, whether the coolant is at a gaseous or liquid state. Another approach to this condition would be to backfill the sensing tube with inert gas and use a movable plug to separate the gas backfill from the reactor fluid. |
claims | 1. A dynamic pattern generator for controllably reflecting charged particles, the apparatus comprising:a controllable light emitter array configured to emit a pattern of light;an optical lens configured to demagnify the pattern of light; andan array of light-sensitive devices configured to receive the demagnified pattern of light and to produce a corresponding pattern of surface voltages. 2. The dynamic pattern generator of claim 1, wherein the charged particles comprise electrons. 3. The dynamic pattern generator of claim 1, further comprising an electronic driver circuit coupled to the light emitter array for controllably driving the light emitter array. 4. The dynamic pattern generator of claim 3, further comprising a flip-chip bond between the light emitter array and the electronic driver circuit. 5. The dynamic pattern generator of claim 1, wherein the light emitter array comprises an array of resonant-cavity light emitting diodes (RCLEDs). 6. The dynamic pattern generator of claim 5, wherein the array of RCLEDs comprises an array of RCLED mesas configured on a thin substrate. 7. The dynamic pattern generator of claim 6, further comprising solder bumps electrically connecting the RCLED mesas with contact pads of a driver array circuit. 8. The dynamic pattern generator of claim 1, wherein the light emitter array comprises an array of vertical light emitting diodes. 9. The dynamic pattern generator of claim 1, wherein the light emitter array comprises an array of vertical-cavity surface emitting lasers. 10. The dynamic pattern generator of claim 1, wherein the lens demagnifies the pattern of light by twenty times or more. 11. The dynamic pattern generator of claim 1, wherein the array of light-sensitive devices comprise a photodiode array. 12. The dynamic pattern generator of claim 1, wherein the array of light-sensitive devices comprises pixels of 0.5 micron by 0.5 micron size or smaller. 13. The dynamic pattern generator of claim 1, wherein the reflected charged particles are demagnified and projected onto a substrate for maskless lithography. 14. A method of controllably reflecting charged particles, the method comprising:controllably emitting a pattern of light from a light emitter array;demagnifying the pattern of light using a lens;receiving the demagnified pattern of light by an array of light-sensitive devices; andproducing a corresponding pattern of surface voltages for reflecting the charged particles. 15. The method of claim 14, wherein the charged particles comprise electrons. 16. The method of claim 15, wherein the reflected electrons are demagnified and projected onto a substrate for maskless lithography. 17. The method of claim 14, wherein the pattern of light is demagnified by at least twenty times. 18. The method of claim 14, wherein the array of light-sensitive devices comprises pixels of 0.5 micron by 0.5 micron size or smaller. 19. An apparatus for controllably reflecting electrons, the apparatus comprising:means for controllably emitting a pattern of light from a light emitter array;means for demagnifying the pattern of light using a lens;means for receiving the demagnified pattern of light by an array of light-sensitive devices; andmeans for producing a corresponding pattern of surface voltages for reflecting the electrons. 20. The apparatus of claim 19, wherein the reflected electrons are demagnified and projected onto a substrate for maskless electron beam lithography. |
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