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	description	This application is a National Stage of International Application No. PCT/RU2015/000364 filed Jun. 11, 2015, claiming priority based on Russian Federation Patent Application No. 2014123858 filed Jun. 11, 2014, the contents of all of which are incorporated herein by reference in their entirety. The invention relates to nuclear power industry and nuclear reactor plants, and more particularly to nuclear reactor plants with liquid-metal coolants. At the same time, this invention may also be applied to various non-nuclear reactor plants. One of the key problems of nuclear reactor plants with liquid-metal coolants is corrosion of reactor structural materials. To prevent corrosion, the technique for formation of protective oxide coatings is used. The corrosion resistance of reactor structural materials, for example, steel, depends on the integrity of these coatings. It should be noted that the mentioned problem may occur both in nuclear reactor plants with non-liquid-metal coolants and in non-nuclear reactor plants. Although, this invention is described in relation to nuclear reactor plants with liquid-metal coolants, it also can be used both in nuclear reactor plants with non-liquid-metal coolants and in non-nuclear reactor plants. Oxygen is traditionally used for formation of oxide coatings. When the reactor plant is in operation, the components of structural materials, such as iron, chrome and others, diffuse into coolant. Due to the fact that the mentioned components of structural materials have higher chemical affinity for oxidizers, for example, oxygen, the increase in concentration of iron, chrome and other components of structural materials in the coolant causes reduction in concentration of oxidizers, such as oxygen. It may lead to dissolution of protective oxide coatings, which will significantly increase the corrosion rate. Consequently, to reduce the corrosion rate to a minimum level ensuring the long-term operation of a reactor plant in safe mode, it is required to supply oxidizer to the coolant to increase its concentration to such a level when the protective oxide coatings are not dissolved in the coolant. In this regard, oxygen is a quite suitable oxidizer as it can be supplied to a coolant in the form of gas or oxides of different materials, for example, those of which the coolant is made. In view of the above, it is important to control and maintain the required concentration of oxidizer in the coolant, in particular, concentration of oxygen, so that the protective oxide coatings on the inner surface of reactor contacting with the coolant are not dissolved in the coolant, thereby preventing corrosion of reactor materials. As oxygen is constantly consumed for oxidation of iron, chrome and other components of construction materials diffusing into coolant, to maintain the concentration of oxygen within the specified range ensuring the minimum corrosion rate of reactor materials, oxygen shall be supplied to the coolant, for example, when the lower limit of the specified range is reached or oxygen concentration is reduced below the admissible level. Patent RU2100480 (issued on Dec. 27, 1997) discloses such methods for increase of oxygen concentration in the coolant as injection of oxygen admixed with inert gas to the protective gas above the coolant surface or directly to coolant, as well as dissolution of coolant component oxides in the coolant. However, the methods described in the mentioned patent have such disadvantages as impossibility to control oxygen injection into the coolant (increase of oxygen concentration in the coolant), namely: start/end of oxygen supply and dissolution of coolant oxides, measuring rate of oxygen concentration in the coolant, i.e. volumes of oxygen to be supplied and coolant oxides to be dissolved. Besides, when supplying the oxygen admixed with inert gas to the volume of protective gas above the coolant surface, the rate of oxygen diffusing into the coolant is relatively low, and the risk of formation of oxide film (crust) on the coolant surface is increased with rise of oxygen fraction admixed with inert gas. Patent RU2246561 (issued on Feb. 20, 2005) discloses the method and device for controlled dissolution of coolant oxides in the coolant, but does not include any data on the possibility for control of oxygen injection into the coolant in the gaseous form. The purpose of this invention is to provide the method and device for control of oxygen concentration in the reactor plant, and more particularly, in the coolant of a nuclear reactor plant supplied in the gaseous form. Moreover, the purpose of this invention is to ensure efficient and safe preparation and operation of nuclear reactor plant in different modes, such as passivation mode of reactor's structural materials, normal operation mode, abnormal mode during destruction of protective oxide coatings and others. In view of the above, other objectives of the invention are to switch between the methods for control (increase) of oxygen concentration in the coolant, improve safety of equipment used for oxygen concentration control and provide the equipment control system ensuring the safe preparation and operation of nuclear reactor plant in all modes. The purpose of this invention is achieved by using the method for control of oxygen concentration in the coolant of a reactor plant containing a reactor, a coolant located in the reactor, a gas system with an outlet to the near-coolant space of reactor, a mass-exchange apparatus installed in the coolant which holds solid-phase coolant oxides and is adapted to flowing of coolant through it, a disperser installed partially in the coolant and partially in the near-coolant space and adapted to gas supply from the near-coolant space to the coolant, and an oxygen sensor in the coolant. Using the method, proceed as follows: estimate the oxygen concentration in the coolant based on the data received from oxygen sensor in the coolant; compare the estimate of oxygen concentration with the permissible value; if the estimated change in the oxygen concentration in the coolant shows reduction in concentration, compare the reduction value and\or rate with the corresponding threshold value; if the estimate of oxygen concentration in the coolant is below the permissible value and the estimated reduction value and\or rate of oxygen concentration is below the corresponding threshold value, activate the mass-exchange apparatus; if the estimate of oxygen concentration in the coolant is below the permissible value and the estimated reduction value and/or rate of oxygen concentration is above the corresponding threshold value, supply oxygen-containing gas from the system to the near-coolant space and/or activate the disperser. If after the activation of mass-exchange apparatus or supply of oxygen-containing gas, and activation of disperser the estimated concentration of oxygen in the coolant reaches or exceeds the allowable value, the preferable option of the method suggests deactivation of the mass-exchange apparatus or disperser and/or stopping the supply of oxygen-containing gas to the near-coolant space from the gas system. Besides, oxygen-free gas can be supplied from the gas system to the near-coolant space in addition to ceasing the supply of oxygen-containing gas from the gas system to the near-coolant space. The purpose of this invention is also achieved by using the control system of oxygen concentration in the coolant of reactor plant which includes a reactor, a coolant located in the reactor, a gas system with an outlet to the near-coolant space of the reactor, a mass-exchange apparatus installed in the coolant which holds solid-phase oxides of the coolant and is adapted to flowing of coolant through it, a disperser installed partially in the coolant and partially in the near-coolant space and adapted to gas supply from the near-coolant space to the coolant, and an oxygen sensor in the coolant. The control system includes: module for estimating the oxygen concentration in the coolant designed so as to receive data from an oxygen sensor in the coolant, to estimate oxygen concentration based on the received data on oxygen concentration in the coolant and transmit the estimation to the module for comparing the estimate of oxygen concentration in the coolant with the permissible value; module for comparing the estimate of oxygen concentration in the coolant with the permissible value adapted to acquire the estimates of oxygen concentration in the coolant from the oxygen concentration estimation module and compare it with the permissible value; module for estimating the reduction in oxygen concentration in the coolant adapted to estimate the reduction value and/or rate of oxygen concentration in the coolant as well as to transmit the estimated reduction value and/or rate of oxygen concentration in the coolant to the module for comparing the estimated reduction in oxygen concentration in the coolant; module for comparing the estimated reduction in oxygen concentration in the coolant adapted to receive the estimated reduction value and\or rate of oxygen concentration in the coolant and its comparison with the corresponding threshold value; module for control of mass-exchange apparatus configured to activate the mass-exchange apparatus in case the estimated oxygen concentration in the coolant is below the permissible value and the estimated change value and/or rate of oxygen concentration is below the corresponding threshold value; module for control of gas system and/or disperser configured to activate the gas system with the supply of oxygen-containing gas to the near-coolant space and/or activate the disperser in case the estimated oxygen concentration in the coolant is below the permissible value and the estimated change value and/or rate of oxygen concentration is above the corresponding threshold value. In one of its adaptations, the module for estimating the reduction in oxygen concentration in the coolant can be configured to estimate the reduction value and/or rate of the oxygen concentration in the coolant based on the estimated oxygen concentration in the coolant received from the module for estimating the oxygen concentration in the coolant. Besides, some versions of the module for comparing the estimate of reduction in oxygen concentration in the coolant can be adapted to determinate the reduction in oxygen concentration in the coolant and transmit information to the module for comparing the estimate of reduction in oxygen concentration in the coolant and/or to the module for control of the mass-exchange apparatus and the module for control of the gas system and/or disperser. In its preferable embodiment, the module for control of mass-exchange apparatus is adapted to deactivate the mass-exchange apparatus and the module for control of the gas system and disperser and/or the module for ceasing the supply of oxygen-containing gas from the gas system to the near-coolant space, if the estimate of oxygen concentration in the coolant assumes or exceeds the permissible value. Besides, the module for control of gas system and disperser can be adapted to supply oxygen-free gas from the gas system to the near-coolant space. The purpose of this invention is also achieved by using the nuclear reactor plant which includes: a reactor, a coolant located in the reactor, a gas system with an outlet to the near-coolant space of the reactor, a mass-exchange apparatus installed in the coolant which holds solid-phase oxides of the coolant and is adapted to the flowing of the coolant through it, a disperser installed partially in the coolant and partially in the near-coolant space and adapted to supply gas from the near-coolant space to the coolant, and an oxygen sensor in the coolant. The mentioned reactor plant is adapted to control hydrogen concentration in the coolant in accordance with a method or system as per any above-described options. This invention enables to achieve such technical result as provision of the method and device for control of oxygen concentration in the reactor plant, in particular, in the coolant of a nuclear reactor plant supplied in the gaseous form. Besides, it enables to achieve such technical result as provision of efficient and safe preparation and operation of nuclear reactor plant in different modes, such as passivation mode of reactor's structural materials, normal operation mode, abnormal modes during destruction of protective oxide coatings and others. Apart of the above mentioned, the following technical results have been achieved: switching between the methods for control (increase) of oxygen concentration in the coolant; improvement of safety, reliability and extension of the operating life of the equipment used for control of oxygen concentration, and provision of the equipment control system ensuring the safe preparation and operation of nuclear reactor plant in all modes. This invention applies to a reactor plant (for example, nuclear reactor plant) which includes, as per FIG. 1, a reactor 101, a coolant 104, a gas system 108, a mass-exchange apparatus 114, a disperser 112 and an oxygen concentration sensor 110, in the coolant 104. A reactor 101 is a tank, the walls 102 of which are made of materials with adequate mechanical, thermal, radiation and other types of durability necessary for safe operation of a reactor plant, such as steel. Safe operation of reactor plants is of particular importance due to the fact that the reactor core 103 contains radioactive materials which release energy in the course of radioactive fission. A certain quantum of this energy in the form of heat is transferred to the coolant 104 located in the reactor and contacting with the core (i.e. the radioactive materials are located in the coolant), and further transported to the heat exchanger 107 where the heat energy is transferred to other materials (for example, water, steam and other heat-absorptive materials), at a distance from the radiation source. In some embodiments of the invention the heat exchanger can be a steam generator designed to generate steam which can be used for heating of other media or activation of turbines. After the heat exchanger 107, the heat energy is transferred through utility systems beyond the reactor without hazard of radiation contamination which, therefore, is concentrated within the reactor. In connection to this, due to drastic, undesired and long-term effects of radiation contamination of surrounding areas the special emphasis is placed on the strength and safe operation of the reactor. It is preferable to circulate the coolant in the reactor 101, in the circuit covering the core and the heat exchanger, for long-term and efficient transfer of heat from the core 103 to the heat exchanger 107 of the reactor. Pumps can be used for circulation (not shown in FIG. 1). One of the important factors to retain the reactor strength through time is preventing or mitigating corrosion of structural materials of reactor walls 102, its reinforcing, fixture, strength and other elements to the admissible level. The mentioned factor shall also be considered when a coolant from liquid metals such as sodium, lithium, lead, bismuth and etc. is used as the coolant 104. Heavy metals (lead, bismuth) have an advantage over light-weight metals because of their increased safety, particularly, in terms of low fire hazard. Besides, the coolants made of heavy metals have such an advantage as stability of their properties in case of water ingress. Naturally, the physical and chemical properties of such a coolant will change in case of water ingress, but such changes will be insignificant and allow further operation. This can be useful for improving safety of a reactor plant in view of possible accidents or leakages of equipment where water is present or flows in the liquid form or in the form of steam, for example, heat exchangers or steam generators. Even if a heat exchanger or steam generator is faulty (have a leakage), the reactor plant can be operated before repair or replacement of faulty (leaking) equipment, as the coolant made of heavy metals allows such operation mode due to the insignificant (uncritical) dependence of its physical and chemical properties on injection of liquid or vaporous water. To reduce corrosion effect on structural materials of the reactor, it is considered advantageous to create oxide coatings on the boundary between the coolant and structural material, for example, by supplying oxygen or oxygen-containing materials to the coolant; upon that such materials can be transferred by the coolant towards the reactor walls where oxygen can react with the structural materials (for example, steel) and form an oxide in the form of an oxide film. An additional advantage of such anticorrosion protection is reduction of heat-exchange rate between the coolant and reactor walls due to low thermal conductivity of oxides. Oxygen can be injected into the coolant in several ways. To implement one of the ways, the reactor plant shall include a gas system 108 with an outlet to the reactor 101 to the space 106 near the coolant 104 (in the preferable embodiment shown in FIG. 1, above the coolant). Coolant 104 occupies only a part of the reactor tank to reduce the hazard of reactor depressurization due to thermal expansion of the coolant during heating. The upper part 106 of the reactor tank located above the surface 105 (“level”) of the coolant 104 shall be filled with inert gas (He, Ne, Ar) or a mixture of inert gases to prevent corrosion and undesired chemical reactions. Gas system 108 is provided to supply gas to the space above the coolant or near it, which in other embodiments can be a space separated from the coolant reservoir. Gas system 108 includes pipelines (pipes), isolation valves 109, filters, pumps and other equipment commonly used in gas systems and known from the background of the invention. The gas system is connected to the sources of inert gases and oxygen and is configured to mix them. Thus, the gas system is able to supply not only an inert gas or a mixture of inert gases. To resist corrosion, an oxygen-containing gas, for example, a mixture of an inert gas and oxygen (pure oxygen is of serious hazard to structural materials of the reactor and liquid-metal coolant) can be supplied to the near-coolant space of the reactor. Gaseous mixture may contain, ⅕ or less of oxygen, such ratio demonstrates sufficient activity of oxygen contained in the gas, without unwanted risks for structural materials and the coolant. Particularly, inert gases and oxygen can be supplied from the tanks with pressurized gases to pipelines or mixing tanks of the gas system by adjusting the isolation valves (for example, valves with electrical or hydraulic actuators) or activating the impelling pumps which pump these gases from storage tanks to the required mixing tanks or pipelines, under relevant conditions of isolation valves on interconnecting pipes/pipelines. These gases or their mixtures can be supplied to the near-coolant space of the reactor by means of pipelines from the storage or mixing tanks by means of proper control of the isolation valves and/or pumps (if the pumps can not be activated, the gas may be supplied by means of increased pressure under which they are kept in the corresponding tanks). If the oxygen-containing gas is supplied to the near-coolant space of the reactor, oxygen can diffuse into coolant or oxidize its components, for example, bismuth and lead; and the coolant oxides can be carried over inward the reactor by means of convection or circulation where they can oxidize the mentioned components upon contact with the components of structural materials such as Fe, Cr, Zn and others. It happens due to the fact that those components have higher chemical affinity for oxygen than bismuth and lead (for example, thereby recovering these coolant components). Such a method for sustaining oxide films on the surface of structural materials to prevent corrosion can be used, for example, in steady-state modes when the consumption of oxygen for oxidation of structural material components complies with flow rate of oxygen delivered from the near-coolant space through the surface of the coolant (and the implementation of this method for the control of oxygen concentration in the coolant can be accounted by the control system of the reactor plant). However, this method for sustaining oxygen concentration in the coolant necessary for anticorrosion protection has such disadvantages as delayed action and low controllability of the process resulting from low efficiency of passive penetration of oxygen into the liquid coolant from gas as well as impossibility of oxygen concentration buildup in the coolant due to the increase of oxygen fraction in gas owing to high adverse impact of oxygen on structural materials in the near-coolant space of reactor and the increase of hazard for formation of oxide film on the coolant surface. Therefore, the injection of oxygen into the coolant by diffusing through the coolant surface provides almost infinite source of oxygen. But such method for the increase of oxygen concentration in the coolant is not very accurate, but slow and uncontrollable. Corrosion resistance of structural materials requires a controlled, accurate and faster method for increase of oxygen concentration in the coolant. Such a method can be provided with the use of mass-exchange apparatus 114 installed in the coolant 104. The mass-exchange apparatus can be a container for the solid-phase oxides of coolant to be kept. For example, if the coolant consists of lead and/or bismuth, the mass-exchange apparatus may contain solid-phase oxides of lead and/or bismuth in the form of small grains. The solid-phase oxides can be dissolved in the coolant and owing to the fact that they are oxides of coolant components, the effect, to a certain extent, will be similar to penetration of oxygen from a gas medium and oxidation of the mentioned components, but in this case there is a possibility to control the intensity of the process. The coolant shall flow through the mass-exchange apparatus to dissolve the solid-phase oxides of coolant components in the coolant. For this purpose, the housing of the mass-exchange apparatus containing the oxides of coolant components, for example, in granular form, shall have holes for the coolant to flow through. Dissolution efficiency (velocity) of solid-phase oxides of coolant components in the coolant depends, particularly, on the velocity of coolant flow through the mass-exchange apparatus. To control the velocity of coolant flow through the mass-exchange apparatus, a pump can be provided in the mass-exchange apparatus or in that part of reactor tank where the mass-exchange apparatus is located. This pump shall pump the coolant with different velocities and the operation of this pump can be controlled externally (remotely). The velocity of coolant flow through the mass-exchange apparatus can be controlled by means of a heater which heats the coolant, and thus its convection occurs. Heater operation can be controlled externally (remotely). The use of the heater has an advantage over the pump due to the fact that the heater is not equipped with moving elements, which is very important for the extension of mass-exchange apparatus operating life and general improvement of reactor safety, since the mass-exchange apparatus (and therefore a heater or a pump) operates in hot coolant under high radiation activity. The dissolution efficiency (velocity) of solid-phase oxides of coolant components in the coolant also depends on the volume and surface area of solid-phase oxides of the components the coolant contacts with. The volume of the tank where the oxides (for example, in the form of small grains) are contained and through which the coolant flows can be controlled with the use of valves which, in turn, can be controlled remotely, for example, with the use of an electric actuator. Besides, the dissolution efficiency (velocity) of solid-phase components in the coolant also depends, on the temperature of interacting coolant and/or solid-phase components of the coolant. Their temperature can also be controlled by means of a heater the operation of which can be controlled externally (remotely). Therefore, there are many different methods to control dissolution efficiency (velocity) of coolant solid-phase components in the coolant; some of them are described above. In this invention all these methods are collectively referred to as “activation” (“to activate”) of mass-exchange apparatus, as it is associated with excessive dissolution of solid-phase components the coolant. In “non-activated” (“deactivated”) state, i.e. when, for instance, a pump or heater which increases the flow of the coolant through the mass-exchange apparatus is switched off, or when the valves are set to such a position that the coolant flows around the minimum quantity of coolant solid-phase components or does not flow around them at all, or when the heater used to raise the temperature of the coolant and/or its solid-phase components in order to increase the interaction efficiency is switched off (the examples are given in accordance with the above described methods for the increase of dissolution efficiency (velocity) of solid-phase components in the coolant; when using other methods the non-activated or deactivated state is determined as per the corresponding minimum efficiency (velocity) of dissolution of coolant solid-phase components in the coolant), the dissolution efficiency (velocity) of coolant solid-phase components in the coolant is minimum or equals zero (in general case it can have some value, as the coolant can pass through mass-exchange apparatus due to common circulation within the reactor (but not due to the inducement of flow by using additional methods described above), and the current temperature of interaction can cause dissolution in its own (not due to additional heating). Consequently, when the term “activate the mass-exchange apparatus” is used, it means that the devices which increase the dissolution efficiency (velocity) of coolant solid-phase components in the coolant are switched on. On the contrary, the term “deactivate mass-exchange apparatus” means that the devices which increase the dissolution efficiency (velocity) of coolant solid-phase components in the coolant are switched off or switched over to the position when the efficiency (velocity) has a minimum possible value. Activation/deactivation can ensure two or more states of equipment activity. In case of two states, when the mass-exchange apparatus may have minimum (or zero) activity and maximum activity, the oxygen delivered to coolant can be controlled by the time during which the mass-exchange apparatus is in the state of maximum activity. If more activity states are established for the mass-exchange apparatus, the velocity of oxygen injection into the coolant can be controlled as well (i.e. the volume of solid-phase components being solved in the coolant per time unit). In a limiting case the discrete, not analog, continuous in its value control of mass-exchange apparatus activity can be provided, which even more enhances the possibility to control dissolution efficiency (velocity) of coolant solid-phase components in the coolant, which, in turn, improves control accuracy. FIG. 2 shows one of the possible embodiments of the mass-exchange apparatus. The mass-exchange apparatus includes a tank formed by its housing 201, limited by the bottom 202 and the cover 203. The tank includes a flow reaction compartment 210 located inside the tank below the coolant level and limited by a perforated grille 204 at the top. The limiting grille 204 prevents the solid-phase granulated oxidant 206 from emergence under the buoyant force. The oxygen-rich coolant comes out of the mass-exchange apparatus through the limiting grille 204 and holes 207 in the housing wall 201 located in the upper part of the housing wall 201 above the limiting grille 204 and mixes with coolant of the reactor plant primary circuit. The solid-phase oxidant 206 (in particular, solid-phase oxides of coolant components) placed under the grille 204 dissolves when interacting with coolant and enriches the coolant with oxygen. The heater 205 located in the reaction chamber 210 and passing through the perforated grille 204 is designed to heat the coolant in the reaction chamber 210. The inlet holes 208 are located in the wall of the housing 201 at the level of lower end plate of the electric heater 205, for the coolant to move through the layer of solid-phase oxidant placed in the reaction chamber 210 in the clearance between the housing 201 and the electric heater 205 during operation of mass-exchange apparatus. The outlet holes 207, inlet holes 208 and holes in the grille 204 are made, preferably, in the form of narrow slots smaller in size than the grains of solid-phase oxidant. When operated the mass-exchange apparatus shall be immersed in the coolant so that the outlet holes 207 are in the coolant. The mass-exchange apparatus shall be located in the reactor so that the coolant flows through the place of installation. If the height of the coolant layer is insufficient for the immersion of mass-exchange apparatus, the place of installation shall be equipped with a pocket in which the housing of mass-exchange apparatus is sunk. The coolant can flow through the pocket owing to convective current of liquid-metal coolant through the reaction chamber during operation of the electric heater 205. The mass-exchange apparatus shown in FIG. 2 operates as follows. When switching on the electric heater 205 by means of natural convection the coolant flows through granulated solid-phase oxidant 206 placed in the flow reaction chamber 210 in the clearance between the housing 201 and the electric heater 205. The coolant 104 (preferably liquid-metal coolant) comes from the surrounding space to the mass-exchange apparatus through inlet holes 208 and moves from the bottom up (as shown with arrows) through the granulated solid-phase oxidant 206 placed in the reaction chamber 210. Small grains of the solid-phase oxidant dissolve in the coolant when interacting with it and enrich the coolant with oxygen. The oxygen-rich coolant comes out of the mass-exchange apparatus through the outlet holes 207 and mixes with coolant of the reactor primary circuit. Capacity value, i.e. the amount of oxygen supplied from the mass-exchange apparatus per unit of time, is controlled by changing the power of the electric heater. The dissolution velocity of solid-phase oxidant is increased at high temperature. As the density of the solid-phase oxidant (for example, lead oxide) is less than the density of the coolant (lead or lead-bismuth), the solid-phase oxides of coolant components move upward and are held within the coolant body by the grille 204 which allows the coolant to flow through. There are wires 115 in the upper part of the heating element 205 which are used for the supply of electric voltage to the heating element 205. Due to the fact that to activate the mass-exchange apparatus it is required only to heat the coolant with the heater 205, the normal operation of the mass-exchange apparatus 114 (shown in FIG. 1) requires wiring (cable 115) through the reactor vessel 102. The wires will supply electric current to heat the heating element 205 of the mass-exchange apparatus, and thereby activate it. It provides safe remote control of the mass-exchange apparatus operation (and therefore control of oxygen concentration in the coolant), as such design minimizes the number and size of holes in the reactor vessel and eliminates the necessity for penetration into the reactor vessel or depressurization of the reactor to control oxygen concentration in the coolant, which ensures a high degree of leak-tightness and strength of the reactor vessel and has a positive effect on the operating life and safe operation of the reactor plant. The mass-exchange apparatus adequately controls the oxygen concentration in the coolant but it may be characterized by insufficient rate/efficiency of oxygen concentration increase. Besides, the reserve of consumables, solid-phase oxides of coolant components, is limited. Several mass-exchange apparatus of increased capacity can be installed in the reactor, but there might be restrictions on reactor volume and space required for other equipment of the reactor plant. Consequently, it requires such a method for oxygen concentration increase which will have a high rate/efficiency of concentration increase and high (infinite) volume of oxygen to be injected into the coolant. To provide such a method for oxygen concentration increase in the coolant, the reactor 101 includes a disperser 112 which also provides a controlled way for the increase of oxygen concentration in the coolant 104 by injecting gas, which may contain oxygen, into the coolant 104 from the space 106 above the surface 105 of the coolant 104. For this purpose, the disperser 112 is installed partially in the coolant 104 and partially in the near-coolant space 104. Oxygen-containing gas can be injected into the coolant directly from the gas system pipeline, but in this case the pipeline will be sunk in the coolant, which may lead to plugging and clogging of the pipeline, thereby affecting safety and decreasing the operating life of the reactor plant. In the preferable option shown in FIG. 1 the disperser 112 is installed vertically, as in this case the space 106 above the coolant 104 may be used as near-coolant space (therefore, no additional measures to arrange a separate space for gas are required), and the disperser 112 is set to position extending its operating life, as the coolant and the solid-phase oxides do not penetrate into the disperser or cause its clogging, which extends its operating life. As the disperser is able to supply gas from the near-coolant space to the coolant, the gas entrained through the hole in the upper part of disperser located, in a particular case, in the above-coolant space passes through a channel in the disperser (for example, in the shaft) downward and comes out of its lower part located in the coolant (the names of directions change accordingly at other layouts of disperser). To inject gas into the coolant, increased pressure may be created in the near-coolant space; this pressure would cause the forced penetration of gas into coolant which has less internal pressure than disperser. Pressure value can be determined by means of pressure sensors in this space or space adjacent to it with the gas system pipeline, or according to the amount of gas pumped to this space which can be determined with the use of flow rate meters. For the disperser outlet holes not to be clogged, they are mainly made on the moving elements of disperser installed in the coolant, for example, on the lower end of a rotating disperser. Apart from the creation of gas increased pressure in the near-coolant space, the gas can be injected into the coolant by creating a local zone of low pressure in the coolant, for example, near the disperser (entrainment of gas with coolant). This can be achieved with the use of discs in the lower part of disperser which may have blades. When rotating, the discs create a low-pressure area in the coolant under the action of centrifugal forces. The gas passing from the above-coolant space to the lower holes near the discs through the longitudinal channel goes to the mentioned low-pressure area. Due to the gradient of coolant velocity near the disperser, in particular, the discs, i.e. when the coolant near the disperser moves faster than in the area away from it, the gas entering the coolant in the form of bubbles is fragmented to smaller bubbles, thereby creating the finely-divided two-component suspension of gas-coolant. If the gas contains oxygen, the conditions for effective increase of oxygen concentration in the coolant are provided. Due to the fact that the disperser has moving (rotating) elements, the coolant moves (flows over) near the disperser surfaces, which washes the solid particles and films out of the disperser, thereby ensuring its automatic self-purification. This property increases the operating life of the disperser as well as the operating life and safety of operation of the reactor plant in general. In the preferable option shown in FIG. 3 the disperser can have two discs, one of which rotates and another one does not. Such a combination creates a low-pressure area of the coolant between the discs; gas may get to this area from the holes in the shaft or in one or two discs. As it is possible to provide a sufficiently small distance between the discs, and one of the discs rotates relative to another, the pressure drops faster compared to a case when both discs rotate. As a result, the efficiency of gas injection into the coolant is improved and the gas bubbles become even smaller, i.e. the dissolution efficiency of gas, in particular, oxygen, in the coolant is improved, and thereby the oxygen concentration is increased. The injection of oxygen-containing gas into the coolant and oxygen concentration in the coolant are regulated due to the control capability of gas system operation which can create increased pressure in the near-coolant space, and due to the control capability of disperser operation which in passive state (without rotation of discs) does not inject gas into coolant from the above-coolant space and in active state (with rotation of discs) injects oxygen-containing gas into the coolant from the above-coolant space, and the rate (efficiency) of gas injection into coolant can depend on the disc rotation speed. Application of dispersers with rotating discs is more reasonable, because it does not require to create increased pressure to inject gas to the coolant from the near-coolant space, but it is sufficient to actuate (“activate”) the disperser, which simplifies and thereby enhances the reliability of control system operation. To actuate (“activate”) the disperser, it is required to rotate the shafts and discs (or one of the shafts and one of the discs). This may be done with the use, for example, of an electric motor. To reduce the destructive effect of high temperatures and vapors of the coolant on the electric motor and, consequently, to extend its operating life, the motor shall be located outside the reactor (although, in some embodiments it can be located inside). To rotate the disperser parts, the shaft may be passed through the reactor wall from the electric motor. For this purpose, the wall shall have an opening. However, to improve the reactor structural strength and thereby its operational safety, the preferable embodiment allows the rotation to be transferred from the electric motor to the disperser elements with the use of magnetic coupling the parts of which are installed opposite each other on the different sides of the reactor wall. The magnetic field formed by a magnetic half-coupling can transfer the rotary force to another half-coupling located on the other side of the reactor wall, thereby actuating the disperser. If the disperser motor is located outside the reactor, it can be controlled through a wire (cable) 113 shown in FIG. 1 designed for the supply of electric power to the electric motor by supplying or not supplying the power voltage or changing its parameters. In this invention the actuation of disperser by means of an electric motor is designated as “activation” of the disperser and the shutdown of an electric motor when the disperser stops operating is designated as its “deactivation”. Rotation speed of the electric motor can be controlled in different ways: in a binary way (cut-off/cut-in), at different rotation speeds or with a possibility to set any rotation speed within the specified range. Consequently, the higher rotation speed is, the more gas (including oxygen) is dissolved in the coolant and the smaller gas bubbles are formed. The solid electrolyte oxygen sensor shown in FIG. 3 consists of the following main elements: disperser housing 301 with a stationary upper disc; hollow shaft 302 connected to the lower rotating disc 303; flange 304 fastening the disperser to the reactor vessel; electric motor 307 with drive magnetic half-coupling 306 transferring rotation to the hollow shaft 302 with the use of a driven magnetic half-coupling 305. The electric motor 307 with half-coupling 306 is installed on the outside of the reactor wall 102, and the half-coupling 305 is installed on the inside of the reactor wall 102. In the preferable option shown in FIG. 3 the upper disc (stator) of the disperser is rigidly connected to the disperser housing 301. The lower rotating disc 303 is connected to the rotating shaft 302. The lower disc and the shaft are hollow, their cavities are interconnected. In the upper part the shaft cavity is connected to the gas circuit through holes. The holes of small diameter (at least 12 holes) are punched on the surface of the lower disc forming a clearance; these holes are located in a circumferential direction. The upper disc can also have small holes for injection of liquid metal into the cavity between the discs. In the upper part the rotating shaft is connected to the shaft of the sealed electric motor 307 powered from the frequency converter by means of magnetic half-couplings 305 and 306. The disperser is immersed in the coolant so that the holes in the upper part of the shaft are above the liquid level, and the upper and lower discs are below the liquid level. When the sealed electric motor is run, the lower disc rotates with the prescribed angular velocity. As a result of coolant movement relative to the lower disc, a low-pressure area is formed in the clearance, which provokes the injection of gas into the clearance from the cavity of the lower disc through the holes in its upper part. Due to the velocity gradient of coolant the bubbles in the clearance are fragmented and the finely-divided gaseous phase together with the coolant comes from the clearance to the main flow of the coolant. In other embodiments of the disperser, the lower disc can be stationary, and the upper disc can be a rotating one. Besides, the cavity connecting the near-coolant space and the hole in the disc can be placed both in the shaft and in the housing. The holes can be made both in the rotating disc and in stationary one (or both). As mentioned above, the operation principle of the gas disperser is based on the fragmentation of gas bubbles in liquid upon injected into the flow with high velocity gradient. Due to the irregularity of Q force applied to the surface elements, the large bubbles in such a flow are broken down into small ones. In the preferable option of the disperser, high-gradient flow of liquid in the gas disperser is formed in the clearance between rotating and stationary discs. The degree of gaseous phase dispersion with all other conditions being equal depends on velocity gradient in the flow. The velocity gradient is increased by reducing the clearance between the discs or increasing the linear speed of the discs' relative motion. The reactor 101 is also equipped with an oxygen sensor 110 in the coolant 104. In the preferable option it is made in the form of an oxygen thermodynamic activity sensor; one of the options is shown in FIG. 4. The solid electrolyte oxygen sensor shown in FIG. 4 contains a ceramic sensing element 401 sealed in the reactor vessel 405, a reference electrode 402 and a center electrode consisting of two parts, the lower part 406 and the upper part 111 located in the sensor cavity. The ceramic sensing element 401 is made of solid electrolyte in the form of a tubular element interlinked with a part of a sphere. Partially stabilized zirconium dioxide, fully stabilized zirconium dioxide or hafnium oxide can be used for the manufacturing of the element 401. The side face of the tubular element is connected to the inner side face of the reactor vessel 405 by means of a joining material 404 which can be a glass ceramic or pressed graphitized carbon fiber. The sensor is equipped with a plug 403 made of metal oxide, for instance, aluminum. The plug has a hole and covers the cross section of the cavity of the ceramic sensing element 401. The plug is designed to fix the reference electrode 402 in the inner cavity of the ceramic sensing elements 401. The reference electrode 402 is located in the cavity between the inner surface of the ceramic sensing element 401 and the surface of the plug 403 and occupies at least a part of the cavity. The reference electrode 402 can be made of bismuth, lead, indium or gallium. Facing the part of the spherical element the free end of the lower part of the center electrode 406 is brought out to the reference electrode 402 through a hole in the plug 403. It enables an electric contact between the reference electrode 402 and the lower part of the center electrode 406. At least a part of the ceramic sensing element sphere 401 protrudes beyond the reactor vessel 405 made e.g. of steel. During operation of the sensor, this protruding part is immersed in molten metal where the oxygen activity is determined. The materials of the reactor vessel 405, ceramic sensing element 401, and joining material 404 have an equal thermal-expansion coefficient and are chemically resistant to operating environment, such as lead melt at temperatures not exceeding 650° C. This allows to keep the sensor operable at a change rate of temperatures (thermal shocks) in liquid metal of up to 100° C./s within the temperature range of 300-650° C. A bushing 408 is welded to the free part of the reactor vessel 405. The upper part of the center electrode 111 shown in FIG. 1 as a cable or wire comes out of the cavity of the bushing 408 and passes through the wall 102 of the reactor vessel. The ring-shaped cavity between the bushing 408 and the upper part of the center electrode 111 is filled with dielectric material 410, preferably, glass ceramic. The material 410 ensures leak-tightness of the sensor inner cavity. It is necessary to prevent ingress of oxygen from the air into the inner cavity of the sensor and changes in the reference electrode properties. The lower part of center electrode 406 located in the internal cavity of the reactor vessel 405 is inserted into an isolator 407, preferably made of aluminum oxide. The operation principle of the oxygen thermodynamic activity sensor is based on measurement of electric potential difference between two electrodes separated by solid electrolyte (for example, ZrO2÷Y2O3) with selective oxygen and ion conductivity. The value of the electric potential difference between two electrodes is formed by the difference of oxygen potentials between the controlled medium and medium with oxygen potential known in advance (reference electrode). As a reference electrode, such “liquid metal—solid oxide” systems as {Bi}-<Bi2O3> can be used. The value of potential difference received from the sensor can be converted to the value of oxygen thermodynamic activity, its concentration or other convenient value. In another embodiment, the means of increasing oxygen concentration can be controlled depending on potential difference value received from the sensor (e.g. as per compliance table or by formula correspondence established by empiric or theoretic method). The direct or converted reading of the oxygen sensor (e.g. oxygen thermodynamic activity) can be compared with the threshold values and, in accordance with the comparison results, decisions on activation of the mass-exchange apparatus or disperser can be taken. For instance, it can be specified that the oxygen concentration is below the threshold value, then the decision on the activation of one of the above mentioned devices shall be taken to increase the oxygen concentration (e.g. its thermodynamic activity). In accordance with this invention, the method for control of oxygen concentration allowing to achieve the above mentioned technical results shall include the following steps shown in FIG. 5. Firstly, it is necessary to obtain the oxygen sensor reading (step 501), estimate the oxygen concentration in the coolant (step 502) based on the data received from the oxygen sensor in the coolant and compare the estimated oxygen concentration in the coolant with the permissible value (step 503). If the oxygen concentration is below the permissible value (below the minimum permissible value, i.e. beyond the range of permissible values), the change in the oxygen concentration in the coolant shall be estimated (step 504); as a result, the type of change in concentration (increase, decrease or maintenance of the former level), rate of change, value of change etc. can be determined. The change in concentration and characteristics of such change can be assessed by comparing the estimated oxygen concentration in the coolant received from the sensor 110 at different times, or such assessments can be received in the form of derivatives with the use of different devices (for example, hardware derivation can be performed with the use of capacitive, inductive elements etc.) or by using any other methods known from the background of the invention. This method allows the change in concentration to be estimated based on the reading of the same sensor used for the determination of oxygen concentration, which decreases the number of equipment located in the reactor. This simplifies and cheapens the design, manufacturing and installation of the oxygen sensor in the coolant and the reactor plant on the whole. Besides, the usage of a single-type sensor enables redundancy in order to ensure safety and extend the operating life of the reactor plant, since sensors of other types do not occupy space in the reactor, and thereby preserve room for additional sensors of a single type. It should be noted that the equipment is unified during redundancy of a single-type sensor. This leads to simplification and cheapening of design, manufacturing and assembly of a reactor plant. In another embodiment, it is possible to use the oxygen concentration sensors which will provide values corresponding to the change characteristics of oxygen concentration in the coolant. Such sensors may be called differential. Consequently, two or more types of sensors may be used (considering the sensor the readings of which allow to estimate the oxygen concentration in the coolant). As the mentioned sensors are designed to determine different characteristics of the same value (oxygen concentration), it allows to receive more precise estimates of those characteristics and values by common application of different-type sensors readings, as well as to replace the readings of sensors of one type with properly processed readings of other sensors in case of failure of any sensors, which, in turn, allows to improve safety and extend the operating life of the reactor plant. To make a decision on the activation of the mass-exchange apparatus or disperser in the preferable embodiment, both assessments, the oxygen concentration and the change in oxygen concentration, are necessary, because it is preferable to activate the mentioned devices after the oxygen concentration is reduced to a level below the admissible (threshold) value (or range of values), which can be estimated in accordance with the readings reflecting the oxygen concentration. The decision, whether to activate the mass-exchange apparatus or the disperser, shall be based on the assessment of the change in oxygen concentration. Next, it is necessary to determine, whether the estimated change in oxygen concentration in the coolant demonstrates reduction in concentration (step 505) and, if so, compare the reduction value and/or rate with the corresponding threshold value (step 506). The reduction in concentration can be determined by different methods. For example, if one or more subsequent values of the oxygen concentration estimate is below one or more preceding ones, it can be assumed that the oxygen concentration has reduced. In another embodiment, if differential oxygen sensors are used, the reduction in oxygen concentration can be determined, if the readings of this sensor have the values corresponding to reduction in concentration. Besides, the reduction in oxygen concentration can be determined as per the assessment of the change value and/or rate of oxygen concentration. If these estimates have negative values, the reduction in oxygen concentration in the coolant can be recognized. If the estimates of the change value and/or rate of oxygen concentration which are opposite in sign to the similar estimates of the oxygen concentration change are used, the reduction in oxygen concentration in the coolant can be recognized, if these estimates have positive values. The change (reduction) value and/or rate of oxygen concentration in the coolant can be determined based on the readings of the oxygen sensor in the coolant (e.g. oxygen thermodynamic activity sensor in the coolant) or based on differential sensors reflecting the change in oxygen concentration. If the estimate of oxygen concentration in the coolant is below the permissible value, the reduction in oxygen concentration is observed, and the estimated reduction value and\or rate of oxygen concentration is below the corresponding threshold value, the mass-exchange apparatus shall be activated (step 507). Otherwise, if the estimated oxygen concentration in the coolant is below the permissible value, the reduction in oxygen concentration is observed and the estimated reduction value and/or rate of oxygen concentration is above the corresponding threshold value, the oxygen-containing gas (gaseous mixture) shall be supplied from gas system to the near-coolant space and/or the disperser shall be activated. In the latter case, five alternatives are possible in step 508. These alternatives lead to the achievement of the necessary result, which is the increase of oxygen concentration in the coolant. One of the alternatives suggests the supply of oxygen-containing gas to the near-coolant space from the gas system, e.g. in the amount not causing the pressure increase, but displacing oxygen-free gas (e.g. through the second pipeline of the gas system). To inject oxygen into the coolant, the disperser shall be in the active state. Consequently, this alternative is used, if before the supply of oxygen-containing gas the disperser was in the active state, for example, used for injection of oxygen-free gas (e.g. hydrogen gaseous mixture) into the coolant. The second alternative provides that the near-coolant space could have already contained the oxygen-containing gas before the activation of the disperser, and to achieve the result, i.e. the inlet of oxygen-containing gas into the coolant, and thereby increase the oxygen concentration, it is enough to activate the disperser. The third alternative suggests that, before achieving the necessary result, the gas in the near-coolant space did not contain oxygen, and the disperser was switched off; therefore, to increase the oxygen concentration, it is required not only to supply oxygen-containing gas to the near-coolant space (in the limiting case, it can be pure oxygen intended for mixing with gas in the mentioned volume), but also to activate the disperser. In the fourth alternative, the disperser is not activated and the oxygen-containing gas is supplied to the near-coolant space from gas system in the amount (volume) or under the pressure sufficient for the creation of such pressure in the near-coolant space which would cause the penetration of gas into the coolant even through the inactive disperser. In the fifth alternative, the oxygen-containing gas is supplied to the near-coolant space from the gas system in the amount (volume) or under the pressure sufficient for the creation of such pressure in the near-coolant space which would cause the penetration of gas into the coolant through the disperser, and the disperser is activated. This allows to extend the operating life of the disperser. What all these alternatives have in common is that the result, i.e. the in increase of oxygen concentration, is achieved only with the presence of oxygen-containing gas in the near-coolant space under the pressure exceeding the internal pressure in the coolant where the outlet hole (holes) of the disperser are located. These alternatives differ only by their method for creating a required pressure difference and initial conditions: whether the disperser is activated or deactivated, and the presence of the oxygen-containing gas in the near-coolant space and its pressure. From this perspective, this invention shall be considered used, if any of the mentioned actions are carried out and lead to the supply of oxygen-containing gas from the near-coolant space to the coolant through the disperser (or by means of the disperser). As mentioned above, the gas (including oxygen-containing gas) may be injected into the coolant even when the increased gas pressure is created in the near-coolant space and the disperser is not activated. But in this case, the outlet hole (holes) of the disperser may be clogged. Therefore, to achieve the result of this invention, i.e. reliability improvement and extension of the operating life of reactor equipment (which leads to improving safety and reactor plant operating life extension), when applying this method of gas supply into the coolant (due to the increased pressure of the gas in the near-coolant space), the disperser shall be activated in any case, so that the outlet hole (holes) at the lower end immersed in the coolant is flown around with the coolant to prevent accumulation of oxides, deposits, films etc. in/on it. It means that in step 508, the disperser shall be preferably activated, even if the oxygen-containing gas is supplied to the near-coolant space from the gas system in the amount causing the increase of gas pressure in the near-coolant space that leads to the inlet of gas (with oxygen) into the coolant without the activation of the disperser (although, the case without activation of disperser is included in this invention). Besides, the very control of gas pressure in the near-coolant space in such a way that the gas penetrates into the coolant through the disperser on its own, even without the activation of the disperser, may be undesired due to formation of large-sized bubbles and is less accurate due to less precision of pressure control in the gas system than the control of disperser rotation speed, and, consequently, local decrease of pressure in the coolant near the rotating end (discs) of the disperser; therefore, it is preferable to control the oxygen concentration in the coolant with the use of an activated disperser. If the oxygen concentration in the coolant is controlled using the methods involving an activated disperser, only the first three of the described step 508 alternatives of this invention shall be used. What these alternatives have in common is that the result, i.e. the increase of oxygen concentration is achieved only if there is oxygen-containing gas in the near-coolant space and the disperser injecting gas from the near-coolant space to the coolant is activated. These alternatives differ only by initial conditions: whether the disperser is activated or deactivated and the presence of oxygen-containing gas in the near-coolant space. From this perspective, this invention shall be considered used, if any of the mentioned actions are carried out and lead to the supply of oxygen-containing gas from the near-coolant space to the coolant by means of the disperser. However, it is necessary to take into account that the supply of oxygen-containing gas to the near-coolant space, both with creation of pressure exceeding the internal pressure of the coolant in this space (not only locally near the disperser but in the whole space) and without creation of such pressure, shall be, in any case, considered a result of supplying oxygen-containing gas to the near-coolant space, and thereby shall be one of the embodiments of this invention, shall fall within the scope of this patent and patent claim protection. After activating the mass-exchange apparatus (step 507) or supplying oxygen-containing gas and/or activating the disperser (step 508), the oxygen concentration shall be checked, e.g. by using the same method as previously, i.e. by estimating the specified concentration. As shown in FIG. 5 this can be done by returning to step 501. When the oxygen concentration in the coolant estimated in step 502 and compared in step 503 assumes or exceeds the permissible value (approaches to/exceeds the upper limit of the permissible range in other embodiments), the mass-exchange apparatus shall be deactivated (step 509) or the disperser shall be deactivated and/or supplying oxygen-containing gas to the near-coolant space from gas system shall be stopped (if the natural consumption of oxygen in the near-coolant space, e.g. due to diffusion process, does not end quickly enough or it is required to completely remove oxygen from this space, the oxygen-free gas may be supplied to the near-coolant space from the gas system; besides, the oxygen-free gas may be immediately supplied from the gas system to the near-coolant space, which means that the supply of the oxygen-containing gas is over, because the gas being supplied does not contain oxygen). This allows to maintain the oxygen concentration in the coolant within the permissible range, i.e. the oxygen concentration in the coolant does not exceed the upper limit of the permissible range. Monitoring of “oxygen concentration in the coolant equals or exceeds the allowable value” condition is related to the fact that this invention aims at preventing the reduction in oxygen concentration, and the mass-exchange apparatus and disperser may only increase the oxygen concentration in the coolant. Therefore, to accomplish the invention objective, it is sufficient to provide oxygen concentration in the coolant equal or exceeding the permissible value with the use of the mass-exchange apparatus or disperser; then the oxygen concentration starts reducing due to the natural consumption of oxygen in the coolant for oxidation of structural material components; the mass-exchange apparatus or disperser are reactivated when the oxygen concentration is below the permissible value. After the inlet of oxygen into the coolant is stopped, its concentration in the coolant is reduced down to the lower limit of the permissible value range, and when the oxygen concentration in the coolant (estimated value) is below the permissible value (which is preferably the lower limit of the permissible value range), the method shall be reapplied, i.e. the mass-exchange apparatus activated, the oxygen-containing gas supplied, and/or the disperser activated. For cyclical re-use of the method as per this invention, proceed to step 501, after the steps 507, 508 and 509 are implemented. In the represented embodiment, we proceed to this step, even if step 505 has determined that the concentration is not being reduced, but increased. In such case we can consider that there is no necessity for steps 507 or 508, as the oxygen concentration increases independently (e.g. if there is oxygen-containing gas in the near-coolant space, and oxygen penetrates from gas into coolant in the amount sufficient for the increase of oxygen concentration in the coolant). Due to the method repeatability, we can ensure its repetition and automatic control of oxygen concentration in the coolant, which allows to lessen the necessity for intervention of qualified personnel and, to a certain extend, exclude their participation in reactor plant operation control. However, there is an option when the method does not cycle as per this invention. For example, step 509 can be implemented not following the condition of the admissible oxygen concentration restoration, but the timer activated after a certain time of the mass-exchange apparatus or disperser operation. Next, the control system may enter the standby mode to run the method from step 501 or run the method from this step automatically, thereby ensuring the repeatability and automatism of operation. It can be useful when the estimation of oxygen concentration has to be devoid of influence of different factors and requires the mass-exchange apparatus or disperser being deactivated and, consequently, not having the effect on the sensor readings at the moment of reading. The threshold values of the change characteristics of oxygen concentration in the coolant such as speed, value and others, as well as the variable (range) of the permissible value of oxygen concentration in the coolant can be determined based on the preliminary theoretical or computed values or can be obtained by experiment during start-up and adjustment procedures or checking works (or combined). The particular threshold and permissible values depend on the design of a reactor plant and its manufacturing features and may vary from one reactor plant to another even within one reactor type and depending on modes of operation or preparation of reactor plant for operation. Ensuing the corrosion stability of the reactor structural materials, its safety and sufficient concentration of oxygen or characteristics of its increase for corrosion stability, safety and long-term operation of the reactor can be the criteria for determination of certain threshold and permissible values. For example, in one of the possible embodiments the threshold (permissible) value of concentration of oxygen dissolved in the coolant can be determined by using the calculation and experimental method and have the value calculated by the following formula:lgC=−0.33−2790/T+lgCs+lgjCPb, where C is the concentration of oxygen dissolved in the coolant, weight %; T is the maximum temperature of coolant in circuit, K; Cs is concentration of oxygen dissolved in the coolant during saturation at temperature T, weight %; j is the factor of lead thermodynamic activity in the coolant, reciprocal weight %; CPb is concentration of lead in the coolant, weight %; lg is mathematical operator of decimal logarithm (i.e. logarithm to base 10). For example, if the reactor vessel is made of KH18N10T stainless steel and the eutectic alloy of lead with bismuth is used as coolant, the lowest feasible concentration of oxygen can be 2.6·10−10 weight % (the value is determined based on the specified data and data obtained by using experimental or calculation method for a certain reactor plant design) at maximum temperature in reactor of 623 K (e.g. in the core or near the reactor wall). Despite the fact that the lowest feasible concentration of oxygen is allowed for operation of a reactor plant and can be used as the threshold (permissible) value, for example, if the oxygen concentration increases fast without time delays after the measured oxygen concentration is reduced below the values of the lowest feasible concentration of oxygen or approximated to this value, such situation are not desirable for improving safety of reactor operation. In connection to this, the threshold or permissible values exceeding the lowest feasible concentration of oxygen can be assumed. For example, an objective to maintain oxygen concentration within the range of 6·00−8-6·10−7 weight % can be set. If the concentration of the dissolved oxygen is reduced to the level of 6·10−8 weight %, it can be determined that the lower threshold value is achieved and the decision on the increase of oxygen concentration in the coolant by using one of the methods described in this invention can be taken. After this decision is taken, the concentration of oxygen dissolved in the coolant increases and when the value of 6·10−7 weight % is achieved, we can determine that the upper threshold value is achieved and, consequently, the decision to stop the increase of oxygen concentration in the coolant can be taken. In some embodiments, the upper threshold value may not be used, and the sufficient increase of oxygen concentration can be determined based on the time or other characteristics of oxygen concentration increase process (e.g. the increase of oxygen concentration can be stopped after the duration of this process from its beginning achieves the target value). The threshold values of velocity, quantitative and/or other characteristics of oxygen concentration increase in the coolant can be determined by using the methods identical to the above-described and/or other methods known from the background of the invention. The method steps shall be preferably implemented in the shown and described sequence, but in some embodiments, whenever possible, the steps can be performed in a different sequence or simultaneously. The advantages of this method for control of oxygen concentration in the coolant are based on the following: The mass-exchange apparatus and disperser have different efficiency (productivity) which can be determined as increase velocity of oxygen concentration, i.e. increment of oxygen in volume per time unit. The mass-exchange apparatus has low (relative to disperser) rate or efficiency of oxygen concentration increase and can be used, for example, under normal operating conditions when the deviations from the threshold value and reduction rate of oxygen concentration to be compensated are low. However, the disperser has high (relative to the mass-exchange apparatus) rate of oxygen concentration increase and can be used, for example, in abnormal modes (e.g. if the oxide film is damage as a result of mechanical effects, such as earthquake etc.) or during the passivation of reactor walls (formation of oxide films on their surfaces) at the beginning of operation when the oxygen consumption rate which corresponds to reduction rate of oxygen concentration to be compensated is high. Such segregation allows, on the one hand, precise control of oxygen concentration in the coolant under normal conditions when using the mass-exchange apparatus and, on the other hand, gives a chance to increase the oxygen concentration (or compensate for a sharp drop in oxygen concentration) in abnormal or other operation modes by means of a disperser. These opportunities, both precise control of oxygen concentration and its rapid growth (compensation of sharp drop) are essential for reactor safety. Besides, such segregation of the devices for the increase of oxygen concentration depending on the required rate of oxygen concentration increase (efficiency of oxygen injection into the coolant) allows to extend the service life of a mass-exchange apparatus without replenishment of coolant component oxides. It is quite an important indicator, as the reserve of coolant component oxides in the mass-exchange apparatus is limited due to its limited size, and also due to the fact that the access to the mass-exchange apparatus or its recoverability should be limited to ensure safe operation of the reactor plant, as the reactor vessel should be sealed. Therefore, the application of two different devices for the increase of oxygen volume (concentration) in the coolant also improves the safety of the reactor by preventing failures of the mass-exchange apparatus due to the exhaustion of consumable material (solid-phase oxides of coolant components) and extends the time of safe operation of the reactor plant (without depressurization of reactor), since the reserve of consumable material in the mass-exchange apparatus is consumed only under normal conditions when the reduction rates of oxygen concentration to be compensated are low. To implement the above-described method of reactor equipment control, the control system can be used as per this invention. Such a control system two embodiments of which are shown in FIGS. 6 and 7 includes: a module 601 for estimating the oxygen concentration in the coolant, a module 602 for comparing the oxygen concentration in the coolant with the permissible value, a module 603 for estimating the reduction in oxygen concentration in the coolant, a module 604 for comparing the estimated reduction in oxygen concentration in the coolant, a module 605 for control of the mass-exchange apparatus and a module 606 for control of the gas system and/or disperser. The module 601 for estimating the oxygen concentration in the coolant is adapted to receive data from the oxygen sensor 110 in the coolant, to estimate oxygen concentration in the coolant based on the received data and transmit the estimated value of oxygen concentration in the coolant to the module 602 for comparing the estimated oxygen concentration in the coolant with the permissible value; The module 602 for comparing the estimated oxygen concentration in the coolant with the permissible value is adapted to receive estimated oxygen concentration in the coolant from the module 601 for estimating the oxygen concentration in the coolant and compare it with the permissible value. The module 603 for estimating the reduction in oxygen concentration in the coolant is adapted to estimate the reduction value and/or rate of oxygen concentration in the coolant as well as to transmit the estimated reduction value and/or rate of oxygen concentration in the coolant to the module 604 for comparing the estimated reduction in oxygen concentration in the coolant. In one of the embodiments, the module 603 for estimating the reduction in oxygen concentration in the coolant can be adapted to determine the reduction in oxygen concentration in the coolant. In this case, the estimated reduction value and/or rate of oxygen concentration in the coolant can be transmitted to the module 604 for comparing the estimated reduction in oxygen concentration in the coolant provided that the module 603 for estimating the reduction in oxygen concentration in the coolant has determined that the oxygen concentration in the coolant is being reduced. Upon that, it is not required to transmit the data on reduction in oxygen concentration in the coolant to the module 604 for comparing the estimated reduction in oxygen concentration in the coolant, and the module 604 for comparing the estimated reduction in oxygen concentration in the coolant can be put into service and control the operation of the module 605 for control of the mass-exchange apparatus and module 606 for control of the gas system and/or disperser (or transmit the results of data processing) upon receipt of the specified data on reduction in oxygen concentration in the coolant from the module 603. In another embodiment, the estimated reduction value and/or rate of oxygen concentration in the coolant can be constantly transmitted to the module 604 for comparing the estimated reduction in oxygen concentration in the coolant. In this case, the module 604 for comparing the estimated reduction in oxygen concentration in the coolant can determine the reduction in oxygen concentration based on the values of estimated reduction value and/or rate of oxygen concentration in the coolant being within the corresponding range (e.g. if the values characterizing the reduction in oxygen concentration in the coolant are transmitted, the positive values of these characteristics shall correspond to the reduction in concentration, and the negative ones shall correspond to the increase of concentration; if the values characterizing the change in oxygen concentration are transmitted, the positive values of these characteristics shall correspond to the increase of concentration, and the negative ones shall correspond to the reduction in concentration; the selection of characteristics being transmitted and the corresponding range shall comply with the major objective of this system, i.e. improvement of the situation when the oxygen concentration in the coolant reduces). The module 604 for comparing the estimated reduction in oxygen concentration in the coolant can be put into service and control the operation of the module for control of the mass-exchange apparatus and the module for control of the gas system and/or disperser (or transmit the results of data processing) when it has been determined that the obtained values are within the range corresponding to the reduction in oxygen concentration. In another embodiment, the estimated reduction value and/or rate of oxygen concentration in the coolant can be constantly transmitted to the module 604 for comparing the estimated reduction in oxygen concentration in the coolant, while the module 603 for estimating the reduction in oxygen concentration in the coolant is additionally adapted to determine the reduction in oxygen concentration in the coolant and transmit a signal on determination of reduction in oxygen concentration in the coolant to the module 604 for comparing the estimated reduction in oxygen concentration in the coolant. Then the module 604 for comparing the estimated reduction in oxygen concentration in the coolant can be activated (perform its functions) upon receipt of such a signal from the module 603 for estimating the reduction in oxygen concentration in the coolant. The module 603 for estimating the reduction in oxygen concentration in the coolant enables to determine the reduction in oxygen concentration in the coolant and characteristics of this reduction based on the readings of a differential sensor which produces readings in the form of detailed data and which is shown in Figures. However, in the preferable embodiment, the module 603 for estimating the reduction in oxygen concentration in the coolant is adapted to estimate the reduction value and/or rate of oxygen concentration in the coolant (and determine the reduction in oxygen concentration in the coolant if provided) based on the estimated value of oxygen concentration in the coolant received from the module 601 for estimating the oxygen concentration in the coolant. As a result, the number of sensors installed in the reactor is decreased. In the final embodiment, the estimated value of oxygen concentration in the coolant can be transmitted to module 603 directly from module 601, as shown in FIG. 7, or through the module 602 for comparing the estimated oxygen concentration in the coolant with the permissible value, as shown in FIG. 6. It should be noted that the connection between modules 602 and 603 shown in FIG. 6 is mainly designed to transmit the comparison result of oxygen concentration assessment with the permissible value to module 603, and the estimated value of oxygen concentration in the coolant may not be transmitted (for example, when module 603 receives the data on the change in oxygen concentration in the coolant from a separate sensor or performs estimations based on the reading of sensor 110). The module 604 for comparing the estimated values of reduction in oxygen concentration in the coolant compares the estimated reduction value and/or rate of oxygen concentration in the coolant with the corresponding threshold value and transmits the comparison result to the module 605 for control of the mass-exchange apparatus and module 606 for control of the gas system and/or disperser. The estimated reduction value and/or rate of oxygen concentration in the coolant is compared with the corresponding threshold value, i.e. the reduction value of oxygen concentration in the coolant is compared with the threshold value of reduction value of oxygen concentration in the coolant, and the reduction rate of oxygen concentration in the coolant is compared with the threshold value of reduction rate of oxygen concentration in the coolant. The module 605 for control of the mass-exchange apparatus can activate the mass-exchange apparatus 114, if the estimated oxygen concentration in the coolant is below the permissible value and if the estimated change value and/or rate of oxygen concentration is below the corresponding threshold value. The module 606 for control of the gas system and/or disperser can activate the gas system with supply of oxygen-containing gas to the near-coolant space and/or activate the disperser (depending on what is necessary for the oxygen-containing gas to start injecting into the coolant), if the estimated oxygen concentration in the coolant is below the permissible value and if the estimated change value and/or rate of oxygen concentration is above the corresponding threshold value. To activate the gas system, the module 606 can control the isolation valves and pumps included into the gas system. Besides, the module 605 for control of the mass-exchange apparatus can deactivate the mass-exchange apparatus, and the module 606 for control of the gas system and disperser can deactivate the disperser and/or stop supplying the oxygen-containing gas to the near-coolant space from the gas system (or can supply the oxygen-free gas to the near-coolant space from the gas system) provided that the estimated oxygen concentration in the coolant assumes or exceeds the permissible value. FIG. 6 shows the linear structure of device for control of reactor plant equipment where the signal and data are transmitted from one module to the next one, from the next one to the subsequent one and so on (except for modules 605 and 606 which are directly connected to the mass-exchange apparatus 114 and the gas system and/or disperser 112 and control their operation). In this case, modules 601-604 processing the data can transmit only the results of their own processing based on the data received from the preceding module or sensor, or can transmit all data received from the preceding module or sensor together with the result of their own processing to the next module. In such embodiment, modules 605 and 606 can receive the signals from module 604 on activation/deactivation of the corresponding devices, signals enabling/disabling the activation/deactivation of the corresponding devices (e.g. in binary form) or signals indicating the degree or scope of the required activation of the corresponding devices which can have a value from zero to maximum. FIG. 7 shows the parallel structure of the control device when modules 601 and 603 transmit the results of their own processing to modules 602 and 604 for comparison with the given threshold values (as shown in FIG. 7; module 601 may also transmit the result of its own processing to module 603, but it is not necessary), and the processing results of modules 602 and 604 are transmitted to the modules 605 and 606 to be further compared and enable the activation/deactivation of the corresponding devices. To activate/deactivate a corresponding device, data on the reduction in oxygen concentration in the coolant below the allowable value (this data is transmitted from module 602) is required, as well as data on the reduction value/rate of oxygen concentration in the coolant (this data is transmitted from module 604). Besides, proper operation of the control device (system) as per this invention requires data on the reduction in oxygen concentration in the coolant and the capability of modules 605 and 606 to withdraw this data from the data on reduction value/rate of oxygen concentration in the coolant received from module 604, to receive the information on reduction in oxygen concentration in the coolant with characteristics of such reduction from module 604, or to receive the data on reduction in oxygen concentration in the coolant from module 603 (the latter embodiment is shown in FIG. 7). In the embodiment of the control device shown in FIG. 7, modules 605 and 606 not only control the actuation devices (mass-exchange apparatus, gas system (in particular, its valves and pumps), disperser), but also analyze the incoming data and take decisions based on this data. The structure of the control device (control system) as per this invention may have other configurations which may combine the above-described interim options or options received by exclusion or replacement. The structural diagrams shown in FIGS. 6 and 7 as well as the block scheme of control method shown in FIG. 5, the embodiments of reactor plant and devices shown in FIG. 1-4 are given for illustrations only and can limit the scope of patent assertion of this invention Any actions, objects, modules, elements, equipment and other attribute indicated in singular can also be considered as used if they are several in the plant or method, and on the opposite, if plurality is indicated, one object or action may be sufficient for the use of such attribute. The control system can be automatic, i.e. the system can independently take and implement all decisions based on the data received and processed by system. Such automatic operation creates a closed cycle which includes an oxygen-containing coolant, an oxygen sensor, modules of processing and decision-making, modules for control of actuation devices which affect the coolant; the results of this effect are re-estimated with the use of oxygen sensors and the decisions on control of oxygen concentration in the coolant are taken again. The advantage of such automatic control of oxygen concentration in the coolant is that the necessity for the qualified personnel to take part in reactor plant control may be eliminated. However, it may cause the risk of reactor plant functioning conditions exceeding the permissible limits due to the closeness of the control cycle in case of unlimited positive feedback, wherein an attempt to control the undesired deviation of a parameter results in a greater deviation of the parameter in the undesired direction (this may occur due to imperfection of processing algorithms and equipment failures). In another embodiment, the control system of oxygen concentration in the coolant can be implemented with personnel involved in data processing and/or decision-making. This option requires involvement of highly qualified specialists. This will ensure the consideration of all possible parameters and exclude the reactor plant switch to hazardous or critical operation modes, as a human being, in contrast to an automatic device, is able to adaptively estimate the current situation and change action plans taking into account security and long-term operation issues. To enable the personnel to receive data and interact with the control system, the reactor plant may have a control board equipped with indicating means such as light indicators (light panels, displays, information boards etc.), audio indicators (loud speakers, buzzers, alert systems etc.) and other, such as tactile displays. Furthermore, the control board can be equipped with input devices for requesting necessary information, testing and input of control commands. The input devices can be buttons, toggle switches, levers, keyboards, sensors, touch pads, trackballs, mice, sensor panels and other input devices known from the background of the invention Considering the variety of information equipment, the control board can be extended, for the personnel to use the board more conveniently. The equipment may include a rolling chair which, apart from operational comfort, ensures quick and easy access to remote parts of the control board and the operator can easily push off the current position and quickly get to the desired position due to progressive motion of the chair rolls. However, it should be noted that both embodiments of the control system, the automatic one and the one involving personnel, have certain disadvantages. The manual control may have such a disadvantage as low speed of data processing and decision-making by personnel compared to the requirements of the reactor plant. On the other hand, the fully automated control system may be unsafe in case of failures or incomplete algorithms of data processing. As a result, the combined embodiment of the control system may be implemented, i.e. data processing and control are performed in automatic mode, but the data is displayed with the use of indicating means and, if any parameter exceeds the permissible limits (or approaches to the permissible limits) or upon any necessity the qualified personnel can adjust the operation of the automated control system or control it manually. The modules of the control system can be executed in hardware on the basis of discrete electronic components, integrated microcircuits, processors, assemblies, racks etc. The control system can be analog, digital or combined. Modules which are electrically connected to equipment located in the reactor or in the control board and control its operation or process the data may include the converters of voltage, current, frequency, analog signals to digital once and contrariwise, drivers, sources of current or voltage and control elements. All these elements and modules can be located on one or several mounting plates, can share one board or component or be separated accordingly, or can be executed and installed without the use of mounting plates. The control system modules may also be executed in software. For this purpose, integrated microcircuits with programmable logic, controllers, processors and computers can be used as hardware; while software will include programs with commands and codes executed by means of the indicated microcircuits, controllers, processors, computers etc. connected to the reactor devices and equipment. The programs shall be stored in memory units which can be executed in various forms known from the background of this invention and can be data carriers read by computer: read-only memory, hard drives and floppy disks, optical disks, flash-drives, frame memory etc. The programs may include chains of codes or commands for implementation of method and algorithms as per this invention, in whole or in part. Microcircuits, controllers, processors and computers can be connected to the input/output devices which may be located separately or be included into the control board. Separate modules of the control system can be software modules or be combined into one or several programs as well as into one or several software packages or elements. The control system and its modules may be executed as both hardware and software, i.e. part of the modules or all the modules may be executed in hardware, and part of the modules or control devices may be made as software. In the preferable embodiment, the control modules of reactor equipment (mass-exchange apparatus, gas system, disperser) and the modules for conversion of sensors can be made in hardware, and the modules for processing of data and commands, information display and control of processing parameters (such as threshold and permissible values) can be made as software on the basis of a computer, processor or controller. Additionally, specialized integrated circuits can be produced. Such circuits shall contain all the necessary hardware elements with programs or parameters of data processing to be downloaded into these circuits. In the preferable embodiment, all electronic and other elements and components shall be made radiation-resistant to allow for operation of components and operability of the system in the whole as part of a nuclear reactor plant, which may be a source of ionizing radiation, and to preserve the capability of reactor operation control even in accident conditions and prevent possible adverse effects, thereby ensuring the enhanced safety and long operating life.
	description	This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0123981, filed on Oct. 17, 2013, the disclosure of which is incorporated herein by reference in its entirety. 1. Field of the Invention The present invention relates to a combustion controller for a combustible gas of a pressurized water reactor nuclear power plant, and more particularly, to a combustion controller for a combustible gas installed in a rear end of a filtered vent system outside a containment vessel or an external chimney, configured to convert a combustible gas such as hydrogen, carbon monoxide, or the like, into steam, carbon dioxide, or the like, and simultaneously, operated by itself with no external power supply. 2. Discussion of Related Art While a filtered vent system of a containment vessel installed at a nuclear power plant performs a function of discharging hydrogen, carbon monoxide and a non-condensable gas to the atmosphere, when hydrogen and a combustible gas are rapidly discharged to the atmosphere, combustion of the hydrogen occurs. In particular, when air is introduced from the outside, combusted flame may cause a backfire in a direction of filtered vent equipment. Accordingly, as the flame is generated, an exhaust tower or an exhaust chimney may be damaged, and of course, when the backfire occurs, the equipment may be seriously damaged according to circumstances. In particularly, when carbon monoxide is incompletely combusted to be directly discharged to the atmosphere, the carbon monoxide may be harmful to human bodies. Meanwhile, a passive apparatus for removing hydrogen is installed in the containment vessel. The passive apparatus is a passive autocatalytic recombiner PAR system. According to a scale of the containment vessel of the nuclear power plant, about 20 to 40 passive apparatuses are installed to remove hydrogen from the containment vessel through hydrogen catalyst combustion. The above-mentioned conventional PAR is a passive PAR disclosed in Korean Utility Model Publication No. 20-0464123, and includes a cover body having an inlet port formed at a lower end thereof and through which air including hydrogen gas is introduced, discharge ports formed at three surfaces of an upper end thereof and through which the introduced air is discharged, and a guide plate inclined from the three surfaces toward the remaining surface to guide the air flow to the discharge ports; a honeycomb type catalyst body mounted on a lower end of the cover body to react with the introduced hydrogen gas to remove hydrogen; and a catalyst body housing assembly, on which the catalyst body sits, configured to detachably mount the catalyst body on the lower end of the cover body, wherein a roof plate installed on the three surfaces, in which the discharge ports are formed, is provided on an upper end of the cover body to prevent liquid dropped from above from being introduced into the cover body through the discharge ports. However, even when an automatic catalyst coupler is installed in the containment vessel, a combustible gas such as hydrogen, carbon monoxide, and so on, in the containment vessel is discharged to the atmosphere through the filtered vent equipment while being incompletely oxidized when the combustible gas is exhausted to the outside of the containment vessel through the filtered vent equipment. Accordingly, even when the passive automatic catalyst recombiner disclosed in the related art is installed in the containment vessel, additional equipment is needed to remove a combustible gas such as hydrogen or carbon monoxide, which is unavoidably discharged to the outside. However, the PAR disclosed in Korean Utility Model Publication No. 20-0464123 is a structure that cannot be installed at the rear end of the filtered vent equipment outside the containment vessel or the external chimney. (Patent Literature 1) Korean Utility Model Publication No. 20-0464123 In order to solve the problems, the present invention is directed to a combustion controller for a combustible gas installed at a rear end of filtered vent equipment outside a containment vessel or a rear end of other exhaust equipment and capable of performing stable combustion control with no probability of explosion of hydrogen through a stable recombining reaction of air with a combustible gas, preventing discharge of toxic carbon monoxide, and preventing backfire of flame through a quenching mesh. In addition, the controller may be used in a discharge pipe of the combustible gas in equipment of a general industry. According to an aspect of the present invention, there is provided a combustion controller for a combustible gas which includes: a support frame having a combustible gas inlet port formed at a lower end thereof and a fluid inlet port formed at a side surface thereof; a quenching mesh disposed on the combustible gas inlet port or under an outlet port of the combustion controller for a combustible gas and fixed to the support frame; and at least one recombiner disposed on or under the quenching mesh and fixedly installed at the support frame. Advantages and features of the present invention and a method of accomplishing these will be apparent from embodiments described below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below but may be implemented in various modifications. The following embodiments are described in order to enable those of ordinary skill in the art to embody and practice the present invention. To clearly describe the present invention, parts not relating to the description are omitted from the drawings. Like reference numerals refer to like elements throughout the description of the drawings. Hereinafter, a combustion controller for a combustible gas according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings, but some elements not related to the spirit of the present invention will be omitted or simplified. However, the omitted elements are not necessary elements in the present invention but may be coupled and used in the present invention by those skilled in the art. FIG. 1 is a view showing an embodiment of a combustion controller for a combustible gas according to the present invention. As shown in FIG. 1, a containment vessel pressure regulation valve 510 to be opened when a pressure in a containment vessel 500 reaches a certain pressure or more is installed outside the containment vessel 500 to uniformly maintain a pressure in the containment vessel 500. Since the containment vessel pressure regulation valve 510 is automatically opened when the pressure in the containment vessel 500 reaches a certain value or more regardless of a hydrogen concentration in the containment vessel 500, a combustible gas and radioactive substances present in the containment vessel 500 are discharged to the containment vessel pressure regulation valve 510 with air to be introduced into filtered vent equipment 600. Here, since the filtered vent equipment 600 performs a function of removing radioactive vapor and fission products included in the introduced air, when the radioactive vapor and the fission products included in the introduced air are removed, concentrations of hydrogen and carbon monoxide in the gas discharged from the filtered vent equipment 600 are increased to relatively high levels. Accordingly, since the combustible gas such as hydrogen, carbon monoxide, and so on, included in the gas discharged from the filtered vent equipment 600 should be removed so as not to be discharged to the outside, an automatic catalyst recombiner should be installed in a nuclear power plant chimney 700 through which the gas filtered in the filtered vent equipment 600 is discharged. While the combustion controller for a combustible gas according to the embodiment of the present invention shown in FIG. 1 has been described as being installed in the nuclear power plant chimney 700, the present invention is not limited thereto, it may be installed in the filtered vent equipment 600. In this case, the combustion controller for a combustible gas may be installed in a flow path of a combustible gas or a storage tank of a combustible gas disposed in the filtered vent equipment 600. FIG. 2 is a cross-sectional view showing a configuration of the combustion controller for a combustible gas of FIG. 1. As shown in FIG. 2, the combustion controller for a combustible gas according to the embodiment of the present invention includes a support frame having an outlet port 150 formed at an upper end thereof, and an external fluid inlet port 120 configured to be open at the bottom so as a combustible gas inlet port 100 to be formed at a lower end thereof through which a combustible gas is introduced, and formed at a sidewall of the support frame to introduce external air, a quenching mesh 200 disposed over the combustible gas inlet port 100 and coupled and fixed to one side of the support frame, and a recombiner 300 disposed over the quenching mesh 200 and coupled and fixed to one side of the support frame. While the quenching mesh 200 of the embodiment of the present invention shown in FIG. 2 has been described as being disposed over the combustible gas inlet port 100, the present invention, is not limited thereto. The quenching mesh 200 may be installed under the outlet port 150 of the combustion controller for a combustible gas. Accordingly, the combustible gas discharged from the outlet port of the filtered vent equipment 600 is introduced into the nuclear power plant chimney 700 through the combustible gas inlet port 100, and here, the external fluid inlet port 120 may have a structure in which the combustible gas can be easily introduced from the outside into the inside, rather than discharged from the inside to the outside. Meanwhile, the combustible gas introduced into the combustible gas inlet port 100 passes through the quenching mesh 200 to arrive at the recombiner 300 having a honeycomb structure, and the quenching mesh 200 is installed to prevent backfire of flame and propagation of the flame performs a stable recombining reaction. That is, a temperature of the flame is decreased due to heat transfer to the quenching mesh 200 while the flame propagates through the quenching mesh 200 to decrease intensity of the flame, and in a chemical aspect, the quenching mesh 200 changes an active radical that accelerates a chain branching reaction into a stable chemical species, and thus, reduces a chemical reaction rate to decrease the intensity of the flame. Accordingly, when a level of the heat transfer and a level of a radical termination reaction are intensified to a certain level or more, the flame may be extinguished, and hydrogen combustion can be controlled using flame intensity attenuation and flame extinguishing phenomena. FIGS. 3A and 3B are views showing embodiments of the quenching mesh of FIG. 2. As shown in FIGS. 3A and 3B, the quenching mesh 200 configured to prevent propagation of the flame is a fine metal net structure, which may be a stainless steel net structure, and the size and structure of the grid of the quenching mesh 200 can be different according to a type of the combustible gas. The combustible gas passing through the quenching mesh 200 is introduced into the recombiner 300 with the air introduced from the fluid inlet port 120, and the combustible gas reacts with the oxygen included in the air. Here, as shown in the drawings, a shape of quenching mesh may be modified according to a shape of the recombiner. FIGS. 4A and 4B are perspective views showing embodiments of the recombiner of FIG. 2. As shown in FIGS. 4A and 4B, the recombiner 300 is a structure in which a catalyst is coated on a surface of the honeycomb structure, and a mixture of platinum or palladium and titanium dioxide or alumina may be used as the catalyst that can recombine the hydrogen and carbon monoxide. The recombiner 300 according to the present invention is not limited to the above-mentioned honeycomb structure and may be formed as a plate structure. A material of the catalyst is not particularly limited as long as the hydrogen gas reacts with the oxygen to be removed. For example, alumina is coated and then platinum is coated thereon to be used as the catalyst. The recombiner 300 shown in FIGS. 4A and 4B are installed in a chimney 700 in a multi-stage such that all of the combustible gas is completely oxidized and then discharged to the outside. Here, the recombiner 300 may be formed in various shapes such as a circular or rectangular shape according to necessity as long as the recombiner 300 can be fixed in the chimney. Meanwhile, combustion may occur over the recombiner 300 when the concentrations of hydrogen and carbon monoxide are high. In this case, the flame may flow backward. In order to prevent the backward flow, the quenching mesh 200 is installed under the recombiner 300 as described above. The combustible gas passing through the quenching mesh 200 is introduced into the recombiner 300 with the air introduced through the fluid inlet port 120, and the combustible gas reacts with the oxygen included in the air to be converted into steam, carbon dioxide, a non-condensable gas, and so on. Since such a reaction is generally an exothermic reaction and the gas is heated, the combustible gas can be discharged by the effect of buoyancy when the combustion controller for a combustible gas is installed in a gravity direction. That is, most of the gases are discharged over the combustion controller for a combustible gas by buoyancy, and a flow rate of the combustible gas discharged to the external atmosphere through the inlet port can be almost neglected. In addition, since the buoyancy of the combustible gas is generated by the heat generated upon recombining and the combustible gas is moved to above the recombiner 300 and discharged, the combustion controller for a combustible gas can be driven as passive equipment without separate power. As described above, since the combustible gas is converted into steam, carbon dioxide, a non-condensable gas, or the like, by recombining of the combustible gas and the air, safe combustion control with no probability of explosion of hydrogen can be performed. In addition, discharge of toxic carbon monoxide can be prevented, and backward flow of the flame can be prevented through the quenching mesh 200. FIG. 5 is a view of another embodiment of the combustion controller for a combustible gas of the nuclear power plant according to the present invention, showing a state in which a separate fan is installed, and FIG. 6 is a cross-sectional view taken along line A-A of FIG. 5. As shown in FIG. 5, the combustion controller for a combustible gas is installed in an annular section of the chimney 700, and a fan 400 is installed at an upper portion of a center of the annular section such that the external air (the atmosphere) is forcibly introduced into a lower portion of the center of the annular section. The center of the annular section functions as an external air introduction passage 410, and the air introduced at this time can pass through a fan fluid inlet port 420 to smoothly discharge the combustible gas introduced into the combustible gas inlet port 100 through the outlet port of the nuclear power plant chimney 700. In this case, the recombiner 300 and the quenching mesh 200 are configured as an annular shape formed along a periphery of the external air introduction passage 410 as shown in FIG. 6. Here, the quenching mesh 200 may be selectively installed on or under the recombiner 300. However, the combustion controller of a combustible gas having the annular shape according to the embodiment has the annular section, a lower portion of which is closed, such that any of the combustible gas introduced into the external air introduction passage 410 is prevented from being directly discharged to the atmosphere. Meanwhile, FIG. 6 is a view of another embodiment of the recombiner 300 having an annular shape, showing a cross-sectional view taken along line A-A of FIG. 5. As shown in FIG. 6, the support frame 800 has an annular shape, the fan 400 is installed at the center of the annular section, and the recombiner 300 having an annular shape is installed in the support frame 800. As can be seen from the foregoing, the combustion controller for a combustible gas according to the present invention is installed at the exhaust pipe or the exhaust chimney of the filtered vent equipment outside the containment vessel and capable of performing stable combustion control with no probability of explosion of hydrogen through a recombining reaction of the combustible gas, preventing discharge of carbon monoxide, which is a toxic gas, and preventing backward flow of the flame and propagation of the flame through the quenching mesh. It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers all such modifications provided they come within the scope of the appended claims and their equivalents.
051026147	abstract	In a boiling water nuclear reactor having its core, fuel support casting, and control rod guide tubes removed to expose the core plate, a method for the submerged welding repair and replacement of the control rod drive housing at the bottom extremity of the reactor vessel is disclosed. An alignment device registers to a hole in the core plate and its corresponding guide pin. A control rod drive housing mating fixture on the depending extremity of the shaft of the alignment device precisely fits and mates to the top of the control rod drive housing. The alignment device includes cross electronic levels sealed for submersion which levels remotely transfer through attached wiring the precise angularity between the top of the control rod drive housing on one hand and the corresponding and overlying hole in the core plate on the other hand. For the welding repair process herein, a welding cylinder apparatus fits over the depending end of the shaft of the alignment device. This welding cylinder protrudes downwardly and around the control rod drive housing mating to the stub tube through which the control rod drive housing is inserted. In the embodiment here illustrated, a rotating raceway is provided interior of the chamber for permitting TIG welding unit to traverse around a path for weldment defined at the side of the control rod drive housing and at the top of the stub tube.
	description	The present disclosure relates to control rods for controlling a nuclear reactor. A pressurized water reactor (PWR) generally employs a central core containing fissile nuclear fuel assemblies or bundles of nuclear fuel rods that contain fissile material. Thermal energy generated by the fissile reaction heats primary coolant, which is typically light water (H2O) optionally including additives such as boric acid or another soluble neutron poison, although other coolants/moderators such as heavy water (D2O) are also contemplated. The primary coolant passes through a steam generator where it transfers heat to a secondary coolant (usually water), turning the water into steam. The steam can subsequently be used to operate a turbine to generate electrical power or can be used for another purpose. Other types of nuclear reactors operate similarly. For example, in boiling water reactors (BWR) the primary coolant/moderator is not as highly pressurized but is allowed to boil and produce steam directly. Control rods are inserted into or removed from the core to control the neutron population density of the fuel assemblies. The control rods are fastened at their top ends to a spider assembly. The control rod typically comprises a stainless steel cladding surrounding a neutron-absorbing material, such as an alloy of silver-indium-cadmium (Ag—In—Cd), boron carbide (B4C), or hafnium (Hf) metal. The control rods are slid into and out of guide tubes that are located within the fuel assemblies. When using hafnium, one consideration that must be taken into account is hydriding. Hydrogen, for example from the reactor coolant, may diffuse through the stainless steel cladding and react with hafnium to form hafnium hydride (HfH2). This is a concern because HfH2 has a greater volume than that of the Hf metal in the original control rod. Swelling of the control rod thus occurs when the Hf metal is converted to HfH2. This may cause problems, depending on the location of and extent of the swelling, that affect the safety of the nuclear reactor. For example, swelling can increase the amount of time needed to fully insert the control rod into the corresponding the guide tube during a rod scram. Stainless steel itself is not a strong neutron absorber. The volume occupied by the stainless steel thus decreases the potential reactivity worth of the control rod. The rod worth refers to the neutron-absorbing ability of the control rod. A higher rod worth is desirable. In addition, passive safety concerns dictate that the control rod should be as heavy as is reasonably achievable, so that gravity can be used to insert the control rod into its corresponding guide tube when needed. Stainless steel has a density of around 7.8 g/cc, while hafnium itself has a density of 13.3 g/cc. It is desirable to provide control rods that have a combination of higher rod worth, increased weight, and greater physical and chemical stability (e.g. no hydride formation as in stainless steel clad Hf rods, or no tritium (H3 or 3H) that is generated in B4C containing rods). Disclosed in various embodiments are control rods suitable for use in a nuclear reactor that have a combination of higher rod worth, increased weight, and greater physical stability. The control rod comprises a bare hafnium skin or cladding, within which rodlets, pills, or powder may be arranged. The rodlets and pills do not have any cladding, or put another way the rodlets are bare. As discussed further herein, the rodlets and pills within the bare hafnium skin can be made of hafnium or Ag—In—Cd. Notably, the control rods do not have a stainless steel cladding. The space freed up by the absence of the stainless steel cladding allows for the presence of material having a higher rod worth, i.e. the hafnium tube. The hafnium tube has a hafnium oxide outer layer which is impermeable to hydrogen. The hafnium tube also has adequate strength and structural integrity to be attached to a spider assembly without the need for a cladding. The hafnium in the rod also increases the weight of the control rod, enhancing its rate of insertion under gravity alone. In some embodiments is disclosed a control rod, comprising a bare hafnium skin having a bullet-nose bottom tip. There may be a hafnium oxide outer layer that is the outermost surface of the control rod. The hafnium skin surrounds a central cavity. The control rod may further comprise a set of rodlets arranged axially within the central cavity. In some embodiments, the set of rodlets comprises a plurality of distal rodlets and at least one central rodlet. The plurality of distal rodlets is adjacent the hafnium skin and forms a distal annular layer. Each distal rodlet has an outer surface and an inner surface, the outer and inner surfaces each having a first arc. There is at least one central rodlet at a center of the control rod, each central rodlet having an outer surface, the outer surface having a second arc. The control rod may have a total of 12 distal rodlets, the first arc being about 30 degrees. Each distal rodlet may have a radial thickness of from about 0.8 millimeter to about 1.2 millimeters. The control rod may have a total of 4 central rodlets, the second arc being about 90 degrees, with each central rodlet further comprising two radial surfaces extending from opposite ends of the outer surface and forming a vertex. Each central rodlet may have a radial thickness of from about 1.6 millimeter to about 2.4 millimeters. In addition to the distal rodlets and the central rodlet(s), the set of rodlets may further comprise a plurality of intermediate rodlets forming an intermediate annular layer between the distal annular layer and the at least one central rodlet. Each intermediate rodlet has an outer surface and an inner surface, the outer and inner surfaces each having a third arc. In some embodiments, the control rod has a total of 8 intermediate rodlets, the third arc being about 45 degrees. Each intermediate rodlet may have a radial thickness of from about 0.8 millimeter to about 1.2 millimeters. In specific embodiments, the set of rodlets comprises: 12 distal rodlets adjacent the hafnium skin and forming a distal annular layer, each distal rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a first arc of about 30 degrees; 4 central rodlets at a center of the control rod, each central rodlet having an outer surface and two radial surfaces extending from opposite ends of the outer surface and forming a vertex, the outer surface having a second arc of about 90 degrees; and 8 intermediate rodlets forming an intermediate annular layer between the distal annular layer and the central rodlets, each intermediate rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a third arc of about 45 degrees. In other versions, the rodlets have a cylindrical shape, a triangular shape, or a rectangular shape. In some embodiments that locate rodlets in the central cavity, hafnium powder may also be used to fill any voids between rodlets and the hafnium skin. In some embodiments, each rodlet has two radial surfaces, an outer surface, and an axial length. Put another way, the rodlets are central rodlets, with the radial surfaces generally having a length substantially equal to the radius of the central cavity. Each rodlet has a plurality of channels along the axial length on the radial surfaces and does not have channels on the outer surface. In some further specific embodiments, the channels on the rodlets are arranged such that channels on one rodlet do not directly face the channels on any adjacent rodlets. In other embodiments, the bottom ends of the rodlets are spaced apart from an inner surface of the hafnium skin to form a void in the bottom tip of the hafnium skin. The hafnium skin may have a radial thickness of from about 0.5 millimeter to about 1.0 millimeters. The hafnium skin may also have a hafnium oxide outer layer forming an outermost surface of the control rod In other embodiments, the control rod comprises the hafnium skin, with either hafnium pills or hafnium powder filling the hafnium skin from the first or bottom end to the second or top end. In still other embodiments, the control rod uses a single solid hafnium rodlet, the rodlet having a bullet-nose bottom tip and an axial length between a top end and a bottom end, to fill the central cavity of the hafnium skin. The single rodlet may comprise a plurality of channels along the axial length to increase the flexibility of the rodlet. The plurality of channels begins above the bullet-nose bottom tip of the rodlet. Each channel extends from an outer surface into the rodlet for a depth of from one-third to one-half of the diameter of the rodlet, the channel forming a chord of the control rodlet. The chords of adjacent channels are rotated with respect to each other. Adjacent channels are also separated axially by a gap of at least 8 centimeters. Also disclosed in embodiments is a control rod, comprising: a hafnium cladding having a bullet-nose bottom tip and a hafnium oxide outer layer that is the outermost surface of the control rod; a plurality of distal rodlets within and adjacent the hafnium cladding and forming a distal annular layer, each distal rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a first arc; at least one central rodlet within the cladding and at a center of the control rod, each central rodlet having an outer surface and two radial surfaces extending from opposite ends of the outer surface and forming a vertex, the outer surface having a second arc; and a plurality of intermediate rodlets within the cladding and forming an intermediate annular layer between the distal annular layer and the at least one central rodlet, each intermediate rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a third arc. In other embodiments is disclosed a control system for use in a nuclear reactor, comprising a spider assembly and a plurality of control rods. Each control rod comprises: a hafnium skin with a top end, a bottom end, and a bullet-nose bottom tip, the skin having a hafnium oxide outer layer that is the outermost surface of the control rod, the hafnium skin being connected at the top end to the spider assembly; and a set of rodlets within the bare hafnium skin, each rodlet being connected at an upper end to the spider assembly and extending to the bottom end of the hafnium skin. The set of rodlets may consist essentially of: a plurality of distal rodlets adjacent the hafnium skin and forming a distal annular layer, each distal rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a first arc; a plurality of central rodlets at a center of the control rod, each central rodlet having an outer surface and two radial surfaces extending from opposite ends of the outer surface and forming a vertex, the outer surface having a second arc; and a plurality of intermediate rodlets forming an intermediate annular layer between the distal annular layer and the at least one central rodlet, each intermediate rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a third arc. In other embodiments, the set of rodlets consists essentially of: a total of 12 distal rodlets, the first arc being about 30 degrees; a total of 4 central rodlets, the second arc being about 90 degrees; and a total of 8 intermediate rodlets, the third arc being about 45 degrees. Also disclosed in embodiments is a cylindrical control rod formed of solid hafnium. The solid hafnium control rod has an outermost surface is which is not covered by a cladding. The control rod has a bullet-nose bottom tip and having an axial length between a top end and a bottom end of the control rod. Again, the solid hafnium control rod may comprise a plurality of channels along the axial length to increase the flexibility of the rod. The plurality of channels begins above the bullet-nose bottom tip of the rod. Each channel extends from an outer surface into the rod for a depth of from one-third to one-half of the diameter of the rod, the channel forming a chord of the control rod. The chords of adjacent channels are rotated with respect to each other. Adjacent channels are also separated axially by a gap of at least 8 centimeters. In some embodiments is disclosed a control rod, comprising a bare hafnium skin having a bullet-nose bottom tip. There may be a hafnium oxide outer layer that is the outermost surface of the control rod. The hafnium skin surrounds a central cavity. The control rod may further comprise a set of rodlets arranged axially within the central cavity. In some embodiments, the set of rodlets comprises a plurality of distal rodlets and at least one central rodlet. The plurality of distal rodlets is adjacent the hafnium skin and forms a distal annular layer. Each distal rodlet has an outer surface and an inner surface, the outer and inner surfaces each having a first arc. There is at least one central rodlet at a center of the control rod, each central rodlet having an outer surface, the outer surface having a second arc. The control rod may have a total of 12 distal rodlets, the first arc being about 30 degrees. Each distal rodlet may have a radial thickness of from about 0.8 millimeter to about 1.2 millimeters. The control rod may have a total of 4 central rodlets, the second arc being about 90 degrees, with each central rodlet further comprising two radial surfaces extending from opposite ends of the outer surface and forming a vertex. Each central rodlet may have a radial thickness of from about 1.6 millimeter to about 2.4 millimeters. In addition to the distal rodlets and the central rodlet(s), the set of rodlets may further comprise a plurality of intermediate rodlets forming an intermediate annular layer between the distal annular layer and the at least one central rodlet. Each intermediate rodlet has an outer surface and an inner surface, the outer and inner surfaces each having a third arc. In some embodiments, the control rod has a total of 8 intermediate rodlets, the third arc being about 45 degrees. Each intermediate rodlet may have a radial thickness of from about 0.8 millimeter to about 1.2 millimeters. In specific embodiments, the set of rodlets comprises: 12 distal rodlets adjacent the hafnium skin and forming a distal annular layer, each distal rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a first arc of about 30 degrees; 4 central rodlets at a center of the control rod, each central rodlet having an outer surface and two radial surfaces extending from opposite ends of the outer surface and forming a vertex, the outer surface having a second arc of about 90 degrees; and 8 intermediate rodlets forming an intermediate annular layer between the distal annular layer and the central rodlets, each intermediate rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a third arc of about 45 degrees. In other versions, the rodlets have a cylindrical shape, a triangular shape, or a rectangular shape. In embodiments that use rodlets to fill the central cavity, hafnium powder may also be used to fill any voids between rodlets and the hafnium skin. The hafnium skin may have a radial thickness of from about 0.5 millimeter to about 1.0 millimeters. In other embodiments, the control rod comprises the hafnium skin, with either hafnium pills or hafnium powder filling the hafnium skin from the first or bottom end to the second or top end. In still other embodiments, the control rod uses a single solid hafnium rodlet, the rodlet having a bullet-nose bottom tip and an axial length between a top end and a bottom end, to fill the central cavity of the hafnium skin. The single rodlet may comprise a plurality of channels along the axial length to increase the flexibility of the rodlet. The plurality of channels begins above the bullet-nose bottom tip of the rodlet. Each channel extends from an outer surface into the rodlet for a depth of from one-third to one-half of the diameter of the rodlet, the channel forming a chord of the control rodlet. The chords of adjacent channels are rotated with respect to each other. Adjacent channels are also separated axially by a gap of at least 8 centimeters. Also disclosed in embodiments is a control rod, comprising: a hafnium cladding having a bullet-nose bottom tip and a hafnium oxide outer layer that is the outermost surface of the control rod; a plurality of distal rodlets within and adjacent the hafnium cladding and forming a distal annular layer, each distal rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a first arc; at least one central rodlet within the cladding and at a center of the control rod, each central rodlet having an outer surface and two radial surfaces extending from opposite ends of the outer surface and forming a vertex, the outer surface having a second arc; and a plurality of intermediate rodlets within the cladding and forming an intermediate annular layer between the distal annular layer and the at least one central rodlet, each intermediate rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a third arc. In other embodiments is disclosed a control system for use in a nuclear reactor, comprising a spider assembly and a plurality of control rods. Each control rod comprises: a hafnium skin with a top end, a bottom end, and a bullet-nose bottom tip, the skin having a hafnium oxide outer layer that is the outermost surface of the control rod, the hafnium skin being connected at the top end to the spider assembly; and a set of rodlets within the bare hafnium skin, each rodlet being connected at an upper end to the spider assembly and extending to the bottom end of the hafnium skin. The set of rodlets may consist essentially of: a plurality of distal rodlets adjacent the hafnium skin and forming a distal annular layer, each distal rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a first arc; a plurality of central rodlets at a center of the control rod, each central rodlet having an outer surface and two radial surfaces extending from opposite ends of the outer surface and forming a vertex, the outer surface having a second arc; and a plurality of intermediate rodlets forming an intermediate annular layer between the distal annular layer and the at least one central rodlet, each intermediate rodlet having an outer surface and an inner surface, the outer and inner surfaces each having a third arc. In other embodiments, the set of rodlets consists essentially of: a total of 12 distal rodlets, the first arc being about 30 degrees; a total of 4 central rodlets, the second arc being about 90 degrees; and a total of 8 intermediate rodlets, the third arc being about 45 degrees. Also disclosed in embodiments is a cylindrical control rod formed of solid hafnium. The solid hafnium control rod has an outermost surface is which is not covered by a cladding. The control rod has a bullet-nose bottom tip and having an axial length between a top end and a bottom end of the control rod. Again, the solid hafnium control rod may comprise a plurality of channels along the axial length to increase the flexibility of the rod. The plurality of channels begins above the bullet-nose bottom tip of the rod. Each channel extends from an outer surface into the rod for a depth of from one-third to one-half of the diameter of the rod, the channel forming a chord of the control rod. The chords of adjacent channels are rotated with respect to each other. Adjacent channels are also separated axially by a gap of at least 8 centimeters. Also disclosed in various embodiments is a control rod that comprises at least one Ag—In—Cd rodlet located within a bare hafnium skin or cladding. The at least one Ag—In—Cd rodlet does not have any cladding, or put another way the rodlet is bare. The bare hafnium skin replaces the traditional stainless steel cladding, or in other words a stainless steel cladding is absent. This replacement allows for the presence of material having a higher rod worth, i.e. the hafnium skin. The hafnium skin (having a thickness of about 0.4 mm to about 1.2 mm) also has adequate strength and structural integrity to be attached to a spider assembly without the need for a cladding. The increased amount of hafnium in the rod (due to the hafnium skin) also increases the weight of the control rod, enhancing its rate of insertion under gravity alone. Disclosed in embodiments is an apparatus comprising a control rod. The control rod comprises a bare hafnium skin and at least one Ag—In—Cd rodlet. The bare hafnium skin has a bullet-nose bottom tip and surrounds the at least one Ag—In—Cd rodlet. The hafnium skin may have a hafnium oxide outer layer forming an outermost surface of the control rod. The control rod may further include a radial gap between the at least one Ag—In—Cd rodlet and the hafnium skin. An inert gas, such as argon, may fill the radial gap. In some embodiments, the hafnium skin has a generally uniform radial thickness. The at least one Ag—In—Cd rodlet(s) is/are tapered to conform to the bottom tip of the hafnium skin. In other embodiments, the bottom tip of the hafnium skin is solid hafnium, i.e. consists of hafnium. A bottom end of the at least one Ag—In—Cd rodlet is a flat surface. The solid hafnium may extend from a nadir of the hafnium skin for an axial length of from about 10 cm to about 20 cm. Alternatively, the ratio of an axial length of the at least one Ag—In—Cd rodlet to an axial length of the solid hafnium bottom end may be from about 10.5 to about 21. In some embodiments, the hafnium tube has a radial thickness of from about 0.04 millimeters to about 1.2 millimeters. The control rod may comprise a single Ag—In—Cd rodlet within the hafnium skin. The single Ag—In—Cd rodlet can sometimes comprise a plurality of channels along an axial length, wherein each channel extends from an outer surface into the rodlet for a depth of from one-third to one-half of the diameter of the rodlet, the channel forming a chord of the rodlet; wherein the chords of adjacent channels are rotated with respect to each other; and wherein adjacent channels are separated axially by a gap of at least 8 centimeters. In other embodiments, the hafnium skin surrounds a plurality of Ag—In—Cd rodlets. Each rodlet may have a circular cross-section with a diameter of from about 0.1 millimeter to about 2 millimeters. The control rod may further comprise a threaded screw connector at a top end. The apparatus may further comprise a nuclear reactor including a reactor core disposed in a pressure vessel. The apparatus is configured to controllably insert the control rod into the reactor core to control reactivity of the reactor core. The nuclear reactor may be a pressurized-water reactor. Also disclosed is a control system for use in a nuclear reactor. The control rod comprises a coupling element or assembly, and a plurality of control rods. Each control rod includes at least one Ag—In—Cd rodlet and a bare hafnium skin. The bare hafnium skin has a bullet-nose bottom tip and surrounds the at least one Ag—In—Cd rodlet, or put another way is disposed about the Ag—In—Cd rodlet. The hafnium skin is connected at a top end to the coupling element or assembly. The at least one Ag—In—Cd rodlet is connected at a top end to the coupling element or assembly, and extends to a bottom end of the bare hafnium skin. These and other non-limiting aspects of the present disclosure are more particularly described below. A more complete understanding of the components, processes, and apparatuses disclosed herein can be obtained by reference to the accompanying figures. These figures are merely schematic representations based on convenience and the ease of demonstrating the present development and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments. Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). When used in the context of a range, the modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the range “from about 2 to about 4” also discloses the range “from 2 to 4.” The term “comprising” is used herein as requiring the presence of the named component and allowing the presence of other components (except as specifically excluded). The term “comprising” should be construed to include the term “consisting of” (which allows the presence of only the named component, along with any impurities that might result from the manufacture of the named component) and “consisting essentially of” (which allows the presence of the named component, impurities, and other materials that do not materially affect the basic characteristics of the component). The terms “single” or “one” are used in some places to denote that there is only one of the referenced component. In particular, when either of these terms is used in conjunction with the term “comprising”, the overall phrase should be construed to allow the presence of only one of the named component, while allowing the presence of other components. The terms “single” or “one” are intended to distinguish from a “plurality”, which allows for two or more of the reference component. In some embodiments disclosed herein, a control rod comprises a bare hafnium skin. In other embodiments disclosed herein, rodlets are arranged axially within the skin. In particular embodiments disclosed herein, a control rod comprises at least one Ag—In—Cd rodlet and a hafnium skin surrounding the at least one Ag—In—Cd rodlet. The control rod may serve as part of a control system when connected to a suitable control rod drive mechanism (CRDM). With reference to FIG. 1, a perspective sectional view of an illustrative pressurized water nuclear reactor (PWR) including an integral steam generator is shown. A nuclear reactor core 10 is disposed inside a generally cylindrical pressure vessel 12, which contains primary coolant 14, which in the illustrative case of a light water reactor is water (H2O) optionally containing additives such as soluble boric acid serving as a soluble neutron poison. The PWR includes a steam bubble 16 in the upper portion of the volume, with a water level 18 delineating between the steam bubble 16 and the liquid primary coolant 14. Pressure is adjusted via the steam bubble 16, using electric heaters or the like or an external pressurizer (components not shown). Reactor control is provided by a control rod system 20 including a drive mechanism (CRDM) that is configured to controllably insert and withdraw neutron-absorbing control rods into and out of the nuclear reactor core 10. In some embodiments disclosed herein, the control rods comprise hafnium (Hf). The CRDM may be divided into multiple units, each controlling one or more control rods, in order to provide redundancy or other benefits. A spider or other coupling element or coupling assembly may be included in order to connect a plurality of control rods with a single CRDM unit which moves the plurality of control rods upward or downward together as a unit. The illustrative control rod system 20 includes internal CRDM units in which the drive motors and other components are disposed inside the pressure vessel 12 and submerged in the primary coolant 14, with only electrical power and control wiring extending outside the pressure vessel 12. Alternatively, external CRDM units may be employed. The pressure vessel 12 is configured to define a desired circulation of the primary coolant 14. In the illustrative example, the circulation is defined by a hollow cylindrical central riser 22 disposed coaxially in the illustrative cylindrical pressure vessel 12. Primary coolant 14 heated by the reactor core 10 flows upward through fluid conduits passing through the control rod system 20 and upward through the hollow central riser 22, discharges at the top of the hollow central riser 22 and is diverted downward by a diverter 24, flows downward through an annulus defined between the cylindrical central riser 22 and the walls of the cylindrical pressure vessel 12, and is then diverted upward at the bottom of the pressure vessel 12 to return to the reactor core 10. Optional primary coolant pumps 26 may be provided to drive the circulation of the primary coolant 14, or to assist natural circulation of the primary coolant 14. The illustrative coolant pumps 26 are internal pumps which are wholly inside the pressure vessel 12 and submerged in the primary coolant 14, with only electrical power and optional control wiring extending outside the pressure vessel 12. Alternatively, natural circulation may be relied upon for circulating the primary coolant. The pressure vessel 12 is suitably positioned substantially vertically. An optional skirt 30 may be provided to support the pressure vessel 12, or to bias against the pressure vessel 12 tipping over. The illustrative skirt 30 is positioned such that the lower portion of the pressure vessel 12 containing the reactor core 10 is located in a recess below ground, which facilitates flooding for safety in the event of a loss of coolant accident (LOCA) or other accident. In the operative state of the nuclear reactor, the control rod system 20 withdraws (or at least partially withdraws) the control rods from the nuclear reactor core 10 to initiate a nuclear reaction in the core 10. In a thermal nuclear reactor, the primary coolant 14 serves as a neutron moderator to thermalize higher energy neutrons so as to maintain or enhance the nuclear reaction. In the operating state of a PWR, the primary coolant 14 is superheated. In the case of a boiling water reactor (BWR) (not illustrated), the primary coolant is not superheated but is boiling. To provide steam generation, the primary coolant 14 heated by the operating reactor core 10 is brought into thermal communication with a secondary coolant (typically light water, H2O optionally containing various additives, solutes, or so forth) flowing in a steam generator. In some embodiments (not illustrated), the steam generator is external to the pressure vessel and connected therewith by a relatively large-diameter vessel penetration carrying the primary coolant. In the illustrative embodiment of FIG. 1, however, an integral steam generator 32 is located inside the same pressure vessel 12 containing the reactor core 10. The illustrative integral steam generator 32 is located in the annulus surrounding the central riser 22, that is, in the annular space between the exterior of the central riser 22 and the inside walls of the pressure vessel 12. Secondary coolant in the form of feedwater is input via a feedwater inlet 34 into an annular feedwater inlet plenum 36 (or, alternatively, into a tubesheet) where it feeds into a lower end of the steam generator 32. The secondary coolant rises generally upward through the steam generator 32 in secondary coolant flow paths or volume that are in thermal communication with (but in fluid isolation from) proximate primary coolant flow paths or volume through which primary coolant flows generally downward. (Note that FIG. 1 does not show details of the steam generator). The steam generator configuration can take various forms. In some embodiments, the steam generator comprises tubes carrying primary coolant generally downward, while the secondary coolant flows generally upward in a volume outside of the tubes. Alternatively, the secondary coolant may flow generally upward through the steam generator tubes while the primary coolant flows generally downward outside of the tubes. The tubes may comprise straight vertical tubes, slanted vertical tubes, helical tubes wrapping around the central riser 22, or so forth. However arranged, heat transfer takes place from the superheated primary coolant to the secondary coolant, which converts the secondary coolant from the liquid phase to the steam phase. In some embodiments the steam generator may include an integral economizer in a lower portion of the steam generator. In some embodiments, the steam generator may comprise a plurality of constituent steam generators to provide redundancy. The resulting steam enters an annular steam plenum 40 (or, alternatively, into a tubesheet) and from there passes out one or more steam outlets 42. The steam (whether generated by an integral steam generator such as the illustrative integral steam generator 32, or by an external steam generator unit) can be used for substantially any purpose suitably accomplished using steam power. In the illustrative electrical plant of FIG. 1, the steam drives a turbine 46 which in turn drives an electrical power generator 48 to produce electrical power. A steam condenser 50 downstream of the turbine 46 condenses the steam back into a liquid phase so as to recreate secondary coolant comprising feedwater. One or more pumps 52, 53 and one or more feedwater heaters 54, 55 or other feedwater conditioning components (e.g., filters, components for adding additives, or so forth) generate feedwater at a desired pressure and temperature for input to the feedwater inlet 34. A feedwater valve 56 suitably controls the inlet feedwater flow rate. The PWR described with reference to FIG. 1 is merely an illustrative example. The control rods disclosed herein are suitably used in the illustrative PWR reactor, or in a PWR reactor coupled with one or more external steam generators, or with a BWR, or so forth. The present disclosure contemplates several different aspects in the construction of the control rod. These different aspects are separately described, but can be combined in any fashion. An exemplary embodiment of the control rod of the present disclosure is shown in FIGS. 2-4. FIG. 2 is a side cross-sectional view of the control rod in combination with a spider assembly. FIG. 3 is a perspective view of the control rod and the spider assembly. FIG. 4 is a top cross-sectional view of the control rod. Generally speaking, the spider assembly 60 comprises a central casing 70 with a plurality of arms 80 extending from the central casing, either radially or longitudinally as shown here. Other coupling elements or assemblies are also contemplated. One or more arms 80 of the spider assembly can interconnect to the top end 112 of the hafnium skin 110. A lip 116 may be present at the top end 112 of the hafnium skin to facilitate this connection. Similarly, in some embodiments, an arm 80 of the spider assembly can interconnect to the top end 142 a rodlet 140 wherein a water tight seal (not shown) prevents coolant from entering the structure of the rod. The hafnium skin and the rodlets all hang under their own weight from the spider assembly. The rodlets do not rest on the bullet-nose bottom tip 114 of the hafnium skin, nor do they depend on the hafnium skin or adjacent rodlets for support. The control rod 100 has a top end 102 and a bottom end 104. The control rod comprises a bare hafnium skin 110 made of elemental hafnium. The hafnium skin may also be described as having a tubular shape. This hafnium skin can also be considered a hafnium cladding. No stainless steel cladding, or cladding of any other material, is present around the hafnium skin. The hafnium skin 110 also has a top end 112 and a bottom end 114. The bottom end 114 of the hafnium skin is located at the bottom end 104 of the control rod. The bottom end of the hafnium skin has a tapered or bullet-nose bottom tip 117. Transition point 111 denotes the point where the hafnium skin begins to taper to form the bottom tip 117. The hafnium skin 110 surrounds a central cavity 130, which has a radius 131. The inner surface of the hafnium skin is labeled with reference numeral 118. The hafnium skin generally maintains a constant radial thickness 113 along the length of the control rod down to the transition point 111. A thin hafnium oxide outer layer 120 may be present on the hafnium skin. The hafnium oxide outer layer is the outermost surface of the control rod. In this regard, the temperature at which Hf metal begins to hydride in water is over 700° C., which is well above the peak temperature of any PWR, or any light water reactor (LWR) in general. However, HfH2 is sometimes observed inside stainless steel clad hafnium rods. Thus, it is expected that bare Hf metal (i.e. without a cladding surrounding the rod) in a PWR (or any water-cooled/moderated reactor) will not hydride, because the Hf metal of the hafnium skin is not clad in stainless steel where the hafnium may experience long-term exposure to water that may be heated or vaporized to temperatures at which the water could interact excessively with the Hf metal. According to the ASM Handbook, Volume 13B (published 2005, ISBN 978-0871707079), hafnium is not expected to interact with oxygen until a temperature of about 400° C., when a protective layer of hafnium oxide (HfO2) is formed. This hafnium oxide outer layer is expected to impede hydriding of the hafnium skin as well. 400° C. is also above the peak temperature of any PWR or LWR. One or more rodlets 140 are arranged axially within the central cavity, i.e. parallel to central axis 105. Put another way, the bare hafnium skin surrounds the rodlet(s). It should be noted that these rodlets are also bare, or in other words there is no cladding surrounding each rodlet either. Each rodlet has a top end 142 which can be interconnected to a spider assembly. Each rodlet also has a bottom end 144 which is proximate to the bottom tip 114 of the hafnium skin. Each hafnium rodlet 140 will become covered with a thin layer of hafnium oxide when exposed to air. This oxide layer will hinder any bonding between the hafnium skin 110 and the rodlet 140, so the rodlet(s) and the skin can slide against each other. If desired, a coating may also be placed on the surfaces of each rodlet to act as a lubricant. Different arrangements of rodlet(s) are contemplated, as will be discussed further herein. These different arrangements or embodiments can achieve a flexible control rod, with the shapes of the rodlet(s) determining the amount of flexibility in the control rod and the relative effective density of the control rod. Each rodlet 140 can be made of elemental hafnium or an Ag—In—Cd alloy. In some embodiments, different forms of hafnium are used. Ag—In—Cd has good relative cost and reduced machining and manufacturing costs. As seen in FIG. 4, in one arrangement, the set of rodlets comprises a plurality of distal rodlets 150, a plurality of intermediate rodlets 160, and at least one central rodlet 170. As shown here, there is a plurality of central rodlets 170. The distal rodlets 150 are located adjacent to the hafnium skin 110 and can be considered to form a distal annular layer 151. The central rodlet(s) 170 is located at the center of the control rod, i.e. adjacent to the central axis 105. The intermediate rodlets 160 are located between the distal annular layer 151 and the central rodlet(s) 170, and can be considered to form an intermediate annular layer 161. FIG. 5 is an exploded view of the rodlets of FIG. 4. Each distal rodlet 150 has an outer surface 152, an inner surface 154, and two radial surfaces 156, 158. The outer and inner surfaces 152, 154 each have a first arc 155, the arc being measured at the vertex 157 where the radial surfaces join. The central rodlet 170 has an outer surface 172. The outer surface 172 has a second arc 175. As shown in FIG. 5, the central rodlet 170 also has two radial surfaces 176, 178 that extend from opposite ends of the outer surface to form a vertex 177. Each intermediate rodlet 160 has an outer surface 162, an inner surface 164, and two radial surfaces 166, 168. The outer and inner surfaces 162, 164 each have a third arc 165, the arc being measured at the vertex 167 where the radial surfaces join. The outer and inner surfaces of each rodlet are relative to the central axis 105. In FIG. 4, there are a total of 12 distal rodlets 150, with the first arc being about 30 degrees. There are a total of 4 central rodlets 170, with the second arc being about 90 degrees. There are a total of 8 intermediate rodlets 160, with the third arc being about 45 degrees. It is contemplated that all three types of rodlets 140 will share the same vertex from which their arc is measured. That vertex is generally located along the central axis 105. The control rod has a total diameter of 9.779 millimeters, which provides some tolerance for variances in the diameter of the guide tube into which the control rod is inserted (˜10 mm). The hafnium skin 110 itself may have a radial thickness 113 of from about 0.5 millimeters to about 1.0 millimeters. Each distal rodlet 150 may have a radial thickness 153 of from about 0.8 millimeter to about 1.2 millimeters. Each intermediate rodlet 160 may have a radial thickness 163 of from about 0.8 millimeter to about 1.2 millimeters. Each central rodlet 170 may have a radial thickness 173 of from about 1.6 millimeters to about 4.9 millimeters, depending on the presence or absence of the distal and/or intermediate rodlets. In particular embodiments, the radial thickness of each central rodlet is from about 1.6 millimeters to about 2.4 millimeters, or from about 3.6 millimeters to about 4.9 millimeters. In FIG. 4, two annular layers 151, 161 surrounded a central rodlet 170. Generally speaking, it is contemplated that the rodlets arranged axially within the central cavity may be arranged in any number of concentric annular layers, like an onion skin, inside the bare hafnium skin 110, within practical reasons (e.g. the ability to attach all of the rodlets to a control rod system). Each annular layer may be made of any number of rodlets, the number in each annular layer in FIG. 4 being merely illustrative. In particular, it is contemplated that in some embodiments, there are four rodlets in each annular layer, with each rodlet in an annular layer having an arc of 90 degrees. It is also contemplated that there may be three annular layers. FIG. 6 illustrates one such variation. Here, a set of rodlets 140 is surrounded by the hafnium skin 110. The set of rodlets here includes only a plurality of distal rodlets 150 and one central rodlet 170. The central rodlet 170 has an outer surface 172 that covers an arc of 360 degrees. There are four distal rodlets 150, each having an arc of 90 degrees. The four distal rodlets 150 are adjacent to the hafnium skin 110 and form an annular layer 151 around the central rodlet 170. No intermediate rodlets are present here. FIG. 7 illustrates another such variation. Here, a set of rodlets 140 is surrounded by the hafnium skin 110. The set of rodlets includes a central rodlet 170, a plurality of distal rodlets 150, and two sets of intermediate rodlets 160, 180. The distal rodlets form a distal annular layer, the first set of intermediate rodlets 160 forms an outer intermediate annular layer 161, and the second set of intermediate rodlets 180 forms an inner intermediate annular layer 181. FIG. 8 illustrates another contemplated variation. Here, the hafnium skin 110 surrounds a plurality of central rodlets 170. Here, there are three central rodlets 170. The outer surface 172 of each central rodlet 170 covers an arc of 120 degrees. It should be noted that in this embodiment, the length of each radial surface 176, 178 is about equal to the radius 131 of the central cavity 130. The control rod itself has a diameter of 9.779 millimeters, and a total length of about 210 centimeters (from the top end of the rod to the end of the bullet-nose bottom tip). One advantage of the structure of the present control rod is that if there is some inadvertent curvature in the control rod or its guide tube, the control rod is physically flexible and can snake past the curvature. Referring back to FIG. 2, each rodlet 140 extends from the top end 102 of the control rod to the bottom end 104 of the control rod. The rodlets 140 vary in length and shape at their bottom ends 144 to conform to the bullet-nose shape of the hafnium skin 110. Thus, for example, the central rodlets 150 are longer than the intermediate rodlets 160 or the distal rodlets 170. The bottom ends 144 of the rodlets could also be described as having a partial bullet-nose shape, or as being tapered. The rodlets 140 are shaped to minimize any loss of theoretical density, or put another way to maximize the percentage of theoretical density, or to obtain a maximal packing density. Constructing the control rod in this manner preserves most of the absorption strength compared to a single stiff solid bare hafnium rod with a diameter of 9.779 millimeters, but provides flexibility as described above. Another embodiment is illustrated in the top cross-sectional view of FIG. 9. A set of rodlets 140 is shown within the hafnium skin 110. Here, the rodlets 140 have a circular cross-section. As shown here, all of the rodlets 140 have the same diameter 145. However, it is also contemplated that the set of rodlets may be made up of groups of rodlets, each group having a different diameter as needed to maximize the percentage of theoretical density. In embodiments, each rodlet has a diameter of from about 0.1 millimeter to about 2 millimeters. Generally, a smaller diameter will result in an increase in the percentage of theoretical density, but will also increase the difficulty of connecting each rodlet to the spider assembly. The length of the rodlets and shape of the rodlets at their bottom end can vary to conform to the bullet-nose shape of the hafnium skin 110; this aspect is not seen here. For ease of assembly, the cylindrical rodlets are generally arranged in a hexagonal lattice (i.e. so that a rodlet is tangent to its six immediate neighbors). Mathematically, the central cavity of the hafnium skin can be most efficiently filled by either a triangular lattice or a square lattice. In other words, the rodlets have either a triangular or a square cross-section when viewed from the top. If desired, the inner surface 118 of the hafnium skin may be crafted or shaped to have a variable thickness to accommodate the shapes of the rodlets. In the embodiment illustrated in the top cross-sectional view of FIG. 10, the rodlets have a triangular cross-section. The term “triangular” is used here to indicate that the rodlets have three sides. In some particular embodiments, the rodlets have three straight sides. As shown here, all of the rodlets have the same side length 146. The side length may be from less than 1 millimeter to about 2 millimeters, as desired. Again, it is also contemplated that the rodlets could have varying side lengths as needed to maximize the percentage of theoretical density. Alternatively, some of the rodlets could have a curved third side, rather than a straight side, as indicated by reference numeral 149. The length of the rodlets and shape of the rodlets at their bottom end can vary to conform to the bullet-nose shape of the hafnium skin 110; this aspect is not seen here. In the embodiment illustrated in the top cross-sectional view of FIG. 11, the rodlets have rectangular cross-sections. The term “rectangular” is used here to indicate that the rodlets have four sides and four right angles. In some particular embodiments, the rodlets have three straight sides. The side lengths 147, 148 may be from less than 1 millimeter to about 2 millimeters, as desired. It is contemplated that the set of rodlets may be made up of several groups of rectangles, each group having different side lengths as needed to maximize the percentage of theoretical density. For example, shown here are two groups of rectangles 141, 143. The length of the rodlets and shape of the rodlets at their bottom end can vary to conform to the bullet-nose shape of the hafnium skin 110; this aspect is not seen here. In particular embodiments, at least one group of rodlets have square cross-sections (a square being a specific case of rectangle). Alternatively, some of the rodlets could have partial rectangular cross-sections, as indicated by reference numeral 139. The term “partial rectangular” is used here to indicate that the rodlets have two right angles and either four or five sides, wherein one or two sides may be curved. The rodlets shown in FIGS. 9-11 may be simpler to make than the rodlets shown in FIGS. 6-8. However, the rodlets of FIGS. 9-11 will have a lower percentage of theoretical density than those of FIGS. 6-8. In addition, the rodlets of FIG. 10 and FIG. 11 have sharp edges contacting the hafnium skin. This may create stress points on the hafnium skin that may make the skin easier to rupture, which would be undesirable. There may be small voids or spaces in the central cavity, for example between adjacent rodlets, as well as between the rodlets and the hafnium skin itself. Hafnium powder may be used to pack these voids (e.g. voids 103 in FIG. 9 or FIG. 11). The hafnium powder may be elemental hafnium, or hafnium oxide. The powder also decreases the friction between rodlets and enhances overall rod flexibility. Using elemental hafnium powder increases the maximum hafnium loading of the overall control rod. However, elemental hafnium powder may be more prone to hydriding if hydrogen-bearing materials enter the hafnium skin. Using HfO2 powder can serve as an additional inhibitor of hydriding if hydrogen-bearing materials enter the hafnium skin, protecting the function of the rodlets. However, using HfO2 decreases the hafnium loading of the overall control rod compared to the use of elemental hafnium powder. In a subsequent sealing step, any remaining voids are preferably filled with a suitable neutral gas, such as argon or nitrogen, at a suitable pressure level before the rod is sealed. It is specifically contemplated that the embodiments shown in FIGS. 4-11 use hafnium rodlets or Ag—In—Cd rodlets. In other embodiments, the hafnium skin can be filled with hafnium pills. The term “pills” refers to pieces of elemental hafnium which are larger than hafnium powder, with minimum dimensions of about 0.1 mm. However, pills do not have an axial length that extends from the top end 112 of the hafnium skin to the bottom end 104 of the hafnium skin. Whereas the rodlets have a length/diameter ratio of about 210, pills have a length/diameter ratio of from about 1 to about 40. The hafnium skin may also be filled with powder, along with the pills. The use of hafnium pills and powder may allow the overall control rod to have less resistance to insertion in a warped guide rube. However, if mechanical flexibility is desired, such embodiments that do not include rodlets may not have adequate spring resistance to return to a “straight” rod configuration. It is also possible that such embodiments are more vulnerable to puncture and/or denting of the hafnium skin. Another embodiment is shown in FIG. 12. Here, the control rod 100 is formed from a hafnium skin 110. The hafnium skin 110 surrounds a central cavity 130. The central cavity 130 is filled with hafnium powder from the bottom end 104 of the control rod to the top end 102 of the control rod. The hafnium powder may be elemental hafnium or hafnium diboride. In the embodiment of FIG. 12, the hafnium powder is separated into a concentric outer region 190 and inner region 200. The outer region 190 is filled with elemental hafnium powder, while the inner region is filled with hafnium diboride (HfB2) powder at 70% t.d. If desired, the HfB2 powder can be enriched in B-10, for example up to 40 wt %. The radial thickness 203 of the inner region 200 may vary from greater than zero to about 3.9 millimeters. The radial thickness 193 of the outer region, along with the thickness 113 of the hafnium skin 110, makes up the remainder of the radius of the control rod. In additional embodiments as shown in FIG. 13, the inner region 200 is separated into a central region 210 and a secondary region 220. The central region 210 contains elemental hafnium powder, while the secondary region 220 contains HfB2 powder. The radial thickness 213 of the central region 210 may vary from greater than zero to about 3.9 millimeters. The radial thickness 223 of the secondary region 220 may also vary from greater than zero to about 3.9 millimeters. When the central cavity of the hafnium skin is filled with hafnium rodlets, pills, or powder, the control rod can achieve a greater rod worth than is available from control rods that incorporate Ag—In—Cd or B4C. Because the control rod is made from mostly hafnium and does not waste volume on stainless steel, the rod worth of the overall control rod can be comparable to that of a standard B4C rod at 80% theoretical density (“t.d.”) without the swelling-with-irradiation issues associated with B4C rods. Due to hafnium's high density, the control rod also has a greater weight than other rod designs, even compared to a design incorporating tungsten rodlets (which also reduce rod worth). This provides a higher rate of insertion under gravity. The control rod also has greater chemical, shape, and physical stability. The combination of these three properties makes this a superior design. The use of a hafnium skin 110 is expected to protect the hafnium rodlets 140 from interaction with the environment in the fuel core. As previously noted, hafnium metal should not hydride at the temperatures to which the hafnium skin will be exposed. The presence of a hafnium oxide outer layer 120, when present, will also reduce hydriding of the rodlets because hydrogen cannot diffuse through hafnium oxide, as it can through stainless steel. Thus, hydriding is not expected to be a major concern. The hafnium oxide layer 120 can be created by applying a surface treatment to the hafnium skin, for example by controlled oxidation. Desirably, the hafnium oxide layer 120 has a thickness of from 5 micrometers to 10 micrometers. In addition, the hafnium metal has adequate strength and structural integrity to be attached to the spider assembly directly, without the need for a stainless steel cladding. FIG. 14 is a graph generated from computer calculations using CASMO5 to compare control rods using different materials and structure. The y-axis is the rod worth, and the x-axis is measured in fuel burnup (Megawatt·day per kg of heavy metal). The calculations were performed with five different control rods: (A) Ag—In—Cd (85-10-5 wt %, respectively); (B) hafnium with steel cladding; (C) hafnium with hafnium skin (no steel cladding); (D) B4C rod with natural B-10 content at 80% t.d.; and (E) B4C rod enriched to 40 wt % B-10 content at 80% t.d. The rod worth was determined according to the formula RW=100%×[(K-inf un-rodded lattice/K-inf rodded lattice)−1]. The fuel lattice was UO2 enriched to 4.95% U-235 and at 96% t.d. The UO2 fuel was fresh, without burnable absorbers or soluble boron present. The fuel lattice consisted of 265 pins per assembly and 24 guide tubes. The graph shows that control rod (C) has a much higher rod worth than control rod (B) with the steel cladding. FIG. 15 is a graph generated from computer calculations using CASMO5 to demonstrate the effect of changing the relative amounts of elemental hafnium and HfB2 in the control rod on the rod worth of the control rod. Here, the control rod is separated into an inner region and an outer region as illustrated in FIG. 12. Using the reference numerals of FIG. 12, the inner region 200 is filled with elemental hafnium, and the outer region 190 is filled with HfB2. Four different radii for the inner region (numeral 203) are used: 0.8895, 1.8895, 2.8895, and 3.8895 mm. The control rod has a total radius of 4.8895 mm, so the radial thickness (numeral 193) of the outer region is the difference between the total radius and the inner region radius. The HfB2 was also modeled with natural B-10 content and enriched to 40 wt % B-10, both at 70% t.d. The new control rods are: (F) inner radius 3.8895, natural B-10 content for the HfB2; (G) inner radius 2.8895, natural B-10 content; (H) inner radius 1.8895, natural B-10 content; (J) inner radius 0.8895, natural B-10 content; (K) inner radius 3.8895, 40 wt % B-10 content for the HfB2; (L) inner radius 2.8895, 40 wt % B-10 content; (M) inner radius 1.8895, 40 wt % B-10 content; and (N) inner radius 0.8895, 40 wt % B-10 content. The control rods (A)-(E) of FIG. 14 are also shown here for comparison. The graph of FIG. 15 shows two trends. First, as the amount of elemental hafnium decreased (i.e. decreasing inner radius), the rod worth also decreased. Second, enriched B-10 content of the HfB2 increased the rod worth when the radius was maintained. FIG. 16 is a graph generated from computer calculations using CASMO5 to demonstrate the effect of changing the relative amounts of elemental hafnium and HfB2 with three concentric regions in the control rod on the rod worth of the control rod. Here, the control rod is separated into a central region, a secondary region, and an outer region as illustrated in FIG. 13. Using the reference numerals of FIG. 13, the central region 210 is filled with elemental hafnium, the secondary region 220 is filled with HfB2, and the outer region 190 is filled with elemental hafnium. The radius 213 of the central region is 2.8895 or 3.4524 mm. The radius 223 of the secondary region is 3.45245 or 3.93568 mm. The control rod has a total radius of 4.8895 mm, so the radial thickness (numeral 193) of the outer region is the difference between the total radius and the secondary region radius 223. The HfB2 was also modeled with natural B-10 content and enriched to 40 wt % B-10, both at 70% t.d. The new control rods are: (P) central radius 2.8895, secondary radius 3.45245 with natural B-10 content; (Q) central radius 3.4524, secondary radius 3.93568 with natural B-10 content; (R) central radius 2.8895, secondary radius 3.45245 with 40 wt % B-10 content; and (S) central radius 3.4524, secondary radius 3.93568 with 40 wt % B-10 content. The control rods (A)-(E) of FIG. 14 are also shown here for comparison. In these calculations, the relative amounts of elemental hafnium and HfB2 in the control rod were held constant, and only their distribution was changed. The graph of FIG. 16 shows that loading the HfB2 at larger radii increases the rod worth because of greater surface area. Another exemplary embodiment of a control rod of the present disclosure is shown in FIG. 17 and FIG. 18. FIG. 17 is a side cross-sectional view of the control rod, and FIG. 18 is a top cross-sectional view. The control rod 300 has a top end 302 and a bottom end 304. The control rod comprises a bare hafnium skin 310. The hafnium skin 310 has a top end 312 and a bottom end 314. The bottom end of the hafnium skin has a tapered or bullet-nose bottom tip 317. The hafnium skin 310 surrounds a central cavity 330. The central cavity has a radius 331 down to transition point 311 (at which point the skin tapers to form the bottom tip). The inner surface of the hafnium skin is labeled with reference numeral 318. The radial thickness 313 of the hafnium skin is generally constant along the length of the control rod. A thin hafnium oxide outer layer 320 may be present on the hafnium skin, and is the outermost surface of the control rod. At least one Ag—In—Cd rodlet 340 is arranged axially within the central cavity, i.e. parallel to central axis 305. Put another way, the bare hafnium skin surrounds the Ag—In—Cd rodlet(s). The rodlet 340 has a top end 342 and a bottom end 344. The rodlet extends from the top end 102 of the control rod to the bottom end 104 of the control rod. The rodlet 140 is tapered at its bottom end 144 to conform to the bottom tip of the hafnium skin 110. In particular embodiments, the control rod comprises a single rodlet 340 having a radial thickness 341 substantially equal to the radius 331 of the central cavity. In some embodiments, the single rodlet 340 is formed from a plurality of segments 347 (denoted in FIG. 17 with dotted lines), wherein each segment has a radial thickness 349 equal to the radius 131 of the central cavity and a length which is less than the length 315 of the control rod. Here, the rodlet 340 may have a radial thickness 341 of from about 3.6 millimeters to about 4.9 millimeters. A radial gap 335 may be present between the Ag—In—Cd rodlet 340 and the hafnium skin 310. In embodiments, the radial gap may be a length 337 of from 0 to about 0.1 millimeters. The radial gap 335 may be filled with an inert gas (indicated with reference numeral 336), and pressurized at a suitable level before it is sealed. Exemplary inert gases include nitrogen and argon. The presence of the radial gap allows the rodlet 340 to expand radially before expanding axially in response to increasing temperature. The top end 312 of the hafnium skin 110 may include a threaded screw connector 317 to facilitate its connection to an arm 80 of the spider assembly 60. The hafnium skin supports the weight of the rodlet 340. The threaded screw connection between the hafnium skin 310 and the arm 80 forms a seal to maintain the inert gas 336 within the hafnium skin. FIG. 19 is a side cross-sectional view of another exemplary embodiment of a control rod 300. Here, the bottom end 314 of the hafnium skin is solid hafnium. Put another way, the hafnium skin has a solid tip and the central cavity 330 has a length 332 which is shorter than the length 315 of the control rod. The top surface 352 of the solid tip is flat. The bottom end 344 of the rodlet 340 has a flat surface that rests on the top surface 352. The rodlet is shown here with a length 343. In specific embodiments, the solid tip may extend for an axial length 351 of from about 10 centimeters to about 20 centimeters. This axial length is measured from the nadir 319 of the bottom end of the hafnium skin. In other embodiments, the ratio of the axial length 332 of the central cavity to the length 351 of the solid tip is from about 10.5 to about 21. Please note that the length 351 does not necessarily correspond to the transition point 311 at which the bottom end begins to taper; it is contemplated that the solid hafnium could extend above the transition point. Again, the rodlet of this embodiment is Ag—In—Cd. Hafnium metal is very stiff. When coupled with possible bowing in the guide tubes of the fuel assemblies after irradiation, greater force may be required to insert the control rod during the allowable time of a rod scram. Thus, it is contemplated that in some embodiments, particularly those in which there is only one rodlet inside the central cavity of the hafnium skin, that a plurality of channels can be made on the outer surface of the rodlet along the axial length of the rodlet. The channels allow the rodlet to flex. FIGS. 20-22 provide an illustration of one such embodiment having channels in the rodlet. FIG. 20 is a side cross-sectional view, FIG. 21 is a top cross-sectional view, and FIG. 22 is an enlarged side view. In this embodiment, a single solid hafnium rodlet 410 fills the central cavity of the hafnium skin 405. The rodlet 410 has a top end 412 and a bottom end 414. A bullet-nose bottom tip 417 is located at the bottom end of the rodlet. The rodlet has an axial length 415 extending between the top end 412 and the bottom end 414. The rodlet also has an outer or outermost surface 418. This single solid rodlet 410 generally spans the required active core height. A plurality of channels 420 is present along the axial length 415 of the rodlet. The channels begin above the bullet-nose bottom tip 417 of the rodlet. In embodiments, the channels begin about 10 centimeters above the transition point 411 where the bottom end 414 begins to taper to form the bottom tip 417 of the rodlet. Referring now to FIG. 21 and FIG. 22, each channel 420 extends from the outer surface 418 into the rodlet for a depth 422 of from one-third to one-half of the diameter of the rodlet. The channel may have a width 426 corresponding to the width of the blade used to make the channel. In embodiments, the width 426 may be from about 0.5 millimeter to about 2 millimeters, particularly about 1 mm. The channel 420 forms a chord 424 of the rodlet. Adjacent channels are separated axially by a gap 428. The separation between channels can vary as desired to provide the desired flexibility along the length/height of the rodlet. The size of the gap generally increases as the channels rise toward the top end 412 of the rodlet. In embodiments, each gap is at least 8 centimeters. In addition, adjacent channels are rotated with respect to each other. In embodiments, adjacent channels can be rotated from 30° to 150°, as measured by the smallest angle formed between the chords of the two channels when viewed in cross-section. These aspects are more clearly seen in FIG. 21 and FIG. 22. Here, three channels 420, 430, 440 are shown. The channel 420 is closest to the bottom end of the rodlet, and extends for a depth 422 depicted here as being one-half the diameter of the rodlet. The channel has a width 426. Channels 420 and 430 are separated by gap 428, while channels 430 and 440 are separated by gap 438. Gaps 428 and 438 may differ from each other, with gaps closer to the top end of the rodlet being larger than gaps closer to the bottom end of the rodlet. Looking at FIG. 21, channel 420 forms chord 424, channel 430 forms chord 434, and channel 440 forms chord 444. The portion of the rodlet removed at channel 420 is on the side seen in FIG. 22. Adjacent channels 420, 430 are rotated relative to each other by an angle A1 of 120°, which is measured here at their intersection. Adjacent channels 430, 440 are also rotated relative to each other by an angle A2 of 120°. The portion removed at channel 440 is on the side opposite that shown in FIG. 22, and is denoted in dotted line to indicate this fact. Please note here that the depth 422 is perpendicular to the width 426; and that the width 426 of the channel is in the same direction as the length 415 and height of the rodlet, i.e. the axial direction. The channels may be made using a saw. The presence of the channels introduces bending flexibility in all directions about the rod axis at a very small cost in the rod worth. In a rod of length 2 meters, with 20 channels each of 1 mm width and a one-half diameter depth, the total material removed is less than 0.5% of the mass of the single rodlet, or roughly less than a 0.5% decrease in the reactivity control worth of the overall control rod. FIG. 23 also shows channels in another embodiment, which is useful when the hafnium skin is filled with a plurality of central rodlets. Each rodlet 440 could be described as having the shape of an angular wedge. Each rodlet 440 has two radial surfaces or internal surfaces 442, 444 and an outer surface 448 which faces the hafnium skin. The radial surfaces have a length 443 about equal to the radius of the central cavity. Here, the channels 420 are located on the radial surfaces 442, 444 instead of the outer surface as in the embodiment of FIG. 21. This construction permits the control rod to flex as well, and also offers the advantage that the channels 420 will not snag on the hafnium skin during such flexing. In particular embodiments, the channels on the rodlets are arranged so that channels on one rodlet do not directly face the channels on any adjacent rodlets. Positive and negative examples are illustrated in FIG. 23. Here, rodlet 450 has channels 452, 454. Rodlet 460 has channels 462, 464. Channel 462 does not directly face channel 452. However, channel 464 does directly face channel 454. Put another way, if the bottom end 451 of rodlet 450 and the bottom end 461 of rodlet 460 are in the same plane, then channels directly face each other when the height 453 is equal to height 463. In specific embodiments, each channel extends from the radial surface into the rodlet for a depth of from one-tenth to two-thirds of the length 443 of the radial surface. FIG. 24 and FIG. 25 illustrate one additional variation that can be used in the control rod of the present disclosure when the hafnium skin contains more than one rodlet. When the control rod is flexed, for example due to insertion in a warped guide tube, the individual rodlets will flex in different ways. This concept can be visualized, for example, as two adjacent metal strips of equal length that are attached together on one end. If the strips are bent into an arc, the inner strip will appear longer than the outer strip. Applied to a control rod, it is possible that some of the rodlets could bend less than the hafnium skin such that the rodlets perforate the hafnium skin through the bullet-nose tip or on the sides of the hafnium skin. This problem is resolved by shortening the rodlets relative to the bullet-nose tip or the bottom end of the hafnium skin. The control rod 500 has a top end 502 and a bottom end 504. The hafnium skin 510 has a top end 512, a bottom end 514, and a bottom tip 517 which tapers beginning at transition point 511. The axial distance (i.e. parallel to central axis 505) between the transition point 511 and the nadir 519 of the bottom tip 514 is indicated as reference numeral 515. This axial distance 515 is from about 5 centimeters to about 8 centimeters. The hafnium skin also surrounds a central cavity 530. A thin hafnium oxide outer layer 520 may be present on the hafnium skin. The inner surface of the hafnium skin is labeled with reference numeral 518. A plurality of rodlets 540 are arranged axially within the central cavity 530. Each rodlet 540 has a top end 542 and a bottom end 544, the top end being interconnected to the spider assembly through arm 80. Again, each rodlet hangs under its own weight from the spider assembly. As seen in FIG. 24, the rodlets can include central rodlet(s) 570, distal rodlets 550, and intermediate rodlets 560. Generally speaking, the bottom ends of the rodlets are spaced apart from the hafnium skin, such that a pocket or void 580 is present between the bottom ends of the rodlets and the tip 517 of the bottom tip of the hafnium skin. Put another way, the void 580 is located in the bottom tip 514 of the hafnium skin. No rodlets 540 are present in the pocket 580. The void 580 is reflected as the distance between the bottom ends 544 of the rodlets and the inner surface 518 of the hafnium skin in the axial direction, as reflected in axial lengths 582 and 584, measured from rodlets 570 and 560, respectively. In embodiments, the void has a minimum axial length, measured relative to each rodlet in the central cavity, of from 1 centimeter to about 5 centimeters, or from 1 centimeter to 2 centimeters. The top end 512 of the hafnium skin may have a lip 516 to facilitate interconnection with the spider assembly. In addition, a seal 590 is present at the top end 502 of the control rod. It is contemplated that the central cavity 530 (including the void 580) will be filled with an inert gas, such as helium or argon or some other suitable gas. The seal 590, as well as the hafnium skin, is impermeable to the inert gas. Any suitable construction that accomplishes this purpose may be used. For example, as seen in FIG. 25, the arms 80 could extend through ports in the seal to interconnect to the rodlets 540 and the hafnium skin 510. This use of slightly shorter rodlets allows the overall control rod 500 to flex while keeping the bottom ends of the rodlets away from the hafnium skin, preventing perforation. This construction is suitable for rodlets made of either hafnium metal or of Ag—In—Cd. The control rod of the present disclosure achieves a number of advantages over other control rods. First, the control rod can achieve a greater rod worth than is available from control rods that use a stainless steel cladding. Because hafnium is used instead of stainless steel, the rod worth of the overall control rod can be comparable to that of a standard B4C rod at 80% theoretical density (“t.d.”) without the swelling-with-irradiation issues associated with B4C rods. The control rod of the present disclosure also has a rod worth about 50% greater than an Ag—In—Cd rod with stainless steel cladding. Due to hafnium's high density, the control rod also has a greater weight than other rod designs, even compared to a design incorporating tungsten rodlets (which also reduce rod worth). The control rod of the present disclosure is about 30% heavier than an Ag—In—Cd rod with stainless steel cladding. This provides a higher rate of insertion under gravity. The control rod also has greater chemical, shape, and physical stability. The overall control rod is also flexible enough for use in a once-through fueling cycle. The relatively low cost of Ag—In—Cd is also a benefit. Some computer calculations were performed on various control rod designs to determine the expected rod worth (RW) of the designs that included Ag—In—Cd rodlets within a hafnium skin. The rod worth was determined according to the formula RW=100%×[(K-inf un-rodded lattice/K-inf rodded lattice)−1]. The fuel lattice was UO2 enriched to 4.95% U-235 and at 96% t.d. The UO2 fuel was fresh, without burnable absorbers or soluble boron present. The fuel lattice consisted of 265 pins per assembly and 24 guide tubes. The calculations were performed for five control rods. The control rod was modeled as illustrated in FIG. 18 and had a total radius of 0.48895 cm. The single rodlet had a radial thickness 341 of 0.4318 cm. The radial gap continued to a radius of 0.43815 cm (i.e. a radial thickness 337 of 0.00635 cm). The skin then continued to a radius of 0.48895 (i.e. a radial thickness 313 of 0.0508 cm). Table 1 shows the resulting rod worth for rods with different materials in the rodlet, radial gap, and skin. The term “GAP” indicated that no material was present. The term “SS” refers to stainless steel. TABLE 1OuterControlControlControlControlControlRadius (cm)Rod 1Rod 2Rod 3Rod 4Rod 50.4318Ag—In—CdAg—In—CdAg—In—CdAg—In—CdHafnium0.43815GapGapAg—In—CdHafniumHafnium0.48895CRSHafniumHafniumHafniumHafniumRW (%)39.3747.1347.6047.6246.94 These results indicate that the rods comprising a Ag—In—Cd rod and a hafnium skin (Control Rods 2-4) achieved rod worths comparable and even better than a bare hafnium rod in the simulations. While the simulations suggest that filling the gap with Ag—In—Cd improves rod worth, this configuration would not allow the Ag—In—Cd rodlet(s) to expand radially at high temperatures. Instead, the Ag—In—Cd rodlet(s) would expand axially, which would lower the rod worth per linear height of the rod at high temperatures. The present disclosure has been described with reference to exemplary embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
055880312	summary	FIELD OF THE INVENTION The present invention relates generally to a core shroud that is contained within a reactor vessel of a nuclear power plant and, more particularly, to an apparatus for reinforcing the core shroud in the event of cracking or other conditions of similar magnitude. BACKGROUND OF THE RELATED ART In a commercial nuclear reactor, heat, from which steam and ultimately electricity are generated, is produced by fissioning of a fissible material, such as enriched uranium, contained in a reactor core which is, in turn, contained within a reactor vessel. The reactor vessel includes a flanged, dish shaped closure head bolted atop a flanged, generally cylindrical shaped reactor body; the reactor vessel is entirely contained within a containment building for containing any unlikely radiation leakage within the containment building should an accident occur. A generally cylindrical shaped core shroud extends coaxially inside the reactor vessel for creating an annulus between the reactor vessel and core shroud. The core shroud typically includes an upper portion with a slightly greater diameter than its middle portion, and its middle portion with a slightly greater diameter than its lower portion. Although the presently known and utilized core shroud is satisfactory, it is not without drawbacks. In the area where its upper, middle and lower portions are respectively joined together, there is a tendency for stress corrosion cracking. Consequently, a need exists for a core shroud repair which is operable for reinforcing the core shroud in the event of stress corrosion cracking or events of similar magnitude. SUMMARY OF THE INVENTION The present invention provides an improvement designed to satisfy the aforementioned needs. Particularly, the present invention is directed to an apparatus, which reinforces a core shroud that is contained within a reactor vessel, operable in the event of cracking or events of similar magnitude in the core shroud, the apparatus comprising: (a) a reactor vessel wall positioned surrounding the shroud; (b) a beam attached to the shroud for absorbing the forces generated in the shroud; and (c) a radial support positioned between said beam and said reactor vessel wall for transmitting any forces absorbed by said beam to said reactor vessel wall which, in effect, reduces the loads in said beam and also maintains generally uniform distribution of the loads absorbed by said beam for allowing said beam to absorb the generated forces. It is an object of the present invention to provide a device for reinforcing the core shroud in the event of cracking. It is a feature of the present invention to provide a beam extending generally vertically on the shroud and a radially extending support attached thereto and resting against a reactor vessel wall for transmitting the forces created in the core shroud by the cracking to the reactor vessel wall. It is an advantage of the present invention to provide the vertically extending beam in a configuration which is easily attached to the core shroud.
055966128	description	TESTING ARRANGEMENT In FIG. 1 is shown a pressurized-water reactor cap 1 placed on a biological concrete shield 2. There are a number of lead-throughs 4 in the cap, normally about 60-75, only two thereof being drawn. A lead-through consists of a tube 6 passing through the cap 1, which tube is sealingly welded to the cap 1 at its lower surface. In the tube 6 there is a sleeve 8 which is essentially coaxial with the tube and which comprises an end-piece, which may be essentially funnel-shaped. The lower end surfaces of the sleeves 8 of all the control rod lead-throughs are normally situated in essentially the same plane, as is shown in FIG. 1. The parts of the sleeves 8 projecting out of each tube 6 have different lengths, depending on where in the cap dome the lead-through in question is situated. A manipulator 10, with three degrees of freedom, for measurement and maintenance purposes, is placed under the cap dome. A testing arrangement 14 according to the invention is attached to the outermost joint 12 of the manipulator through a manipulator tool interface, in this case a dovetail. The testing arrangement 14 is dockable to an end-piece of the cap lead-through, and is docked by means of the manipulator 10 for the insertion of a probe sword, comprised in the testing arrangement 14, into a gap of the lead-through. It is shown in FIG. 1 how the testing arrangement by means of the manipulator 10 is positioned at a cap lead-through 4 before the docking. The positions of the lead-throughs have been determined beforehand in manipulator coordinates by means of a camera, and the positioning of the testing arrangement at a selected lead-through is carried out by utilizing the already present manipulator control system. For the mounting of the inventive testing arrangement at the manipulator, the manipulator end joint is brought to shuttable opening in the concrete shield, whereupon an operator, through the opening, leans or steps into the radioactive environment and carries out the mounting. In a further developed embodiment of the invention, a foldable arm is anticipated, which at least should allow the possibility to project the testing arrangement through the opening for e.g. exchange of the probe sword without the operator having to lean in under the cap dome. FIG. 2 shows a cut away cap lead-through 4, whereby the thickness B of the cap 1 normally is about 200-250 mm. The tube 6 passing the cap 1 is sealingly fastened to the cap by virtue of a pipe weld 16 running around the tube at the lower side of the cap. Between the tube 6 and the cap 1 there is above the weld a narrow first gap 18, hereinafter called a tube gap. The tube 6 has normally an outside diameter of about 100 mm and an inside diameter of about 70 mm. The lower part of the tube 6 has an inside cone-shaped ending 19, which for convenience hereinafter is called a tube cone. The tube cone 19 has a cone angle which is typically a few degrees, e.g. 3.degree.. In the tube 6 there is a sleeve 8 which normally has an outside diameter of about 64 mm, comprising an end-piece 9 which in this example is funnel-shaped and which hereinafter also is called a sleeve funnel. The sleeve 8 is (not shown) at its upper end sealingly joined to the end of the tube which projects on the upper side of the cap 1. When the control rods are lifted, it is possible to elevate the sleeve to a pivotable position. Between the sleeve 8 and the tube 6, there is a second gap 20, hereinafter also called sleeve gap, with a nominal gap width of normally about 3 mm. At the upper part of the lead-through there is in the sleeve gap, means to hold the sleeve in a selected position, which can be changed by elevating the sleeve. The distance A between the lower end surface of the sleeve 8 and the lower end surface of the tube 6 varies, depending on the position of the lead-through 4 in the dome-shaped cap 1 and due to the fact that the sleeves 8 are arranged in order that the lower end surfaces of all the sleeves 8 be located in essentially the same plane. Cracks can, as has been mentioned, occur in the tube 6 close to the tube weld 16. When there are cracks in the area above the weld, fluid pressurized in the reactor may come out in the tube gap 18 and therethrough come up on the top of the cap 1. When there are cracks in the area below the tube weld 16, there is no external leakage, but also these cracks shall be detected. In the figure, a testing area C is indicated in the axial direction overlapping and around the tube weld 16. The area C comprises an area D above the tube weld 16, an area E overlapping the entire tube weld 16 and an area F below the tube weld 16. Today there is required a testing of the material in an area extending over the weld and covering an area D of about 50 mm above the weld and an area F of about 50 mm below the weld. Materials testing over the described area is executed according to the invention by inserting a probe sword into the sleeve gap 20 and by rotating it along the gap around the axis of symmetry of the lead-through. The probe sword is then maneuvered in a movement that follows the tube weld 16 and its associated testing area. Since the tube weld 16 follows the intersection between the dome-shaped inner surface of the cap and the tube-shaped outer surface of the tube 6, the testing area unfolded in a plane describes an essentially sinus-shaped stripe 22 according to FIG. 3. In FIG. 3 the stripe widths of the testing area have the same designations as in FIG. 2, whereby the zero point of said axis is assumed to be situated at the lower end surface of the tube. When a probe sword rotates along the testing area in the sleeve gap 20, it should thus cover the whole width C and follow the stripe 22, and should therefore in the vertical direction have a length of stroke, taken from the end surface of the tube 6, that at the periphery of the cap normally may be about 280 mm. The length of stroke is indicated with a G in FIGS. 2 and 3. To assure a complete scanning of the testing area, the probe sword is rotated more than 360.degree. around the sleeve 8, normally about 400.degree.. FIG. 4 shows as an example a sketch of a preferred embodiment of the inventive testing arrangement 14. The testing arrangement 14 is characterized in that it comprises a pinching arrangement 32, by means of which a pinching force may be applied between the outer surface of the tube 6 and the outer surface of the projecting part of the sleeve 8 in order to widen the sleeve gap 20 at one side (cf FIG. 2), a sword-guiding arrangement cooperating with a pinching arrangement to guide the sword into the widened part of the gap, a first lifting arrangement for bringing the pinching arrangement on a level with the lower part of the outer tube, a second lifting arrangement for inserting the sword into the gap and a turning arrangement for, in cooperation with the pinching arrangement, displacing the widened part of the gap along the inner periphery of the first tube, whereby the testing arrangement is attachable to said manipulator, and the testing arrangement is dockable at a chosen lead-through by means of the manipulator, whereby the lifting arrangements are arranged at the turning arrangement and whereby the pinching arrangement is arranged at the first lifting arrangement, and a sword-guiding arrangement carrying the sword is arranged at the second lifting arrangement, both lifting arrangements being linearly movable in the axial direction of the tubes. The first lifting arrangement of the testing arrangement 14 comprising a central structure 24 which is rotatably attached to a frame 26. The frame 26 comprising a turning arrangement comprising a rotational driving unit (not shown) for the central structure 24 and a connection means (not shown) for the connection of control systems which will be further described below. A manipulator tool interface 30 is attached to the frame 26, in this embodiment a so-called dovetail, intended to be connected to a corresponding means at the manipulator. At the upper end of the central structure 24, there is a frustrum of a cone, hereinafter called docking cone 34, which fits against the sleeve funnel 9 and serves as a geometrically locking docking means at the docking of the testing arrangement 14 to a cap lead-through 4. At the top of the central structure 24 there is arranged a camera, a lighting means and an aiming means (not shown) for visual support by the maneuvering of the docking. A safe centering of the central structure 24 in relation to the axis of the lead-through 4 can be executed by means of the aiming arrangement. A fluid-collecting vessel 35 is arranged at the lower part of the central structure 24 for collecting fluid, which during use of the testing arrangement flows down the central structure 24 originating from an accumulation of fluid in a lead-through 4, from cleaning of the sleeve gap and from contract medium in connection with ultrasonic testing. The pinching arrangement is built up around the central structure 24, which pinching arrangement is mobile in the vertical direction and is, in its entirety, designated 32. The pinching arrangement 32 is detachably attached to the central structure 24 by means of an associated upper fastening means 36 and an associated lower fastening means 38. The first lifting arrangement comprises a beam which is vertically displaceable along the central structure 24, here called vertical beam 40, by means of which the pinching arrangement 32, in its entirety, is displaceable in the vertical direction. The vertical beam is maneuvered in the vertical direction by means of a vertical beam driving unit 42 and a vertical beam brake 44, whereby the vertical beam driving unit 42 is comprised in the lower fastening means 38 and the vertical beam brake 44 is comprised in the upper fastening means 36. FIG. 5 shows a cross-section of the lower fastening means 38, comprising a remote controllable vertical beam driving unit 42, with which a vertical beam 40 is connected locked by virtue of force and geometry via two vertical bars 41. The vertical bars 41 are attached to and runs along the sides of the beam 40. In the present embodiment, the bars are attached to the beam by bolts. The lower fastening means 38 comprises a clamping means 46 for, by means of at least one bolt 48, a detachable fastening of the fastening means with the vertical beam driving unit at the central structure 24. The vertical beam driving unit 42 is connected to the clamping means by means of at least another bolt 48 and comprises a remote controllable electric motor, a gear 52, a position sensor 54, two, by virtue of bearings 56 rotationally journalled, transverse shafts 58 and 60, whereof one shaft 58 has a power transmitting connection with a motor 50, and thus serves as a driving shaft for the vertical beam 40. The two shafts are hereinafter call transverse driving shaft 58 and transverse support shaft 60. A groove wheel 62 is arranged at each, from the central structure 24 turned, end of the transverse shafts 58,60, which grooves are partly wedge-shaped. The vertical beam 40 presents a prismatic cross-section, the short sides of which also presents wedge-shaped grooves. The mentioned vertical bars 41 are arranged between each groove wheel 62 and the respective short side of the vertical beam 40. In order to displace the vertical beam 40 and the vertical bars 41, a rotational movement of the groove wheels 62 is converted to a linear movement by virtue of the friction between the wheels and the bars. The upper part of FIG. 5 shows a shaft suspension means 64 comprised in vertical beam driving unit. The shaft suspension means 64 is shown from its, towards the central structure 24 turned, side, at the side of the central structure 24 which is closest to the vertical beam. FIG. 6 shows in the same way as FIG. 5 a cross-section of the upper fastening means 36, comprising a vertical beam brake arrangement 44 by virtue of which said vertical beam 40, in the same way as by the vertical beam driving unit 42, is connected via the vertical bars 41 locked by virtue of force and geometry. The upper fastening means 36 is assembled according to the same principles as the above described lower fastening means 38, but presents a remote controllable brake 70 instead of a driving motor, which brake brakes the rotational movement of the transverse support shaft 68 via an intermediate brake shaft 72. The linear movement of the vertical beam 40 can thus be stopped or prevented by means of the brake 70. The means that are similar or corresponding in FIGS. 5 and 6, are indicated with the same reference numerals. The upper part of FIG. 6 shows a lateral view of the upper fastening means 36 from the side which is turned away from the central structure 24, at the side of the central structure which is situated opposite the side of the vertical beam. Again referring the FIG. 4, the pinching arrangement 32 comprises, as mentioned above, the vertical beam 40 with associated vertical bars. The sword-guiding arrangement cooperating with the pinching arrangement comprises a sword guide 74 arranged at the vertical beam 40, which by means of at least one linearly displacing sword guide maneuvering means 76 and a sword guide arm 77 is maneuverably pivotable around a sword guide shaft 75. The vertical beam presents at its top an upwardly open aperture which allows the sword guide 74 to be turned in towards the central structure 24 between the short sides of the vertical beam 40. The reason for this arrangement is to make it possible to place the upper bearing of the vertical beam, via the groove wheels, as high up the central structure 24 as possible. An essentially S-shaped guide slit 73 runs through the sword guide 74 and debouches at the top of the sword guide. The mentioned guide slit 73 has in the present embodiment an essentially rectangular cross-section which gives the sword a certain allowance in the cross-section. A pinching arm 78 is arranged at the pinching arrangement 32 at the opposite side of the central structure 24 across the sword guide 74. The pinching arm 78 is maneuverably pivotable around a pinching arm shaft 81 by means of at least one linearly displacing pinch maneuvering means 80 and an arm 79. In the preferred embodiment of the invention the linearly displacing maneuvering means 76,80 are constituted by pneumatic cylinders. In the present embodiment the pinching arrangement 32 is designed essentially symmetrically with a collar surrounding the central structure 24 and the linear displacement means 76,80 fastened with a collar on each side of the central structure 24. A probe sword driving unit 83 is arranged along the vertical axis at the vertical beam 40 of the lifting arrangement, at which probe sword driving unit 83 a probe sword 85 is detachable arranged. The probe sword 85 is at its uppermost part slidably inserted in the sword guide 34. The probe sword 85 is maneuverably mobile by means of the probe sword driving unit 83 in the vertical direction, whereby the sword is guided by the sword guide 74. The movement of the probe sword 85 is achieved by means of an electric motor (not shown), comprised in the probe sword driving unit 83, and a lead-screw 82 with a cooperating lead-screw nut 84, at which nut the probe sword is attached. A fluid section muzzle 88 is arranged at the top of the sword guide 74 for evacuation of fluid and dirt originating from the cleaning of the sleeve gap or from contact medium at ultrasonic testing. The evacuated material is brought along the vertical beam via a conduit to a separate collecting vessel. Furthermore, a verifying means 90 is arranged at the sword guide 74 for verification of the function of the testing probe being arranged at the top of the probe sword 85. In the present case, the verifying means 90 is designed as a piece of metal, which serves as a remote boundary surface when controlling an ultrasonic probe. A monitoring camera 92 is arranged at the pinching arrangement 72 for monitoring the movements of the pinching arm 78, the sword guide 74 and the probe sword 85 at the docking and the testing movement after the docking. The movements of the testing arrangement 14 at docking and testing will now be explained in more detail with the aid of FIGS. 1, 7 and 8. FIG. 7 shows the testing arrangement 14 in a position docked to a lead-through 4. In FIG. 7 is also explanatory shown peripheral systems associated to the testing arrangement. FIG. 8 shows the upper part of the testing arrangement docked to a cap lead-through 4 and with the pinching arm 78 and the sword guide 74 of the pinching arrangement 32 in a position suitable for insertion of the probe sword 85 into the sleeve gap. In FIG. 1 the central structure 24 of the testing arrangement 14 is positioned essentially coaxially below a lead-through 4, to which position the testing arrangement has been maneuvered by means of the manipulator 10. With the aid of said camera and said aiming arrangement, which are arranged at the top of the central structure, the testing arrangement 14 is maneuvered with precision by means of the manipulator 10 to the docked position shown in FIG. 7, at which position the docking cone of the testing arrangement is connected, locked by virtue of geometry, to the sleeve funnel 9 of the cap lead-through. The sleeve 8, which thus is docked to the testing arrangement 14 is then slightly elevated in order to increase its lateral mobility. Thereafter, see FIG. 8, the pinching arrangement 32 is elevated by means of the vertical beam driving unit 42 past the sleeve funnel 9. When the top of the sword guide 74 has passed the sleeve funnel 9, the upper part of the sword guide 74 is led by means of the sword guide actuating means 76 towards the sleeve so that a sleeve contracting surface 71 arranged at said upper part is in close contact with the sleeve 8. The pinching arrangement 32 is elevated further until the top of the sword guide contacts or is close to the lower end surface of the tube 6. The limit position is indicated by a limit switch, for example an inductive sensor, comprised in the top of the sword guide. Thereafter, the upper part of the pinching arm 78 is led towards the tube by means of the pinch-actuating means 80 so that a pinching surface 86 of the last mentioned upper part is in close contact with the outside surface of the tube 6. The sleeve 8 is now pressed out, by means of the pinching arm 78, the sword guide 74 and the actuating means 76,80, against the side of the tube 6, where the pinching arm is applied, in order to widen the sleeve gap before the insertion of the probe sword. There is in the sleeve 8 and in the manipulator with the attached testing arrangement a compliance that allows a deflection of the end of the sleeve and the end of the testing arrangement that are docked to each other, the deflection being of the magnitude of the few millimeters. The probe sword can now, via the sword guide 74, be inserted vertically into the widened sleeve gap by means of the sword driving unit 83 and be maneuvered by means of said driving unit over the height of the defined testing area. In order to lead the probe over the above described entire testing area, along the inside surface of the tube, the central structure 24 is turned with the thereto non-rotatingly mounted pinching arrangement 32 by means of the rotation driving unit comprised in the frame 26. The movements are sequency-controlled and are controlled step by step by means of signals from limit switches arranged in said testing arrangement. FIG. 9a shows an explanatory cross-section of a lead-through after the deflection of the sleeve 8 towards the inner wall of the tube 6. The pinching surface 86, the probe sword 85 and the top of the sword guide 74 are schematically shown in the figure. Pinching forces are drawn as arrows and are designated with an F. As the central structure 24 with the pinching arrangement 32 rotates, the pinching surface 86 slides relative to the outer surface of the sleeve and the sleeve contacting surface 71 of the sword guide slides relative to the outside surface of the sleeve, while the engagement of the docking cone with the sleeve funnel is maintained. In FIG. 9b it is explanatory shown how the probe sword 85 in the inserted position acquires an essentially S-shaped bending due to the forced curvatures. Further, peripheral support systems for control, schematically shown in FIG. 7, are associated with the testing arrangement. The following systems are, in the present example, connected to the testing arrangement: a control system for controlling the movements of the testing arrangement, an eddy current measurement system, a camera system for monitoring the movements of the testing arrangement, an ultrasonic system for determination of defects, a fluid-supplying system for supplying the sword with cleaning fluid and a contact medium, and a pneumatic system for actuating the pneumatic means comprised in the embodiment. PROBE SWORD The purpose of the inventive probe sword is, in accordance with the above description, to insert it in a gap between two concentric tubes and to displace it in the axial direction of the tubes as well as in a circular movement around an axis of symmetry. The probe sword is characterized in that it comprises a probe end, an elastic swordblade with a bent cross-section adapted to the shape of the gap, a connection means at the end opposite the probe end and a probe attached at the probe end, whereby the sword comprises at least one conduit, running along one edge of the sword, for conveyance of a fluid onto the probe end, and possibly at least one electric wire, running in the same way as the conduit, for the connection of the probe, and whereby the connection means serves for attachment at the sword-actuating means and for connection of an inlet conduit for fluid and of an elctric wire. In FIG. 10 is shown an explanatory sketch of an inventive probe sword 85 comprising a sword head 94, adapted for a recessed attachment of a probe 100, and a connection means 96. The probe sword 85 comprises at least one electric wire 97 and at least one fluid conduit 98, which are running in the sword blade along its edges from the connection means 96 to the sword head 94. The electric wire 97 is provided for possible power supply to and for transmitting measuring signals from the probe 100, while the fluid conduit 98 is provided for possible conveyance of fluid to said probe. The connection means 96 at the lower end of the sword comprises at least one electric connection 99 and at least one fluid conduit connection 101. The connection means 96 also comprises a means for fastening the sword at the lead-screw nut of the probe sword driving unit 83. FIG. 11 shows, as an example, the upper part of a probe sword 85 together with cross-sections a, b, c, d and e from indicated parts of the sword. The sword head presents a through-aperture 102, which is provided for recessed mounting of a probe. The cross-sections a-e shows the curvature of the sword, whereby the curvature of the outer contour is adapted to the curvature of the inner surface of the outer tube 6, while the inner radius of the sword is determined by tensile property conditions. The essentially S-shaped curve, shown in FIG. 9b, described by the sword in a position inserted into the gap puts high demands on the resiliency of the sword in two directions. Likewise, the movement of the sword around the gap puts high demands on the stiffness of the sword in one of its transverse directions. During displacement through the sword guide, parts of the sword are successively subject to flexural stress, where the cross-section of the sword takes an essentially plane shape and resumes its curved shape in the sleeve gap. In order to stand up to the stress at the flexing of the sword, the cross-section is thin in the middle, while it has a thicker cross-section along the edges in order to attain a high moment of inertia against bending in the transverse direction of the sword and in order to contain said conduits and wires. Electric wires 97 and fluid conduits 98 are visible at the edges of the sword. Electrid wires and fluid conduits are, in the present embodiment recessed side by side at the two edges of the sword. It is clear from FIG. 11 how the electric wires 97 protrudes out of the sword at the lower edge of the recess 102, and from there they can be connected to a probe arranged at the recess. In the preferred embodiment the electric wires are realized in the form of coaxial cables. The fluid conduits are running in the sword head along the edges of the recess and debouches after a bend of 180.degree. downwards at the upper edge of the recess. In this way, fluid can be fed to and be flushed over the attached probe. In order to fulfill the demands for strength and to be able to integrate said conduits and wires with the sword, the material is important. In one embodiment, the sword is realized in carbon fiber-reinforced plastic material. In the preferred embodiment, however, the sword is reinforced with Kevlar.RTM. and the plastic material may be an isoester. FIGS. 12a and 12b show, from the front and from the side, respectively, the upper part of an inventive probe sword 85 with a cleaning probe 104 for cleaning the sleeve gap attached at the sword head. The cleaning probe 104 is fastened to a resilient holder 106, which at one end in its turn is fastened to the sword. One or more brushes 108 are comprised in the cleaning probe. In the course of cleaning, the cleaning probe is led around in the sleeve gap, and cleaning fluid is fed via the fluid conduit 98 and is flushed over the brushes. FIGS. 13a and 13b show in the same way a probe sword 85 with an eddy current probe 110 for eddy current testing at the testing area in the sleeve gap. The eddy current probe 110 is likewise fastened to a resilient holder 106, which is fastened to the sword, and is (not shown) connected to the electric wire 97. FIGS. 14a and 14 b show in the same way as the preceding FIGS. 12-13, a probe sword 85 with an ultrasonic probe 112 for ultrasonic testing at the testing area in the sleeve gap. The ultrasonic probe is, as the above mentioned probes, fastened to a resilient holder 106 and is (not shown) connected to the electric wire 97. In the ultrasonic testing, at the frequencies at issue, a contact medium is needed. Water is preferably used as contact medium in the ultrasonic testing described in the present text. The contact medium is, during the testing, flushed over the ultrasonic probe via the fluid conduit 98. The fluid flushed out during the cleaning and the ultrasonic testing is, if it is a liquid, sucked in at the suction muzzle which is situated at the upper edge of the sword guide. Fluid or material moving along the side of the testing arrangement is collected in the collecting vessel situated at the frame. SUMMARY OF A TESTING PROCEDURE The positions of the lead-throughs are determined before the testing by means of a camera and the present manipulator. The testing arrangement, equipped with a cleaning sword according to the invention, is mounted to the manipulator and is placed in a docking position at a selected lead-through. The testing arrangement is docked to the lead-through with the aid of an aiming arrangement and a camera, whereupon the pinching arrangement and the sword guide arrangement are placed in working position at the lower part of the lead-through tube. The testing arrangement is thereafter rotated around the lead-through with the sword still withdrawn in order to check that there are no obstacles. The cleaning sword is thereafter inserted in and led around the gap, whereby the testing area is flushed and brushed clean before scanning for cracks. The cleaning procedure is repeated for all lead-throughs, and the cleaning sword is thereafter exchanged against a sword with an ultrasonic probe. Ultrasonic measurement is thereafter executed at all lead-throughs by leading the sword around the testing area defined for each lead-through. In the proposed testing procedure as described above, no eddy current testing is undertaken, but the possibility is provided by virtue of the described probe sword equipped with an eddy current probe.
	abstract	A method, system, and computer program product for performing prognosis and asset management services is provided. The method includes calculating an accumulated damage estimate for a component via a diagnostics function and applying future mission data for the component to at least one model that calculates accumulated damage or remaining life of the component. The method also includes inputting the accumulated damage estimate to the model and aggregating damage over time and quality assessments produced by the model. The method further includes calculating a damage propagation profile and remaining life estimate for the component based on the aggregating and providing an uncertainty estimate for the damage estimate and the remaining life estimate.
	summary
	claims	1. In an irradiation arrangement for irradiation of products with a beam of accelerated charged particles, wherein the arrangement comprises a particle accelerator device, a radiation chamber for reception of products for irradiation comprising a radiation sector in which the irradiation of said products takes place, and a carrier device for presenting said products for irradiation from at least two sides, controllable means for scanning said beam of charged particles over the surface of said products alternately from at least two sides, said controllable means comprising: redeflection means comprising redeflection magnets positioned at at least two sides of said radiation sector; a controllable scanning magnet disposed to deflect respective portions of said particle beam so that each of said particle beam portions is incident toward one of said redeflection magnets; and each of said redeflection magnets has a geometrical shape which by its magnetic field deflects each incident particle beam portion from said scanning magnet towards said radiation sector in a direction substantially perpendicular to that direction the beam axis has immediately before the passage of the beam through said scanning magnet, whereby substantially the entire particle beam will pass through both the deflection in the scanning magnet and the redeflection in the redeflection magnets. 2. Irradiation arrangement according to claim 1 , further comprising: claim 1 at least one absorption means for absorption of accelerated particles; and that said redeflection magnets has a geometrical shape which by its magnetic field, besides the deflection of said particle beam towards said radiation sector at the same time deflect that particle radiation which passes said radiation sector without being absorbed, towards said absorption means. 3. Irradiation arrangement according to claim 2 , wherein said absorption means further includes a particle stopper, which is arranged in the space between the pole pieces of said redeflection magnets. claim 2 4. Irradiation arrangement according to claim 1 , wherein each product during the irradiation is placed in the irradiation sector with the normal of the surface to be irradiated directed in a direction substantially different from the original direction of the radiation beam. claim 1 5. Irradiation arrangement according to claim 4 , wherein each product during the irradiation is placed in the radiation sector with the normal of the surface to be irradiated directed substantially perpendicular to the original direction of the radiation beam. claim 4 6. Irradiation arrangement according to claim 1 , wherein said controllable means also comprises a focusing lens for charged particles, whereby the focusing lens is controllable synchronous with the controllable scanning magnet to give rise to a constant beam size in the radiation sector. claim 1 7. Irradiation arrangement according to claim 1 , wherein said particles are electrons. claim 1 8. Irradiation arrangement according to claim 1 , wherein the particle energy used at the irradiation in the radiation sector is selected from the range 1 to 10 McV and preferably from the range 1.5 to 2.5 McV. claim 1 9. Irradiation arrangement according to claim 1 , wherein said carrier device comprises a transport device which transports the products through the radiation sector, fixes the products to said transportation device during transport through said irradiation arrangement and which is connected with actuating means, whereby the actuation velocity is controllable from a position outside the radiation space. claim 1 10. Irradiation arrangement according to claim 9 , wherein a predetermined radiation dose is achieved by that the actuation velocity of said carrier device through the radiation sector is controllable and dependent of the scanning width of said controllable means and the beam power of said particle acceleration device. claim 9 11. Irradiation arrangement according to claim 9 , wherein the transport device comprises a conveyor belt consisting of two webs of metal wire net, connected with said actuating means, extended along the sides, and which in between fasten said products, said webs are driven, separately, but co-ordinated with each other, by respective actuating means in a closed loop each, said loops are connected to each other along at least the distance the products are transported through the irradiation arrangement, whereby said products are fixed to said transport device through jamming between said webs. claim 9 12. Irradiation arrangement for irradiation of products with a beam of accelerated charged particles and comprising a particle accelerator device, a radiation chamber for reception of products for irradiation and comprising a radiation sector, in which the irradiation of said products takes place, a carrier device for said products to be irradiated for irradiation of said products from at least two sides and controllable means for scanning of said beam of charged particles over the surface of said products alternately from at least two sides, said controllable means comprising a controllable scanning magnet for deflection of said particle beam and redeflection means, wherein said particles are electrons, which at the irradiation in said radiation sector has an energy selected from the range of 1.5 to 2.5 MeV, and wherein: said redeflection means comprises, at at least two sides of said radiation sector, positioned redeflection magnets which are substantially circular arch shaped, said scanning magnet deflecting said particle beam so that every portion of said particle beam is incident on one of said redeflection magnets, and so that substantially all portions of said electron beam pass both the deflection in said scanning means and redeflection in said redeflection magnets and are incident to said radiation sector in a direction substantially perpendicular to the direction that the beam axis has immediately before the passage of the beam through said scanning magnet; two particle stoppers are arranged in the space between respective pole pieces of said redeflection magnets, which particle stoppers are constituted of water cooled copper or aluminum; the electron beam incident from said scanning magnet is deflected towards said radiation sector at the same time as the electron radiation passing said radiation sector without being absorbed, is deflected towards the particle stoppers; said scanning magnet deflects said electron beam by an angle, the absolute value of which falls within the range of 15-45 degrees; each product under irradiation is positioned in said radiation sector with the normal of the surface to be irradiated directed in a direction substantially perpendicular to the direction that the radiation axis has immediately before the passage of the beam through said scanning magnet; the controllable means also comprises a focusing electron lens, which is controllable synchronously with said controllable scanning magnet to give rise to a constant beam size in said radiation sector, said carrier device comprises a conveyor belt made of two webs of metal wire net, which transports said products through said radiation sector, fixes said products to said transport device during transport through the irradiation arrangement by jamming the products between said webs and is connected with actuating means, whereby said webs are driven, separately, but in co-operation with each other, by respective actuating means in a closed loop, said loops are connected to each other along at least the distance the products are transported through the irradiation arrangement, and a predetermined radiation dose is achieved by controlling the actuation velocity of said conveyor belt from a position outside of the radiation space and is dependent on the scanning width of the controllable means and the beam power of said particle acceleration device. 13. Method for irradiating products in a radiation chamber with charged particles from a particle acceleration device by using a controllable means for scanning the beam of charged particles over the surface of said products alternately from at least two sides, whereby said method comprises the steps of: positioning said products to be irradiated in a radiation sector; scanning said beam of charged particles over the surface of said products alternately from at least two sides; scanning said beam by controlling the deflection from a scanning magnet to at least one range of deflection angles and use of redeflection from at least two redeflection magnets so that every portion of said particle beam is deflected by said scanning magnet and redeflected by one of said redeflection magnets; and the positioning of each product in said radiation sector is performed in such a way that the normal of the surface to be irradiated is directed in a direction substantially different from the direction that the beam axis has immediately before the passage of the beam through said scanning magnet. 14. Method according to claim 13 , wherein absorption of particles, passing the irradiation position without being absorbed, in a particle stopper. claim 13 15. Method according to claim 13 , wherein said controlling of said scanning magnet comprises changing of the end points for at least one range of deflection angles, whereby requested scanning width is achieved. claim 13 16. Method according to claim 15 , wherein said change in the angle range of said scanning magnet is performed such that the ranges of deflection angles, giving rise to particle paths not irradiating said products, rapidly are passed or avoided. claim 15 17. Method according to claim 13 , further including focusing said particle beam with a lens for charged particles, whereby the focusing is controlled synchronously with the control of said scanning magnet so that the extension of the beam spot across the scanning direction over the irradiated product surface becomes constant. claim 13 18. Method according to claim 13 , wherein the positioning of the products to be irradiated in said radiation sector and the removal of the products from said radiation sector is performed by transportation at a conveyor belt during the operation of said irradiation arrangement. claim 13 19. Method according to claim 18 , further including controlling of said radiation dose by controlling the feeding velocity of said conveyor belt. claim 18 20. Method according to claim 19 , wherein said controlling of the radiation dose is based on information about the power of said particle accelerating device. claim 19 21. System for production of sterile products comprising an irradiation arrangement for irradiation of products with a beam of accelerated charged particles, which irradiation arrangement comprises a particle accelerator device, a radiation chamber for reception of products for irradiation and comprising a radiation sector, in which the irradiation of said products takes place, a carrier device for presenting said products for irradiation from at least two sides and controllable means for scanning said beam of charged particles over the surface of said products alternately from at least two sides, said controllable means comprising: redeflection means comprising redeflection magnets positioned at at least two sides of said radiation sector; a controllable scanning magnet disposed to deflect respective portions of said particle beam so that each of said particle beam portions is incidental toward one of said redeflection magnets; and each of said redeflection magnets has a geometrical shape which by its magnetic field deflects each incident particle beam portion from said scanning magnet towards said radiation sector in a direction substantially perpendicular to that direction the beam axis has immediately before the passage of the beam through said scanning magnet.
	description	This application is a divisional application of U.S. Ser. No. 13/832,082, filed on Mar. 15, 2013, entitled APPARATUS AND METHOD TO INSPECT NUCLEAR REACTOR COMPONENTS IN THE CORE ANNULUS, CORE SPRAY AND FEEDWATER SPARGER REGIONS IN A NUCLEAR REACTOR, and claims priority thereto. This invention generally concerns robotic systems and is specifically concerned with an improved apparatus and method for inspecting nuclear reactor components in limited access areas, such as, the core annulus, core spray and feedwater sparger regions of a nuclear reactor. A nuclear reactor produces electrical power by heating water in a reactor pressure vessel that contains a nuclear fuel core in order to generate steam which is used in turn to drive a steam turbine. The reactor pressure vessel includes a cylinder surrounding the nuclear fuel core. This cylinder is referred to as the core shroud. Feed water is admitted into the reactor pressure vessel and flows through an annular region which is formed between the reactor pressure vessel and the core shroud. Within the annular region, jet pump assemblies are circumferentially distributed around the core shroud. The core shroud and other components in the reactor pressure vessel are examined periodically to determine their structural integrity and the need for repairs. Visual inspection is a known technique for detecting cracks in nuclear reactor components. The components to be examined may be difficult to access. For example, examination access of the core shroud is limited to the annular space between the outside of the shroud and the inside of the reactor pressure vessel, between adjacent jet pumps. Further, the inspection areas in a reactor pressure vessel are highly radioactive, and are located under water 50 to 80 feet below the operator's work platform. Thus, inspection of the internal components of the reactor pressure vessel requires a robotic device which can be installed remotely and operated within a narrowly restricted space. Remote operation is preferred due to safety risks associated with radiation in the reactor. During reactor shutdown, servicing of components typically requires installation of inspection manipulators or devices 30 to 100 feet deep within reactor coolant. The inspection equipment consists of manually controlled poles and ropes to manipulate servicing devices and/or positioning of these devices. Relatively long durations are required to install or remove manipulators and can impact the plant shutdown duration. In addition, different inspection scopes can require several manipulator reconfigurations requiring additional manipulator installations and removals. The long durations cannot only impact plant shutdown durations, but also increase personnel radiation and contamination exposure. Plant utilities have a desire to reduce the number of manipulator installations and removals to reduce radiological exposure as well as cost and plant outage impact. This invention allows the number of reconfigurations, installations and removals to be minimized. In addition, plant utilities have relatively small working areas near the access point of the reactor cavity. Therefore, the size of the manipulators can impact other activities during plant shutdown. The invention provides apparatus and methods for inspecting at least one component in an annulus region of a reactor vessel. In one aspect, the invention provides an apparatus for remotely operating and positioning at least one inspection device for inspecting a component in a reactor pressure vessel of a nuclear power plant. The apparatus includes a track positioned on an annular rim of a core shroud in the reactor pressure vessel and horizontally movable along the rim, a braking system, and a frame assembly. The frame assembly includes a frame movably connected to the track such that the frame is horizontally movable along the track. The apparatus further includes at least one mast assembly, at least one mast rotation assembly, and at least one pan and tilt assembly. The at least one inspection device is attached to the pan and tilt assembly and the at least one inspection device travels along the rim due to horizontal movement of at least one of the track and the frame assembly. The braking system can be activated such that the track is stationary and the frame assembly is horizontally movable along the track or the braking system can be released such that the track is horizontally movable along the rim of the reactor component and the frame assembly is stationary. A first mast assembly can be positioned on one side of the frame and a second mast assembly can be positioned on an opposite side of the frame. A first mast rotation assembly can positioned on one side of the frame and a second mast rotation assembly can be positioned on an opposite side of the frame. A first pan and tilt assembly can be positioned on one side of the frame and a second pan and tilt assembly can be positioned on an opposite side of the frame. The frame assembly can include a positioning motor and gear combination to move the frame assembly along the track. The inspection device can be a camera. In another aspect, the invention provides a method for inspecting an annulus region of a reactor pressure vessel in a nuclear power plant. The method includes positioning a track on an annular rim of the reactor pressure vessel such that the track is horizontally movable along the rim and positioning a frame assembly on the track. The frame assembly includes a frame movably connected to the track such that the frame is horizontally movable along the track. The method further includes connecting at least one mast assembly to the frame assembly, connecting at least one mast positioning assembly to the frame assembly, at least one pan and tilt assembly to the frame assembly and at least one inspection device to the frame assembly. The method further includes connecting a braking system to the track and the frame assembly, and moving horizontally at least one of the track and the frame assembly along the rim. Engaging the braking system can result in the track being horizontally moved from a first position to a second position along the rim and the frame assembly remains stationary or the frame assembly being horizontally moved from a first position to a second position along the track and the track remains stationary. The method can further include assessing the inspection results and determining if modification or repair of the component is needed. The invention relates to robotic devices for remotely inspecting nuclear reactor components in a reactor pressure vessel of a nuclear power plant, such as components in the core annulus, core spray and feedwater sparger regions. The invention incorporates motion and electro pneumatics to provide position feedback for remotely inspecting the internal components of a reactor pressure vessel. The compact design of the invention allows for positioning and operation of the device in limited access areas. In certain embodiments, the nuclear power plant includes a light water reactor, such as a boiling water reactor or a pressurized water reactor. For example, boiling water reactors typically utilize a jet pump system as a means of regulating reactor flow. In a common arrangement, jet pumps are located in the annulus area just inside the reactor vessel invert. The annulus, the jet pumps and the core shroud are subject to scheduled and augmented inspections that may result in required maintenance. It is to be understood that the apparatus of the invention can be applied to inspecting a variety of nuclear components and structures in a reactor pressure vessel and various known inspection devices can be attached to the apparatus of the invention for use in performing the inspections, as well as modifications and repairs. In certain embodiments, the inspection devices include a camera. Referring to FIG. 1, there is illustrated a reactor pressure vessel (RPV) 4 of a conventional boiling water reactor (BWR). Feedwater is admitted into the RPV 4 via a feedwater inlet (not shown) and a feedwater sparger 6, which is a ring-shaped pipe having suitable apertures for circumferentially distributing the feedwater inside the RPV 4. The feedwater from the sparger 6 flows downwardly through a downcomer annulus 8, which is an annular region formed between a core shroud 2 and the RPV 4. The core shroud 2 is a stainless steel cylinder surrounding the nuclear fuel core, the location of which is generally designated by numeral 10 in FIG. 1. The core is made up of a plurality of fuel bundle assemblies (not shown). Each array of fuel bundle assemblies is supported at the top by a top guide and at the bottom by a core plate (neither of which are shown). The core top guide provides lateral support for the top of the fuel assemblies and maintains the correct fuel channel spacing to permit control rod insertion. The feedwater flows through the downcomer annulus 8, around the bottom edge of the shroud 2 and into the core lower plenum 12. The feedwater subsequently enters the fuel assemblies, wherein a boiling boundary layer is established. A mixture of water and steam enters a core upper plenum 14 under a shroud head 16. The steam-water mixture than flows through vertical standpipes (not shown) atop the shroud head 16 and enters steam separators (not shown), which separate liquid water from steam. The liquid water then mixes with feedwater in the mixing plenum, which mixture then returns to the reactor core via the downcomer annulus 8. The steam is withdrawn from the RPV via a steam outlet. The BWR also includes a coolant recirculation system which provides the forced convection flow through the core which is necessary to attain the required power density. A portion of the water is removed from the lower end of the downcomer annulus 8 via a recirculation water outlet (not visible in FIG. 1) and forced by a centrifugal recirculation pump (not shown) into jet pump assemblies 18 (two of which are shown in FIG. 1) via recirculation water inlets 20. The BWR has two recirculation pumps, each of which provides the driving flow for a plurality of jet pump assemblies. The jet pump assemblies are circumferentially distributed around the core shroud 2. The apparatus can be positioned on the annular rim, e.g., circumferential steam dam, of the reactor pressure vessel. In certain embodiments, the apparatus can be set on the steam dam and held in place by its center of gravity. In alternate embodiments, the apparatus can be attached to the steam dam using a clamping device. In certain embodiments, such as when performing an inspection of a core shroud, the apparatus is positioned on the steam dam to support an inspection device which is lowered into the annulus formed between the reactor pressure vessel and the core shroud. The apparatus of the invention includes a traversing assembly and a frame structure. The traversing assembly includes a track. In certain embodiments, the track is connected relative to reactor hardware via remotely controlled track clamping and/or breaking mechanisms and the frame structure is movably positioned relative to the track via remotely controller motors. In certain embodiments, the frame structure travels along the track from a first position to a second position. In alternative embodiments, the frame structure is stationary relative to reactor hardware via remotely controlled frame clamping and/or braking mechanisms and the track may be positioned relative to the frame via the same remotely controlled motors such that the track is moved from a first position to a second position. Thus, the frame structure is movable to travel horizontally along the track and, the track contains motors and brakes which are systemically configured to move the track which allows the use of this apparatus with a partial track such that a complete track ring is not needed. At least one mast assembly, at least one positioning, e.g., rotation, assembly, at least one pan and tilt assembly and at least one inspection device are connected or coupled to the frame structure. Referring to FIG. 2, there is illustrated a nuclear reactor component inspecting apparatus generally referred to by reference character 100 for inspecting a nuclear reactor component in a reactor pressure vessel, in accordance with certain embodiments of the invention. The apparatus 100 includes a traversing assembly generally referred to by reference character 110 and a frame assembly generally referred to by reference character 120. The traversing assembly 110 includes a clamping device 112, a track 114 and a braking system 116. The clamping device 112 is operable to movably connect the track 114 to an annular rim, e.g., circumferential steam dam, of the reactor pressure vessel. In certain embodiments, the clamping device 112 connects the track 114 to a steam dam of a reactor pressure vessel (not shown). The braking system 116 when activated is operable to retain the track 114 in a stationary position and when deactivated, is operable to allow the track 114 to horizontally move relative to the frame assembly 120. The frame assembly 120 is movably connected to the track 114 and includes a frame 122, a first mounting assembly 123A positioned to the right side of the frame 122, a second mounting assembly 123B positioned to the left side of the frame 122, a first mast assembly 124A positioned to the right side of the frame 122, a second mast assembly 124B positioned to the left side of the frame 122, a first mast rotation assembly 125A positioned to the right side of the frame 122 and a second mast rotation assembly 125B positioned to the left side of the frame 122. Each of the two mounting structures 123A,B house a movable mast assembly 124A,B, respectively, for deployment of an inspection device 130A,B. In certain embodiments, the inspection device 130A,B is a camera. Mast rotation assemblies 125A,B are provided to allow rotation of the mast assemblies 124A,B relative to the traversing system 110 to provide at a given radial location within the reactor component. The mast rotation assemblies 125A,B include load bearing hardware and remotely operated motors (both not shown). In certain embodiments, the invention includes the use of a mast assembly system which is commercially available under the trade name RolaTube. This mast assembly system includes a remotely controlled drive system, such as a motor/cog drive system, to position the inspection device to a given elevation. This roll-up type of mast can be rolled up to 10% of its extended length which allows for a compact and efficient system. FIG. 2 also includes a first pan and tilt assembly 126A positioned on one side of the frame 122 and a second pan and tilt assembly 126B positioned on an opposite side of the frame 122. The pan and tilt assemblies 126A,B are mounted to the first and second mast rotation assemblies 124A,B, respectively, and provide a means for positioning an inspection device at a vector angle relative to the mast rotation assemblies 125A,B. The pan and tilt assemblies 126A,B include remotely operated motors and gearing (both not shown) to support and protect the inspection device. The inspection devices 130A,B are attached to the pan and tilt assemblies 126A,B, respectively. As shown in FIG. 2, the inspecting apparatus 100 has two mast assemblies, two mast rotation assemblies and two pan and tilt assemblies. However, it is contemplated that in other embodiments of the invention, the inspecting apparatus can include only one of each of the mast assembly, mast rotation assembly and pan and tilt assembly. For example, referring to FIG. 2, in certain embodiments, the invention can include the mast assembly 124A or 124B on either side of the frame assembly 122. Further, it is contemplated that the inspecting apparatus 100 can include more than one inspection device 130A,B attached to the pan and tilt assembly 126A,B. Referring to FIG. 2, when the braking system 116 is activated, the track 114 remains stationary and the frame assembly 120 is horizontally movable along the track 114 and when the braking system 116 is deactivated or released, the track 114 is driven into a different position, for example, along the rim of the core shroud. The braking system 116 allows the frame assembly 120 to walk along, for example, the steam dam of the reactor pressure vessel, without requiring a complete guide track ring. Thus, frame assembly 120 is horizontally movable to drive along the track 114, or alternatively, the track 114 is horizontally movable to be driven into a different position along the steam dam of the reactor pressure vessel. In certain embodiments, the inspecting apparatus 100 includes two sets of two brakes. One set is connected to the track 114 and one set is connected to the frame assembly 120. Referring to FIG. 2A, there is illustrated the inspecting apparatus 100 of FIG. 2 wherein the component assemblies are shown in a spaced apart arrangement. In FIG. 2A, the traversing assembly 110 is shown to include the clamping device 112, the track 114 and the braking system 116 (as shown in FIG. 2). The frame assembly 120 is shown to include the frame 122 and the first and second mounting assemblies 123A,B (as shown in FIG. 2). The mast rotation assemblies 125A,B are shown to include the first and second mast assemblies 124A,B. Further, shown in FIG. 2A are the pan and tilt assemblies 126A,B and the inspection devices 130A,B connected thereto. Referring to FIG. 3, there is illustrated the inspecting apparatus 100 of FIG. 2 wherein the rotation of the pan and tilt assemblies 126A,B are identified. Referring to FIG. 4, there is illustrated a top view of the inspecting apparatus 100 of FIG. 2, wherein the traverse movement and mast rotation are identified. In certain embodiments of the invention, the frame assembly houses articulating mast assemblies that deploy a mast that is capable of becoming rigidly stable in both an extended tube form and a retracted rolled form, with inspection end effectors attached, into the vessel to examine reactor pressure vessel components. Further, in certain embodiments, the frame assembly utilizes Rolatube as a mast. The frame assembly houses articulating mast assemblies that deploy a Rolatube mast, with inspection end effectors attached, into the vessel to examine reactor pressure vessel components. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
	description	This application is a divisional application of U.S. patent application Ser. No. 09/819,737, filed Mar. 29, 2001 now U.S. Pat. No. 6,965,153. The present invention pertains to the technical field of an electrooptic system suitable for an exposure apparatus using charged-particle beams such as electron beams, and relates to an electrooptic system array having an array of a plurality of electrooptic systems. In the production of semiconductor devices, an electron beam exposure technique receives a great deal of attention as a promising candidate of lithography capable of micro-pattern exposure at a line width of 0.1 μm or less. There are several electron beam exposure methods. An example is a variable rectangular beam method of drawing a pattern with one stroke. This method suffers many problems as a mass-production exposure apparatus because of low throughput. To attain a high throughput, there is proposed a pattern projection method of reducing and transferring a pattern formed on a stencil mask. This method is advantageous with respect to a simple repetitive pattern, but disadvantageous with respect to a random pattern, such as a logic interconnection pattern, in terms of the throughput, and a low productivity disables practical application. To the contrary, a multi-beam system for drawing a pattern simultaneously with a plurality of electron beams without using any mask has been proposed and is very advantageous for practical use because of the absence of physical mask formation and exchange. What is important in using multi-electron beams is the number of electron lens arrays used in this system. The number of electron lenses formed in an array determines the number of beams, and is a main factor which determines the throughput. Downsizing the electron lenses while improving the performance of them is one of the keys to improve the performance of the multi-beam exposure apparatus. Electron lenses are classified into electromagnetic and electrostatic types. The electrostatic electron lens does not require any coil core or the like, is simpler in structure than the electromagnetic electron lens, and is more advantageous to downsizing. Principal prior art concerning downsizing of the electrostatic electron lens (electrostatic lens) will be described. A. D. Feinerman et al. (J. Vac. Sci. Technol. A10(4), page 611, 1992) disclose a three-dimensional structure made up of three electrodes as a single electrostatic lens by a micromechanical technique using a V-groove formed by a fiber and Si crystal anisotropic etching. The Si film has a membrane frame, membrane and an aperture formed in the membrane, so as to transmit an electron beam. K. Y. Lee et al. (J. Vac. Sci. Technol. B12(6), page 3, 425, 1994) disclose a multilayered structure of Si and Pyrex glass fabricated by using anodic bonding. This technique fabricates microcolumn electron lenses aligned at a high precision. Sasaki (J. Vac. Sci. Technol. 19, page 693, 1981) discloses an Einzel lens made up of three electrodes having lens aperture arrays. Chang et al. (J. Vac. Sci. Technol. B10, page 2,743, 1992) disclose an array of microcolumns having Einzel lenses. In the prior art, if many aperture electrodes are arrayed, and different lens actions are applied to electron beams, the orbit and aberration change under the influence of the surrounding electrostatic lens field, and so-called crosstalk occurs in which electron beams are difficult to operate independently. Crosstalk will be explained in detail with reference to FIG. 10. Three types of electrodes, i.e., an upper electrode 1, middle electrodes 2, and a lower electrode 3 constitute an Einzel lens. The upper and lower electrodes 1 and 3 are 10 μm in thickness and have 80-μm diameter apertures arrayed at a pitch of 200 μm. The middle electrodes 2 are 50 μm in thickness, have a cylindrical shape of 80 μm in inner diameter, and are arrayed at a pitch of 200 μm. The distances between the upper and middle electrodes 1 and 2 and between the middle and lower electrodes 2 and 3 are 100 μm. The upper and lower electrodes 1 and 3 receive a potential of 0 [V], middle electrodes 2 on central and upper rows B and A receive −1,000 [V], and middle electrodes 2 on a lower row C receive −950 [V]. The potential difference between adjacent electrodes is 50 [V]. When an electron beam having a beam diameter of 40 μm and an energy of 50 keV enters a central aperture from the left of the upper electrode 1, a downward shift angle Δθ of the electron beam becomes several tens of μ rad or more. A typical allowable value of the shift angle Δθ is 1 μ rad or less. In this electrode arrangement, the shift angle exceeds the allowable range. That is, the electron beam is influenced by the surrounding lens field, and so-called crosstalk occurs, which must be solved. The present invention has been made to overcome the conventional drawbacks, and has as its principal object to provide an improvement of the prior art. It is an object of the present invention to provide an electrooptic system array which realizes various conditions such as downsizing, high precision, and high reliability at a high level. It is another object of the present invention to provide an electrooptic system array improved by reducing crosstalk unique to a multi-beam. It is still another object of the present invention to provide a high-precision exposure apparatus using the electrooptic system array, a high-productivity device manufacturing method, a semiconductor device production factory, and the like. According to the first aspect of the present invention, there is provided an electrooptic system array having a plurality of electron lenses, comprising at least two electrodes arranged along paths of a plurality of charged-particle beams, each of at least two electrodes having a plurality of apertures on the paths of the plurality of charged-particle beams, and a shield electrode, which is interposed between at least two electrodes and has a plurality of shields corresponding to the respective paths of the plurality of charged-particle beams. According to a preferred mode of the present invention, each shield has an aperture on a path of a corresponding charged-particle beam, and/or the shield electrode is constituted by integrating the plurality of shields. According to another preferred mode of the present invention, the shield electrode may be insulated from at least two electrodes or may be integrated with one of at least two electrodes. According to still another preferred mode of the present invention, the plurality of shields of the shield electrode receive the same potential, and/or receive a potential different from a potential applied to at least two electrodes. According to still another preferred mode of the present invention, the aperture of each shield of the shield electrode is larger in size than the apertures of at least two electrodes. According to still another preferred mode of the present invention, at least two electrodes include first and second electrodes, each of the first and second electrodes has a plurality of electrode elements with apertures on the paths of the plurality of charged-particle beams, the plurality of electrode elements of the first electrode are grouped in units of rows in a first direction, electrode elements which belong to each group being connected, and the plurality of electrode elements of the second electrode are grouped in units of rows in a second direction different from the first direction, electrode elements which belong to each group being connected. According to the second aspect of the present invention, there is provided an electrooptic system array having a plurality of electron lenses, comprising upper, middle, and lower electrodes arranged along paths of a plurality of charged-particle beams, the upper, middle, and lower electrodes having pluralities of apertures on the paths of the plurality of charged-particle beams, an upper shield electrode which is interposed between the upper and middle electrodes and has a plurality of shields corresponding to the respective paths of the plurality of charged-particle beams, and a lower shield electrode which is interposed between the lower and middle electrodes and has a plurality of shields corresponding to the respective paths of the plurality of charged-particle beams. According to a preferred mode of the present invention, the middle electrode includes a plurality of electrode elements having apertures on the paths of the plurality of charged-particle beams. According to another preferred mode of the present invention, the electrooptic system array preferably further comprises a middle shield electrode between the plurality of electrode elements of the middle electrode. According to still another preferred mode of the present invention, it is preferable that the plurality of electrode elements of the middle electrode be grouped in units of, e.g., rows, and electrode elements which belong to each group be electrically connected to each other. Alternatively, it is preferable that the middle electrode have a plurality of rectangular electrode units electrically separated in units of rows, and each electrode unit have a plurality of apertures on the paths of corresponding charged-particle beams. According to still another preferred mode of the present invention, the respective shields of the upper and lower shield electrodes preferably have apertures on the paths of the charged-particle beams. According to still another preferred mode of the present invention, it is preferable that the upper shield electrode be constituted by integrating the plurality of shields, and the lower shield electrode be constituted by integrating the plurality of shields. According to still another preferred mode of the present invention, it may be possible that the upper shield electrode is insulated from the upper and middle electrodes, and the lower shield electrode is insulated from the lower and middle electrodes, or that the upper shield electrode is integrated with the upper electrode, and the lower shield electrode is integrated with the lower electrode. According to still another prefer-red mode of the present invention, the plurality of shields of the upper shield electrode and the plurality of shields of the lower shield electrode receive the same potential, and/or receive a potential different from a potential applied to the upper and lower electrodes. According to still another preferred mode of the present invention, an aperture of each shield of the upper shield electrode and an aperture of each shield of the lower shield electrode are larger in size than an aperture of the middle electrode. According to still another preferred mode of the present invention, an interval between the middle electrode and the upper shield electrode and an interval between the middle electrode and the lower shield electrode are smaller than a pitch of a plurality of apertures of the middle electrode. According to the third aspect of the present invention, there is provided a charged-particle beam exposure apparatus comprising a charged-particle beam source for emitting a charged-particle beam, an electrooptic system array which has a plurality of electron lenses and forms a plurality of intermediate images of the charged-particle beam source by the plurality of electron lenses, and a projection electrooptic system for projecting on a substrate the plurality of intermediate images formed by the electrooptic system array, the electrooptic system array including at least two electrodes arranged along paths of a plurality of charged-particle beams, each of at least two electrodes having a plurality of apertures on the paths of the plurality of charged-particle beams, and a shield electrode which is interposed between at least two electrodes and has a plurality of shields corresponding to the respective paths of the plurality of charged-particle beams. According to the fourth aspect of the present invention, there is provided a charged-particle beam exposure apparatus comprising a charged-particle beam source for emitting a charged-particle beam, an electrooptic system array which has a plurality of electron lenses and forms a plurality of intermediate images of the charged-particle beam source by the plurality of electron lenses, and a projection electrooptic system for projecting on a substrate the plurality of intermediate images formed by the electrooptic system array, the electrooptic system array including upper, middle, and lower electrodes arranged along paths of a plurality of charged-particle beams, the upper, middle, and lower electrodes having pluralities of apertures on the paths of the plurality of charged-particle beams, an upper shield electrode which is interposed between the upper and middle electrodes and has a plurality of shields corresponding to the respective paths of the plurality of charged-particle beams, and a lower shield electrode which is interposed between the lower and middle electrodes and has a plurality of shields corresponding to the respective paths of the plurality of charged-particle beams. According to the fifth aspect of the present invention, there is provided a device manufacturing method comprising the steps of installing a plurality of semiconductor manufacturing apparatuses including the charged-particle beam exposure apparatus in a factory, and manufacturing a semiconductor device by using the plurality of semiconductor manufacturing apparatuses. In this case, this manufacturing method preferably further comprises the steps of connecting the plurality of semiconductor manufacturing apparatuses by a local area network, connecting the local area network to an external network of the factory, acquiring information about the charged-particle beam exposure apparatus from a database on the external network by using the local area network and the external network, and controlling the charged-particle beam exposure apparatus on the basis of the acquired information. According to the sixth aspect of the present invention, there is provided a semiconductor manufacturing factory comprising a plurality of semiconductor manufacturing apparatuses, including the charged-particle beam exposure apparatus, a local area network for connecting the plurality of semiconductor manufacturing apparatuses, and a gateway for connecting the local area network to an external network of the semiconductor manufacturing factory. According to the seventh aspect of the present invention, there is provided a maintenance method for a charged-particle beam exposure apparatus, comprising the steps of preparing a database for storing information about maintenance of the charged-particle beam exposure apparatus on an external network of a factory where the charged-particle beam exposure apparatus is installed, connecting the charged-particle beam exposure apparatus to a local area network in the factory, and maintaining the charged-particle beam exposure apparatus on the basis of the information stored in the database by using the external network and the local area network. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. <Electrooptic System Array> An electrooptic system array according to an embodiment of the present invention will be described. FIG. 1A is an exploded sectional view of the electrooptic system array. The electrooptic system array shown in FIG. 1A is constituted by sequentially stacking, on the paths of a plurality of electron beams (charged-particle beams), an upper electrode 1, upper shield electrode 4, middle electrode 2, lower shield electrode 5, and lower electrode 3, each of which has a plurality of apertures. FIG. 1B is a plan view of the upper electrode 1 when viewed from the top, FIG. 1C is a plan view of the upper shield electrode 4 when viewed from the top, and FIG. 1D is a plan view of the middle electrode 2 when viewed from the top. The upper electrode 1 has a thin-film structure 10 μm in thickness that is formed from an electrode layer of a conductive material (e.g., Cu or Au), and has a plurality of 80-μm diameter circular apertures 8 arrayed regularly at a pitch of 200 μm. The lower electrode 3 also has the same structure, and has a plurality of apertures 14 at positions corresponding to the apertures of the upper electrode. The middle electrode 2 comprises cylindrical electrode elements (apertured electrode elements) 11 of a conductive material (e.g., Cu or Au) (thickness: 50 μm, inner diameter: 80 μm, outer diameter: 170 μm) having apertures 10. The cylindrical electrode elements 11 are grouped in units of rows (rows A, B, and C), and cylindrical electrode elements 11 included in each row are electrically connected by a wiring line 12 of Cu, Au, or the like with a width of 4 μm. The upper and lower shield electrodes 4 and 5 respectively have circular apertures 9 and 13 with an inner diameter of 160 μm that are formed in an 88-μm thick conductive (e.g., Cu or Au) plate regularly at a pitch of 200 μm. The sizes (inner diameter sizes) of the apertures of the upper and lower shield electrodes 4 and 5 are larger than those of the middle, upper, and lower electrodes 2, 1, and 3. This reduces the influence of inserting the shield electrode on the lens action. The apertures regularly arrayed in the upper electrode 1, upper shield electrode 4, middle electrode 2, shield electrode 5, lower electrode 3, and middle electrode 2 are formed on the paths of electron beams such that the centers of the apertures coincide with each other when viewed along the optical axis. The upper electrode 1 and upper shield electrode 4 are joined via an insulating layer 6, whereas the lower electrode 3 and lower shield electrode 5 are joined via an insulating layer 7. The insulating layers 6 and 7 are 1 μm in thickness, so that the distances between the upper electrode 1 and the upper shield electrode 4 and between the lower electrode 3 and the lower shield electrode 5 are 1 μm. The distances between the upper and middle electrodes 1 and 2 and between the lower and middle electrodes 3 and 2 are 100 μm. The upper shield electrode 4 is insulated from the middle electrode 2, while the lower shield electrode 5 is insulated from the middle electrode 2. In the electrooptic system array having this arrangement, similar to FIG. 10, the upper electrode 1, upper shield electrode 4, lower shield electrode 5, and lower electrode 3 receive a potential of 0 [V], row B (central row) and row A of the middle electrode 2 receive a potential of −1,000 [V], and row C of the middle electrode 2 receives a potential of −950 [V]. The adjacent potential difference between rows B and C is 50 [V]. At this time, the beam shift angle Δθ is 0.8 mμ rad, and the beam diameter (least circle of confusion) is 0.6 μm, which fall within their allowable ranges and are suppressed to a negligible degree in practical use. According to this embodiment, the shield electrodes 4 and 5 are respectively interposed between the upper and middle electrodes 1 and 2 and between the middle and lower electrodes 2 and 3 in correspondence with a plurality of apertures in the electrooptic system array having the upper, middle, and lower electrodes 1, 2 and 3, which have pluralities of apertures and are stacked along the electron beam path. This structure can suppress the influence of an adjacent lens field and can satisfactorily suppress crosstalk. A method of fabricating an electrooptic system array having the above structure will be explained. For descriptive convenience, only one aperture will be exemplified. A method of fabricating a structure made up of the upper electrode 1 and upper shield electrode 4 will be described with reference to FIGS. 2A to 2F. A structure made up of the lower electrode 3 and lower shield electrode 5 can also be formed by the same method. A silicon wafer 101 of the <100> direction is prepared as a substrate, and 300-nm thick silicon nitride films are formed on the respective surfaces of the silicon wafer 101 by CVD (Chemical Vapor Deposition). By resist and etching processes, patterned silicon nitride films 102 and 103 are formed as a result of removing the silicon nitride films at a portion serving as a prospective optical path of an electron beam and a portion used to align electrodes (FIG. 2A). The silicon substrate 101 is anisotropically etched to a depth of 1 to 2 μm with an aqueous tetramethylammonium hydroxide solution using the silicon nitride films 102 and 103 as a mask, thus forming V-grooves 104 in at least one surface of the substrate. Chromium and gold films are successively deposited to film thicknesses of 50 nm and 1 μm as an upper electrode 105 (corresponding to 1 in FIG. 1A) on the surface having the V-grooves 104. A resist pattern is formed on these films, and the gold and chromium films are etched using the resist pattern as a mask, thereby forming an electron beam aperture 106 (FIG. 2B). An SiO2 film (insulating film) 107 is sputtered to 1 μm and patterned. Chromium and gold films are successively deposited to film thicknesses of 5 nm and 50 nm as a plating electrode film 108 for forming an upper shield electrode 110 (corresponding to 4 in FIG. 1A), and patterned (FIG. 2C). A resist pattern 109 serving as a plating mold is formed on the plating electrode 108. More specifically, the resist is made of SU-8 (MicroChem. Co) mainly consisting of an epoxidized bisphenol A oligomer, and is formed to a film thickness of 110 μm. Exposure employs a contact type exposure apparatus using a high-pressure mercury lamp. After exposure, post-exposure bake (PEB) is done on a hot plate at 85° C. for 30 min. After the substrate is gradually cooled to room temperature, the resist is developed with propylene glycol monomethyl ether acetate for 5 min to complete the plating mold pattern 109. An 89-μm thick gold pattern 110 serving as an upper shield electrode (corresponding to 4 in FIG. 1A) is buried in the apertures of the resist pattern 109 by electroplating (FIG. 2D). The SU-8 resist 109 is removed, and the substrate is cleaned and dried by IPA (FIG. 2E). The plating surface is protected with polyimide (not shown). The silicon substrate 101 is etched back from the other surface at 90° C. with a 22% aqueous tetramethylammonium hydroxide solution. Etching is continued until silicon is etched away and the silicon nitride film 102 is exposed. The substrate is cleaned with water and dried. The silicon nitride film 102 exposed after etching of silicon is etched away by using tetrafluoromethane in a dry etching apparatus. The polyimide film which protects the other surface is removed by ashing (FIG. 2F). The middle electrode 2 is fabricated as follows. A silicon wafer is prepared as a substrate 201, and an SiO2 film 202 is formed to a thickness of 50 nm by sputtering. A plating electrode film 203 for fabricating a middle electrode 205 (corresponding to 2 in FIG. 1A) is formed by depositing gold to a film thickness of 50 nm and patterning it (FIG. 3A). A resist pattern 204 serving as a plating mold is formed. More specifically, the resist is made of SU-8 (MicroChem. Co) mainly consisting of an epoxidized bisphenol A oligomer, and is formed to a film thickness of 80 μm. Exposure employs a contact type exposure apparatus using a high-pressure mercury lamp. After exposure, post-exposure bake (PEB) is done on a hot plate at 85° C. for 30 min. After the substrate is gradually cooled to room temperature, the resist is developed with propylene glycol monomethyl ether acetate for 5 min to complete the plating mold pattern 204 (FIG. 3B). A 50-μm thick gold pattern 205 is buried as the middle electrode (corresponding to 2 in FIG. 1A) in the apertures of the resist pattern 204 by electroplating (FIG. 3C). The SU-8 resist 204 is removed in N-methyl-pyrrolidone (NMP), and the substrate is cleaned and dried by IPA (FIG. 3D). A method of joining the middle electrode and a structure made up of a lower electrode and lower shield electrode will be explained with reference to FIGS. 4A to 4D. As described above, the structure made up of the lower electrode and lower shield electrode is fabricated by the same method as the method of fabricating the structure made up of the upper electrode and upper shield electrode. A lower electrode and lower shield electrode shown in FIG. 2F that are fabricated by the procedures of FIGS. 2A to 2F are prepared. After an SiO2 film (insulating film) 111 is formed to 10 μm by sputtering and patterned, a gold film 112 is deposited to 50 nm and patterned (FIG. 4A). The middle electrode prepared by the procedures shown in FIGS. 3A to 3D is turned over and pressed against the gold film 112 by gold-to-gold contact bonding (FIGS. 4B and 4C). Only the silicon wafer of the middle electrode is wet-etched with a jig. The gold and SiO2 films are sequentially dry-etched away by 50 nm each to obtain a lower electrode/middle electrode structure (FIG. 4D). FIG. 5 is a view for explaining the final assembly. The structure shown in FIG. 4D that is fabricated by the procedures shown in FIGS. 4A to 4D and constituted by the joined lower electrode 105 (corresponding to 3 in FIG. 1A), lower shield electrode 110 (corresponding to 5 in FIG. 1A), and middle electrode 205 (corresponding to 11 in FIG. 1A) faces the structure shown in FIG. 2F that is fabricated by the procedures shown in FIGS. 2A to 2F and constituted by the upper electrode 105 (corresponding to 1 in FIG. 1A) and upper shield electrode 110 (corresponding to 4 in FIG. 1A). Fibers 20 are set in the alignment V-grooves 104 formed on the two sides of the substrate. The two structures are pressed to achieve alignment in directions parallel and perpendicular to the joined surface. The aligned members are fixed with an adhesive. Accordingly, an electrooptic element array with high assembly precision is completed. Several modifications of the above-described electrooptic system array will be explained. FIG. 6 is an exploded view showing an arrangement having a plurality of middle electrodes. Compared to the embodiment of FIG. 1A using one middle electrode, the electrooptic system array of FIG. 6 has two middle electrodes 2A and 2B which sandwich a middle shield electrode 15. FIGS. 7A to 7C show another embodiment of an electrooptic system array in which a shield electrode is not separate, but is integrated into one electrode. FIG. 7A is an exploded sectional view of the electrooptic system array, FIG. 7B is a plan view of a middle electrode 2 when viewed from the top, and FIG. 7C is a perspective view of a lower electrode 3, lower shield 5, upper electrode 1, and upper shield 4. In this electrooptic system array, the upper electrode 1 and upper shield electrode 4 and the lower electrode 3 and lower shield electrode 5 are integrated structures of a metal material, respectively, and no insulating layer is interposed in each electrode and a corresponding shield electrode. This can simplify the manufacturing process. FIGS. 8A to 8D show an electrooptic system array having still another structure. FIG. 8A is an exploded sectional view of the electrooptic system array, FIG. 8B is a plan view of a middle electrode 2 when viewed from the top, FIG. 8C is a sectional view of the middle electrode 2, and FIG. 8D is a perspective view of a lower electrode 3, lower shield 5, upper electrode 1, and upper shield 4. Middle shield electrodes 16 are arranged between a plurality of cylindrical electrode elements of the middle electrode 2. This reduces the influence of an adjacent electric field in the cylindrical electrode elements of the middle electrode 2, and improves the anti-crosstalk effect. FIGS. 9A to 9C show an electrooptic system array having still another structure. A middle electrode 2 comprises a plurality of rectangular electrode elements 2A, 2B, and 2C arrayed in units of rows, which enables applying different potentials to the respective arrays. These rectangular electrode elements increase the rigidity of the structure and also increase the process precision. FIGS. 11A to 11E are views showing an electrooptic system array according to still another embodiment. FIG. 11A is a sectional view of the electrooptic system array, which has an upper, a middle and lower electrodes 1, 2, and 3, each having a plurality of aperture electrodes. Upper and lower shield electrodes 4 and 5 set to a common potential are arranged to sandwich the aperture electrodes (electrode elements) of the middle electrode 2. The aperture electrodes of the upper and lower shield electrodes 4 and 5 are arranged on the electron beam path. The electrodes 1, 2, and 3 and the shields 4 and 5 are stacked and integrated via insulating spacers 20. FIG. 11B shows the structure of the upper or lower electrode 1 or 3 in which all the aperture electrodes are grounded to a potential of 0 [V]. FIG. 11C shows the structure of the upper or lower shield electrodes 4 or 5 in which a common potential Vs (e.g., −500 V) is applied to all the aperture electrodes. FIG. 11D shows the structure of the middle electrode 2 in which different potentials V1, V2, and V3 (e.g., V1=−900 V, V2=−950 V, and V3=−1,000 V) are applied in units of rows of the aperture electrodes. Einzel lenses having middle electrodes on different rows exhibit different lens actions, and the middle electrodes can be regarded as setting electrodes for setting the lens actions of the Einzel lenses. The potentials may be applied in this manner not only in this arrangement but also in the other arrangements described above. To effectively reduce crosstalk, intervals s between the middle electrode 2 and the upper and lower shield electrodes 4 and 5 are set smaller than a layout interval (pitch) p between aperture electrodes formed in the middle electrode 2, as shown in FIG. 11A. To reduce the influence of inserting the shield electrode on lens action, an aperture size Ds (inner diameter) of each electrode in the shield electrode 4 or 5 (see FIG. 11C) is set larger than an aperture size Dc (inner diameter) of each electrode in the middle electrode 2 (see FIG. 11D). The aperture size of each electrode of the shield electrode 4 or 5 is set larger than the aperture size of each electrode of the upper or lower electrode 1 or 3. Instead of this structure, the middle electrode may be constituted as shown in FIG. 11E. In FIG. 11E, the middle electrode 2 comprises middle shield electrodes 15 linearly formed between the rows of electrode elements 11 set to different potentials (V1, V2, and V3). The middle shield electrodes 15 receive the same common potential Vs as the shield electrodes 4 and 5. Crosstalk is effectively prevented by shielding the electrode rows from each other within the middle electrode. FIGS. 12A and 12B show still another modification. This modification adopts an integrated structure of a unit LA1 including a middle electrode 24 on which rows of electrode elements 11 are formed in the Y direction, and a unit LA2 including a middle electrode 27 on which rows of electrode elements 11 are formed in the perpendicular X direction. One electrode 22 serves as both the lower electrode of the unit LA1 and the upper electrode of the unit LA2. An upper electrode 21, the electrode 22, and a lower electrode 23 are grounded, and a total of four shield electrodes 25, 26, 28, and 29 receive the same potential Vs. <Electron Beam Exposure Apparatus> A multi-beam charged-particle exposure apparatus (electron beam exposure apparatus) will be exemplified as a system using an electrooptic system array as described in the various embodiments. FIG. 13 is a schematic view showing the overall system. In FIG. 13, an electron gun 501 as a charged-particle source is constituted by a cathode 501a, grid 501b, and anode 501c. Electrons emitted by the cathode 501a form a crossover image (to be referred to as an electron source ES hereinafter) between the grid 501b and the anode 501c. An electron beam emitted by the electron source ES irradiates a correction electrooptic system 503 via an irradiation electrooptic system 502 serving as a condenser lens. The irradiation electrooptic system 502 is comprised of electron lenses (Einzel lenses) 521 and 522 each having three separate electrodes. The correction electrooptic system 503 includes an electrooptic system array to which the electrooptic system arrays are applied, and forms a plurality of intermediate images of the electron source ES (details of the structure will be described later). The correction electrooptic system 503 adjusts the formation positions of intermediate images so as to correct the influence of aberration of a projection electrooptic system 504. Each intermediate image formed by the correction electrooptic system 503 is reduced and projected by the projection electrooptic system 504, and forms an image of the electron source ES on a wafer 505 as a surface to be exposed. The projection electrooptic system 504 is constituted by a symmetrical magnet doublet made up of a first projection lens 541 (543) and second projection lens 542 (544). Reference numeral 506 denotes a deflector for deflecting a plurality of electron beams from the correction electrooptic system 503 and simultaneously displacing a plurality of electron source images on the wafer 505 in the X and Y directions; 507, a dynamic focus coil for correcting a shift in the focal position of a light source image caused by deflection aberration generated when the deflector 506 operates; 508, a dynamic stigmatic coil for correcting astigmatism among deflection aberrations generated by deflection; 509, a θ-Z stage which supports the wafer 505, is movable in the optical axis AX (Z-axis) direction and the rotational direction around the Z-axis, and has a stage reference plate 510 fixed thereto; 511, an X-Y stage which supports the θ-Z stage and is movable in the X and Y directions perpendicular to the optical axis AX (Z-axis); and 512, a reflected-electron detector for detecting reflected electrons generated upon irradiating a mark on the stage reference plate 510 with an electron beam. FIGS. 14A and 14B are views for explaining details of the correction electrooptic system 503. The correction electrooptic system 503 comprises an aperture array AA, blanker array BA, element electrooptic system array unit LAU, and stopper array SA along the optical axis. FIG. 14A is a view of the correction electrooptic system 503 when viewed from the electron gun 501, and FIG. 14B is a section view taken along the line A–A′ in FIG. 14A. As shown in FIG. 14A, the aperture array AA has an array (8×8) of apertures regularly formed in a substrate, and splits an incident electron beam into a plurality of (64) electron beams. The blanker array BA is constituted by forming on one substrate a plurality of deflectors for individually deflecting a plurality of electron beams split by the aperture array AA. The element electrooptic system array unit LAU is formed from first and second electrooptic system arrays LA1 and LA2 as electron lens arrays each prepared by two-dimensionally arraying a plurality of electron lenses on the same plane. The electrooptic system arrays LA1 and LA2 have a structure as an application of the electrooptic system arrays described in the above embodiments to an 8×8 array. The first and second electrooptic system arrays LA1 and LA2 are fabricated by the above-mentioned method. The element electrooptic system array unit LAU constitutes one element electrooptic system EL by the electron lenses of the first and second electrooptic system arrays LA1 and LA2 that use the common X-Y coordinate system. The stopper array SA has a plurality of apertures formed in a substrate, similar to the aperture array AA. Only a beam deflected by the blanker array BA is shielded by the stopper array SA, and ON/OFF operation of an incident beam to the wafer 505 is switched for each beam under the control of the blanker array. Since the charged-particle beam exposure apparatus of this embodiment adopts an excellent electrooptic system array as described above for the correction electrooptic system, an apparatus having a very high exposure precision can be provided and can increase the integration degree of a device to be manufactured in comparison with the prior art. <Example of Semiconductor Production System> A production system for producing a semiconductor device (e.g., a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin-film magnetic head, a micromachine, or the like) using the exposure apparatus will be exemplified. A trouble remedy or periodic maintenance of a manufacturing apparatus installed in a semiconductor manufacturing factory, or maintenance service such as software distribution is performed by using a computer network outside the manufacturing factory. FIG. 15 shows the overall system cut out at a given angle. In FIG. 15, reference numeral 1010 denotes a business office of a vendor (e.g., an apparatus supply manufacturer), which provides a semiconductor device manufacturing apparatus. Assumed examples of the manufacturing apparatus are semiconductor manufacturing apparatuses for performing various processes used in a semiconductor manufacturing factory, such as pre-process apparatuses (e.g., a lithography apparatus including an exposure apparatus, a resist processing apparatus and an etching apparatus, an annealing apparatus, a film formation apparatus, a planarization apparatus, and the like) and post-process apparatuses (e.g., an assembly apparatus, an inspection apparatus, and the like). The business office 1010 comprises a host management system 1080 for providing a maintenance database for the manufacturing apparatus, a plurality of operation terminal computers 1100, and a LAN (Local Area Network) 1090, which connects the host management system 1080 and computers 1100 to construct an intranet. The host management system 1080 has a gateway for connecting the LAN 1090 to Internet 1050 as an external network of the business office, and a security function for limiting external access. Reference numerals 1020 to 1040 denote manufacturing factories of the semiconductor manufacturer as users of manufacturing apparatuses. The manufacturing factories 1020 to 1040 may belong to different manufacturers or the same manufacturer (e.g., a pre-process factory, a post-process factory, and the like). Each of the factories 1020 to 1040 is equipped with a plurality of manufacturing apparatuses 1060, a LAN (Local Area Network) 1110, which connects these apparatuses 1060 to construct an intranet, and a host management system 1070 serving as a monitoring apparatus for monitoring the operation status of each manufacturing apparatus 1060. The host management system 1070 in each of the factories 1020 to 1040 has a gateway for connecting the LAN 1110 in the factory to the Internet 1050 as an external network of the factory. Each factory can access the host management system 1080 of the vendor 1010 from the LAN 1110 via the Internet 1050. Typically, the security function of the host management system 1080 authorizes access of only a limited user to the host management system 1080. In this system, the factory notifies the vendor via the Internet 1050 of status information (e.g., the symptom of a manufacturing apparatus in trouble) representing the operation status of each manufacturing apparatus 1060. The vendor transmits, to the factory, response information (e.g., information designating a remedy against the trouble, or remedy software or data) corresponding to the notification, or maintenance information such as the latest software or help information. Data communication between the factories 1020 to 1040 and the vendor 1010 and data communication via the LAN 1110 in each factory typically adopt a communication protocol (TCP/IP) generally used in the Internet. Instead of using the Internet as an external network of the factory, a dedicated-line network (e.g., an ISDN) having high security, which inhibits access of a third party, can be adopted. It is also possible that the user constructs a database in addition to one provided by the vendor and sets the database on an external network and that the host management system authorizes access to the database from a plurality of user factories. FIG. 16 is a view showing the concept of the overall system of this embodiment that is cut out at a different angle from FIG. 15. In the above example, a plurality of user factories having manufacturing apparatuses and the management system of the manufacturing apparatus vendor are connected via an external network, and production management of each factory or information of at least one manufacturing apparatus is communicated via the external network. In the example of FIG. 16, a factory having a plurality of manufacturing apparatuses of a plurality of vendors, and the management systems of the vendors for these manufacturing apparatuses are connected via the external network of the factory, and maintenance information of each manufacturing factory is communicated. In FIG. 16, reference numeral 2010 denotes a manufacturing factory of a manufacturing apparatus user (e.g., a semiconductor device manufacturer) where manufacturing apparatuses for performing various processes, e.g., an exposure apparatus 2020, a resist processing apparatus 2030, and a film formation apparatus 2040 are installed in the manufacturing line of the factory. FIG. 16 shows only one manufacturing factory 2010, but a plurality of factories are networked in practice. The respective apparatuses in the factory are connected to a LAN 2060 to construct an intranet, and a host management system 2050 manages the operation of the manufacturing line. The business offices of vendors (e.g., apparatus supply manufacturers) such as an exposure apparatus manufacturer 2100, a resist processing apparatus manufacturer 2200, and a film formation apparatus manufacturer 2300 comprise host management systems 2110, 2210, 2310 for executing remote maintenance for the supplied apparatuses. Each host management system has a maintenance database and a gateway for an external network, as described above. The host management system 2050 for managing the apparatuses in the manufacturing factory of the user, and the management systems 2110, 2210, and 2310 of the vendors for the respective apparatuses are connected via the Internet or dedicated-line network serving as an external network 2000. If trouble occurs in any one of a series of manufacturing apparatuses along the manufacturing line in this system, the operation of the manufacturing line stops. This trouble can be quickly solved by remote maintenance from the vendor of the apparatus in trouble via the external network 2000. This can minimize the stoppage of the manufacturing line. Each manufacturing apparatus in the semiconductor manufacturing factory comprises a display, a network interface, and a computer for executing network access software and apparatus operating software, which are stored in a storage device. The storage device is a built-in memory, a hard disk, or a network file server. The network access software includes a dedicated or general-purpose web browser, and provides a user interface having a window as shown in FIG. 17 on the display. While referring to this window, the operator who manages manufacturing apparatuses in each factory inputs, in input items on the windows, pieces of information such as the type of manufacturing apparatus (4010), serial number (4020), subject of trouble (4030), occurrence date (4040), degree of urgency (4050), symptom (4060), remedy (4070), and progress (4080). The pieces of input information are transmitted to the maintenance database via the Internet, and appropriate maintenance information is sent back from the maintenance database and displayed on the display. The user interface provided by the web browser realizes hyperlink functions (4100 to 4120), as shown in FIG. 17. This allows the operator to access detailed information of each item, to receive the latest-version software to be used for a manufacturing apparatus from a software library provided by a vendor, and to receive an operation guide (help information) as a reference for the operator in the factory. A semiconductor device manufacturing process using the above-described production system will be explained. FIG. 18 shows the flow of the whole manufacturing process of the semiconductor device. In step 1 (circuit design), a semiconductor device circuit is designed. In step 2 (creation of exposure control data), exposure control data of the exposure apparatus is created based on the designed circuit pattern. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. In step 4 (wafer process), called a pre-process, an actual circuit is formed on the wafer by lithography using a prepared mask and wafer. Step 5 (assembly), called a post-process, is the step of forming a semiconductor chip by using the wafer manufactured in step 4, and includes an assembly process (dicing and bonding) and a packaging process (chip encapsulation). In step 6 (inspection), inspections such as the operation confirmation test and durability test of the semiconductor device manufactured in step 5 are conducted. After these steps, the semiconductor device is completed and shipped (step 7). For example, the pre-process and post-process may be performed in separate dedicated factories. In this case, maintenance is done for each of the factories by the above-described remote maintenance system. Information for production management and apparatus maintenance is communicated between the pre-process factory and the post-process factory via the Internet or dedicated-line network. FIG. 19 shows the detailed flow of the wafer process. In step 11 (oxidation), the wafer surface is oxidized. In step 12 (CVD), an insulating film is formed on the wafer surface. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted in the wafer. In step 15 (resist processing), a photosensitive agent is applied to the wafer. In step 16 (exposure), the above-mentioned exposure apparatus draws (exposes) a circuit pattern on the wafer. In step 17 (developing), the exposed wafer is developed. In step 18 (etching), the resist is etched except for the developed resist image. In step 19 (resist removal), an unnecessary resist after etching is removed. These steps are repeated to form multiple circuit patterns on the wafer. A manufacturing apparatus used in each step undergoes maintenance by the remote maintenance system, which prevents trouble in advance. Even if trouble occurs, the manufacturing apparatus can be quickly recovered. The productivity of the semiconductor device can be increased in comparison with the prior art. The present invention can provide, e.g., an electrooptic system array which solves crosstalk unique to a multi-beam and realizes various conditions such as downsizing, high precision, and high reliability at a high level. The present invention can also provide a high-precision exposure apparatus using the electrooptic system array, a high-productivity device manufacturing method, a semiconductor device production factory, and the like. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.
	claims	1. A pressurized water nuclear reactor comprising:a pressure vessel having a core region for supporting fuel assemblies;a core barrel removably disposed within the pressure vessel;a core shroud disposed within the core barrel, the core shroud having an alignment slot;an upper core support plate removably disposed above the core shroud, the upper core support plate having an alignment slot; andan alignment plate attached to the core barrel and disposed within the alignment slot of the core shroud and within the alignment slot of the upper core support plate. 2. The pressurized water nuclear reactor of claim 1, wherein the core barrel has an inner surface and an outer surface and the alignment plate is attached to the inner surface of the core barrel and further comprising a reinforcement pad disposed on the outer surface of the core barrel and attached to the alignment plate. 3. The pressurized water nuclear reactor of claim 2 wherein the reinforcement pad is attached to the alignment plate with at least two dowel pins that engage the reinforcement pad and alignment plate through the core barrel. 4. The pressurized water nuclear reactor of claim 3 wherein the dowel pins are shrink fit into the reinforcement pad, core barrel and alignment plate or reinforcement pad and core barrel. 5. The pressurized water nuclear reactor of claim 3 wherein the alignment plate and reinforcement pad are affixed in a vertical direction, including a bottom hole and a top hole in the alignment plate with corresponding aligned holes in the core barrel and reinforcement pad, wherein the holes respectively on the alignment plate, the core barrel and the reinforcement pad are positioned spaced one above the other and are sized to receive the dowel pins. 6. The pressurized water nuclear reactor of claim 5 wherein one of the bottom or top dowel pin-alignment plate holes is designed to accommodate differential axial thermal growth between the core barrel and alignment plate, whereby a gap exists between a top, bottom and side surfaces of the one of the top or bottom dowel pin alignment plate holes and the corresponding dowel pins with machined flats on the vertical surfaces of the one of the bottom or top dowel pin-alignment plate holes allowing differential thermal growth in the vertical direction. 7. The pressurized water nuclear reactor of claim 2 wherein the alignment plate is attached to the core barrel with threaded fasteners. 8. The pressurized water nuclear reactor of claim 7 wherein the reinforcement pad is welded to the core barrel. 9. The pressurized water nuclear reactor of claim 8 wherein the reinforcement pad is welded to the core barrel with a fillet weld. 10. The pressurized water nuclear reactor of claim 1 wherein a back of the alignment plate fits in a recess in the core barrel. 11. The pressurized water nuclear reactor of claim 1 wherein a back of the alignment plate that interfaces with the core barrel is machined to have the same curvature as the core barrel. 12. The pressurized water nuclear reactor of claim 1 wherein the pressure vessel has an inlet nozzle and the alignment plate is positioned on the inner circumference of the core barrel radially in-line with the inlet nozzle. 13. The pressurized water nuclear reactor of claim 1 wherein the pressure vessel has a plurality of inlet nozzles and a plurality of alignment plates, with each alignment plate positioned on the inner circumference of the core barrel radially in-line with a corresponding one of the plurality of inlet nozzles. 14. The pressurized water nuclear reactor of claim 1 including an insert in the core shroud alignment slot and an insert in the upper core support plate alignment slot so that a predetermined clearance can be obtained between the sides of the slots and the alignment plate.
	abstract	The present invention relates to a method and covalent bonding process for fixing tritiated water into a polystyrene based product for the permanent elimination of tritiated water from the environment.
	abstract	An apparatus including a heating element and a sublimation vessel disposed adjacent the heating element such that the heating element heats a portion thereof. A collection vessel is removably disposed within the sublimation vessel and is open on an end thereof. A crucible is configured to sealingly position a solid mixture against the collection vessel.
051397358	claims	1. A system for controlling nuclear reactivity in a nuclear reactor vessel having a reactor core for boiling water to produce stream in said vessel at a vessel pressure comprising: a reservoir having a top end, a bottom end, a fluid port, and filled with a liquid nuclear poison to a level therein; a stationary, hollow control blade extending vertically into said core, and including a top end, a bottom end, and a fluid port; a poison conduit disposed in flow communication between said reservoir and said blade fluid ports for channeling said poison between said reservoir and said blade; and means for controlling level of said poison in said blade for selectively varying nuclear reactivity in said core by variably draining said poison from said reservoir through said poison conduit for variably filling said blade for variably reducing reactivity in said core, and by variably draining said poison from said blade through said poison conduit for variably filling said reservoir for increasing reactivity in said core, said blade poison level being variable between a poison minimal level and a poison maximum level, and said level controlling means including a pump disposed in series flow communication in said poison conduit and operable for selectively pumping said poison between said blade and said reservoir. 2. A reactivity control system according to claim 1 wherein said level controlling means include disposing said reservoir fluid port at said reservoir bottom end, disposing said blade fluid port at said blade bottom end, and positioning said reservoir vertically relative to said blade so that said poison in said reservoir may drain by gravity to fill said blade to said poison maximum level. 3. A reactivity control system according to claim 2 wherein said reservoir is disposed outside said vessel and said poison conduit extends sealingly through said vessel. 4. A reactivity control system according to claim 2 wherein said reservoir is disposed inside said vessel. 5. A reactivity control system according to claim 2 wherein said poison in said reservoir and in said blade is maintained at a pressure at least as high as said vessel pressure. 6. A reactivity control system according to claim 1 wherein said pump is effective for drawing said poison from said blade and pumping said poison into said reservoir for decreasing said poison in said blade, and for allowing gravity to drain said poison from said reservoir and into said blade. 7. A reactivity control system according to claim 6 wherein said pump comprises a fluid-driven eductor. 8. A reactivity control system according to claim 2 wherein said blade has a cruciform transverse configuration. 9. A reactivity control system according to claim 2 wherein said blade has an H-shaped transverse configuration. 10. A reactivity control system according to claim 2 wherein said blade has a Y-shaped transverse configuration. 11. A reactivity control system according to claim 2 wherein said blade has a circular transverse configuration. 12. A reactivity control system according to claim 2 wherein said core includes a plurality of transversely spaced apart fuel bundles and said blade is positioned between adjacent ones thereof. 13. A reactivity control system according to claim 2 wherein said core includes a plurality of transversely spaced apart fuel bundles and said blade is fixedly positioned in one of said fuel bundles. 14. A reactivity control system according to claim 7 further including a second pump disposed in flow communication between said reservoir and said eductor pump for receiving and pressurizing a portion of said poison from said reservoir and ejecting said poison portion in said eductor pump for pumping said poison from said blade into said reservoir.
	abstract	Embodiments of an apparatus and methods for offsetting systematic non-uniformities using a gas cluster ion beam are generally described herein. Other embodiments may be described and claimed.
	abstract	Disclosed herein is an apparatus suitable for detecting X-ray, comprising: an X-ray absorption layer comprising an electrode; an electronics layer, the electronics layer comprising: a substrate having a first surface and a second surface, an electronics system in or on the substrate, an electric contact on the first surface, a via, and a transmission line on the second surface; wherein the via extends from the first surface to the second surface; wherein the electrode is electrically connected to the electric contact; wherein the electronics system is electrically connected to the electric contact and the transmission line through the via.
	abstract	A focusing and shielding device for encephalic photon knife consisting of a body of ray source, a switch and an armet, the ray source body is a hemispherical shell with certain thickness, a ray source cavity for placing ray source and a pre-collimation hole are defined on the hemispherical shell; the ray source cavity is defined on the outer surface of the hemispherical shell, and the pre-collimation hole is define on the inner surface of the hemispherical shell and connecting with the ray source cavity; the switch is defined inside the body of the ray source, and the outer surface of the switch is in hemispherical shape, a middle collimation hole is set on the switch; the armet is deposited inside the switch, and the inner surface is in columnar shape, an end collimation hole is defined on the armet, a therapy path is defined where the middle collimation hole connected with the pre-collimation hole to form the end collimation hole. The focusing and shielding device for encephalic photon knife of the present invention is simple in structure and low in cost, and as the inner surface of the armet is in a column shape, it expand the space for therapy.
041697596	summary	BACKGROUND OF THE INVENTION This invention pertains to control rods for the control of nuclear reactors and more particularly to a part length rod useful for controlling power oscillations and for contributing to reactor shutdown. DESCRIPTION OF THE PRIOR ART It is well understood in the art of nuclear reactor power generation that larger reactors exhibit unstable oscillatory distortion of the nuetron flux in the axial direction. These power oscillations occur as a result of local increases in the neutron flux leading to the "burn-out" of xenon 135 (produced by radioactive decay of iodine 135) which increases reactivity, and leads to a further flux distortion and so on. In the course of time the concentration of xenon 135 begins to build up because of the higher flux level, and the whole process is reversed. Various attempts have been made by the prior art to provide specially designed control rods for the purpose of controlling such xenon produced power oscillations. One such earlier attempt is illustrated in U.S. Pat. No. 3,081,248 issued to P. J. Grant on Mar. 12, 1963. This attempted solution to the control problem proposed the provision of a control rod or control means comprising a pair of neutron absorber members adapted to be inserted into different parts of the reactor core and linked or coupled whereby movement of one member into, or out of, the reactor core was accompanied by a corresponding movement of the other member out of, or into, the reactor core, the arrangement being such that by the differential movement of the two members, the fluxes in the two parts of the reactor core are relatively adjusted without substantially effecting the total flux. This solution, however, was fraught with difficulties which rendered the solution generally unacceptable to the power industry. One of the difficulties was that the special control rod had a length in excess of the length of the active portion of the reactor which necessarily tended to increase the length of the pressure vessel surrounding the reactor core. Unnecessary increases in pressure vessel size are extremely expensive and are avoided if at all possible. A second difficulty was that each of the special control rods had to be driven with a special control rod drive mechanism which could not be scrammed when a rapid shutdown of the reactor was required. A second prior art solution to the control of power distribution oscillations within the core is the use of a part length control rod. Such rods are controlled independently of the main control rods and generally contain the neutron poison in the lower portion of the rod, with the upper portion of the rod being substantially non-neutron absorbing. In operation the poison portion is normally positioned in the central region of the core. If these rods are allowed to scram when a rapid shutdown of the reactor is required, the rods drop to the bottom of the reactor and the poison could be removed from a position of higher control worth to a position of lower control worth. This would tend to increase the reactivity of the reactor just at a time when every effort is being made to reduce the reactivity. Accordingly, utilization of the prior art linear motion devices for part length control rods of commercial nuclear power plants, did not result in a fail safe system. Simultaneously tripping of several part length control rods could result in an undesirable increase in the reactivity unless all the full length rods are tripped at the same time. Hence, the use of these prior art part length rods requires the use of a different type of linear motion device which is incapable of scramming the part length control rods. One such non-scrammable part length control rod drive mechanism is disclosed in U.S. Pat. No. 3,825,160 issued to Lichtenberger et al on July 23, 1974 and assigned to the present assignee. As can appreciated from the above discussion, the prior art solutions to the control of power oscillations required two distinct control rod drive mechanisms; a scrammable drive mechanism and a non-scrammable drive mechanism. In addition to the increased cost associated with providing two distinct types of drive mechanisms on each nuclear reactor, the prior art solutions have the effect of decreasing the control flexibility of the reactor. This follows since the positions of the part length rods and their drive mechanisms become fixed once the drive mechanisms are installed by welding on the reactor pressure vessel. Hence, the reactor designers to not have the flexibility of relocating the part length rods from these initially fixed positions without expensive and complex disassembly and relocation of the drive mechanisms. Thus a need is felt for a part length rod which may be scrammed into the core when a rapid reactor shutdown is necessary so that additional flexibility in the positioning of the part length rod may be achieved by simply moving the part length rod from one scrammable control rod drive mechanism to another identical scrammable control rod drive mechanism. SUMMARY OF THE INVENTION A part length rod is provided which may be mounted on a scrammable control rod drive mechanism and which may be scrammed into the reactor core when a rapid reactor shutdown is required. The part length control rod of this invention has first and second ends with a first neutron absorbing material at its first end, a second neutron absorbing material at its second end spaced from the first neutron absorbing material by a distance less than the length of the core, and a third intermediate portion connecting the first and second neutron absorbing materials, the intermediate material being substantially non-neutron absorbing. The first neutron absorbing material is a material of high macroscopic neutron absorption cross-section. The second neutron absorbing material has a smaller macroscopic neutron absorption cross-section than the first neutron absorbing material. The second neutron absorbing material is normally positioned in the central region of the core for control of power oscillations. The first neutron absorbing material is normally positioned outside of the reactor core where it has little or no effect on the neutron flux of the reactor core. Upon the requirement for a rapid reactor shutdown, the part length control rod is scrammed or inserted into the core so that both first and second ends of the control rod are simultaneously positioned within the core at opposite ends of the core or so that at least a fraction of each end of said first and second ends are simultaneously positioned within the core.
047160187	claims	1. An improved end plug for attachment on an end of a cladding tube of a nuclear fuel rod which facilitates using a gripper tool for loading the fuel rod into a nuclear fuel assembly, comprising: (a) an inner portion adapted to be inserted into said end of said tube; and (b) an outer portion adapted to extend from said end of said tube when said inner portion is inserted therein, said outer portion including a body part disposed adjacent said tube end and a leading part disposed remote from said tube end; (c) said leading part having a hollow interior cavity defined therein, a continuous exterior annular truncated surface defined on a terminal end of said leading part and a continuous exterior annular tapered surface defined on a lateral side of said leading part; (d) said exterior tapered surface extending between and merging with said body part and said exterior truncated surface and providing sufficient angular inclination so as to facilitate insertion of the end plug when mounted on the fuel rod tube end into the fuel assembly; (e) said interior cavity in said leading part having an inner end, an outer opening defined at and surrounded by said exterior annular truncated surface and a continuous interior annular wall surface interconnecting said inner end and said outer opening, said interior wall surface being of the same constant diameter from said inner end to said outer opening; (f) said interior wall surface of said cavity having a continuous undercut annular groove defined therein having a larger diametrical size than that of inner and outer annular portions of said interior wall surface on opposite sides of said groove, said groove being axially spaced from said cavity opening and engageable by the gripper tool fitted through said cavity opening for loading the fuel rod into the nuclear fuel assembly; (g) said leading part having a thickness between said exterior tapered surface thereon and said interior cavity undercut groove therein which is less than the radius of said groove and greater than the width of said exterior truncated surface, said interior wall surface of said cavity within said leading part having an axial length between said exterior truncated surface and said undercut groove which is greater than than the axial width of said groove such that said leading part is provided with sufficient wall structure laterally surrounding said interior cavity to react the forces created by engagement of the gripper tool within the cavity groove. (a) an inner portion adapted to be inserted into said end of said tube; and (b) an outer portion adapted to extend from said end of said tube when said inner portion is inserted therein, said outer portion including a body part disposed adjacent said tube end and a leading part disposed remote from said tube end; (c) said leading part having a hollow interior cavity defined therein, a continuous exterior annular truncated surface defined on a terminal end of said leading part and a continuous exterior annular tapered surface defined on a lateral side of said leading part; (d) said exterior tapered surface extending between and merging with said body part and said exterior truncated surface and providing sufficient angular inclination so as to facilitate insertion of the end plug when mounted on the fuel rod tube end into the fuel assembly; (e) said interior cavity in said leading part having an inner end, an outer opening defined at and surrounded by said exterior annular truncated surface and a continuous interior annular wall surface interconnecting said inner end and said outer opening, said interior wall surface being of the same constant diameter from said inner end to said outer opening; (f) said interior wall surface of said cavity having a continuous undercut annular groove defined therein having a larger diametrical size than that of inner and outer annular portions of said interior wall surface on opposite sides of said groove, said groove being axially spaced from said cavity opening and engageable by the gripper tool fitted through said cavity opening for loading the fuel rod into the nuclear fuel assembly; (g) said inner end of said cavity being located within said leading part at an axial distance from said outer opening substantially the same as the axial distance through which said exterior tapered surface of said leading part extends from said truncated surface to said body part such that said cavity at its inner end extends outwardly away from said body part of said outer end plug portion; (h) said body part having an exterior annular cylindrical surface which merges with said exterior tapered surface of said leading part and is of a diametrical size substantially equl to that of the fuel rod tube; (i) said leading part having a thickness between said exterior tapered surface thereon and said interior cavity undercut groove therein which is less than the radius of said groove and greater than the width of said exterior truncated surface, said interior wall surface of said cavity within said leading part having an axial length between said exterior truncated surface and said undercut groove which is greater than the axial width of said groove such that said leading part is provided with sufficient wall structure laterally surrounding said interior cavity to react the forces created by engagement of the gripper tool within the cavity groove. 2. The end plug as recited in claim 1, wherein said inner end of said cavity is located within said leading part at an axial distance from said outer opening substantially the same as the axial distance through which said exterior tapered surface of said leading part extends from said truncated surface to said body part such that said cavity at its inner end extends outwardly away from said body part of said upper end plug portion. 3. The end plug as recited in claim 1, wherein said body part has an exterior annular cylindrical surface which merges with said exterior tapered surface of said leading part and is of a diametrical size substantially equal to that of the fuel rod tube. 4. An improved end plug for attachment on an end of a cladding tube of a nuclear fuel rod which facilitates using a gripper tool for loading the fuel rod into a nuclear fuel assembly, comprising:
	claims	1. An extreme ultraviolet light source apparatus for generatingextreme ultraviolet light by introducing a laser beam and irradiating a target material with the laser beam to turn the target material into plasma, said apparatus comprising: a chamber in which the extreme ultraviolet light is generated;a target supply unit configured to supply the target material toward a plasma emission point within said chamber;a collector mirror configured to collect the extreme ultraviolet light radiated from the plasma;a first magnetic source;a first magnetic material to be magnetized by said first magnetic source, said first magnetic material having a leading end portion projecting from an inner wall of said first magnetic source toward the plasma emission point;a second magnetic source, anda second magnetic material to be magnetized by said second magnetic source, said second magnetic material having a leading end portion projecting from an inner wall of said second magnetic source toward the plasma emission point,wherein the leading end portion of said first magnetic material and the leading end portion of said second magnetic material face each other with the plasma emission point in between. 2. The extreme ultraviolet light source apparatus according to claim 1, further comprising a yoke passing through an opening formed in the first magnetic source,wherein the first magnetic material has one leading end portion connected to a leading end portion of the yoke, and another leading end portion located to face the plasma. 3. The extreme ultraviolet light source apparatus according to claim 1, wherein the first and second magnetic materials are located between a trajectory of the target material and said collector mirror. 4. The extreme ultraviolet light source apparatus according to claim 1, further comprising a target collecting tube configured to collect the target material, wherein:the first magnetic material has a cylinder shape surrounding said target supply unit, andthe second magnetic material has a cylinder shape surrounding said target collecting tube. 5. The extreme ultraviolet light source apparatus according to claim 4, wherein a volume of said first magnetic material is smaller than a volume of said second magnetic material. 6. The extreme ultraviolet light source apparatus according to claim 1, wherein a path configured to circulate a refrigerant is formed within the first magnetic material. 7. The extreme ultraviolet light source apparatus according to claim 1, wherein one of said first and second magnetic materials has a through hole through which the laser beam passes. 8. The extreme ultraviolet light source apparatus according to claim 1, wherein:said first and second magnetic sources are provided outside of said chamber, andeach of said first and second magnetic materials have one leading end portion connected to a respective one of the first and second magnetic sources outside of said chamber, and another leading end portion extending into said chamber. 9. The extreme ultraviolet light source apparatus according to claim 1, further comprising within said chamber:an extreme ultraviolet (EUV) light amount sensor;laser beam focusing optics; anda target location monitor unit,wherein the first magnetic material is located to form a magnetic field between the plasma and at least one of said EUV light amount sensor, said laser beam focusing optics, and said target location monitor unit. 10. The extreme ultraviolet light source apparatus according to claim 1, further comprising:an electrode formed on a rear surface of said collector mirror; anda power supply configured to apply a voltage to said electrode. 11. The extreme ultraviolet light source apparatus according to claim 10, further comprising:a charging unit configured to charge particles radiated from the plasma. 12. The extreme ultraviolet light source apparatus according to claim 1, further comprising:a power supply configured to apply a voltage to the first magnetic material. 13. The extreme ultraviolet light source apparatus according to claim 12, further comprising:a charging unit configured to charge particles radiated from the plasma. 14. The extreme ultraviolet light source apparatus according to claim 1, further comprising:two electrodes facing each other with the plasma in between; anda power supply configured to apply a voltage between said two electrodes. 15. The extreme ultraviolet light source apparatus according to claim 14, wherein one of the two electrodes has a through hole through which the laser beam passes. 16. The extreme ultraviolet light source apparatus according to claim 15, further comprising:a charging unit configured to charge particles radiated from the plasma. 17. The extreme ultraviolet light source apparatus according to claim 14, further comprising:a charging unit configured to charge particles radiated from the plasma. 18. The extreme ultraviolet light source apparatus according to claim 1, wherein the surface of the first magnetic material is coated with a material including one of TiN, Si3N4, BN, Al2O3, TiO2, MgAl2O4, carbon (C), titanium (Ti), and porous titanium. 19. An extreme ultraviolet light source apparatus for generating extreme ultraviolet light by introducing a laser beam and irradiating a target material with the laser beam to turn the target material into plasma, the apparatus comprising:a chamber in which the extreme ultraviolet light is generated;a target supply unit configured to supply the target material toward a plasma emission point within the chamber;a collector mirror configured to collect the extreme ultraviolet light radiated from the plasma;a plurality of electromagnetic coils disposed outside of the chamber;a plurality of magnetic cores which respectively project from an inner wall of said plurality of electromagnetic coils toward the plasma emission point to face each other with the plasma emission point in between; anda yoke configured to connect said plurality of magnetic cores to each other.
	description	The present invention relates generally to semiconductor processing systems, and more specifically to an apparatus and method for controlling a quality and precision of motion of a substrate during ion implantation. In the semiconductor industry, various manufacturing processes are typically carried out on a substrate (e.g., a semiconductor wafer) in order to achieve various results on the substrate. Processes such as ion implantation, for example, can be performed in order to obtain a particular characteristic on or within the substrate, such as limiting a diffusivity of a dielectric layer on the substrate by implanting a specific type of ion. Conventionally, ion implantation processes are performed in either a batch process, wherein multiple substrates are processed simultaneously, or in a serial process, wherein a single substrate is individually processed. Traditional high-energy or high-current batch ion implanters, for example, are operable to achieve a short ion beam line, wherein a large number of wafers may be placed on a wheel or disk, and the wheel is simultaneously spun and radially translated through the ion beam, thus exposing all of the substrates surface area to the beam at various times throughout the process. Processing batches of substrates in such a manner, however, generally makes the ion implanter substantially large in size. In a typical serial process, on the other hand, an ion beam is either scanned in a single axis across a stationary wafer, or the wafer is translated in one direction past a fan-shaped, or scanned ion beam. The process of scanning or shaping a uniform ion beam, however, generally requires a complex and/or long beam line, which is generally undesirable at low energies. Furthermore, a uniform translation and/or rotation of either the ion beam or the wafer is generally required in order to provide a uniform ion implantation across the wafer. However, such a uniform translation and/or rotation can be difficult to achieve, due, at least in part, to substantial inertial forces associated with moving the conventional devices and scan mechanisms during processing. Therefore, a need exists for a device for scanning an ion beam across a substrate, wherein the substrate is uniformly translated and/or rotated with respect to the ion beam. The present invention overcomes the limitations of the prior art. Consequently, the following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The present invention is directed generally toward a scanning mechanism for processing a substrate, wherein the scanning mechanism further comprises a two-link rotary subsystem. According to one exemplary aspect of the invention, a base portion is provided, wherein a first link is rotatably coupled to the base portion by a first joint, and wherein the first link is operable to rotate in a first rotational direction about a first axis associated with the first joint. A second link is further rotatably coupled to the first link by a second joint spaced a predetermined distance from the first joint, and wherein the second link is further operable to rotate in a second rotational direction about a second axis associated with the second joint. The second link further comprises an end effector, wherein the end effector is further spaced the predetermined distance from the second joint. According to another exemplary aspect of the invention, a first actuator and a second actuator are provided, wherein the first and second actuators are operable to respectively rotate the first link and the second link about the respective first axis and second axis. The first actuator, for example, is operable to continuously rotate the first link in the first rotational direction, and the second actuator is operable to continuously rotate the second link in the second rotational direction. According to one exemplary aspect, the first rotational direction and the second rotational direction are opposite one another, wherein the end effector is operable to oscillate in a generally linear first scan path. According to another exemplary aspect, the end effector is further coupled to the second link via a third joint, wherein the end effector is operable to rotate and/or tilt with respect to the second link. In accordance with another exemplary aspect of the invention, the first link and the second link are of approximately equal length, wherein a continuous oscillatory motion along the first scan path is generally permitted, and wherein the first and second joints rotate in a single respective direction. In accordance with still another exemplary aspect of the invention, a generally constant velocity of the end effector can be maintained in a predetermined range of motion along the first scan path, wherein a rotational velocity of the respective first link and second link is controlled, and wherein the rotational velocities are maintained at non-zero values throughout the movement of the end effector. According to yet another exemplary aspect, a translation mechanism is further provided, wherein the base portion and associated rotary subsystem is further operable to translate along a second scan path, generally referred to as a slow scan axis, wherein the second scan path is generally perpendicular to the first scan path. According to another exemplary aspect of the invention, a scanning system is provided, wherein a controller is operable to control the respective rotational velocity of the first link and second link such that the movement of the substrate within the predetermined range is maintained at a substantially constant value. Also, a method for scanning a substrate is provided, wherein the method comprises rotating the first link and second link in a predetermined manner, wherein the substrate is translated within the predetermined range along the first scan path at a generally constant velocity. Furthermore, the method comprises maintaining the respective rotational velocity of the first link and second link such that the rotational velocities do not cross zero velocity. To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. The present invention is directed generally towards a scanning mechanism for moving a substrate relative to a beam. More particularly, the scanning mechanism limits the amount of inertial force seen by the substrate, wherein a motion of the scanning mechanism oscillates via a two-link rotary subsystem. Accordingly, the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It should be understood that the description of these aspects are merely illustrative and that they should not be taken in a limiting sense. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident to one skilled in the art, however, that the present invention may be practiced without these specific details. Referring now to the figures, FIG. 1 illustrates an exemplary scanning mechanism 100 according to one exemplary aspect of the present invention. The scanning mechanism 100, for example, may be further associated with an ion beam (not shown) for use in an ion implantation process, as will be discussed hereafter. It should be noted that the present invention may be utilized in conjunction with various semiconductor processing systems, and all such systems are contemplated as falling within the scope of the present invention. The scanning mechanism 100, for example, comprises a base portion 105 operably coupled to a rotary subsystem 110. The base portion 105, for example, may be stationary with respect to the beam (not shown), or may be further operable to move with respect to the beam, as will be discussed hereafter. The rotary subsystem 110 comprises a first link 115 and a second link 120 associated therewith, wherein, for example, the rotary subsystem is operable to linearly translate a substrate (not shown) with respect to the base portion 105 via a predetermined movement of the first link and the second link. According to one example, the first link 115 is rotatably coupled to the base portion 105 via a first joint 125, wherein the first link is operable to continuously rotate about a first axis 127 in a first rotational direction 128 (e.g., the first link is operable rotate clockwise or counter-clockwise with respect to the first joint). The second link 120 is further rotatably coupled to the first link 115 via a second joint 130, wherein the second joint is spaced a predetermined distance L from the first joint 125. The second link is further operable to continuously rotate about a second axis 132 in a second rotational direction 133 (e.g., the second link is operable to rotate clockwise or counter-clockwise with respect to the second joint). The first link 115 and the second link 120, for example, are further operable to rotate in separate, yet generally parallel first and second planes (not shown), respectively, wherein the first and second planes are generally perpendicular to the respective first and second axes 127 and 132. Furthermore, the first link 115 and second link 120 are operable to continuously rotate 360° in a respective first rotational path 134 and second rotational path 135 about the respective first joint 125 and second joint 130. According to one exemplary aspect of the invention, the first rotational direction 128 is generally opposite the second rotational direction 133, wherein an end effector 140 associated with the second link 120 is operable to linearly translate along a first scan path 142 associated with the predetermined movement of the first link 115 and the second link. The end effector 140, for example, is operably coupled to the second link 120 via a third joint 145 associated with the second link, wherein the third joint is spaced the predetermined distance L from the second joint 130. The third joint 145, for example, is operable to provide a rotation 147 of the end effector 140 about a third axis 148. Furthermore, according to another example, the third joint 145 is further operable to provide a tilt (not shown) of the end effector 140, wherein, in one example, the end effector is operable to tilt about one or more axes (not shown) which are generally parallel to the second plane (not shown). The end effector 140, for example, is further operable to secure the substrate (not shown) thereto, wherein the movement of the end effector generally defines a movement of the substrate. The end effector 140, for example, may comprise an electrostatic chuck (ESC), wherein the ESC is operable to substantially clamp or maintain a position of the substrate with respect to the end effector. It should be noted that while an ESC is described as one example of the end effector 140, the end effector may comprise various other devices for maintaining a grip of a payload (e.g., the substrate), and all such devices are contemplated as falling within the scope of the present invention. The predetermined movement of the first link 115 and second link 120, for example, can be further controlled in order to linearly oscillate the end effector 140 along the first scan path 142, wherein the substrate (not shown) can be moved in a predetermined manner with respect to the ion beam (e.g., an ion beam coincident with the first axis 127). A rotation of the third joint 145, for example, can be further controlled, wherein the end effector 140 is maintained in a generally constant rotational relation with the first scan path 142. It should be noted that the predetermined distance L separating the first joint 125 and second joint 130, as well as the second joint and third joint 145, provides a general congruity in link length when measured between the respective joints. Such a congruity in length of the first link 115 and second link 120, for example, generally provides various kinematic advantages, such as those which will be described hereafter. FIGS. 2A–2L illustrate the rotary subsystem 110 in various progressive positions according to another exemplary aspect of the present invention, wherein the first rotational direction 128 and the second rotational direction 133 generally remain constant, and do not reverse throughout the predetermined movement of the first link 115 and second link 120. For example, in FIG. 2A, the end effector 140 is at a first position 150 along the first scan path 142, wherein the third joint 145 is spaced a distance of approximately twice the predetermined distance L from the first joint 125, thus defining a maximum position 155 of the end effector. Upon a rotation of the first link 115 and second link 120 about the respective first and second joints 125 and 130 in the respective first rotational direction 128 and second rotational direction 133, as illustrated in FIGS. 2B–2L, the end effector 140 can be moved along the first scan path 142 in a generally straight-line manner. In FIG. 2G, for example, the end effector 140 is at another maximum position 160 along the first scan path 142, wherein the third joint 145 is again spaced a distance of approximately twice the predetermined distance L from the first joint 125. In FIG. 2H, for example, it should be noted that the end effector 140 is moving back toward the first position 150, while the first rotational direction 128 and second rotational direction 133 remain unchanged. Following the position illustrated in FIG. 2L, the rotary subsystem 110 is operable to move again to the first position 150 of FIG. 2A, while still maintaining the constant rotational directions 128 and 133, wherein the linear oscillation can be continued. Maintaining constant rotational directions 128 and 133 of the respective first link 115 and second link 120 can provide various mechanical and kinematic advantages associated with moving the end effector 140 along the generally straight first scan path 142. For example, during the oscillation of the end effector 140, a substantially constant velocity of the end effector 140 is generally desirable within a predetermined range of motion thereof. FIG. 3 illustrates the rotary subsystem 110 in the various positions of FIGS. 2A–2L, wherein a substrate 165 (illustrated in phantom) further resides on the end effector 140. It should be noted that the rotary subsystem 110 is not drawn to scale, and that the end effector 140 is illustrated as substantially smaller than the substrate for clarity purposes. An exemplary end effector 140 can be approximately the size of the substrate 165, wherein adequate support for the substrate can be provided. It shall be understood, however, that the end effector 140 and other features illustrated can be of various shapes and sizes, and all such shapes and sizes are contemplated as falling within the scope of the present invention. As illustrated in FIG. 3, the scanning mechanism 100 is operable to linearly oscillate the substrate 165 along the first scan path 142 between maximum positions 155 and 160 of the end effector 140. Therefore, a maximum scan distance 166 traveled by opposite ends 167 of the substrate 165 can be generally defined along the scan path 142 (e.g., opposite ends of the circumference of the substrate along the first scan path), wherein the maximum scan distance is associated with the maximum positions 155 and 160 of the end effector 140. According to one exemplary aspect of the invention, the maximum scan distance 166 is greater than twice a diameter D of the substrate 165. The amount by which the maximum scan distance 166 is greater than twice the diameter D is defined as an overshoot 167. The overshoot 167, for example, can be advantageously utilized when the oscillation of the substrate 165 along the first scan path 142 changes directions, such as between the position illustrated in FIG. 2G which is between the positions of FIGS. 2F and 2H. It should be therefore noted that while the rotational directions 128 and 133 remain constant (i.e., unchanged), the movement of the end effector 140 and substrate 165 oscillates along the first scan path 142, thus changing direction at the maximum positions 155 and 160. Such a change in direction of the end effector 140 (and hence, the substrate 165) is associated with a change in velocity and acceleration of the end effector and substrate. In ion implantation processes, for example, it is generally desirable for the end effector 140 to maintain a substantially constant velocity along the scan path 142 when the substrate 165 passes through an ion beam (not shown), such as an ion beam which is generally coincident with the first axis 127. Such a constant velocity provides for the substrate 165 to be generally evenly exposed to the ion beam throughout the movement through the ion beam. However, due to the oscillatory motion of the end effector 140, acceleration and deceleration of the end effector is inevitable; such as when the third joint 145 (e.g., associated with the end effector and substrate 165) approaches the maximum positions 155 and 160 at either extent of the linear oscillation. Such an acceleration and deceleration near the maximum positions 155 and 160 (e.g., during scan path turn-around), should be maintained at reasonable levels in order to minimize inertial forces and associated reaction forces transmitted to the base portion 105 of the scanning mechanism 100. Variations in velocity of the end effector 140 during exposure of the substrate 165 to the ion beam, for example, can lead to a non-uniform ion implantation across the substrate. Therefore, a generally constant velocity is desired for a predetermined range 168 associated with the movement of the substrate 165 through the ion beam. For example, the predetermined range 168 is associated with the physical dimensions of the substrate 165 (e.g., twice a diameter of the substrate), such that the acceleration and deceleration of the end effector can be generally accommodated within the overshoot 167. Accordingly, once the substrate 165 completely passes through the ion beam, the acceleration and deceleration of the end effector 140 will not substantially affect an ion implantation process or dose uniformity across the substrate. FIG. 4 illustrates another exemplary aspect of the present invention, wherein the base portion 105 of the scanning mechanism 100 is further operable to translate in one or more directions. For example, the base portion 105 is operably coupled to a translation mechanism 170, wherein the translation mechanism is operable to translate the base portion and rotary subsystem along a second scan path 175, wherein the second scan path is substantially perpendicular to the first scan path 142. According to one exemplary aspect of the invention, the first scan path 142 is associated with a fast scan of the substrate 165, and the second scan path 175 is associated a slow scan of the substrate, wherein the substrate is indexed one increment along the second scan path for every translation of the substrate between maximum positions 155 and 160 along the first scan path. Therefore, for a full oscillation of the substrate 165 along the first scan path 142 (e.g., as illustrated in FIGS. 2A–2L), the translation mechanism 170 will translate the substrate two increments along the second scan path 175. A total translation 176 of the base portion, for example, is approximately the diameter D of the substrate 165. The translation mechanism 170 of FIG. 4, for example, may further comprise a prismatic joint. The translation mechanism 170 may still further comprise a ball screw system (not shown), wherein the base portion 105 can be smoothly translated along the second scan path 175. Such a translation mechanism 170, for example, is operable to “paint” the substrate 165 residing on the end effector 140 by passing the substrate through the ion beam in an incremental manner during the oscillation of the end effector, thus uniformly implanting ions across the entire substrate. FIG. 5 illustrates another exemplary aspect of the present invention in block diagram form, wherein a scanning system 200 comprises the scanning mechanism 100 of FIG. 1. In FIG. 5, for example, a first rotary actuator 205 is associated with the first joint 125 and a second rotary actuator 210 is associated with the second joint 130 wherein the first actuator and second actuator are operable to provide a rotational force to the first and second links 115 and 120, respectively. For example, the first and second rotary actuators 205 and 210 comprise one or more servo motors or other rotational devices operable to rotate the respective first link 115 and second link 120 in the first rotational direction 128 and the second rotational direction 133 of FIG. 1, respectively. The scanning system 200 of FIG. 5, for example, further comprises a first sensing element 215 and a second sensing element 220 associated with the respective first and second actuators 205 and 210, wherein the first and second sensing elements are further operable to sense position, or other kinematic parameters, such as velocity or acceleration, of the respective first and second links 115 and 120. Furthermore, according to another exemplary aspect of the invention, a controller 225 (e.g., a multi-axes motion controller) is operably coupled to drivers and/or amplifiers (not shown) of the first and second rotary actuators 205 and 210 and the first and second sensing elements 215 and 220, wherein the controller 225 is operable to control an amount of power 230 and 235 (e.g., a drive signal) provided to the respective first and second rotary actuators for an associated control duty cycle (e.g., a movement of the end effector 140 between maximum positions 155 and 160 illustrated in FIG. 4). The first and second sensing elements 215 and 200 of FIG. 5, such as encoders or resolvers, are further operable to provide respective feedback signals 240 and 245 to the controller 225, wherein the drive signals 230 and 235 to the respective actuators 205 and 210, for example, are calculated in real-time. Such real-time calculations of the drive signals 230 and 235 generally permits a precise adjustment of the power delivered to each respective rotary actuator 205 and 210 at predetermined time increments. The general scheme of motion control of the present invention generally provides a smoothness of motion of the end effector 140, and can minimize velocity errors associated therewith. According to another example, the controller 225 further comprises an inverse kinematic model (not shown), wherein the articulated motion of the end effector 140 is derived for each joint 125 and 130 at each duty cycle. The controller 225, for example, is further operable to control each actuator 205 and 210 by calculating a feed forward, model-based complimentary torque for each respective joint 125 and 130 during each control duty cycle. As discussed in the above example, the amount of power 230 and 235 provided to the respective first and second rotary actuators 205 and 210 is based, at least in part, on the positions sensed by the respective first and second sensing elements 215 and 220. Accordingly, the position of the end effector 140 of the scanning mechanism 100 can be controlled by controlling the amount of power provided to the first and second actuators 205 and 210, wherein the amount of power is further associated with a velocity and acceleration of the end effector along the first scan path 142 of FIG. 1. The controller 225 of FIG. 5, for example, is further operable to control the translation mechanism 170 of FIG. 4, wherein the movement of the base portion 105 along the second scan path 175 can be further controlled. According to one example, an incremental motion (e.g., a “slow scan” motion) of the translation mechanism 170 is synchronized with the motion of the end effector along the first scan path 142 (e.g., a “fast scan” motion), such that the translation mechanism is incrementally moved after each pass of the substrate 165 through the ion beam (e.g, during a change of direction of the wafer along the fast scan path). According to another exemplary aspect of the present invention, a rotational velocity profile and acceleration profile of the first and second links 115 and 120 of FIG. 3 is predetermined, wherein inertial forces associated with the velocity and acceleration are minimized within the predetermined range 168. For example, the maximum scan distance 166 generally defines a workspace of the rotary sub-system 110 with respect to ion beam utilization, wherein the first and second links 115 and 120 are at full extension at the start of the oscillation (e.g., the first position 150 of FIG. 2A). Advanced trajectory and path planning techniques may be used to design motion profiles in operational space, as well as in joint space, wherein large inertial forces associated with joint accelerations are substantially minimized. These techniques, in turn, can reduce size and power requirements associated with the joint actuators 205 and 210 of FIG. 5. For example, FIGS. 6A, 6B, and 6C illustrate exemplary forward kinematic graphs showing respective acceleration, velocity, and position of the end effector 140 of FIG. 3 at various times. Time, in this instance, is associated with end effector position along the first scan path 142, wherein a constant velocity is desirable within the predetermined range 168. During periods of changing velocity (and hence an acceleration or deceleration of the end effector 140), it is desirable that the substrate be in the region of overshoot 167. According to another exemplary aspect of the invention, proper inverse kinematics techniques can be utilized to overcome singularities when the first and second links 115 and 120 of FIG. 3 are at or close to full extension at the maximums 155 and 160, or when they are folded upon one another (e.g., FIGS. 2A and 2G illustrate full extension, and FIGS. 2D and 2J illustrate the first link 115 and second link 120 folded upon one another). Model-based, predictive control architectures, for example, may be utilized to provide a substantially smooth motion of the substrate 165 along the first scan path 142. As illustrated in FIGS. 7A. 7B, and 7C, inverse kinematics can be utilized to define a respective rotational acceleration profile 305 and 310, velocity profile 315 and 320, and position profile 325 and 330 of the respective first joint 125 and second joint 130 of FIG. 3 in order to provide a generally uniform velocity of the substrate 165 within the predetermined range 168. It should be noted that the present invention advantageously maintains the rotational velocity of the first and second joints 125 and 130 such that neither joint rotational velocity crosses zero throughout the full 360° rotation of the first and second links 115 and 120, as illustrated in FIG. 7B. Maintaining the rotational velocities (and hence, the respective rotational directions) such that they do not cross zero velocity generally minimizes large inertial forces associated with acceleration and deceleration of the joints. Therefore, a great advantage is provided over the prior art, in that the first and second actuators continuously rotate in the same rotational direction. FIG. 8 further illustrates exemplary torque profiles 335 and 340 for the respective first joint 125 and second joint 130 of FIG. 3 using inverse kinematics. It should be further noted that the torque associated with the first joint 125 and second joint 130 is significantly reduced in accordance with the present invention, as compared with conventional wafer scan mechanisms. According to still another exemplary aspect of the present invention, FIG. 9 is a schematic block diagram of an exemplary method 400 illustrating the integration and operation of the exemplary scanning mechanism of FIG. 1. While exemplary methods are illustrated and described herein as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events, as some steps may occur in different orders and/or concurrently with other steps apart from that shown and described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Moreover, it will be appreciated that the methods may be implemented in association with the systems illustrated and described herein as well as in association with other systems not illustrated. As illustrated in FIG. 9, the method 400 begins with providing a two-link rotary mechanism in act 405, wherein a distance between the joints is approximately equal. A rotational velocity of the links is controlled in act 410, wherein the end effector oscillates between two maximum positions, and wherein the velocity of the end effector is maintained generally constant within a predetermined range. Within the predetermined range, for example, an ion beam impinges upon the substrate, wherein the substrate is substantially uniformly exposed to the ion beam throughout the motion of the substrate. A predetermined control scheme may be utilized, such that non-linear inertial, coriolis and/or centripetal forces induced by links on joint actuators are compensated. The scanning mechanism 100 (e.g., an articulated arm) of the present invention provides sufficient dexterity such that the scanning mechanism can further easily participate in material handling tasks. Such material handling tasks, for example, may comprise placing or transferring processed wafers to another transfer mechanism. Conversely, loading or picking of un-processed wafers can further be accomplished by mating with another transfer device. In accordance with another exemplary aspect of the present invention, the scanning mechanism 100 can be further utilized in a process chamber (not shown) that is in state of high vacuum, wherein no mechanical components such as lubricated bearings or actuators are directly exposed to the environment. In order to achieve such ends, the joints of the mechanism 100, for example, are further provided with vacuum seals, such as Ferro-fluidic seals. It should be understood that any type of movable vacuum seal that provides an integrity of cleanliness of the process is contemplated as falling within the scope of the present invention. Therefore, the present invention is further operable to provide a motion generation and wafer scanning in a clean, vacuum environment. Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more other features of the other embodiments as may be desired and advantageous for any given or particular application.
	claims	1. A plasma injection system for space charge neutralization of an ion beam, comprising:a first array of magnets and a second array of magnets positioned along at least a portion of an ion beam path the first array being on a first side of the ion beam path to produce a first multi-cusp magnetic field, and the second array being on a second side of the ion beam path to produce a second multi-cusp magnetic field, and the first side opposing the second side, at least two adjacent magnets in the first array of magnets having opposite polarity; anda plasma source configured to generate a plasma in a plasma chamber, the plasma source having a magnetic source to generate a local dipole magnetic field in the plasma chamber, and the plasma source having an aperture, wherein the local dipole magnetic field is aligned with the aperture and the first multi-cusp magnetic field to distribute the plasma along the ion beam path. 2. The plasma injection system according to claim 1, wherein at least two adjacent magnets in the second array of magnets have opposite polarity. 3. The plasma injection system according to claim 1, wherein the plasma source is further configured to generate the plasma by colliding electrons with a gas, and wherein the gas comprises at least one of an inert gas, an electronegative gas and an electropositive gas. 4. The plasma injection system according to claim 1, wherein the plasma source is embedded in a pole piece along at least a portion of the ion beam path. 5. The plasma injection system according to claim 4, wherein the first array of magnets and second array of magnets are positioned in a beamguide comprising alternating sloped concave portions and sloped convex portions. 6. The plasma injection system according to claim 5, wherein the first array of magnets or the second array of magnets are located at the convex portion of the beamguide. 7. The plasma injection system according to claim 5, wherein the beamguide further comprises a plurality of apertures located at the concave portion of the beamguide. 8. The plasma injection system according to claim 1, wherein at least one of the first array of magnets or the second array of magnets is a permanent magnet or a coil. 9. The plasma injection system according to claim 1, wherein the at least one magnet in the first array or the at least one magnet in the second array is configured to direct the flow of the plasma in a cross-B loop. 10. The plasma injection system according to claim 9, wherein the cross-B loop is formed by at least one of diamagnetic drift, E cross B drift, and curvature drift. 11. The plasma injection system according to claim 1, wherein the first array of magnets are configured interdigitally. 12. The plasma injection system according to claim 1, wherein the second array of magnets are configured interdigitally. 13. The plasma injection system according to claim 1, wherein the first array of magnets and the second array of magnets are positioned in an analyzer magnet. 14. The plasma injection system according to claim 1, wherein the first array of magnets and the second array of magnets are positioned in a collimator magnet. 15. The plasma injection system according to claim 1, wherein the plasma source comprises a microwave source and the magnetic source comprises a coil.
	claims	1. A fission reactor, comprising:a shell encompassing a reactor space having a longitudinal axis;an axial cylinder including an inner diameter surface defining a central longitudinal channel having an axis that is co-located with the longitudinal axis of the reactor space;a plurality of axially extending rings located within the reactor space and concentrically positioned relative to the axial cylinder, wherein the plurality of axially extending rings are radially separated forming, for any two adjacent axially extending rings, both a radially inward adjacent ring and a radially outward adjacent ring, and wherein an outer diameter surface of the radially inward adjacent ring and an inner diameter surface of the radially outward adjacent ring define an annular cylindrical space;a first plurality of primary axial tubes located circumferential within the annular cylindrical space, wherein each primary axial tube includes an inner diameter surface forming a primary channel and an outer diameter surface;a plurality of webbings, wherein the outer diameter surface of each of the plurality of primary axial tubes is connected to the radially inward adjacent ring by a first webbing and is connected to the radially outward adjacent ring by a second webbing;a plurality of secondary channels within the cylindrical space, wherein circumferentially adjacent primary axial tubes are separated by one of the plurality of secondary channels; anda fissionable nuclear fuel composition located in at least some of the plurality of secondary channels. 2. The fission reactor according to claim 1, wherein the fissionable nuclear fuel composition located in at least some of the plurality of secondary channels form a set of fissionable nuclear fuel elements that are volumetrically identical throughout the fission reactor. 3. The fission reactor according to claim 1, wherein a ratio of an area of a radial cross-section of the primary channels to an area of a radial cross-section of the secondary channels is constant throughout the fission reactor. 4. The fission reactor according to claim 1, wherein inner surfaces of the secondary channel include portions of the outer diameter surface of the circumferentially adjacent primary axial tubes, surfaces of the first webbing and the second webbing associated with each of the circumferentially adjacent primary axial tubes, and portions of the outer diameter surface of the radially inward adjacent ring and portions of the inner diameter surface of the radially outward adjacent ring. 5. The fission reactor according to claim 4, wherein the fissionable nuclear fuel composition is in thermal transfer contact with the inner surfaces of the secondary channel. 6. The fission reactor according to claim 1, wherein a primary coolant is flowable through the primary channel of each of the circumferentially adjacent primary axial tubes that are separated by one of the plurality of secondary channels which contain the fissionable nuclear fuel composition. 7. The fission reactor according to claim 1, wherein the circumferentially adjacent primary axial tubes are non-contactingly distributed within the annular cylindrical space. 8. The fission reactor according to claim 1, including a second plurality of primary axial tubes located circumferential between an inner diameter surface of the most radially inward, axially extending ring and an outer diameter surface of the axial cylinder, wherein the outer diameter surface of each of the second plurality of primary axial tubes is connected to the outer diameter surface of the axial cylinder by a first webbing and is connected to the most radially inward, axially extending ring by a second webbing. 9. The fission reactor according to claim 8, including a third plurality of primary axial tubes located circumferential between an inner diameter surface of the shell and an outer diameter surface of the most radially outward, axially extending ring, wherein the outer diameter surface of each of the third plurality of primary axial tubes is connected to the outer diameter surface of the most radially outward, axially extending ring by a first webbing and is connected to the inner diameter surface of the shell by a second webbing. 10. The fission reactor according to claim 9, wherein the shell, the axial cylinder, the plurality of axially extending rings, the plurality of primary axial tubes, and the plurality of webbings are an integral, unitary structure. 11. The fission reactor according to claim 10, wherein the shell, the axial cylinder, the plurality of axially extending rings, the plurality of primary axial tubes, and the plurality of webbings are formed from a metal alloy. 12. The fission reactor according to claim 1, wherein the shell, the axial cylinder, the plurality of axially extending rings, the plurality of primary axial tubes, and the plurality of webbings are an integral, unitary structure. 13. The fission reactor according to claim 12, wherein the shell, the axial cylinder, the plurality of axially extending rings, the plurality of primary axial tubes, and the plurality of webbings are formed from a metal alloy. 14. The fission reactor according to claim 1, including a reflector around an outer diameter surface of the shell. 15. The fission reactor according to claim 1, including at least one of a moderator, a control rod, and a scientific instrument is located in one or more primary channels. 16. The fission reactor according to claim 1, wherein the first plurality of primary axial tubes in each of the cylindrical space has a six-fold rotational symmetry relative to the longitudinal axis of the reactor space. 17. The fission reactor according to claim 1, wherein one or more of the central longitudinal channel of the axial cylinder and the primary channel of one or more of the primary axial tubes is accessible from an outer surface of the fission reactor. 18. The fission reactor according to claim 1, wherein the primary axial tube has a longitudinal axis that is parallel with the axis of the reactor. 19. The fission reactor according to claim 18, wherein the inner diameter surface of the primary axial tubes forming the primary channel varies as a function of axial position relative to the longitudinal axis of the primary axial tube. 20. The fission reactor according to claim 1, wherein the primary axial tubes are chambered. 21. The fission reactor according to claim 1, wherein a cross-section of the secondary channel perpendicular to the longitudinal axis has a shape of a cross-section of a hyperboloid of one sheet.
	summary
	abstract	A neutron sealed source holds cermet wire sources, such as Californium-252/Palladium wires, in separate blind apertures within a stainless steel block. The stainless steel block is part of an inner encapsulation and includes blind apertures arranged in rotational symmetry for receiving the cermet wire sources. The cermet wire sources are separated from each other and the fission and decay heat is rejected through the stainless steel block.
047012994	description	DETAILED DESCRIPTION FIGS. 1 and 2 show the core containment 1 of a pressurized water nuclear reactor, welded at its lower part to the core support plate 2 on which the assemblies forming the reactor core 3 rest. The core containment 1 is fixed at its upper part to the collar of the reactor vessel and arranged co-axially with the vessel. The core containment 1 and the support plate 2 form part of the lower internal equipment of the reactor. FIG. 1 shows that the outer surface of the core 3 bearing against the modular lining 5 has a complex shape comprising numerous steps corresponding to the peripheral assemblies 4 of the reactor. The modular lining 5, which occupies virtually all the volume of the annular space between the outer surface of the core and the inner surface of the containment 1, consists of three types of modular element 5a, 5b and 5c of different shapes. All these modular blocks have the same height and the modular lining consists of successive layers of modular elements 5a, 5b and 5c arranged noncontiguously on top of one another over the height of the core. FIG. 2 shows that the modular lining as a whole consists of nine layers of modular elements such as shown in FIG. 1, arranged on top of one another. FIG. 1 also shows that the elements 5a are not all identical to one another and that the same applies to the elements 5b and 5c, which are designed to match the external shape of the core. The elements 5a, 5b and 5c are arranged along the inner surface of the containment in a non-contiguous manner relative to this containment, packing pieces 7 being arranged between the modular elements and the inner surface of the containment 1. These packing pieces 7 make it possible to create a space 6 for the circulation of the reactor cooling water between the modular lining 5 and the containment 1. Arranged between the modular elements 5a and 5b and between the elements 5b and 5c, there are also packing pieces 8 making it possible to maintain, under hot conditions, a certain distance between the modular blocks for the circulation of reactor cooling water. In the cold, there is a small clearance between the packing pieces 8 which are firmly fixed to one of the modular elements (for example 5a), and the adjacent face of the other modular element (for example 5b), which enables the elements 5a and 5b to expand freely within the limit allowed by the clearance, and this reduces the thermal stresses. This also produces correct cooling of the modular blocks without the need to machine cooling channels and thus with the introduction of only a small amount of water into the modualr lining, which does not lower the reflectance. Finally, the small size of the modular blocks limits their thermal deformation, which makes it possible to overcome the problems relating to the geometry of the modular lining and aviod the need to provide an excessive clearance between the blocks and the core, which would detract from holding the core in the event of an earthquake and would be liable to result in starving the peripheral assemblies of cooling fluid. The modular blocks 5a, 5b and 5c are joined to the core containment 1 by means of fixing devices 10, which will be described in detail with reference to FIGS. 3 and 4. The blocks 5a are joined to the core containment by four devices 10, two of which are arranged at the upper part of the block and two at the lower part. The fixing devices are located in the region of the packing pieces 7. The central block 5a, however, is fixed to the core containment by only two devices 10, one of which is located at its upper part and the other at its lower part. The modular elements 5b, of profile shape, are joined to the core containment 1 by four screws arranged in pairs on either side of the block 5a, the block 5b which surrounds the block 5a towards the inside bearing against the core containment on either side of this block 5a. The blocks 5c are also fixed to the core containment by a set of four devices 10. FIG. 3 shows the core containment 1 through which a bore 12 passes, the said bore comprising a part 12a, of large diameter, towards the outside of the core containment, ending in a bearing surface 12b, and a part 12c of small diameter. The modular lining element 5 joined to the core containment 1 bears against the latter via the packing piece 7 possessing a groove 14 for the passage of water, in communication with the space 6, permitting the circulation of the reactor cooling water between the core containment and the modular blocks. This modular block 5 has a blind hole 15 tapped over a part 15a of its inner surface. A threaded sleeve 16 is screwed inside the blind hole 15 and then locked against rotation relative to the element 5 by a circular weld 17. Before the sleeve is fixed in the blind hole in the modular block 5, it is equipped with a screw 18 whose head 20, possessing two flat parts 19 visible in FIG. 4, is inserted in a housing 21 machined in the end of the sleeve 16. The length of the sleeve 16 is less than that of the blind hole 15, with the result that a space is created between the end of the sleeve in which the housing 21 is machined and the bottom 15b of the blind hole 15. The end of the sleeve 16 is hollowed out over a width corresponding to the width of the screw head 20 between the two flat parts 19, in order to create the housing 21. The screw head 20 can thus be locked in rotation when it is inserted in the housing 21 (FIG. 4). The diameter of the central bore 24 of the sleeve 16 is substantially equal to the diameter of the part 12c of the bore passing through the core containment 1, and when the modular block is placed in the fixing position along the core containment, the bore 12 and the sleeve 16, or its central bore 24, have a common axis 25. The diameter of the bore 24 and the diameter of the bore 12c are slightly greater than that of the non-threaded part of the screw 18, so that the latter is caused to bend and not to shear, which very substantially improves its fatigue characteristics. For a given screw size, this design makes it possible to make a maximum reduction in the length of the thread and consequently to maximize its bending length, leading to good fatigue characteristics, which are essential since the screws must take up the movements of the blocks resulting from the temperature transitions. The sleeve 16 has a radial hole 26 passing right through it. Between this hole 26 and that end of the sleeve which is located towards the bottom of the blind hole 15b, the diameter of the sleeve is less than the diameter of the blind hole 15, with the result that an annular space brings the entrance of the radial hole 26 on the outer surface of the sleeve into communication with the space created between the bottom of the blind hole 15b and that end of the sleeve which possesses the housing 21. The screw 18 has an axial hole 28 over the whole of its length, emerging, when the screw is in place in the sleeve, in the terminal space in the blind hole 15. At its other end, the central hole 28 emerges on the outside of the core containment 15, the screw being inserted in the bore 12 passing through the core containment, so that its end opposite the head 20, having a thread 29, is inside the large diameter 12a of the bore in communication with the outer part of the containment. A nut 30, bearing against the outer surface of the containment, in the region of the bearing surface 12b, is fitted to this threaded part 29. Between its threaded part 29 and its head 20, the screw comprises a tubular body 31 whose diameter is less than the internal diameter of the part 12c of the bore 12 and of the central bore 24 of the sleeve 16. An annular channel 32 is therefore created around the screw over the whole of its passage through the sleeve 16 inside the block 5 and the containment 1. To be put in place, the block 5 is brought into a position opposite the packing piece 7 fixed to the inner surface of the core containment, this block 5 being equipped with the sleeve 16 and with the screw 18, which is then inserted in the bore 12 passing through the containment, until the part 29 of this screw reaches the outside of the containment 1. The nut 30 is then screwed on to the part 29 in order to tighten and fix the block 5 against the packing piece 7. This tightening can be carried out since the screw 18 is locked against rotation by its head 20, comprising flat parts 19, in the housing 21. The same procedure is adopted for the four screws belonging to the four devices 10 for fixing the block 5. When the tightening has been carried out, the nut is locked against rotation by means of a weld 33. When the nuclear reactor is operating, there is a pressure difference between the cooling water located outside the containment and the cooling water located inside the containment. In fact, the water cooled by the steam generators, which is returned to the base of the core through the space existing between the core containment 1 and the vessel, undergoes a pressure drop on passing through the core, which is itself substantially in pressure equilibrium at a given height with the space 6 for the circulation of the cooling water between the core containment and the blocks 5. There is hence a pressure difference between the outside of the core containment and the groove 14 for the passage of water in communication with the water circulation space 32. A circulation of cooling water is therefore established between the outside and the inside of the core containment through the hole 28 in the screw, the terminal space in the blind hole 15, the annular space between the end of the sleeve 16 and the bottom 15b of the blind hole, the radial hole 26, the annular channel 32 and, finally, the groove 14 for the passage of water. This continuous circulation of water inside and around the screw makes it possible to avoid thermal gradients in the screw and cools the latter to a certain extent. This circulation is obtained without it being necessary to make holes in the modular blocks of the lining or to make holes in the screw in the radial direction. FIG. 5 shows a second type of solid modular lining fixed to the core containment 40 by fixing devices 50 identical to the fixing device shown in FIGS. 3 and 4. This solid modular lining, comprising modular blocks 45, can be used in the case of a pressurized water nuclear reactor of the undermoderated type in which the assemblies 41 have a hexagonal cross-section (instead of a square cross-section as for the reactor shown in FIG. 1). The various modular blocks 45 are arranged next to one another on the periphery of the core, without overlapping. Some of these blocks have a few vertical cooling holes 42 over their entire height. The number of cooling holes is small in this case, because undermoderated reactors are surrounded by a covering of fertile material arranged between the core and the modular lining, which reduces the heating due to the effect of the radiation on the modular blocks. As in the case of the modular lining shown in Figures 1 and 2, the modular lining as a whole is made up by the juxtaposition of layers of blocks, as shown in FIG. 5, arranged non-contiguously above one another. Arranged between two successive blocks 45 and between any one block 45 and the core containment 40, there are packing pieces 48 making it possible to create a cooling water circulation space 46 or 47. FIGS. 6 and 7 show a third type of modular lining which can be used in the case of a core consisting of assemblies of square cross-section, as shown in FIG. 1. This modular lining comprises modular blocks 55a and 55b fixed to the core containment 51 by fixing devices 60 identical to the devices described with reference to FIGS. 3 and 4. The modular blocks 55b are arranged so as to overlap with the blocks 55a, and the blocks 55a and 55b are fixed along the containment 51 in a non-contiguous manner by means of packing pieces 52. Keys 56 are fixed to some of the modular blocks 55a or 55b and are welded to the corresponding modular block and pass right through it. These keys 56 make it possible to fix a third type of modular block 55c to the modular blocks 55a or 55b by means of pins 57. The modular blocks 55c are not joined directly to the core containment 51, but only via the modular blocks 55a or 55b. Located between the blocks 55a, 55b and 55c, there are packing pieces 58 creating a space for the cooling and the relative movement of the blocks under the effect of expansion. It is seen that the main advantages of the lining according to the invention are that it permits cooling and relative movement of the blocks under the effect of expansion while avoiding the use of a large number of cooling channels, which reduce the mass of metal in the modular blocks and make them unsuitable as neutron reflectors. The particular type of fixing device described makes it possible to cool the screws for fixing the modular lining elements to the core containment and to make their temperature uniform, to a high degree of efficiency, without reducing the mechanical strength of the screws. This fixing device can be used in the case of solid modular blocks forming a modular lining occupying virtually all the volume of the annular space between the core and the inner surface of the core containment. The massive modular linings thus obtained are very firmly fixed to the core containment and have perfectly defined positions. The arrangement of these modular blocks for forming the modular lining makes it possible to reserve free spaces for the passage of the cooling water, without it being necessary to machine the blocks by drilling. The invention is not limited to the embodiments which have been described; on the contrary, it includes all the variants thereof. Thus, solid blocks having shapes different from those which have been described can be used. The end housing in the sleeve for locking the screw in rotation can have any non-cylindnrical shape in order to make it possible to lock a screw head of the corresponding shape. The sleeve can be fixed in any manner inside the blind hole created in the modular lining element. The fixing device described applies not only in the case of a solid reflecting modular lining according to the invention, comprising thick modular blocks, but also in the case of a conventional modular lining consisting of relatively thin metal plates. In this case, the fixing device according to the invention can advantageously be used for fixing the shape adaptors to the core containment. The invention applies to any pressurized water nuclear reactor for which an improvement in the neutron balance is desired.
	claims	1. A radiation therapy system comprising:a megavoltage radiation source and beam modulator producing a programmable radiation beam;a rotatable patient positioning system, comprising:a patient interface surface; andan aperture to permit passage of the anatomy to be treated through the patient interface surface;means to move the patient positioning system about a substantially vertical axis with respect to said radiation source;a beam stop to substantially absorb the radiation beam which bypasses or is transmitted through the patient during operation;an integrated shielding system cooperating with the patient interface surface configured to shield the patient, except for the anatomy to be treated, from substantially all direct and scattered radiation from the radiation source, beam modulator, and beam stop. 2. The radiation therapy system of claim 1 further including x-ray imaging means for visualizing the patient anatomy. 3. The radiation therapy system of claim 1 where the system is mounted in a mobile enclosure. 4. The radiation therapy system of claim 1 including a shielded enclosure which encloses the radiation source and modulator where the patient interface surface cooperates with the enclosure to shield the patient, except for the anatomy to be treated, from substantially all direct and scattered radiation from the radiation source, modulator and beam stop. 5. The radiation therapy system of claim 1 where said radiation source is a linear accelerator. 6. The radiation therapy system of claim 1 where the anatomy to be treated is a breast.
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062352237	claims	1. A method for producing a sintered nuclear fuel body containing (U, Pu)O.sub.2 mixed crystals, which comprises: adding at least one powdered substance selected from the group consisting of aluminum oxide, titanium oxide, niobium oxide, chromium oxide, vanadium oxide, aluminum hydroxide, chromium hydroxide, aluminum monostearate, aluminum distearate and aluminum tristearate as an additive to powdered starting materials of uranium dioxide UO.sub.2+X and plutonium dioxide PuO.sub.2 ; grinding the starting materials; compressing the ground starting materials into a body; and sintering the body at a sintering temperature of at least 1400.degree. C. in a hydrogen-containing sintering atmosphere having an oxygen partial pressure of no higher than 10.sup.-10 bar resulting in mixed (U, Pu)O.sub.2 crystals having a mean particle size in a range from 7.5 .mu.m to 50 .mu.m. grinding powdered starting materials of uranium dioxide UO.sub.2+X and plutonium dioxide PuO.sub.2 ; compressing the ground starting materials into a body; sintering the body during a holding time of 10 minutes to 8 hours at a sintering temperature in a range from 1400.degree. C. to 1800.degree. C. in a hydrogen-containing sintering atmosphere having a first oxygen partial pressure of 10.sup.-10 to 10.sup.-20 bar during a first portion of the holding time and having a second and higher oxygen partial pressure of 10.sup.-8 to 10.sup.-10 bar during an ensuing second portion of the holding time; and then cooling down the body in a hydrogen-containing atmosphere with an oxygen partial pressure of 10.sup.-10 to 10.sup.-20 bar; the sintering and cooling resulting in mixed (U. Pu)O.sub.2 crystals having a mean particle size in a range from 7.5 .mu.m to 50 .mu.m. adding at least one powdered substance selected from the group consisting of aluminum oxide, titanium oxide, niobium oxide, chromium oxide, vanadium oxide, aluminum hydroxide, chromium hydroxide, aluminum monostearate, aluminum distearate and aluminum tristearate as an additive to powdered starting materials of uranium dioxide UO.sub.2+X and plutonium dioxide PuO.sub.2 ; grinding the starting materials; compressing the ground starting materials into a body; and sintering the body during a holding time of 10 minutes to 8 hours at a sintering temperature in a range from 1400.degree. C. to 1800.degree. C. in a hydrogen-containing sintering atmosphere having a first oxygen partial pressure of 10.sup.-10 to 10.sup.-20 bar during a first portion of the holding time and having a second and higher oxygen partial pressure of 10.sup.-8 to 10.sup.-10 bar during an ensuing second portion of the holding time; and then cooling down the body in a hydrogen-containing atmosphere with an oxygen partial pressure of 10.sup.-10 to 10.sup.-20 bar; the sintering and cooling resulting in mixed (U, Pu)O.sub.2 crystals having a mean particle size in a range from 7.5 .mu.m to 50 .mu.m. 2. A method for producing a sintered nuclear fuel body containing (U, Pu)O.sub.2 mixed crystals, which comprises: 3. A method for producing a sintered nuclear fuel body containing (U, Pu)O.sub.2 mixed crystals, which comprises: 4. The method according to claim 1, which comprises adding the at least one powdered substance at an early stage during grinding. 5. The method according to claim 1, which comprises adding the at least one powdered substance at a later stage during grinding. 6. The method according to claim 3, which comprises adding the at least one powdered substance at an early stage during grinding. 7. The method according to claim 3, which comprises adding the at least one powdered substance at a later stage during grinding. 8. The method according to claim 1, which comprises maintaining a sintering temperature at an at least approximately constant value in a range from 1600.degree. C. to 1800.degree. C. 9. The method according to claim 2, which comprises maintaining the sintering temperature at an at least approximately constant value. 10. The method according to claim 3, which comprises maintaining the sintering temperature at an at least approximately constant value. 11. The method according to claim 1, which comprises heating the body to a sintering temperature in the hydrogen-containing atmosphere having an oxygen partial pressure of 10.sup.-10 to 10.sup.-20 bar. 12. The method according to claim 1, which comprises maintaining a sintering temperature in a range from 1600.degree. C. to 1800.degree. C. 13. The method according to claim 2, which comprises maintaining the sintering temperature in a range from 160020 C. to 1800.degree. C. 14. The method according to claim 3, which comprises maintaining the sintering temperature in a range from 1600.degree. C. to 1800.degree. C. 15. The method according to claim 1, which comprises maintaining a sintering temperature in a range from 1650.degree. C. to 1750.degree. C. 16. The method according to claim 2, which comprises maintaining the sintering temperature in a range from 1650.degree. C. to 1750.degree. C. 17. The method according to claim 3, which comprises maintaining the sintering temperature in a range from 1650.degree. C. to 1750.degree. C. 18. The method according to claim 1, which comprises heating the body to a sintering temperature in temperature stages. 19. The method according to claim 2, which comprises heating the body to the sintering temperature in temperature stages. 20. The method according to claim 3, which comprises heating the body to the sintering temperature in temperature stages. 21. The method according to claim 1, which comprises carrying out the sintering in a hydrogen-containing sintering atmosphere containing from 2 to 10 volume % hydrogen and at least one gas selected from the group consisting of noble gas, nitrogen, CO.sub.2, CO, O.sub.2 and water vapor. 22. The method according to claim 2, which comprises providing the hydrogen-containing sintering atmosphere with from 2 to 10 volume % hydrogen and at least one gas selected from the group consisting of noble gas, nitrogen, CO.sub.2, CO, O.sub.2 and water vapor. 23. The method according to claim 3, which comprises providing the hydrogen-containing sintering atmosphere with from 2 to 10 volume % hydrogen and at least one gas selected from the group consisting of noble gas, nitrogen, CO.sub.2, CO, O.sub.2 and water vapor. 24. The method according to claim 2, which comprises selecting the first portion of the holding time to be in a range from 10 minutes to 4 hours. 25. The method according to claim 3, which comprises selecting the first portion of the holding time to be in a range from 10 minutes to 4 hours. 26. The method according to claim 2, which comprises selecting the second portion of the holding time to be in a range from 10 minutes to 4 hours. 27. The method according to claim 3, which comprises selecting the second portion of the holding time to be in a range from 10 minutes to 4 hours. 28. The method according to claim 2, which comprises selecting the second portion of the holding time to be in a range from 2 to 3 hours. 29. The method according to claim 3, which comprises selecting the second portion of the holding time to be in a range from 2 to 3 hours.
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052710440	claims	1. A start-up process of a boiling water nuclear reactor having a pressure vessel in which a core loaded with nuclear fuel is incorporated, cooling water is retained and steam is generated, wherein said process comprises: (a) first step of controlling the pressure in the pressure vessel so as to keep the cooling water in the pressure vessel in a single-phase flow state while raising the temperature of the cooling water by heat of nuclear reaction in the core, at the time of starting-up of said rector; (b) a second step of controlling at least the pressure in the pressure vessel so as to make said cooling water in said pressure vessel transit from said single-phase flow state into a two-phase flow state after said first step; and (c) a third step of heating said cooling water in said two-phase flow state by heat of nuclear reaction in the core. said first step includes a step of isolating said pressure vessel by closing said main steam isolation valve and said feed water stop valve, a step of pressurizing the inside of said pressure vessel by said pressure regulator, and a step of heating said cooling water in said single-phase flow state by withdrawing said control rods; and said second and third steps include a step in which the pressurization by said pressure regulator is released and said main steam isolation valve and said turbine bypass stop valve are opened so that the pressure in said pressure vessel is reduced and a water level is formed in said pressure vessel. said first step further includes a step of closing said turbine steam stop valve and said turbine bypass stop valve, opening said feed water bypass stop valve and operating said feed water pump to thereby circulate feed water to said condenser, and thereafter pressurizing the inside of said pressure vessel. a pressure vessel in which a core loaded with nuclear fuel is incorporated, cooling water is retained and steam is generated; pressure regulating means disposed outside said pressure vessel and made to communicate with said pressure vessel for pressurizing the inside of said pressure vessel at the time of starting-up of said reactor; control rod drive means for moving control rods for insertion into and withdrawal from the core to control an output power of the core; and control means for actuating said pressure regulating means and said control rod drive means at the time of starting-up of said reactor in such a manner as to control the pressure in the pressure vessel so as to keep the cooling water in the pressure vessel in a single-phase flow state while raising the temperature of the cooling water by heat of nuclear reaction in the core, and then to control at least the pressure in the pressure vessel so as to make said cooling water in said pressure vessel transit from said single-phase flow state into a two-phase flow state, and thereafter to heat said cooling water in said two-phase flow state by heat of nuclear reaction in the core. 2. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in said first step said cooling water is kept in said single-phase flow state by controlling the pressure in said pressure vessel so as to make the pressure in said pressure vessel higher than the saturation pressure of said cooling water corresponding to the temperature of said cooling water in said pressure vessel. 3. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in said first step the inside of said pressure vessel is pressurized solely first and thereafter said cooling water is heated while controlling the pressure in said pressure vessel. 4. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in said first step the pressurization in the inside of said pressure vessel is started simultaneously with start of heating said cooling water so that the heating of said cooling water and the pressurization in the inside of said pressure vessel are carried out simultaneously and parallelly with each other. 5. A start-up process of a boiling water nuclear reactor according to claim 1, wherein said reactor comprises a start-up feed water line formed by bypassing a feed water line and having a start-up feed water stop valve, a cooling water outlet of said start-up feed water line being connected in a portion below said core in said pressure vessel, and wherein in at least one of said first, second and third steps, said cooling water is heated by nuclear reaction and at the same time said cooling water is forcedly circulated to said core by a feed water pump through said start-up feed water line to thereby increase the core flow rate. 6. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in said second step said cooling water is made to transit from said single-phase flow state into said two-phase flow state by controlling the pressure in said pressure vessel so as to make the pressure in said pressure vessel gradually approximate to the saturation pressure of said cooling water corresponding to the temperature of said cooling water in said pressure vessel until predetermined pressure not higher than the rated running pressure of said reactor is reached. 7. A start-up process of a boiling water nuclear reactor according to claim 6, wherein said control on the pressure in said pressure vessel is performed so that the pressure in said pressure vessel is kept to be substantially constant to thereby make the pressure in said pressure vessel gradually approximate to said saturation pressure. 8. A start-up process of a boiling water nuclear reactor according to claim 6, wherein said control on the pressure in said pressure vessel is performed so that the pressure in said pressure vessel is reduced to thereby make the pressure in said pressure vessel gradually approximate to said saturation pressure. 9. A start-up process of a boiling water nuclear reactor according to claim 6, wherein when said control on the pressure in said pressure vessel is performed, the quantity of heat for heating said cooling water is reduced. 10. A start-up process of a boiling water nuclear reactor according to claim 6, wherein when said control on the pressure in said pressure vessel is performed, heating said cooling water is once stopped. 11. A start-up process of a boiling water nuclear reactor according to claim 1, wherein said second and third steps are performed in a single step of continuously controlling the pressure in said pressure vessel so as to make the pressure in said pressure vessel reach the saturation pressure of said cooling water corresponding to the temperature of said cooling water in said pressure vessel at the rated running pressure of said reactor. 12. A start-up process of a boiling water nuclear reactor according to claim 1, wherein said second step includes a step of controlling the pressure in said pressure vessel so as to make the pressure in said pressure vessel reach the saturation pressure of said cooling water corresponding to the temperature of said cooling water in said pressure vessel at predetermined pressure not higher than the rated running pressure of said reactor, and wherein said third step includes a step of increasing the pressure in said pressure vessel by heating said cooling water. 13. A start-up process of a boiling water nuclear reactor according to claim 1, wherein said first step includes a step of calculating a first critical thermal power in said single-phase flow on the basis of respective measured values of the temperature of said cooling water, the pressure in said pressure vessel, and the flow rate of said core to thereby set amounts of withdrawal of control rods for controlling an power of said core so that the thermal power of said core becomes not larger than said first critical thermal power, and wherein said third step includes a step of calculating a second critical thermal power in said two-phase flow on the basis of respective measured values of the temperature of said cooling water, the pressure in said pressure vessel, and the flow rate of said core to thereby set the amounts of withdrawal of said control rods so that the thermal power of said core becomes not larger than said second critical thermal power. 14. A start-up process of a boiling water nuclear reactor according to claim 1, wherein said second and third steps include: a step of controlling related valves so as to keep the water level in said pressure vessel at a proper value on the basis of respective measured values of the pressure and water-temperature in said pressure vessel, the water temperature at an inlet of said core, the water level in said pressure vessel, the power of said core and the amounts of insertion of control rods; and a step of controlling respective openings of the related valves to make a flow rate of feed water proper on the basis of respective measured values of the power of said core and the subcool temperature at the inlet of said core. 15. A start-up process of a boiling water nuclear reactor according to claim 1, said reactor comprising: a main steam line for feeding steam generated in said core to a turbine; a feed water line for feeding condensate water condensed in a condenser after driving of said turbine into said pressure vessel as cooling water; a main steam isolation valve, a turbine steam stop valve for stopping a steam flow into said turbine, and a control valve for controlling a flow rate of a steam flow into said turbine which are arranged in said main steam line; a feed water pump and a feed water stop valve which are arranged in said feed water line; a turbine bypass line for connecting said main steam line to an inlet of said condenser at a portion of said main steam line between said main steam isolation valve and said turbine steam stop valve; a turbine bypass stop valve arranged in said turbine bypass line; control rods for controlling the power of said core; and a pressure regulator provided in at least one of said pressure vessel, said main steam line and said feed water line; wherein 16. A start-up process of a boiling water nuclear reactor according to claim 15, said reactor further comprising a feed water bypass line for connecting said feed water line, at a outlet side of said feed water pump, to said an inlet of said condenser, and a feed water bypass stop valve arranged in said feed water bypass line, wherein 17. A start-up process of a boiling water nuclear reactor according to claim 15, wherein said second step includes a step of inserting said control rods to reduce the power of said core after increase of the cooling water temperature, and said third step includes a step of withdrawing said control rods again to heat said cooling water in said two-phase flow state. 18. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in said first step, said cooling water is heated by nuclear reaction while keeping said cooling water in the single-phase flow state by making the pressure P1 in said pressure vessel satisfy the condition P1>P2 while keeping the condition T2<T1-Tb, where T1 represents the saturation temperature of said cooling water at the pressure P1, T2 represents the temperature of said cooling water, P2 represents the saturation pressure corresponding to the temperature T2, and Tb represents the maximum value of core inlet subcool temperature to start boiling. 19. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in said second step, said cooling water is made to transit from said single-phase flow state into said two-phase flow state by making the pressure P1 in said pressure vessel satisfy the condition P1>P2 while keeping the condition T1<T2+Ts, where T1 represents the saturation temperature of said cooling water at the pressure P1, T2 represents the temperature of said cooling water, P2 represents the saturation pressure corresponding to the temperature T2, and Ts represents the maximum value of core inlet subcool temperature in a region in which stable boiling occurs. 20. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in said second step, said cooling water is made to transit from said single-phase flow state into said two-phase flow state by making the pressure P1 in said pressure vessel satisfy the condition P1=P2 while keeping the condition T1<T2+Ts, where T1 represents the saturation temperature of said cooling water at the pressure P1, T2 represents the temperature of said cooling water, P2 represents the saturation pressure corresponding to the temperature T2, and Ts represents the maximum value of core inlet subcool temperature in a region in which stable boiling occurs. 21. A start-up process of a boiling water nuclear reactor according to claim 1, wherein said reactor comprises an electric heater provided in at least one of said pressure vessel, said main steam line and said feed water line, and wherein in at least one of said first, second and third steps, said cooling water is heated by nuclear reaction and at the same time heated by said electric heater. 22. A start-up process of a boiling water nuclear reactor according to claim 1, wherein in at least one of said first, second and third steps, said cooling water is heated by nuclear reaction and at the same time heated by heat due to rotation of a feed water pump operated. 23. A start-up process of a boiling water nuclear reactor having a pressure vessel in which a core loaded with nuclear fuel is incorporated, cooling water is retained and steam is generated, wherein the cooling water in the pressure vessel is heated by nuclear reaction in the core while the pressure in said pressure vessel is controlled so as to be made higher than the saturation pressure of the cooling water corresponding to the temperature of the cooling water in said pressure vessel, and thereafter the pressure in said pressure vessel is made substantially coincident with the saturation pressure of the cooling water corresponding to the temperature of the cooling water in said pressure vessel whereupon the cooling water is heated. 24. A boiling water nuclear reactor comprising: 25. A boiling water nuclear reactor according to claim 24, wherein said pressure regulator means includes a pressurized tank connected to a feed water line connected to said pressure vessel for pressurizing the inside the pressure vessel, a high pressure gas tank connected to the pressurized tank for supplying to the pressurized tank a gas of pressure higher than the pressure vessel at the time of initiating starting-up of the reactor, means provided between said pressurized tank and said gas tank for controlling a supply of the gas from said gas tank to said pressurized tank, and means for controlling release of the pressure in the pressure vessel. 26. A boiling water nuclear reactor according to claim 24, wherein said pressure regulator means includes a leakage test system connected to a feed water line for testing leakage of said pressure vessel and a reactor primary cooling water line. 27. A boiling water nuclear reactor according to claim 24, wherein said pressure regulator means includes a pressurized tank connected to a feed water line connected to the pressure vessel and having an electric heater disposed therein for applying to the pressure vessel a pressure higher than the pressure vessel at the time of initiating starting-up of the reactor. 28. An boiling water nuclear reactor according to claim 24, wherein said pressure regulator means includes a high pressure gas tank connected to one of said pressure vessel and main steam line connected to the pressure vessel for supplying a gas of pressure higher than the pressure vessel at the time of initiating starting-up of the reactor.
047524391	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The invention concerns gas cooled high temperature reactors having a cylindrical steel pressure vessel, heat exchanger devices, cooling gas circulation devices and circulating blowers. 2. Background of the Prior Art The state-of-the-art includes installations wherein a high temperature reactor for the nuclear generation of heat and the devices serving the utilization of the heat obtained are installed together in a pressure vessel. The heat is removed by means of a cooling gas which is being circulated with the aid of blowers in a closed loop or primary loop through the reactor core and the heat exchanger devices. For the removal of the residual heat, special devices, such as auxiliary heat exchangers and auxiliary blowers are often provided It is also possible to eliminate these special devices by means of a particular arrangement and layout of the primary loop components. Thus for example in the thorium high temperature reactor (THTR-300), the heat exchangers and the blowers together with the pipe circuits on the secondary side and their components are laid out so that the entire secondary heat is removed by means of the operating systems of the heat exchangers on the primary side The flow of the cooling gas from top to bottom through the reactor core and from bottom to top through the heat exchangers in this case is similar to that in normal operation. To assure the removal of secondary heat, however, the blowers must at all times be ready to function so that the area of the cold gas will not be endangered by the hot gas rising in free convection. In a further nuclear reactor installation with a gas cooled high temperature reactor, the so-called AVR plant, the heat exchanger is arranged above the nuclear reactor and the cooling gas flows from bottom to top both through the reactor core and through the heat exchanger. In the event of a failure of the blower located underneath the core, the residual heat is removed by natural convection to the structures surrounding the reactor core. The latter include in addition to a reflector jacket of graphite, a carbon brick enclosure surrounding the graphite jacket and providing shielding and thermal insulation. To safely contain the fission products released, the aforementioned structures are surrounded by a double, gas-tight steel pressure vessel. A layer of magnetite and limonite between the two steel pressure vessels serves as a biological shield. In the above mentioned THTR-300 the function of the biological shield is effected by the prestressed concrete pressure vessel, which houses in a centercavity, the reactor core and the heat exchangers. The prestressed concrete pressure vessel not only serves as the radiation shield, but also provides a complete, pressure resistant containment of the nuclear reactor installation. SUMMARY OF THE INVENTION The present invention is based on a nuclear reactor installation of the type described hereinabove and arranged in a steel pressure vessel. It is an object of the invention to provide such an installation that safely protects the outside and the environment against radiation and the consequences of accidents which may occur within the plant. Another object is to assure the removal of secondary heat in the event of an accident. According to the invention, the nuclear reactor installation is characterized in that the steel pressure vessel is tightly enclosed in a safety enclosure comprising two essentially cylindrical concrete shells in a spaced apart arrangement, a concrete cover monolithically joined with the outer concrete shell and a cantilever ring monolithically joined with both concrete shells and supporting the steel pressure vessel and a concrete cooling system in the innerconcrete shell. The concrete cooling system operates by natural means and comprises cooling water circulating in a closed loop and a second cooling water system to provide for the recooling of the cooling water circulating in the concrete cooling system. An adequate radiation shielding of the nuclear reactor and the components of the primary loop is obtained by means of the safety enclosure according to the invention. The enclosure also functions as a biological shield. Secondly, in the case of a possible release of radiation from the steel pressure vessel, the safety enclosure assures the safe containment of the installation against leakage from the primary loop. The safety enclosure thereby forms a containment barrier for the cooling gas in the steel pressure vessel and an additional barrier to retain fission products. (A first barrier to retain fission products is the fuel elements themselves. A nuclear reactor with spherical fuel elements contains the fissionable substance in the form of coated particles.) By means of the safety enclosure according to the invention, leakages of the primary loop may be retained until a controlled removal of the cooling gas to the environment through filters or a gas purification installation is assured. The safety enclosure further protects the nuclear reactor installation against external effects. These effects may consist, for example, of earthquakes, aircraft crashes or pressure waves in the case of explosions. At the same time, the safety enclosure serves as a supporting structure of the steel pressure vessel. The outer concrete shell has the further function of a protective reactor building, while the inner concrete shell provides protection against debris and fragments. In order to enable the safety enclosure to perform these different functions, the concrete material of the enclosure must be protected against excessive heating. For this reason, a concrete cooling system is provided within the inner concrete shell. In normal operation, the concrete cooling system removes the heat generated in the concrete by radiation. The heat loss of the steel pressure vessel is also removed by the concrete cooling system. Heat is transferred from the steel pressure vessel primarily by thermal radiation while it is removed from the concrete by direct contact. This concrete cooling system is further used according to the invention for the removal of the secondary heat. In the event of an accident, for example, the devices normally eliminating the secondary heat are rendered ineffective and the concrete cooling system provides a backup. Initially, the devices for the removal of secondary heat consist of the heat exchanger blower units with the operational secondary loop and possibly an auxiliary cooling system. Even in the case of a failure of the blowers, the removal of secondary heat on the primary side may be assured if the cooling gas pressure in the primary circuit is high enough so that natural convection is adequate and may be maintained as such. If, however, the heat sink on the primary side is eliminated, the secondary heat is conducted according to the invention by means of natural convection, conduction and radiation of the steel pressure vessel. The heat is then transferred from the steel pressure vessel essentially by radiation to the concrete cooling system located in the inner concrete shell. Even in the case of the loss of cooling gas (pressure relief incident) and the failure of all cooling in the primary loop, the secondary heat is transferred from the surface of the steel pressure vessel to the concrete cooling system. In this event, no increased release of fission products by the fuel elements is experienced. The concrete cooling system comprises preferably an elevated annular reservoir placed onto the inner concrete shell and maintained under atmospheric pressure, together with ascending pipes and downpipes. Ascending pipes are arranged on the side facing the steel pressure vessel and the downpipes are arranged on the side facing the outer concrete shell of the inner concrete shell. The recooling of the water circulating in the concrete cooling system is effected by a second cooling water system, which removes the heat generated to the elevated reservoir and then to the outside. In the event of partial or complete failure of the auxiliary cooling of the concrete cooling system, the water content of the elevated reservoir and the pipe system evaporates at a rate of approximately 2 to 3 t/h. Depending on the volume and water supply of the elevated reservoir, the removal of secondary heat may thereby be assured for several days without any active measures. The temperatures of the steel pressure vessel remain in such a hypothetical incident clearly under 400.degree. C. Preferably, a device for the continuous supply of water is provided on the elevated reservoir. By the actuation of this device either the removal of the secondary heat may be continued following the evaporation of the concrete cooling system or the concrete cooling system may be operated with a higher heat removal capacity. It is appropriate to connect the elevated reservoir with a blow-off line and to arrange a pressure relief valve in the blow-off line. As the transfer of heat from the steel pressure vessel to the ascending pipes of the concrete cooling system takes place essentially by radiation, it is advantageous to equip the ascending pipes with azimuthal fins or a finned wall. Cooling plates of a cast material maybe applied further to the ascending pipes. In order to be able to perform maintenance and repair work on the primary loop components installed within the steel pressure vessel, such as heat exchangers and circulating blowers, several large passages are provided conveniently in the safety enclosure. These passages permit the dismantling of the components. The passages are closed off by removable pressure resistant and gastight covers, placed onto the outer concrete shell or set into it. In its center area, the inner concrete shell may be equipped with a thickened part directed inwardly. This thickened part is preferably in the form of a flange upon which a supporting ring is resting. The supporting ring is mounted on the jacket of the steel pressure vessel. The supporting ring has the function of securing the steel pressure vessel in case of exposure to an earthquake. The pressure vessel is thereby supported only by the inner concrete shell. Additional support on the outer concrete shell would result in a direct impact of a crashing aircraft on the steel pressure vessel. The safety enclosure in turn may rest on concrete support rings joined monolithically with both concrete shells as well as on the cantilever ring upon which the steel pressure vessel rests. The annular space between the two concrete shells, which is accessible to a limited extent during operation, may beused advantageously as a working space.
	description	This application is a continuation-in-part application of co-pending U.S. application Ser. No. 15/563,267, filed Sep. 29, 2017, the disclosure of which is incorporated herein by reference. This application claims priority benefits under 35 U.S.C. § 1.119 to Korean Patent Application No. 10-2016-0042413, filed Apr. 6, 2016. The present invention relates to a correlation tolerance limit setting system using repetitive cross-validation and method therefor. More particularly, the present invention relates to a correlation tolerance limit setting system using repetitive cross-validation and a method therefor to prevent intentional or unintentional distortion of material properties by human intervention or otherwise and a risk caused thereby or to quantify the influence induced by the distortion of the material properties for correlation optimization and tolerance limit setting. Hitherto, according to Korean Patent Laid-Open Publication No. 2011-0052340, as a method of evaluating a trip setpoint of a reactor core state, the trip setpoint is calculated by using information on neutron flux distribution calculated in advance with respect to each of more than 600 reactor core states, information on instruments for regional overpower protection, and information on thermal-hydraulics. Upon completion of a trip setpoint calculation, by deriving an optimal correlation between information on a signal distribution of instruments for regional overpower protection and the trip setpoint, a method is provided to determine the trip setpoint corresponding to each reactor core state using only the signal distribution of instruments. In the conventional art, in a way to deal with the intolerable risk, correlation optimization is performed on the basis of data partitioning (training set versus validation set) of one round or limited number of cases, or, upon completion of related tasks of data partitioning at the level where the independent test datasets having same design or similar design characteristics are operated separately, the tolerance limit and application scope of the correlation are set individually through statistical analysis at a simple level for the separated dataset. In the limited case, correlation optimization and tolerance limit setting based on the separated dataset have problems such that a risk caused by intentional or unintentional distortion of material properties by human intervention or otherwise is unable to be prevented, and the influence of the distortion of the material properties is unable to be quantified. In addition, as an influence due to the difference of detailed design characteristics along with scope of reproducibility of test dataset is potentially involved when independent dataset having the same design or similar design characteristics is operated separately, there may be limitations in separating the intolerable risk or the influence thereof. Consequently, it inevitably increases cost for additional production of testing dataset. The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art. An object of the present invention is to solve the above problems and to provide a correlation tolerance limit setting system using repetitive cross-validation and a method therefor to perform correlation optimization and tolerance limit setting within the limit complying with technical/regulatory requirements or to verify the effectiveness thereof. Another object of the present invention is to provide a correlation tolerance limit setting system using repetitive cross-validation and a method therefor to prevent intentional or unintentional distortion of material properties by human intervention or otherwise and a risk caused thereby, or to quantify the influence induced by the distortion of the material properties. In order to achieve the above object, according to one aspect of the present invention, there is provided a correlation tolerance limit setting system using repetitive cross-validation, the system including: a variable extraction unit randomly classifying data of an initial database (DB) set into training data and validation data at a specific rate, and then matching each of the training data and the validation data with each run identifier (ID) assigned thereto and storing them in a training initial set and a validation initial set, respectively, thereby extracting variables for determining a departure from nucleate boiling ratio (DNBR) limit by optimizing coefficients of a selected correlation based on the data stored in the training initial set; a normality test unit performing a normality test for data of a training set and data of a validation set after extracting the variables; and a DNBR limit unit determining the DNBR limit by a parametric method or a nonparametric method depending on a result of the normality test. The variable extraction unit may preferably include: an initialization module classifying the data of the initial DB set into the training data and the validation data, and then matching the training data and the validation data with each run ID assigned thereto and storing them in the training initial set and the validation initial set, respectively, wherein the data for which the run ID of a full DB set and the run ID of the training initial set are the same to each other is stored in the training set, and the data for which the run ID of the full DB set and the run ID of the validation set are the same to each other is stored in the validation set; a correlation coefficient optimization module optimizing for fitting of the coefficients of the selected correlation using the data of the training initial set; an extraction module deriving the measured/predicted (M/P) for each run ID of the training set by applying optimized coefficients of the selected correlation to the data of the training set, and then extracting a maximum M/P for each run ID of the training set among the derived MP's; a location and statistics change determination module determining whether a measurement location of the core is changed or not with each run ID, having the extracted maximum M/P, of the training set or the statistics are changed or not with an average value of the derived M/P of each run ID of training initial set, wherein the optimized coefficients of the selected correlation are output when there is no change of the core measurement location, having the extracted maximum M/P, or statistics on the average value of the derived M/P's by iteratively performing optimization of the coefficients of the selected correlation until there is no change of the core measurement location, having the extracted maximum M/P, or statistics on the average value of the derived M/P's; and a variable extraction module applying the optimized coefficients of the selected correlation to each data of the validation set, and then extracting dependent variables, having the maximum M/P, of the data of the validation set as the variables for determining the DNBR limit. The normality test unit may preferably perform the normality test for an M/P of each run ID of the poolable set by the parametric method or the nonparametric method when the data of the training set and the data of the validation set have the same population by the parametric method depending on a result of the normality test for the data of the training set and the data of the validation set. In addition, the normality test unit may determine whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set, and when the data of the training set and the data of the validation set have the same population, the normality test unit performs the normality test for the M/P of each run ID of the poolable set by the parametric method or the nonparametric method; and the normality test unit determines whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set, and when the data of the training set and the data of the validation set do not have the same population, the normality test unit performs the normality test for the M/P of each run ID of the validation set by the parametric method or the nonparametric method. The DNBR limit unit may preferably include: an output module determining whether the data of the training set and the data of the validation set have a same population or not by the parametric method or the nonparametric method depending on a result of the normality test for an M/P of a run ID of the training set and an M/P of a run ID of the validation set derived for each case, and performing the normality test for an M/P of a run ID of a poolable set which is combined with the training set and the validation set or the M/P of the run ID of the validation set by the parametric method or the nonparametric method depending on the result of whether the data of the training set and the data of the validation set have the same population or not; and a limit determination module deriving a distribution of 95/95 DNBR values for all N cases after calculating the 95/95 DNBR values by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of the run ID of the poolable set or the M/P of the run ID of the validation set from the output module for each case, and determining a 95/95 DNBR limit using the derived distribution of the 95/95 DNBR values. A correlation tolerance limit setting method using repetitive cross-validation, the method may include: step a) of randomly classifying data of an initial DB set into training data and validation data at a specific rate, and then matching each of the training data and the validation data with each run ID assigned thereto and storing them in a training initial set or a validation initial set, respectively, thereby extracting variables for determining a departure from nucleate boiling ratio (DNBR) limit by optimizing coefficients of a selected correlation based on the data stored in the training initial set; step b) of performing a normality test for data of a training set and a validation set after extracting the variables; and step c) of determining the DNBR limit by a parametric method or a nonparametric method depending on a result of the normality test. The step a) may include: initialization substep a-1) of classifying the data of the initial DB set into the training data and the validation data, and then matching the training data and the validation data with each run ID assigned thereto and storing them in the training initial set and the validation initial set, respectively, wherein the data for which the run ID of a full DB set and the run ID of the training initial set are the same to each other is stored in the training set, and the data for which the run ID of the full DB set and the run ID of the validation set are the same to each other is stored in the validation set; correlation coefficient optimization substep a-2) of optimizing for fitting of the coefficients of the selected correlation using the data of the training initial set; extraction substep a-3) of deriving an M/P for each run ID of the training set by applying optimized coefficients of the selected correlation to the data of the training set, and then extracting a maximum M/P for each run ID of the training set among the derived MP's; location and statistics change determination substep a-4) of determining whether a measurement location of the core is changed or not with each run ID, having the extracted maximum M/P, of the training set or the statistics are changed or not with an average value of the derived M/P of each run ID of training initial set, wherein the optimized coefficients of the selected correlation are output when there is no change of the core measurement location, having the extracted maximum M/P, or statistics on the average value of the derived M/P's by iteratively performing optimization of the coefficients of the selected correlation until there is no change of the core measurement location, having the extracted maximum M/P, or statistics on the average value of the derived M/P's; and variable extraction substep a-5) of applying the optimized coefficients of the selected correlation to each data of the validation set, and then extracting the dependent variables, having the maximum M/P, of the data of the validation set as the variables for determining the DNBR limit. At the step b), when the data of the training set and the data of the validation set have the same population by the parametric method depending on a result of the normality test for the data of the training set and the data of the validation set, the normality test for the M/P of each run ID of the poolable set may be performed by the parametric method or the nonparametric method. In addition, at the step b), it may be determined whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set, and when the data of the training set and the data of the validation set have the same population, the normality test for the M/P of each run ID of the poolable set may be performed by the parametric method or the nonparametric method; it may be determined whether the data of the training set and the data of the validation set have the same population or not by the nonparametric method depending on the result of the normality test for the data of the training set and the data of the validation set; and when the data of the training set and the data of the validation set do not have the same population, the normality test for the M/P of each run ID of the validation set may be performed by the parametric method or the nonparametric method. In addition, the step c) may include: substep c-1) of determining whether the data of the training set and the data of the validation set have a same population or not by the parametric method or the nonparametric method depending on a result of the normality test for the M/P of a run ID of the training set and an M/P of a run ID of the validation set derived for each case, and performing the normality test for an M/P of the run ID of a poolable set which is combined with the training set and the validation set or the M/P of the run ID of the validation set by the parametric method or the nonparametric method depending on the result of whether the data of the training set and the data of the validation set have the same population or not; and substep c-2) of deriving a distribution of a 95/95 DNBR value for all N cases after calculating the 95/95 DNBR value by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of the run ID of the poolable set or the M/P of each run ID of the validation set from the output module for each case, and determining a 95/95 DNBR limit using the derived distribution of the/a 95/95 DNBR value. As described above, there is an effect of preventing intentional or unintentional distortion of material properties by human intervention or otherwise and a risk caused thereby or an effect of quantifying the influence induced by the distortion of the material properties for correlation optimization and tolerance limit setting. Specific characteristics and advantageous features of the present invention will become clearer through the description below with reference to the accompanying drawings. Prior to this, it should be noted that detailed descriptions of known functions and components incorporated herein have been omitted when it is determined that the gist of the present invention may be unnecessarily obfuscated thereby. The present invention has a number of stored correlations expressing a relationship between each dependent variable and a reactor core trip setpoint in order to derive the reactor core trip setpoint from measured values of dependent variables instrumented at a predetermined location of a reactor core. Here, the correlation is a relational expression that relates distribution information of the measured values of the instrumented dependent variables to the reactor core trip setpoint, and a technique for selecting a correlation is disclosed in detail in Korean Patent Laid-Open Publication No. 2011-0052340. Nevertheless, in the present embodiment, in order to derive a departure from nucleate boiling ratio (DNBR) limit, one of many correlations that expresses a relationship of a critical heat flux (CHF) and the measured value of each of the instrumented dependent variables is described as an example, but is not limited thereto. In the present embodiment, a measured value of each of dependent variables instrumented at a predetermined location of the reactor core and a CHF which is an independent variable derived from a selected correlation are set as one data, and then the one data is assigned with a run ID and stored in an initial DB set. That is, the run ID is assigned to each measurement location, and the measured value of each of the instrumented dependent variables and the data including the CHF which is the independent variable are stored by being matched with the assigned run ID of the initial DB Set. Meanwhile, an estimate of the CHF derived from the dependent variables and the selected correlation is derived for each node of the reactor core through a predetermined algorithm. Then, each of the dependent variables derived for each node and the data including the estimate of the CHF are stored in the full DB set by being matched with the run ID assigned to each node. Accordingly, the dependent variables and the estimate of the CHF which is the independent variable, at each node, are stored by being matched with the run ID of the full DB set assigned to each node. In addition, in the present embodiment, training data for optimizing the coefficients of the selected correlation among the data of the initial DB set is stored in the training initial set, and the validation data for verifying the optimized coefficient is stored in the validation initial set, wherein the training data and the validation data are randomly classified. For example, six numbers of the training data of ten numbers of the data stored in the initial DB set are stored in the training initial set, and remaining four numbers of the validation data are stored in the validation initial set. In addition, in the present embodiment, the training set stores the training data for which the run ID of the full DB set and the run ID of the training initial DB correspond to each other, and the validation set stores the validation data for which the run ID of the full DB set and the run ID of the classified validation initial DB correspond to each other. In addition, since the run ID of the training set in the present specification refers to the data stored by being matched with the run ID of the training set, the run ID of the training set, the data of the training set, and the data of the run ID of the training set may be mixed with each other to describe in the present specification. In addition, since the run ID of the validation set in the present specification refers to the data stored by being matched with the run ID of the validation set, the run ID of the validation set, the data of the validation set, and the data of the run ID of the validation set may be mixed with each other to describe in the present specification. In addition, in the present embodiment, the coefficients included in the correlation between the dependent variables and the CHF may be optimized for fitting through a signal distribution of the measured values of the dependent variables and a predetermined analysis algorithm. Further, the technique of optimizing the coefficients of the selected correlation may be applied to the process of obtaining the determination coefficients of the variable using general statistical analysis techniques. Therefore, the present invention is configured to perform the normality test for the M/P of a run ID of the training set including the data of the CHF derived from the correlation having the measured values of the instrumented dependent variables and the optimized coefficients and for the M/P of a run ID of the validation set, and to derive the DNBR limit by a predetermined parametric method or a nonparametric method depending on the result of the normality test. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating a correlation tolerance limit setting system using repetitive cross-validation according to an embodiment of the present invention, FIG. 2 is a diagram illustrating a process of variable extraction of a correlation tolerance limit setting system using repetitive cross-validation according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a process of a normality test and a DNBR limit determination of a correlation tolerance limit setting system using repetitive cross-validation according to an embodiment of the present invention. As illustrated in FIG. 1, the correlation tolerance limit setting system using repetitive cross-validation according to the embodiment of the present invention includes a variable extraction unit 100, a normality test unit 200, a DNBR limit unit 300, and a controller 400. First, the variable extraction unit 100 randomly classifies the data of the initial DB set into the training data and the validation data at a specific rate, and then stores the training data and the validation data in the training initial set and the validation initial set, respectively. In this case, the data, for which the run ID of the training initial set and the run ID of the full DB set correspond to each other, of the training initial set is stored in the training set, and the data, for which the run ID of the validation set and the run ID of the full DB set correspond to each other, of the validation initial set is stored in the validation set. In addition, the variable extraction unit 100 may optimize the coefficients of the selected correlation using the data of the training initial set; derive the maximum M/P of each run ID of the validation set by applying the optimized coefficients to the data of each run ID of the validation set; and extract dependent variables, having the derived maximum M/P of the run ID, of the validation set as variables for deriving a DNBR limit. Here, a series of processes for extracting the variables for deriving the DNBR limit is iterated N times (N cases), wherein the N is a number determined arbitrarily. The variable extraction unit 100 for performing a function of extracting variables for deriving the DNBR limit value includes an initialization module 110, a correlation coefficient optimization module 120, an extraction module 130, a location and statistics change determination module 140, and a variable extraction module 150. Here, the initialization module 110 randomly classifies the data of the initial DB set into the training data and the validation data; matching each of the training data and the validation data with each run ID assigned to each measurement location, in a training initial set and a validation initial set and storing them, respectively; and generates the training set and the validation set with the training data and the validation data, respectively, wherein the run ID of the training initial set and the run ID of the full DB set correspond to each other for the training data, and the run ID of the validation initial set and the run ID of the full DB set correspond to each other for the validation data. Meanwhile, the correlation coefficient optimization module 120 performs a function of optimizing the coefficients of the selected correlation based on the data of the training initial set classified in the initialization module 110. Next, the extraction module 130 derives a measured value of the CHF, which is the independent variable, by applying the correlation to which the optimized coefficients are applied to the data of each run ID of the training set and extracts the run ID, having the maximum M/P, of the training set after deriving a ratio of the derived measured value M of the CHF to the estimate P of the CHF for each node of the full DB set for each run ID. In this case, since a series of processes of extracting the run ID, having the maximum M/P, of the training set is proceeded iteratively for each node of the full DB set, the measurement location of the core for the run ID having the maximum M/P and the statistics on the M/P may be changed every time a series of processes of extracting the run ID, having the maximum M/P, of the training set is iterated. Here, the statistics are the average value of the M/P's each derived for a run ID. Next, the location and statistics change determination module 140 determines whether the measurement location of the core is changed or not or the statistics on the average value of the M/P's is changed or not with the run ID, having the extracted maximum M/P, of the training set, and when the measurement location of the core changes, performs iteratively a series of processes of optimizing the coefficients of the selected correlation until there is no change of the core measurement location. At this time, the coefficient of the selected correlation is optimized with the data of the training initial set. In addition, the location and statistics change determination module 140, when the statistics on the average value of the M/P's changes, performs iteratively a series of processes of optimizing for fitting of the coefficients of the selected correlation until there is no statistical change with respect to the derived average value of the derived M/P's. In addition, when there is no change in the measurement location of the core having the maximum M/P and the statistics on the average value of the M/P's in the location and statistics change determination module 140, the optimized coefficients are transmitted to the extraction module 150. The variable extraction module 150 derives the measured value of the CHF by applying the optimized coefficients to the data of each run ID of the validation set, derives a ratio M/P of the derived measured value of the CHF to the estimate of the CHF for each node of the full DB set, and extracts the dependent variables, having the maximum M/P, of the data of the validation set as the variables for deriving the DNBR limit. In this case, since the inverse of the maximum M/P is the DNBR limit, the maximum M/P is applied to obtain the minimum DNBR limit in an embodiment of the present invention. The process of extracting the variables is performed by iterating an arbitrarily predetermined number of times (N times, N cases) in the variable extraction unit 100, then the normality test is performed for the data of the training set and the data of the validation set for each case in the normality test unit 200, and the DNBR limit is derived either by a parametric method or a nonparametric method depending on the result of the normality test. Here, the ‘N’ may be arbitrarily set to 5, 10, 20, 100, 200, 500, 1000, 5000 or greater, and even about 1000 times in the exemplary embodiment of the present invention would be appropriate. FIG. 5 shows views illustrating conceptual results of a correlation tolerance limit setting system using repetitive cross-validation according to another embodiment of the present invention. Conceptual results in an exemplary embodiment are shown in Table 1 and FIG. 5 below. TABLE 1IndividualtoleranceDatasetNo. ofdistributionclassificationcaseAverageS.D.RemarkPoolabilityPoolable (T + V)9411.11610.0017Non-poolable (V)591.13750.0220Combined(T + V) and (V)10001.11730.00751.1234(39thvalue)In the Table 1 above, indicates nonparametric fractile. The normality test unit 200 extracts variables for determining the DNBR limit and then performs the normality test for the data of the training set of the extraction module 130 and the data of the validation set of the variable extraction module 150. Here, the normality test unit 200 performs the normality test for each case and iteratively performs up to a predetermined number of N times (N cases). In addition, when the result of the normality test for the data of the training set and the data of the validation set is a normal distribution, the normality test unit 200 determines whether the data of the training set and the data of the validation set have a same population or not by the parametric method. Here, the parametric method is a conventional art widely known as a statistical analysis technique for estimating a specific value of an unknown population parameter on an assumption that data (population parameter) is a normal distribution. In this case, when the data of the training set and the data of the validation set have the same population by the parametric method, the normality test unit 200 performs the normality test for the data of the poolable set, wherein the data of the poolable set is formed by combining the data of the data of the training set and the data of the validation set. On the other hand, when the result of the normality test for the data of the training set and the data of the validation set is not a normal distribution, the normality test unit 200 determines whether the data of the training set and the data of the validation set have a same population or not by the nonparametric method. Here, the nonparametric method is a conventional art widely known as a statistical analysis technique for estimating a specific value of an unknown population parameter on an assumption that data (population parameter) is not a normal distribution. In addition, when the result of the normality test for the data of the training set and the data of the validation set is not a normal distribution, and the data of the training set and the data of the validation set have a same population by the nonparametric method, the normality test unit 200 performs the normality test for the M/P of each run ID of the poolable set. In addition, when the result of the normality test for the data of the training set and the data of the validation set is not a normal distribution, and the data of the training set and the data of the validation set do not have a same population by the nonparametric method, the normality test unit 200 performs the normality test for the M/P of each run ID of the validation set. Meanwhile, when the data of the training set and the data of the validation set have the same population by the parametric method or the nonparametric method, the DNBR limit unit 300 may generate a DNBR value for the M/P of each run ID of the poolable set by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of each run ID of the poolable set; output a distribution of the 95/95 DNBR value generated for each case; perform the normality test for the distribution of the 95/95 DNBR value output above; and determine the 95/95 DNBR limit by the parametric method or the nonparametric method depending on the result of the normality test. In addition, when the data of the training set and the data of the validation set do not have the same population by the parametric method, the DNBR limit unit 300 may generate a DNBR value for the M/P of each run ID of the validation set by the parametric method; output a distribution of the 95/95 DNBR value generated for N cases; perform the normality test for the distribution of the 95/95 DNBR value output above; and determine the 95/95 DNBR limit by the parametric method or the nonparametric method depending on the result of the normality test. In addition, when the data of the training set and the data of the validation set have the same population by the nonparametric method, the DNBR limit unit 300 may generate a DNBR value for the M/P of each run ID of the poolable set by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of each run ID of the poolable set; output a distribution of the 95/95 DNBR value generated for each case; perform the normality test for the distribution of the 95/95 DNBR value output above; and determine the 95/95 DNBR limit by the parametric method or the nonparametric method depending on the result of the normality test. Meanwhile, when the data of the training set and the data of the validation set do not have the same population by the nonparametric method, the DNBR limit unit 300 may generate a DNBR value for the M/P of each run ID of the validation set by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of each run ID of the validation set; output a distribution of the 95/95 DNBR value generated for all N cases; perform the normality test for the distribution of the 95/95 DNBR value output above; and determine the 95/95 DNBR limit by the parametric method or nonparametric method depending on the result of the normality test for the distribution of the 95/95 DNBR value. The DNBR limit unit 300 like this may determine the tolerance limit from the distribution of the 95/95 DNBR value with 95/95 criteria (95% confidence and 95% probability); and prevent a distortion of data characteristics and a risk caused thereby and also quantify an influence of a distortion of data characteristics and a risk caused thereby. Here, since the tolerance limit is determined by estimating and evaluating the statistics on the population of the sample of the M/P, the tolerance limit in the embodiment of the present invention is the DNBR limit determined from the distribution of the 95/95 DNBR value. The DNBR limit unit 300 for performing this function includes an output module 310 and a limit determination module 320. The output module 310 determines whether the data of the training set and the data of the validation set have the same population or not by the parametric method or the nonparametric method for each case, and when the data of the training set and the data of the validation set have the same population, performs the normality test for the M/P of each run ID of the poolable set. In addition, the limit determination module 320 generates the 95/95 DNBR value by the parametric method depending on the result of the normality test for the M/P of each run ID of the poolable set of the output module 310. In addition, the limit determination module 320 generates a 95/95 DNBR value by the nonparametric method depending on the result of the normality test for the M/P of each run ID of the poolable set of the output module 310. The limit determination module 320 generates a distribution of a 95/95 DNBR value for all N cases. In addition, the limit determination module 320 is configured to determine a 95/95 DNBR limit by the parametric method or a 95/95 DNBR limit by the nonparametric method for a distribution of the 95/95 DNBR value for all N cases. In addition, when the data of the training set and the data of the validation set do not have the same population by the parametric method for each case of the output module 310, the limit determination module 320 generates a 95/95 DNBR value for the M/P of each run ID of the validation set by the parametric method; and generates a distribution of the 95/95 DNBR value for all N Cases. In addition, when the data of the training set and the data of the validation set do not have the same population by the parametric method for each case of the output module 310, the limit determination module 320 performs the normality test for the M/P of each run ID of the validation set; generates a 95/95 DNBR value for the M/P of each run ID of the validation set by the nonparametric method or the parametric method depending on the result of the normality test; and generates a distribution of the 95/95 DNBR value for all N Cases. The limit decision module 320 determines a 95/95 DNBR limit by the parametric method or determines a 95/95 DNBR limit by the nonparametric method for the distribution of the 95/95 DNBR values for all N cases. For reference, the DNBR is a quantitative reference value that assesses whether a CHF occurs or not on the surface of a nuclear fuel rod as a variable for deriving the allowable limit (DNBR limit) for controlling the reactor core from the CHF derived from the selected correlation, and is determined by statistically assessing the prediction uncertainty of the correlation of the CHF. According to the thermal design criteria for a reactor core, the DNBR limit should be so set that the probability that the CHF will not occur should be 95% or greater at the confidence level of 95% or greater. In addition, the DNBR is defined as the ratio of the CHF prediction (=P) to the actual local thermal flux (=A). That is DNBR=P/A. In an experimental condition for the CHF, as the actual local thermal flux is identical to the CHF measurement (=M), the DNBR has the same meaning as P/M. In addition, the CHF estimate P predicted by the selected correlation at a given local hydrothermal condition is always calculated as a constant value, but the actual measured CHF measurement value M may have some arbitrary value due to the randomness of the physical phenomena. From this point of view, a random variable for statistical evaluation of the DNBR is selected as M/P. To meet the design criteria for the CHF, an actual local heat flux in an arbitrary operating condition should be smaller than the measured critical thermal flux. That is, A<M, and here, provided the uncertainty of M is taken into consideration, the above condition is expressed as follows according to the 95/95 design criteria,A<M(95/95 lower limit). By applying DNBR=P/A, with both sides divided by P, it becomes,DNBR>1/(M/P)95/95 lower limit. From this, a DNBR limit is defined as,DNBR limit=1/(M/P)95/95 lower limit. FIG. 6 is a conceptual diagram of a probability distribution and tolerance limit of a correlation M/P, and the tolerance limit set by estimating and assessing the population statistics on the (M/P)95/95 lower limit is determined as described below, and the DNBR limit which is the tolerance limit is determined as the (M/P)95/95 lower limit. The controller 400 is configured to control the variable extraction unit 100, the normality test unit 200, and the DNBR limit unit 300. A method using, by the controller, the correlation tolerance limit setting system using repetitive cross-validation according to an embodiment of the present invention is described as follows. FIG. 4 is a flowchart illustrating the method using the correlation tolerance limit setting system using repetitive cross-validation according to an embodiment of the present invention. First, at step a), the controller classifies the data of the initial DB set into the training data and the validation data, and then matching each of the training data and the validation data with each run ID assigned to each measurement location, in a training initial set and a validation initial set and storing them, respectively; optimizes the coefficients of the selected correlation with the data of the training initial set and then derives the maximum M/P of the validation set by applying the optimized coefficients to each run ID of the validation set; and allows the derived dependent variables, having the derived maximum M/P, of the validation set to be extracted as variables for determining the DNBR limit. Next, at step b), the controller performs the normality test for the M/P of each run ID of the training set and the M/P of each run ID of the validation set. Subsequently, at step c), the controller determines the DNBR limit by the parametric method or the nonparametric method depending on the result of the normality test at the step b). At the step a), the correlation optimization and the variable extraction processes are performed as follows. {circle around (1)} First, the data of the initial DB set is randomly classified (data partitioning) into the training data and the validation data, and then the training initial set and the validation initial set are set, respectively. {circle around (2)} Next, the coefficients of the selected correlation are optimized with the data of the training initial set until there is no change of the measurement location of the reactor core having the maximum M/P of each run ID of the training set or the statistics on the average value of the M/P's of each run ID of the training set. {circle around (3)} Next, the M/P of each run ID of the validation set is calculated, and then the dependent variables, having the maximum M/P, of each run ID of the validation set are extracted as the variables for determining the DNBR limit. {circle around (4)} Next, the derived M/P is stored by being matched with the run ID of the training set and the run ID of the validation set. {circle around (5)} Next, the processes of {circle around (0)} to {circle around (4)} are iterated N times (N cases). Specifically, the variable extraction processes at the step a) are as follows. At initialization substep a-1), the data of the initial DB set is randomly classified into the training data and the validation data; then, the classified training data and validation data are assigned with run ID and stored in the training initial set and the validation initial set, respectively; and subsequently, the training set is set with the data for which the run ID of the full DB set and the run ID of the training initial DB set are the same to each other; and the validation set is set with the data for which the run ID of the full DB set and the run ID of the validation initial DB set are the same to each other. Thereafter, at correlation coefficient optimization substep a-2), the coefficients of the selected correlation are optimized for fitting with the data of the training initial set. Next, at extraction substep a-3), the optimized coefficients of the correlation are applied to the data of each run ID of the training set, whereby the run ID, having the maximum M/P, of the training set is allowed to be extracted. Subsequently, at location and statistics change determination substep a-4), whether the measurement location and the statistics which are the average value of the M/P's are changed or not is determined by the run ID, having the extracted maximum M/P, of the training set, wherein the processes of optimizing the coefficients of the selected correlation are iterated until there is no change of measurement location or the statistics on the maximum M/P. In addition, next, at variable extraction substep a-5), when there is no change of the measurement location of the reactor core having the extracted maximum M/P or statistics on the average value of M/P's, the optimized coefficients of the correlation are applied to the data of each run ID of the validation set, whereby the dependent variables, having the maximum M/P, of the data of the validation set are extracted as variables for determining the DNBR limit. The above-described series of processes for extracting the variables is iteratively performed N times, wherein the N is a number determined arbitrarily. At the step b), normality tests depending on extraction results of the variables are performed as follows. {circle around (6)} Next, the normality test for the M/P of each run ID of the training set and the M/P of each run ID of the validation set is performed for each case. {circle around (7)} Next, whether the data of the training set and the data of the validation set have the same population or not is determined by the parametric method or the nonparametric method depending on the results of the normality test for the M/P of each run ID of the training set and the M/P of each run ID of the validation set for each case. Subsequently, when the data of the training set and the data of the validation set have the same population, the normality test is performed for the M/P of each run ID of the poolable set which is combined with the training set and the validation set, and when the data of the training set and the data of the validation set do not have the same population, the normality test is performed for the M/P of each run ID of the validation set. {circle around (8)} In calculating the 95/95 DNBR value for each case, when the data of the training set and the data of the validation set have the same population, the 95/95 DNBR value is determined with the M/P of each run ID of the poolable set. That is, the 95/95 DNBR value is calculated by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of each run ID of the poolable set. When the data of the training set and the data of the validation set do not have the same population, the 95/95 DNBR value is calculated by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of each run ID of the validation set. {circle around (9)} The distribution of the 95/95 DNBR value calculated for all cases based on the result of ‘{circle around (8)}’ is generated for the training set, validation set, poolable set (training set+validation set), non-poolable set (validation set), and combined set (poolable set+non-poolable set). {circle around (10)} Then, the normality test is performed for the distribution of 95/95 DNBR value of ‘{circle around (9)}’. At the step b), the normality test is performed for the data of the training set and the data of the validation set for each case, whether the data of the training set and the data of the validation set have the same population or not is determined by the parametric method or the nonparametric method, the normality test is performed for the M/P of each run ID of the poolable set and the M/P of each run ID of the validation set, respectively, depending on the determination result of whether the data of the training set and the data of the validation set have the same population or not. At the step c), {circle around (11)} when the result of the normality test for each of the M/P of each run ID of the poolable set and the M/P of each run ID of the validation set is a normal distribution at ‘{circle around (10)}’, the 95/95 DNBR limit is determined by the parametric method, and when the result of the normality test for each of the M/P of each run ID of the poolable set and the M/P of each run ID of the validation set is not a normal distribution at ‘{circle around (10)}’, the 95/95 DNBR limit is determined by the nonparametric method. {circle around (12)} In determining the 95/95 DNBR limit, the 95/95 DNBR limit for the data of the ‘combined set’ is determined to be 1.1234→1.124 in one embodiment, and the average of the distribution of the data of the ‘validation set’ is determined as 1.1337→1.134 in another embodiment. In addition, the step c) includes substep c-1) outputting the distribution of the 95/95 DNBR value based on the 95/95 DNBR value determined for each case depending on the result of the normality test for the M/P of each run ID of the poolable set and the result of the normality test for the M/P of each run ID of the validation set by the parametric method and the nonparametric method; and substep c-2) determining the 95/95 DNBR limit by the parametric method or determining the 95/95 DNBR limit by the nonparametric method depending on the result of the normality test for the distribution of the 95/95 DNBR value. In an embodiment of the present invention, the data partitioning should be a random classification base for each case, but may be allowed to include k-folds. A k-folds technique implements data partitioning into k subgroups being not to overlap each other and iterates k times by setting k-1 subgroups as the training set and one subgroup as the validation set. The normality test in an embodiment of the present invention may be able to perform the tolerance limit setting and verification thereof for the distribution of the 95/95 DNBR value by using not only the M/P but also the M/P-1, M-P, or P/M, P/M-1, P-M, and the like of each run ID of each of the training set, validation set, poolable set, non-poolable set, and combined (poolable+non-poolable) set. In another embodiment, as an extension of the exemplary embodiment provided, ‘generation of the distribution of the 95/95 DNBR value determined for each case’ may be possibly implemented in a form of iterative operation until the case N is reached. In addition, in each case, the configuration and analysis of an embodiment of the present invention may be possibly implemented for ‘the distribution of the 95/95 DNBR value’ by combining the case of same population and the case of not the same population with respect to the data of the training data set and the data of the validation data set. TABLE 2TolerancelimitNo. ofdistributionGroupcaseAverageS.D.RemarkAllTraining10001.11680.0027Validation10001.13370.01511.134 An effect by an operation of the correlation tolerance limit setting system using repetitive cross-validation according to the present invention is in reduction of the tolerance limit by maximum 2.5% compared with existing one, and the reduction of the tolerance limit is possibly to be utilized for the increase of safety margin or enhancement of actual performance. Compared with domestic technology level, the effect is the improvement by maximum 5%. TABLE 3PresentedExpectedtolerancetoleranceCaselimitRisk/EffectlimitExisting/Similar technology1.113Max.1.18not implemented (domestic level)Existing/Similar technology1.08-1.18Case-by-1.15implemented (overseas level)caseInventionTypical—~1%1.124technologyembodiment (95/95DNBR valuedistributioncriteria withrespect tocombined data)Other—~2%1.134embodiment (95/95DNBR valuedistributioncriteria withrespect tovalidation data)* Compared with domestic technology level FIG. 7 is a graph illustrating the distribution of averages of a variable extracted through the variable extraction unit of the correlation tolerance limit setting system using repetitive cross-validation according to an embodiment of the present invention. FIG. 7 is a graph illustrating the average of the variables (M/P's) extracted from the data of the training set and the data of the validation set for each case by the correlation tolerance limit setting system illustrated in FIGS. 2 to 4 for each training set, validation set, poolable set, and non-poolable set. The correlation tolerance limit setting system using repetitive cross-validation according to an embodiment of the present invention may confirm whether the extracted M/P of each run ID of the training set and the extracted M/P of each run ID of the validation set for each case have a same population or not by the parametric method or the nonparametric method, and when the population is confirmed to be same, may derive the 95/95 DNBR values by the parametric method or the nonparametric method. In other words, the 95/95 DNBR values for the case of the same population or for the case of not the same population are generated by the parametric method or the nonparametric method, and the 95/95 DNBR limit may be determined by the parametric method or the nonparametric method depending on the result of the normality test for the generated 95/95 DNBR values. A correlation tolerance limit setting method using repetitive cross-validation according to another embodiment of the present invention is as follows. {circle around (1)} First, the data of the initial DB set is randomly classified (data partitioning) into the training data and the validation data, and then the training initial set and the validation initial set are set, respectively. {circle around (2)} Next, in optimizing the coefficients of the selected correlation with the data of the training initial set, the coefficients of the selected correlation are optimized until there is no change of the measurement location of the reactor core having the derived maximum M/P of each run ID of the training set or the statistics on the average value of the M/P's of each run ID of the training set. {circle around (3)} Next, the M/P of each run ID of the validation set is calculated by applying the optimized coefficients to the validation set, and then the dependent variables, having the maximum M/P, of the data of the validation set are extracted as the variables for determining the DNBR limit. {circle around (4)} Then, each of the derived M/P of the training set and the derived M/P of the validation set is stored for each run ID assigned thereto. {circle around (5)} Next, the processes {circle around (1)} to {circle around (4)} are iterated N times (N cases). {circle around (6)} Next, the normality test for the M/P of each run ID of the training set and the M/P of each run ID of the validation set is performed for each case. {circle around (7)} Next, whether the data of the training set and the data of the validation set have the same population or not is determined by the parametric method or the nonparametric method depending on the results of the normality test for the M/P of each run ID of the training set and the M/P of each run ID of the validation set for each case. Subsequently, when the data of the training set and the data of the validation set have the same population, the normality test is performed for the M/P of each run ID of the poolable set which is combined with the training set and the validation set, and when the data of the training set and the data of the validation set do not have the same population, the normality test is performed for the M/P of each run ID of the validation set. {circle around (8)} In calculating the 95/95 DNBR value for each case, when the data of the training set and the data of the validation set have the same population, the 95/95 DNBR value is determined with the M/P of each run ID of the poolable set. That is, the 95/95 DNBR value is calculated by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of each run ID of the poolable set. When the data of the training set and the data of the validation set do not have the same population, the 95/95 DNBR value is calculated by the parametric method or the nonparametric method depending on the result of the normality test for the M/P of each run ID of the validation set. {circle around (9)} The distribution of the 95/95 DNBR value calculated for all cases based on the result of ‘{circle around (8)}’ is generated for the training set, validation set, poolable set (training set+validation set), non-poolable set (validation set), and combined set (poolable set+non-poolable set). {circle around (10)} Then the normality test is performed for the distribution of 95/95 DNBR value of ‘{circle around (9)}’. {circle around (11)} When the result of the normality test for each of the M/P of each run ID of the poolable set and the M/P of each run ID of the validation set is a normal distribution at ‘{circle around (10)}’, the 95/95 DNBR limit is determined by the parametric method, and when the result of the normality test for each of the M/P of each run ID of the poolable set and the M/P of each run ID of the validation set is not a normal distribution at ‘{circle around (10)}’, the 95/95 DNBR limit is determined by the nonparametric method. {circle around (12)} In determining the 95/95 DNBR limit, the 95/95 DNBR limit for the data of the ‘combined set’ is determined to be 1.1234→1.124 in one embodiment, and the average distribution of the data of the ‘validation set’ is determined as 1.1337 →1.134 in another embodiment. 100: Variable extraction unit, 110: Initialization module. 120: Correlation coefficient optimization module. 130: Extraction module. 140: Location and statistics change determination module. 150: Variable extraction module. 200: Normality test unit, 300: DNBR limit unit. 310: Output module. 320: Limit determination module.
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054835623	summary	TECHNICAL FIELD The present invention relates to a device, during work with contaminated parts, to prevent or limit contamination of a surrounding liquid medium, especially suitable for machining, such as repair or scrapping, of radioactive components from a nuclear reactor. BACKGROUND ART, PROBLEMS In nuclear reactors it has hitherto been common to store scrap and rejected parts in their present condition in the reactor pool associated with the reactor. The space in many reactor pools has therefore been reduced and compaction has begun to be applied. It has also been normal practice to carry out repairs direct in the fuel or reactor pool, which has resulted in the water therein being contaminated. Consequently, after completed work, cleaning of large volumes of water and large areas is required. Swedish patent publication 465 236 discloses a processing vessel for scrapping rejected parts. The vessel is composed of a bottom end plate and a casing which can be mounted on the bottom end plate and consists of one or more detachably connected shell sections, arranged one after the other. Outside the processing vessel there is arranged a sealable shipping container for decomposed scrap. This container is detachably joined to the processing vessel and is arranged to communicate with the interior of the vessel via a sealable sluice opening. The shipping container is connectible to a cleaning plant for cleaning of a medium located in the shipping container. The disadvantage of this device is that a transport flask, in which the scrap is to be stored, is arranged outside the processing vessel whereby the scrap must be moved out to this flask, and this movement out takes place by means of the shipping container. Further, the processing vessel, which is usually made of stainless steel, is large, heavy and,unwieldy, which is annoying particularly during transport and storage. The processing vessel is also difficult to clean since gaps and pockets are formed between the shell sections and since metal chips of the same material as the processing vessel will easily adhere to the surfaces thereof. The processing vessel is also expensive to manufacture. SUMMARY OF THE INVENTION, ADVANTAGES According to the present invention, contamination of the surrounding environment is prevented by the use of a volume delimitation tank. The tank is arranged, for example in the fuel or reactor pool of a nuclear reactor, such that the water in the tank has a sealed or at least limited connection with the surrounding pool water during the machining phase. The volume delimitation tank comprises a sack or channel which constitutes at least the substantially vertical walls of the tank and is made of a material which is foldable, radiation-resistant and resistant to puncture due to sharp objects. The material should produce little waste during scrapping and combustion. The material consists, for example, of a fabric, or a cloth or a plate, of strong plastic fibres which are organic or synthetic and have a high strength, for example polyethylene, where the fibres have a high molecular weight and a high degree of order. An example of such a material is the fibre called Dyneema, marketed by DSM High Performance Fibers B.V. and by Nippon Dyneema Ltd. Another example is the fibre called Spectra, marketed by Allied Signals. The material stated is, in the fabric and cloth design, permeable to water to a limited extent and can be used as such or be made Watertight by lamination, either in conventional manner or by means of calandering. To increase the strength of the cloth or the fabric, several layers can be laminated, thus obtaining a more or less stiff plate. In addition to the sack or channel, the volume delimitation tank comprises a bottom part and support rods intended to support the sack or channel. The bottom part and the support rods can be made of the same material as the sack or the channel. The bottom part can either be made weak, that is, be made with only one layer of cloth or fabric, or be made stiff as the support rods, or of aluminum or of stainless steel. When using a sack, the bottom part can be integral with the sack or be arranged as a loose part therein. When using a channel, the lower part thereof is attached to the bottom part. When mounting the tank, support rods are arranged at at least the vertical walls of the tank such that these are distended, whereafter the tank is lowered into the pool and filled with water therefrom. When using a tank with walls of cloth or fabric, sinkers can be used which are arranged at, for example, the bottom part. The vertical walls of the tank are then folded out and the tank is arranged at the pool's edge. The tank is attached, for example, to a substantilly horizontal beam structure arranged at the pool edge with beams projecting over the pool. It is also possible to allow the tank to stand on the bottom of the pool. Depending on the machining that is to be carried out, a suitable frame structure may possibly be lowered down into the tank. The bottom part may possibly be arranged in this frame structure. The frame structure may be provided with a platform for tools and positions for the objects that are to be machined. Disintegration of scrap and repair of objects, respectively, take place with the aid of remotely operated members which are operated from a work platform arranged on top of the pool. During scrapping, some type of cutting device is used, for example, whereafter the separated pieces of scrap are brought, by means of the same or some other remotely operated member, to a scrap stand arranged in the tank. The water in and outside the tank constitutes a radiation shield. During such chip-forming machining where the particles are difficult to remove by means of conventional cleaning, that is, by flushing and slurry exhaustion, an inner sack is arranged in the tank. The inner sack is made of a water-transmitting material which suitably is inflammable. The inner sack is, for example, of the same material as that of which at least the vertical walls of the tank are made. The inner sack is attached to the tank wall and the bottom part, by, for example, lines and loops, before the tank is lowered down into the pool. When dismantling, the inner sack is raised at such a speed that the water has time to pass out through the limiting surfaces of the sack. To accelerate the emptying, a pump can be arranged to pump out the water from the inner sack via the cleaning plant. Thereafter, the inner sack is burnt and the ashes passed to ultimate storage. The tank can be connected to a cleaning plant for continuous cleaning of a medium located in the tank. After completed work, the entire enclosed volume of water is cleaned. When cutting methods have been used, the bottom part is slurry-exhausted to capture chips or the like. Objects which are lifted out of the tank are possibly flushed clean. Thereafter, the tank can be opened wholly or partially to insert new objects which are to be machined. This opening of the tank can take place in several ways (see the embodiments below). The tank may possibly be provided with a sluice so that it can be used repeatedly without the entire enclosed water volume having to be cleaned (see the embodiments below). When the tank is not used, it is dismantled and stored at some other location. All loose parts, such as tools, are flushed clean and raised from the tank whereupon the frame is raised, flushed clean and dismantled. Also the tank walls and the supports are flushed as they are raised and dismantled. Where necessary, the bottom part is slurry-exhausted. Any final cleaning is carried out in the reactor hall belonging to the pool, whereupon the parts are packed for storage or transport. The invention offers many advantages. The foldable and light material in at least the walls of the tank contributes to a small space requirement and to a considerable simplification of transport, installation and storage. Since the tank is relatively inexpensive to manufacture in combination with its small space requirement when not being used, it is possible to use several tanks of different sizes and shapes in parallel. In this way a volume, which is suitable in relation to the size and shape of the object in question, can be simply delimited, which permits repair and scrapping of contaminated parts to be made in a not unnecessarily small/large delimited volume. The volume delimitation tank made of a plastic material permits a construction without gaps and pockets, which makes it easy to clean. Further, it is an advantage to have a tank of plastic material since the chips are hydrophilic whereas the tank is hydrophobic, which prevents the scrap particles from adhering to the tank and further facilitates cleaning. It is also an advantage that the tank can be made so large that the scrap container can be arranged inside the tank, thus avoiding sluices for sluicing out scrap parts. The tank can be made wholly of plastic. After scrapping and combustion, the tank produces little waste. In comparison with other materials, a fabric, a cloth or a plate of a suitable fibre is strong and is not essentially damaged by falling objects or by abrasion. The friction between the fibres is low, which permits the fabric to be folded in a simple manner. The light material in the tank means that the tank has a low weight, which in turn entails a considerable simplification of suspension devices and lifting tools for the tank.
046655417	summary	DESCRIPTION The present invention relates to x-ray lithography, and particularly to submicron x-ray lithography using an ultraviolet, laser produced plasma as a source of x-rays. The present invention is especially suitable for use in producing high-resolution, submicron patterns in resist material for use in constructing integrated circuits. The invention also has application wherever high resolution, submicron patterns are needed, which photolithography is incapable of producing. X-ray lithography has been proposed wherein the x-rays are generated by the interaction of an electron beam and a metal target (see U.S. Pat. No. 3,743,842, issued July 3, 1973). The production of pulses of x-rays for lithography using a laser produced plasma has also been suggested (see U.S. Pat. No. 4,184,078, issued Jan. 15, 1980). Relatively long exposures of the x-ray sensitive material (e.g., x-ray resist) have, however, been required. For example, the system proposed in U.S. Pat. No. 4,184,078 requires the use of 90 laser shots to obtain sufficient absorbed x-ray energy to obtain an acceptable pattern after exposure and developing (see D. J. Nagel, et al., Electronic Letters, 14, 24, p. 781 (1978)). The minimum exposure which has been reported is a multi-nanosecond laser shot (a ten nanosecond pulse followed by a one nanosecond pulse) (see P. J. Mallozzi, et al., in Advances in X-ray Analysis (Plenum Press, New York, 1979)). It has been found, in accordance with the invention that high resolution, submicron x-ray lithography can be carried out using an ultraviolet-laser produced plasma as a source of x-ray pulses. Only a single shot of about one nanosecond (ns) duration of UV laser energy is necessary to produce x-ray flux sufficient for exposure of conventional x-ray resist material. The exposure with the x-ray flux has been carried out with the aid of a shield which blocks the high temperature plasma in the form of debris from the target on which the UV laser pulse is incident. The shield is in thermally coupled relationship with the resist and causes the resist to be heated upon exposure by the x-ray flux. While shields have been used, they have not been used to heat the resist (see U.S. Pat. No. 4,184,078 and the Electronic Letters article, referenced above). The x-ray flux which is incident upon the resist is about an order of magnitude smaller than what has heretofore been required in order to obtain comparable exposures with x-rays from a laser produced plasma. While the invention is not limited to any theory of operation, the increased efficiency of transfer of x-ray energy to the resist enabling the reduction in the required x-ray flux may be due to an abrupt rise in the resist temperature contemporaneous with or after exposure and prior to the development of the resist to produce the pattern. It is therefore a feature of the present invention to provide an improved method and apparatus for x-ray lithography wherein high resolution submicron patterns may be produced with a minimum of exposure by x-ray energy. It is another feature of the invention to provide an improved method and apparatus for submicron, high resolution x-ray lithography through the use of conventional x-ray resists and conventional methods of developing such resists after exposure wherein the amount of x-ray energy which is generated is minimized. It is a still further feature of the invention to provide an improved method of and apparatus for x-ray lithography using laser produced plasma as a source of x-rays, wherein long duration or multiple pulses of laser energy are not required for complete exposure of a pattern for lithographic purposes.
048141372	abstract	A fuel pellet for a nuclear reactor fuel rod is fabricated with smooth and gently sloping surfaces having no sharp edges or areas of high stress concentration. The bearing surfaces of the fuel pellets are contoured so that the pellets are easily stacked within a fuel rod and permit pivoting action between the fuel pellets. The fuel pellets are stacked end to end in a fuel rod which is incorporated into a fuel assembly for a nuclear reactor.
	description	This application is a divisional of U.S. patent application Ser. No. 10/860,654, filed on Jun. 4, 2004, now U.S. Pat. No. 7,012,264, which issued on Mar. 14, 2006, the entire content of which is incorporated herein by reference. 1. Field of the Invention The present invention relates to a movable carriage for moving an article support member in a lithographic apparatus, a method of manufacturing a movable carriage, and a device manufacturing method. 2. Description of Related Art A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction. In conventional structures for moving and supporting the article support member, in particular, a wafer table for supporting a wafer to be irradiated by a radiation beam of the lithographic apparatus, or, a mask table for supporting a mask defining a circuit pattern, due to the extreme accurate positioning requirements, a carriage structure is used wherein the mechanical stiffness properties are optimal. Furthermore, due to the heat generated by the actuators for moving the carriage, and radiation received on the structure to be irradiated, a substantial need exists to provide cooling in the carriage structure. To this end, conventional materials like aluminum and titanium are used which are cooled by cooling circuits integrated in the structure. One problem related to the cooling and stiffness requirements of the carriage is that the options to provide further reduction of the weight thereof are rather limited, since there are minimum thicknesses to be observed for the carriage in order to maintain sufficient mechanical integrity. Such cooling is essential for these conventional materials, since slight temperature variations can result in unacceptable contracting or expanding of the material. Even a temperature fluctuation as little as 2° K. can cause sensors that are arranged for driving actuators for actuating the carriage to be displaced over a distance to be out of tolerance for placing the substrate on a predetermined position. It is an aspect of the present invention to overcome the above indicated problems and provide a lithographic that includes an illumination system for providing a projection beam of radiation; an article support member for supporting an article to be placed in a beam path of the projection beam of radiation on the article support; and a carriage for a lithographic apparatus that is light, stiff, and adequate in terms of cooling and mounting properties. In another aspect of the invention, there is provided a movable carriage for use in a lithographic apparatus. The movable carriage is provided for moving an article support member in the lithographic apparatus. The article support member is constructed and arranged to move and support an article to be placed in a beam path of the lithographic apparatus. The carriage includes a compartmented composite structure. In still another aspect of the invention, there is provided a method for manufacturing a movable carriage for moving an article support member in a lithographic apparatus. The article support member is constructed and arranged to move and support an article to be placed in a beam path of the lithographic apparatus. The method includes forming the carriage from a compartmented composite structure, and providing the compartmented composite structure with a non-composite mounting interface and/or cooling interface. In a further aspect of the invention, a method for manufacturing a device with a lithographic apparatus is provided. The method includes projecting a beam of radiation, supporting an article with an article support member so that the article can be placed in a beam path of the beam of radiation, and moving the article support member with a carriage that includes a compartmented composite structure. In particular, according to the invention, a carriage is provided. The carriage includes a compartmented composite structure. With such an arrangement, conventional interfacing, for example, using metal or ceramic materials, can be applied in combination with the advantages of composite structures, such as a low specific weight, a high Young's modulus at places and directions where required, high strength, high stability, high electrical resistivity, and a low coefficient thermal expansion (CTE). Due to the low CTE value, there is no need for applying a separate cooling arrangement for the carriage, which means that the carriage is made lighter and simpler in construction. Furthermore, unlike the conventional materials, like aluminum and titanium, no magnetic damping occurs, which, where a long stroke actuator in the form of a magnetic motor is used, is highly beneficial. Furthermore, this particular arrangement offers a low cost product since it can be manufactured by gluing together very simple shaped structures. In addition, composite materials offer a range of complex shapes that are not possible to manufacture by conventional metals and ceramics. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal displays (LCDs), thin film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed before or after exposure in, for example, a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5–20 nm), as well as particle beams, such as ion beams or electron beams. The term “patterning device” used herein should be broadly interpreted as referring to a device that can be used to impart a projection beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the projection beam may not exactly correspond to the desired pattern in the target portion of the substrate. Generally, the pattern imparted to the projection beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions; in this manner, the reflected beam is patterned. In each example of patterning device, the support structure may be a frame or table, for example, which may be fixed or movable as required and which may ensure that the patterning device is at a desired position, for example, with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device”. The term “projection system” used herein should be broadly interpreted as encompassing various types of projection system, including refractive optical systems, reflective optical systems, and catadioptric optical systems, as appropriate for example for the exposure radiation being used, or for other factors such as the use of an immersion fluid or the use of a vacuum. Any use of the term “lens” herein may be considered as synonymous with the more general term “projection system”. The illumination system may also encompass various types of optical components, including refractive, reflective, and catadioptric optical components for directing, shaping, or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”. The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. The lithographic apparatus may also be of a type wherein the substrate is immersed in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. Immersion liquids may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the first element of the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. FIG. 1 schematically depicts a lithographic apparatus according to a particular embodiment of the invention. The apparatus includes: an illumination system (illuminator) IL for providing a projection beam PB of radiation (e.g. UV or EUV radiation); a first support structure (e.g. a mask table) MT for supporting a patterning device (e.g. a mask) MA and connected to a first positioning device PM for accurately positioning the patterning device with respect to item PL; a substrate table (e.g. a wafer table) WT for holding a substrate (e.g. a resist coated wafer) W and connected to a second positioning device PW for accurately positioning the substrate with respect to item PL; and a projection system (e.g. a reflective projection lens) PL for imaging a pattern imparted to the projection beam PB by the patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask or a programmable mirror array of a type as referred to above). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The illuminator IL receives a beam of radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example, when the source is a plasma discharge source. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is generally passed from the source SO to the illuminator IL with the aid of a radiation collector including for example suitable collecting mirrors and/or a spectral purity filter. In other cases, the source may be integral part of the apparatus, for example, when the source is a mercury lamp. The source SO and the illuminator IL, may be referred to as a radiation system. The illuminator IL may include an adjusting device for adjusting the angular intensity distribution of the beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator provides a conditioned beam of radiation, referred to as the projection beam PB, having a desired uniformity and intensity distribution in its cross section. The projection beam PB is incident on the mask MA, which is held on the mask table MT. Being reflected by the mask MA, the projection beam PB passes through the lens PL, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioning device PW and position sensor IF2 (e.g. an interferometric device), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the beam PB. Similarly, the first positioning device PM and position sensor IF1 can be used to accurately position the mask MA with respect to the path of the beam PB, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the object tables MT and WT will be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the positioning devices PM and PW. Another part of the positioning device PM and/or PW is a carriage which further embodies the invention and which will be further explained with reference to FIG. 2. Generally, this carriage may be seen as a stiff structure that moves over a perfectly flat surface, moved by the long stroke module. Generally, such a long stroke module may be provided by linear magnetic motors, which are mounted in transverse directions for covering a two-dimensional range of positions. However, preferably, the long stroke module includes a planar electro magnetic motor of the type that is for instance described in European patent EP-A-1243972, the contents of which are herein incorporated by reference. On top of the carriage, generally, the short stroke module is mounted for providing a fine positioning of the wafer table, which is mounted on top of the short stroke module. Thus, the carriage provides a frame between the long and short stroke modules and as such must be light weight and must provide high stiffness in combination with heavy loads. However, in the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The depicted apparatus can be used in the following preferred modes: 1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the projection beam is projected onto a target portion C in one go (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the projection beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT is determined by the (de-)magnification and image reversal characteristics of the projection system PL. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the projection beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. Turning to FIGS. 2a and 2b, there is illustrated a top view of a compartmented composite structure 1. The composite structure 1 is manufactured of fiber enforced composite materials, such as carbon fibers, etc., and assembled as further indicated with reference to FIG. 4. A characteristic feature of the shown exemplary embodiment is a rectangular outer box 2 and a triangular inner box 3 provided in the outer box 2. Such an arrangement provides a very stiff structure, while still providing access to the interior of the compartmented structure which is used for housing wiring and electronics etc. (not shown). The triangular inner box 3 may be further divided by sub boxes and ribbing structures such as illustrated in FIG. 4 and FIGS. 9–11 in particular. A structure providing optimum access to the interior of the carriage is provided, while cooling ducts 4 are provided and arranged along the ribs of the structure, such as is illustrated in FIG. 2b. Here, the composite structure 1 of FIG. 2a is shown provided with a non-composite mounting interface 5 arranged near the corners of the triangle 3, for mounting a short stroke motor (not shown). Furthermore, the cooling duct 4, which is preferably constructed from aluminum, titanium, or stainless steel material or the like, provides cooling to the short stroke motor. The duct 4 may partly be formed by the composite box structure, for instance, by using an elongate compartment as a cooling duct. For such an embodiment, the metal surface may be only present at the cooling interface, which provides coolant to relevant electronic parts such as the short-stroke actuator (not shown), which may further minimize weight. The coolant ducts 4 are provided as a triangular metal plate 6 that covers the top face of the boxed structure 1, and corners of the plate are used for mounting the short-stroke module, thereby providing an optimum mounting arrangement for ultra stable positioning of the wafer table. Furthermore, robust corner elements 7 are added, generally of a metal material, for providing a high load interface providing improved stiffness and protection when the carriage structure 1 unexpectedly crashes against a side wall of the surface on top of which it is actuated. FIG. 3 clearly shows that the complex composite structure of the invention may be provided by assembly of substantially simple shaped structures such as square or triangular shapes that are easy to manufacture using molds 8, as also indicated with reference to the FIGS. 12 and 13. By using these molds 8, more complex shapes can be realized and integrated in order to reduce the amount of parts (production steps) that have to be glued together afterwards. As shown in FIG. 4, a series of assembly steps using these molds 8 is depicted, starting from the right bottom picture and adding subsequently a first upstanding rim contour 10 on a bottom plate 9. Next, a square upstanding rectangular contour 11 is provided, which is mounted on the bottom plate 9. A triangular shaped box 12 is inserted in the rectangular contour 11, the triangular box provided with an L-form extremal mounting profile for gluing to a top plate 13. Next, further box elements 14 for providing greater stiffness to the carriage may be added. Finally top plate 13 is mounted and glued on top of the upstanding contours 11, 12 and 14. FIG. 5 shows a top view of the triangular structure 11, further elucidated with reference to FIG. 6-8 showing a plurality of cross-sectional views for the composite structure. FIG. 6 shows a cross-sectional view of the triangular structure 12, at position A—A (FIG. 5). Here, upstanding profile may be a U-formed profile, having L-form extremal mounting profiles for gluing the structure 12 to a bottom plate 9 and/or top plate 13. Between the rectangular outer contour 11 and the triangular inner structure 12, a mounting interface of, for example, an aluminum plate 15 may be provided. FIG. 7 and FIG. 8 show alternatives for the cross sectional area depicted as B—B in FIG. 5. According to FIG. 7, the outer contours 11 and inner contour 12 are provided as boxes, which is also depicted in FIG. 4. Thus, the inner triangular box 12 is glued on base plate 9, having upstanding contours 11 integral with the base plate 9. Top plate 13 is mounted on the upstanding contours 11, 12 using L-form extremal mounting profiles 16. FIG. 8 shows an alternative configuration, where a complex upper member 17 partly forms the rectangular structure 11 (side chambers 18) and triangular structure 12 (inner chamber). A lower bottom plate 19 forming a bottom plate for the triangular structure 12 may be glued to the complex member 17. FIGS. 9–11 show a plurality of alternative boxing and ribbing structures for providing the carriage according to the invention. FIG. 9 shows that a complex structure 20 as shown, for example, in FIG. 8 may be further provided with ribbing structures 21 by using a single sheet 22 of composite material. After removing a top section 23 of the complex structure 20, the ribs 21 stand upright and may be glued to a top sheet afterwards. FIG. 10 shows a variety of ribbing elements 21, in particular, a narrow asymmetrical rib 24, which only has one side L-form extremal mounting profile 16, a wide rib 25 which forms an interior chamber 26 and a symmetrical rib 27, which only has both sides L-form extremal mounting profiles 16. These interior chambers 26 could, for example, be used as cooling ducts, or, such as indicated by FIG. 9, have the top side 28 milled to provide two asymmetrical ribs. Also, as indicated by FIG. 11, extra boxes 29 may be added to create symmetrical ribs. FIGS. 12–13 provide exemplary embodiments for molds 8 for use in assembling the carriage according to the invention. The molds 8 are wrapped up to provide a single piece 30. By using a single sheet and several molds, multiple compartments 31 may be provided. The molds 8 are removed by milling the top surface of the pieces 30. FIG. 13 may be used in combination with the interior molds 8, such as depicted in FIG. 12. Depicted is an exterior mold 32 which, by side walls 33 defines the contour of rectangular box 11, and by interior bulk part 34 defines the triangular shape of triangular structure 12. FIG. 14 shows a movable carriage 35 for moving a wafer table 36 in a lithographic apparatus for moving and supporting an article 37 to be placed in a beam path of the lithographic apparatus. The carriage 35 includes a compartmented composite structure as indicated with reference to the FIGS. 2a and 2b. As can be seen in the figures, a plurality of sensors 38, 39 are mounted on the carriage 35, which are used for positioning the article 37 with respect to a positional reference 40. These sensors are located at a distance D, which, in principle, can be responsible for position measurement problems due to temperature effects. However, due to the very low coefficient of thermal expansion, especially where the used composite materials 41 include carbon fibers, these variations can be kept within a controllable range. Additional cooling of the carriage frame 35 may thereby be circumvented. This results in a lighter and simpler construction. A first sensor 38 is for positioning the carriage with respect to the long stroke actuator, which, for example may be a planar motor 42. A second sensor 39, located at a position different from the first sensor 38, is for positioning the wafer table 36 with respect to the carriage 35, in order to position the article 37. The second sensor 39 communicates with the short stroke actuator 43 that is mounted on top of the carriage 35. This may be performed by conventional mounting interfaces 44, optionally included with cooling interfaces, that are glued on the composite material of the carriage 35. Although the invention has been described with reference to a carriage structure specifically designed for carrying the short stroke module of a wafer table, it is not limited thereto, but, in practice, could also be used for other interfaces between long- and short stroke actuators. These actuators, for example, could be present in a mask table of a photolithographic apparatus using reflective mask technology or arrangements for actuating other elements into the light beam such as a obscuring blades or the like. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention.
054886430	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactors. More specifically, the present invention relates to a support arrangement by way of which a shroud can be supported within a reactor pressure vessel without a need for welding, drilling, or other machining of the shroud structure. 2. Description of the Related Art As is well known, safety is a paramount concern in devices such as nuclear reactors and stringent measures muse be exercised to ensure that mechanical failures, such as which tend to be induced by the formation of cracks and the like in various and numerous structures which comprise a nuclear reactor, are eliminated. It has been discovered that various stresses which are induced in a shroud structure used to enclose the fuel assemblies, tend to produce cracks in the top guide support ring area of the core shroud assembly. For example, it could be envisioned the cracks could form in the shroud at the horizontal weld joint between the top guide support ring and the shroud. This, of course induces a safety concern in that, if the weld were to break, the shroud could shift and cause a problem with control rod insertion. SUMMARY OF THE INVENTION It is an object of the invention to provide an arrangement via which a shroud can be supported within a reactor pressure vessel (RPV) in a manner which does not induce stresses that induce cracking and the like type of deterioration of the shroud assembly, which can be connected to the shroud using only light clamping, and which does not require any welding, drilling, or other machining of the shroud assembly. It is a further object of the present invention to provide a hanger rod arrangement via which a shroud or the like type of structure can be supported within a RPV or the like type of vessel without the need to weld, drill holes and the like. It is yet a further object of the present invention to provide a hanger rod arrangement which makes use of a basic upper hanger rod and multi-segment ring combination and which is supplemented with lower hanger rods which are hung on the multi-segment ring and which engage a shoulder or the like on the structure being supported, in the event that vertical displacement of the suspended structure needs to be attenuated or prevented. In brief, according to the present invention, in order to eliminate the need to weld, drill or otherwise machine a shroud structure which is used to surround a plurality of fuel assemblies in a nuclear reactor, a plurality of upper hanger rods interconnect a structure located above the shroud to a support ring assembly which is clamped about the upper periphery of the shroud below the top guide support ring assembly. Lower hanger rods interconnect the lower edge of the shroud with the support ring. Thus, through the upper and lower hanger rods and support ring assembly, the shroud can be supported within the RPV. The upper support ring is arranged to clamp the lower ends of the upper hanger rods against an upper outer peripheral portion of the shroud while the lower ends of the lower hanger rods are clamped against a lower peripheral wall portion of the shroud by a lower support ring in a manner which ensures a good connection between the lower end of the lower hanger rods and an edge such as defined by a stepped diameter portion or the like. In a specific embodiment of the invention, the top guide support ring, together with the upper part of the shroud, is held in place by a support ring assembly that is clamped around the shroud below the top guide support ring. The support ring consists of four segments which are bolted together. The segments are formed to define a polygonal ring with 12 symmetrical sides. During installation of the shroud support ring, the ring is suspended from upper hanger rods which are spaced around the shroud. When the shroud support ring is clamped around the shroud, the upper hanger rods are clamped between the support ring and the shroud, and become an integral part of the clamping assembly. The upper end of each hanger rod has a cross bar which fits between and is supported by separator latch brackets. To prevent vertical separation between the shroud and the top guide support ring, the shroud support ring is locked against vertical movement by a plurality (e.g. twelve) lower hanger rods, which are hooked over the shroud support ring. The lower ends of the lower hanger rods lock under a recess defined by a stepped diameter of the shroud located further down on the shroud. The lower hanger rods are maintained engaged with this recess by a lower support ring which surrounds the lower hanger rods and clamps the lower ends of these rods radially inward against the side of the shroud. Before the shroud support ring is finally tightened in a clamping condition, the lengths of the upper hanging rods are adjusted using adjusting nuts provided at their upper ends, so the vertical installation gap between the lower hanger rods and the horizontal surface of the recess or the like located at the lower end of the shroud and against which the lower ends of the lower hanger rods engage, is closed. It should, however, be noted that with the present invention, in the event that the risk of vertical separation between the top guide ring and the shroud is of little or no concern, the lower hanger rods and the lower support ring can be omitted, and the installation gap is closed between the upper hanger rods and the underside of the top guide support ring. More specifically, a first aspect of the present invention resides in a nuclear reactor which features: a shroud disposed within a reactor vessel so as to surround at least one fuel assembly; and a shroud support arrangement for supporting the shroud in the reactor vessel, comprising: an upper support ring clamped about the upper periphery of the shroud; and an upper hanger rod which has a lower end engaged with the upper support ring and an upper end adapted for connection to a predetermined structure located within the reactor vessel above the shroud. A second aspect of the present invention resides in a nuclear reactor which features: a shroud disposed within a reactor vessel so as to surround at least one fuel assembly; and a shroud support arrangement for supporting the shroud in the reactor vessel, comprising: a first multi-segment ring member disposed about the upper periphery of the shroud, the first ring member having a plurality of joints which allow the size of the ring to be adjusted and selectively clamped against the shroud; a first adjustable length hanger rod which has a lower end engaged with the first ring member and an upper end adapted for connection to a predetermined structure located within the reactor vessel above the shroud. A third aspect of the invention resides in a support arrangement for supporting a shroud structure within a vessel, which features: a multi-segment ring assembly which can be selectively tightened about the shroud; a plurality of first hanger rods, the first hanger rods each having hook members at the lower ends thereof, the hook members being arranged to engage with the ring assembly and to be clamped against the external surface of the shroud when the ring assembly is selectively tightened, the upper ends of the first hanger rods being arranged to be engageable with a structure which is disposed in the vessel above the shroud. A further aspect of the present invention resides in a method of supporting a shroud in a pressure vessel of a nuclear reactor comprising the steps of: suspending a plurality of upper hanger rods on a structure disposed in the pressure vessel above the level at which the shroud is suspended; connecting the plurality of upper hanger rods to a multi-segment ring member which is disposed about the shroud by arranging hooks which are provided on the lower end of the upper hanger rods to engage with the ring member so that when the ring member is tightened, portions of the hooks are pressed into engagement with the shroud; and tightening the ring member to clamp the portions of the hooks against the shroud.
	description	The present invention relates to an installation method of equipment such as a vertical pump used at, for example, an atomic power plant, an anchor member supporting mechanism and an anchor bolt unit used when the installation method of equipment is executed. Conventionally, a bottomed cylindrical container made of a steel plate called as a pit can is used for a placement of, for example, a large vertical pump in an atomic power plant and so on. The vertical pump and so on is fixed by foundation bolts under a state that a lower side of a pump main body is inserted into the pit can embedded in base concrete. Besides, an installation method and so on to efficiently install the pit can are proposed. Namely, anchor bolts for equipment installation such as the vertical pump are attached at a periphery of the pit can in advance at a manufacturing factory in this installation method. Further, a coupling member is attached at a bottom portion of the pit can. After that, a pit can module is formed by attaching reinforcing steels for reinforcement at the periphery of the pit can in this installation method. Further, the pit can module is mounted on a member to be coupled placed on a base of an installation field of the vertical pump and so on via the coupling member in this installation method. After that, an installation of the pit can main body is completed by depositing concrete. Reference 1: JP-A 2004-309406 (KOKAI) Reference 2: JP-A 2002-147392 (KOKAI) However, in the above-stated installation method, the anchor bolds for equipment installation are attached at the periphery of the pit can main body when the pit can module is manufactured. After that, the installation method further goes through a working process in which the reinforcing steels for reinforcement are attached at the periphery of the pit can main body. Accordingly, a relatively difficult work to place the reinforcing steels at the periphery of the pit can while avoiding interference with the anchor bolts on component layout is required in this installation method. It is therefore required to improve working efficiency as for the installation work of equipment including the installation of the pit can. The present invention is made to solve the above-stated problems and an object thereof is to provide an installation method of equipment, an anchor member supporting mechanism, and an anchor bolt unit capable of enhancing installation work efficiency of the equipment. To attain the above-stated object, an installation method of equipment according to an aspect of the present invention includes: disposing a first frame at a position different from an installation location of the equipment; disposing reinforcing steels to reinforce the first frame and a pit container in a bottomed cylindrical state to be placed on the first frame from a periphery thereof; placing the pit container on the first frame positioning inside the reinforcing steels; attaching an anchor member supporting mechanism to the pit container, the anchor member supporting mechanism including a supporting member to support an anchor member in a ring state at an outer peripheral side of the pit container, and a reinforcing member in a ring state having a center hole and in which a part of each reinforcing steel is penetrated from a gap formed between the center hole and an outer peripheral portion of the pit container while reinforcing the supporting member from the outer peripheral side of the pit container; placing a second frame on a base to be the installation location of the equipment; placing a pit container unit on the second frame via the first frame, the pit container unit being formed by integrating the first frame, the reinforcing steels, the pit container and the anchor member supporting mechanism; embedding a portion at a lower side than the anchor member supporting mechanism of the pit container unit, together with the second frame, by primary concrete; disposing an anchor bolt unit in which respective bottom sides of plural foundation bolts for equipment installation are respectively fixed to the anchor member on the anchor member supporting mechanism after the embedding by the primary concrete; correcting a relative positional relationship of the respective foundation bolts relative to the pit container by using a template member having plural positioning holes into which the plural foundation bolts on the anchor bolt unit can be individually inserted from upper end sides thereof; embedding the pit container unit and the anchor bolt unit by secondary concrete except the template member under a state in which the positional relationship is corrected, an opening portion at upward of the pit container, and upper end sides of the plural foundation bolts; and carrying the equipment into the pit container after the template member is removed and fixing the carried equipment through the respective foundation bolts of which bottom sides are embedded. In this installation method, the pit container unit in which the first frame, the pit container, the reinforcing steels reinforcing the above from a periphery, and the anchor member supporting mechanism are integrated is manufactured in advance, and the pit container unit is placed on a base to be the installation location of the equipment via the first and second frames. Further, in the installation method, the anchor bolt unit is disposed on the anchor member supporting mechanism after the portion at the lower side than the anchor member supporting mechanism of the pit container unit is embedded by primary concrete. Next, in this installation method, the relative positional relationship of the respective foundation bolts on the anchor bolt unit relative to the pit container is corrected by using the template member. Further, in this installation method, secondary concrete is deposited under the state in which the positional relationship of the respective foundation bolts is corrected. After that, in this installation method, the equipment is carried into the pit container, and an installation of the equipment such as a vertical pump is completed by fixing the carried equipment through the respective foundation bolts of which bottom sides are embedded. Namely, the installation method of equipment according to this aspect is the one in which the reinforcing steels to reinforce the first frame and the pit container from the periphery thereof are disposed before the anchor bolt unit in which the plural foundation bolts are fixed is disposed at the pit container side. Accordingly, it is possible to perform the disposition work of the reinforcing steels around the pit container relatively easily without concerning the interference with the foundation bolts and so on, on the component layout according to the installation method. Besides, according to the installation method, it is possible to dispose the anchor bolt unit on the anchor member supporting mechanism under a state in which a part of each reinforcing steel is penetrated from a gap formed between the center hole of the ring state reinforcing member included by the anchor member supporting mechanism and the outer peripheral portion of the pit container (namely, under a state in which the positions of the reinforcing steels are controlled). According to the installation method, it is possible to improve the workability at the component disposition time. Besides, the supporting member of the anchor member supporting mechanism may be made up of, for example, plural plate state members respectively protruding in a radial pattern from an outer peripheral portion of the pit container. Besides, the reinforcing member in the ring state may be made up to integrally support the plural plate state members from a bottom side. Further, the anchor bolt unit is made up by respectively welding the respective bottom sides of the plural foundation bolts at predetermined positions on the anchor member respectively corresponding to positions of plural installation holes bored at a casing of the equipment in advance and positions of the plural positioning holes on the template member and so on. As stated above, it is possible to further improve the workability at the equipment installation time by applying the anchor bolt unit in which the plural foundation bolts and the anchor member are integrated in advance. According to the present invention, it is possible to provide the installation method of equipment, the anchor member supporting mechanism, and the anchor bolt unit capable of enhancing the efficiency of the installation work of equipment. Hereinafter, embodiments of the present invention are described based on the drawings. Here, FIG. 1 is a partial sectional view schematically illustrating a state in which an ECCS (Emergency Core Cooling System) pump 71 is installed by an installation method of equipment according to an embodiment of the present invention. Note that a peripheral structure at an embedded portion of the ECCS pump 71 is not illustrated in FIG. 1. As illustrated in FIG. 1, the ECCS pump 71 is one of equipments placed in an atomic power plant and so on. The ECCS pump 71 is a vertical pump to supply cooling water to a reactor core in an emergency. The ECCS pump 71 includes a base part 74 and a lower casing 75 constituting a casing portion (a casing of a pump main body called also as a barrel), a water inlet part 72 where the water is entered, and a water outlet part 73 to be a discharge side of water, and so on. The ECCS pump 71 is installed under a state in which the lower casing 75 is accommodated in a later-described pit can 20a of a pit can unit 20 embedded inside secondary concrete (concrete body) 61. In detail, plural installation holes 74a for equipment installation are bored in advance at the base part 74. The ECCS pump 71 is installed on the secondary concrete 61 under a state in which respective foundation bolts 54 of which bottom sides are embedded are inserted into these installation holes 74a, and engaged by nuts 54a. Next, the installation method of equipment of the present embodiment is described by using flowcharts illustrated in FIG. 2 to FIG. 4, and views mechanically illustrating respective working processes of FIG. 1 and FIG. 5 to FIG. 24. Here, the working processes illustrated by dotted lines in FIG. 2 to FIG. 4 represent construction side works (works relating to construction application), on the other hand, the working processes illustrated by solid lines represent mechanical side works (works relating to attachment of various components) other than the construction side works. At first, as illustrated in FIG. 2 and FIG. 5, a surface plate (ground assembling surface plate) 15 is placed on a G.L (Ground Line) 12 by the construction side work at the other location (manufacturing factory and so on) different from a final installation location of the ECCS pump 71. Besides, temporary receiving structures 14 are provided on the surface plate 15. Further, a scaffold (ground assembling scaffold) 16 is provided on the G.L 12 (S[ step]1). Next, as illustrated in FIG. 2 and FIG. 6, an upper side frame (first frame) 17 made of, for example, steel to place the pit can 20a on the surface plate 15 via the temporary frame 14 is mounted and a level adjustment in a height direction is performed (S2). Further, as illustrated in FIG. 2 and FIG. 7, vertical reinforcing bars 18 to be reinforcing steels to reinforce the upper side frame 17 and the pit can 20a from a periphery thereof are disposed (inserted and temporary disposed) by the construction side work so that an upper side thereof becomes a posture standing in a vertical direction (S3) before the pit can 20a is placed (temporary set) on the upper side frame 17. Next, as illustrated in FIG. 2 and FIG. 8, a temporary placing (temporary setting) of the pit can 20a to which suspended pieces (suspended clasps) 46 are attached is performed by suspending on the upper side frame 17 by an equipment side work (S4). Here, the pit can 20a is constituted by a bottomed cylindrical pit container made of, for example, a steel plate having a space capable of accommodating the lower casing 75 of the ECCS pump 71 from an upper side as illustrated in FIG. 1 and FIG. 8. Subsequently, as illustrated in FIG. 2 and FIG. 9A to FIG. 9C, an anchor plate supporting mechanism (anchor member supporting mechanism) 21 including an anchor plate supporting member (called also as an anchor plate receiving beam) 22 functioning as a supporting member and a ring state dummy anchor plate 22a functioning as a reinforcing member are attached to a pit can 20a side (S5). Here, the anchor plate supporting member 22 is constituted by plural plate state (or block state) members respectively protruding from an outer peripheral portion of the pit can 20a in a radial pattern. The anchor plate supporting member 22 supports a later-described ring state anchor plate 58 (refer to FIG. 20) at an outer peripheral side of the pit can 20a. Here, the attachment of the anchor plate supporting member 22 is described in more detail. As illustrated in FIG. 9A and FIG. 9B, marking positions of an angle member 23 attached to the pit can 20a are checked. For example, 12 pieces of anchor plate supporting members 22 are welded at the marking positions (positions spaced with intervals of, for example, every 30 degrees in a circumferential direction of the angle member 23) of the angle member 23. At this time, it should be noted not to directly weld the anchor plate supporting member 22 and the pit can 20a. Besides, suspended pieces (suspended clasps) 24 are attached to the upper side frame 17 as illustrated in FIG. 9B. As illustrated in FIG. 9A to FIG. 9C, the ring state dummy anchor plate 22a has a center hole 22b formed with, for example, an inside diameter of P1. The dummy anchor plate 22a reinforces the anchor plate supporting member 22 from an outer peripheral side of the pit can 20a. In the dummy anchor plate 22a, a part (a tip portion) of each vertical reinforcing bar 18 is penetrated from a gap formed between the center hole 22b and the outer peripheral portion of the pit can 20a as illustrated in FIG. 9A. Next, as illustrated in FIG. 2, FIG. 10A and FIG. 10B, a ground assembling of reinforcing steels for reinforcement around the pit can 20a is performed. Namely, circumferential reinforcing bars 26, hairpin reinforcements 27, and setup reinforcements 25 are placed (S6). The circumferential reinforcing bar 26 is a reinforcing steel to reinforce an outer peripheral side of the vertical reinforcing bar 18. The hairpin reinforcement 27 is a reinforcing steel to reinforce between an inner side of the vertical reinforcing bar 18 and the lower side of the pit can 20a. The setup reinforcement 25 is a reinforcing steel to reinforce between the inner side of the vertical reinforcing bar 18 and the anchor plate supporting member 22, and between the inner side of the vertical reinforcing bar 18 and the hairpin reinforcement 27. When the reinforcing steels for reinforcement as stated above are placed, the ground assembling of the reinforcing bars around the pit can 20a is performed so that a separation distance P2 falls within a tolerance range in consideration of the inside diameter P1 of the dummy anchor plate 22a as illustrated in FIG. 10A and FIG. 10B, and thereby, the vertical reinforcing bars 18 are permanently placed. The separation distance P2 is a distance between the outer peripheral portion of the pit can 20a and the inner side portion of the vertical reinforcing bar 18. The pit can unit (pit container unit) 20 in which the upper side frame 17, the pit can 20a, the anchor plate supporting mechanism 21, and the reinforcing steels (the vertical reinforcing bars 18, the circumferential reinforcing bars 26, the hairpin reinforcements 27, and the setup reinforcements 25) around the pit can 20a including the vertical reinforcing bars 18 are unitized (prefabricated), is thereby constituted. Here, in the installation method of equipment of the present embodiment, the reinforcing steels (the vertical reinforcing bars 18, the circumferential reinforcing bar 26, and so on) around the pit can 20a are constructed as illustrated in FIG. 10A and FIG. 10B before a later-described anchor bolt unit 57 to which the foundation bolts 54 are fixed is disposed at the pit can 20a side. According to the installation method of equipment of the present embodiment, it is possible to easily perform a disposing work of the reinforcing steels around the pit can 20a without concerning interference with the foundation bolts 54 on a component layout. On the other hand, the ground is dug down until a base rock exposes at the installation location of the ECCS pump 71, and an inspection of the exposed base rock is performed as illustrated in FIG. 3 (S11). Next, concrete is deposited on the base rock after the inspection is completed while curing is performed (S12), and an MMR (MerMaid Rock) 11 being so-called an artificial base rock is formed as illustrated in FIG. 11A. Subsequently, as illustrated in FIG. 11A and FIG. 11B, a post cast plate 32 is placed on the MMR 11 via a metal anchor and so on after a marking of a placement position of a lower side frame (second frame) 30 constituted by steel and so on for placing the pit can unit 20 is performed on the MMR 11. Further, the lower side frame 30 which is already prefabricated (which is already component processed and temporary assembled) is carried in by using a crane and so on. After a positioning and a level adjustment (height adjustment) of the carried lower side frame 30 are performed, respective leg parts of the lower side frame 30 are fixed on the post cast plate 32 by welding. Besides, span seals 31 as a sealing material are attached to the respective leg parts of the lower side frame 30 as illustrated in FIG. 3 and FIG. 12. Further, lower step reinforcing members 33 are stretched across at the lower side of adjacent leg parts of the lower side frame 30 with each other to reinforce the lower side frame 30 (S13). After the lower side frame 30 is placed, bottom reinforcements (reinforcing steels for reinforcement of bottom end portion) 34 are disposed in a matrix state as illustrated in FIG. 3, FIG. 13A, and FIG. 13B. Next, units of the bottom reinforcements 34 are disposed in the matrix state are overlaid for three steps, upper step reinforcing members 35 are stretched across at upper sides of the adjacent leg parts of the lower side frame 30 with each other, to further reinforce the lower side frame 30 (S14). Next, as illustrated in FIG. 14, bottom reinforcements (reinforcing steels) 36 are disposed in a matrix state at a further upper part of the upper step reinforcing members 35. Subsequently, a work reinforcement frame 37 is placed in a vicinity of the lower side frame 30 on the bottom reinforcements 36. Next, as illustrated in FIG. 15, a work scaffold 40 is placed by using the reinforcement frame 37. After that, wires 41, 43 and a suspended balance 42 are attached to the pit can unit 20 carried from a temporary assembling location. In this state, the pit can unit 20 is suspended in (carried in) to an upper surface of the lower side frame 30, and the pit can unit 20 is placed on the lower side frame 30 via the upper side frame 17 (S21) as illustrated in FIG. 4 and FIG. 15. In detail, the upper side frame 17 is welded along with marking lines and so on marked on the lower side frames 30 in advance, and the pit can unit 20 is installed. Further, as illustrated in FIG. 15 and FIG. 16, wires (stay materials) 45 to prevent the pit can 20a from floating and falling in liquid state cement and mortar are each coupled between the suspended piece 46 at the pit can 20a side and the suspended piece 24 of the upper side frame 17. Here, it is checked if a placement position in a plane direction, a level in a height direction, and a vertical degree (and a circularity) of the pit can 20a falls within the tolerance range. After that, a portion at the lower side of the pit can unit 20 than the anchor plate supporting mechanism 21 is embedded by primary concrete 51 together with the lower side frame 30 as illustrated in FIG. 4 and FIG. 17 (the primary concrete 51 is deposited up to a primary concrete deposit virtual surface 51a illustrated in FIG. 17) (S22). As illustrated in FIG. 4 and FIG. 18, after the embedding process by the primary concrete 51 is completed, the wires 45 as the stay materials and the suspended pieces 46 of the pit can 20a are removed (S23). Next, as illustrated in FIG. 19A to FIG. 21B, the anchor bolt unit 57 to which respective bottom sides of the plural foundation bolts (called also as the anchor bolt) 54 for equipment installation are respectively fixed to the anchor plate 58 is disposed on the anchor plate supporting mechanism 21 of the pit can unit 20 as illustrated in FIG. 20 (S24). Here, in the installation method of equipment of the present embodiment, it is possible to dispose the anchor bolt unit 57 on the anchor plate supporting mechanism 21 under the state in which the tip portions of the vertical reinforcing bars 18 are penetrated from the gap formed between the center hole 22b of the ring state dummy anchor plate 22a included by the anchor plate supporting mechanism 21 and the outer peripheral portion of the pit can 20a (a state in which the positions of the reinforcing steels around the pit can 20a are controlled) as illustrated in FIG. 9A and FIG. 9B. Accordingly, the working efficiency at the component disposing time can be improved. Besides, as illustrated in FIG. 19A and FIG. 19B, in the plural foundation bolts 54 on the anchor bolt unit 57, the respective bottom sides of the foundation bolt main bodies are respectively (engaged by nuts 54b, 54c and) welded at predetermined positions on the anchor plate 58 respectively corresponding to the positions of the plural installation holes 74a bored in advance at the base part 74 of the ECCS pump 71 and positions of plural positioning holes 53a on a later-described template (template member) 53 (refer to FIG. 21A). Besides, the respective positioning holes 53a on the template 53 are bored (coaxially processed) at, for example, the same step as a boring process of the installation holes 74a on the base part 74 so as to place the foundation bolts 54 with high accuracy. Further, as illustrated in FIG. 21A and FIG. 21B, a relative positional relationship of the respective foundation bolts 54 relative to the pit can 20a is corrected by using the template 53 made of, for example, a steel plate having the plural positioning holes 53a into which the plural foundation bolts 54 on the anchor bolt unit 57 can be individually inserted from upper end sides thereof. In detail, for example, the template 53 is positioned such that, for example, positions of marks marked on the template 53 in advance match with positions of marks marked on the pit can 20a in advance. In more detail, a temporary disposition (temporary setting) of the template 53 is performed firstly as illustrated in FIG. 4, FIG. 21A, and FIG. 21B (S25). Specifically, the template 53 is fixed via the nuts 54a under the state in which the respective foundation bolts 54 are inserted into the positioning holes 53a. Further, a position (a position in height and plane directions) of the template 53 is displaced by using, for example, a liner (spacer) and so on, the positional relationship is fallen within the tolerance range, and thereafter, the anchor plate supporting member 22 on the anchor plate supporting mechanism 21 and the anchor plate 58 at a bottom portion of the anchor bolt unit 57 are spot welded. After that, the template 53 is temporary removed (S26), and top reinforcements 55 being reinforcing steels to reinforce around an upper side of the pit can unit 20 are disposed for, for example, two steps in a matrix state (S27) as illustrated in FIG. 4 and FIG. 22. After that, as illustrated in FIG. 4 and FIG. 23, the template 53 is placed again (permanent disposition) (S28), and the position of the template 53 is displaced. Accordingly, the relative positional relationship of the respective foundation bolts 54 relative to the pit can 20a is finally corrected (S29). Next, the pit can unit 20 and the anchor bolt unit 57 are embedded by secondary concrete 61 (deposit the secondary concrete 61 up to a secondary concrete deposit virtual surface 61a illustrated in FIG. 23) as illustrated in FIG. 4 and FIG. 24 except the template 53 in the state in which the positional relationship thereof is finally corrected, an opening portion at upside of the pit can 20a, and upper end sides of the respective foundation bolts 54 (S30). After the secondary concrete 61 is deposited, various measurements are performed after the template 53 is removed as illustrated in FIG. 4 and FIG. 24 (S31). For example, it is checked if concentricity of a center of the template 53 and a center of the pit can 20a falls within the tolerance range. Besides, it is checked if a height level at an upper end of the foundation bolt 54 falls within the tolerance range, and so on. Further, as illustrated in FIG. 4 and FIG. 24, the ECCS pump 71 is carried into an accommodating space of the pit can 20a after the template 53 is removed as illustrated in FIG. 1, and the carried ECCS pump 71 is fixed via the respective foundation bolts 54 of which bottom sides are embedded and the nuts 54a (S32). As stated above, in the installation method of equipment according to the present embodiment, the pit can unit 20 in which the upper side frame 17, the pit can 20a, various reinforcing steels including the vertical reinforcing bars 18 reinforcing the above from a periphery thereof, and the anchor plate supporting mechanism 21 are integrated is manufactured in advance. Further, the manufactured pit can unit 20 is placed on the MMR 11 to be the installation location of the equipment via the lower side frame 30 and the upper side frame 17. Further, the anchor bolt unit 57 is disposed on the anchor plate supporting mechanism 21 after the portion at the lower side of the pit can unit 20 than the anchor plate supporting mechanism 21 is embedded by the primary concrete 51. Next, the positional relationship of the respective foundation bolts 54 on the anchor bolt unit 57 relative to the pit can 20a is corrected by using the template 53. Further, the secondary concrete 61 is deposited under a state in which the positional relationship of the respective foundation bolts 54 is corrected. After that, the ECCS pump 71 is carried into the pit can 20a, and the installation of the ECCS pump 71 is completed by fixing the carried ECCS pump 71 through the respective foundation bolts 54 of which bottom sides are embedded. Namely, the installation method of equipment of the present embodiment is the method in which the reinforcing steels around the pit can 20a such as the vertical reinforcing bars 18 and the circumferential reinforcing bars 26 are disposed as illustrated in FIG. 10A and FIG. 10B before the anchor bolt unit 57 to which the plural foundation bolts are fixed is disposed at the pit can 20a side. According to the installation method of equipment of the present embodiment, it is possible to easily perform the disposition work of the reinforcing steels around the pit can 20a without concerning the interference with the foundation bolts 54 on the component layout. Besides, according to the installation method of equipment of the present embodiment, it is possible to dispose the anchor bolt unit 57 on the anchor plate supporting mechanism 21 under the state in which the tip portions of the vertical reinforcing bars 18 are penetrated from the gap formed between the center hole 22b of the ring state dummy anchor plate 22a included by the anchor plate supporting mechanism 21 and the outer peripheral portion of the pit can 20a (namely, under the state in which the positions of the reinforcing steels around the pit can 20a are controlled) as illustrated in FIG. 9A and FIG. 9B. Accordingly, it is possible to improve the assembling workability at the component disposition time according to the installation method of equipment of the present embodiment. In other words, the dummy anchor plate 22a enables the function to reinforce the anchor plate supporting member 22 and the function to control the positions of the reinforcing steels around the pit can 20a including the vertical reinforcing bars 18 by a single member. As stated above, the present invention is concretely described by the embodiments, but the present invention is not limited only to these embodiments, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. The present invention is also useful in a case when an equipment, for example, such as a sump tank is installed in addition to the installation of the vertical pump such as the ECCS pump. 17 . . . upper side frame, 18 . . . vertical reinforcing bar, 20 . . . pit can unit, 20a . . . pit can, 21 . . . anchor plate supporting mechanism, 22 . . . anchor plate supporting member, 22a . . . dummy anchor plate, 22b . . . center hole, 25 . . . setup reinforcement, 26 . . . circumferential reinforcing bar, 27 . . . hairpin reinforcement 30 . . . lower side frame, 51 . . . primary concrete, 53 . . . template, 53a . . . positioning hole, 54 . . . foundation bolt, 55 . . . top reinforcement, 57 . . . anchor bolt unit, 58 . . . anchor plate, 61 . . . secondary concrete, 71 . . . ECCS pump, 74 . . . base part, 74a . . . installation hole, 75 . . . lower casing
054810612	abstract	The present invention relates to a method of solidifying radioactive waste with cement, comprising forming a mixture comprising water, a hydrophilic material and cement substantially non-shrinkable or expansible with respect to volume change upon hardening, mixing said mixture with the radioactive waste, followed by hardening to form a solid body.. The present invention enables the formation of a compact solid body having voids, such as capillary voids, of reduced volume, which makes it possible to reduce the leaching rate of hazardous materials. Further, since no shrinkage accompanies hardening, no tensile stress occurs in the cement surrounding minute waste particles within the hardened material, thereby enabling a decrease in the strength of the solid body to be minimized. This in turn enables an increase in the amount of packing of waste. Prior addition of a hydrophilic material enables the cement fluidity before hardening to be maintained even after complete absorption of water by a water absorptive waste. This is extremely advantageous in carrying out hardening.
056195451	claims	1. A process for purifying cyclotron produced .sup.123 I which comprises: (a) passing a recovered solution of a cyclotron produced iodide over an anion exchange resin; (b) washing the ion exchange resin in (a) with a weak solution comprising NaOH; (c) washing the ion exchange resin in (a) with a stronger solution of NaOH than used in (b); and (d) recovering the wash solution of (c). (a) passing a recovered solution of a cyclotron produced iodide over an anion exchange resin; (b) washing the ion exchange resin in (a) with about a 0.002N solution of NaOH; (c) washing the ion exchange resin in (a) with about a 0.02N solution of NaOH; and (d) recovering the wash solution of (c). (a) passing a recovered solution comprising iodide over an anion exchange resin; (b) washing the ion exchange resin in (a) with a solution comprising from about 0.0005N to about 0.005N of a weak base; (c) washing the ion exchange resin in (a) with a solution comprising from about 0.01N to about 1N of a weak base; and (d) recovering the wash solution of (c). 2. The process of claim 1 in which the NaOH solution of (b) is from about 0.0005N to about 0.005N. 3. The process of claim 1 in which the NaOH solution of (c) is from about 0.005N to about 1.0N. 4. A process for purifying cyclotron produced .sup.123 I which comprises: 5. A process for purifying cyclotron produced radioiodides selected from the group consisting of .sup.121 I, .sup.123 I, .sup.124 I, .sup.125 I, and .sup.126 I which comprises:
054815789	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 24 of the tie plate assembly 18 flows upwardly through a flow volume 26 defined by a peripheral wall 28 of the lower tie plate assembly 18, through the lower tie plate grid 16, and then along and about the fuel rods 12. As indicated previously, it is important that debris in the coolant be prevented from flowing through the lower tie plate assembly and into the area between the channeled fuel rods 12. Referring now to FIGS. 2 and 3, there is illustrated a lower tie plate grid 16 according to the present invention, forming a part of the lower tie plate assembly 18. Lower tie plate grid 16 is preferably formed separately from the lower portion (including the peripheral wall 28 and the bottom nozzle 24) of the assembly, and secured thereto by, for example, welding. The lower tie plate grid 16 supports the fuel rods 12 above the grid and to this end, the grid 16 includes a plurality of generally cylindrical, vertically extending bosses 30 having centerlines arranged at corners of substantially square matrices of such bosses. Interconnecting (and forming the sides of) the square matrices are webs 32 adjoining the adjacent cylindrical bosses 30 along radial lines of the bosses 30 and extending between the upper and lower surfaces of the grid 16. Consequently, it will be seen that the webs 32 have portions formed along the sides of each square matrix and, together with convex outer portions of the cylindrical bosses 30, define side walls of openings or flow areas 34 which permit coolant to flow through the grid 16 and into the channeled fuel bundle assembly. The debris catching function is performed by a plurality of perforated tubes 36 (see FIG. 5), each having a cylindrical shape including a peripheral wall 38 formed with a plurality of substantially uniformly distributed perforations or flow openings 40. Each tube 36 is open at its lower end and, depending on how the fuel rods 12 are secured to the grid 16, may have open or closed upper ends. More specifically, for those lower tie plate arrangements where the fuel rod end plugs are simply supported by the bosses 30 of the grid 16, the upper ends of the tubes 36 will be closed or capped, and the tubes may be secured by any suitable means to the lowermost ends of the bosses 30. For those lower tie plate configurations, however, where the fuel rod end plugs are threaded into the grid bosses 30, the tubes may be formed with open upper ends (as shown in FIG. 5) and, again, the tubes 36 may be secured to the bosses 30 by any suitable means. A plate 42 (see FIG. 4) is secured to the upstream or lowermost ends of the array of tubes 36, such that flow openings 44 formed in the plate are aligned with the tube ends. The plate 42 is also sized and shaped so that it can be secured continuously about its periphery to the inner surface of the wall 28 of the lower tie plate assembly. In this way, substantially all coolant is constrained to flow into the tubes 36, through perforations or flow openings 40 and then through the flow areas 34 in the grid 16 and finally, upwardly into the fuel rod bundle. In alternative arrangements, the tubes 36 may be secured initially to the plate 42 and then plate 42 can be secured to the inner surface of wall 28. In this arrangement, the downstream ends of tubes 36 need only abut the underside of the grid, such that flow induced vibrations are held within acceptable limits. It will be appreciated that some leakage either in the area of plate 42 or at the tube/grid interface can be tolerated, so long as flow rate and pressure drop are not significantly altered. It is significant to the debris catching function of the tubes 36 that the coolant is forced to change direction in order to exit the tubes. In other words, as the flow direction changes substantially 90.degree., momentum of the debris entering the tubes 36 will generally carry the debris past the perforations 40 and impinge on the closed upper end of the tube or on the lower surface of the fuel rod end plug. Some debris, of course, may be too large to pass through the openings 40 in any event, while other debris of the long narrow type may have a cross-sectional area which might otherwise pass through the openings, but is nevertheless unable to negotiate the tortuous path through the tubes 36. Thus, the debris catcher effectively prevents debris from entering the fuel bundle area. With regard to pressure drop across the debris catcher, the flow area through the tubes 36 (i.e., through openings 40) is directly proportional to the axial length of the tubes. Thus, the flow area can be made large enough to produce lower fluid velocities through the openings 40. The objective is to have the total area of openings 40 at least equal the flow area through the grid to minimize velocity changes. To achieve this goal, the tubes 36 should have an axial length of between about 0.5 and about 1.0 inch and a diameter approximately equal to the bosses 30. By increasing the tube length, even better flow characteristics can be achieved. It will be recognized, of course, that the configuration of the lower tie plate assembly places practical limitations on the lengths of the tubes 36, and that only so many holes or openings 40 can be provided in the tubes 36 before the structural integrity of the tubes is negatively impacted. With these caveats, the objective is nevertheless to maximize flow area of the tube openings relative to the area of the grid opening. The overall result is minimal or no additional flow resistance and thus little or no additional pressure drop attributable to the debris catcher. 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.
	description	This application is a continuation of Provisional Patent Application No. 60/531,390 filed Dec. 19, 2003. The invention relates to a method of inspecting pressure vessels for corrosion wastage and other forms of degradation and more particularly to a method of inspecting the regions of pressure vessels adjacent penetration tubes installed with clearance fits and welded to the pressure vessels. The penetration tubes welded to pressure vessels may become susceptible to stress corrosion cracking after years of on-line operation at high temperatures and high pressures. Micro-cracks may form and grow into leak paths through which the contained fluids may seep and eventually corrode the pressure vessels. Thus, it has been found that the penetration tubes extending through the heads of reactor pressure vessels in the primary systems of pressurized water nuclear reactors are susceptible to cracking. In one case, it was found that a crack had grown in a penetration tube beyond its J-groove weld and that primary water (which is a dilute boric acid solution) had leaked through the crack and corroded the shell of the pressure vessel so that a stainless steel liner was the only structure maintaining the pressure of the system. The nuclear industry now inspects the wetted surfaces of the heads of certain reactor pressure vessels in the course of each refueling outage in accordance with NRC Order EA-03-009. Thus, the wetted surfaces of the heads are inspected visually and the portions of the penetration tubes from the J-groove welds to two inches above the J-groove welds are inspected using ultrasonic, eddy current or dye penetrant techniques. The Applicants have realized that the inspections now conducted by the nuclear industry may not detect chemical wastage or other degradation in the regions of pressure vessel penetrations adjacent clearances behind some penetration tubes (such as vents in the their heads) until boric acid residues from evaporated leaking water are visually detected on the outer surfaces of the heads during refueling outages. It is an object of the present invention to provide a method of inspecting the penetrations of pressure vessels surrounding penetration tubes installed with clearance fits and welded to the pressure vessels. It is a further object to provide a method of inspecting such penetrations for degradation. With these objects in view, the present invention resides in a method of inspecting a pressure vessel having an inner surface and an outer surface with a penetration extending therebetween. An eddy current probe is passed through a penetration tube installed in the penetration with a clearance fit and welded at the inner surface of the pressure vessel. Eddy currents are induced in the pressure vessel as the probe passes through the penetration tube and degradation of the pressure vessel adjacent the penetration tube is determined based upon the eddy currents induced in the pressure vessel by the probe. In preferred practices, the probe introduces eddy currents into the pressure vessel while it passes from either the inner or outer surface of the pressure vessel. The preferred practice of the present invention was made to inspect the regions of reactor pressure vessels adjacent their vent tubes for corrosion wastage or other degradation. Thus, FIG. 1 shows a reactor pressure vessel 10 having a thickness 12 defined by an inner surface 14 and an outer surface 16 with a penetration tube 18 extending through a penetration 20. Such reactor pressure vessels 10 may have a shell 22 of carbon or low alloy steel or other suitable structural material and an inner liner 24 of stainless steel or other suitable structural material. The penetration tube 18 is shown as a vent tube, which may be sometimes referred to as a vent pipe or simply as a vent. Vent tubes in reactor pressure vessels may be Schedule 160 one inch diameter pipes made of stainless steel, Alloy 600 or other suitable structural material. Such penetration tubes 18 may be installed with clearance fits on the order of one to three thousandths of an inch and then welded to the inner surfaces 14 of the pressure vessels 10. The welds 26 may be J-groove welds where the penetration tubes 18 extend from reactor pressure vessel heads. As shown, there is corrosion wastage 30 in a region adjacent the penetration tube 18, which may not physically contact the outer surface of the penetration tube 18. It should be noted that the relative size of the clearance and the wastage 30 region is shown out of proportion in FIG. 1 for purposes of illustration. In the practice of the present invention, an eddy current probe 40 is passed through the penetration tube 18. Preferably, the probe 40 has a circumferential surface 41 and at least one circumferential coil. FIG. 1 shows a coil pair 42, including coils 44 and 46. The coil pair 42 induces eddy currents in the pressure vessel 10 as the probe 40 passes through the penetration tube 18. The two coils 44 and 46 may be electrically connected to oppose each other and operated in differential mode. The coils 44 and 46 may also operate in absolute mode. The two coils 44 and 46 may be operated at frequencies of between about 2 and about 100 kHz. For example, they may operate at 2, 4, 50 or 100 kHz. Probes 40 having a pair of circumferential coils 44 and 46 (sometimes known as “bobbin” coils) are commercially available from Zetec, Inc. of Issaquah, Wash. and other suppliers. Degradation of the pressure vessel 10 adjacent the penetration tube 18, such as for example wastage 30 of sidewall 28, is determined based upon the eddy currents induced in the pressure vessel 10 by the coil pair 42. Tests conducted at 2 kHz and at 4 Hz using an Alloy 600 tube inserted within carbon steel rings having inner diameters of 0.01 inch and 0.1 inch greater than the tube diameter (to simulate gaps of 0.005 inch and 0.05 inch, respectively, in a pressure vessel), showed that eddy current signal responses in the impedance plane can detect differences in the clearance gaps between pressure vessels and penetration tubes. In some practices of the present invention, the pressure vessel 10 may be inspected by introducing eddy currents into the pressure vessel 10 while the probe 40 passes from one surface 22 or 24 of the pressure vessel 10 to the other surface 22 or 24 of the pressure vessel 10. In a preferred practice, the entire thickness 12 of the pressure vessel 10 may be inspected in a single pass of the probe 40 through the penetration tube 18. In some practices of the present invention, the penetration tube 18 itself may be inspected by a probe 40 also having multiple eddy current arrays (which are shown as four arrays 62–68 by FIG. 1) while the pressure vessel 10 is being inspected for degradation. Each array 62–68 may have several eddy current coils (for example, four coils spaced at 90°) around the circumference of the probe 40, which may be circumferentially offset from the coils of the other arrays. Preferably, there are at least twelve circumferentially spaced coils in the arrays when the inner diameters of the penetration tubes 18 do not exceed 0.614″ inch. For inner diameters ranging from 0.614 to 0.815 inch, the array may consist of sixteen circumferentialy spaced coils. The eddy current coils in the arrays preferably are cross-point or, or plus point, coils and do not contact the inner surface of the penetration tube 18. A cross-point coil is in fact a differential pair of coils. In one practice, the primary examination frequency for such coils may be 400 kHz (differential mode only) and the secondary examination frequency may be 250 kHz. Such eddy current coils are commercially available under the designation “+Point” from Zetec, Inc. Preferably, the probe 40 is rotatable and the entire surface of the vent tube 18 from a height about six inches above outer surface 22 of the pressure vessel 10 to the bottom surface of the pressure vessel 10 can be inspected in a single vertical pass of the probe 40 while the pressure vessel is inspected for corrosion wastage or other indications of degradation. In some practices of the present invention (for example, where all wetted surfaces of a reactor vessel head are inspected), either before or after the region of the pressure vessel 10 adjacent the penetration tube 18 is inspected for degradation, the weld 26 may be inspected with an array of eddy current coils. FIG. 2 shows a rotatable tool 74 having an array of eddy current coils (represented by four coils 76) for inspecting the weld 26. In preferred practices, the weld 26 may be inspected by one rotation of the array of coils 76. The tool 74 shown in FIG. 2 preferably has up to thirty-two radially and circumferentially offset eddy current coils 76 or more to provide full coverage of the weld surface 72. As shown, the coils 76 may be urged by springs (represented by spring 78) against a plate 82. The coils 76 may have wear resistant caps or plastic surface riding shoes to extend their lives. The coils 76 may be cross point, or plus point, eddy current coils, such as +Point coils commercially available from Zetec, Inc., operated in differential mode. In some practices, the frequencies may be 250 (primary) and 600 (secondary) kHz in differential mode. The preferred operating range is 50–600 kHz and more preferably 100–600 kHz. As is shown in FIG. 2, the plate 82 may be supported on gimble screws (shown by screw 83) extending from a gimble ring 84 and yoke 86 arrangement so that the plate 82 may be oriented at any angle and the eddy current coils 76 may be maintained in constant contact with the surface 72 of the weld 26. As shown, the tool 74 may have a pivotally connected centering shaft 88 extending through the middle of the plate 82 with guides 90 that may be inserted into the penetration tube 18 to center the tool 74. The tool 74 may be manually positioned against the weld 26 (e.g., at the end of a hand held shaft) or positioned remotely using a robotic device. In a preferred practice, the weld 26 may inspected by one rotation of the array of eddy current coils 76. While a present preferred embodiment of the present invention has been shown and described, it is to be understood that the invention may be otherwise variously embodied within the scope of the following claims of invention.
052895114	summary	BACKGROUND OF THE INVENTION The present invention relates to a nuclear reactor used for power generation, research and the like, and in particular, a liquid-metal cooled nuclear reactor using liquid metal coolant such as sodium wherein the integrity or soundness of its coolant pressure boundary is improved and maintained. A fast breeder reactor using liquid sodium as a coolant will be explained as a typical example of liquid-metal cooled reactors. FIG. 2 is a schematic diagram illustrating the fast breeder reactor "Monju", wherein heat generated in a reactor vessel 1 including a reactor core 2 therein is transferred to a primary sodium coolant contained in the reactor vessel 1. Heat is then transferred to a secondary sodium coolant via an intermediate heat exchanger 3, and further to water in an evaporator 4 to generate steam therein. The steam is supplied, via a superheater 5, to a turbine 6 to drive a generator 7, thus generating electricity. The steam coming out of the turbine 6 is condensed into water in a condenser 8. The primary sodium system (encircled by single-dot and dash lines in FIG. 2) is composed of a primary sodium system pump 9 and a primary sodium system main piping 10 which in combination circulate primary sodium coolant through the reactor vessel 1 and the intermediate heat exchanger 3. A secondary sodium system is composed of a secondary sodium system pump 11 and a secondary sodium system main piping 12 which in combination circulate secondary sodium coolant through the intermediate heat exchanger 3, the evaporator 4, and the superheater 5. Further, a water/steam system is composed of a water feed pump 13 and a water/steam main piping 14 which in combination circulate the water/steam through the evaporator 4, the superheater 5, the turbine 6 and the condenser 8. The primary sodium system is usually installed in a nuclear reactor containment vessel, whereas the secondary sodium system and the water/steam system are installed outside the reactor containment facility. The coolant pressure boundary, i.e. the boundary between the vessels and piping containing the primary or secondary sodium coolant and the external region thereof, is extremely important in terms of safety. Therefore, in the design and manufacture of such a nuclear reactor as described above, it is imperative to be very careful not to allow the sodium to leak from the vessels and the piping, and the materials of these vessels and pipings should be of steel having a great strength at high temperature and having excellent resistances to sodium corrosion, neutron irradiation, thermal shock and the like. Further, in order to better deal with an emergency that would occur should there be leakage across the coolant pressure boundary, there have been provided with various precautionary measures such as the installation of the main piping 10 at higher locations, the arrangement of guard vessels 15 around the reactor vessel 1, the intermediate heat exchanger 3 and the primary sodium system pump 9, and further substitution of nitrogen for the ambient air. These countermeasures, however, more or less compromise the economical efficiency of the sodium-cooled reactor. SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a liquid-metal cooled nuclear reactor which is capable of alleviating the demand for the soundness of the steel walls of the vessels and the piping which accommodate the sodium coolant. The present invention provides an improved liquid-metal cooled nuclear reactor using liquid metal as a coolant and having a coolant pressure boundary which is the boundary between the vessels and piping accommodating the liquid metal coolant and an external region thereof. The improvement according to the present invention is characterized in that the entire or part of a region surrounding the coolant pressure boundary is occupied by a mass of a solidified liquid metal. In the present invention as described above, the vessels and the piping containing therein the liquid metal are embedded and sealed in the mass of solidified liquid metal, whereby this solid mass of solidified liquid metal forms the pressure boundary. As result, the burden for ensuring the soundness of the walls of the vessels and the piping can be substantially reduced.
	abstract	A method of producing a nuclear fuel product is provided. The method includes the steps of providing a core comprising aluminum and low-enriched uranium; and sealing said core in a cladding. The low-enriched uranium has a proportion of U235 below 20 wt %. The core includes more than 80 wt % of a mixture of UAl3 phase and UAl4 phase, and the mixture has a weight fraction of UAl3 phase higher than or equal to 50%, or the core includes more than 50 wt % of UAl2 phase. The core has a low-enriched uranium loading higher than 3.0 gU/cm3. The core includes less than 10 wt % in total of one or several material(s) taken from the list consisting of aluminum phase and aluminum compounds other than UAl2 phase, than UAl3 phase, and than UAl4 phase. A corresponding nuclear fuel product is also provided.
	abstract	A plasma electron flood system, comprising a housing configured to contain a gas, and comprising an elongated extraction slit, and a cathode and a plurality of anodes residing therein and wherein the elongated extraction slit is in direct communication with an ion implanter, wherein the cathode emits electrons that are drawn to the plurality of anodes through a potential difference therebetween, wherein the electrons are released through the elongated extraction slit as an electron band for use in neutralizing a ribbon ion beam traveling within the ion implanter.
059230401	summary	This invention relates generally to retaining samples of semiconductor wafers for viewing by electron microscopes such as a scanning electron microscope ("SEM"). BACKGROUND OF THE INVENTION Electron microscopes are used in semiconductor manufacturing operations to enable engineers to view the semiconductor wafers that are populated by features which are too small to visualize. Usually a sample of a disk shaped wafer is formed and an edge of that wafer or other pertinent portion is viewed under the electron microscope. The electron microscope magnifies the features of the sample and allows its configuration to be studied. Scanning electron microscopes are commonly utilized to determine whether features which are formed in the semiconductor wafer correspond to what was designed, intended or most desirable. Traditionally, the samples are secured to an adjustably positionable base in the electron microscope. The base may be connected to a sample holder which actually retains the semiconductor wafer samples. These samples are secured to an upstanding member on the sample holder using copper tape and curable adhesive. Commonly, the curable adhesive must be allowed to dry for several hours before the sample can be studied in the electron microscope. Thus, existing techniques require considerable effort to secure the sample for viewing. Perhaps more importantly, the procedure takes an excessive amount of time, thereby delaying the feedback to the design engineers. Therefore, it would be desirable to provide a technique for readily securing the wafer samples in the hostile environment inside an electron microscope. SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, a wafer sample retainer for an electron microscope includes a base and a sample holder removably connectable to the base. A spring biased member is arranged to contact a wafer sample and to secure the sample against the sample holder. In accordance with another aspect of the present invention, a wafer sample retainer for an electron microscope includes a rail, a base adjustably positionable along the rail, and a sample holder. The sample holder is removably connectable to the base. The sample holder includes an upstanding post. A spring biased member is mounted for pivotal rotation on the holder. The member has a free end pivotable towards and away from the post. In accordance with still another aspect of the present invention, a method of retaining a wafer sample for examination under an electron microscope includes the step of securing a sample retainer to a base. A spring biased arm is biased against the sample to secure the sample between the arm and the retainer. At least certain embodiments of the present invention are advantageous, among other reasons, because they simplify and expedite sample holding in electron microscopes.
	summary
	summary
059784318	abstract	A method of producing mixed oxide fuel pellets. The method uses oxides of at least two fissile elements and includes a mixing, milling, spheroidising and sintering step to produce a fuel pellet incorporating a neutron poison.
	abstract	Various geometric constructs are configured for use in modeling a system, for example a fissile system, using an analysis method, such as Monte Carlo, to model such systems based upon the interstitial regions formed by these geometric constructs. The various geometric constructs are configured to provide for modeling of, for example, complex arrays and lattices and allows for embedding of these constructs and virtual filling of arrays of these modeled units.
	description	This application is a Division of U.S. patent application Ser. No. 16/554,734, titled “Thorium Fuel Rod Structure and Assembly,” which is a Continuation of U.S. patent application Ser. No. 16/517,195, titled, “Thorium Molten Salt System for Energy Generation,” filed on Jul. 19, 2019, which is a Continuation of U.S. patent application Ser. No. 16/517,096, titled, “Thorium Molten Salt Assembly for Energy Generation,” also filed on Jul. 19, 2019. Not applicable. Not applicable. Field of the Invention The inventions disclosed and taught herein relate generally to a system for generating power using a Thorium-containing liquid molten salt fuel and, more specifically, an accelerator-driven Thorium molten salt system for generating process heat and/or electricity resulting from nuclear fission reactions. Attempts have been made to provide an accelerator-driven system for the generation of energy using fuel material containing Thorium. To date, such systems have primarily been focused on the use of a solid or molten lead (or other heavy metal) spallation target to generate neutrons used to initiate or sustain nuclear fission reaction and fuel initially comprising of mixtures of Plutonium and Thorium. Examples of such systems are discussed below. Ashley, Coats et. al, “The accelerator-driven Thorium reactor power station,” Energy, Vol. 164, Issue EN3 at 127-135 (August 2011 Issue) discusses an accelerator-driven Thorium reactor in which a particle accelerator injects high-energy particles into a molten lead target to release neutrons via the spallation process. The article indicates that a fissile starter, such as Plutonium from spent fuel, is required, and that the core of the system includes a series of fuel pins, each containing mixed-oxide pellets comprised of Plutonium and Thorium. A similar system is disclosed in Ludewig and Aronson, “Study of Multi-Beam Accelerator Driven Thorium Reactor” (March 2011). U.S. Patent Application Publication No. US2013/0051508, “Accelerator Driven Sub-Critical Core” purports to disclose “a fission power generator [that] includes a sub-critical core and a plurality of proton beam generators” where the generated proton beams “via spallation” generate neutrons for use in the system. The use of heavy metal spallation targets poses several challenges as does the use of fuel initially containing Plutonium or Uranium. The present inventions are directed to providing an enhanced system for energy generation providing benefits over, and overcoming shortcomings of, the systems and methods discussed in the materials referenced above, and other existing systems. A brief non-limiting summary of one of the many possible embodiments of the present invention is: A Thorium fuel rod assembly including first and second support elements; and a plurality of Thorium fuel rods positioned between the first and second support elements, where each Thorium fuel rod includes both (a) an outer fuel element containing a solid Thorium containing material that: (i) is in the general form of a fuel element rod having a longitudinal length; (ii) defines an interior cavity extending along at least a majority of the longitudinal length of the fuel element rod; and (iii) defines a plurality of fins that project radially outwardly; and (b) an inner core element formed from a Beryllium-containing material positioned within the interior cavity defined by the outer fuel element that: (i) is generally tubular in form and has longitudinal length; (ii) has a longitudinal length greater than the longitudinal length of the outer fuel element such that at least a portion of the inner core element extends out of the top of the outer fuel element; and (iii) defines an inner cavity extending along at least a majority of the longitudinal length of the inner core element. In this example, the outer fuel element and the inner core element are formed such that beam of high energy particles may be directed into the inner cavity of the inner core element such that particles forming the impinge upon a Beryllium nucleus within the core to produce a (p, n) reaction resulting in the emission of a neutron and the emitted neutron may interact with a Thorium nucleus in the outer fuel element to cause the Thorium nucleus to fission. Additionally, or alternatively, the present disclosure teaches a Thorium fuel rod that includes a fuel element containing solid Thorium, having a length and defining a central bore extending along at least a majority of the length; and an inner core element positioning within the central bore defined by the fuel element, the inner core having a length that extends along at least 75% of the length of the fuel element, the inner core defining an interior cavity, the interior cavity defining a void space, wherein the void space of the interior cavity is subject to a vacuum; and an end cap 416 sealed to the inner core element in such a manner that the vacuum within the void space is maintained, the end cap 416 being formed of a material capable of passing particles through the end cap 416 such that the particles can impinge upon an nucleus forming the inner core, wherein the particles are of a sufficient level that impingement of a particle upon an nucleus forming the inner core can induce a (p, n) reaction resulting in the emission of a neutron having an energy level of 0.7 MeV or greater. Additionally, or alternatively, the present disclosure also teaches a Thorium fuel rod comprising: a first rod-shaped element formed of a solid material containing Thorium, the rod defining a bore extending through at least the majority of its length, and wherein at least a majority of the length of the rod defining a plurality of radially extending fins; and a second rod-shaped element comprising Beryllium, the second rod-shaped element having a first section positioned within the bore defined by the first rod-shaped element and extending longitudinally along at least a majority of the length of the first rod-shaped element and a second section extending longitudinally outwardly from the bore. Other potential aspects, variants and examples of the disclosed technology will be apparent from a review of the disclosure contained herein. None of these brief summaries of the inventions is intended to limit or otherwise affect the scope of the appended claims, and nothing stated in this Brief Summary of the Invention is intended as a definition of a claim term or phrase or as a disavowal or disclaimer of claim scope. FIGS. 1A and 1B illustrate, in block and rough schematic form a first embodiment of an exemplary accelerator-driven sub-critical Thorium molten salt system 1000 for generating useful energy (for example in the form of process heat and/or electricity) in accordance with certain teachings of this disclosure. As reflected in FIG. 1A-1B, the exemplary system 1000 includes a particle beam source 200 for producing a particle beam. In the example of FIG. 1A-1B, the particle beam source 200 is adapted to vary the energy level of the produced particle beam such that the energy of the particles comprising the proton beam can vary between at least a first energy level and a second energy level, where the first energy level is at least approximately 4.5 MeV (and potentially up to or above 6 MeV) and the second energy level is at least 2.4 MeV. As reflected in FIG. 1A the particle beam source 200 includes a power input 201 for receiving the power required to drive the particle source. FIG. 2A provides details of the exemplary particle beam source 200 of FIG. 1. As reflected in FIG. 2, the exemplary particle beam source 200 includes a particle generator 202 for generating charged particles. In the example, of FIG. 2, the charged particles may take the form of a negatively charged hydrogen nucleus (for example, a neutral hydrogen atom with an added electron). The use of a neutral hydrogen atom with an added electron is exemplary for purposes of the present discussion and other charged particles may be used without departing from the teachings of the present disclosure. It should also be noted that the use of negatively charged particles is exemplary as well. One could implement the teachings of the present disclosure using positively-charged particles, although the references to positive and negative voltages in the discussion relating to how the particles are accelerated should be considered reversed when dealing with positively-charged particles (i.e., references to negative voltage should be replaced with positive voltage and vice versa). In the example of FIG. 2A, the negatively charged generated particles from the particle generator 202 are applied to a vacuum accelerator assembly 204 that includes several individual vacuum voltage chambers. The vacuum accelerator assembly 204 receives the negatively charged particles from the particle generator 202 and accelerates the generated particles to provide a high energy particle beam at its output. The high energy output beam from the vacuum accelerator assembly 204 is provided to an electromagnetic forming and steering assembly 208 that converts the received particle beam into an output particle beam having desired shape and directional characteristics. FIG. 2B illustrates an exemplary vacuum accelerator assembly 204 that may be used to form the particle beam source 200 of FIG. 2A. In the example of FIG. 2B, the vacuum accelerator assembly 204 is formed from ten individual vacuum voltage chambers 206a-206j. Each of the vacuum voltage chambers is coupled to a vacuum source and to a source of electrical power such that the voltage chamber can be evacuated to provide a vacuum interior and such that a relatively uniform electrical potential (voltage) level within the chamber can be established. The vacuum voltage chambers may be arranged in four groups, a first group comprising chambers 206a-206b, a second group comprising chambers 206c-206d a third group comprising chambers 206g-206h and a fourth group comprising chambers 206i and 206j. Chambers 206e-206f may collectively be used to form a nitrogen stripping chamber as discussed in more detail below. FIG. 2C generally illustrates the way the exemplary particle beam source 200 may be operated to generate particles having a first energy level. Referring to the figure, in this mode, during operation of the assembly 204, the first and second groups of vacuum voltage chambers (i.e., each of the voltage chambers 206a-206d) is energized such that the voltage potential in these chambers is positive, with the magnitude of the electrical potential increasing from chamber 206a to 206d. Because the particles generated by the particle generator 202 will have a negative charge, the positive voltage potential within chambers 206a-206d, and the differential in the magnitude of the positive voltage between chambers 206a-206d will cause the generate particles to move into and accelerate through chamber 206a towards chamber 206b, with the particles accelerating as they move through the identified chambers as the result of the increasing voltage potential from chamber 206a to 206b. The particles will move into chamber 206b and be accelerated, in the same manner, towards and into chamber 206c. The process will be repeated with the particles continuing to accelerate, and gain energy, as they pass into and through chamber 206d. In the illustrated example of FIG. 2C, during this first mode of operation, vacuum voltage chambers 206e and 206f are configured such that they have no net voltage potential. As a result, the particle moving through these chambers will not be accelerated but will—in essence—“coast” through the chambers 206e and 206f as a result of the momentum created by the movement and acceleration provided by chambers 206a-206d. In the illustrated example, chambers 206e and 206f, while not maintained at a specific voltage level, are filled with charged nitrogen gas to form a nitrogen stripping chamber. This gas will tend to strip off electrons from the particles traveling through chambers 206e and 206f, thus causing the moving particles to transition from negatively charged particles to particles having a positive charge. In the specific example under discussion, the stripping chamber will strip off the two electrons associated with the negatively charged hydrogen generated by particle accelerator to provide a positively charged particle consisting of a single proton. In the illustrated example of FIG. 2C, in the operating mode, the vacuum voltage chambers in the third and fourth groups (i.e., chambers 206g-206j) are activated such that the voltage levels within the chambers are negative, with the magnitude of the voltage levels within the chambers increasing from chamber 206g-206j. As a result of these established voltage levels, the positively charged particles traveling through chamber 206f will be attracted into chamber 206g and accelerated through chamber 206g to chamber 206h where they will be further attracted toward, and accelerated through, chambers 206i and 206j. Because of the increasingly negative voltages created within chambers 206g-206j, the particles passing through the chamber will continue to accelerate as they pass through the identified chambers to and from a high energy particle beam at the exit of vacuum accelerator assembly 204. In the example of FIG. 2B, the voltage levels of the chambers 206a-206j are established such that the energy level of the particles exiting the particle beam source 200 are at least on the order of approximately 4.5 MeV. FIG. 2D illustrates a second mode of operating the particle beam source 200 of FIG. 2A may be operated to produce a proton beam of a second energy level, where the second energy level is less than the first energy level discussed above. The operation reflected by FIG. 2C is like that discussed above with respect to FIG. 2B except that, in the example of FIG. 2C, only the vacuum voltage chambers in the first and third groups are activated such that no voltage potential is established within chambers 206b, 206d, 206h or 206j. As such, the protons traveling through the illustrated assembly will not be accelerated through those chambers and the energy level of the traveling protons will not increase as they pass through the chamber. As a result, the energy level of the protons emitted by the particle beam source 200 will be at a reduced energy level which, in the example of FIG. 2C is an energy level of at least about approximately 2.5 MeV and below the first energy level. While a specific exemplary proton generator was described with respect to FIGS. 2A-2D, it should be accepted that other particle beam sources may be used in the exemplary system 1000 of FIG. 1 without departing from the teachings of this disclosure. Additionally, while the exemplary particle beam source of FIG. 2A was illustrated and described as using a vacuum accelerator assembly having only ten voltage chambers, it should be understood that particle beam sources having fewer or more chambers may be used to carry out the teachings of this disclosure. Still further, while the above example describes operation of a particle beam generator to generate beams comprising particles having either a first or a second energy level it will be appreciated that the teachings of this disclosure can be used to provide a particle beam source where the particles comprising the provided beam can have multiple energy levels in excess of the two discussed herein and/or where the energy levels of the particles comprising the provided beam are well above the first energy level discussed herein, and/or below the second discussed energy level. For example, embodiments are envisioned wherein the first energy level exceeds about 10 MeV. Referring to FIG. 2A, the particle beam generated by the vacuum accelerator assembly 204 is provided to an electromagnetic forming and steering assembly 208 that transforms the received particle beam into an output beam having desired projection pattern (i.e., a desired shape) and directional characteristics. In the example of FIG. 2A, the electromagnetic forming and steering assembly 208 may take the form of a beam focusing/defocusing instrument. Such an instrument may, in some embodiments, take the form of a quadrupole magnetic assembly that may be energized to provide output beams having at least first and second shaped characteristics and multiple directional characteristics. FIGS. 2E1, 2E2, 2E3 and 2E4 illustrate exemplary first, second, third, and fourth beam shapes that may be generated using the exemplary electromagnetic forming and steering assembly 208 of FIGS. 2A-2D As reflected in FIG. 2E1, the beam provided as an output of the forming and steering assembly 208 may take the form of a focused “spot” beam or a beam having a relatively small primary point of focus. Through proper energization of the beam forming and steering assembly 208, the spot beam may be directed to a single point, to various points at different times or, in some embodiments, to scan across a general area. As reflected in FIG. 2E2, the forming and steering assembly 208 can adjust the overall size of the spot beam such that the general diameter of the beam can be greater than the diameter of the narrower spot beam reflected in FIG. 2E1. In addition to providing spot beams of first and second diameters, as reflected in FIG. 2E2, the forming and steering assembly 208 can also be used to provide a spot beam that varies, smoothly or in steps, from a first, relatively narrow spot, to a second, larger-diameter spot. FIGS. 2E3 and 2E4 reflect operation of the forming and steering assembly 208 in an alternate matter to generate a beam that takes the general form of a ring, with FIG. 2E3 illustrating a ring having a first inner and first outer diameter, and FIG. 2E4 illustrating a ring having a second inner and second outer diameter, where the second inner diameter is greater than the first inner diameter and where the second outer diameter is greater than the first. Although not illustrated in FIGS. 2E1-2E4, embodiments are envisioned where rings of various inner and outer diameters can be produced by assembly 208 and/or where rings of variable sizes may be generated such that the beam can be varied from a spot to rings of increasing inner and outer diameters until a maximum outer diameter is reached, down again to a spot through rings of progressively decreasing inner/outer diameters, and then have the process repeated again in a cyclic fashion. This variation can be accomplished by smoothly changing beam shapes or through steps. During such cyclic operation, the amount of time the system is maintained at the various shape and directional points can be varied such that the system, for example, dwells at a spot point for a first period of time, and then cycles through rings of various sizes for a second period of time, where the first period of time is longer than—and potentially multiples of—the second period of time. In addition to providing particle beams of varying shapes and varying general energy levels, the particle beam source 200 of the present example can be controlled to provide particle beams of varying intensity (or current). This can be accomplished by controlling the operation of the particle generator 202 to generate fewer or more particles at any given time. Referring to FIGS. 1A and 1B, in the exemplary system, the particle beam generated by the particle beam source 200 is provided to a Thorium molten salt assembly 300. FIGS. 3A-3H2 and 3J1-3J3 illustrate aspects of exemplary Thorium molten salt assemblies 300 that may be used in connection with the exemplary system 1000 of FIG. 1. Turning first to FIGS. 3A-3D, a first exemplary Thorium molten salt assembly 300 is illustrated. As reflected in the figure, the illustrated Thorium molten salt assembly 300 includes a main body 302 in the form of a large, tub-like structure. The main body 302 forms a vessel which may contain molten salt including Thorium. In general, the main body 302 should be formed from a substance that can withstand the environment that will exist within and outside of the assembly 300. In particular, the main body 302 should be formed from a material that is generally resistant to the chemical characteristics of the molten salt fluid that will be contained within the assembly 300. While a variety of different materials may be suitably utilized, nickel-based steel alloys, such as Hastelloy-N, may be used to form the main body 302 and, indeed, all components in contact with molten salts comprising the various exemplary molten salt assemblies discussed herein. Other potentially suitable materials include stainless steels or Incolloy. Additionally, coatings can optionally be applied to the identified (and other) materials to enhance their resistance to corrosion. As reflected in FIGS. 3A-3D the bottom of the main body 302 is generally rounded. This rounded bottom shape is believed to be beneficial in promoting optional fluid circulation within the assembly 300. The round bottom can also be of benefit in properly locating the assembly 300 within a shielding structure, as discussed in more detail below. In the example of FIGS. 3A-3D the main body 302 is coupled by, for example welding to a lower flange element 304. The lower flange element 304 defines a lower flange surface that, in turn, defines a plurality of bolt openings (unlabeled in FIGS. 3A-3B). An upper lid assembly 306 is coupled to the lower flange element 304. The outer portions of the upper lid assembly 306 define an upper flange section (not separately labeled) that is arranged in general alignment with the lower flange element 304. The upper flange section of the lid assembly 306 defines a plurality of bolt holes where the bolt holes are preferably of the same number and sized to align with the bolt openings of the lower flange element 304. While the number of bolt openings can vary, in preferred embodiments at least eight bolt openings are provided. In the example of FIGS. 3A-3B both the lower flange element 304 and the upper flange section of lid 306 defines sixteen bolt openings. Bolts 308 (only one of which is labeled in FIGS. 3A-3D are used to couple the lid 306 to the lower flange element 304. The use of bolts to couple the lid 306 to the lower flange element 304 is exemplary and other forms of coupling may be used. For example, screws, clamps and other mechanical assemblies may be use. In embodiments where ready separation of the lid assembly from the lower flange element 304 is undesirable, welding may be used. The use of bolts in FIGS. 3A-3D permits ready attachment and separation of the lower flange element 304 and the upper flange section of lid 306, simplifying the assembly and disassembly of the exemplary molten salt assembly 300. As illustrated in FIGS. 3A-3D, the bolt openings in the lid assembly 306 and the lower flange element 304 are such that they open outside the interior of the main body 302 in which the molten salt will be located. As such, the bolt openings do not give rise to any penetrations into the interior of the main body 302. Referring to FIG. 3D, which shows a top-view of the lid assembly 306, it may be seen that in the illustrated exemplary embodiment (in addition to defining bolt openings 310, only four of which are labeled in FIG. 3D) the lid assembly defines four impeller openings 312a-312d that pass from the outside of the lid assembly 306 into the interior of the main body. The lid 306 further defines two heat exchanger openings 314a and 314b that provide openings that extend from the exterior of the main body 302 into the interior of the main body 302. As best reflected in FIG. 3D, the lid 306 is a two-piece assembly that includes a generally ring-shaped main section of a first thickness and an inner disc-element 316 of a second thickness, where the second thickness is less than the first thickness. The window element 316 is intended to provide a “window” into the interior of the main body 302 through which certain types of particles, specifically at least the particles provided by the particle beam source 200 (and, potentially, neutrons) can pass. In the example of FIGS. 3A-3D, the window 316 is formed from a disk of any suitable material and may take the form of titanium, or aluminum titanium, or any other suitable material that will pass the particles provided by the particle beam source 200. The window element 316 should have a thickness sufficient to pass particle beams of the type necessary for operation of the systems described in this disclosure. The window element 316 maybe coupled to the ring-shaped section of lid 306 in any suitable manner. In some embodiments, the window element may be bolted onto, screwed onto, screwed into or otherwise mechanically coupled to the ring-shaped section of lid 306. In other embodiments, the window element 316 may be welded to, brazed to, integrally formed within or otherwise attached to the ring-shaped section. While the window element 316 is illustrated as being circular in shape in FIG. 3D, it should be understood that the window element 316 may take the form of other shapes such as, for example, a square, oval, or pentagon. In still other alternative embodiments, instead of a single large window element 316, multiple window elements are provided where the collection of window elements collectively define multiple passages through which high energy protons can enter the main body 302. As best shown in FIGS. 3A-3C, in the example under discussion, a plurality of motor-driven impeller pumps 318a-318d are provided. The general construction of each of the impeller pumps is shown in FIGS. 3E1-3E2. As reflected in FIGS. 3E1-3E2, in the exemplary embodiment under discussion, each of the impeller pumps 318 includes a variable speed motor 320 that is coupled to a shaft 330. The variable speed motor may take the form of any suitable variable speed motor such as a variable frequency induction motor, a brushless permanent magnetic motor or a switched reluctance motor. In the example of FIGS. 3E1-3E3, the variable speed motor 320 takes the form of a variable frequency driven induction motor. Although not illustrated, it will be understood that such a motor will include a rotor and a stator with windings and the windings will be coupled to a variable frequency drive that can provide power to the motor 320 in such a manner that the rotational speed of the motor can be controlled. As shown in FIG. 3E3, the motor shaft 330 extends downward from the motor and is coupled to an impeller element 332. In the example under discussion, the pump further includes a bearing assembly 322 through which the shaft 330 passes. As described in more detail below, the bearing assembly 322 of each impeller pump 318 in the example under discussion is positioned within one of the impeller openings of the lid 306. Because the impeller shaft has to pass through the top lid, the penetration should include high temperature seals to prevent the leakage of materials and gases from the interior of the main body 302 to the exterior of the body. The illustrated impeller pump 318 also include a pump body 324 that defines an upper fluid opening 326 and a lower fluid opening 328. The impeller pump 318 is designed such that, during operation, activation of the motor 320 will result in rotation of the shaft 330 and, therefore, rotation of the impeller element 332. The rotation of impeller element 330 will create a pressure differential across the inner chamber defined by the pump body 324 such that fluid will tend to be drawn into the upper fluid opening 326, flow through the chamber defined by pump body 324, and out the lower fluid opening 328. The rotational speed of the motor can be controlled to vary the pressure drop through the pump body 324 and, thus, the extent of the fluid flow through the pump. Referring to FIG. 3C it may be seen that the molten salt assembly 300 also includes a tubular member 340 positioned within the main body 302. The tubular member 340 includes openings at both its top and bottom ends such that liquid, such as a Thorium-containing molten salt, can flow into the bottom of the tubular member 340, up through the tubular member, and out, over the top of the tubular member 340. As best reflected in FIG. 3C, the bottom of the tubular member 340 can define a lower ledge structure. In general, the tubular member 340 defines an interior space within the main body 302 within which, and among, various structures can be positioned and through which liquid can flow. Referring to FIGS. 3B, 3C and 3F, it may be seen that the tubular member 340 and the impeller pumps 318 are dimensioned such that the upper fluid opening 326 opening of the pump body 324 includes a portion that extends below the top of the tubular member 340 and the lower fluid opening 328 of the tubular member 340 is positioned above the bottom of the tubular member 340. As reflected in the figures, the length of the tubular member 340 and the impeller pump 318 are such that the bottom end of the tubular member and the lower fluid opening 328 of the impeller pumps 318 are within the lower portion of the main body 302 such that an adequate flow path (to the left in the figure) is provided. In the specific example in the referenced figures, the lower fluid openings of the impeller pumps are within the lower one-third of the main body 302. The result of such positioning is that operation of the impeller pumps 318 will tend to cause fluid to flow up and out of the tubular member 340, over the top of the tubular member 340 and down through the main body 302 (and partially through the pump body 324). Thus, operation of the impeller pumps 318a-318d will tend to cause fluid flow within the main body 302 along the path generally reflected by the arrows in FIG. 3F. As will be appreciated, the fluid flow path depicted in FIG. 3F will exist for each of the four impeller pumps 318a-318d illustrated in FIGS. 3A-3F. As such, operation of the impeller pumps will tend to result in a circulating flow of fluid where fluid flows through a circulation path whereby it initially circulates into the bottom of the tubular member 340, flows up through the tubular member 340, then out and over the top of the tubular member 340, and down the outside of the tubular member 340, where it circulates back up and into the bottom of the tubular member and the cycle is repeated. In the embodiment of the molten salt assembly 300 previously described, and in all embodiments of the assembly 300 discussed herein a Thorium containing molten salt will be held in the main body 302. While the exact composition of the molten salt within the main body 302 will vary, embodiments are envisioned where the molten salt will contain at least a Lithium salt, a Beryllium salt and a Thorium salt, such that Lithium, Beryllium and Thorium exist within the molten salt. One suitable salt is a FLiBe salt containing dissolved Thorium. Other embodiments are envisioned wherein the molten salt does not include Beryllium but does include Lithium. One such salt is FLiNaK. In general, the quantity of molten salt within the main body 302 should be such that the upper level of the molten salt is over the top of the tubular member 340. Still further embodiments are possible where the molten salt is a chloride salt that contains chlorine, as opposed to fluorine. FIG. 3G1 illustrates a cross-section of the main body 302 and includes a dashed line 342 reflecting the general level of molten salt in the exemplary assembly 300. As reflected in FIG. 3G1, the upper level of the molten salt is both above the upper surface of the tubular member 340 and below the lower surface of the lid assembly 306. As such, an open region 346, not including any molten salt, but capable of containing gases, exists between the level of the molten salt and the lower surface of the lid 306 (and the lower surface of window element 317 for the interior region of the illustrated assembly). This open region 346 is further illustrated by the dark gray areas of FIG. 3G2. This open region 346 may be used to store gases generated as a result of fission processes that can occur within the main body 302. In certain embodiments, the open region 346 can initially be filled with an inert gas, such as argon, prior to the operation of the system. In the embodiment of FIGS. 3A-3F, impeller pumps 318a-318d are used to circulate the fluid in the main body 302. Alternate embodiments are envisioned wherein natural circulation is used to provide a fluid flow, generally along the path described above with respect to FIG. 3F. Such an alternate embodiment is depicted in FIGS. 3J1, 3J2 and 3J3. Referring to FIGS. 3J1 and 3J2, it may be noted that the overall structure of the illustrated exemplary molten salt assembly 300′ is like that described above in connection with FIGS. 3A-3F, with the primary differences being that the main body 302′ of the embodiment of FIGS. 3J1 and 3J2 is taller and narrower than the main body 302 of the first-described embodiment, the tubular member 340′ is longer and narrower than the tubular member 340 in the first-described embodiment and the helical heat exchanger assembly 500 (discussed in more detail) below is positioned about the upper two-thirds of the tubular member 340′ and not about the lower one-third of the tubular member 340′. In general, this arrangement creates a situation whereby the removal of heat through use of the helical heat exchanger assembly 500 creates conditions where natural circulation causes the fluid within the main body to flow along the paths identified by the arrows in FIG. 3G2. Advantages of the embodiment reflected in FIGS. 3J1-3J2, include simplification of the design and construction of the assembly 1000 through the elimination of the impeller pumps and the need for equipment to control the pumps; elimination of the need for impeller openings in the lid coupled to the main body 302′, thus reducing the number of penetrations that must be made into the main body, and elimination of the need to provide energy for operation of the motors driving the impeller pumps. The minimal penetrations required for implementation of this embodiment is reflected in FIG. 3J3, where only two penetrations 314a′ and 314b′ into the main body are provided, one for the inflow of a heat exchange fluid for the outflow of heat exchange fluid. In certain embodiments of the molten salt assemblies 300 described previously one or more solid Thorium fuel rods will be positioned and located within the interior of the tubular member 340 (or 340′). References herein to a solid Thorium fuel rod are intended to indicate that the fuel rod contains solid Thorium (as opposed to Thorium dissolved in a molten salt). As such, a solid Thorium fuel rod, as that term is used herein, may define internal openings or chambers. In embodiments as described above, Thorium fuel will be available within the interior of the tubular member 340 (or 340′) both in the form of solid Thorium within the Thorium fuel rod, but also in the form of dissolved Thorium within the molten salt. FIGS. 4A-4E illustrate one example of a novel Thorium fuel rod 400 constructed in accordance with certain teachings of this disclosure. Referring to FIGS. 4A-4E a Thorium fuel rod 400, is illustrated that includes an interior Beryllium core element 402 and an outer, solid Thorium-containing fuel element 404. In the illustrated example, the Thorium containing fuel element 404 is formed from a solid Thorium-containing material, such as metallic Thorium. Alternative embodiments are envisioned where the element 404 is formed from a Thorium-containing solid material (such as Thorium Dioxide) and an outer cladding In the example of FIG. 4A-4E, the outer surface of the Thorium fuel element 404 defines a series of fins that may be twisted to form a generally spiral-like outer structure. Alternative embodiments are envisioned wherein the fins on the Thorium fuel element are straight or generally straight. In the example of FIGS. 4A-4E, the Beryllium core element 402 is formed from a generally tubular element of Beryllium-containing material, such as metallic Beryllium. The generally tubular element is formed from a structure that defines an interior cavity 412 that, at any given cross-sectional point, defines an open cross section roughly in the form of a four-leaf clover surrounding a central circular opening. In the illustrated example, the Beryllium core element 402 has a length that is greater than the length of the solid Thorium fuel element 404 such that the Beryllium core element 402 extends out from the top of the Thorium fuel element. In one embodiment, the length of the Beryllium core element 402 is such that the solid Thorium fuel element 404 can be completely submerged within the molten salt while the top of the Beryllium core element is above the level of the molten salt. In general, the length of the Beryllium core element 402 extends along a majority of the length of the solid Thorium element 404, and preferably along at least 75% of the length of the solid fuel element 404. Embodiments are envisioned wherein the Beryllium core element 404 extends along 100% of the length of the solid fuel element 404. In one embodiment, the length of the Beryllium core element 402 is such that the solid Thorium fuel element 404 can be completely submerged within the molten salt while the top of the Beryllium core element is above the level of the molten salt. In general, the length of the Beryllium core element 402 extends along a majority of the length of the solid Thorium element 404, and preferably along at least 75% of the length of the solid fuel element 404. Embodiments are envisioned wherein the Beryllium core element 404 extends along 100% of the length of the solid fuel element 404. The cross-section of the Beryllium core element 402 at a given exemplary point is roughly reflected in FIG. 4E. As reflected in FIG. 4E, at any given point along the Beryllium core element 402, four solid Beryllium projections (410a, 410b, 410c and 410d) project into the interior of the core and define four lobe-shaped openings 412a, 412b, 412c and 412d and a generally circular central opening 414. The construction of the Beryllium core element 402 is such that, from the top of the element 402 to the bottom, the relative position of the solid Beryllium projections 412a, 412b, 412c and 412d change such that they form a general spiral down the interior of the core element 402. The result of such a construction is that they define a central cavity 412 having a circular cross-section that extends from the top of the core element 402 to approximately the bottom of the element 402 and generally clover-leaf openings 412a-412d that have the characteristics described below. In the illustrated example, the clover-leaf openings are such that, for any particular cross-section, there is at least a portion of at least one of four of the solid projections from a lower cross section that extend into the openings. This means that particles passing through the openings 412a-412d at any given cross-sectional point will always have at least some solid Beryllium beneath the openings upon which the particles may impinge. In general, the specific pitch of the spiral and the size of the projections and lobe-shaped openings will depend on the amount of power to be generated, the energy of the incident protons, and other factors. As reflected in FIGS. 4A-4D, the length of the Beryllium core element 402 is greater than the length of the Thorium fuel element 404 such that the core element 402 extends from the top of the solid Thorium fuel element 404. In at least one embodiment of the present example, the exemplary embodiment of FIG. 4A-4E the interior void space within the Beryllium core will be subjected to a vacuum and the void space of the Beryllium core sealed to maintain a vacuum. The sealing can be done through any suitable end cap 416 provided that the end cap 416 is formed of a material through which the particles provided by the particle beam source 200 can pass. For clarity, FIGS. 4D and 4E show the top end cap 416 removed from the element 402. Alternate embodiments are envisioned wherein the top ends of each Beryllium inner core are left open and all the ends are coupled to a manifold assembly that is attached to a vacuum pump to maintain a vacuum within the interior void space of the Beryllium core. In general, each of the Thorium fuel rods 400 is capable of generating power through fission reaction that can be caused to occur by directing a beam of energetic particles, such as protons with an energy level on the order of above 4.2 MeV into the interior of the Beryllium core. Particles in such a beam may pass into the void space of the Beryllium core and travel until they contact a Beryllium nucleus on one of the surfaces extending into the core. The collision of the high-energy particle (in one exemplary embodiment a proton) with the Beryllium nucleus can result in a (p, n) reaction that produces a neutron having an incident energy level on the order of 1 MeV or greater. One or more of such generated “fast” neutrons can strike a Thorium nucleus within the Thorium element 404 and cause a fission reaction in which the Thorium nucleus undergoes nuclear fission and releases a significant amount of energy. Depending on the desired operating characteristics of the assembly 1000 one or more of the Thorium fuel rods 400 may be positioned within the tubular member 340. In certain embodiments, the Thorium fuel rods to be positioned within the tubular member 340 are positioned between two support elements and the support elements are configured to rest within the tubular element 340 in such a manner that the solid Thorium fuel elements 404 in the fuel rods 400 are submerged in the molten salt, and the top portions of the Beryllium cores 402 within the fuel rods extend above the level of the molten salt. In these embodiments, the top positions of the fuel rods 400 are all positioned such they are under the window element 316 such that particles from the particle beam provided by particle beam source 200 can pass through the window 316 and into the various Beryllium core elements. FIGS. 4F1 and 4F2 illustrate an exemplary embodiment in which a single Thorium fuel rod 400 is positioned within the tubular member 340. In the illustrated example, as in the other examples discussed below, the Thorium fuel rod (or rods) 400 are positioned between an upper support element 430 and a lower support element 432. FIG. 4F1 illustrates a top-down view, showing where the Thorium control rod 400 is positioned within the window element 316. FIG. 4F2 provides a generally isometric view indicating the positioning of the assembly containing the Thorium fuel rod 400 relative to the lid 406. In the isometric view of FIG. 4F2—and the isometric views of the other Thorium rod structures discussed in more detail below, the portion of the Beryllium core element 402 that extends out of and above the solid Thorium fuel element 404 is not illustrated but should be understood to be present. FIGS. 4G1 and 4G2, 4H1, 4H2 and 4H3 illustrate alternate fuel arrangements that include either five Thorium fuel rods (FIGS. 4G1 and 4G2), thirteen Thorium fuel rods (FIGS. 4H1 and 4H2) or seventeen Thorium fuel rods (FIG. 4H3). As reflected in FIGS. 4G1, 4G2, 4H1 and 4H2, in certain illustrated embodiments the Thorium fuel rods to be used in the system are combined in a single solid Modular Thorium fuel package that includes the solid Thorium fuel rods (or rod) positioned between two support elements. The use of such a solid Modular Thorium fuel package can permit efficient refurbishing of the system 1000 described herein for subsequent operations. In addition, the use of a Modular Thorium fuel package as disclosed herein also permits the construction of systems of different power levels through the use of one fuel package in place of another. As briefly discussed in the previously illustrated embodiments, the Beryllium core elements are used to provide solid targets upon which high energy protons can impinge to generate high energy (for example over 0.7 MeV) neutrons that can strike Thorium to induce a fission reaction within the Thorium nucleus, generating additional high energy neutrons and energy. FIGS. 4G1 and 4G2 illustrate an alternative solid Modular Thorium fuel package in which a different approach is used to generate high energy neutrons for the fast fission of Thorium. Referring to FIGS. 4J1 and 4J2, a solid Thorium fuel assembly is illustrated that includes four solid Thorium rods (FIGS. 460a-460d) surrounding a single, central solid Beryllium rod 462. In the illustrated embodiment, the central solid Beryllium rod 462 is used as a target in which the high energy particle beam from the particle beam source 200 is projected. When such high energy particles strike the Beryllium rod 462, high energy (fast) neutrons can be generated which can exit the Beryllium rod and impact upon Thorium in the solid Thorium rods (460a-460d) to cause fast Thorium fission reaction. In the embodiments of FIGS. 4J1 and 4J2 the central Beryllium rod 462 is solid. As such, the particles impinging on the rod from the particle beam source 200 may not penetrate the lower portions of the Beryllium rod 462. To promote such penetration and utilization of the entirety of the Beryllium rod to generate fast neutrons, a Beryllium rod in the general form of the one described above in connection with FIGS. 4D and 4E may be substituted for the solid rod 462. In the embodiments discussed above in connection with FIGS. 4A-4H3 and 4J1-4J2 the Beryllium within the Beryllium rods may be in the form of solid Beryllium. Alternative embodiments are envisioned wherein the Beryllium within the Beryllium rods takes alternative forms, such as a Beryllium-containing salt (e.g., FLiBe). In such embodiments, the Beryllium-containing rods would comprise a vessel capable of containing a molten Beryllium-containing salt. Referring to FIGS. 1A and 1B and 3H1 and 3H2 a primary heat exchange assembly 500 is shown as extending around the central tubular member 312. The illustrated exemplary primary heat exchanger includes an input pipe 502 and an output pipe 504. The input pipe 502 is coupled to an input manifold 506 (illustrated in FIGS. 3H1-3H2) and the output pipe 504 is coupled to an output manifold 508. Notably, the lengths of the input and output pipes are sufficiently long so as to pass through the top level of the Thorium-containing molten salt, into the gaseous head maintained above the molten salt and potentially through the top lid of the main body. As reflected in the exemplary figures, a plurality of helically formed coiled pipes 510, ten in the illustrated example, have one end coupled to the input manifold 506 and another end coupled to the output manifold 508. As reflected in the figures, each of the helical pipes 510 winds downwardly around and back up the tubular member 12 from the input manifold to the output manifold 508. The illustrated number of helically formed coiled pipes is exemplary only and a different number of pipes could be used without departing from the teachings of the present disclosure. In the embodiment of FIGS. 1A-1B the primary heat exchange assembly includes a non-Thorium containing molten salt within the pipes 510 and input and output manifolds 506 and 508. As described in more detail below, this non-Thorium containing molten salt is circulated through the primary heat exchanger to remove heat from the Thorium molten salt assembly 300. Pumps (not illustrated) may be used to circulate the non-Thorium containing molten salt. Select details of an exemplary primary heat exchange assembly 500 are shown in FIGS. 3H1 and 3H2. FIG. 3H2 reflects the construction of an exemplary manifold 506. The illustrated manifold construction may be used for both the input manifold and the output manifold. Referring to FIG. 3H1 in the illustrated example, the manifold includes a box-like main manifold base 560 that defines a single input (or output) opening 562 of a first diameter at the top of the base 560 and a plurality of output (or input) openings 564 of a second diameter at the bottom of the base, only two of which are labeled in the figure. In this embodiment, the second diameter is less than the first diameter. In the illustrated example, the input 562 is axially offset from each of the plurality of openings 564, such that there is no straight flow path through the first opening 562 and any of the second openings 564. In the illustrated example, there are twelve (12) openings 562. Each of the second openings is coupled to a heat exchange coiled pipe 566. Use of the exemplary manifold described above permits the use of a plurality of lesser-diameter heat exchange coils (twelve in the example) within the main body 502, while requiring only two penetrations through the main body 502. In the exemplary embodiment discussed herein, heat generated within the main body 502 will be transferred to the molten salt flowing through the primary heat exchange assembly 500. In the illustrated example, that heat is transferred from the primary heat assembly 500 to a secondary heat assembly 512. Details of the secondary heat exchanger assembly 512 are shown in FIG. 1B. As reflected in FIG. 1B a secondary heat exchange path 516 is provided and arranged to absorb heat from the primary heat exchange coil. In the example of FIG. 1B, a vapor-forming liquid—such as water or carbon dioxide—is contained within the secondary heat exchange path (or coil) 516 and the piping attached to the secondary heat exchanged coil. A condenser 518 is also provided in the illustrated system as is piping (not labeled) that can transport liquid from the condenser 518 to the input of the secondary heat exchange coil and steam from the output of the secondary heat exchange coil to the input of the condenser. Not illustrated in FIG. 1A or 1B are pumps that can be used to circulate non-Thorium containing molten salt through the primary heat exchange loop and vapor-producing liquid (such as water or carbon dioxide) through the secondary heat exchange loop. In the example of FIG. 1, the energy transfer assembly 500 is used to transfer energy from the Thorium molten salt assembly 300 to a power generator assembly 600. High level details of such a system may also be found in FIGS. 1A-1B which reflect the application of the vapor generated by the heat exchange tank 512 to a turbine assembly 602 which, in turn, is coupled to an electric generator 604. In accordance with the general operation of turbine-driven electrical generators, the vapor produced by the energy transfer that occurs within the heat exchange tank 512 is used to drive/turn turbine 602 which turns the rotor of the electrical generator 604, producing electrical power at the output 606 of the electrical generator 604. In the illustrated system the output 606 of the electrical generator 604 is provided to a distribution element which distributes the generated electric power such that the majority of the generated power is provided to a main power output 608 and a portion of the generated power is provided to the power input of the proton generator 201 to drive the particle beam source 200. Because the operating of the system 100 of FIGS. 1A and 1B can generate nuclear particles and radiation emission, appropriate shielding 700 is provided to block the transmission of undesired particles and waves. FIG. 5 illustrates one exemplary way this shielding may be provided. In the illustrated example of FIG. 5, many of the components of the system 1000 are placed in a containment system 700. In the exemplary embodiment, the containment system 700 comprises a first containment structure 702 in which the particle generator 202 and the vacuum accelerator assembly 204 are located. Vacuum tubes (unlabeled) are coupled to the output of the vacuum accelerator assembly 204 and couple the output of the vacuum accelerator 204 to the forming and steering assembly 208, which is positioned in second containment structure 704. The molten salt assembly 300 is partially placed within the ground under the second containment structure 704 such that the lid of the molten salt assembly is accessible above ground. A third containment structure 708 is provided below the molten salt assembly 300. The space 706 between the molten salt assembly 300 and the third containment structure 708 may be filled with any suitable material, such as soil, borated material, concrete, or any other suitable material or blend of materials. Depending on the particular application of the system 1000, and the extent to which safety requirements dictate, the containment units 702, and 704 may take the form of a simple metallic structure (if the earth, rock or ground structure is capable of providing the desired shielding) or a structure intended to block the transmission of radiation (e.g., lead-walls or a lead-brick structure). The structure 708 should be formed of a material sufficient to contain molten salt in the possibility that there is damage to the molten salt assembly. Alternate embodiments are envisioned wherein the containment unit 700 comprises a structure having an internal dry core area into which the components of system 1000 to be shielded are placed and an external structure capable of holding water (or a water/chemical mix (e.g., borated water) which acts as a shielding material. In any or all the various embodiments of the containment unit 700 a surface layer of shielding material 702 (e.g., a lead blanket) may be used. In operation, at a very high level, the system illustrated in FIGS. 1A and 1B operates by powering the particle beam source 200 to generate a proton beam that is applied to the Thorium molten salt assembly 300. One or more of the protons within the proton beam may impact upon one or more of the atoms within the Thorium molten salt assembly 300 to either: (a) produce neutrons or (b) result in a nuclear fission reaction, which will generate heat and further neutrons. These generated neutrons may, in turn, impact and interact with other atoms within the Thorium molten salt assembly 300 to generate additional heat. The generated heat may be removed through operation of the primary and secondary heat exchange systems, and the removed energy may be converted to electric energy through use of the electric generation system 600, described above. The exemplary system 1000 of FIGS. 1A and 1B may be arranged to permit operation of the system in one of several alternative operating modes. In one operating mode, the proton beam provided by the particle beam source 200 is shaped and aimed such that the proton beam provided by the generator is directed through the window element 316 primarily into the Thorium containing molten salt within the tubular member 302 without a substantial number of the protons (or any) impinging upon the Beryllium cores of the Thorium fuel rods 400 positioned within the tubular member 340. In this operating mode, one (or more) of the protons from the proton beam from generator 200 may impact one (or more) of the atoms within the Thorium containing molten salt. For example, one or more of the protons from the proton beam may impact with a Lithium nucleus forming part of the molten salt. This interaction of the proton with the Lithium nucleus can cause a (p, n) reaction under which the Lithium nucleus absorbs the incident proton and emits a neutron. The neutrons emitted by such proton-Lithium reactions may be of varying energy levels, the greatest number of neutrons resulting from several such reactions would be at an energy level of between 0.1 and 0.7 MeV. As another example, one or more of the protons from the proton beam may impact with a Beryllium nucleus forming part of the molten salt to cause a (p, n) reaction in which the Beryllium nucleus may absorb the incident proton and produce a neutron at a particular energy level. The neutrons emitted by such proton-Lithium reactions may be of varying energy levels, the greatest number of neutrons resulting from several such reactions would be at an energy level of between 0.7 MeV and just over 1.0 MeV. Notably, the peak energy level of the neutrons emitted by the described proton-Beryllium (p, n) reaction will be greater than those emitted as a result of the described proton-Lithium (p, n) reaction. In a second operating mode, the proton beam provided by the particle beam source 200 may be shaped and aimed such that all or a substantial portion of the proton beam is directed through the window assembly in such a manner that a substantial number of the protons forming the proton beam are directed to one or more of the Beryllium cores of the Thorium fuel rods within the tubular member 340. This may be accomplished by forming the proton beam into a generally narrow beam shape and directing the narrow beam to the Beryllium core of the central Thorium fuel rod. This may also be accomplished by forming the proton beam into a ring and directing the ring such that it covers either the first group of Thorium fuel rods or the second group of fuel rods. Alternatively, the beam may be formed such that it transitions from a beam directed to the central Thorium fuel rod, to a first ring directed to the first group of fuel rods to a second ring directed to the second group of fuel rods. In general, forming and aiming the proton beam as described in connection with the second operating mode will tend to cause protons within the proton beam to strike Beryllium, thus generating neutrons through the process described above. In the embodiment of FIGS. 1A and 1B the average energy levels of the protons within the proton beam generated by the particle beam source 200 may be varied, depending on the operating mode of the system to prefer proton-Lithium interactions, thus producing neutrons with average energies below 0.7 MeV or to prefer proton-Beryllium interactions, this producing neutrons with average energies above 0.7 MeV. For example, when the system is operated in accordance with the first operating mode, the energy level of the protons provided by the proton generator may be set to be on the order of at least approximately 2.4 MeV and about 3.0 MeV. The size and form of the proton beam, along with the energy level of the proton beam and the fact that it is directed into the Thorium containing molten salt, are such that operation of the system in the first operating mode will tend to result in proton production of neutrons of an energy level on the order of between 0.1 MeV and just over 1.0 MeV with the peak energy level of the produced neutrons being on the order of about 0.7 MeV. In the same example, using the system described above in connection with FIGS. 2A-2D, when the system is operated in accordance with the second operating mode, the particle beam source 200 may be operated to produce a beam of protons where the protons forming the beam have energy levels on the order of 4.5 MeV. The size and form of the proton beam, along with the energy level of the proton beam and the fact that it is directed into the Thorium containing molten salt, are such that operation of the system in the first operating mode will tend result in proton production of neutrons of an energy level on the order of 0.1 MeV-1.2 MeV, with the majority of the produced neutrons having energy levels on the order of between 1.0-1.1 MeV. The likelihood of the particles from the particle beam 200 interacting with one or more of the atoms within the main body 302 will vary depending on a large number of factors including, but not limited to: the energy level of the particle provided by the accelerator, the particular nucleus involved in the potential interaction, and the other atoms within the body 302. The system 1000 takes advantage of some of these variables, and of the different types of reactions that can occur within the main body 302 to provide a system that can be operated in various modes, to provide various output characteristics. To understand the various modes in which the exemplary system of the present disclosure may be operated, it is helpful to understand some of the operations that can occur within the body 302. As briefly discussed above, in the system of FIGS. 1A and 1B, once neutrons are created within the main body 302 (e.g., by a high energy proton provided by the proton beam colliding with a Lithium nucleus or a Beryllium nucleus within the molten salt or as a result of a fission reaction occurring within the main body and producing resultant neutrons) some of the neutrons within the main body 302 may collide with a Thorium nucleus in the molten salt solution and cause a nuclear reaction. In the illustrated system, the nuclear reaction caused by the described collision can be one of at least two different types of reactions. In one type of nuclear reaction, referred to as a “fission” reaction, the nucleus of the involved Thorium atom will split into, typically two, smaller nuclei. Such a fission reaction will release a very large amount of energy and one or more neutrons. The energy released by the fission reaction will tend to increase the amount of energy stored in the molten salt within assembly 300 as heat. One or more of the neutrons released by such fission reaction may interact a Thorium nucleus within the molten salt fuel to cause further Thorium fission reactions. In a second type of nuclear reaction, known as “neutron capture” (or “neutron absorption”) the nucleus of the involved Thorium nucleus will absorb the involved neutron to form an isotope of Thorium, namely Thorium-233 (233TH). Thorium-233 is an unstable isotope that will decay to Protactenium-233. The decay of Thorium-233 to Protactinium occurs relatively quickly as the half-life of Thorium-233 is about 22 minutes. Protactenium-233 is an unstable element that will tend to decay to Uranium-233, with the half-life of Protactinium-233 being approximately 27 days. Uranium-233 is fissile material. As such, whenever Uranium-233 exists within the molten salt and neutrons are available—either from the particle beam source 200 or from the fission of other atoms within the molten salt—there is the potential that a neutron can strike a Uranium-233 nucleus causing a fission reaction. The fission reaction will produce heat. As with fission of the Thorium nucleus, fission of a Uranium-233 will result in the release of substantial energy and several neutrons, those neutrons may, in turn, interact with a Uranium-233 nucleus within the molten salt to produce a secondary Uranium-233 fission reaction, with a Thorium-232 nucleus to produce a Thorium-233 nucleus, or with other materials within the molten salt assembly 300. Some of the neutrons may pass through and escape the molten salt assembly. Once started and put into operation, the illustrated embodiment of FIGS. 1A and 1B can be self-sustaining in the sense that it can operate to provide usable energy without the addition of any other external power or energy as long as the energy generated by the system is sufficient to provide the power needed to drive and operate the particle beam source 200. Once the embodiment of FIGS. 1A and 1B begins to operate, the constituent components comprising the molten salt solution will change over time. At a high level, in certain embodiments, the composition of the molten salt will initially include no, or negligible, Protactinium and no, or negligible, Uranium. For purposes of this disclosure a negligible amount of an element is intended to refer to a substantially non-detectable amount of an element that exists in the absence of any intentional inclusion or addition of the element to the material. Alternate embodiments are envisioned wherein the molten salt could initially contain at least some Uranium. FIG. 6 provides a very crude, approximated, generalized relative indication of the amount of Thorium-232 and Uranium-233 that can exist for the system of FIG. 1 over time if it assumed that the neutron source provides a relatively constant supply of neutrons. As reflected in FIG. 6, at a time To, before the application of any neutrons to the system, the quantity of Thorium in the molten salt will be at its maximum level. As neutrons begin to be applied to the system, some of the neutrons will interact with the Thorium-233 causing one or more of the nuclear reactions discussed above. These nuclear reactions will cause the quantity of Thorium in the molten salt to decrease over time, as reflected by the line 232Th. As also reflected in FIG. 6, by the time T1, some of the Thorium that were subjected to a nuclear capture reaction will have converted to Protactinium-233 and some of those Protactinium-233 would have decayed to Uranium-233. As such, the number of Uranium-233 in the molten salt will begin to increase over time starting at time T1. It should be appreciated that the representation in FIG. 6 is intended to be a very crude approximation of the relative number of Thorium-232 and Uranium-233 in the molten salt and that the actual shape of the represented curves will not necessarily be in line with the specific curve characteristics illustrated in FIG. 6 (and can potentially be controlled as described below). As those of ordinary skill will appreciate, the likelihood of a nuclear reaction occurring when a specific nucleus is bombarded with a beam of particles having a specific incident energy level, is sometimes described by a concept known as the nuclear cross-section. In general, a nuclear cross-section is a quantity that expresses the extent to which neutrons interact with particles of a given energy level. Nuclear cross-section information may be obtained through consultation of JANIS (the Java based Nuclear data Information System) provided by the Nuclear Energy Agency and accessible at https://www.oecd-nea.org/janis/ FIGS. 7A-7D provide JANIS-generated graph reflecting the cross-sections of various isotopes that may exist within the molten salt assembly 300 of FIGS. 1A-1B. Referring first to FIG. 7A, data reflecting the cross-section of Thorium-232 as a function of the incident energy is illustrated for both the absorption reaction, reflected by line 2, and for the fission reaction, reflected by line 4. Also illustrated in FIG. 7A are the fission 6 and absorption 8 cross-sections for Uranium-233 as a function of incident energy. As the graph indicates, for Thorium-232 and Uranium-233, the cross-sections for the absorption and fission reactions vary as a function of incident energy in such a manner that the cross-section values may be considered to lie, for any incident energy level, within one of four regions. FIG. 7B illustrates the cross-sectional information of FIG. 3A divided into four regions. In the first region, designated by Roman numeral I, the absorption cross-section of Thorium-232 is comparatively large relative to the negligible fission cross section and decreases in a relatively smooth manner with respect to changes in the incident energy level. In that same region, the fission and absorption cross-sections of Uranium-233 exceed the absorption cross-section of Thorium-232. In the example of FIG. 3A, Region I extends from neutron energy levels of roughly 1×10−11 to roughly 1×10−6 mega electron volts (MeV). Within the second region, designated by Roman numeral II, the absorption and fission cross-sections of Thorium-233 and Uranium-233 vary substantially in a resonate-like manner with changes in the incident energy level. Over this region there are specific energy levels where the absorption cross-section of Thorium-232 exceeds both the fission and absorption cross-sections of Uranium-233. It may be further noted that, over this region the absorption cross-section of Thorium-232 reaches its maximum value. In the example of FIG. 3A, Region II extends from neutron levels of roughly 1×10−6 to roughly 0.007 MeV. Within the third region, designated by Roman numeral III, the absorption cross-section of Thorium-232 continues to remain comparatively large relative to the negligible fission cross-section of Thorium-232. Over that same region, the fission cross-section of Uranium-233 exceeds both the absorption cross-section of Thorium-232 and the absorption cross-section of Uranium-233. In the example of FIG. 3A, Region III extends from neutron levels of roughly 0.07 MeV to roughly 0.8 MeV. Finally, within the fourth region, designated by Roman numeral IV, the fission cross-section of Thorium-233 is comparatively large relative to its absorption cross section, and both the fission and absorption cross-sections of Thorium-232 vary in a roughly smooth manner with variations in the incident energy level. Over this same region, the fission cross-section of Uranium-233 exceeds the fission cross-section of Thorium-233 and the absorption cross-section of Uranium-233. The system of FIGS. 1A and 1B takes advantage of the different cross-sections of the various atoms that will exist within the Thorium molten salt assembly 300 to implement a novel operational and control scheme wherein the incident energy level of the particles provided by the particle beam source 200 are varied over time to adjust the operating state of the molten salt system such that the energy provided by the system is predominantly generated by fission of Thorium-232 at certain times, predominantly by fission of Uranium-233 at other times, and—potentially—fission of both Thorium-232 and Uranium-233 at other times. Examples of how such a novel operating method may be implemented are generally reflected in FIGS. 7A-7E. At an initial time, the system of FIGS. 1A and 1B is operated such that the incident energy level of the neutrons provided by particle beam source causes operation of the system in Region IV. This operating region is highlighted in FIG. 7C. This will be accomplished by controlling the energy level of the particles provided by the particle beam source 200 such that they are at a sufficiently high level that interaction between such particles and the Beryllium within the molten salt can result in the generation of neutrons having energy levels within the level of the neutrons within Region IV (i.e., over about 0.7 MeV). During this period of operation, given the small quantity of Uranium-233 in the molten salt assembly 300, the energy generated by the system 1000 will be predominantly generated through fission of Thorium-232. However, as reflected in FIG. 7C, such operation will also result in a non-trivial number of absorption reactions involving Thorium-232, which will ultimately result in the formation and buildup of Uranium-233 in the system 300. As the number of Uranium-233 atoms in the system increases, a point will be reached where the level of Uranium-233 is such that fission of Uranium-233 would be enough to provide the desired output power. At that point, the system of FIGS. 1A and 1B 1 can transition to operate in Region II, by adjusting the incident energy level of the provided proton beam to a level where it will tend to cause interactions between the incident protons and the Lithium within the molten salt assembly such that neutrons having energy levels within Region III are generated by proton-Lithium (p, n) reactions (i.e., neutrons with energy levels between about 1×10−6 to 0.007 MeV). Operation in this region, provides neutrons wherein fission of Uranium-233 is possible, but the fission of Thorium-232 as the result of neutrons generated as a result of bombardment of particles from the particle beam source 200 is negligible. In that same region, the neutrons within the molten salt assembly 300 will—in addition to causing fission reactions of Uranium-233, also cause absorption reactions involving Thorium-232, thus providing a source of Uranium-233 for sustained operation. The system can then operate in Region III for a sustained period of time, providing the desired power output until the number of Uranium-233 atoms in the system is inadequate to support the desired power output, or until other conditions warrant a change in the operation of the system or system shut down. Operation in this Region is reflected by the highlighted portion on FIG. 7D. FIGS. 8A-8H illustrated examples of how the particle beam from the particle source 200 may be directed, shaped and controlled to operate the exemplary systems described herein within the various Regions discussed above in connection with FIGS. 7A-7D. As described above, in the exemplary systems under discussion particle beam source 200 may be used to generate particles (such as protons) having incident energy levels of above 4.5 MeV when the generation of neutrons having energy levels of above 0.7 MeV through a (p, n) reaction of the incident particles and Beryllium, and the direct fission of Thorium, is desired. FIG. 8A, illustrates an example of system 1000, from a top-down perspective, that uses five Thorium fuel rods where of the Thorium fuel rods includes a Beryllium core generally as described above in connection with FIGS. 4A-4D. In the example of FIG. 8A, the proton beam provided by the particle beam source 200 is a solid beam spot concentrated on the Beryllium core of the central Thorium fuel rod. As such the incident high energy protons will potentially collide and interact with Beryllium within the Beryllium core, producing a (p, n) reaction that results in the generation of relatively high-energy (sometimes referred to as “fast” neutrons). These generated “fast” neutrons can then interact with a Thorium nucleus in the solid Thorium fuel element surrounding the Beryllium core to cause a Thorium fission reaction to occur which, in turn, will generate more fast neutrons that can cause further Thorium fissions to occur. FIG. 8B illustrates a similar situation, but this time with the high energy proton beam from the proton beam source 200 being directed to the Beryllium core of the Thorium fuel rod at the top of the image. As will be appreciated, using the approach of FIGS. 8A and 8B, a beam spot of particles of the appropriate type and energy level (e.g., protons with energy levels at or above about 4.5 MeV) provided by the proton beam source 200 and the proton beam may be directed to the Beryllium cores of each of the Thorium fuel rods in the system individually. Thus, by applying the beam for a limited period to each of the Beryllium cores, a supply of fast neutrons can be provided for each of the solid Thorium fuel elements to maintain at least some level of Thorium fission within the system. This energy released by such Thorium fissions can be used to operate the system. FIG. 8C reflects an alternate way the system 1000 can be operated to provide fast neutrons and to produce Thorium fissions. In the example of FIG. 8C, the high energy particle beam from the particle beam source 200 is focused at a spot within the molten salt within the molten salt assembly 300. Because at least some of the particles from the beam will have energy levels in excess of 4.5 MeV, the particles can strike a Beryllium within the molten salt, thus causing a (p, n) reaction and producing a fast neutron that can, in turn strike a Thorium atom within the molten salt or within a solid Thorium fuel element (if present) to cause a Thorium fission reaction. FIGS. 8D and 8E illustrate still other alternate approaches for producing fast neutrons and inducing Thorium fission reactions. In these examples, the beam size of the high energy particle beam from the particle beam source 200 is adjusted such that some of the particles comprising the high energy beam will impinge on both the Beryllium core of one or more Thorium fuel rods (thus producing fast neutrons and inducing Thorium fissions as generally described in connection with FIGS. 8A and 8B) and others may impinge upon Beryllium atoms within the molten salt in the assembly 300 (thus inducing the generation of fast neutrons and Thorium fission as described above in connection with FIG. 8C). Still further alternate embodiments are envisioned wherein the high energy particle beam provided by the particle beam source 200 is “strobed” from a small diameter beam spot (as generally illustrated in FIG. 8A) to a larger diameter beam spot (as generally illustrated in FIG. 8E) to vary the manner in which fast neutrons are generated. FIGS. 8F-8H illustrate yet another alternate mode of generating fast neutrons. In this mode, the particle beam from the particle beam source 200 is configured to a have a ring shape and the dimension and direction of the provided ring is varied to impinge upon the Beryllium cores of the Thorium fuel rods within the system and/or the molten salt within the assembly 300. It should be noted that, while the above discussion focused on the manner in which fast neutrons may be generated and the fast fission of Thorium induced, operation of the system as described above will also result in a number of different nuclear reactions including the generation of neutrons having lower energy levels (sometimes referred to as “thermal” neutrons) and the fission of any fissionable materials (Uranium-233 for example) that may exist within the assembly. This is because the neutrons generated within the assembly (either through reactions involving a particle from the particle beam source 200 or as the result of fission reactions within the assembly) will be of various energy levels, such that—while proton-Beryllium (p, n) reactions, proton-Lithium (p, n) reactions (generating neutrons with lower, potentially thermal, energy levels) will be occurring, as will fission reactions of Thorium and, likely, fission reactions of Uranium-233 (if present). Absorption reactions will also be occurring, as will non-reactions where some of the generated neutrons simply escape the assembly without producing any nuclear reactions within the assembly. Moreover, neutrons generated with “fast” energy levels will tend to have their energy levels reduced as they pass through the materials and elements within the assembly 300 (such as the molten salt) such that they will become thermal neutrons that can be involved in a Uranium-233 fission operation or a Thorium-232 absorption operation. Operation of the system as described above, however, to direct high energy particles (specifically protons) at energy levels sufficient to produce a Beryllium (p, n) reaction will tend to promote the generation of fast neutrons and the direct fission of Thorium within the assembly 300. FIGS. 8A-8H (and primarily FIGS. 8C-8E) also illustrate how the exemplary systems described herein may be operated to promote the generation of thermal neutrons and Uranium-233 fission reactions. By operating the particle beam source 200 to provide particles (such as protons) with energy levels of between about 2.5 MeV and 4.5 MeV, a situation may be created wherein proton-Lithium (p, n) reactions are promoted. These reactions will tend to produce neutrons having an energy level below the fast neutrons generated by a Beryllium (p, n) reactions. These neutrons will typically be at a level below that require for Thorium fission, but at a level where they can be involved in both a fission reaction involving a Uranium-233 reaction, or an absorption reaction in which Thorium-232 is ultimately converted into Uranium-233. Thus, by operating the system 1000 in this manner, Uranium-233 fissions may be promoted. Again, it should be noted however that, because any fission reactions involving of Uranium-233 or Thorium-232 that occurs during a time when the lower energy particles (such as protons) from the particle beam source 200 are provided to the assembly 300 will produce fast neutrons that can result in a fission reaction involving Thorium-232, such that fission reactions involving Thorium-232 can occur within the assembly 300 alongside fission reactions of Uranium-233. Considering the above, it should be clear that the novel system 100 described herein can, by adjustment of the energy level of the particles provided by the particle beam source 200, and by controlling the direction and shape of the provided particle beam, be operated in manner to promote: (i) generation of fast neutrons and the direct fission of Thorium (when high energy particles (such as protons with energy levels above 0.7 MeV) are provided) and (ii) generation of thermal neutrons with energy levels below 0.7 MeV and the fission of Uranium-233. FIG. 9A illustrates one exemplary method of operating a system 1000 constructed in accordance with the teachings of the present disclosure. Over a first initial time period 902, the system will be operated from an external power source (such as a diesel generator) that will provide the input power to the particle source 200. Over this time period, the system 1000 can be operated to promote the generation of fast neutrons and the direct fission of Thorium through the generation of a high energy particle beam and the direction of that particle beam to the Beryllium cores of any Thorium fuel assemblies within the system 1000. Over this time period, the output energy level of the system can be monitored at a step 904. Once it is determined that the energy being produced by the system is adequate to provide power necessary to power the particle beam source 200, the external power source can be removed, and the system can begin to operate without the addition of any external power. After the system begins to operate without the provision of external power, it can continue to operate in accordance with Region IV, described above, where direct fission of Thorium is promoted and used to provide a desired level of energy output. This is reflected by operating step 906. As described above, over this period, Uranium-233 will begin to be produced within the assembly. At step 908, the level of Uranium-233 in the assembly can be monitored and, when it is determined that the quantity of Uranium-233 in the assembly is sufficient to support the desired energy level output through fission of Uranium-233, the operation of the particle beam source 200 can be adjusted to provide particles (such as protons) of a lower energy level to promote Uranium-233 fission reactions in a Region II operation. Notably, over this region, Uranium-233 will continue to be produced as the result of the Thorium-232 absorption reaction occurring within the system. Operation in this mode is reflected by step 910. It is anticipated that the systems 1000 described herein can be operated as described above for Step 910 for most of its operating time, for example over a period of between 5-10 years. Of note, in embodiments where the molten salt does not include Beryllium (for example when the molten salt is FLiNaK, the generation of fast neutrons through use of the particle beam source 200 will be through bombardment of the Beryllium cores within the Thorium fuel rods. In addition to producing desired energy (and generating Uranium-233 for later use) operation of the system 1000 in accordance with a Region IV moderation can beneficially reduce (or “burn up”) undesirable waste elements that could otherwise build up within the assembly 300. In general, nuclear fission reactions typically result in the production of by-products generally known as fission products. Certain fission reactions, such as the fission of Uranium-233 can result in the production of fission products in the form of actinides, including trans-uranium (TRU) actinides, and other long-lived fission products. In general, such by-products are undesirable because they typically emit relatively high amounts of radiation and have relatively long-half-lives. The handling, disposing and processing of such TRUs and long-lived fission products is subject to various regulations and safe-handling precautions that must be followed when dealing with such materials. Many TRU's and long-lived fission products can be broken down into elements and isotopes that are less radioactive and/or have substantially shorter half-lifes such that they are safer to handle than the original fission products. Such TRUs and long-lived fission products can be broken down though interactions with neutrons having certain incident energy levels, typically those on the order of the “fast” neutrons, whose generation can be promoted through operation of the system as described above. Thus, operation of the system in a manner where generation of “fast” neutrons is promoted to reduce the amount of undesirable waste in the system. The exemplary system 1000 described above may be operated in various ways to reduce the amount of undesirable waste in the system. One exemplary operation is reflected in FIG. 9B. In this operational mode, the system can be operated as described above in connection with FIG. 9A for most of its operating life. This operation is reflected at Step 912. Towards the end of its operating cycle, however, the system 1000 can be transitioned to operate in the manner described above, where the generation of fast neutrons is promoted. This is reflected in Step 914. The system 1000 could then be operated at this Step 910 until the desired reduction of waste produces has occurred. Note, that embodiments are envisioned where the “burn-up” Step 914 is accomplished at a location separate from, and using a particle beam source, different from the location at which the main running Step 912 occurs. For example, embodiments are envisioned wherein a system 1000 constructed in accordance with the teachings of this disclosure is operated for a lengthy period of time at a location where energy generation is desired and then the Thorium assembly 300 is removed and taken to a different location where it can be bombarded with high energy particles that result in the generation of fast neutrons for purposes of waste burn up. In accordance with other embodiments, the systems 1000 described herein may be operated to “burn-up” waste materials during the main period of operation of the assembly. Such embodiments are particularly suited for applications where the energy output demands from the system are not constant. For example, if the system of FIGS. 1A-1B is used to generate electricity, the demand for electricity may vary depending based on time, day, month, or weather conditions. For example, if the system of FIGS. 1A-1B is used to power a remote manufacturing plant, the plant may be operational—and thus have high energy demands—only weekdays during normal business hours or only during certain peak months of the year. In such applications, after an amount of Uranium-233 has been generated that is sufficient to provide the desired power output, the system could be operated in Region II during the periods of high energy demand (such that the production of energy though fission of Uranium-233 is maximized) and then be operated in Region IV during periods of low energy demand, such that the high-energy neutrons generated by the system during such operational periods can be used to burn some of the TRUs and long-lasting fission products within the system, thus reducing the total overall waste produced by the system. This mode of operation is generally discussed in FIG. 9C. Referring to FIG. 9C, the system may initially be operated in accordance where the generation of thermal neutrons and the fission of Uranium-233 is promoted as discussed above at Step 950. During these intervals, the energy demand of the system can be monitored at Step 952. If the output demand of the system is not below a certain threshold (or in alternate embodiments if the output demand is above a certain threshold level), the system will continue to operate in a manner where thermal-neutron production and Uranium-233 fission is promoted. If the energy demand, however, is below a certain threshold (and, potentially predicted based on data to remain at that lower level for a particular period time) the operation of the system can be adjusted to promote the generation of fast neutrons and the potential burn-up of undesired waste. This is reflected in Step 954. While operating within Step 954, the output demands of the system can be monitored (at Step 956) and, if they increase, the system can transition back to operating in the manner described above in connection with Step 950. In the embodiments described above, the system 1000 is designed (and the particle beam source 200) operated so that the system—not including the neutrons generated as a result of the operation of the particle beam source 200—is operated in a sub-critical manner. As used herein, operation of the system in a sub-critical manner means that, if the power to the particle beam source is removed such that the particle beam source provides no particles to the system, the number of neutrons generated within the Thorium molten salt assembly 300 as the result of fission or other nuclear reactions will be insufficient to sustain permanent and on-going fission reactions within the system. As such, in the embodiments described above, substantial nuclear fission reactions within the system will ultimately cease if the particle beam source ceases to operate. This sub-critical operation of the described systems is believed to provide a safety margin that can eliminate (or at least substantially reduce) the potential for an uncontrolled series of nuclear reactions (sometimes referred to as a “meltdown”) of the assembly 300. In the embodiments discussed previously in this disclosure, the neutrons relied upon to support the nuclear reactions desired for system operation were generated within the Thorium molten salt assembly 300. Alternate embodiments are envisioned wherein the neutrons relied upon for operation on of the system are primarily generated outside the assembly 300. FIG. 10 illustrates one of many alternate embodiments of the system 1000 of FIGS. 1A and 1B in which fast and/or thermal neutrons desired for operation of the system are generated outside of the molten salt assembly. Referring to FIG. 10, the alternate embodiment includes a particle beam source 200, a Thorium molten salt assembly 300, a heat transfer assembly 400, a generator 500, and a shielding assembly 600 substantially as described above. The system 1000′ also includes, however, a neutron source target 230. As described in more detail below, in this alternate embodiment, the neutron source target 230 comprises one or more elements that are bombarded with the particle beam from the particle beam source 220 and that, in response, generates neutrons having various desired energy levels. FIGS. 11A-11F illustrate exemplary neutron source targets 230 that may be used in connection with the embodiment of FIG. 10. For purposes of the following discussion, it is presumed that the particle beam source 200 is as described above in connection with FIGS. 2A-2D in that it can generate protons having energies at two levels, where the first energy level is above 4.5 MeV and the second energy level is between about 2.5 MeV and just below 4.5 MeV. Referring first to FIG. 11A, an exemplary neutron target source 252 is illustrated that comprises a core of neutron reflecting/shielding material (such as graphite) 254 defining an opening passing therethrough and a neutron-generating target 256 positioned within the opening. FIG. 11A illustrates the cross-section of such a structure. In operation, particles from the particle beam source 200 (protons for example) enter the core and pass through the opening on the core and strike the neutron generating target 256. The interaction between the high energy proton beam and the target generates one or more neutrons that pass through the opening within the core and out of the neutron generator 252 where they can be provided to the Thorium molten salt assembly 300 to produce reactions as generally described above. The neutron generating target 256 can take the form of any target that includes a material that, when struck by highly energized particles, emits neutrons. In the example of FIG. 11A the neutron generating target 256 comprises a cone coated with a sufficient amount of Lithium (Li) such that the interaction with the Lithium on the cone with the incident proton beam provided by the particle beam source 200 will cause a Lithium (p, n) reaction producing neutrons at a generally thermal energy level. FIG. 11B illustrates such a Lithium cone 256. When the neutron generating target 256 is Lithium, the incident energy level of the proton beam provided by the accelerator should be greater than about 2.4 MeV to generate the desired neutron density for operation of the system 1000′. As such, the embodiments of the accelerator discussed above that can generate proton beams on the order of 3 MeV can be used with the neutron generating target of FIG. 11B. In the embodiment of FIG. 11B bombardment of illustrated neutron generating target 256 with a proton beam greater than or about 2.4 MeV will result in the generation of neutrons having an energy level of between roughly about 1×10−5 and 0.07 MeV. Neutrons at such an energy level can be applied to the Thorium molten salt system 300 to cause the reactions discussed above during periods where the generation of thermal neutrons is promoted (e.g., fission of Uranium-233). FIG. 11C illustrates an alternative neutron generating target 258. In general, the alternate neutron target 258 is like that of target 256, but it contains Beryllium, instead of Lithium. The target 258 operates generally as described with respect to the target 256, with the exception that the impingement of high energy particles on the Beryllium of target 258 will cause the generation of neutrons having a generally higher energy level than the neutrons generated using the Lithium target 256 of FIG. 11B. In general, the neutrons generated through bombardment of the Beryllium target of FIG. 11C will have an energy level in excess of 0.7 MeV. In the embodiment of FIG. 11C, when the Beryllium target 258 is used the incident energy level of the protons applied to the target should be in excess of 4.5 MeV. The various particle accelerators discussed above in connection with FIGS. 2A-2D would be suitable to provide protons of such an energy level. In some embodiments of the system of FIG. 10, it will be desirable to simultaneously provide neutrons having different energy levels and, specifically at energy levels around those using the Lithium target 256 described above and the Beryllium target 258 described above in connection with FIG. 11C. For such embodiments, it may be possible to utilize the particle beam source 200, discussed above, in combination with two neutron generating targets. Such an arrangement is shown in FIG. 11D, where both Lithium and Beryllium neutron targets are provided and the particle beam can be directed to one or the other target (or alternated between the two) to promote the generation of thermal or fast neutrons, respectively. FIGS. 11E and 11F illustrate still further alternate embodiments for generating fast and thermal neutrons. In the example of FIG. 11E a single neutron generating target is provided that includes upper segments 264 formed of Lithium and a lower core 266 formed of Beryllium. In this example, a particle beam of relatively high energy level particles and a beam shape in the form of a spot can be directed to the lower core to generate fast neutrons and a ring-shaped beam of a lower energy level can be directed to the upper segments to promote the generation of thermal neutrons. In FIG. 11F a neutron generating target is provided in which a Beryllium core 272 is provided and Lithium is sputtered on to produce discrete regions 274 of Lithium containing material. In such an embodiment the surface areas of the target will include areas of both exposed Lithium and exposed Beryllium such that the provision of high energy particles will result in the production of fast and/or slow neutrons. In the example of FIG. 11F, the energy level of the incident particles can be adjusted to promote the generation of fast neutrons over thermal (e.g., by increasing the energy level of the incident particles above 4.5 MeV) or to promote the generation of thermal neutrons over fast neutrons (e.g., by maintaining the energy level of the particles comprising the particle beam between about 2.5 MeV and 3.5 MeV). FIG. 12 generally illustrates the generated neutron flux levels and energy levels when neutron generating targets such as those illustrated in FIG. 11D are used: (a) a Beryllium target is bombarded with protons having energy levels of approximately 4.5 MeV (reflected by the triangles), and (b) a Lithium target is bombarded with approximately 3.0 MeV protons (reflected by the diamonds). The Figures described above, and the written description of specific structures and functions below are not presented to limit the scope of what I have invented or the scope of the appended claims. Rather, the Figures and written description are provided to teach any person skilled in the art to make and use the inventions for which patent protection is sought. Those skilled in the art will appreciate that not all features of a commercial embodiment of the inventions are described or shown for the sake of clarity and understanding. Persons of skill in this art will also appreciate that the development of an actual commercial embodiment incorporating aspects of the present inventions will require numerous implementation-specific decisions to achieve the developer's goal for the commercial embodiment. Such implementation-specific decisions may include, and likely are not limited to, compliance with system-related, business-related, government-related, and other constraints, which may vary by specific implementation, location and from time to time. While a developer's efforts might be complex and time-consuming in an absolute sense, such efforts would be, nevertheless, a routine undertaking for those of skill in this art having benefit of this disclosure. It must be understood that the inventions disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Lastly, the use of a singular term, such as, but not limited to, “a,” is not intended as limiting of the number of items. Also, the use of relational terms, such as, but not limited to, “top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” and the like are used in the written description for clarity in specific reference to the Figures and are not intended to limit the scope of the invention or the appended claims. Aspects of the inventions disclosed herein may be embodied as an apparatus, system, method, or computer program product. Accordingly, specific embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects, such as a “circuit,” “module” or “system.” Furthermore, embodiments of the present inventions may take the form of a computer program product embodied in one or more computer readable storage media having computer readable program code. Reference throughout this disclosure to “one embodiment,” “an embodiment,” or similar language means that a feature, structure, or characteristic described in connection with the embodiment is included in at least one of the many possible embodiments of the present inventions. The terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise. Furthermore, the described features, structures, or characteristics of one embodiment may be combined in any suitable manner in one or more other embodiments. Those of skill in the art having the benefit of this disclosure will understand that the inventions may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure. Aspects of the present disclosure are described with reference to schematic flowchart diagrams and/or schematic block diagrams of methods, apparatuses, systems, and computer program products according to embodiments of the disclosure. It will be understood by those of skill in the art that each block of the schematic flowchart diagrams and/or schematic block diagrams, and combinations of blocks in the schematic flowchart diagrams and/or schematic block diagrams, may be implemented by computer program instructions. Such computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to create a machine or device, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, structurally configured to implement the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks. These computer program instructions also may be stored in a computer readable storage medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable storage medium produce an article of manufacture including instructions which implement the function/act specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks. The computer program instructions also may be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions that execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. The schematic flowchart diagrams and/or schematic block diagrams in the Figures illustrate the architecture, functionality, and/or operation of possible apparatuses, systems, methods, and computer program products according to various embodiments of the present inventions. In this regard, each block in the schematic flowchart diagrams and/or schematic block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It also should be noted that, in some possible embodiments, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more blocks, or portions thereof, of the illustrated figures. Although various arrow types and line types may be employed in the flowchart and/or block diagrams, they do not limit the scope of the corresponding embodiments. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the depicted embodiment. For example, but not limitation, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted embodiment. It will also be noted that each block of the block diagrams and/or flowchart diagrams, and combinations of blocks in the block diagrams and/or flowchart diagrams, may be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. The description of elements in each Figure may refer to elements of proceeding Figures. Like numbers refer to like elements in all figures, including alternate embodiments of like elements. In some possible embodiments, the functions/actions/structures noted in the figures may occur out of the order noted in the block diagrams and/or operational illustrations. For example, two operations shown as occurring in succession, in fact, may be executed substantially concurrently or the operations may be executed in the reverse order, depending upon the functionality/acts/structure involved. The inventions have been described in the context of preferred and other embodiments and not every embodiment of the invention has been described. Obvious modifications and alterations to the described embodiments are available to those of ordinary skill in the art. The disclosed and undisclosed embodiments are not intended to limit or restrict the scope or applicability of the invention conceived of by the Applicants, but rather, in conformity with the patent laws, Applicants intend to protect fully all such modifications and improvements that come within the scope or range of equivalent of the following claims.
	summary
053002580	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for separating contaminated resins from particulate materials such as soils, which resins are contaminated with a variety of contaminants, such as heavy metals, radioactive compounds and organics, often in combination, through fluidization of the soil/resin mixture, removal of soil particles not fluidized, and separation of the fluidized resins from those soil particles which are fluidized. 2. Background Information Contaminated soil and groundwater is becoming a more serious environmental problem every day. The contaminants can include heavy metals, such as for instance, copper, lead and mercury; radioactive species, such as for example, radium, uranium and thorium; and organics, such as for example, oils, grease, polychlorinated biphenyls, (PCB's), benzylamine hydrochloride, flue soot and others. Various techniques have been developed to remove specific contaminants from soil and groundwater. For instance, heavy metals are known to be found predominantly in the silt, humic or clay fraction of soil. Hence, they can sometimes be removed by size separation techniques, such as tiltable tables, concurrent flow in a mineral jig and by chemical techniques, such as the use of leachates. The radioactive compounds, when originating as a spill, can sometimes be removed to a large extent by leaching. Since these compounds are often also present in the finer particles, the most severely contaminated fraction can also be removed by countercurrent flow size separation. Organics can sometimes be removed by washing with surfactants, thermal treatment or biological processes. Special problems develop when the different types of contaminants are present in the same soil and/or groundwater. Generally, biological or thermal processes are more effective for removing organics than washing, in the case of finer grain soils and clays. However, toxic inorganics such as lead or chromium (+6), if present, tend to deactivate biological systems due to their toxicity and aggravate air pollution problems endemic to thermal destruction processes. In addition, thermal processes may mobilize contaminants that were otherwise fixed in the treated soil. Radioactive contamination (e.g., uranium, thorium radium, etc.) can sometimes be removed by soil washing, which can provide a means to process soils having multiple contaminants. The washed soil is compatible with subsequent biological or thermal treatment. Inorganic and radioactive compounds may be separated from organics for sale or disposal. Many soil washing processes are presently available. Most of these processes use mine equipment to provide intimate soil/extractant contact. U.S. Pat. No. 4,783,253 discloses a process for separating radioactive contaminants from soil using a concurrent flow of water to float away lighter uncontaminated particles from heavy contaminated particles. The slurry of lighter particles is dewatered using a spiral classifier, centrifuge, filter or the like. U.S. Pat. No. 4,783,263 is directed to a process for removing toxic or hazardous substances, in particular organics, from soils and the like by converting the material to a slurry, adding surfactants and/or alkaline agents, and concentrating the toxic substance in the liquid phase, preferably with a modifier in a froth flotation cell. In certain cases, contamination has been found to be concentrated in ion exchange materials that have accidentally been spilled onto the soil. This is likely to be a problem at any mining site or processing facility which utilizes resins in its processes. Also, the addition of resins to contaminated soils has been found to be an effective means for concentrating the contaminants, and thus decontaminating the soil. Because of the high affinity of the ion exchange resins for the contaminants, however, the contaminants cannot be readily extracted or mobilized from the resins. The contaminated resins must therefore be segregated from the soil. There is thus a need for an improved process for treating particulate materials, such as soil and the like, contaminated with a mixture of wastes such as radioactive materials, organics and heavy metals. There is yet another need for such a process which is not capital intensive, is economical to operate and can be made portable for on-site treatment. There is a further need for a system that can effectively recover the contaminants once they have been removed from the soil, requiring a minimal amount of equipment, chemicals, and being portable to the job site, which further allows for the processing of recovered contaminants, such as metals, through mining and/or smelting operations. There is yet an additional need for such a process which may be used to treat soils which contain contaminated resins, such as ion exchange materials. As used herein, the term "fluid" is intended to include both compressible and incompressible fluids, such as liquids, gasses, mixtures and solutions thereof. As used herein, the term "soil" includes all forms of particulate matter to which contaminants may adhere, such as, for example, clay, fines, sand, rock, humus, etc. As used herein, the term "heavy metal contaminants" includes both radioactive and non-radioactive metals, and is otherwise intended to encompass the full breadth of metal contaminants known to those skilled in the art. As used herein, the term "organic contaminants" is intended to refer to all organic compounds which tend to adhere to soil, and which present environmental hazards when permitted to remain in the soil or groundwater. SUMMARY OF THE INVENTION According to the present invention, a method of decontaminating soil containing resins, for example, ion exchange resins contaminated with organic, heavy metal and/or radioactive contaminants is disclosed. The method comprises fluidizing a soil mixture containing contaminated resin particulates at a fluid velocity sufficient to entrain the resin particles and a portion of the soil particles. Because of the difference in specific gravity of ion exchange resins and soil, the entrained resin particles have an average particle size significantly larger than the entrained soil particles. If the fluidizing velocity is chosen so as to be rapid enough to entrain substantially all of the resin particles, but not similarly-sized soil particles, size separation of the entrained resins from the soil is readily achieved. Soil particles which are too large to be entrained in the fluidized stream are separated, for example, by settling, while those soil particles which have been entrained along with the resin particles are separated using size-selective separating means, such as a mineral jig and screen. In another preferred embodiment of the invention, oversized soil particles are used in the process to achieve separation of the resin particles, the oversized soil particles having an average particle size tending to provide a tortuous path which inhibits settlement of the contaminated resin particles, and further tending to inhibit channeling of the resin particles in the fluidized mixture.
	abstract	In a method for sealing a hollow, elongate member within a reactor pressure vessel of a nuclear reactor, a section of the elongate member may be removed to separate the elongate member into an upper portion and a lower portion with an opening there between. The lower portion may be attached to a surface of the reactor pressure vessel in-situ, so as to seal off a potential leakage path through the elongate member.
050193260	claims	1. A pellet handling equipment for conveying pellets comprising: (a) a first roller means supported generally horizontal and rotatable about an axis thereof for a rotation in a predetermined direction; (b) a second roller means disposed parallel and adjacent to the first roller means, supported rotatable about an axis thereof for a rotation in a same direction with the first roller means, the second roller means being provided with a slot formed in a circumferential surface thereof and extending in the axial direction, the slot being capable of receiving each one of the pellets; (c) a pellet supplying means for intermittently supplying the pellets to the first and second roller means, (a) a first pellet transfer unit provided adjacent to the second roller means on a side generally opposite to the first roller means for receiving the pellets; (b) a second pellet discard unit provided adjacent to the second roller means underneath thereof for receiving the pellets; and (c) a sorting means provided adjacent to the second roller means for receiving the pellets from the second roller means and selectively sending the pellets to one of the first pellet transfer unit and the second pellet discard unit. (a) a first roller means supported generally horizontal and rotatable about an axis thereof for a rotation in a predetermined direction; (b) a second roller means disposed parallel and adjacent to the first roller means, supported rotatable about an axis thereof for a rotation in a same direction with the first roller means, the second roller means being provided with a slot formed in a circumferential surface thereof and extending in the axial direction, the slot being capable of receiving each one of the pellets; (c) a pellet supplying means for intermittently supplying the pellets to the first and second roller means; (d) a flaw detecting means capable of detecting flaws of each of the pellets by taking images of the pellets as the pellets are being supported and rotated by the first and the second roller means, and judging existence of flaws on the pellets; (e) a sorting means disposed adjacent to the second roller means for receiving the pellets from the second roller means, the sorting means comprises a shutter for selectively proceeding the pellets according to the judgement of the flaw detecting means; (f) a first pellet transfer unit provided adjacent to the sorting means for receiving the pellets on which flaw is not detected; and (g) a second pellet discard unit provided adjacent to the second roller means underneath thereof for receiving the pellets on which flaws are detected, (a) a pellet conveying means for conveying the pellets in a direction parallel to an axis of the pellets; (b) a direction switching means for switching a direction of conveyance; (c) a primary flaw detecting means for detecting major flaws on the pellets; and (d) a primary sorting means for preliminary ejecting the pellets having major flaws. 2. A pellet handling equipment according to claim 1 which further comprises: 3. A pellet handling equipment according to claim 2 wherein the sorting means is disposed between the second roller means and the first pellet transfer unit, and comprises a shutter for selectively allowing and prohibiting the entrance of the pellets into the first transfer unit, whereby the pellets conveyed to the other side of the first roller means are selectively sent into one of the first transfer unit and second discard unit. 4. A pellet handling equipment according to claim 3 wherein the slot formed in the second roller means have at least two different curvatures. 5. A pellet handling equipment according to claim 4 wherein the slot has a first concave wall facing to the direction of rotation of the second roller means and a second concave wall facing the first wall opposedly, curvature of the first concave wall being greater than that of the second concave wall. 6. A pellet handling equipment according to claim 1 which further comprises a vacuum means for evacuating a space between the first and the second roller means, whereby cleaning the debris which may appear therebetween. 7. A pellet handling equipment according to claim 1 which further comprises at least one flaw detecting means capable of detecting flaws on each of the pellets. 8. A pellet handling equipment according to claim 7 wherein the flaw detecting means comprises at least an imaging means for taking images of the pellets as the pellets are being supported and rotated by the first and the second roller means, whereby a whole surface of the each pellet is imaged. 9. A pellet handling equipment according to claim 8 wherein the flaw detecting means further comprises means for judging existence of flaws on each of the pellets. 10. A pellet handling equipment for conveying pellets, and detecting and ejecting flawed pellets, the pellet handling equipment comprising: 11. A pellet handling equipment according to claim 7 which further comprises a dryer means for drying the pellets before the pellets are provided to the first and second roller means. 12. A pellet handling equipment according to claim 11 which further comprises: 13. A pellet handling equipment according to claim 12 wherein the direction switching means comprises a tray for arranging the pellets thereon and a handling means for conveying the pellets by holding a surface of the pellets. 14. A pellet handling equipment according to claim 12 wherein the pellets are proceeded in a direction perpendicular to their axis by being rolled on their peripheral surface, the primary flaw detecting means comprising a means for imaging the pellets. 15. A pellet handling equipment according to claim 12 wherein the primary flaw detecting means comprises a disc having ditches formed in a surface thereof for supporting and conveying the pellets thereby, the disc being rotated intermittently at a predetermined angle about an axis thereof, imaging means for imaging both end faces of each of the pellets, and judgement means for judging existence of flaws according the image of the both end faces of the pellets. 16. A pellet handling equipment according to claim 13 wherein the pellets are arrayed parallel to one another on the tray and the pellet handling means holds the pellets by the end faces thereof.
055704026	summary	BACKGROUND OF INVENTION 1. Field of the Invention This invention relates to supports and, more particularly, to boiling water reactor control rod drive housing supports. Still more particularly, this invention relates to control rod drive housing supports with radiation shields. 2. Description of Prior Art In boiling water reactors the control rod drive housing supports are generally located underneath the reactor vessel near the control rod housings. The control rod drive housing supports limit the travel of and support a control rod in the event that a control rod drive housing is ruptured. The supports help prevent a loss of control as a result of a housing failure, thus protecting the fuel barrier. Typically, control rod drive housing supports consist of hanger rods that are attached and supported at their upper end at a beam structure immediately underneath the reactor pressure vessel and support bars which are bolted between the hanger rods below the control rod drives. Another grid of bars is installed on the support bars to transfer the load of a ruptured control rod drive housing to the support bars. Generally, a pair of grid bars support each control rod drive. Each pair of grid bars are held together by two grid clamps and a bolt. In this support system of the prior art, when it is necessary to change or replace a control rod drive, the grid bars must be removed. In order to remove the grid bars the operator must manually unscrew the grid clamp bolt, remove the two grid clamps and then remove the grid bars, each weighing approximately forty pounds. The number of grid bars which must be removed depends on the number of control rods which must be replaced. Furthermore, since the grid bars are interlocking, they must be removed starting from the outer peripheral row. Thus, if a large number of control rod drives must be replaced or if an inner control rod drive must be replaced, a large number of grid bars must be removed. The result is a time consuming and cumbersome process. Moreover, as the grid bars are heavy and awkward to handle, a dropped bar could result in serious injury. Further still, the persons handling the grid bars or working under the reactor pressure vessel are subject to substantial radiation doses. The more time a person must spend replacing the control rod drives, the more that person is subject to dangerous radiation doses. Thus, there is a need in the art for an apparatus to reduce and minimize the radiation exposure of a person working under the reactor pressure vessel of a boiling water nuclear reactor. SUMMARY OF THE INVENTION It is an object of the present invention to provide radiation shields to minimize the amount of radiation a person is subject to when replacing a control rod drive or working under the reactor pressure vessel. It is another object of the present invention to support a control rod drive housing in the event that a control rod housing is ruptured while allowing for quick and easy replacement of a control rod drive. It is another object of the present invention to provide a control rod drive housing support which can be removed automatically. Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by the appended claims. To achieve the foregoing and other objects, in accordance with the present invention, as embodied and broadly described herein, the control rod housing support system of this invention may comprise a first means for supporting a control rod drive in the case of a housing failure; a second means for supporting the control rod drive in the case of a housing failure and for shielding persons working under the reactor vessel from radiation, the second means being supported by the first supporting means, wherein the second means can be raised and lowered between a non-support position where the control rod drive is not supported and a support position where the control rod drive is supported; and a radiation shield means for shielding persons working under the reactor vessel from radiation, the shield means being provided about the control rod drive above the second supporting means. The first supporting means may comprise a plurality of support members provided in rows on opposing sides of a lower portion of a plurality of control rod drives and the second supporting means may comprise a plurality of support cups, each of the support cups receiving, and shielding a lower portion of the control rod drive and supporting the control rod drive in the case of a housing failure. Further, the radiation shield means may comprise a plurality of shield rings, each of the shield rings being disposed about a control rod drive housing and including pin means for maintaining the shield rings in position about the control rod drives when the support cups are removed. The shield rings are supported on the support cups when the cups are in their installed position. The shield rings may also include slots for accommodating seismic restraints between adjacent control rod drives. In accordance with a further aspect of the present invention, in accordance with its objects and purposes, the device hereof may also comprise a radiation shield apparatus for use in a nuclear reactor, comprising a cylindrical-shaped ring member having an inner diameter slightly larger than a control rod drive housing of the reactor, a lower abutment surface for engagement with a control rod drive support system, and a hanger means for supporting the ring member on a control rod drive when the lower abutment surface is not engaged by a support system.
	claims	1. A method for welding a flange to a tube using an apparatus which includesa welding unit located on an axially conveying line to carry the tube for welding a surface of the tube inserted thereinto and a surface of the flange, the welding unit including a mandrel unit and a welding torch group,a flange supplying unit for supplying the flange at a tube inlet of a welding chamber onto the axially conveying line,wherein the flange supplying unit comprises:a magazine vertically perforated, on which a plurality of the flanges are piled up;a stopper located beneath the magazine to discharge the flanges one by one;conveying blocks for seating the discharged flanges thereon; anda pneumatic cylinder for moving the conveying blocks in order to locate the flanges on the axially conveying line of the tubea conveying unit mounted on the axially conveying line in such a way as to move the tube and the flange on the axially conveying line, so that the tube and the flange are inserted into and drawn from the welding unit, anda controlling unit for controlling the apparatus,the method comprising:supplying the flange, by the flange supplying unit, onto the axially conveying line on which the welding unit is mounted;conveying the tube, by the conveying unit, toward the welding unit along the axially conveying line;joining an end of the flange to an end of the tube;inserting at least the joined portion of the flange and the guide thimble tube into the welding chamber;welding the joined portion by the welding torch group while the mandrel unit rotates the flange and the tube;drawing out the tube and the flange from the welding chamber; andlaterally conveying the tube and the flange drawn-out from the welding chamber. 2. The method according to claim 1, further comprising:sealing the welding chamber from an outside by a chamber side sealing unit and a stopper side sealing unit,wherein the chamber side sealing unit is mounted in the tube inlet of the welding chamber and seals the welding chamber by contacting with an outer circumferential surface of the tube inserted into the welding chamber, and the stopper side sealing unit is mounted in the other end side of the tube inserted into the welding chamber and seals the welding chamber by sealing the other end of the tube. 3. The method according to claim 1, further comprising:measuring a vibration width of the flange by a tremor measuring unit to inspect a welded status of the flange and the tube while the flange and the tube are rotated,wherein the tremor measuring unit is mounted on the axially conveying.
	summary
	claims	1. A spacer grid comprising:interlocked straps comprising metal sheets or plates welded together to define a spacer grid having a top and bottom, the interlocked straps defining a plurality of cells comprising vertical passages connecting the top and bottom of the spacer grid, the cells including:upper dimples disposed proximate to the top of the spacer grid and distal from a mid-plane of the spacer grid,lower dimples disposed proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid,cantilevered upper springs having fuel rod engagement surfaces disposed proximate to the top of the spacer grid and distal from the mid-plane of the spacer grid, andcantilevered lower springs having fuel rod engagement surfaces disposed proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid,wherein the upper springs and the lower springs are anchored to the straps by a single base that is in a plane of its corresponding strap at the mid-plane of the spacer grid. 2. The spacer grid of claim 1, wherein the fuel rod engagement surfaces of the cantilevered upper and lower springs comprise flat topped domes. 3. The spacer grid of claim 1, wherein the fuel rod engagement surfaces of the cantilevered upper and lower springs comprise hooks. 4. The spacer grid of claim 1, wherein the outermost straps of the interlocked straps do not include cantilevered upper springs and do not include cantilevered lower springs. 5. The spacer grid of claim 4, wherein the outermost straps of the interlocked straps have the same thickness as the other straps. 6. The spacer grid of claim 1, wherein the upper and lower dimples face inward toward the center of the spacer grid and the upper and lower springs face outward away from the center of the spacer grid. 7. The spacer grid of claim 1, wherein each cell configured to receive a fuel rod includes:a first cell defining wall having upper and lower dimples;a second cell defining wall having upper and lower dimples;a third cell defining wall opposite from and facing the first cell defining wall wherein the third cell defining wall has upper and lower springs; anda fourth cell defining wall opposite from and facing the second cell defining wall wherein the fourth cell defining wall has upper and lower springs. 8. The spacer grid of claim 7, wherein the first and second cell defining walls face toward the center of the spacer grid and the third and fourth cell defining walls face away from the center of the spacer grid. 9. A spacer grid comprising:interlocked straps of metal sheets or plates welded together to form a spacer grid having a top and bottom, the interlocked straps defining a plurality of cells comprising vertical passages connecting the top and bottom of the spacer grid; anda fuel rods retention system comprising a set of dimples protruding from walls of the cells and a set of springs protruding from walls of the cells, the set of dimples not including any dimples configured to contact fuel rods at the mid-plane of the spacer grid, the set of springs not including any springs configured to contact fuel rods at a mid-plane of the spacer grid,wherein the set of springs is anchored to the straps by a single base that is in a plane of its corresponding strap at the mid-plane of the spacer grid. 10. The spacer grid of claim 9, wherein the set of dimples includes:a set of upper dimples configured to contact fuel rods above the mid-plane of the spacer grid; anda set of lower dimples configured to contact fuel rods below the mid-plane of the spacer grid. 11. The spacer grid of claim 10, wherein the set of springs includes:a set of upper springs configured to contact fuel rods above the mid-plane of the spacer grid; anda set of lower springs configured to contact fuel rods below the mid-plane of the spacer grid.
	summary
	claims	1. System for point of care diagnosis and/or analysis of a body fluid of a patient, comprising:at least one cartridge, having:a sample receiving room for receiving a sample of the body fluid to be diagnosed and/or analyzed,a diagnosing and/or analyzing arrangement for measuring at least one physiological parameter of the sample,a first interface for connecting the cartridge to at least one handheld diagnosis and/or analysis device, the at least one handheld diagnosis and/or analysis device, having:at least one second interface for connecting one of said cartridges to the handheld device,a measurement arrangement co-operating with the connected cartridge for measuring the physiological parameter and generating measurement data thereof,at least one third interface for connecting the handheld device to a data processing device, the data processing device, having:at least one fourth interface for connecting one of said handheld devices to the data processing device,a data processing unit co-operating with the connected handheld device for further processing the measurement data; and whereinat least one of said handheld devices comprises a memory for unambiguously storing the measurement data together with sample-specific data, andthe data processing unit of the at least one of said data processing device co-operates with the memory of the connected handheld device. 2. System according to claim 1, whereinat least one of said handheld devices comprises a rechargeable battery, and, whereinthe data processing device comprises a power supply for charging the battery of the handheld device, when the handheld device is connected to the data processing device. 3. System according to claim 2, wherein the power supply of the data processing device is provided for charging the battery of the handheld device via the coupled third interface and fourth interface. 4. System according to claim 1, wherein the handheld device and the data processing device are configured in such a way, that they automatically or manually by user request create a master-slave-configuration. 5. System according to claim 4, wherein:the data processing device comprises a data input unit and/or a data output unit,the handheld device comprises a data input unit and/or a data output unit, such that when the handheld device and the data processing device are coupled together the data input units of one of the measuring device and the handheld device are connected and the data output units are automatically or manually by user request transferred to the master-member of the master-slave-configuration. 6. System according to claim 1, wherein the sample-specific data is at least a patient identification code and/or an operator identification code and/or time and date of the sample. 7. System according to claim 1, wherein at least one of said handheld devices is provided for storing the measurement data and sample-specific data of at least two cartridges. 8. System according to claim 1, wherein at least one of said handheld devices has at least two second interfaces for connecting two different types of said cartridges. 9. System according to claim 1, whereinthe first interface and the complementary second interface, and/orthe third interface and the complementary fourth interface are provided for wired and/or wireless data transfer. 10. System according to claim 1, wherein at least one of the handheld devices has an ergonomic casing. 11. System according to claim 1, wherein the data processing device and the handheld device are configured in such a way, that a wireless data transfer is only provided as long as the handheld device is in a predetermined close proximity to the respective data processing device. 12. System according to claim 1, whereinthe system comprises at least one adapter, whereinthe data processing device is connectable to the adapter, and whereinthe adapter is connectable to at least one peripheral device. 13. System according to claim 1, wherein the data processing device is or comprises a personal computer and/or a database. 14. The system according to claim 1, wherein the diagnosing and/or analyzing arrangement is configured to provide electrical or optical signals correlating with the physiological parameter. 15. System for point of care diagnosis and/or analysis of a body fluid of a patient, comprising:at least one cartridge, having:a sample receiving room for receiving a sample of the body fluid to be diagnosed and/or analyzed,a diagnosing and/or analyzing arrangement for measuring at least one physiological parameter of the sample,a first interface for connecting the cartridge to each of or at least two handheld diagnosis and/or analysis devices,each of the at least two handheld diagnosis and/or analysis devices, having:at least one second interface for connecting one of said cartridges to each handheld device,a measurement arrangement co-operating with the connected cartridge for measuring the physiological parameter and generating measurement data thereof,at least one third interface for connecting each handheld device to a data processing device,the data processing device, having:at least one fourth interface for connecting one of said at least two handheld devices to the data processing device,a data processing unit co-operating with the connected handheld device for further processing the measurement data; and whereinat least one of said handheld devices comprises a memory for unambiguously storing the measurement data together with sample-specific data, andthe data processing unit of the data processing device co-operates with this memory of the connected handheld device, and whereineach of the at least two handheld devices are provided with complementary interfaces for coupling the handheld devices together, whereinthe coupled handhold devices are configured for connection to the data processing device via the third interface of one of the coupled handhold devices,wherein all coupled handheld devices communicate via this one third interface with the data processing unit of the data processing device. 16. System according to claim 15, wherein each of the at least two handheld devices are configured in such a way, that the coupled handheld devices automatically create a master-slave-configuration. 17. System according to claim 16, wherein each of the at least two hand held devices include a data in input unit and a data output unit and the hand held devices are configured to be coupled in a stack such that data inputs and data outputs are transferred automatically or manually by user request to the data input unit and data output unit of the master hand held device. 18. The system according to claim 15, wherein the diagnosing and/or analyzing arrangement is configured to provide electrical or optical signals correlating with the physiological parameter. 19. Handheld device for use in connection with a system for point of care diagnosis and/or analysis of a body fluid of a patient comprising:at least one second interface for connecting a first interface of a cartridge having a sample receiving room for receiving a sample of a body fluid to be diagnosed and/or analyzed to the handheld device,a measurement arrangement co-operating with the connected cartridge for measuring the parameter and generating measurement data thereof,at least one third interface for connecting the handheld device to a data processing device of the system;a memory for unambiguously storing the measurement data together with sample-specific data, andthe data processing unit of the data processing device co-operates with this memory of the connected handheld device.
056446080	description	DETAILED DESCRIPTION OF THE INVENTION Although the principles of the invention are applicable to other cooling systems, the invention will be described in connection with a known type of spent fuel and reactor component cooling system. Such a system is illustrated in the accompanying drawings along with the added apparatus of the invention. As shown in FIG. 1, the known system comprises a spent fuel pool 1 filled with water 2 which can contain additives of a known type. Spent radioactive fuel assemblies 3 which have been removed from a reactor, not shown, are immersed in the pool of water 2. The water 2 must be kept at a temperature well below its boiling temperature, and the water 2 is cooled by pumping it out of the pool 1 by means of a pump 4 and sending it through pipes and valves 5 and 6 to a water conduit assembly 7, which can be a plurality of tubes, from which it returns to the pool 1 by way of a pipe 8. In a conventional cooling system, the assembly 7 through which the water 2 from the spent fuel pool is circulated is contained in a water-tight housing 9 of a heat exchanger 10 which receives and returns cooling water from and to another heat exchanger 11 of known construction which forms part of a cooling system for reactor components, e.g. reactor coolant pumps. Cooling water from a suitable source, e.g. a river, is supplied by a line 12 to the heat exchanger 11 and then dumped back to the source via line 11a. In the arrangement of the invention, the water from the spent fuel pool can be passed through the conventional heat exchanger 9, or the conventional heat exchanger can be bypassed, or the conventional heat exchanger and the heat exchanger of the invention can both be used. As examples of the spent fuel pool water cooling which can be required, it can be necessary to remove 13 million BTU/hour, 131 hours after a third of the reactor fuel assemblies are immersed in the water 2 and 12 million BTU/hour, 174 hours after such immersion of the assemblies. In a full core discharge case, i.e. when all of the reactor fuel assemblies are immersed in the water 2, the heat removal rate can be as much as 26 million BTU/hour, 360 hours after immersion of the assemblies in the water 2. When the reactor is shut down for maintenance and refueling, all of the assemblies are transferred from the reactor to the spent fuel pool. The procedure can take about twelve hours, which provides only a relatively short time for the maintenance or repair of the service water/component cooling system. Also, if there is a failure of the component cooling system 11 or the supply of water by way of the line 12, the reactor operation must be discontinued, and there would be a loss of spent fuel pool water cooling. In accordance with the invention, these problems can be overcome by the addition of the apparatus described hereinafter without a substantial modification of the known system, and with equipment of relatively small size and cost as compared to the size and cost of a conventional water-water heat exchanger such as the heat exchanger 10. The heat exchanger which is added in accordance with the present invention also is more reliable than a water-water heat exchanger. In the preferred embodiment of the invention, the added apparatus comprises a pump 13, valves 14, 15, 16 and 17, a heat exchanger 18 which uses air and water spray for the coolant and the interconnecting pipes shown in the drawing. The heat exchanger unit 18 comprises a spray water conduit W, a duct 22, one bank 20 of water spray heads or nozzles 20a and a fan 25. Air is supplied to the duct 22 from any convenient source, which can be the known spent fuel ventilation system normally used in the known cooling system, and water is supplied through the conduit W to the nozzles or spray heads 20a of the bank 20 from any convenient source thereof, e.g. public water mains, but preferably, the water is supplied thereto from a storage tank so that the spray water is always available and is independent of other sources which can more readily fail. When valves 14 and 17 are open and valves 5 and 6 are closed, water 2 of the spent fuel pool is circulated by the pump 13 and is returned to the pool 1 by way of the interconnecting pipe lines 30, 31, 32, as shown by the arrows in FIG. 1. As the water 2 passes through the heat exchange unit 18, a stream of air driven by the fan 25 impinges on the heat exchange surfaces, and water is sprayed into the flow of air and onto the unit 18 from the spray head nozzles 20a of bank 20 to thereby remove heat from the water 2. With the temperature of the water 2 at 150.degree. F., with the temperature of the ambient air entering the duct 22 at 75.degree. F., the heat exchanger 18 can remove heat from the water 2 in an amount equal to about 22 million BTU/hour. For this result, the operating conditions of the heat exchanger are as follows: ______________________________________ Air flow rate 72,000 cfm through duct 22 Total water flow 2,250 g./min. through unit 18 Air flow area 180 sq.ft. Air flow velocity 900 ft./min. Spray water flow 120 g./min. ______________________________________ About one-third of the water sprayed into the air stream is being evaporated to achieve the above result. If a larger fraction of the sprayed water is evaporated, the cooling effect will be enhanced. If the temperature of the air entering the duct 22 is lower, the amount of heat removed under the same conditions is greater. Let it be assumed that the heat exchanger 10 for the spent fuel water 2 is not available for cooling the water 2 or that the component cooling heat exchanger 11 or cooling water supplied from a river or other source by the line 12 is not available (first case), and that the heat removal requirements are 22 million BTU/hour. With the heat exchanger 18 and the operating conditions thereof described hereinbefore, the added equipment of the invention can assume the entire cooling load under the following conditions: ______________________________________ Component Condition ______________________________________ Pump 13 Operating Valve 14 Open Valve 5 Closed Valve 16 Closed Valve 17 Open Valve 6 Closed Valve 15 Open or closed ______________________________________ Let it be assumed that the heat exchanger 10 is operative but that supplemental cooling is required (second case), such as in the full discharge case previously described. With the heat exchanger 18 and the described operating conditions thereof, the added equipment can provide supplemental cooling with the components in the following conditions: ______________________________________ Component Condition ______________________________________ Pumps 4 and 13 Operating Valve 14 Open Valve 5 Open Valve 16 Closed Valve 17 Open Valve 6 Open Valve 15 Closed ______________________________________ Let it be assumed that the supply of water by the line 12 is lost and that it is desired to continue cooling of the water 2 and the reactor components, e.g. pump seals, etc. (third case). With the heat exchanger 18 and the described operating conditions thereof, the added equipment of the invention can provide such cooling with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 13 Operating Valve 14 Open Valve 5 Closed Valve 16 Open Valve 17 Closed Valve 6 Open Valve 15 Open or closed ______________________________________ Although not preferred, the added apparatus can be simplified by the elimination of the pump 13 and the valve 15, the valve 14 being connected directly to the pump 4 and the valve 5. For that modified apparatus, in the first case assumed hereinbefore, the heat exchanger 18 can assume the entire cooling load with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 4 Operating Valve 14 Open Valve 5 Closed Valve 16 Open or closed Valve 17 Open Valve 6 Closed ______________________________________ In the second case assumed hereinbefore, the modified apparatus can supply supplemental cooling with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 4 Operating Valve 14 Open Valve 5 Open Valve 16 Open or closed Valve 17 Open Valve 6 Open ______________________________________ In the third case assumed hereinbefore, the modified apparatus can continue cooling of the water 2 and the reactor components with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 4 Operating Valve 14 Open Valve 5 Closed Valve 16 Open Valve 17 Closed Valve 6 Open ______________________________________ The heat exchanger unit 18, which uses air entraining a sprayed mist of water as the coolant medium, is shown to be of known cross-flow plate-fin construction as illustrated in FIGS. 2 and 3, wherein the liquid to be cooled flows in channels between pairs of parallel sheets (the water side) while the coolant medium comprising air carrying a mist of fine droplets flows in channels arranged alternately with the water channels between the parallel sheets (the air side). That is, flows of mist-carrying air and of water being cooled flow past opposite sides of the parallel sheets for indirect heat exchange through the sheets. By cross-flow, it is meant that the flows of water and air are essentially directed at right angles to each other in a well known mode of operation, illustrated for example in FIG. 9-3 of Kays and London, Compact Heat Exchangers, second edition, 1954 and in the accompanying FIG. 3. Strip-fins can be employed only on the side of the heat exchange surfaces over which air carrying the water spray passes, or on both sides of the heat exchange surfaces. The strip-fins are preferably formed of copper. When strip-fins are employed on both sides of the heat exchange surfaces, a lower water spray rate can be used to produce a given cooling rate. Although the heat exchange unit of the type described is illustrated in FIG. 1, in many applications more than one heat exchange unit can provide the higher cooling rates as shown in FIG. 4. The number of heat exchange units to be arranged in tandem can be determined in accordance with the cooling capacity requirements of any given application. In certain cases, the first of a plurality of heat exchange units can be operated without any water spray, in which case, a downstream unit (or units) that is sprayed with water droplets, is more effective. Such an arrangement is shown in FIG. 4. FIG. 4 shows an alternate form of sprayed water heat exchanger according to the invention. In the embodiment of FIG. 4 three heat exchangers in tandem are employed, rather than the single heat exchanger unit 18 shown in FIG. 1. Each of the heat exchanger units 19, 20 and 21 can have the same structure as the single unit 18 that constitutes the heat exchanger of FIG. 1, and therefore the units 19, 20 and 21 are not described in detail. The heat exchanger units 20 and 21 are shown in FIG. 4 to have their own, individually operable banks 23 and 24 of water headers and respective spray nozzles 23a, 24a. The arrangement of FIG. 4 can provide greater cooling and more flexibility than that of FIG. 1. Experimental tests have been performed to compare the performance of similarly dimensioned tube-fin and plate-fin heat exchangers, both provided with means for spraying finely atomized droplets of water into the flow of coolant air through the heat exchangers. The results for the tube-fin heat exchanger demonstrated that the cooling capacity could be increased by a factor of four times that of the same heat exchanger with no water spray. Test results for the plate-fin heat exchanger demonstrated that the cooling capacity of the exchanger with sprayed water droplets exceeded by a factor of eight times that of the same heat exchanger with no water spray. The test heat exchangers represented approximately one-thirtieth of full scale air side frontal area of the heat exchanger which would actually be employed in an alternate spent fuel cooling system for a nuclear power generating plant, but the results are believed to demonstrate that either tube-fin or plate-fin air cooling heat exchangers augmented by spraying atomized water droplets having a mean diameter of 250 microns or less into the cooling air can be used for the purpose of the invention. The water spray can be produced by use of suitable high inlet pressure, hydraulic or air atomizing spray nozzles such as those available from suppliers such as Spraying Systems Co. of Wheaton, Ill. The nozzles can be arranged on headers that are opened and closed by solenoid valves for control of the amount of water sprayed. That is, one or more of a plurality of spray headers can be activated to provide the desired spray flow. Preferably the nozzles have built-in strainers. When the air flow through the heat exchanger is directed horizontally, the nozzles are arranged to spray water droplets concurrently with the air flow while the flow of water to be cooled on the water side of the plates is in a direction perpendicular to the direction of the flow of cooling air. Other arrangements will suggest themselves to those acquainted with the art of heat transfer.
041893476	description	Referring now to the drawing and first, particularly, to FIG. 1 thereof, there are shown graphite blocks 1 to 8, disposed in a horizontal plane, and assembled to form a side wall sector of a nuclear reactor vessel which is bounded on two sides by radial parting lines that are not in contact with the adjacent side wall sectors. Toward the pebble bed of numerous fuel spheres 9, provided in the interior of the vessel, this side wall sector is bounded by two surfaces inclined convexly to one another, which are formed by the blocks 1, 3, 5 and 7. Toward the outside, this side wall sector is likewise bounded by two surfaces that are inclined convexly to one another, which are formed by the blocks 2, 4, 6 and 8 and are braced through rolling planes 10 and rolling elements 11 against two rolling planes 12 and 13 which are inclined concavely to one another. Actually, these rolling elements 11 are not spheres but cylindrical rolling elements which, however, act in principle like spheres between two planes. The forces exerted by the pebble bed on the blocks 1, 3, 5 and 7 can be considered, grossly simplified, as acting perpendicularly on the respective surface, even if force directions locally deviating somewhat from the perpendicular are to be expected due to the friction between the fuel spheres 9 and the wall. In the case of the rolling elements 11, on the other hand, it can be assumed that the respective bearing forces are transmitted only perpendicularly to the rolling plane. All in all, the external forces acting upon a side wall sector have the effect that this body, since it cannot absorb any appreciable tensile forces, is held together in the horizontal direction under all operating conditions and is pushed against a fixed point 14 which is located at the intersection of the outer rolling plane thereof. Since the friction at the rolling elements 11 is very much lower than the friction in the boundary surfaces between the pebble bed and the side wall sector, the angle .beta. between the two outer rolling planes can be selected so that it is considerably smaller than the angle .alpha. between the two inner boundary surfaces. In a non-illustrated vertical section of a base sector, the forces originating from the pebble bed and the support act in a manner similar to those acting in the configuration of FIG. 1 i.e. so that also the base sector is held together and is forced into a defined position. In FIGS. 2 and 3, the reactor vessel, shown without cover and without pebble bed, is formed by a total of twelve sectors 20, with parting lines or gaps 21 therebetween. Each of these sectors 20 is made up of numerous blocks, for example, of graphite, and is bounded in the region of the base against the pebble bed in gable roof-shaped fashion with a radial ridge 22 which declines towards the center of the reactor. The blocks which are immediately adjacent to the subsequent pebble bed have numerous vertical, parallel ducts or channels, through which the reactor coolant is conducted, in a manner not otherwise described in detail, to a collecting channel or manifold 24. In the center of the reactor base, a cone-like body 25 with the apex thereof pointing upwardly is disposed. It is similarly constructed of individual blocks and has a polygonal parting line or gap 26 opposite the sectors 20 surrounding it. This cone-like body 25 serves to conduct the fuel spheres away from the center and toward the discharge channels 27, indicated by broken lines, and from there to several discharge tubes 28. The side wall 29, which is likewise constructed of numerous blocks, also has, in direction toward the pebble bed, two boundary surfaces inclined toward each other in gable-roof-fashion with a vertical ridge 30. Toward the outside, the side wall 29 is braced, through rolling bodies disposed in separate cages 31, against a metallic polygonal ring 32, through which numerous vertical ducts 33 pass for cooling purposes. This polygonal ring 32 rests on cylindrical rolling bodies 34 and, when heated, travels outwardly together with the side wall sector 29 and the base sector. The base sectors 20 are supported on separate rolling bodies 35 which are shown in FIG. 6 and described in detail hereinafter. From FIG. 3 it is apparent, however, that these rolling bodies 35 are disposed in planes that ascend or slope upwardly toward the center of the reactor, so that the base sectors 20 are forced outwardly against the polygonal ring 32 by their own weight and the weight of the pebble bed which will subsequently rest thereon. The central cone-like body 25 rests on rolling bodies 36 which, as shown in detail in FIG. 6, are disposed in rolling planes declining or falling off toward the center of the reactor. This body 25 is thereby held uniformly together toward the center by its own weight and due to the weight of the pebble bed resting thereon. This body 25, in fact, also has radial and annular parting lines, however, they are always closed, in contrast with the side wall sectors and the base sectors 20. In FIG. 4, respective pairs of cylindrical rolling bodies 40 which are provided with an annular slot, rest on a plate 41 which has a ridge 42 for guiding these rolling bodies 40. On the two lower rolling bodies 40, there is disposed a middle plate 43 which has ridges 42 on the underside and on the upper side thereof which are transposed 90.degree. to one another. Thereabove, again two upper rolling bodies 40 are disposed which are offset 90.degree. relative to the lower rolling bodies and support an upper plate 44 which is also provided with a ridge 42 similarly engaging in the annular slot of the rolling bodies 40. In the illustrated position of FIG. 4, this roller or antifriction bearing is freely movable in horizontal direction and has as an advantage over rolling spheres which are disposed between two planes, that the contact surface and, therefore, the load capacity is greater. If one wishes to dispose such roller or antifriction bearings in vertical planes, as is intended in the invention of the instant application, these rolling bodies must be guided in a conventional manner by gears which mesh with appropriately shaped racks, so that they do not travel downwardly. FIG. 5 illustrates how the base sectors 20 are supported on numerous column-shaped rolling bodies 35, and the inner, cone-like body 25 is supported on numerous rolling bodies 36. In addition, FIG. 5 shows the location of the cylindrical rolling bodies 34 for supporting the polygonal ring illustrated in FIGS. 2 and 3. In FIG. 6, the column-shaped rolling bodies 35 and 36 have, at the respective upper and lower ends thereof, curved rolling surfaces which have a common center of curvature and are supported above and below on inclined but, in themselves, planar rolling surfaces 37 and 38. The displacement paths of the parts supported on rolling bodies 35 and 36 are so small that the contact points of the rolling bodies 35 and 36 with the upper and lower bearing surfaces always remain within the respective spherical or curved rolling surface thereof, and the column-shaped rolling bodies 35 and 36, therefore, cannot topple over. Holders 39 are, nevertheless provided, primarily during assembly to minimize the possibility of toppling. It is of particular importance that all of the rolling bodies 35 belonging to one base sector 20, are disposed in two planes which, on the one hand, are inclined toward one another valley-like and, on the other hand, ascend toward the center of the reactor. In this manner, this base sector is held together in itself and is forced outwardly against the polygonal ring 32. Since the rolling bodies 35 are supposed to permit movements in the respective rolling plane, they must be defined by two spherical surfaces with a common center of curvature. The rolling bodies 36, on the other hand, which support the central, cone-like body 25, may have cylindrical end surfaces, also with a common center of curvature, since this cone-like body 25 can only expand or contract in radial direction. FIGS. 7 to 9 show diagrammatically another embodiment of the invention in a gas-cooled pebble bed reactor with a cylindrical core vessel of about 12 m diameter and 10 m height, which has a funnel-shaped base and a central cone having an upwardly directed apex disposed therein. With a temperature difference i.e. increase, of about 1000.degree. C., the diameter of such a base of graphite would have to expand about 60 mm if no special measures were taken. In FIGS. 7 and 8, the cylindrical core vessel 51 contains a bed of numerous fuel spheres 52. The base of the vessel 51 is formed of an outer, funnel-shaped part 53 and an inner, conical part 54 with an annular gap 55 therebetween. As is evident from FIG. 7, the funnel 53 and the cone 54 are constructed of numerous blocks, of which several, stacked on top of one another, form a respective column which is supported on a rolling body 56 that, together with other rolling bodies 56, is supported on plates 57 and 58 which, in turn, rest on a horizontal, flat base 61 through the intermediary of foundations 59 and 60. The cylindrical side walls of the core vessel are constructed from the inside to the outside thereof, successively, of a layer of graphite blocks 62 acting as a reflector, a layer, for example, of carbon blocks 63 acting as insulation, and an outer polygonal wall of metallic elements 64 which are bolted together and are cooled from the outside. Since the temperature and, therefore, also the dimensions of this outer polygonal wall change only little, it can be considered as a fixed abutment or bracing for the blocks of the funnel 53 which, upon becoming heated, move radially toward the center of the vessel, on the one hand, and vertically upwardly into the pebble bed, on the other hand. Upon cooling down, these blocks, due to their own weight and the weight of the pebble bed resting thereon, move back again on the inclined plates 8 in radial direction toward the fixed outer abutment. In contrast, the blocks of the inner cone 4, when heated up, expand in radially outward direction, on the one hand, and also upwardly into the pebble bed, on the other hand. Upon cooling down, these blocks travel back again radially toward the center due to their own weight and due to the weight of the pebble bed pushing on their inclined surfaces. In this manner, the blocks of the funnel 53, as well as the blocks of the cone 54 are stressed only in compression. In FIG. 8, there are again shown both the cone 54 built of the multiplicity of columns of blocks 70, 71 and 72, as well as the outer funnel 53 built of the multiplicity of columns of blocks 73, 74 and 75 which, respectively, form segment-shaped or annular segment-shaped groups. Between adjacent columns of the inner core 54, parting lines or joints but no expansion gaps are provided because the blocks thereof are all forced toward the center due to their own weight. Between the block 70 of the inner core 4 and the block 73 of the outer funnel 53, an annular expansion gap 55 is provided, which is supposed to remain in existence even at the highest possible temperature. Between the block 73 and the radially adjacent block 77, there is likewise provided an expansion gap 78 extending in radial direction, whereas, on the opposite side of the block 73 along the adjacent block 79, in fact, a parting line or joint is provided, but no expansion gap. FIG. 9 shows, with the same reference numerals applied to like parts as in FIGS. 7 and 8, how the annular or ring segments of the outer funnel 53, that are constructed of a multiplicity of column of blocks, are mounted through roller bearings 56 on the planar base 61. It is apparent therein how the weight of the blocks per se and the weight of the bed of fuel pebbles 52 disposed thereon, hold together the blocks of a ring segment in horizontal direction. It is also readily apparent that the inclincation of the plane above the blocks is opposite to the inclination of the roller planes below the blocks, but does not have the same angle of inclination with respect to the horizontal. While the inclination at the upper side of the blocks is determined by the flow characteristics or behavior of the fuel pebbles, the inclination at the underside of the blocks must be selected to be only so great that the friction in the roller bodies is overcome.
	summary
	description	The invention relates to a control rod drive for a nuclear reactor, in particular for a boiling water reactor, and to a method for moving a control rod into a reactor core of the nuclear reactor, in particular for the emergency shutdown of the nuclear reactor. In a nuclear reactor, in particular in a light water reactor, a regulation of the nuclear chain reaction takes place, above all, by what are known as control rods that are moved into individual fuel assemblies or between these and absorb neutrons. The control rods are used both for regulating the power of the nuclear reactor, for example during start-up and during its normal operation, and for an emergency shutdown of the nuclear reactor in the event of an accident. In a boiling water reactor, the control rods are conventionally introduced from below into the reactor core disposed within a reactor pressure vessel. A control rod drive, with the aid of which the control rods are moved in and out, is disposed outside the reactor pressure vessel. In the event of an emergency shutdown, the control rods are shot hydraulically into the reactor core in the shortest possible time. For this purpose, the control rod drive is connected to a pressure line, what is known as the scram line. German Patent DE 44 41 751 C1, corresponding to U.S. Pat. No. 5,854,817, describes an emergency shutdown system and a method for the emergency shutdown of a nuclear rector, in which the individual control rods are divided into groups capable of being activated independently of one another. It is accordingly an object of the invention to provide a control rod drive for a nuclear reactor and a method for moving a control rod into a reactor core of a nuclear reactor that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, in which it is possible for the control rod to be moved in carefully and in an improved way in the event of an emergency shutdown. With the foregoing and other objects in view there is provided, in accordance with the invention, a control rod drive for a nuclear reactor. The control rod drive contains a drive housing, a throttle bush disposed at least partially in the drive housing, a drive unit, and a control rod carrying element disposed in the drive housing and moveable between a basic position and a moved-in end position. A part of the control rod carrying element is guided in the throttle bush and the control rod carrying element has a lower end cooperating with the drive unit. The control rod carrying element and the throttle bush define there-between a flow path for a pressure fluid, the flow path leading beyond the throttle bush and has a free flow cross section varying in dependence on a position of the control rod carrying element. In the control rod drive, there is provision for the free flow cross section of the flow path leading beyond the throttle bush to be changed as a function of the current position of the control carrying element. The flow path is in this case formed, in particular, by the gap between the throttle bush and a control rod carrying element configured, in particular, as a hollow piston. The invention proceeds, in this case, from the notion of varying the pressure acting on the hollow piston (control rod carrying element) by suitably influencing the pressure drop across the throttle bush and of setting the pressure to the effect that the speed of the hollow piston changes when the latter is being shot in. As a result, a suitable speed profile, which avoids critical load peaks, can therefore be formed over the move-in length of the hollow piston. Therefore before the moved-in end position of the hollow piston is reached, the speed is reduced as far as possible, in order to keep the impact forces low when the hollow piston butts against the throttle bush. Thus, by a suitable choice of the flow conditions between the throttle bush and the hollow piston, it becomes possible, as a function of the position of the hollow piston, to have a moving-in which entails markedly lower mechanical loads, as compared with a conventional control rod drive. By virtue of the lower loads, additional braking devices, such as, for example, a spring element, can have a simpler and, in particular, shorter configuration. Overall, the construction length of the entire control rod drive can thereby be shortened. In an expedient development, the free flow cross section increases from the basic position in the moved-out state to the moved-in end position. By the basic position, it is meant, in this context, that the control rod is moved completely out of the reactor core. What is achieved by this measure is that the pressure acting on the hollow piston and consequently the speed of the hollow piston are reduced when the latter approaches the moved-in end position. The flow resistance for the pressure fluid between the throttle bush and the hollow piston is therefore reduced, so that the pressure fluid can pass with a low resistance into the interior of the reactor pressure vessel. In order to achieve these varying flow conditions with a simple design, there is provision, in a preferred development, for the control rod carrying element to have a changing outside diameter. That is to say, when the control rod carrying element moves through the throttle bush, the gap between these two elements changes automatically due to the changing outside diameter. Expediently, in this case, the control rod carrying element has a reduced outside diameter in a lower region facing the drive unit, in order to achieve the desired braking behavior of the hollow piston when the latter reaches the moved-in end position. With a view to a suitable flow routing, the control rod carrying element preferably narrows continuously to the reduced outside diameter in a narrowing region, so that the flow resistance changes continuously. In particular, in this case, the control rod carrying element has a conically running region, as seen in cross section. With a view to suitable braking behavior, while at the same time maintaining a sufficiently rapid shoot-in of the respective control rod, the control rod carrying element has a reduced diameter uniformly over a defined length only. For the changing flow resistances as a function of the position of the control rod carrying element, alternatively to or in combination with the reduction in the outside diameter of the control rod carrying element, preferably a bypass orifice is provided in the control rod carrying element configured as a hollow body. A flow path leading beyond the throttle bush is therefore also open to the pressure fluid via the bypass orifice, but is effective only when the bypass orifice is in the region of the throttle bush during moving-in and, in particular when the bypass orifice has run through the throttle bush, that is to say located inside the reactor pressure vessel. The change in the flow resistance in this case is determined essentially according to the size of the bypass orifice. A plurality of bypass orifices in different length positions of the hollow body may also be provided. In the combination of the reduced outside diameter with the bypass orifice, the latter is disposed preferably in the region upstream or in the region of the narrowing of the control rod carrying element to the reduced outside diameter. Advantageously, therefore, a change in the flow conditions is achieved even before the reduced outside diameter becomes effective. By virtue of the two independent measures of the bypass orifice and of the reduced outside diameter, a desired speed profile can be set in a simple way. Expediently, the control rod carrying element has, in the region with the reduced outside diameter, an outer web which is located within the throttle bush when the control rod carrying element is positioned in the moved-in end position. This measure brings about an increase in the flow speed when the hollow piston has reached the moved-in position. The penetration of dirt particles is consequently avoided. Expediently, the outer web is configured as a peripheral annular web, the outside diameter of which corresponds approximately to the inside diameter of the throttle bush. The annular web therefore largely seals off, with the exception of a tolerance clearance, the gap that exists between the reduced outside diameter and the throttle bush. For reliable guidance of the control rod carrying element in a guide tube provided for this purpose, preferably longitudinal webs are disposed in the region of the reduced outside diameter. These virtually interrupt the reduced outside diameter and extend in the radial direction as far as the normal outside diameter, that is to say the original outside diameter, which is not yet reduced. The longitudinal webs are in this case disposed in such a way that, when the control rod carrying element is moved in, they are guided by guide elements, in particular guide rollers, disposed inside the guide tube. The object is achieved furthermore, according to the invention, by a method for moving a control rod into a reactor core of a nuclear reactor. Accordingly, there is provision, during moving-in, for the flow resistance formed for the pressure fluid across the throttle bush to be changed. The advantages and preferred embodiments given with regard to the control rod drive may also be transferred accordingly to the method. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a control rod drive for a nuclear reactor and a method for moving a control rod into a reactor core of a nuclear reactor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 4 thereof, there is shown the basic construction of a control rod drive 2. FIG. 4 shows the control rod drive 2 in a partially sectional illustration and in its position mounted on a reactor pressure vessel 4. Only a detail of the reactor pressure vessel 4 can be seen in FIG. 4. The control rod drive 2 is fastened by a drive housing 8 to a connection piece 6 extending into an interior 7 of the reactor pressure vessel 4. A drive unit 9 is provided on the drive housing 8 on the end face, outside the reactor pressure vessel 4, the drive unit 9 contains a motor 10 which drives a drive shaft 14 by a spindle drive 16 via a gear unit 12. The spindle drive 16 is formed from a spindle 18 which is produced on the drive shaft 14 and which is guided by a nut 20. The nut 20 is guided within a guide tube 22 and carries a hollow piston 24 that, with its lower end configured in the manner of a flange 25, sits loosely on the nut 20. Both the nut 20 and the hollow piston 24 are guided via guide rollers 26 in the guide tube 22 disposed concentrically to the drive housing 8. The hollow piston 24 has, at its upper closed end 27, a coupling 28, to which is fastened a control rod 29 to be moved, which is indicated merely in a rudimentary and greatly simplified manner. The coupling 28 therefore extends into the interior of the reactor pressure vessel 4. In an upper region of the drive housing 8, specifically in the region of the connection piece 6, is disposed what is known as a throttle bush 30 which surrounds the hollow piston 24 so as to form a tolerance clearance. During normal operation, the control rod 29 is moved in and out with the aid of the spindle drive 16. In the event of an emergency shutdown, a pressure fluid that is under a very high pressure of, for example, 150 bar is injected via a pressure line connection 32 and causes the hollow piston 24 to shoot upward, irrespective of the position of the nut 20. Since only the tolerance clearance (leakage gap) forming a flow path is present between the throttle bush 30 and the hollow piston 24, the pressure provided by the pressure fluid builds up completely and leads to an acceleration of the hollow piston 24. When the latter, with its flange 25, reaches the throttle bush 30 acting as a counterstop, a virtually abrupt braking of the hollow piston 24 takes place. Although the forces occurring at the same time are absorbed by a suitable mounting and, in particular, by a suitably dimensioned spring element 34, the mechanical load is nevertheless very high. Moreover, there is the problem that, when the pressure line connected to the pressure line connection 32 is opened, a pressure pulse occurs that may lead to excess speed and to an increased load. According to the invention and as shown in FIGS. 1 and 2, a control rod carrying element 40 configured as a hollow piston is guided by the throttle bush 30. The throttle bush 30 and the control rod carrying element 40 are disposed within the drive housing 8 illustrated only in greatly simplified form here. The throttle bush 30 is disposed only in the region of the connection piece 6 (FIG. 4), that is to say extends only over a comparatively short length of the control rod carrying element 40. The pressure line connection 32 issues laterally into the drive housing 8. According to FIG. 1, the control rod carrying element 40 is in an intermediate position between a lower basic position and the upper moved-in end position illustrated in FIG. 2. In the basic position, the upper closed end 27 of the control rod carrying element 40 is approximately flush with the upper end of the throttle bush 30. The control rod carrying element 40 extends from the flange 25 at its lower open region to its upper closed end 27. Whereas a cavity 46 enclosed by the control rod carrying element 40 has a constant inside diameter, the outside diameter of the control rod carrying element 40 changes over its length. As a result, a gap width of a gap located between the throttle bush 30 and the control rod carrying element 40 changes as soon as a relative position between the throttle bush 30 and the control rod carrying element 40 changes. A flow path 42 is therefore formed from the inside of the drive housing 8 into the interior 7 of the reactor pressure vessel 4, the free flow cross section of the flow path 42 varies as a function of the position of the control rod carrying element 40. In this case, the control rod carrying element 40 has, in the region of its upper end 27, the maximum outside diameter which is maintained over part of its overall length. The control rod carrying element 40 subsequently narrows continuously in a narrowing region 48 to a reduced outside diameter which the control rod carrying element 40 maintains as far as the flange 25. The reduction in the outside diameter is achieved by a reduction in the wall of the control rod carrying element 40. Furthermore, in the exemplary embodiment, the control rod carrying element 40 has a bypass orifice 52 which is disposed in the region above the narrowing region 48 and, in particular, adjoins the latter. As a result, with the control rod carrying element 40 being in a suitable position, a further flow path for the pressure fluid is formed via the interior 46 through the wall of the control rod carrying element 40 into the interior 7 of the reactor pressure vessel 4. The configuration of the bypass orifice 52 is not absolutely necessary. Disposed approximately centrally between the narrowing region 48 and the flange 25 is a peripheral annular web 50, the outside diameter of which, in the exemplary embodiment, corresponds approximately to the maximum outside diameter in the upper region of the control rod carrying element 40. As may be gathered from FIG. 2, the annular web 50 is disposed in such a way that it is located at the upper end of the throttle bush 30 when the control rod carrying element 40 is positioned in the upper moved-in end position. The flange 25 in this case acts as a counterstop, with which the control rod carrying element 40 butts against the throttle bush 30 during moving-in. By virtue of this special configuration of the control rod carrying element 40 with its varying outside diameters and with the bypass orifice 52, the flow resistance for the pressure fluid, which can flow beyond the throttle bush 30 into the interior 7 of the reactor pressure vessel 4, changes as a function of the position which the control rod carrying element 40 in each case currently assumes. In the event of an emergency shutdown, a pressure fluid is injected via the pressure line connection 32 and can escape only partially via the flow path 42 because of the high flow resistance of the latter. The control rod carrying element 40 therefore experiences high acceleration due to the high pressure build-up and is moved upward at high speed. When the control rod carrying element 40 reaches the middle position illustrated in FIG. 1, the flow resistance gradually decreases, that is to say the pressure acting on the control rod carrying element 40 is reduced, so that, overall, the control rod carrying element 40 is braked somewhat. The reduction in flow resistance takes place initially via the bypass orifice 52 which allows the pressure fluid to flow out of the cavity 46 over into the flow path 42 and from there into the interior of the reactor pressure vessel 4. When the control rod carrying element 40 is moved upward even further, the bypass orifice 52 allows an immediate flow of the pressure fluid out of the cavity 46 over into the interior 7. The flow resistance is subsequently additionally achieved by the reduction in the outside diameter along the narrowing region 48. By virtue of the constant and continuous narrowing, a continuous and uniform reduction in the speed of the control rod carrying element 40 likewise takes place. The continuous change in the outside diameter and consequently the continuous change in the flow resistance are advantageous for a moving-in which is as uniform and as jolt-free as possible and is consequently as careful as possible in terms of material. When the narrowing region 48 passes the throttle bush 30, the control rod carrying element 40 is brought into the upper moved-in end position (FIG. 2) at an essentially constant low speed over the last travel segment. As soon as the annular web 50 enters the flow path 42, the flow resistance of the latter and consequently the outflow speed rise again, with the result that a dirt-repelling flow is achieved. The flow path via the bypass orifice 52 is still open. In order to ensure a reliable guidance of the control rod carrying element 40 during moving-in, longitudinal webs 54 are disposed in the region of the reduced outside diameter, as may be gathered from FIG. 3. In the exemplary embodiment, two mutually opposite longitudinal webs 54 are provided, which define an outside diameter that corresponds, in particular, to the normal outside diameter of the control rod carrying element 40 upstream of the narrowing region 48. By the longitudinal webs 54, the control rod carrying element 40 is guided reliably, within the guide tube 22 illustrated in FIG. 4, on the guide rollers 26 provided in the region of the throttle bush 30. The longitudinal webs 54 may, if required, also be configured as rails. By the device according to the invention, a setting of the moving-in speed of the control rod element 40 as a function of its respective position is achieved by simple measures. As a result, in particular, a suitable braking of the control rod carrying element 40 before the moved-in end position is reached can be obtained. Furthermore, there is thereby the possibility of reducing a system-related excess speed caused by pressure peaks generated during the inflow operation of the pressure fluid. By virtue of these measures, the components of the control rod drive, in particular the components provided for braking, such as, for example, the spring element 34 (FIG. 4), are subjected to a markedly lower load than in the conventional configuration. This makes it possible, overall, to have a simpler configuration of the components necessary for the braking operation and, as compared with the conventional configuration, is accompanied by a shortening of the construction length of these components, since, for example, the forces to be absorbed by the spring element 34 are lower and the spring element 34 can thereby be shortened. The principle illustrated in FIGS. 1 and 2 is used preferably in the control rod drive 2 for a boiling water reactor, such as is illustrated, for example, in FIG. 4. The control rod drive 2 illustrated in FIG. 4 is therefore modified to the effect that the control rod carrying element 40 illustrated diagrammatically in FIGS. 1 to 3 is used instead of the hollow piston 24, illustrated in FIG. 4, with the constant outside diameter.
062228986	claims	1. A method for treating a surface of a metal body comprising applying a graphite coating to the surface to be protected, and applying a material reactive with the metal body on the uncoated surface. 2. A method for treating a surface of aluminum comprising applying a graphite coat to one surface of an aluminum body, and applying a material reactive to aluminum on the uncoated surface. 3. A method for protecting the exterior of an aluminum container during boding to a uranium slug comprising applying a graphite coat to the exterior surface of the container, and applying a bonding agent reactive to aluminum, to the interior surface of the container and the slug. 4. A method for protecting the exterior of an aluminum container during immersion in an aluminum-silicon alloy comprising applying a coating comprising colloidal graphite in water to the exterior surface of the container, and applying an alloy containing aluminum and silicon to the interior surface of the container. 5. A method for protecting the exterior of an aluminum container during immersion in an aluminum-silicon alloy comprising applying a coating to the external surface of the container, the coating comprising colloidal graphite in water, permitting the coating to dry, and applying an alloy of aluminum and silicon to the interior surface of the container at a temperature between 588.degree. and 594.degree. C. 6. A method of jacketing a uranium slug to an aluminum container comprising applying a coating to the exterior of the container, the coating consisting of colloidal graphite in water, permitting the coating to dry, applying an alloy of aluminum and silicon to the interior surface of the container at a temperature between 588.degree. and 594.degree. C., inserting the slug into the container in complete contact with the alloy, and quenching the assembly. 7. A method of jacketing a uranium slug to an aluminum container comprising applying a coating to the exterior of the container, the coating consisting of colloidal graphite in water, permitting the coating to dry, applying an alloy of aluminum and silicon to the interior surface of the container at a temperature between 588.degree. and 594.degree. C., inserting the slug into the container in complete contact with the alloy, and quenching the assembly, the time interval between applying the alloy and the quenching being a maximum of forty seconds.
	claims	1. An apparatus to provide reliable attachment of an X-ray tube, the apparatus comprising:a collimator frame having a wrap-around capture mechanism, the wrap-around capture mechanism and the collimator frame formed as one piece from the same material; andan X-ray tube operably mounted to the collimator frame. 2. The apparatus of claim 1, wherein the wrap-around capture mechanism further comprises:an L-shaped wrap-around capture mechanism in which an appendage of the wrap-around capture mechanism extends over the X-ray tube. 3. The apparatus of claim 1, wherein the apparatus further comprises:a passive capture device mounted to the wrap-around capture mechanism, wherein at least a portion of the passive capture device is positioned between the wrap-around capture mechanism and the X-ray tube. 4. The apparatus of claim 3, wherein the passive capture device further comprises:a C-shaped passive capture device. 5. The apparatus of claim 1, wherein the X-ray tube further comprises:an X-ray tube mounting bracket mounted to the collimator frame; andan X-ray tube casing mounted to the X-ray tube mounting bracket. 6. The apparatus of claim 5, wherein the wrap-around capture mechanism further comprises:a L-shape in which an appendage of the wrap-around capture mechanism extends over the X-ray tube mounting bracket. 7. The apparatus of claim 5, wherein the X-ray tube mounting bracket further comprises a channel formed into a surface of the X-ray tube mounting bracket wherein the X-ray tube casing further comprises a channel formed into a surface of the X-ray tube casing, and wherein the apparatus further comprises:an interposer plate that fits into the channel of the X-ray tube mounting bracket and that fits into the channel of the X-ray tube casing. 8. The apparatus of claim 1, wherein the X-ray tube mounting bracket is mounted to the collimator frame by a plurality of bolts. 9. The apparatus of claim 1, wherein the apparatus further comprises:a medical imaging apparatus. 10. A collimator comprising:an X-ray collimator frame;a wrap-around capture mechanism operably coupled to the X-ray collimator frame;a gantry operably coupled to the X-ray collimator frame;an X-ray tube mounting bracket mounted to the X-ray collimator frame by a plurality of bolts; andan X-ray tube casing mounted to the X-ray tube mounting bracket, anda passive capture device mounted to the wrap-around capture mechanism, wherein at least a portion of the passive capture device is positioned between the wrap-around capture mechanism and the X-ray tube mounting bracket,wherein the passive capture device further comprises a C-shaped passive capture device. 11. The collimator of claim 10, wherein the wrap-around capture mechanism further comprises:a wrap-around capture mechanism formed integrally as a portion of the collimator. 12. The collimator of claim 10, wherein the X-ray collimator further comprises:a medical X-ray collimator frame. 13. The collimator of claim 10, wherein the passive capture device includes a portion that is positioned between a surface of the wrap-around capture mechanism and an opposing surface of the X-ray tube mounting bracket. 14. The collimator of claim 13, wherein the wrap-around capture mechanism further comprises:an L-shaped wrap-around capture mechanism in which an appendage of the wrap-around capture mechanism extends over the X-ray tube mounting bracket. 15. The collimator of claim 14, wherein a surface of the appendage is about parallel with an opposing surface of the X-ray tube mounting bracket. 16. The collimator of claim 15, wherein movement between the X-ray tube mounting bracket and the collimator frame, the two parallel surfaces meet, and the movement between the X-ray tube mounting bracket and the collimator frame proceeds no further. 17. The collimator of claim 13, wherein the X-ray tube mounting bracket further comprises a channel formed into a surface of the X-ray tube mounting bracket wherein the X-ray tube casing further comprises a channel formed into a surface of the X-ray tube casing, and wherein the apparatus further comprises:an interposer plate that fits into the channel of the X-ray tube mounting bracket and that fits into the channel of the X-ray tube casing. 18. A computer tomography imaging system comprising:a medical X-ray tube casing;an X-ray tube mounting bracket operably coupled to the medical X-ray tube casing;an X-ray collimator frame having a wrap-around capture mechanism, the wrap-around capture mechanism having an L-shape in which a portion of the L-shape extends over the X-ray tube mounting bracket, the wrap-around capture mechanism formed integrally as a portion of the X-ray collimator frame;a gantry operably coupled to the X-ray collimator frame; anda C-shaped passive capture device operably coupled to the wrap-around capture mechanism, wherein at least a portion of the C-shaped passive capture device is positioned between the wrap-around capture mechanism and the X-ray tube mounting bracket. 19. The computer tomography imaging system of claim 18, wherein the passive capture device includes a portion that is positioned between a surface of the wrap-around capture mechanism and an opposing surface of the X-ray tube mounting bracket. 20. The computer tomography imaging system of claim 19, wherein the portion takes up a portion of the space between the surfaces and the opposing surface, thus limiting and reducing the amount of distance that the X-ray collimator frame and the medical X-ray tube casing move in opposite directions relative to each other under an urging of a force. 21. The computer tomography imaging system of claim 18, wherein the X-ray tube mounting bracket further comprises a channel formed into a surface of the X-ray tube mounting bracket and wherein the X-ray tube casing further comprises a channel formed into a surface of the X-ray tube casing, and wherein the computer tomography imaging system further comprises:an interposer plate that fits into the channel of the X-ray tube mounting bracket and that fits into the channel of the X-ray tube casing. 22. A method to attach an X-ray tube to a rotatable gantry comprising:placing an interposer plate into a channel formed in a surface of the X-ray tube collimator frame, the X-ray tube collimator frame operably coupled to the rotable gantry, the X-ray tube collimator frame further comprising a wrap-around capture mechanism;positioning an X-ray tube along an X axis, the X-ray tube having a mounting bracket;moving the X-ray tube and the rotatable gantry into contact;tightening bolts between the rotatable gantry and the mounting bracket; andplacing a passive capture device on the wrap-around capture mechanism. 23. The method of claim 22, wherein the positioning further comprises:sliding the mounting bracket under the wrap-around capture mechanism. 24. An apparatus comprising:an interposer plate placed into a channel formed in a surface of the X-ray tube collimator frame, the X-ray tube collimator frame operably coupled to a rotable gantry, the X-ray tube collimator frame further comprising a wrap-around capture mechanism; an X-ray tube positioned along an X axis of the apparatus, the X-ray tube having a mounting bracket;the X-ray tube in contact with the rotatable gantry;bolts attaching the rotatable gantry to the mounting bracket; anda passive capture device placed on the wrap-around capture mechanism.
043472141	abstract	Disclosed is an apparatus for detecting the location of failed fuel in a reactor, the apparatus comprising means for collecting tag gas from cover gas containing tag gas at ambient temperature and enriching the collected tag gas to an analyzable concentration and tag gas analysis means for analyzing the enriched tag gas to determine the composition thereof.
	summary
	description	The present invention relates to a radiation imaging apparatus for capturing multiple radiation images used in energy subtraction and an imaging control device for performing energy subtraction imaging. In the field of medical radiation imaging, energy subtraction technique is known. With the energy subtraction technique, images in which specific tissue is enhanced, e.g. soft tissue images and bone part images are obtained. A soft tissue image representing soft tissue, e.g. lungs and esophagus, is obtained by removing a component of bones, e.g. ribs and the backbone, from an image of a subject or patient. On the other hand, a bone part image representing the component of bones is obtained by removing a component of the soft tissue. The energy subtraction technique is based on the fact that tissue such as bones or the soft tissue has specific radiation energy absorption properties. Two kinds of radiations different in energy distribution are emitted onto the same object of interest to obtain two kinds of raw images, namely, a high energy image and a low energy image, for energy subtraction. These two raw images are properly weighted, and then a pixel value of one of the images is subtracted from a pixel value of the other image to obtain a difference. Thus, a subtracted image in which images of specific tissues are enhanced, e.g. a soft tissue image or a bone part image, is obtained. A two-shot method in which radiations of two different energy levels are emitted in sequence to a subject is known as one of methods to obtain two raw images, a high energy image and a low energy image (see, for example, U.S. Pat. No. 4,482,918 corresponding to Japanese Patent Laid-Open Publication No. 2-063439). To obtain the radiations of two different energy levels, a radiation tube voltage of the radiation source may be changed, for example. When a high radiation tube voltage is applied to the radiation source, the radiation source generates high-energy radiation having an energy distribution with a larger high energy component. When a low radiation tube voltage is applied to the radiation source, the radiation source generates low-energy radiation having an energy distribution with a larger low energy component. The energy distribution of low-energy radiation and the energy distribution of high-energy radiation partly overlap with each other. Since the energy subtraction technique uses a difference between the energy components of the two kinds of radiations, a smaller overlap in the energy components, which enables high energy separation performance, is preferable. To improve energy separation between the high-energy radiation and the low-energy radiation, a low energy component of the high-energy radiation is cut or filtered out during the emission of high energy radiation (see Japanese Patent Laid-Open Publication No. 2003-210442). For an imaging apparatus of Japanese Patent Laid-Open Publication No. 2003-210442, a filter has a disc-shape and rotates at a constant speed. The filter has a filter area formed on a semicircular area of the disc. The filter area cuts the low energy component of radiation. Rotating the filter at a constant speed allows the filter area to be inserted and retracted from a path of radiation at a fixed cycle. Two successive radiation emissions are synchronized with the phases of the filter, respectively. Specifically, high-energy radiation is emitted while the filter area is inserted into the path of the radiation, and low-energy radiation is emitted while the filter area is retracted from the path. In other words, the imaging apparatus of Japanese Patent Laid-Open Publication No. 2003-210442 controls the emission timing in synchronization with the fixed area shifting cycle or shift cycle of the filter. On the other hand, an imaging apparatus of U.S. Pat. No. 7,636,413 (corresponding to Japanese Patent Laid-Open Publication No. 2003-325504) discloses a filter composed of four rectangular filter plates each having a different filter area. The four filter plates are attached to a rotary hub at 90-degree intervals. In accordance with a switch pulse which is outputted in synchronization with the exposure start signal, the rotary hub rotates by 90 degrees to insert the filter plates into the radiation path in sequence. Unlike the imaging apparatus of Japanese Patent Laid-Open Publication No. 2003-210442, the area shifting cycle of the filter is not fixed in the imaging apparatus of U.S. Pat. No. 7,636,413. The switch timing or positioning of the filter plates is controlled such that the filter plates are rotated or shifted in accordance with the emission timing. It is known that the two-shot method has problems, such as to improve energy separation performance and to reduce motion artifacts or virtual images caused by body motion. For example, for chest imaging, a motion artifact caused by a heartbeat is generated in a subtracted image, which is obtained by energy subtraction processes, when cardiac phases of the two raw images for the energy subtraction do not coincide with each other, for example, the first emission or first exposure is performed during diastole or relaxation phase of a heartbeat, and the second emission or second exposure is performed during systole or contraction phase. For an imaging technique to reduce motion artifacts, cardiac cycles of a patient are monitored to perform two successive emissions at the same cardiac phases, respectively (see U.S. Pat. No. 6,643,536, corresponding to Japanese Patent Laid-Open Publication No. 2002-325756). For imaging using the energy subtraction, U.S. Pat. No. 4,482,918, Japanese Patent Laid-Open Publication No. 2003-210442, and U.S. Pat. No. 7,636,413 disclose techniques in which two successive emissions and filter switch timings are synchronized, respectively, to improve energy separation performance. On the other hand, U.S. Pat. No. 6,643,536 discloses techniques to perform two successive emissions at the same cardiac phases, respectively, to reduce the motion artifact. However, none of the above discloses the technique capable of improving the energy separation performance and reducing the motion artifact at the same time. To improve energy separation performance and reduce motion artifacts at the same time, an applicant contemplates to combine the techniques disclosed in U.S. Pat. No. 6,643,536 and the techniques disclosed in U.S. Pat. No. 4,482,918, Japanese Patent Laid-Open Publication No. 2003-210442, and U.S. Pat. No. 7,636,413. That is, two successive emission timings and the filter switch timings are synchronized respectively, while the two successive emissions are performed at the same cardiac phases, respectively. Cardiac cycles vary among individuals, and even vary within the same person. If the filter is switched or shifted at a fixed area shifting cycle, and when the area shifting cycle and the cardiac cycle are asynchronous, an operator needs to wait for the timing at which the filter phase and the cardiac phase coincide with each other. As a result, imaging time becomes long. For example, when the area shifting cycle of the filter and the cardiac cycle are synchronous, two radiation emissions can be performed at the same cardiac phases, respectively. As a result, the imaging time becomes short. On the other hand, when the area shifting cycle of the filter and the cardiac cycle are asynchronous, even if the first radiation emission is performed at timing in which the filter phase and the cardiac cycle coincide with each other, the area shifting cycle of the filter do not synchronize with subsequent cardiac cycle. In this case, the operator needs to wait for the timing at which the filter phase and the cardiac phase coincide with each other again. Body motion, for example, heart motion or lung motion of a patient occurs due to breathing in addition to heartbeats. To reduce the motion artifact caused by breathing, a patient is often asked to hold his or her breath during the imaging. A long time interval between the first and second radiation emissions extends the imaging time. As a result, the patient needs to hold his or her breath for a long time, which increases physical burdens of the patient. The imaging time can be shortened with the use of the imaging apparatus disclosed in U.S. Pat. No. 7,636,413. This imaging apparatus uses a filter switching device capable of synchronizing the insert timing of the filter and the emission timing. It is unnecessary to wait for the timing in which the filter phase and the cardiac phase coincide with each other. Thus, the imaging time becomes short. However, the filter switching device shown in FIG. 7 of U.S. Pat. No. 7,636,413 generates switch pulses in synchronization with each exposure start signal to switch or shift the filter during the radiation emission. Accordingly, the filter is accelerated or decelerated in a short time to place the filter in the intended position, which requires a motor with high responsiveness and the motor control with high precision. As a result, the device cost significantly increases. An object of the present invention is to provide a radiation imaging apparatus for performing energy subtraction imaging in a short time and an imaging control device capable of controlling this energy subtraction imaging. Another object of the present invention is to provide a radiation imaging apparatus and an imaging control device at low cost. Still another object of the present invention is to provide a radiation imaging apparatus and an imaging control device with high separation performance for radiation energy. In order to achieve the above and other objects, the radiation imaging apparatus of the present invention includes a radiation source, a filter, a cycle determining section, and a driver. The radiation source performs multiple radiation emissions to a subject. The filter has at least one filter area for changing energy distribution of radiation in at least one of the radiation emissions. The filter periodically shifts between an inserted state in which the filter area is inserted in a path of the radiation and a retracted state in which the filter area is retracted from the path. The cycle determining section determines a shift cycle of the filter for shifting the filter area between the inserted state and the retracted state based on subject information. The driver drives the filter to shift at the determined shift cycle. The driver drives the filter to start shifting before a start of the first radiation emission and to shift until an end of the last radiation emission after the first radiation emission. It is preferable that the radiation imaging apparatus further includes an emission controller for outputting a signal for starting the radiation emission to the radiation source to control emission timing of the radiation. It is preferable that the subject information is cardiac cycle information or respiration information of the subject, and the radiation imaging apparatus further includes a signal detector for detecting at least one of a cardiac signal indicating a state of the cardiac cycle information and a respiratory signal indicating a state of the respiration information. It is preferable that the cycle determining section determines the shift cycle so as to be in synchronization with the cardiac cycle information or the respiration information. It is preferable that the cycle determining section determines the shift cycle so as to be in synchronization with the cardiac cycle information, and the emission controller synchronizes the emission timing with a phase of the respiration based on the respiratory signal. It is preferable that the radiation imaging apparatus further includes a filter phase detector for detecting a phase of the filter, and the emission controller synchronizes the emission timing with the phase of the filter. It is preferable that the subject information is body thickness of the subject, and the cycle determining section determines the shift cycle in accordance with a maximum exposure time determined based on the body thickness. It is preferable that the filter includes multiple filter areas and the multiple filter areas are selectively inserted in sequence into the path. It is preferable that the filter includes multiple filters each having at least one filter area, and the filters are selectably used. It is preferable that each of the filters is individually rotatable, and arranged to be insertable into the path, and has a transmission area for retracting the filter area of the filter when the filter area of another filter is inserted in the path. The imaging control device for controlling the radiation source and the filter of the present invention includes a cycle determining section and a controller. The cycle determining section determines a shift cycle of the filter for shifting the filter area between the inserted state and the retracted state based on subject information. The controller controls a driver for driving the filter. The controller controls the driver to shift the filter at the determined shift cycle by starting before a start of the first radiation emission and until an end of the last radiation emission after the first radiation emission. According to the present invention, the shift cycle of the filter is previously determined based on the subject information. The filter starts to shift at the determined shift cycle before the start of the first radiation emission and continues to shift until the end of the last radiation emission after the first radiation emission. Thus, the radiation imaging apparatus and the imaging control device capable of performing the energy subtraction imaging in a short time at low cost, and with high separation performance for radiation energy are provided. In the present invention, the filter rotates at a constant speed during the energy subtraction imaging, namely, before the start until the end of the radiation emissions. Accordingly, the present invention eliminates the use of a device such as a conventional high-performance filter switching device which inputs a pulse in accordance with the exposure start signal outputted during imaging to switch filters as described in U.S. Pat. No. 7,636,413. As a result, no additional device cost is incurred. The shift cycle of the filter is determined based on, for example, the cardiac cycle information which is the subject information, allowing two radiation emissions within two successive heartbeats. As a result, the energy subtraction imaging is performed in a short time, reducing physical burdens of the subject. In FIG. 1, a radiation imaging apparatus 10 is composed of a radiation source 11 for generating and emitting radiation, a radiation image detector 12 for receiving the radiation passed through a subject P to detect a radiation image, an imaging control device 13 for controlling the radiation source 11 and the radiation image detector 12, and a console 14 for inputting operation instructions such as exposure conditions and instructions for imaging to the imaging control device 13. The radiation imaging apparatus 10 is, for example, a laying-type imaging apparatus for capturing images of the subject P laid down on a patient table 15. The radiation source 11 is provided with a radiation tube, for example, an X-ray tube 16 having a cathode filament and an anode target. A high voltage is applied between the cathode and the anode, so that thermal electrons released from the filament hit the target. Thus, X-ray is generated. The target has a disc-like shape, and rotates while the filament releases the thermal electrons. Rotating the target increases a target area which thermal electrons hit. As a result, a thermal capacity of the target is increased, which reduces thermal damage. For example, molybdenum (Mo) and tungsten (w) are used as materials of the target. Changing the X-ray tube voltage (unit: kV) changes the energy distribution of X-ray emitted from the radiation source 11. An amount of X-ray emission (hereinafter referred to as emission amount or dose) is defined by the product (unit: mAs) of an X-ray tube current (unit: mA) and an exposure time (unit: second or abbreviated as “s”). If the dose is unchanged, the exposure time increases as the X-ray tube current decreases, and the exposure time decreases as the X-ray tube current increases. A voltage generated by a high voltage generator 17 is applied to the radiation source 11. The radiation imaging apparatus 10 has a function to perform energy subtraction imaging. To perform energy subtraction imaging, the radiation source 11 emits X-rays at two wavelengths, high-energy X-ray and low-energy X-ray, in sequence. The high-energy X-ray has an energy distribution in which peak energy and average energy are high. The low-energy X-ray has an energy distribution in which peak energy and average energy are low compared to the high-energy X-ray. The imaging control device 13 sends an exposure start signal, the maximum exposure time, an exposure stop signal, and control signals to the high voltage generator 17 in order to control the radiation source 11. The exposure start signal defines exposure timing of the radiation source 11. The maximum exposure time is determined in accordance with imaging conditions. The exposure stop signal causes radiation source 11 to stop the exposure when the exposure amount reaches a predetermined value. The control signals control an X-ray tube voltage, an X-ray tube current, and the like. When an instruction for energy subtraction imaging is inputted through the console 14, the imaging control device 13 sends two types of control signals, the control signal for high voltage and the control signal for low voltage, to the high voltage generator 17 so as to allow the radiation source 11 to emit the high-energy X-ray and the low-energy X-ray in sequence. The imaging control device 13 monitors a status of the voltage generated by the high voltage generator 17. The imaging control device 13 judges that the voltage is in an anomalous status when the generated voltage does not reach its intended value or the voltage largely fluctuates. When the imaging control device 13 detects a voltage anomaly, the imaging control device 13 controls the radiation source 11 to stop the exposure, and raises an alarm indicating the voltage anomaly. The radiation image detector 12 is a flat panel detector having a photoconductive layer, a capacitor, and a detector-element array on an insulation substrate such as a glass substrate. The photoconductive layer photoelectrically converts X-ray into signal charge. The capacitor stores the signal charge. The detector-element array has multiple detector elements (pixels) arranged in matrix and composed of TFTs (thin film transistors) for reading the stored signal charge. The radiation image detector 12 turns off the TFTs during the X-ray emission and performs signal charge accumulation. After the X-ray emission is ended, the radiation image detector 12 turns on the TFTs to read the accumulated signal charge. The signal charge in each pixel is read by the TFT, and then converted into digital image data by an A/D converter (not shown). The digital image data is outputted from the radiation image detector 12 to the console 14 through the imaging control device 13. The imaging control device 13 synchronizes the operations of the radiation source 11 and the radiation image detector 12 such that the accumulation operation of the radiation image detector 12 starts in synchronization with X-ray emission start timing of the radiation source 11, and the reading operation is performed in synchronization with the emission stop timing. The radiation image detector 12 is provided with an exposure control device (not shown) for controlling exposure to the X-ray emitted from the radiation source 11. When the amount of exposure received by the radiation image detector 12 reaches a predetermined value, the exposure control device notifies the imaging control device 13. When the imaging control device 13 receives this notification, the imaging control device 13 sends the exposure stop signal to the high voltage generator 17 to stop the X-ray emission of the radiation source 11, even if a maximum exposure time has not been reached. The maximum exposure time refers to the longest duration of a single exposure performed by the radiation source 11. Even if the emission amount or dose of the X-ray emitted from the radiation source 11 is unchanged, an X-ray transmission amount passing through the subject P varies with the body thickness of the subject P. The body thickness varies among individuals. Even the body thickness of the same person varies with a region. For this reason, the imaging control device 13 sets in the high voltage generator 17 the maximum exposure time determined based on the body thickness of the region surrounding the object of interest of the subject P. Imaging conditions such as an object of interest (e.g. chest or abdomen), an X-ray tube voltage, and an X-ray tube current are inputted through the console 14, and set in the imaging control device 13. A numeral 18 indicates a body thickness measuring device 18 for measuring the body thickness of a region surrounding an object of interest (e.g. chest or abdomen) of the subject P. The imaging control device 13 calculates the maximum exposure time based on the set X-ray tube current and the body thickness measured by body thickness measuring device 18. The body thickness measuring device 18 transmits ultrasonic waves or laser to the object of interest of subject P, and then measures the body thickness based on the intensity of the echo waves or reflected laser, for example. Alternatively, the body thickness may be set in the imaging control device 13 using the following methods. One method is to assume the body thickness from the weight and the height of the subject P. In the case where a body-weight measuring scale is provided in the patient table 15, the imaging control device 13 obtains the weight measured at the patient table 15. An approximate body thickness is calculated based on the obtained weight and the height of the subject P input through the console 14. Another method is to input the body thickness actually measured in advance through the console 14. Any of the above methods can be used for setting the body thickness. A vital sign measuring device 19 is connected to the imaging control device 13. The vital sign measuring device 19 measures vital signs, e.g. cardiac cycles and respiration of the subject P. The vital sign measuring device 19 detects electrical signals generated in the heart muscle during alternate contraction and relaxation of the heart of the subject P through multiple electrodes attached to the body of the subject P, and then outputs in real time cardiac signals indicating conditions or statuses (contraction and relaxation phases) of cardiac cycles or heartbeats. The vital sign measuring device 19 may output respiratory signals in real time. The respiratory signals indicate expansion and contraction of the lungs of the subject P. Impedance becomes high in the lung when air is breathed into the lung, which restricts or hinders the flow of AC current. Impedance becomes low in the lung when air is breathed out of the lung, which promotes the flow of the AC current. The vital sign measuring device 19 passes high-frequency AC current between multiple electrodes attached to the body of the subject P, and then detects changes in the impedance in the lungs between the breathing-in and the breathing-out of air. Thereby, the vital sign measuring device 19 outputs respiratory signals. In energy subtraction image processing, a low energy image L is subtracted from a high energy image H, and thus a subtracted image is obtained as shown in FIG. 2. The high and low energy images H and L are captured with two successive X-ray emissions, respectively. If the phase of the cardiac cycle of the heart in the high energy image H and the phase of the cardiac cycle of the heart in the low energy image L are different, for example, the heart in the relaxation phase is captured in the high energy image H and the heart in the contraction phase is captured in the low energy image L, a motion artifact is generated in the subtracted image due to the motion of the body of the subject P. To reduce the motion artifact, the imaging control device 13 receives the cardiac signals and the respiratory signals from the vital sign measuring device 19 so as to control the radiation source 11 to match the phases of the cardiac cycle of the two sequential X-ray emissions with each other or to match the phases of the respiration of the two sequential X-ray emissions with each other. A captured image is displayed on a monitor (not shown) of the console 14, which allows an operator to check whether the image has been captured successfully. When the image is captured successfully, the image is stored in an image server 20. Two radiation images (in this example, X-ray images) obtained at different energy levels, the high energy image H and the low energy image L, are stored in the image server 20 for the energy subtraction imaging. The radiation image data outputted from the radiation image detector 12 is transferred to the console 14 via the imaging control device 13. The console 14 has an image processing function. The console 14 reads an image from the image server 20, and performs image processing for the energy subtraction. Alternatively, an image processing device other than the console 14, for example, an external terminal connected to the image server 20 via a communication network such as a LAN may be used for the image processing for the energy subtraction. Referring to FIG. 2, the image processing for the energy subtraction is described using chest imaging as an example. Bones (e.g. backbone and ribs) and soft tissue (e.g. lungs) are recorded together in each of the high energy image H and the low energy image L. The bones and the soft tissue differ in X-ray energy absorption, namely, X-ray attenuation. Accordingly, a density ratio between the bones and the soft tissue of the high energy image H is different from that of the low energy image L. To be more specific, in the high energy image H, a density ratio between the bones and the soft tissue becomes small. On the other hand, in the low energy image L, the density ratio between the bones and the soft tissue becomes large. This is because the soft tissue has relatively low absorption rates (high transmittance) of both the high and low energy components, and there is a small difference between the absorption rates of the high and low energy components. For the bones, conversely, there is a large difference between the absorption rates of the high and low energy components. Image processing using the energy subtraction is based on the fact that the density ratios between the bones and the soft tissue differ between the high energy image H and the low energy image L. Two subtracted images, the bone part image S1 and the soft tissue image S2, are obtained using the following mathematical expressions (1) and (2).for the bone part image: S1=α1×H−β1×L+B1 (1)for the soft tissue image: S2=α2×H−β2×L+B2 (2) For (1) and (2), each of α1, β1, α2, and β2 represents a weighting factor. Each of B1 and B2 represents a bias value. To obtain the bone part image S1, the weighting factors α1 and β1 are determined for each of the high energy image H and the low energy image L to make the density of the soft tissue in the high energy image H and the density of the soft tissue in the low energy image L equal. When each of the high energy image H and the low energy image L is multiplied by the determined weighting factors α1 and β1, the density of the soft tissue in high energy image H and that in the low energy image L become equal. The energy subtraction of the two images makes the bone part image S1. To obtain the soft tissue image S2, on the other hand, the weighting factors α2 and β2 are determined for each of the high energy image H and the low energy image L to make the density of the bones in the high energy image H and that in the low energy image L equal. When each of the high energy image H and the low energy image L is multiplied by the weighting factors α2 and β2, the density of the bones in high energy image H and that in the low energy image L become equal. The energy subtraction of the two images makes the soft tissue image S2. In FIG. 1, a collimator (a movable aperture stop) 21 and a filter 22 are placed below the X-ray tube 16 of the radiation source 11. The collimator 21 limits an emission field of X-ray emitted from the X-ray tube 16. The filter 22 changes energy distribution of the emitted X-ray. The collimator 21 is, for example, a rectangular grid of lead (Pb) plates. Moving each lead plate adjusts the size of the opening area of the grid to pass through the X-ray. As shown in FIG. 3, the filter 22 is composed of a circular rotary plate as a base or substrate. On the surface of the rotary plate, two areas, a semi-circular filter area 22a and a transmission area 22b, are provided. The filter area 22a is an area to which an X-ray absorbing material, e.g. copper (Cu) or gadolinium (Gd), is applied as a layer or coating. This X-ray absorbing material absorbs the low energy component of the X-ray. Thus, the filter area 22a cuts the low energy component of the X-ray emitted from the X-ray tube 16, but passes through the high energy component. The rotary plate is formed from a material with high X-ray transmission. On the other hand, the transmission area 22b is a through area without the application of the X-ray absorbing material and not having a filter function. A cutout or an opening formed in the rotary plate may also be used as the transmission area 22b. The filter 22 is rotated or shifted such that the filter area 22a is alternately and periodically inserted and retracted from a path 23 of radiation (in this example, X-ray). Upon the retraction of the filter area 22a from the path 23, the transmission area 22b is inserted into the path 23. In other words, the filter area 22a and the transmission area 22b are alternately inserted and retracted from the path 23 of X-ray. A motor 24 is a driver to rotate or shift the filter 22. During the energy subtraction imaging, the motor 24 starts to rotate before the start of the first radiation emission (first X-ray emission) and keeps rotating at a constant speed until the end of the second radiation emission (second X-ray emission). The filter 22, driven by the motor 24, also rotates or shifts at a constant speed. As a result, an area shifting cycle or shift cycle to insert and retract the filter area 22a of the filter 22 from the path 23 also becomes constant. A filter position detector 25 detects a rotational position of the filter 22. The filter position detector 25 is, for example, a photosensor for detecting a marker (not shown) on the filter 22. The filter position detector 25 outputs an ON signal while the filter area 22a is inserted into the path 23 of X-ray (radiation) and an OFF signal while the filter area 22a is retracted from the path 23. The ON and OFF signals outputted from the filter position detector 25 are inputted to the imaging control device 13. The filter area 22a and the transmission area 22b are alternately inserted into the path 23 by the rotation of the filter 22. In accordance with the output signal (filter position detecting signal) from the filter position detector 25, the imaging control device 13 detects a phase of the filter 22, e.g. the timing for the filter area 22a to start entering the path 23, a time period in which the filter area 22a covers the entire path 23, the timings for the filter area 22a to retract from the path 23 and for the transmission area 22b to start entering the path 23. In each of FIGS. 4A to 4C, the horizontal axis indicates energy, and the vertical axis indicates relative intensity in each of the high and low energy components. The relative intensity is standardized with the maximum value of the radiation, in this case, X-ray of each energy distribution. The energy subtraction imaging is commonly used for chest images where lungs are mostly covered with ribs. For the energy subtraction imaging of the chest images, for example, X-rays of two different energy distributions, high-energy X-ray generated with the X-ray tube voltage of 120 kV (see FIG. 4A) and low-energy X-ray generated with the X-ray tube voltage of 60 kV (see FIG. 4C), are used. As shown in FIG. 4A, peak energy of the high-energy X-ray is 120 kV. The peak energy and average energy of the high-energy X-ray are higher than those of the low-energy X-ray shown in FIG. 4C. As is well known, abruptly increasing portions close to the center of the energy distribution of the high-energy X-ray indicate characteristic X-rays. When an electron from an outer shell transfers to a vacancy, created by ejection of an electron in an inner shell, a difference in orbital energy between two electrons are released as characteristic X-rays or electromagnetic waves. Characteristic X-ray energy is specific to an element, and defined by a material of the target of the X-ray tube 16. As shown in FIG. 4C, peak energy of the low-energy X-ray (60 kV) is 60 kV. The peak energy and average energy of the low-energy X-ray are lower than those of the high-energy X-ray. The energy distribution of the high-energy X-ray includes an energy component of equal to or less than 60 kV. Thus, the energy distribution of the high-energy X-ray and that of the low-energy X-ray are partly overlapped with each other. The graph of FIG. 4B shows the energy distribution (solid lines) of the high-energy X-ray with the use of the filter 22, that is, the energy distribution of the high-energy X-ray passed through the filter area 22a, and the energy distribution (dotted lines) of the high-energy X-ray without the use of the filter 22, that is, the energy distribution of the high-energy X-ray not having been passed through the filter area 22a. The distribution of the high-energy X-ray without the use of the filter 22, depicted in dotted lines in FIG. 4B, is the same as the distribution shown in FIG. 4A. On the other hand, in the case where the filter 22 is used, as depicted in solid lines, the low energy component is cut down. With the use of the filter 22, an overlapping amount of the energy component of the low-energy X-ray and the energy component of high-energy X-ray is reduced, and thus the separation of the high-energy X-ray and the low-energy X-ray is improved. Each graph shown in FIG. 4B is normalized with the maximum value of the energy distribution. Although the high energy components (with the use of the filter 22) depicted in solid lines and the high energy components (without the use of the filter 22) depicted in dotted lines have the same intensity regardless of the use of the filter 22, a part of the high energy component is actually cut down in addition to the low energy component with the use of the filter 22. As a result, the intensity of the high energy component (solid lines) is reduced with the use of the filter 22, compared to the intensity of the high energy component (dotted lines) without the use of the filter 22. As shown in FIG. 5, the imaging control device 13 is provided with a cardiac signal detector 13a, a motor controller 13b, and an emission controller 13c. The cardiac signal detector 13a detects cardiac signals outputted from the vital sign measuring device 19. The detected cardiac signals are outputted to the motor controller 13b. The motor controller 13b determines the area shifting cycle or shift cycle of the filter 22 based on the cardiac signal. The motor controller 13b adjusts the drive speed (rotation speed) of the motor 24 so as to rotate the filter 22 at the determined area shifting cycle. Namely, the motor controller 13b determines the drive speed of the motor 24 to synchronize the area shifting cycle of the filter 22 with the cardiac cycle. As shown in FIG. 6, the motor controller 13b determines the drive speed of the motor 24 based on the cardiac signal when, for example, imaging conditions inputted via the console 14 are set in the imaging control device 13, and starts rotating the motor 24 accordingly. The motor controller 13b rotates the motor 24 at the determined constant drive speed to rotate the filter 22 at a constant speed during the sequential two X-ray emissions, T1 and T2, in the energy subtraction imaging. The area shifting cycle of the filter 22 synchronizes with the cardiac cycle (approximately 1 second). Accordingly, the filter area 22a and the transmission area 22b are alternately inserted into the path 23 of X-ray in each cardiac cycle or heartbeat while the motor 24 rotates. The emission controller 13c controls the emission timing based on or in accordance with the filter position detecting signal and the cardiac signal. First, the emission controller 13c detects a phase of the filter 22, namely, the emission controller 13c detects whether the filter area 22a is inserted or retracted from the path 23 of X-ray based on the filter position detecting signal. To be more precise, after the instruction for imaging has been inputted, the emission controller 13c detects the rising edge of the filter position detecting signal to detect that the filter area 22a has started to enter the path 23. In a single cardiac cycle, a P wave, a QRS complex, and a T wave appear. The P wave corresponds to the duration of the activation of atria. The QRS complex corresponds to the duration of the ventricular activation and the subsequent expansion and contraction of the ventricles. The T wave corresponds the duration of the contraction of the activated ventricles. During the T-P interval or a time period after the T-wave and before the next P wave, the heart is contracted and remains relatively stable. After detecting the rising edge of filter position detecting signal, the emission controller 13c detects a phase of the cardiac cycle or heartbeat based on the cardiac signal. To be more precise, the emission controller 13c detects that the phase of the cardiac cycle is within the T-P interval where the heart is in a steady or stable state. When the phase of the cardiac cycle is within the T-P interval, the emission controller 13c outputs the exposure start signal for the first X-ray emission T1 of the high-energy X-ray. At this time, the filter area 22a has been inserted into the path 23 of X-ray. The high-energy X-ray passes through the filter area 22a so that the low energy component of the high-energy X-ray is absorbed by the filter area 22a. The high-energy X-ray passes through the subject P and reaches the radiation image detector 12. After the first X-ray emission T1, the filter area 22a is retracted from the path 23, and the transmission area 22b is inserted into the path 23 for the next cardiac cycle. The emission controller 13c detects a falling edge of the filter position detecting signal, which indicates the retraction of the filter area 22a from the path 23. Then, the emission controller 13c detects the phase of the cardiac cycle is within the T-P interval, and outputs the exposure start signal for the second X-ray emission T2 of the low-energy X-ray. At this time, the transmission area 22b has been inserted into the path 23. The transmission area 22b allows the low-energy X-ray to pass therethrough without cutting its low energy component. Thus, the low-energy X-ray passes through the subject P and reaches the radiation image detector 12. In this example, to control the emission timings, the emission controller 13c detects the phase of the filter 22 and the phase of the cardiac cycle in accordance with the filter position detecting signal and the cardiac signal, respectively. The area shifting cycle of the filter 22 and the cardiac cycle are previously synchronized before the start of the X-ray emission. Accordingly, the detection of one of the phases of the filter 22 and the cardiac cycle allows controlling the emission timing. For example, during the T-P interval in the cardiac signal, the phase of the filter 22 is synchronized with the phase of the cardiac cycle in order that the rising edge or the falling edge of the filter position detecting signal can be outputted. Thereby, the emission timing can be controlled only with the filter position detecting signal. Additionally, monitoring both the filter position detecting signal and the cardiac signal improves accuracy and safety of the emission timing control as described in the above example. With referring to FIG. 7, an operation of the above configuration is described. To perform energy subtraction imaging, imaging conditions, e.g. an X-ray tube current, an X-ray tube voltage, and an object of interest are inputted through the console 14 to be set in the imaging control device 13 (S101). The imaging control device 13 calculates the maximum exposure time based on the object of interest and the body thickness inputted from the body thickness measuring device 18. The cardiac signal detector 13a of the imaging control device 13 detects the cardiac signal from the vital sign measuring device 19, and then outputs the cardiac signal to the motor controller 13b. Based on or in accordance with the cardiac signal, the motor controller 13b determines the area shifting cycle of the filter 22 such that the area shifting cycle synchronizes with the cardiac cycle (S102). The drive speed of the motor 24 is determined to achieve the area shifting cycle. The motor controller 13b starts to rotate the motor 24 at the determined drive speed. Thus, the filter 22 starts to rotate (S103). As shown in FIG. 6, when the instruction for imaging is inputted from the console 14 (S104), the emission controller 13c of the imaging control device 13 outputs two exposure start signals in sequence such that the phase of the filter 22, the phase of the cardiac cycle, and the emission timing are synchronized based on or in accordance with the filter position detecting signal and the cardiac signal. In accordance with the exposure start signal, the radiation source 11 performs two X-ray emissions, T1 with high-energy X-ray and T2 with low-energy X-ray (S105). After the two X-ray emissions, T1 and T2, are ended, the motor controller 13b stops the rotation of the motor 24, which stops the rotation of the filter 22 (S106). In the radiation imaging apparatus 10 of the present invention, the filter 22 starts to rotate before the instruction for energy subtraction imaging is inputted, namely, the filter 22 starts to rotate before the first radiation emission or first X-ray emission T1. During the imaging until the end of the second radiation emission or second X-ray emission T2, the filter 22 rotates at the constant area shifting cycle or shift cycle. Accordingly, area shifting control which requires inputting of a pulse to shift the filter 22 is unnecessary during two X-ray emissions, T1 and T2. The radiation imaging apparatus 10 of the present invention eliminates the use of a high-performance filter switching device or filter controller which inputs a pulse in accordance with the exposure start signal outputted during imaging to switch filters as described in U.S. Pat. No. 7,636,413, incurring no additional device cost. The radiation imaging apparatus 10 of the present invention is provided with a function to adjust the area shifting cycle of the filter 22 to synchronize it with the cardiac cycle. It is not necessary for the radiation imaging apparatus 10 of the present invention to wait for the timing at which the area shifting cycle and the cardiac cycle coincide each other after the first X-ray emission unlike the conventional imaging apparatus disclosed in Japanese Patent Laid-Open Publication No. 2003-210442. Accordingly, two X-ray emissions are performed over two successive cardiac cycles or heartbeats, which shorten the imaging time. As a result, physical burdens of the subject are reduced. In the above embodiment, the cardiac signal is used as subject information, that is, information related to the subject, and the area shifting cycle or the shift cycle of the filter 22 is determined based on or in accordance with the cardiac signal by way of example. Alternatively, a respiratory signal may be used for determining the area shifting cycle of the filter 22. Respiration is periodic as with the cardiac cycle, and one breathes in and out repeatedly. In the case where the area shifting cycle of the filter 22 is determined based on the respiratory signal, the drive speed is determined so as to synchronize the area shifting cycle of the filter 22 with the respiratory cycle. The emission timing is synchronized with a phase of respiration such that two successive X-ray emissions are performed at the time when, for example, the subject breathed in fully with the lungs expanded to the maximum and is just about to breathe out. Thus, the motion artifact caused by breathing is prevented. Respiration, unlike the cardiac cycle, can be temporarily controlled consciously. To prevent lung motion due to breathing during the X-ray imaging, it is common to instruct the subject P to fully breathe in and hold his/her breath with the lungs expanded. However, holding one's breath may be physically burdensome. If the subject P is a small child or infant, such instruction is difficult to follow. In such cases, it is particularly effective to synchronize the emission timings with the phases of the respiration to control the emission timings. As shown in FIGS. 8A and 8B, in addition to the synchronization between the emission timing and the phase of the cardiac cycle, the X-ray emission may be performed at the timing synchronized with a phase of the respiration where lung motion is small. In FIGS. 8A and 8B, two successive X-ray emissions (Ta1 and Ta2) performed at around the time when the subject breathed in fully with the lungs expanded and two successive X-ray emissions (Tb1 and Tb2) performed during the breathing out are compared. An amount d1 indicating an amount of change in the size of lungs between Ta1 and Ta2 is smaller than an amount d2 indicating an amount of change in the size of lungs between Tb1 and Tb2. Performing the X-ray emissions at the timings of Ta1 and Ta2 reduces motion artifact due to respiration. In the above first embodiment, the first and second X-ray emissions are performed in the two successive cardiac cycles, respectively. Alternatively, as shown in FIG. 9, two X-ray emissions, T1 and T2, may be performed within one cardiac cycle. The cardiac cycle is of approximately 1 second on average. The radiation source 11 is capable of sequentially emitting X-rays at an interval in a range from approximately 100 milliseconds (abbreviated as ms) to 200 ms, so that two X-ray emissions can be performed within one cardiac cycle. In this case, the area shifting cycle or shift cycle is determined such that the filter area 22a is inserted and retracted from the path of the X-ray within one cardiac cycle. In order to prevent body motion during imaging, it is preferable to determine the area shifting cycle to remain within the T-P interval where the heart is in a relatively steady state. Thereby, two X-ray emissions, T1 and T2, are performed within the T-P interval, preventing the motion artifact. In the above first embodiment, the filter 22 having one type of the filter area 22a and the transmission area 22b is described as an example. Instead of the transmission area 22b, a second filter area different from the filter area 22a may be provided. This second filter area cuts the high energy component of the energy distribution like a K-edge filter or K-edge absorption filter disclosed in Japanese Patent Laid-Open Publication No. 5-27043. The low energy component of the high-energy X-ray is cut with the filter area 22a, and the high energy component of the low-energy X-ray is cut with the second filter area. Thus, addition of the second filter area improves the separation of the high-energy X-ray and the low-energy X-ray. The filter 22 may be provided with three or more filter areas. In this case, two of the three filter areas are selected for the X-rays of two different energy distributions. The area shifting cycle or the shift cycle of the filter 22 is determined such that the selected two filter areas are inserted into the path of the X-ray based on the cardiac cycle and/or the respiratory cycle. Alternatively, the X-rays of three or more different energy distributions may be emitted in sequence for the energy subtraction imaging as described in, for example, Japanese Patent Laid-Open Publication No. 2009-78035. In this case, the area shifting cycle of the filter is determined such that three or more filter areas formed on the filter is selectively inserted in sequence into the path of the X-ray based on the cardiac cycle. In the above example, the filter 22 is used as an energy separation filter for blocking a high or low energy component of X-rays. Alternatively, X-ray of the same X-ray tube voltage may be emitted twice, for example, and the filter 22 is used for one of the X-ray emissions to generate X-rays of two different energy distributions. Thus, the filter 22 can be used for generating X-rays of different energy distributions in addition to the use as the energy separation filter. In the above example, the rotary filter is described as an example. Alternatively or in addition, as shown in FIG. 10, a filter 31 that linearly reciprocates may be used. The filter 31 is, for example, rectangular in shape, and provided with a layer or coating as a filter area on a substrate of the filter 31. The filter 31 is movable between an insert position where the filter 31 is inserted into the path 23 of X-ray and a retract position where the filter 31 is retracted from the path 23. A conversion mechanism 32 converts rotary motion of the motor 24 into linear reciprocal motion of the filter 31. The conversion mechanism 32 is composed of, for example, a spring and a cam. The spring biases the filter 31 against the retract position and the cam presses the filter 31 into the inserted position against the bias of the spring. Thus, the rotary motion of the motor 24 is converted into the linear motion of the filter 31. A motor is described as an example of a driver. Alternatively, an actuator other than the motor, e.g. a solenoid may be used as the driver as long as it is capable of shifting or moving the filter at a predetermined area shifting cycle or shift cycle. As described above, the X-ray transmission amount varies according to the body thickness even if the dose of the X-ray emission from the radiation source 11 is unchanged. To obtain an appropriate dose, the X-ray tube current and the maximum exposure time are set in accordance with the body thickness. In FIG. 11, the horizontal axis represents the body thickness, and the vertical axis represents the dose. As shown in FIG. 11, as the body thickness increases, the required dose increases. The dose is a product (unit: mAs) of an X-ray tube current (unit: mA) and the X-ray emission time or exposure time (unit: s). As shown in the combinations 1 to 3 in FIG. 12, there are various combinations of the X-ray tube current and the X-ray emission time to obtain the same dose. The imaging control device 13 has a memory in which table information indicating the relations between the body thickness and the dose as shown in FIG. 11 and table information indicating combinations of the X-ray tube current and the X-ray emission time as shown in FIG. 12 are stored. With referring to the table information, a required dose is retrieved in accordance with the body thickness, and then an appropriate combination of the X-ray tube current and the X-ray emission time for the retrieved dose is selected. In the above example, the imaging control device 13 sets the maximum exposure time such that it remains within one cardiac cycle, more preferably, within a T-P interval in one cardiac cycle. To be more specific, the imaging control device 13 selects a combination of an X-ray tube current and an X-ray emission time from the table information of the combinations shown in the FIG. 12 such that the X-ray emission time of the selected combination remains within one cardiac cycle. For example, the table information contains multiple combinations of X-ray emission time and X-ray tube current, and the X-ray emission time remains within one cardiac cycle in some of the combinations while the X-ray emission time exceeds one cardiac cycle in other combinations. In this case, the imaging control device 13 selects the combination with the X-ray emission time within one cardiac cycle. A subject may have the body thickness higher-than-average, which may require the dose of higher-than-average. In that case, a suitable combination may not be contained in the previously prepared table information. In this case, the imaging control device 13 sets the maximum exposure time which remains within one cardiac cycle, and then calculates the X-ray tube current to obtain the required dose with the set maximum exposure time. Alternatively, the required dose may be obtained with multiple X-ray exposures over multiple cardiac cycles. For example, in the case where the maximum exposure time determined in accordance with the body thickness is 0.08 seconds, the X-ray exposure of 0.04 seconds is allocated to each of the two cardiac cycles. Thus, the maximum exposure time is 0.08 seconds in total over two cardiac cycles. In this case, the radiation source 11 operates as follows. To perform high-energy X-ray emission T1, the radiation source 11 performs X-ray emission T1 for 0.04 s within the first cardiac cycle in which the filter area 22a is inserted into the path 23. Thereafter, the radiation source 11 temporarily stops the X-ray emission T1, and then resumes the X-ray emission T1 in the second cardiac cycle when the filter area 22a is inserted into the path 23 again and performs the remaining X-ray emission T1 for 0.04 s. After the high-energy X-ray emission T1 is ended, the low-energy X-ray emission T2 is performed twice over two cardiac cycles with the transmission area 22b being inserted into the path 23. Allocating the X-ray emission time to multiple cardiac cycles is effective in the case where the highest X-ray tube current is limited, and the X-ray emission time for obtaining the required dose exceeds the cardiac cycle. In the first embodiment, the cardiac cycle and respiration are used as examples of the subject information. Alternatively, the body thickness may be used as the subject information. In this case, the area shifting cycle or shift cycle of the filter 22 may be determined in consideration of the body thickness. In other words, the imaging control device 13 determines the area shifting cycle of the filter 22 in accordance with the maximum exposure time determined based on the body thickness, regardless of the cardiac cycle or respiratory cycle. For the energy subtraction imaging, the imaging control device 13 obtains the imaging time required for the two successive X-ray emissions, T1 and T2, based on or in accordance with the maximum exposure time. For example, in the case where the maximum exposure time for each of the high-energy X-ray emission T1 and the low-energy X-ray emission T2 is 0.08 seconds, the total maximum exposure time is 0.16 seconds. To calculate the imaging time, an interval time between the two X-ray emissions, T1 and T2, is added to the total maximum exposure time. The motor controller 13b determines the area shifting cycle based on the calculated imaging time, and determines the driving speed of the motor 24 in accordance with the area shifting cycle. To obtain the maximum exposure time, there are, for example, two ways of thinking. One is aimed to reduce an influence (motion artifact) caused by body motion of the subject P. To reduce the motion artifact, shorter maximum exposure time is the better. Accordingly, the maximum exposure time is set as short as possible, and then the X-ray tube current is calculated to obtain the required dose. The other is aimed for durability of the X-ray tube 16 and the high voltage generator 17. As shown in FIGS. 11 and 12, the dose is a product of the X-ray emission time (exposure time) and the X-ray tube current. The shorter the X-ray emission time, the larger the X-ray tube current becomes. However, if the X-ray tube current is too large, the durability of the X-ray tube 16 and the high voltage generator 17 decreases, e.g. the target of the X-ray tube 16 deteriorates due to thermal damage. To aim for the durability of the X-ray tube 16 and the high voltage generator 17, the low X-ray tube current is used with the extended the maximum exposure time. Each of the two ways of thinking has advantages and disadvantages. An aim in obtaining the maximum exposure time may change depending on the subject. It is preferable that a user can select the way of determining the maximum exposure time depending on the aim. In this case, the imaging control device 13 is provided with two modes, a first calculation mode and a second calculation mode. The first calculation mode is aimed to reduce the motion artifact. The second calculation mode is aimed for the durability of the X-ray tube 16 and the high voltage generator 17. One of these modes is selected through the console 14. The table information shown in FIG. 12 is stored in the memory of the imaging control device 13. In the case where the first calculation mode is selected, the imaging control device 13 selects from the table information a combination of an X-ray tube current and a relatively short X-ray emission time to achieve the required dose which is determined based on the body thickness. On the other hand, in the case where the second calculation mode is selected, the imaging control device 13 selects from the table information a combination of a relatively small X-ray tube current and an X-ray emission time to achieve the required dose which is determined based on the body thickness. In addition to the first calculation mode and the second calculation mode, a third calculation mode may be used. In the third calculation mode, the maximum exposure time is calculated in consideration of both the reduction of the motion artifact and the durability of the X-ray tube 16 and the high voltage generator 17. In the third calculation mode, for example, a combination of the X-ray tube current of medium amount and the X-ray emission time of medium length is selected from among the combinations for obtaining the required dose. In the above second embodiment, as an example, the body thickness is used as the subject information instead of the heartbeat and respiration, and the area shifting cycle of the filter 22 is determined based on the maximum exposure time in accordance with the body thickness. This second embodiment can be combined with an example of the first embodiment shown in FIG. 9 where two X-ray emissions are performed within one heartbeat. In other words, the area shifting cycle of the filter 22 can be determined using both the heartbeat and the body thickness as the subject information. To be more specific, the cardiac cycle is obtained based on the cardiac signal, and then the area shifting cycle of the filter 22 is determined within one cardiac cycle in consideration of the maximum exposure time determined based on the body thickness. In the above embodiment, the filter, that is, a rotary plate is used as an example. In addition, a filter set 40 composed of multiple rotary plates may be used as shown in FIG. 13. The filter set 40 is composed of three filters 41 to 43. The filters 41 to 43 are composed of the rotation axes and motors 46 to 48, respectively, such that each of the filters 41 to 43 rotates individually with a predetermined area shifting cycle or shift cycle. As shown in FIG. 14, rotation centers of the filters 41 to 43 are respectively located on a line 49. The filter 41 has two different filter areas 41a and 41b each located in a quadrant area of a circular rotary plate, and a transmission area 41c formed in a remaining semi-circular area thereof. A filter 42 has two different filter areas 42a and 42b each located in a quadrant area of a circular rotary plate, and a transmission area 42c formed in a remaining semi-circular area thereof. The filter 43 has two different filter areas 43a and 43b each located in a quadrant area of a circular rotary plate, and a transmission area 43c formed in a remaining semi-circular area thereof. A different layer or coating is formed on each of the filter areas 41a, 41b, 42a, 42b, 43a, and 43b. As shown in FIG. 14, in the case where a filter, for example, the filter 41 is used, the transmission areas 42c and 43c of the filters 42 and 43 are inserted into the path 23. Similarly, in the case where the filter 42 or the filter 43 is used, the transmission areas of the filters not being used are inserted into the path 23. There are various layers or coatings used for the filter areas, which differ in radiation (for example, X-ray) absorption properties. In addition to copper (Cu) and gadolinium (Gd) used in the above example, there are coatings composed of aluminum (Al), molybdenum (Mo), or rhodium (Rh). The radiation absorption properties vary among the coatings made from the same material depending on the thickness thereof. The filter area with filter layers or coatings may be selected in accordance with an object of interest, e.g. abdomen, chest, or breast. In the case where the subject P is a small child, which requires minimum radiation exposure, the filter areas with coatings capable of cutting substantially entire range of radiation energies in addition to specific energy components are used. Using the filter set 40 increases the kinds of the available filter areas with various coatings than in the case of using just one filter. With the increased choices, the filter areas can be selected in accordance with various purposes. In addition, the already attached multiple filters save an operator time and trouble of changing the filter compared to an apparatus having just one filter. The filter set 40 can be used for the energy subtraction imaging described in the above first to the third embodiments. In addition, the filter set 40 can be used for imaging other than the energy subtraction imaging. In the case where the filter set 40 is used, the filter areas are previously associated with imaging menus which are selectable using the console 14, respectively. In other words, when an imaging menu is selected using the console 14, a filter area previously associated with the selected imaging menu is used. For example, a filter area with a coating to cut low energy radiation is associated with the imaging menu for small children as the subjects, trading off image contrast for reduced exposure. On the other hand, a filter area with a coating which cuts a smaller amount of low energy radiation compared to the filter area for the small children is associated with the imaging menu for adults as the subjects. Thus, sufficient exposure for sharp radiation image is obtained. The console 14 is provided with a memory in which the imaging menus and the coated filter areas are associated with each other and stored. After the imaging menu is selected, the console 14 reads from the memory the information of the filter area with the coating corresponding to the selected imaging menu, and sends the information to the imaging control device 13. The imaging control device 13 sends a control signal to the radiation source 11 so as to insert the filter area corresponding to the received information into the path 23 of radiation, for example, X-ray. The radiation source 11 drives the motors 46 to 48 to insert the filter area with the selected coating into the path 23, and shifts the filters with filter areas of unnecessary coatings to retract the filter areas and insert the transmission areas thereof to the path 23. The following invention can be understood with the configuration of this embodiment. An imaging apparatus is provided with multiple filters selectably used and each having at least one kind of filter area. Each filter has a disc-shape, and the rotation axes of the filters are arranged along a straight line, and each filter can be rotated individually. It is preferable that each filter is provided with a transmission area (through area). When a filter area of a selected or associated filter is inserted into a radiation path, the transmission areas of the remaining filters are inserted into the path to retract the filter areas of the remaining filters from the path. It is preferable that the filter is selected in accordance with an imaging menu selected using a console. The present invention may be applied to an apparatus using X-rays as the radiation. Alternatively, the present invention may be applied to an apparatus using radiation other than X-rays such as gamma rays and megavoltage X-rays for radiation therapy. Various changes and modifications are possible in the present invention and may be understood to be within the present invention.
061817597	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention allows the value of the sub-critical eigenvalue (K.sub.eff), also referred to as the effective neutron multiplication factor, to be determined using measured source range detector signal change with respect to time information. The effective neutron multiplication factor is the ratio of the average rate of neutron production by fission to the average rate of loss by absorption and leakage. The system is critical if K.sub.eff =1, subcritical if K.sub.eff <1, and supercritical if K.sub.eff >1. Referring to the drawings, FIG. 1 is a simplified schematic representation of a reactor core 10 having a plurality of control rods 12 positioned inside the core. A rod control system 14 raises and lowers the rods within the reactor core. A plurality of source range detectors 16 are also positioned within the core. These detectors are connected to a computer 18 by conductors 20 and 22. The computer 18 receives signals from the source range detectors and also receives a signal indicating the status of the movement of the control rods on line 24. These signals are processed in accordance with the invention to achieve an estimate of the criticality of the reactor. FIG. 2 is a flow diagram that illustrates the steps performed in practicing the method of the invention. In order to start the approach to criticality, block 26 shows that the control rods are withdrawn. After the withdrawal of the rods stops, the output signal from at least one neutron flux detector is recorded at time t.sub.1 as shown in block 28. The output signal from the neutron detector will transition from the initially recorded level to a higher level. Block 30 shows that the output signal is recorded again at time t.sub.2 during the transition. At the end of the transition, the signal is again recorded at time t.sub.3 as shown in block 32. Based on the signal levels recorded in blocks 28, 30 and 32, the effective neutron multiplication factor is calculated as shown in block 34. Then the calculated factor is used to determine the closeness to criticality of the reactors as shown in block 36. An apparatus used to perform the method of this invention is designated as the K-Effective Estimation Processing System (KEEPS). The KEEPS computations can be performed on various types of hardware such as a personal computer or workstation based computer platform. Typically, source range detector signal information, the corresponding time and date information, and the control bank motion status (moving or not moving) is input to the computer hardware executing the KEEPS calculation algorithms. The instantaneous neutron flux period in a reactor when the control banks are being withdrawn, in the absence of spatial neutron flux changes, may be closely approximated by the Point-Kinetics based expression: ##EQU1## The values or these parameters would be readily available to one skilled in the art, since the values are routinely generated during the core design process. The term "period" typically refers to the time it takes the neutron flux to increase by a factor of e. The instantaneous period considers the fact that the period is changing as a function of time because reactivity is changing as a function of time. After the control banks stop moving, at time t.sub.s, the instantaneous period may be expressed as: ##EQU2## After the control banks stop moving, the change in the source range detector signal with time is no longer influenced by the changes in the spatial distribution of the neutron flux. The assumptions inherent in the Point-Kinetics representation of the neutron flux dynamics become more valid. The value of K.sub.eff corresponding to the core condition immediately following completion of the control bank withdrawal may be determined by measuring the time required for the source range detector signal to achieve a specific fraction of it's equilibrium signal level at the current value of K.sub.eff. The equilibrium value of the source range detector signal is determined from the source range signal value measured after the count rate stops increasing. This value can be determined from the point at which the startup rate returns to zero, or by a simple visual determination from either a graph of source range signal versus time, or by simply looking at a count rate meter located on a control panel. Conversely, the value of K.sub.eff may also be determined by measuring the relative change in the source range signal that occurs a specific time after the control banks stop moving. The above equation may be solved for n(t), for times greater than t.sub.s to yield: ##EQU3## The above equation may be solved for K.sub.eff at time t.sub.s to yield: ##EQU4## and: t=a time after completion of the control rod withdrawal step, PA0 n(t.sub.s)=the value of the output signal measured at a time t.sub.s following completion of the control rod withdrawal step, PA0 n(t)=the value of the output signal measured at a time t following completion of the control rod withdrawal step, and PA0 n(.infin.)=the value of the output signal measured after neutron flux stops increasing. Typical application of this methodology will require that the operator record source range detector signals immediately after the rods stop moving, at some time following the cessation of rod motion (but before the signal stops increasing), and after the signal stops increasing. The fact that the signal stops increasing may be determined graphically, visually, or by determining that the startup rate has returned to zero. The startup rate indication is the presently preferred embodiment, as this is the easiest to automate in KEEPS. The startup rate will be based on the observed change in the signal over a preset time. The elapsed time between the time of cessation of rod withdrawal and the time corresponding to the signal value recorded during the signal increase portion of the transient must also be determined. Inserting these values into the appropriate locations in the above equation for K.sub.eff will allow K.sub.eff to be calculated. The reactor operator may use this information to determine how subcritical the reactor is currently, and whether the next planned reactivity insertion will cause the reactor to exceed the desired reactivity state. Each step of the control bank withdrawal process has an expected value of K.sub.eff associated with it. The operator may first verify that the value of K.sub.eff is less than 1.0000, indicating that the reactor is subcritical, and then confirm that the actual value of K.sub.eff is in adequate agreement with the expected value of K.sub.eff. The measured value of K.sub.eff can then be used to determine whether the next planned control bank withdrawal will cause the reactor to become critical. This process will ensure that the operator does not unexpectedly achieve criticality, and validate the predicted critical condition calculation well before an inaccurate calculation can cause a problem. The method of this invention could be easily automated. A computer based system that detects the start and end of control bank motion and automatically records virtually continuous values of source range detector signals and the corresponding elapsed times from the cessation of control bank withdrawal could easily be developed. This type of system could use the data obtained at each time step following the stopping of rod motion to compute multiple and essentially independent values of K.sub.eff to provide the best possible estimate of the actual core subcritical eigenvalue corresponding to the current control bank configuration. This invention provides a method and apparatus for estimating the effective neutron multiplication factor in a nuclear reactor. In the foregoing specification certain preferred practices and embodiments of this invention have been set out, however, it will be understood that the invention may be otherwise embodied within the scope of the following claims. For example, signals from the intermediate range detectors and the corresponding time information could also be used as inputs to the calculation algorithms. The data could either be automatically input to the calculation hardware (on-line mode), or could be input manually by the reactor operator (off-line mode). The required values of .lambda.-effective and .beta.-effective corresponding to the reactor depletion at the time of the calculation may be either manually input into the KEEPS calculation algorithm, or coded directly into in the computational software as a function of core depletion. It is therefore intended that the invention includes the elements of the following claims and equivalents thereof.
047675900	claims	1. In a tokamak, which includes a toroidal vacuum chamber and a magnetically confined main plasma disposed therein, and a scrape-off region disposed between said main plasma and said vacuum chamber, said main plasma having an edge region and a main current, wherein the improvement comprises: means for generating and maintaining an electric current having a current density greater than the average current density of said main current, in the edge region of said main plasma, said edge current being maintained in a direction parallel to said main current for a period of the order of one edge current decay time, wherein said edge current flowing in the direction of said main current, will penetrate radially into said main plasma thereby augmenting and maintaining said main current. a cathode disposed in the plasma scrape-off region and and anode disposed in the plasma scrape-off region such that said edge current is driven only in the same toroidal sense as that of the main current, and energizing means for energizing said anode and said cathode such that the edge current generated therefrom has a current density greater than the average current density of said main current. (a) generating an electric current in said edge region, said electric current being generated in a direction parallel to said main current and having a current density greater than the average density of said main current; and (b) maintaining said edge current for a period of the order of one edge current decay times, wherein said edge current flowing in the direction of said main current will penetrate radially into said main plasma thereby augmenting and maintinaing said main current. creating a null point in said poloidal magnetic field, said null point being disposed between said main plasma and said toroidal ringlet; and driving said edge current across said null point. 2. The system of claim 1 wherein the means for generating and maintaining said edge current comprises: 3. The system of claim 2 wherein said energizing means is a repeatedly pulsed energizing means, such that said cathode and said anode generate said edge current in a repeatedly pulsed manner. 4. The system of claim 2 wherein said energizing means is a steady-state energizing means, such that said cathode and said anode generate and edge current which is steady-state in time. 5. The system of claim 2 wherein said cathode material comprises lanthanum hexaboride (LaB.sub.6). 6. The system of claim 2 wherein said cathode and said anode are disposed in a position to allow said edge current to flow in a toroidal shell, said toroidal shell enveloping said main plasma. 7. The system of claim 6 wherein said cathode and said anode are disposed in said scrape-off region such that they function as plasma limiters. 8. The system of claim 2 further including a divertor and a divertor region, said cathode and said anode being disposed in said divertor region. 9. The system of claim 1 wherein said means for generating and maintaining said edge current comprises an inductive transformer disposed without said main plasma. 10. The system of claim 9 wherein said inductive transformer comprises a coil and means for energizing said coil. 11. The system of claim 10 wherein said coil is a loop disposed substantially coaxial with said toroidal main plasma. 12. The system of claim 9 wherein said inducive transformer comprises a ferromagnetic transformer core and a primary coil operatively associated therewith, said ferromagnetic core surrounding the minor radius of said main toroidal plasma. 13. The system of claim 9 wherein said inductive transformer is operable in a repeatedly pulsed manner as to produce edge currents alternatingly flowing in opposite toroidal senses, and wherein said edge current flowing in the same toroidal sense as that of the main plasma current will preferentially penetrate into said main plasma. 14. The system of claim 1 wherein said means for generating and maintaining said edge current are operable to produce said edge current in a toroidal ringlet, said ringlet being disposed immediately adjacent to said toroidal main plasma, and further comprising: means for creating a null point in said poloidal magnetic field, said null point disposed between said main plasma and said toroidal ringlet, and means for driving said edge current across said null point. 15. The system of claim 14 wherein said means for creating a null point in said poloidal magnetic field comprises a divertor, wherein said null point is the divertor x-point, said divertor creating said scrape-off region. 16. The system of claim 14 wherein said means for generating and maintaining said toroidal ringlet comprises an inductive transformer. 17. A method for maintaining a steady-state toroidal plasma current in a tokamak , said tokamak including a toroidal vacuum chamber and a magnetically confined main plasma disposed therein, and a scrape-off region disposed between said main plasma and said vacuum chamber, main plasma having an edge region and a main current, which comprises the steps of: 18. The method of claim 17 wherein said edge current is generated in a toroidal shell, said toroidal shell enveloping said main plasma. 19. The method of claim 17 wherein said edge current is generated in a toroidal ringlet, said ringlet being disposed immediately adjacent to said toroidal main plasma, further comprising the steps of:
	claims	1. A process for enhancing the critical current density of a bulk body article composed having Li intimately distributed in a composition of a high temperature superconducting composition, comprising the steps of: L 1 M 2 Cu 3 O 6+d , T 2 Mxe2x80x2 2 Ca n Cu n+1 O 6+2n , (L+M) 3-z D z Cu 3 O 6+d , or T 2 Mxe2x80x2 2 Ca n (Cu 1-zxe2x80x2 D zxe2x80x2 ) n+1 O 6+2n , wherein L is yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, or lutetium, or mixtures thereof including mixtures with scandium, cerium, praseodymium, terbium, M is barium, strontium or mixtures thereof; xe2x80x9czxe2x80x9d is greater than zero and equal to or less than 0.3; xe2x80x9cdxe2x80x9d is from about 0.7 to about 1.0; T is bismuth and Mxe2x80x2 is strontium or T is thallium and Mxe2x80x2 is barium; and xe2x80x9cnxe2x80x9d is a number from about 1 to about 3, xe2x80x9czxe2x80x2xe2x80x9d is greater than zero and less than or equal to 0.5; and D is Li; wherein the Li is present in an amount to provide for a 6 Li:Cu ratio of at least about 2.5xc3x9710 xe2x88x928 ; radiating the bulk body article with thermal neutrons until a quantity of the Li content of such body portion undergoes thermal neutron induced reaction to produce 4 He. positioning a bulk body article in a position to be irradiated comprised of a composition of the formula 2. The process of claim 1 wherein the body article is comprised of L 1 M 2 (Cu 3 O 6+d in which Li is intimately distributed and further wherein Li is present in an amount to provide for a 6 Li:Cu ratio of at least about 1xc3x9710 xe2x88x925 . claim 1 3. The process of claim 2 wherein 6 Li is intimately distributed within such body article composition in an atomic ratio relative to copper equal to or less than 0.5. claim 2 4. The process of claim 2 wherein the body article is exposed to a thermal neutron fluence sufficient to react at least one lithium atom per each 10 9 copper atoms. claim 2 5. The process of claim 4 wherein said body article is composed of Y 1 Ba 2 Cu 3 O 6+d and contains 6 Li in an atomic ratio relative to copper of at least about 1xc3x9710 xe2x88x923 . claim 4 6. The process of claim 1 wherein said body article is composed of claim 1 (L+M) 3-z D z Cu 3 O 6+d wherein L is yttrium, lanthanum, samarium, europium, and gadolinium; M is barium or a mixture of barium and strontium; D is Li; xe2x80x9cdxe2x80x9d is about 0.7 to 1.0; xe2x80x9czxe2x80x9d is from about 1xc3x9710 xe2x88x927 to about 2xc3x9710 xe2x88x922 ; and the ratio L:M is from about 0.45 to about 0.55. 7. The process of claim 6 , wherein portions of such body are exposed to a thermal neutron fluence sufficient to react at least one D atom per each 10 7 copper atoms. claim 6 8. The process of claim 7 , wherein L is Y and M is Ba. claim 7 9. The process of claim 1 , wherein claim 1 L is yttrium, lanthanum, samarium, europium or gadolinium; M is barium; xe2x80x9cdxe2x80x9d is about 0.7 to 1.0; xe2x80x9czxe2x80x9d is from about 3xc3x9710 xe2x88x925 to about 1.5xc3x9710 xe2x88x921 ; and the ratio L:M is about 0.5. 10. The process of claim 9 , wherein portions of such body are exposed to a thermal neutron fluence sufficient to react at least one D atom per each 10 7 copper atoms. claim 9 11. The process of claim 10 , wherein L is Y and M is Ba. claim 10 12. The process of claim 1 , wherein claim 1 L is yttrium, lanthanum, samarium, europium and gadolinium; M is barium or a mixture of barium and strontium; D is L 6 Li; xe2x80x9cdxe2x80x9d is about 0.7 to 1.0; xe2x80x9czxe2x80x9d is from about 3xc3x9710 xe2x88x928 to about 0.3; and the ratio L:M is from about 0.45 to about 0.55 provided that L does not exceed one and M does not exceed two. 13. The process of claim 12 , wherein portions of such body are exposed to a thermal neutron fluence sufficient to react at least one D atom per each 10 9 copper atoms. claim 12 14. The process of claim 13 , wherein L is Y and M is Ba. claim 13 15. The process of claim 14 , wherein portions of such body are exposed to a thermal neutron fluence sufficient to react at least one D atom per each 10 7 copper atoms. claim 14 16. The process of claim 1 wherein the body article is comprised of Bi 2 Sr 2 Ca n Cu n+1 O 6+2n in which Li is intimately distributed. claim 1 17. The process of claim 16 wherein 6 Li is intimately distributed within such body article composition in an atomic ratio relative to copper equal to or less than 0.5. claim 16 18. The process of claim 1 , wherein said body article is composed of claim 1 T 2 Mxe2x80x2 2 Ca n (Cu 1-zxe2x80x2 D zxe2x80x2 ) n+1 O 6+2n wherein T is bismuth and Mxe2x80x2 is strontium, or T is thallium and Mxe2x80x2is barium; xe2x80x9cnxe2x80x9d is a number from about 1 to about 2; xe2x80x9czxe2x80x9dxe2x80x2 is greater than zero and less than or equal to 0.5. 19. The process of claim 18 , wherein portions of such body are exposed to a thermal neutron fluence sufficient to react at least one D atom per each 10 9 copper atoms. claim 18 20. The process of claim 19 , wherein T is bismuth and Mxe2x80x2 is strontium and xe2x80x9czxe2x80x2xe2x80x9d is from about 2.5xc3x9710 xe2x88x928 to about 5xc3x9710 xe2x88x921 . claim 19 21. The process of claim 20 , wherein portions of such body are exposed to a thermal neutron fluence sufficient to react at least one D atom per each 10 9 copper atoms. claim 20 22. The process of claim 21 , wherein xe2x80x9czxe2x80x2xe2x80x9d is from about 1xc3x9710 xe2x88x926 to about 1xc3x9710 xe2x88x921 . claim 21 23. The process of claim 22 , wherein portions of such body are exposed to a thermal neutron fluence sufficient to react one Li atom per each 10 7 copper atoms. claim 22
	description	This application is based upon and claims the benefit of priority from Japanese patent application No. 2006-155306, filed on Jun. 2, 2006, the disclosure of which is incorporated herein its entirety by reference. This invention relates to improvements in a beam processing system and a beam processing method for uniformly irradiating a beam of light, electrons, ions, or the like (particle beam) onto processing objects. As a method of irradiating a beam of electrons, ions, or the like onto processing objects to thereby process them, there is known a method in which a plurality of processing objects are mounted on the same circumference of a rotary disk and, by rotating the rotary disk, a beam crosses the processing objects to scan them. In this method, the rotary disk is generally also reciprocated in its radial direction to thereby allow the beam to be irradiated over the entire surface of each processing object, which is called a mechanical scan. As a typical application example of such a mechanical scan, there is an ion implantation system for implanting ions into silicon wafers in the manufacturing process of semiconductor devices. Referring to FIG. 1, a description will be given of particularly the rotary disk side in a mechanical scan type ion implantation system. A plurality of wafers (processing objects) 110 are mounted on the same circumference near the rim of a rotary disk 100. A scan direction by rotation of the rotary disk 100 and a scan direction by reciprocating movement (vertical direction in FIG. 1) of the rotary disk 100 are set perpendicular to each other. A beam 120 is fixedly irradiated at a specific position of a moving path of the wafers 110. By the combination of such two-direction scans, ion implantation is performed over the entire surface of each wafer 110. Normally, the rotational speed of the rotary disk 100 is sufficiently higher than the reciprocating speed of the rotary disk 100. Therefore, the scan by the rotation of the rotary disk 100 is called a high-speed scan, while the scan by the reciprocating movement of the rotary disk 100 is called a low-speed scan or a Y scan. Since the rotary disk 100 is normally rotated at a constant speed (constant angular velocity), the scan speed of a high-speed scan increases in proportion to a radial distance R, where the beam hits on the rotary disk 100, as seen from the center of the rotary disk 100. Therefore, if a Y scan is simply performed with a uniform motion, the ion implantation density (concentration) becomes low at a portion where the scan speed of the high-speed scan is high, while the ion implantation density becomes high at a portion where the scan speed is low. For compensation thereof, the Y scan is slowed down at a portion where the high-speed scan becomes fast (i.e. the distance R is large), while, the Y scan is speeded up at a portion where the high-speed scan becomes slow (i.e. the distance R is small), thus achieving a uniform implantation amount (dose) by combining them. That is, the Y scan is performed by changing its speed so as to be inversely proportional to the radial distance R where the beam hits on the rotary disk 100. The method of changing the speed of the Y scan in inverse proportion to the radial distance R of the rotary disk 100 as described above is called a (1/R) scan and employed in most batch-type ion implantation systems using a rotary disk [e.g. Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 2006-60159]. The Y scan is repeated with a constant stroke. This stroke is defined between an outer overscan position and an inner overscan position. The outer overscan position is a position where beam irradiation is offset from the wafer 110 on the outer side of the rotary disk 100 due to movement of the rotary disk 100 downward in FIG. 1. The inner overscan position is a position where beam irradiation is offset from the wafer 110 on the inner side of the rotary disk 100 due to movement of the rotary disk 100 upward in FIG. 1. Referring to FIG. 1, assuming that the beam is initially located at the outer overscan position, the rotary disk 100, while being rotated, is driven upward until the beam reaches the inner overscan position. When the beam has reached the inner overscan position, the direction of the Y scan of the rotary disk 100 is reversed so that the rotary disk 100 is driven downward. When the beam has reached the outer overscan position, the direction of the Y scan of the rotary disk 100 is reversed so that the rotary disk 100 is driven upward. One reciprocating operation in which a beam starts from the outer overscan position and returns to the outer overscan position via the inner overscan position is given as one Y scan (one reciprocating scan). On the other hand, for positioning control of the rotary disk 100, an initial position detection target portion 101 is provided at a predetermined position on the rotary disk 100 and a target portion sensor (not shown) for detecting the initial position detection target portion 101 is provided in the vicinity of the rim of the rotary disk 100. A detection signal from the target portion sensor is sent to a controller (not shown) having a function to control a motor which drives the rotary disk 100, and the controller uses this detection signal to implement positioning control of the rotary disk 100 [e.g. Patent Document 2: Japanese Patent (JP-B) No. 2909932]. The diameter of a wafer is mainly 200 mm or 300 mm. On the other hand, a beam normally has a circular cross section, but may have a flat cross section elongated in the horizontal direction. Hereinbelow, the diameter size in the case of the beam with the circular cross section and the vertical size in the case of the beam with the flat cross section will be collectively referred to as a “beam size”. In either event, since the beam size of the beam irradiated onto the wafers 110 is smaller than the diameter of each wafer, beam overlap irradiation like so-called overlap painting is carried out for achieving better uniformity of ion implantation. This is, in terms of one wafer, a method of causing regions of continuous twice beam irradiation on the wafer to partially overlap each other and is realized by performing a Y scan so that scan regions by a high-speed scan partially overlap each other. That is, if the beam is irradiated onto a partial region of the wafer at a certain rotation timing of the rotary disk 100, the beam is, at the next rotation of the rotary disk 100, irradiated onto the wafer so as to provide a region overlapping part of the above partial region on the wafer. Hereinafter, this overlap region will also be called a “beam overlap amount”. The reason for employing such an overlap irradiation method is as follows. The (1/R) scan is ignored in the following explanation. In the batch-type ion implantation system, when the rotary disk 100 is rotated at a low rotational speed reduced to half or less a normal high rotational speed, assuming that the Y-scan speed is equal to that at the time of the high-speed rotation, the distance of the Y-scan (scan pitch) moving during one rotation of the rotary disk 100 increases. As the scan pitch during one rotation of the rotary disk 100 increases, the beam overlap amount in beam irradiation decreases. With respect to the beam size, as the beam size decreases, the beam overlap amount decreases. Then, if the scan pitch increases to be greater than a certain value or if the beam size decreases to be smaller than a certain value, the beam overlap amount decreases to be smaller than zero so that there is no overlap at all. As shown in FIG. 1 as “High-Speed Rotation”, a scan pitch PH during one rotation of the rotary disk 100 is considerably small in the case of normal high-speed disk rotation (e.g. 800 to 1200 rpm) and, therefore, even if the beam size decreases, the beam overlap amount does not become zero unless the beam size becomes equal to or less than the scan pitch PH. Accordingly, even if the rotation start position of disk rotation is random every time a Y scan is started, no problem arises. However, as shown in FIG. 1 as “Low-Speed Rotation”, in the case of low-speed disk rotation (e.g. 150 to 300 rpm), assuming that the Y-scan speed is equal to that in the case of “High-Speed Rotation”, a scan pitch PL during one rotation of the rotary disk 100 becomes large. In this case, under the conditions that the beam size is small and so on, possibility is expected that there is no beam overlap to cause occurrence of ion implantation unevenness or nonuniformity. Since the Y scan and the disk rotation are controlled independently of each other, it is considered that, in the case of the beam size that can achieve a certain beam overlap amount, if the Y scan is performed a plurality of times, ions are randomly implanted, so that the ion implantation unevenness finally disappears even in the case of the low-speed disk rotation. However, as shown in FIG. 2, there occurs a case where the rotation start position of the rotary disk 100 at the start of a Y scan synchronizes (not “coincides”) or pseudo-synchronizes with the last rotation start position of the rotary disk 100. In this case, ion implantation is concentrated at certain portions of the wafers, so that there occurs a case where even if the Y scan is performed N times, the ion implantation uniformity is degraded to exceed 1%. This occurs particularly when a beam size Bs is not sufficiently large with respect to a scan pitch P (=Y-scan speed×disk rotation period), (P≧Bs), i.e. there is no beam overlap. FIG. 2 shows a transition of beam irradiation with respect to one wafer when a Y scan (reciprocating scan) is performed N times while the rotary disk 100 makes i rotations. If an irradiation state (state of the rotating wafer 110 observed at the same passing point) shown as “Final Implantation State” at the final stage in FIG. 2 is expressed in a plan view up to five Y-scan times, FIG. 6A is obtained, wherein regions with no beam overlap are formed. Naturally, FIG. 2 exaggeratingly shows the transition of beam irradiation for facilitating better understanding. Of course, the foregoing problem is solved by reducing the Y-scan speed so as to produce beam overlap. However, in this case, there arises a new problem such as a problem of reduction in processing speed due to a reduction in Y-scan speed or a problem of rise in temperature of wafers due to prolongation of a beam irradiation time. Accordingly, there are also circumstances that cannot allow the Y-scan speed to be unlimitedly lowered. It is therefore an exemplary object of this invention to provide a beam processing system and a beam processing method that do not reduce uniformity of beam irradiation onto processing objects even if the rotational speed of a rotary disk is low. It is another exemplary object of this invention to accomplish the above object without reducing the processing speed so much. A beam processing system according an exemplary aspect of this invention comprises a disk mounted thereon with a plurality of processing objects on the same circumference, a rotation drive mechanism for rotating the disk about a disk axis, a reciprocating drive mechanism for causing the disk, while rotating, to perform a reciprocating scan motion in a direction perpendicular to the disk axis within a stroke range defined by an inner overscan position and an outer overscan position, and a controller for controlling at least the reciprocating drive mechanism. The beam processing system causes the plurality of processing objects to pass through an irradiation position of a processing beam by rotation and the reciprocating scan motion of the disk, to thereby irradiating the processing beam onto the plurality of processing objects. The beam processing system further comprises a beam width measuring unit for measuring a beam width of the processing beam. The controller sets the inner overscan position and the outer overscan position depending on a measured value of the beam width or a predetermined value of the beam width. The controller, based on the number of rotation of the disk per unit time, a scan speed and the number of reciprocating scan times of the reciprocating scan motion, a reversal start timing of the disk at at least one of the inner overscan position and the outer overscan position, and the measured value of the beam width or the predetermined value of the beam width, controls the reciprocating drive mechanism so as to ensure an overlap region between a last and a current processing beam irradiation region on each of the plurality of processing objects, the overlap region overlapping at least half of the last processing beam irradiation region. A beam processing method according to another exemplary aspect of this invention causes a disk mounted thereon with a plurality of processing objects on the same circumference to rotate about a disk axis, causes the disk, while rotating, to perform a reciprocating scan motion in a direction perpendicular to the disk axis within a stroke range defined by an inner overscan position and an outer overscan position, and causes the plurality of processing objects to pass through an irradiation position of a processing beam by rotation and the reciprocating scan motion of the disk, thereby irradiating the processing beam onto the plurality of processing objects. The beam processing method comprises measuring a beam width of the processing beam and setting the inner overscan position and the outer overscan position depending on a measured value of the beam width or a predetermined value of the beam width. The beam processing method further comprises, based on the number of rotation of the disk per unit time, a scan speed and the number of reciprocating scan times of the reciprocating scan motion, a reversal start timing of the disk at at least one of the inner overscan position and the outer overscan position, and the measured value of the beam width or the predetermined value of the beam width, controlling the reciprocating scan motion so as to ensure an overlap region between a last and a current processing beam irradiation region on each of the plurality of processing objects, the overlap region overlapping at least half of the last processing beam irradiation region. In an exemplary aspect of this invention, in order to solve the foregoing problem, it is configured such that, by controlling the reversal start timing of each reciprocating scan, the beam overlap amount is ensured in every beam irradiation onto each processing object and is uniformly distributed on each processing object. Accordingly, the disk rotation and the reciprocating scan are prevented from having the relationship therebetween that causes a problem in uniformity of beam irradiation (prevented from causing synchronization or pseudo-synchronization), thereby enabling uniform beam irradiation onto each processing object. According to this invention, even when the rotational speed of the disk is low, it is possible to uniformly irradiate the beam onto the processing objects without largely reducing the processing speed. Hereinbelow, a beam processing system and a beam processing method according to this invention will be described. The gist of an exemplary embodiment of this invention resides in that, based on the number of rotation of a rotary disk per unit time, a Y-scan (reciprocating-scan) speed, the number of Y-scan times, a reversal start timing of the rotary disk at at least one of an inner overscan position and an outer overscan position referred to before, and a measured value of a beam width or a predetermined value of a beam width, beam irradiation is carried out continuously or discontinuously onto wafers so as to always provide an overlap region overlapping at least half of a previous beam irradiation region on each wafer, and particularly resides in a Y-scan control manner therefor. Accordingly, this invention is applicable to any existing beam processing system as long as it is a batch-type beam processing system employing the mechanical scan type. Hereinbelow, a description will be given of an exemplary embodiment in which this invention is applied to a batch-type ion implantation system employing the mechanical scan type. As is well known, the ion implantation system comprises an ion source, a mass analysis magnet device, a wafer chamber, and so on. Detailed illustration and description are omitted with respect to the structures other than the wafer chamber. The measured value of the beam width represents a beam size measured by a beam profile measuring unit having a function of a beam width measuring unit. On the other hand, the predetermined value of the beam width represents a value set based on average data of measured values of the beam width size measured by the beam profile measuring unit when performing test evaluation of the ion implantation system based on setting of respective ion species (arsenic (As), phosphorus (P), boron (B), etc.), beam energy, and a beam current value. FIG. 3 shows a schematic structure on the inside and outside of the wafer chamber in the ion implantation system, i.e. a schematic structure of a rotary disk and its drive system. As the rotary disk, use is made of the rotary disk 100 explained with reference to FIG. 1. In FIG. 3, the ion implantation system comprises a guide chamber 12 for guiding an ion beam 10 from an ion source (not shown) and a wafer chamber 13 for implanting the ion beam 10 from the guide chamber 12 into wafers 110. The rotary disk 100 is installed in the wafer chamber 13. The rotary disk 100 is rotated at high speed about a rotation shaft provided at its center by a high-speed scan drive mechanism (rotation drive mechanism) 16. By this rotation, the wafers 110 mounted at intervals on the same circumference of the rotary disk 100 are scanned at high speed and, simultaneously, the wafers 110 are also scanned at low speed in the vertical direction in FIG. 3. A low-speed scan drive mechanism (reciprocating drive mechanism) 17 is provided for the latter scan, i.e. for allowing each of the wafers 110 to be also scanned at low speed in the radial direction with respect to the rotation shaft. Herein, as the low-speed scan drive mechanism 17, use is made of a drive mechanism that can control a low-speed scan (reciprocating scan) operation. As described before, a scan direction by the rotation of the rotary disk 100 and a Y-scan direction by the reciprocating movement (vertical direction in FIG. 3) of the rotary disk 100 are set perpendicular to each other and the ion beam 10 is fixedly irradiated at a specific position of a moving path of the wafers 110. By the combination of such two-direction scans, ions are uniformly implanted the whole of each wafer 110. A beam current measuring device 20 is installed rearward of the rotary disk 100 arranged in the wafer chamber 13, i.e. on the side opposite to the ion beam irradiation surface of the rotary disk 100. In the wafer chamber 13, there are further provided a beam profile measuring unit 14 which serves as a beam width measuring unit and referred to above and a target portion sensor (target detecting unit) 15 for detecting the initial position detection target portion 101 explained with reference to FIG. 1. The beam profile measuring unit 14 is allowed to appear on and disappear from a trajectory of the ion beam 10 by a drive mechanism (not shown). A controller 22 performs a predetermined calculation based on the detection results from the beam profile measuring unit 14, the target portion sensor 15, and the beam current measuring device 20 so as to control a Y scan of the low-speed scan drive mechanism 17, thereby uniformly implanting ions into each wafer 110. Further, the controller 22 controls the high-speed scan drive mechanism 16. Referring to FIG. 4, a description will be given of the control operation by the controller 22, i.e. the operation for the control such that, based on the number of rotation of the rotary disk 100 per unit time, the Y-scan speed, the number of Y-scan times, the reversal start timing of the rotary disk 100, and the measured value of the beam width or the predetermined value of the beam width, the beam is always overlap-irradiated onto each wafer 110 regardless of the beam size. FIG. 4 shows, like FIG. 2, a transition of beam irradiation with respect to one wafer, wherein a rotation period (time required for each rotation) of the rotary disk 100 is T and the number of Y-scan times N is 5. One reciprocating movement between the outer overscan position and the inner overscan position is given as one Y scan. As shown at the final stage in FIG. 4 as “Total of 5 Scans”, when the rotating wafer 110 is observed at the same passing point, beam irradiation forms beam irradiation regions that uniformly overlap each other over the entire diameter region of the wafer 110. Further, each overlap region is set to be half the beam irradiation region. It is preferable that each overlap region be set to half or more the beam irradiation region. For achieving it, the controller 22 performs a Y-scan control in the following manner according to a predetermined control program stored in an internal storage device 22-1. The internal storage device 22-1 may be replaced by an outer storage device. 1. The reversal start timing at a scan start reference position (overscan position) is delayed for every Y scan based on a disk sync signal by a time (T/N) derived by dividing the rotation period T of the rotary disk 100 by the number of Y-scan times N, thereby forcibly shifting the reversal start timing. This serves to prevent the phenomenon of accidental synchronization. Herein, the disk sync signal is a detection signal indicative of the initial position detection target portion 101 (FIG. 1) obtained from the target portion sensor 15. In this exemplary embodiment, this detection signal is used for determining the reversal start timing of the Y scan. 2. If the number of Y-scan times N becomes too large, the delay time (T/N) becomes too small, thus making actual control difficult. Therefore, the following is preferable. A certain number of Y-scan times N′ is determined and the rotation period T is divided by Nx equal to N′ or more and less than 2N′. That is, when the number of Y-scan times N is large, Nx increases by stages as the number of Y-scan times approaches N. In actual control software, N′ is set to 4 so that the scan pitch at 200 rpm of the rotary disk 100 virtually becomes equivalent to that at 815 rpm. Accordingly, when the number of Y-scan times N=4 to 7, the delay time is set to T/N as it is. On the other hand, when the number of Y-scan times N=8, two sets of delay times T/4 are derived and, when the number of Y-scan times N=9 to 11, one set of a delay time T/4 and one set of a delay time T/(N−4) are derived. N′ is set to 4 herein because 200 rpm of the rotary disk 100 is set to a target and, therefore, there is no absolute meaning. 3. There are the following two methods for controlling the Y-scan reversal start timing. 3-1. The reversal start timing is controlled only at the inner overscan position or only at the outer overscan position. 3-2. The reversal start timing is controlled at both the inner overscan position and the outer overscan position. Naturally, the method of controlling the reversal start timing at both positions achieves a higher effect for improving the ion implantation unevenness. 4. It is not necessary to reduce the Y-scan speed in the above control. However, in actual control, the Y-scan speed is changed depending on a change in beam current and is further changed by a (1/R) scan and, therefore, it is of course preferable to perform the control also taking into account a change in Y-scan speed. Now, the operation of this embodiment will be described. 1) The Y-scan speed and the number of Y-scan times N are determined depending on the required total beam irradiation amount for the wafers 110. 2) The delay time Tdelay=T/N is determined from the rotation period T of the rotary disk 100 and the number of Y-scan times N. 3) The inner overscan position and the outer overscan position are determined by measuring a beam profile. Specifically, the inner overscan position and the outer overscan position are set by measuring a beam width and one end position and the other end position in a scan direction on a beam cross section. 4) The timing of reversal of the rotary disk 100 is derived based on a disk sync signal at at least the inner overscan position selected from the inner overscan position and the outer overscan position. 5) The first scan is started with no delay. From the second scan and thereafter, the start timing (reversal start timing) from the overscan position is regularly delayed per delay time Tdelay. As a result, the third scan is delayed by 2Tdelay from the start time point and the fourth scan is delayed by 3Tdelay from the start time point. It is preferable that the N-th scan returns to the disk sync position at the start time point. If an irradiation state (state of the rotating wafer 110 observed at the same passing point) shown as “Total of 5 Scans” at the final stage in FIG. 4 is expressed in a plan view, FIG. 6B is obtained, wherein the beam is always overlap-irradiated onto the wafer 110. 6) As a result, the risk of accidental synchronization is reduced and thus the ion implantation uniformity is improved. It is preferable that the relationship between the required total beam irradiation amount and the Y-scan speed/the number of Y-scan times N be prepared as a table in advance and be stored in the internal storage device 22-1. FIG. 5 shows a beam irradiation trajectory with respect to the respective wafers 110 during one rotation of the rotary disk 100. As described above, in this exemplary embodiment, even when the number of rotation of the rotary disk is as low as about 150 to 300 rpm, by always ensuring overlap of beam irradiation per rotation of the rotary disk, it is possible to maintain the ion implantation uniformity to an extent that does not exceed 1% without largely reducing the Y-scan speed. The description given above is for the exemplary embodiment of this invention. The controller 22 may implement control operation in the following manner. The control is performed to ensure overlap regions each overlapping at least half of a last beam irradiation region on each wafer 110, by regularly delaying per scan the reversal start timing of the rotary disk 100 at at least one of the inner overscan position and the outer overscan position. Herein, “regularly” represents a shift by a pitch Pz equal to half the beam size per scan, so that Pz×N≧stroke pitch (Y-scan stroke distance). Of course, the reversal start timing is determined based on a disk sync signal. The reversal start timing of the rotary disk 100 is randomly controlled based on random numbers. The reversal start timing of the rotary disk 100 is controlled based on a programmed function Z=f (r, n, v, w) representing the relationship among the number of rotation r of the rotary disk 100 per unit time, the number of Y-scan times n, the Y-scan speed v, and the measured value w of the beam width. The relationship among the number of rotation of the rotary disk 100 per unit time, the number of Y-scan times, the Y-scan speed, and the measured value of the beam width is stored as table data in the internal storage device in advance and the reversal start timing of the rotary disk 100 is controlled based on the stored table data. Although the relationship among them changes depending on the ion implantation conditions, the following is one example thereof. Ion Implantation Condition : Total Necessary Dose Amount A ion/cm−2 [Ion Species: Phosphorus (P), Beam Energy: 50 keV, Beam Current Value: 10 mA] Number of Rotation of Rotary Disk: 150 to 800 rpm Number of Y-Scan Times: 1 to 100 Reciprocation Times Y-Scan Speed: 0.1 to 10 cm/sec Measured Value of Beam Width: 1 to 100 mm When the number of rotation of the rotary disk 100 is 400 rpm or less, a nonuniformity risk reduction judgment index based on the following formula is used as a standard. That is, the nonuniformity risk reduction judgment index and uniformity measurement values are used to derive a standard for “target uniformity %”. Uniformity ⁢ ⁢ Risk = Magnitude ⁢ ⁢ of ⁢ ⁢ Nonuniformity ⁢ ⁢ upon ⁢ ⁢ Occurrence × Probability ⁢ ⁢ of ⁢ ⁢ Occurrence = ( Beam ⁢ ⁢ Size ⁢ / ⁢ Scan ⁢ ⁢ Pitch ) × Number ⁢ ⁢ of ⁢ ⁢ Y - Scan ⁢ ⁢ Times As mentioned above, it is preferable that the controller in the beam processing system accordong to this invention has the following functions. The controller sets the inner overscan position and the outer overscan position depending on the measured value of the beam width and measured values of one end position and the other end position in a scan direction on a cross section of the processing beam. The controller determines the scan speed and the number of reciprocating scan times of the reciprocating scan motion depending on a required total beam irradiation amount. The controller ensures the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by regularly delaying per scan the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position. In case where the beam processing system further comprises a target detecting unit provided at a position adjacent to the disk for detecting an initial position detection target portion provided at a predetermined position of the disk while the disk is rotating, and the target detecting unit outputting a detection signal, the controller delays the reversal start timing based on the detection signal. The controller ensures the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by delaying per scan the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position by a delay time (T/Nx) derived by dividing a rotation period T of the disk by a value Nx set based on the number of reciprocating scan times N. When the number of reciprocating scan times N is large, the controller sets the value Nx so as to increase by stages as the number of reciprocating times approaches the number N. The controller ensures the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by randomly controlling, based on random numbers, the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position. The controller ensures the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by controlling the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position, based on a programmed relationship of the number of rotation of the disk, the number of reciprocating scan times, the scan speed, and the measured value of the beam width. The controller stores a relationship between the number of rotation of the disk and the number of reciprocating scan times as table data in a storage device in advance and ensures the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by controlling, based on the table data, the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position. In the beam processing method according to this invention, it may comprises setting the inner overscan position and the outer overscan position depending on the measured value of the beam width and measured values of one end position and the other end position in a scan direction on a cross section of the processing beam. In the beam processing method according to this invention, it may comprises determining the scan speed and the number of reciprocating scan times of the reciprocating scan motion depending on a required total beam irradiation amount. In the beam processing method according to this invention, it may comprises ensuring the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by regularly delaying per scan the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position. In the beam processing method according to this invention, it may comprises using, as a reference for delaying the reversal start timing, a detection signal obtained by detecting an initial position detection target portion provided at a predetermined position of the disk while the disk is rotating. In the beam processing method according to this invention, it may comprises ensuring the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by delaying per scan the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position by a delay time (T/Nx) derived by dividing a rotation period T of the disk by a value Nx set based on the number of reciprocating scan times N. In the beam processing method according to this invention, it may comprises using, as a reference for delaying the reversal start timing, a detection signal obtained by detecting an initial position detection target portion provided at a predetermined position of the disk while the disk is rotating. In the beam processing method according to this invention, it may comprises, when the number of reciprocating scan times N is large, setting the value Nx so as to increase by stages as the number of reciprocating times approaches the number N. In the beam processing method according to this invention, it may comprises ensuring the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by randomly controlling, based on random numbers, the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position. In the beam processing method according to this invention, it may comprises ensuring the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by controlling the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position, based on a programmed relationship of the number of rotation of the disk, the number of reciprocating scan times, the scan speed, and the measured value of the beam width. In the beam processing method according to this invention, it may comprises preparing a relationship between the number of rotation of the disk and the number of reciprocating scan times as table data in advance and ensuring the overlap region between the last and current processing beam irradiation regions on each of the plurality of processing objects by controlling, based on the table data, the reversal start timing of the disk at the at least one of the inner overscan position and the outer overscan position. Furthermore, this invention may be carried out in the following aspects. (First Aspect) A beam processing system, wherein a controller sets a Y-scan speed based on selection and setting of the number of rotation of a rotary disk per unit time so that a distance of a Y-scan moving during one rotation of the rotary disk becomes smaller than a measured value of a beam width or a predetermined value of a beam width and, after determining the number of Y-scan times, sets a reversal start timing of the Y scan, thereby controlling a low-speed scan drive mechanism so that beam irradiation is performed onto wafers so as to always provide an overlap region overlapping at least half of a previous beam irradiation region on each wafer in every beam irradiation. (Second Aspect) A beam processing method of setting a Y-scan speed based on selection and setting of the number of rotation of a rotary disk per unit time so that a distance of a Y-scan moving during one rotation of the rotary disk becomes smaller than a measured value of a beam width or a predetermined value of a beam width and, after determining the number of Y-scan times, setting a reversal start timing of the Y scan, thereby controlling the Y scan so that beam irradiation is performed onto wafers so as to always provide an overlap region overlapping at least half of a previous beam irradiation region on each wafer in every beam irradiation. (Third Aspect) A beam processing system, wherein a controller sets a Y-scan speed based on selection and setting of the number of rotation of a rotary disk per unit time so that a distance of a Y-scan moving during one rotation of the rotary disk becomes greater than a measured value of a beam width or a predetermined value of a beam width and, after selecting the number of Y-scan times, sets a reversal start timing of the Y scan, thereby controlling a low-speed scan drive mechanism so that beam irradiation is performed onto wafers so as to always provide an overlap region overlapping at least half of a previous beam irradiation region on each wafer. (Fourth Aspect) A beam processing method of setting a Y-scan speed based on selection and setting of the number of rotation of a rotary disk per unit time so that a distance of a Y-scan moving during one rotation of the rotary disk becomes greater than a measured value of a beam width or a predetermined value of a beam width and, after selecting the number of Y-scan times, setting a reversal start timing of the Y scan, thereby controlling the Y scan so that beam irradiation is performed onto wafers so as to always provide an overlap region overlapping at least half of a previous beam irradiation region on each wafer. While the present invention has thus far been described in connection with the exemplary embodiments thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners.
	description	The present invention relates to a scintillator panel and a radiation detector. As a conventional scintillator panel there is, for example, the one described in Patent Literature 1. In this conventional configuration, a 0.05-mm glass substrate is used as a support body for a scintillator layer. Furthermore, a buffer to relieve force from the outside of a housing and a high-stiffness member with stiffness higher than that of the scintillator layer are disposed between the housing and the scintillator layer. In the scintillator panel described in Patent Literature 2, a graphite substrate coated with a polyimide-based resin film or with a poly-para-xylylene film is used as a support body. Furthermore, in the scintillator panel described in Patent Literature 3, the entire surface of the substrate comprised of amorphous carbon or the like is covered by an intermediate film such as a poly-para-xylylene film. Patent Literature 1: Japanese Patent Application Laid-open Publication No. 2006-58124 Patent Literature 2: International Publication WO 2009/028275 Patent Literature 3: Japanese Patent Application Laid-open Publication No. 2007-279051 The scintillator panel applied, for example, to a solid-state detector such as a thin-film transistor (TFT) panel is required to have flexibility enough to satisfy shape-following capability to the solid-state detector. In addition, if there is a difference between the coefficient of thermal expansion of the TFT panel and the coefficient of thermal expansion of the substrate of the scintillator panel, fine flaws on the substrate of the scintillator panel or flaws made between the scintillator panel and the TFT panel by abnormally grown portions produced in formation of the scintillator layer by evaporation can transfer to the light receiving surface because of heat during operation, raising a problem that effort of calibration becomes troublesome. For solving the problem of flexibility and the problem of coefficient of thermal expansion as described above, it is conceivable to use extremely thin glass, e.g., in the thickness of not more than 150 μm as the substrate of the scintillator panel. However, when the extremely thin glass is used, there arises a problem that the end (edge part) of glass is brittle under an impact to chip or crack. The present invention has been accomplished in order to solve the above problems and it is an object of the present invention to provide a scintillator panel capable of ensuring satisfactory flexibility while preventing the glass substrate from chipping or cracking, and a radiation detector using it. In order to solve the above problems, a scintillator panel according to the present invention comprises: a glass substrate with a thickness of not more than 150 μm having radiotransparency; an organic resin layer formed so as to cover a one face side and a side face side of the glass substrate; a scintillator layer formed on the one face side of the glass substrate on which the organic resin layer is formed; and a moisture-resistant protection layer formed so as to cover the scintillator layer along with the glass substrate on which the organic resin layer is formed. In this scintillator panel, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of thermal expansion coefficient. In addition, in this scintillator panel the organic resin layer is formed so as to cover the one face side and the side face side of the glass substrate. This reinforces the glass substrate, whereby the edge part thereof can be prevented from chipping or cracking. Furthermore, stray light can be prevented from entering the side face of the glass substrate, while transparency is ensured for light incident to the other face side of the glass substrate because the organic resin layer is not formed on the other face side of the glass substrate. Another scintillator panel according to the present invention comprises: a glass substrate with a thickness of not more than 150 μm having radiotransparency; an organic resin layer formed so as to cover an other face side and a side face side of the glass substrate; a scintillator layer formed on a one face side of the glass substrate on which the organic resin layer is formed; and a moisture-resistant protection layer formed so as to cover the scintillator layer along with the glass substrate on which the organic resin layer is formed. In this scintillator panel, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of thermal expansion coefficient. In addition, in this scintillator panel the organic resin layer is formed so as to cover the other face side and the side face side of the glass substrate. This reinforces the glass substrate, whereby the edge part thereof can be prevented from chipping or cracking. Furthermore, stray light can be prevented from entering the side face of the glass substrate and, since the organic resin layer is present on the other face side of the glass substrate, internal stress of the scintillator layer can be cancelled, so as to suppress warping of the glass substrate. In the foregoing scintillator panel, the organic resin layer may be selected from silicone resin, urethane resin, epoxy resin, and fluorine resin. Another scintillator panel according to the present invention comprises: a glass substrate with a thickness of not more than 150 μm having radiotransparency; a resin film layer stuck so as to cover a one face side of the glass substrate; a scintillator layer formed on the one face side of the glass substrate on which the resin film is stuck; and a moisture-resistant protection layer formed so as to cover the scintillator layer along with the glass substrate on which the the resin film is stuck. In this scintillator panel, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of thermal expansion coefficient. In addition, in this scintillator panel the resin film layer is formed so as to cover the one face side of the glass substrate. This reinforces the glass substrate, whereby the edge part thereof can be prevented from chipping or cracking. Furthermore, since the resin film layer is not formed on the other face side of the glass substrate, transparency is ensured for light incident to the other face side of the glass substrate. Another scintillator panel according to the present invention comprises: a glass substrate with a thickness of not more than 150 μm having radiotransparency; a resin film layer stuck so as to cover an other face side of the glass substrate; a scintillator layer formed on a one face side of the glass substrate on which the resin film is stuck; and a moisture-resistant protection layer formed so as to cover the scintillator layer along with the glass substrate on which the resin film is stuck. In this scintillator panel, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of thermal expansion coefficient. In addition, in this scintillator panel the resin film layer is formed so as to cover the other face side of the glass substrate. This reinforces the glass substrate, whereby the edge part thereof can be prevented from chipping or cracking. Furthermore, since the resin film layer is present on the other face side of the glass substrate, internal stress of the scintillator layer can be cancelled, so as to suppress warping of the glass substrate. Another scintillator panel according to the present invention comprises: a glass substrate with a thickness of not more than 150 μm having radiotransparency; a resin film layer stuck so as to cover a one face side and an other face side of the glass substrate; a scintillator layer formed on the one face side of the glass substrate on which the resin film is stuck; and a moisture-resistant protection layer formed so as to cover the scintillator layer along with the glass substrate on which the resin film is stuck. In this scintillator panel, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of thermal expansion coefficient. In addition, in this scintillator panel the resin film layer is formed so as to cover the one face side and the other face side of the glass substrate. This reinforces the glass substrate, whereby the edge part thereof can be more effectively prevented from chipping or cracking. Furthermore, since the resin film layer is formed on the one face side and on the other face side of the glass substrate, warping of the glass substrate can be suppressed. In the foregoing scintillator panel, the resin film may be selected from PET, PEN, COP, and PI. Another scintillator panel according to the present invention comprises: a glass substrate with a thickness of not more than 150 μm having radiotransparency; an organic resin layer formed so as to cover a one face side and a side face side of the glass substrate; a resin film layer stuck so as to cover an other face side of the glass substrate; a scintillator layer formed on the one face side of the glass substrate on which the organic resin layer and the resin film layer are formed; and a moisture-resistant protection layer formed so as to cover the scintillator layer along with the glass substrate on which the organic resin layer and the resin film layer are formed. In this scintillator panel, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of thermal expansion coefficient. In addition, in this scintillator panel the organic resin layer is formed so as to cover the one face side and the side face side of the glass substrate and the resin film layer is formed so as to cover the other face side of the glass substrate. This reinforces the glass substrate, whereby the edge part thereof can be prevented from chipping or cracking. Furthermore, stray light can be prevented from entering the side face of the glass substrate and, since at least one of the organic resin layer and the resin film layer is formed over the entire surface, warping of the glass substrate can be suppressed. Another scintillator panel according to the present invention comprises: a glass substrate with a thickness of not more than 150 μm having radiotransparency; an organic resin layer formed so as to cover an other face side and a side face side of the glass substrate; a resin film layer stuck so as to cover a one face side of the glass substrate; a scintillator layer formed on the one face side of the glass substrate on which the organic resin layer and the resin film layer are formed; and a moisture-resistant protection layer formed so as to cover the scintillator layer along with the glass substrate on which the organic resin layer and the resin film layer are formed. In this scintillator panel, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of theimal expansion coefficient. In addition, in this scintillator panel the organic resin layer is formed so as to cover the other face side and the side face side of the glass substrate and the resin film layer is formed so as to cover the one face side of the glass substrate. This reinforces the glass substrate, whereby the edge part thereof can be prevented from chipping or cracking. Furthermore, stray light can be prevented from entering the side face of the glass substrate and, since at least one of the organic resin layer and the resin film layer is formed over the entire surface, warping of the glass substrate can be suppressed. In the foregoing scintillator panel, the organic resin layer may be selected from silicone resin, urethane resin, epoxy resin, and fluorine resin and the resin film may be selected from PET, PEN, COP, and PI. Furthermore, a radiation detector according to the present invention comprises: the scintillator panel as described above; and a light receiving element arranged opposite to the scintillator layer on which the protection layer is formed. In this radiation detector, the glass substrate with the thickness of not more than 150 μm serves as a support body, thereby to achieve excellent radiotransparency and flexibility and also relieve the problem of thermal expansion coefficient. In addition, in this radiation detector the organic resin layer or the resin film layer reinforces the glass substrate, whereby the edge part thereof can be prevented from chipping or cracking. The present invention has made it feasible to ensure satisfactory flexibility while preventing the glass substrate from chipping or cracking. Preferred embodiments of the scintillator panel and the radiation detector according to the present invention will be described below in detail with reference to the drawings. [First Embodiment] FIG. 1 is a cross-sectional view showing a configuration of a radiation detector according to the first embodiment of the present invention. As shown in the same drawing, the radiation detector 1A is constructed by fixing a light receiving element 3 to a scintillator panel 2A. The light receiving element 3 is, for example, a TFT panel in which photodiodes (PD) and thin-film transistors (TFT) are arrayed on a glass substrate. The light receiving element 3 is stuck on a one face side of the scintillator panel 2A so that a light receiving surface 3a thereof is opposed to a below-described scintillator layer 13 in the scintillator panel 2A. The light receiving element 3 to be also used herein besides the TFT panel can be an element configured so that an image sensor such as CCD is connected through a fiber optic plate (FOP: an optical device composed of a bundle of several-micrometer optical fibers, e.g., J5734 available from Hamamatsu Photonics K.K.). The scintillator panel 2A is composed of a glass substrate 11 as a support body, an organic resin layer 12 to protect the glass substrate 11, a scintillator layer 13 to convert incident radiation to visible light, and a moisture-resistant protection layer 14 to protect the scintillator layer 13 from moisture. The glass substrate 11 is, for example, an extremely thin substrate having the thickness of not more than 150 μm and preferably having the thickness of not more than 100 μm. Since the glass substrate 11 is extremely thin in thickness, it has sufficient radiotransparency and flexibility and ensures satisfactory shape-following capability of the scintillator panel 2A in sticking it on the light receiving surface 3a of the light receiving element 3. The organic resin layer 12 is formed, for example, of silicone resin, urethane resin, epoxy resin, fluorine resin, or the like so as to cover a one face 11a and a side face 11c of the glass substrate 11. A method for forming the organic resin layer 12 is, for example, coating by the spin coating method or the like. The thickness of the organic resin layer 12 is, for example, approximately 100 μm. The scintillator layer 13 is formed on the one face 11a side of the glass substrate 11 on which the organic resin layer 12 is formed, for example, by growing and depositing columnar crystals of CsI doped with T1 by the evaporation method. The thickness of the scintillator layer 13 is, for example, 250 μm. The scintillator layer 13 is highly hygroscopic and could deliquesce with moisture in air if kept exposed to air. For this reason, the moisture-resistant protection layer 14 is needed for the scintillator layer 13. The protection layer 14 is formed, for example, by growing poly-para-xylylene or the like by the vapor phase deposition such as the CVD method, so as to cover the scintillator layer 13 along with the glass substrate 11 on which the organic resin layer 12 is formed. The thickness of the protection layer 14 is, for example, approximately 10 μm. In the radiation detector 1A having the configuration as described above, radiation incident from the glass substrate 11 side is converted to light in the scintillator layer 13 and the light is detected by the light receiving element 3. Since in the scintillator panel 2A the glass substrate 11 with the thickness of not more than 150 μm serves as a support body, it has excellent radiotransparency and flexibility. The glass substrate 11 has sufficient flexibility, thereby satisfying the shape-following capability in sticking the scintillator panel 2A to the light receiving surface 3a of the light receiving element 3. Furthermore, when the TFT panel is used as the light receiving element 3 and when the light receiving surface 3a is a glass panel, the coefficient of thermal expansion of the light receiving surface 3a can be made equal to that of the glass substrate 11 of the scintillator panel 2A. This can prevent fine flaws on the glass substrate 11 or flaws made between the scintillator panel and the TFT panel by abnormally grown portions produced during formation of the scintillator layer 13 by evaporation, from transferring to the light receiving surface 3a because of heat during operation, and can also avoid the need for troublesome effort of calibration. In addition, in this scintillator panel 2A the organic resin layer 12 is formed so as to cover the one face 11a and the side face 11c of the glass substrate 11. This reinforces the glass substrate 11, whereby the edge part thereof can be prevented from chipping or cracking. This also contributes to improvement in handling performance during manufacture and during use. Furthermore, stray light can be prevented from entering the side face 11c of the glass substrate 11 and the absence of the organic resin layer 12 on the other face 11b side of the glass substrate 11 ensures transparency for light incident to the other face 11b side of the glass substrate 11, so as to decrease reflection of light toward the light receiving element 3, with the result that resolution can be maintained. Moreover, since the organic resin layer 12 is formed so as to cover the one face 11a and the side face 11c of the glass substrate 11, it also becomes possible to adjust the surface condition of the glass substrate 11 so as to achieve appropriate surface energy and surface roughness in formation of the scintillator layer 13. [Second Embodiment] FIG. 2 is a cross-sectional view showing a configuration of a radiation detector according to the second embodiment of the present invention. As shown in the same drawing, the radiation detector 1B according to the second embodiment is different from the first embodiment in that in a scintillator panel 2B, the organic resin layer 12 is foinied so as to cover the other face 11b, instead of the one face 11a of the glass substrate 11. In this configuration, just as in the above embodiment, the glass substrate 11 is also reinforced by the organic resin layer 12, whereby the edge part thereof can be prevented from chipping or cracking and whereby stray light can be prevented from entering the side face 11c of the glass substrate 11. In addition, since the organic resin layer 12 is present on the other face 11b side of the glass substrate 11, internal stress of the scintillator layer 13 can be cancelled, so as to suppress warping of the glass substrate 11. The effect of suppressing warping of the glass substrate 11 becomes particularly prominent in a case where the glass substrate 11 is a small substrate of about 10 cm×10 cm. [Third Embodiment] FIG. 3 is a cross-sectional view showing a configuration of a radiation detector according to the third embodiment of the present invention. As shown in the same drawing, the radiation detector 1C according to the third embodiment is different from the first embodiment in that in a scintillator panel 2C, instead of the organic resin layer 12, a resin film layer 16 is stuck so as to cover the one face 11a of the glass substrate 11 and the side face 11c is not covered by the organic resin layer 12. More specifically, the resin film layer 16 is stuck on the surface (one face 11a) side where the scintillator layer 13 is formed, in the glass substrate 11 by means of a laminator or the like. The resin film layer 16 to be used herein can be, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), COP (cycloolefin polymer), PT (polyimide), or the like. The thickness of the resin film layer 16 is, for example, approximately 100 μm. Furthermore, the edge of the resin film layer 16 is preferably coincident with the edge of the glass substrate 11 or slightly projects out therefrom. In this configuration, the glass substrate 11 is also reinforced by the resin film layer 16, whereby the edge part thereof can be prevented from chipping or cracking, as in the above embodiments. In addition, since the resin film layer 16 is not formed on the other face 11b side of the glass substrate 11, the transparency is ensured for light incident to the other face 11b side of the glass substrate 11, so as to reduce reflection of light toward the light receiving element 3, with the result that the resolution can be maintained, as in the first embodiment, Moreover, since the resin film layer 16 is formed so as to cover the one face 11a of the glass substrate 11, it also becomes possible to adjust the surface condition of the glass substrate 11 so as to achieve appropriate surface energy and surface roughness in formation of the scintillator layer 13. [Fourth Embodiment] FIG. 4 is a cross-sectional view showing a configuration of a radiation detector according to the fourth embodiment of the present invention. As shown in the same drawing, the radiation detector 1D according to the fourth embodiment is different from the third embodiment in that in a scintillator panel 2D, the resin film layer 16 is stuck so as to cover the other face 11b, instead of the one face 11a of the glass substrate 11. In this configuration, the glass substrate 11 is also reinforced by the resin film layer 16, whereby the edge part thereof can be prevented from chipping or cracking, as in the above embodiments. In addition, since the resin film layer 16 is present on the other face 11b side of the glass substrate 11, internal stress of the scintillator layer 13 can be cancelled, so as to suppress warping of the glass substrate 11, as in the second embodiment. [Fifth Embodiment] FIG. 5 is a cross-sectional view showing a configuration of a radiation detector according to the fifth embodiment of the present invention. As shown in the same drawing, the radiation detector 1E according to the fifth embodiment is different from the third embodiment and the fourth embodiment in that in a scintillator panel 2E, the resin film layer 16 is stuck so as to cover the both faces of the glass substrate 11. In this configuration, both of the one face 11a and the other face 11b of the glass substrate 11 are reinforced by the resin film layer 16, whereby the edge part thereof can be more effectively prevented from chipping or cracking. In addition, the resin layer of the same material is formed on the one face 11a side and on the other face 11b side of the glass substrate 11, whereby warping of the glass substrate 11 can be suppressed. Moreover, since the resin film layer 16 is formed so as to cover the one face 11a and the other face 11b of the glass substrate 11, it also becomes possible to adjust the surface condition of the glass substrate 11 so as to achieve appropriate surface energy and surface roughness in formation of the scintillator layer 13. [Sixth Embodiment] FIG. 6 is a cross-sectional view showing a configuration of a radiation detector according to the sixth embodiment of the present invention. As shown in the same drawing, the radiation detector 1F according to the sixth embodiment is different from the first embodiment in that in a scintillator panel 2F, the resin film layer 16 is added. More specifically, on the glass substrate 11 in which the organic resin layer 12 is formed so as to cover the one face 11a side and the side face 11c side, the resin film layer 16 is further stuck so as to cover the other face 11b side. In this configuration, the entire surface of the glass substrate 11 is reinforced by the organic resin layer 12 and the resin film layer 16, whereby the edge part thereof can be more effectively prevented from chipping or cracking. Furthermore, just as in the first embodiment, the organic resin layer12 is formed so as to cover the side face 11c of the glass substrate 11, whereby stray light can be prevented from entering the side face 11c of the glass substrate 11. In addition, since the respective resin layers are formed on the one face 11a side and on the other face 11b side of the glass substrate 11, warping of the glass substrate 11 can be suppressed. Moreover, since the organic resin layer 12 and the resin film layer 16 are formed so as to cover the entire surface of the glass substrate 11, it also becomes possible to adjust the surface condition of the glass substrate 11 so as to achieve appropriate surface energy and surface roughness in formation of the scintillator layer 13. [Seventh Embodiment] FIG. 7 is a cross-sectional view showing a configuration of a radiation detector according to the seventh embodiment of the present invention. As shown in the same drawing, the radiation detector 1G according to the seventh embodiment is different from the second embodiment in that in a scintillator panel 2G, the resin film layer 16 is added. More specifically, on the glass substrate 11 in which the organic resin layer 12 is formed so as to cover the other face 11b side and the side face 11c side, the resin film layer 16 is further stuck so as to cover the one face 11a side. In this configuration, the entire surface of the glass substrate 11 is reinforced by the organic resin layer 12 and the resin film layer 16, whereby the edge part thereof can be more effectively prevented from chipping or cracking, as in the sixth embodiment. Furthermore, just as in the sixth embodiment, the organic resin layer12 is formed so as to cover the side face 11c of the glass substrate 11, whereby stray light can be prevented from entering the side face 11c of the glass substrate 11; since the respective resin layers are formed on the one face 11a side and on the other face 11b side of the glass substrate 11, warping of the glass substrate 11 can be suppressed. Moreover, since the organic resin layer 12 and the resin film layer 16 are formed so as to cover the entire surface of the glass substrate 11, it also becomes possible to adjust the surface condition of the glass substrate 11 so as to achieve appropriate surface energy and surface roughness in formation of the scintillator layer 13. 1A-1G radiation detectors; 2A-2G scintillator panels; 3 light receiving element; 11 glass substrate; 11a one face; 11b other face; 11c side face; 12 organic resin layer; 13 scintillator layer; 14 protection layer; 16 resin film layer.
	abstract	A method for sealing an opening extending radially from an outer circumferential surface to an inner circumferential surface of a tubular object in a nuclear power plant includes inserting a stopper from outside of the outer circumferential surface through the opening into the tubular object; and actuating a fastener from the outside of the circumferential surface to force the stopper radially outward to seal the opening. A mechanical seal assembly for plugging an opening in a tubular object by contacting an inner circumferential surface of the tubular object includes a stopper configured for insertion into an interior of the tubular object for plugging the opening. The stopper includes a surface configured for matching the inner circumferential surface of the tubular object. The mechanical seal assembly also includes a fastener passing through a hole in the stopper such that the fastener is actuatable from outside of the tubular object to force the surface of the stopper against the inner circumferential surface of the tubular object.
053735412	summary	BACKGROUND OF THE INVENTION The present invention relates to fuel rods for use in fuel assemblies for a water cooled and moderated nuclear reactor, in particular in assemblies for a pressurized water reactor. These rods are made of fuel pellets enclosed in cladding of an alloy having low neutron absorption. The cladding must satisfy numerous conditions, some of which are difficult to reconcile. It must remain watertight, it must conserve its mechanical properties under irradiation at high temperature, and its amount of creep must be low. It must resist corrosion by the aqueous medium in which it is immersed. It must have little interaction with the fuel contained inside the cladding. Until now, cladding has been made above all from a zirconium based alloy known as "Zircaloy 4" which contains: 1.20% to 1.70% tin; PA1 0.18% to 0.24% iron; PA1 0.07% to 0.13% chromium; PA1 0.35% to 0.65% tin; PA1 0.18% to 0.25% iron; PA1 0.07 to 0.13% chromium, and PA1 0.19% to 0.23% oxygen with the sum of the iron, chromium, tin, and oxygen content being less than 1.26%; PA1 up to 200 ppm silicon PA1 and/or 0.80% to 1.20% niobium, the oxygen content then being in range of 0.10% to 0.16% by weight, PA1 the thickness of the outer layer being in the range of 10% to 25% of the total thickness of the cladding. the total iron plus chromium content being in the range 0.28% to 0.37%. Standards concerning "Zircaloy 4", also known under the reference UNSR 60804, place a limit on the content of elements other than zirconium and those specified above, except with respect to oxygen, where it is merely stated that the oxygen content must be specified in each case. The usual oxygen content of "Zircaloy 4" does not exceed 0.12%, and is generally much less. While the mechanical strength of "Zircaloy 4" claddings has been found satisfactory, it has been observed that corrosion by the surrounding high temperature aqueous medium considerably reduces the length of time they can be kept in a reactor. Proposals have already been made to avoid this defect by using "duplex" or "triplex" claddings (see FR-A-1 547 960; EP-A-212 351; U.S. Pat. No. 4,649,023) which have at least an inner layer of "Zircaloy 4", or of a similar alloy, and an outer layer which is considerably thinner than the inner layer and which is made of a zirconium-based alloy that withstands corrosion better than "Zircaloy 4". In particular, cladding has been proposed that has an inner layer of "Zircaloy 4" and an outer layer made of a zirconium-based alloy having a reduced or zero tin content, but containing additional elements such as niobium, vanadium and nickel, which improve corrosion resistance. It has long been known (e.g., U.S. Pat. No. 4,717,534) that Zr--Nb alloys having about 2.5% niobium have good corrosion resistance in a high temperature aqueous medium. The composition of the alloy constituting the outer layer must be such that the cladding can be obtained by co-rolling or co-extrusion, with a high thickness reduction ratio at each manufacturing step. In addition, the presence of the outer layer must not significantly degrade the mechanical characteristics of the cladding as a whole. Unfortunately, to a first approximation, the mechanical properties of the cladding is the result of summing the properties of both layers, weighted by a factor representing the fraction of the total thickness applicable to each layer. It is well-known that ordinary zirconium-niobium alloys, having a very low oxygen content, have mechanical properties that are greatly inferior to those of Zircaloys. SUMMARY OF THE INVENTION An object of the present invention is to provide cladding for a nuclear fuel rod where the cladding includes at least one inner layer of "Zircaloy 4" and an outer layer that is thinner than the inner layer, which better fulfils practical requirements than previously known cladding, in particular by having considerably increased resistance to corrosion in the ambient aqueous medium while conserving mechanical characteristics that are quite comparable to those of cladding of solid "Zircaloy 4". To this end, the invention provides a nuclear fuel rod whose cladding comprises at least an inner portion of "Zircaloy 4" and an outer portion of a zirconium-based alloy that contains by weight, besides zirconium and unavoidable impurities: (a) (b) In a modification, a 0% to 0.05% content of iron, chromium or niobium is replaced by an equivalent content of vanadium. When the outer layer contains tin and does not have an appreciable niobium content, an oxygen content that is much higher than in ordinary Zircaloy 2, 3 and 4 type alloys makes it possible to obtain mechanical characteristics that come close to those of Zircaloy 4, providing the cladding is in relaxed condition (stress-relieved). When the outer layer has only one metal additive (ignoring unavoidable impurities) constituted by niobium, then the alloy in relaxed condition, even when its oxygen content is high, suffers from very poor resistance to hot creep. This drawback is avoided by having an alloy which is simultaneously doped with oxygen and by subjecting the cladding to a final recrystallization heat treatment. The invention also provides a method of manufacturing cladding suitable for use in a rod of the type defined above. In order to obtain a duplex tube for a fuel rod in accordance with the present invention, a composite billet is made having an inner portion of "Zircaloy 4", and in particular having a tin content in the low end of the range specified by the standard, and an outer portion made of a zirconium--niobium--oxygen alloy or of a zirconium-based alloy containing tin, iron, chromium and oxygen. These two billets are assembled together by welding their ends. The billets obtained in this way for the two types of alloy are hot extruded, typically at 650.degree. C. It is during this coextrusion operation that metallurgical bonding is obtained between the two zirconium alloys. The duplex tube blanks obtained in this way are transformed into finished duplex tubes by a succession of thermomechanical cycles. Typical dimensions of finished duplex-tubes are 9.50 mm outside diameter and 0.625 mm thickness, or 10.75 mm and 0.725 mm, with an outer layer of zirconium-based alloy containing niobium and oxygen (or iron, chromium, tin, oxygen) having a thickness in the range of about 80 .mu.m to about 140 .mu.m. Cold rolling steps, typically in a pilgrim step machine, of the thermo-metallurgical sequence are identical for both alloys studied, for all passes, in terms of cross-section reduction ratio and of Q factor (ratio between variation in thickness and variation in diameter), even at high deformation ratios. Transformation takes place without difficulty, and without creating crack-type defects. However, intermediate recrystallization annealing operations and the final annealing operation are adapted to each of the two alloys. For the zirconium-tin-iron-chromium-oxygen alloy, intermediate recrystallization annealing takes place in the range of 700.degree. C. to 750.degree. C. If there are five steps, the first two are advantageously at about 735.degree. C. and the last two at about 700.degree. C., while final annealing is performed at about 485.degree. C. As for the zirconium-niobium-oxygen alloy, the intermediate recrystallization annealing operations between rolling passes are performed first at about 580.degree. C..+-.15.degree. C. in order to avoid corrosion during the respective rolling phases. The last three annealing operations may be carried out at 700.degree. C..+-.15.degree. C. for Zircaloy 4 to have satisfactory resistance in a PWR. The final annealing operation is performed at about 580.degree. C. For a finished duplex-tube, the thermal mechanical transformation sequences selected for the two alloys give rise to sizes and distributions of intermetallic precipitates that are optimal mainly with respect to generalized corrosion, namely, precipitation that is fine (precipitate diameter of about 50 nm) and uniform for the zirconium alloy containing niobium and oxygen, and precipitation that is uniform and of sufficient size (intermetallic particle diameter greater than 0.18 .mu.m) for the zirconium-tin-iron-chromium- and oxygen-alloy.
044180365	description	DESCRIPTION OF THE PREFERRED EMBODIMENT In the operation of a spectral shift pressurized water reactor it is desirable to be able to selectively insert and remove displaced rods from the fuel assemblies in the reactor core. The invention described herein provides a fuel assembly capable of being used in a mechanical spectral shift nuclear reactor. Referring to FIG. 1, the nuclear reactor is referred to generally as 20 and comprises a reactor vessel 22 with a removable closure head 24 attached to the top end thereof. An inlet nozzle 26 and an outlet nozzle 28 are connected to reactor vessel 22 to allow a coolant such as water to circulate through reactor vessel 22. A core plate 30 is disposed in the lower portion of reactor vessel 22 and serves to support fuel assemblies 32. Fuel assemblies 32 are arranged in reactor vessel 22 and comprise reactor core 34. As is well understood in the art, fuel assemblies 32 generate heat by nuclear fissioning of the uranium therein. The reactor coolant flowing through reactor vessel 22 in heat transfer relationship with fuel assemblies 32 transfers the heat from fuel assemblies 32 to electrical generating equipment located remote from nuclear reactor 20. A plurality of control rod drive mechanisms 36 which may be chosen from those well known in the art are disposed on closure head 24 for inserting or withdrawing control rods (not shown) from fuel assemblies 32. In addition, a plurality of displacer rod drive mechanisms 38 are also disposed on closure head 24 for inserting or withdrawing displacer rods 40 from fuel assemblies 32. Displacer rod drive mechanism 38 may be similar to the one described in copending U.S. patent application Ser. No. 217,055, filed Dec. 16, 1980 in the name of L. Veronesi et al. entitled "Hydraulic Drive Mechanism" and assigned to the Westinghouse Electric Corporation. For purposes of clarity, only a selected number of displacer rods 40 are shown in FIG. 1. However, it should be understood, that the number of displacer rods 40 are chosen to correspond to the number of displacer rod guide tubes in fuel assemblies 32. Displacer rods 40 are elongated cylindrical substantially hollow rods which may be of the type disclosed in copending U.S. patent application Ser. No. 217,052, entitled "Displacer Rod For Use In A Mechanical Spectral Shift Reactor" filed Dec. 16, 1980 in the name of R. K. Gjertsen et al. and assigned to the Westinghouse Electric Corporation. Displacer rods 40 are arranged so as to be in colinear alignment with the guide tubes in fuel assemblies 32 so that displacer rods 40 may be inserted therein when it is desired. The insertion of displacer rods 40 into fuel assemblies 32 displaces water moderator from core 34 which reduces core moderation. A plurality of displacer rod guide structures 42 are located in the upper section of reactor vessel 22 with each being in alignment with a displacer rod drive mechanism 38 for guiding the movement of displacer rods 40 through the upper section of reactor vessel 22. A calandria 44 may be arranged between fuel assemblies 32 and displacer rod guide structures 42 and comprises a multiplicity of hollow stainless steel tubes arranged in colinear alignment with each displacer rod and control rod for providing guidance of the displacer rods and control rods through the calandria area and for minimizing flow induced vibrations in the displacer rods and control rods. Referring now to FIGS. 2-5, fuel assemblies 32 comprise fuel elements 48, grids 50, bottom nozzle 52, top nozzle 54, and guide tubes 56. Fuel elements 48 may be elongated cylindrical metallic tubes containing nuclear fuel pellets and having both ends sealed by end plugs. Fuel elements 48 may be arranged in a substantially 20.times.20 rectangular array and are held in place by grids 50. When held by grids 50, fuel elements 48 may be arranged in a 0.470 inch square pitch to form a 9.40.times.9.40 inch square fuel assembly. Guide tubes 56 which may number 25 are arranged in a generally 5.times.5 array within each fuel assembly 32. Each guide tube 56 occupies the space of about four fuel elements 48 and extend from bottom nozzle 52 to top nozzle 54 and provide a means to support grids 50, top nozzle 54 and bottom nozzle 52. Guide tubes 56 may be hollow cylindrical metallic tubes manufactured from a metal such as Zircaloy tubing and capable of accommodating rods such as displacer rods 40 or control rods. Guide tubes 56 may have openings in the sides or in the bottom ends thereof for allowing reactor coolant to pass therethrough for cooling purposes. Displacer rods 40 and control rods are manufactured to be approximately the same size so that each guide tube 56 can equally accommodate either a displacer rod or a control rod. When not occupied by a rod, guide tubes 56 are filled with reactor coolant; however, when displacer rods 40 are inserted in guide tubes 56 displacer rods 40 displace the coolant therein. Grids 50 which may number about 12 per fuel assembly are positioned at various locations along the length of fuel assembly 32 and serve to space fuel element 48 and guide tubes 56 at appropriate distances from each other and to allow the reactor coolant to circulate in heat transfer relationship with fuel elements 48. A more detailed description of grids similar to grids 50 may be found in U.S. Pat. Nos. 3,379,617 and 3,379,619. The grid 50 located closest to top nozzle 54 is referred to as top grid 58 and the grid 50 located closest to bottom nozzle 52 is referred to as bottom grid 60 with the ten grids 50 located therebetween being referred to as intermediate grids 62. Both top grid 58 and bottom grid 60 may be of the well-known spring-dimple type and may be made of Inconel for providing greater lateral support for fuel elements 48 when the grids are irradiated. Intermediate grids 62 may be of the dimple-type grids with no spring clips and made of Zircaloy for providing greater flow area for the reactor coolant. Twenty-four stainless steel sleeves 64 are brazed to each top grid 58 and each bottom grid 60 and twenty-four Zircaloy sleeves 66 are welded to each intermediate grid 62. All guide tubes 56 except center guide tube 68 are mechanically attached by internal bulging to each grid 50. Having twenty-four guide tubes 56 attached to all twelve grids 50 produces a fuel assembly with significantly greater lateral stiffness than most existing fuel assemblies. Additionally, twenty-four stainless steel sleeves 70 are welded to each top adapter plate 72 which forms part of top nozzle 54. Each top adapter plate 72 may be constructed as shown in FIG. 5 but are preferably formed as shown in FIG. 4. Stainless steel sleeves 70 are welded to each adapter plate 72 by four axial welds. A bottom adapter plate 74 which may be similar to top adapter plate 72 forms part of bottom nozzle 52. A plurality of stainless steel screws 76 penetrate through bottom adapter plate 74 and are used to attach guide tubes 56 to bottom nozzle 52. Screws 76 may also have a channel therethrough for allowing the reactor coolant to enter the guide tubes for cooling purposes. A locking pin (not shown) may be used to secure screws 76 to bottom adapter plate 74 by welding the pin to bottom adapter plate 74. As an alternative, a locking cup (not shown) may be used to secure screws 76. Referring now to FIG. 6, core plate 30 has a plurality of guide pins 80 mounted thereon that are formed to fit into semi-circular notches 82 of bottom nozzle 52. Guide pins 80 are arranged to fit into four adjacent fuel assembly notches 82 so as to provide alignment of fuel assemblies 32 on core plate 30. Similarly, top nozzle 54 may also have semi-circular notches 82 for accommodating such guide pins from a top core plate (not shown) if so desired. Referring now to FIGS. 6-12, a fuel assembly locking mechanism 84 is provided in each fuel assembly 32 for removably attaching each fuel assembly to core plate 30 thereby eliminating the need for holddown springs that were used in the prior art. For clarity the fuel assemblies shown in FIGS. 6-12 have been simplified; however, it should be understood that these fuel assemblies are identical to those shown in FIGS. 2-4. Thus, all fuel assemblies 32 may be provided with a locking mechanism 84. Locking mechanism 84 comprises a stainless steel lower member 86 which is slidably disposed in the center of bottom adapter plate 74. Lower member 86 has a first bore 88 therein for allowing reactor coolant to pass therethrough and has external threads 90 around the outside of its lower portion for engaging anchor mechanism 92. A Belleville spring washer 94 is disposed in a notch in bottom adapter plate 74 and is compressed when lower member 86 is forced downwardly relative to bottom adapter plate 74 as shown in FIG. 6. Spring washer 94 prevents loss of axial preload due to small unlocking rotation of external threads 90. Anchor mechanism 92 comprises a stainless steel lower anchor 96 which may be screw attached or welded to core plate 30. A removable insert 98 is captured and held by lower anchor 96. Insert 98 may be made of an antigalling and wear-resistant, austenitic, stainless steel and is provided with internal threads 100 for engaging external threads 90 thereby locking lower member 86 to core plate 30. Insert 98 may also have a second bore 102 therein for allowing reactor coolant to pass therethrough and into first bore 88 of lower member 86. A locking collar 104 may be provided with internal threads (not shown) that mate with external threads (not shown) on insert 98 so that locking collar 104 may be screwed onto insert 98 thereby pulling both insert 98 and locking collar 104 into tight contact with lower anchor 96. In addition, a locking pin 106 may be provided for locking insert 98 to locking collar 104 thereby preventing inadvertent unlocking of the two members. Center guide tube 68 which may be made of Zircaloy is bulged attached to lower member 86 and extends into top nozzle 54. A ratchet mechanism 108 is attached to the top center guide tube 68 for locking center guide tube 68 to top nozzle 54. Ratchet mechanism 108 comprises a slotted member 110 that is welded to the upper end of center guide tube 68. A slider member 112 having lugs 114 on its inner surface is slidably disposed over slotted member 110 such that lugs 114 are slidably disposed in slots 116 of slotted member 110. This arrangement allows axial movement but not rotation of slider member 112 relative to slotted member 110. Slider member 110 also has a first set of ratchet teeth 118 mounted around the outside thereof. A second set of ratchet teeth 120 are mounted on retainer housing 122 in a manner so as to mate with first set of ratchet teeth 118. Retainer housing 122 is disposed around slider member 112 and is attached to top adapter plate 72 so that slider member 112 may slide relative to retainer housing 122. A biasing mechanism 124 which may be a coil spring is disposed between top adapter plate 72 and first set of ratchet teeth 118 and around slider member 112 for urging slider member 112 upwardly thus moving first set of ratchet teeth 118 into contact with second set of ratchet teeth 120. A turning key 126 which may be a long metal member having an hexagonal head 128 on the lower end thereof may be inserted through center guide tube 68 for screwing external threads 90 into internal threads 100. Turing key 126 may also have a crossbar 130 on the top end thereof that is capable of being disposed in groove 132 of slider member 112. When it is desired to lock a fuel assembly 32 to core plate 30, turning key 126 may be inserted into center guide tube 68 so that crossbar 130 is disposed in groove 132 and head 128 is disposed in lower member 86. Since center guide tube 68 is not firmly attached to top adapter plate 72, center guide tube 86 is free to rotate and slide relative to top adapter plate 72 but may not be removed therefrom because of the interaction of slotted member 110 and slider member 112. So turning key 126 may be used to push lower member 86 into contact with lower adapter plate 74 and to turn external threads 90 into internal threads 100 thus locking fuel assembly 32 to core plate 30. Since first set of ratchet teeth 118 is arranged to override second set of ratchet teeth 120, it is not necessary to depress slider member 112 in order to engage external threads 90 and internal threads 100. However, when it is necessary to unlock lower member 86 from anchor mechanism 92, it is necessary to depress slider member 112 thereby compressing biasing mechanism 124 and disengaging first set of ratchet teeth 118 from second set of ratchet teeth 120. When slider member 112 has been thus depressed as shown in FIG. 9, slider member 112 can be held in this position and rotated so as to release lower member 86 from anchor mechanism 92 thereby unlocking the fuel assembly from core plate 30. Since top nozzle 54 is connected to retainer housing 122 by means of top adapter plate 72 and to bottom adapter plate 74 by means of guide tubes 56, when first set of ratchet teeth 118 is engaged with second set of ratchet teeth 120 fuel assembly 32 is locked onto core plate 30 and cannot be unlocked until the ratchet teeth are disengaged. Therefore, the invention provides a fuel assembly that is capable of being used in a spectral shift nuclear reactor.
	abstract	A solution for evaluating trust in a computer infrastructure is provided. In particular, a plurality of computing devices in the computer infrastructure evaluate one or more other computing devices in the computer infrastructure based on a set of device measurements for the other computing device(s) and a set of reference measurements. To this extent, each of the plurality of computing devices also provides a set of device measurements for processing by the other computing device(s) in the computer infrastructure.
	description	The invention relates to ultrasonic diagnostic techniques, especially to an ultrasonic front-end device and operating method thereof and a digital reordering unit for use in the ultrasonic front-end device, which is highly reliable, real-time and consumes less hardware resources. The ultrasonic front-end device plays an important role in an ultrasonic diagnostic system. The number of reception channels in an ultrasonic diagnostic system determines the system cost as well as the system performance. There is a need to develop an ultrasonic front-end with good compatibility to satisfy the requirements of ultrasonic diagnostic systems with various performances, which may mitigate workload in development of an ultrasonic diagnostic system, thus decreasing cost in development of the ultrasonic diagnostic system and reducing future cost in maintenance of the ultrasonic diagnostic system. When an ultrasonic diagnostic system is carrying out ultrasonic transmissions and receptions, due to the changes of the number of scan lines, the transmission and reception channels will choose to operate different array elements in the probe of the ultrasonic diagnostic system every time. Thus, the transmission and reception channels need to be reordered in both the transmission and reception processing. Reordering methods may be classified into analog reordering and digital reordering. Compared with analog reordering, digital reordering has the advantage of having higher reliability and lower cost. Therefore, it is of great importance for the ultrasonic front-end device to have a digital reordering unit, which is highly real time and consumes less hardware resources. As shown in FIG. 1, a prior-art ultrasonic system 1 mainly comprises a probe 2, an ultrasonic front-end 3, a detector 4, a DSC (Digital Scan Conversion) unit 5, a display 6, and a primary controller 7, wherein the primary controller 7 is configured to perform man-machine interaction and control operations of the ultrasonic front-end device 3, the detector 4 and the DSC unit 5. The ultrasonic front-end device 3 includes two parts: an ultrasonic transmission part 31 and an ultrasonic reception part 32. The ultrasonic transmission part 31 comprises a transmission beamformer 311, a transmission drive unit 312 and a high-voltage analog switch 313. High-voltage transmission pulses originated from the ultrasonic transmission part 31 are fed into the probe 2, to activate the array elements 9 included in the probe 2 to emit ultrasonic waves. The probe 2 receives echoes of the ultrasonic waves, converts them into electric signals and provides the electric signals to the ultrasonic reception part 32. The ultrasonic receiving part 32 comprises a high-voltage analog switch 321, a high-voltage isolation circuit 322, an amplifier 323, an analog reordering unit 324, an ADC (Analog-to-Digital Converter) 325 and a reception beamformer 326. The electric signals received from the probe 2 are amplified, analog reordered and AD (Analog-to-Digital) converted and ultimately the received beam signals are formed. The detector 4 detects the beamformed signals received from the ultrasonic front-end 3, so as to acquire information to be displayed and feeds the information into the DSC unit 5. The DSC unit 5 coordinates transformation of the information and provides the transformed information to the display 6 for presentation. The analog reordering unit 8 is typically implemented with an expensive matrix of analog switches or a multi-stage analog switch. The number of transmission and reception channels (especially the reception channels) in most conventional ultrasonic systems is less than the number of array elements included in the probe, thus high-voltage analog switches have to be employed to select a suitable number of array elements from those included in the probe, for connection to their respective channels. The conventional ultrasonic systems may be classified into two types: type A and type B. For type A, the transmission and reception channels of an ultrasonic system share a single high-voltage analog switch and thus one high-voltage analog switch may be saved. However it brings difficulty in the implementation of synthetic aperture. For type B, the transmission and reception channels of an ultrasonic system use their own high-voltage analog switches, respectively, as shown in FIG. 1. Technical solutions disclosed in U.S. Pat. No. 5,617,862, U.S. Pat. No. 6,029,116, U.S. Pat. No. 5,882,307 and U.S. Pat. No. 5,551,433 relate to Type B ultrasonic systems, with an advantage of allowing the aperture of the reception channels and that of the transmission channels to have different sizes and thus provides a possibility to implement various aperture synthesis techniques. The conventional ultrasonic system of FIG. 1 has several drawbacks. First, the use of high-voltage analog switches leads to high cost of the ultrasonic system. Second, the analog reordering unit adopts a multi-stage analog switch, thus affecting the quality of signal reception. Third, the use of high-voltage analog switches and multi-stage analog switches results in poor stability of the ultrasonic system. There exists another type of ultrasonic system in the prior arts. This ultrasonic system is different from the one of FIG. 1 in that its ultrasonic transmission part has digital reordering function, but its ultrasonic reception part has no analog reordering unit and the reception beamformer has digital reordering function. As shown in FIG. 2, the ultrasonic transmission part 31 in the ultrasonic system 1 comprises a transmission beamformer 311, transmission driving units 312 and a high-voltage analog switch 313 connected in a sequential order. Referring to FIG. 3, the transmission beamformer 311 comprises a transmission parameter storing unit 3111 and a transmission parameter digital reordering unit 3112 whose output is provided to the transmission driving unit 312. As shown in FIG. 6, a digital reordering unit 40, such as the transmission parameter digital reordering unit 3112 of FIG. 3, comprises M M:1 multiplexers 41 followed by M corresponding D-type flip-flops (DFFs) 42, so as to implement a selection from M inputs to M outputs, where M denotes the number of array elements included in the probe of the ultrasonic system. Furthermore, the ultrasonic reception part 32 comprises a high-voltage analog switch 321, a high-voltage isolation circuit 322, amplifiers 323, an analog reordering unit 324, ADCs 325 and a reception beamformer 326 with digital reordering function, all of them serially connected. The reception beamformers having digital reordering function in prior arts may be classified into two types. The first type of reception beamformer for performing digital reordering on the received parameters is shown in FIG. 4. The reception beamformer 326 comprises delay units 3261, a delay parameter read controller 3262, a delay parameter digital reordering unit 3263, apodization units 3264, an apodization parameter read controller 3265, an apodization parameter digital reordering unit 3266 and an adding unit 3267. The reception beamformer 326 delays, apodises and adds the signals received from the ADCs 325, to synthesize the received beam signals. The second type of reception beamformer for performing digital reordering on the received signals is shown in FIG. 5. The reception beamformer 326 comprises a signal digital reordering unit 3268, delay units 3261, a delay parameter read controller 3262, apodization units 3264, anapodization parameter read controller 3265 and an adding unit 3267. The reception beamformer 326 delays, apodises, reorders and adds the signals received from the ADCs 325, so as to synthesize the received beam signals. The prior art of the digital reordering method is shown in FIG. 6 M M:1 multiplexers are used to complete the selection from M inputs to M outputs. This architecture is not optimal, because the delay from the inputs to outputs is large, and it consumes much hardware resource. An ultrasonic diagnosing system disclosed in a U.S. patent application with publication No. 20060074317A has a function similar to digital reordering, but it fails to present a specific structure which may be real time and consumes less hardware resources. A Chinese patent application with publication No. CN1649645A discloses an ultrasonic diagnostic equipment, which comprises an ultrasonic transmission part and an ultrasonic reception part. The ultrasonic reception part comprises a limiter (i.e. isolation circuit), low-voltage analog switches and ADCs. A cross point switch network is connected between these low-voltage switches and ADCs, for reordering and adding the received signals and providing the resultant signals to the ADCs for AD conversion. The ultrasonic diagnostic equipment has the drawbacks of incapable of implementing an ultrasonic system with a different number of channels. The present invention is made in view of the drawbacks in the prior arts by providing an ultrasonic front-end device and its usage and a digital reordering unit for use in the ultrasonic front-end device. The ultrasonic front-end device is compatible with ultrasonic diagnostic systems having different numbers of reception channels and implemented on the same PCB (Print Circuit Board). According to the requirements of ultrasonic diagnostic systems with different numbers of reception channels, a corresponding number of amplifiers and ADCs may be soldered on the PCB to implement the corresponding number of reception channels. In one aspect of the invention, a digital reordering unit for an ultrasonic front-end device is provided, comprising a plurality of 2:1 multiplexers and a plurality of DFFs coupled thereto correspondingly. A digital reordering unit with such a configuration implements a selection from M inputs to M outputs, to obtain a pipeline architecture from inputs to outputs, thus making the implementation of an ultrasonic system high-speed and real-time. In another aspect of the invention, there is provided an ultrasonic front-end device for use in an ultrasonic system which is compatible with P types of reception channels, where P is an integer larger than or equal to 1; the ultrasonic front-end device being connected between a probe and a detector of the ultrasonic system and controlled by a primary controller of the ultrasonic system; the probe having M array elements, where M is an integer larger than or equal to 1, the ultrasonic front-end device having an ultrasonic transmission part and an ultrasonic reception part, wherein the ultrasonic transmission part comprises a transmission beamformer and M transmission driving units, and has M transmission channels; the ultrasonic reception part comprises M high-voltage isolation circuits, RC amplifiers, RC ADCs and a beamformer electrically connected in said order and has RC reception channels, where RC=[N,2N,3N, . . . pN], N being an integer larger than or equal to 1; the ultrasonic front-end device being characterized in that, M low-voltage analog switches and a network of resistors are serially connected between the M high-voltage isolation circuits and the RC amplifiers, wherein M low-voltage analog switches are configured to electrically connect RC array elements of the M array elements in the probe and the RC respective reception channels in the ultrasonic reception part as the scan lines of the ultrasonic diagnostic system change, and the network of resistors configured to connect the RC reception channels connected by the M low-voltage analog switches with the RC amplifiers the, the network of resistors comprising M inputs IN[1, 2, 3, . . . , M] connected to the outputs of the low-voltage analog switches and RC outputs OUT[1, 2, . . . , RC] connected to the inputs of the RC amplifiers; the structure of the network of resistors can be expressed by the following formula: OUT[jj]=IN[jj+kkRC], indicating that the output OUT[jj] and the input IN[jj+kkRC] of the network of resistors are connected through resistors, where 1≦jj≦RC, 0≦kk≦INT(M/RC), INT denotes taking the integer part, if jj+kkRC>M, since such an input does not exist, there is no resistor connecting the input and the output of the network of resistors; and a digital reordering unit included in the reception beamformer comprises a plurality of 2:1 multiplexers and a plurality of DFFs coupled thereto correspondingly. In an embodiment, the low-voltage switches are single-stage analog switches. In an embodiment, the connection between the network of resistors and the low-voltage analog switches and the amplifiers is implemented through resistors, wherein based on the number of RC, the corresponding resistors in the network of resistors are soldered with the low-voltage analog switches and the amplifiers. In an embodiment, the transmission beamformer comprises a transmission parameter storage unit and a transmission parameter reordering unit, wherein the outputs from the transmission parameter reordering unit being provided to the transmission driving units, and the transmission parameter reordering unit comprising a plurality of 2:1 multiplexers followed with respective DFFs. In an embodiment, the transmission beamformer sets and stores a set of ordered transmission parameters corresponding to the transmission channels respectively, to provide a binary control parameter B[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change, the control parameter controls an array of 2:1 multiplexers to convert the ordered transmission parameters into parameters for the current transmission channels, the array of 2:1 multiplexers comprises multiple stages, each of which stage having M 2:1 multiplexers, each bit of the parameter B controls M 2:1 multiplexers at a corresponding stage, where 2K+1≧M, K being an integer larger than or equal to 0, wherein the inputs at the 0th stage are the ordered transmission parameters for the M transmission channels; each bit of the parameter B is used to control M 2:1 multiplexers at a stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers are output, otherwise, the data on the “1” inputs of the 2:1 multiplexers are output; the signals on the “1” inputs of the array of 2:1 multiplexers are shifted 2K units rightward, the shift complies with the binary coding format and the outputs from the 2:1 multiplexers at the last stage are M digitally reordered transmission parameters. In an embodiment, the reception beamformer that performs digital reordering on the reception parameters, the digital reordering unit included in the reception beamformer comprises delay parameter digital reordering units and apodization parameter digital reordering units, the delay parameter digital reordering units and apodization parameter digital reordering units each comprising a plurality of 2:1 multiplexers having a “0” input and a “1” input and DFFs coupled thereto correspondingly. In an embodiment, for the reception beamformer that performs digital reordering on the received signals, the digital reordering unit included in the reception beamformer comprises multiple stages of 2:1 multiplexers and DFFs connected thereafter, each stage comprising PN 2:1 multiplexers having a “0” input and a “1” input and PN DFFs coupled thereto correspondingly; based on a binary control parameter C[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change, an array of 2:1 multiplexers are controlled to perform digital reordering on the received signals, the array of 2:1 multiplexers including k+1 stages, each stage having PN 2:1 multiplexers, where 2K+1≧PN, K being an integer larger than or equal to 0, wherein signals from the ADCs are received at the inputs of the PN 2:1 multiplexers at the 0th stage, each bit of the control parameter C is used to control M 2:1 multiplexers at a corresponding stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers are output; the signals on the “1” inputs of the array of 2:1 multiplexers are shifted 2K units rightward, for example, the signals on the inputs of the multiplexers at the C[0] stage are shifted 1 unit rightward, the signals on the inputs of the multiplexers at the C[1] stage are shifted 2 units rightward, the signals on the inputs of the multiplexers at the C[2] stage are shifted 4 units rightward, the signals on the inputs of the multiplexers at the C[3] stage are shifted 8 units rightward, . . . , and the signals on the inputs of the multiplexers at the C[K] stage are shifted 2K units rightward, the shift complies with the binary coding format and the outputs from the 2:1 multiplexers at the last stage are PN digitally reordered signals. In an embodiment, for the reception beamformer that performs digital reordering on the reception parameters, the digital reordering unit included in the reception beamformer comprises delay parameter digital reordering units and apodization parameter digital reordering units, the delay parameter digital reordering units and apodization parameter digital reordering units each comprising multiple stages of 2:1 multiplexers and DFFs connected thereafter, each stage having PN 2:1 multiplexers having a “0” input and a “1” input and PN DFFs coupled thereto correspondingly for the reception beamformer that performs digital reordering on the reception parameters, the reception beamformer sets and stores a set of ordered reception parameters corresponding to the reception channels respectively, to provide a binary control parameter C[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change the control parameter controlling an array of 2:1 multiplexers to convert the ordered reception parameters into parameters for the current reception channels, the array of 2:1 multiplexers comprising K+1 stages, each stage having PN 2:1 multiplexers, where 2K+1≧PN, K being an integer larger than or equal to 0, wherein the inputs of the PN 2:1 multiplexers at the 0th stage are set to the reception parameters for the corresponding reception channels each bit of the parameter C is used to control 2:1 multiplexers at a corresponding stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers are output, otherwise, the data on the “1” inputs of the 2:1 multiplexers are output; the signals on the “1” inputs of the whole array of 2:1 multiplexers are shifted 2K units rightward, for example, signals on the inputs of the multiplexers at the C[0] stage are shifted 1 unit rightward, signals on the inputs of the multiplexers at the C[1] stage are shifted 2 units rightward, signals on the inputs of the multiplexers at the C[2] stage are shifted 4 units rightward, . . . , and signals on the inputs of the multiplexers at the C[K] stage are shifted 2K units rightward. In this way, the ultrasonic diagnostic system using the ultrasonic front-end may achieves the following beneficial technical effects: 1. High-voltage analog switches are replaced by low-voltage analog switches, thus reducing cost of the ultrasonic system; 2. Ultrasonic systems with different numbers of channels may be accommodated through low-voltage analog switches and a network of resistors, thus improving the compatibility of the ultrasonic front-end of the ultrasonic diagnostic system; and 3. The digital sorting unit has a pipeline architecture from inputs to outputs, thus making the implementation of an ultrasonic system high-speed and real-time. In still another aspect of the invention, there is provided a operating method of an ultrasonic front-end device in an ultrasonic diagnostic system, wherein the ultrasonic front-end device is compatible with P types of reception channels, where P is an integer larger than or equal to 1; the ultrasonic front-end device is connected between a probe and a detector of the ultrasonic system and controlled by a primary controller of the ultrasonic system, the probe comprising M array elements, where M is an integer larger than or equal to 1, the ultrasonic front-end device comprising an ultrasonic transmission part and an ultrasonic reception part, wherein the ultrasonic transmission part comprises a transmission beamformer and M transmission driving units, and has M transmission channels, and the ultrasonic reception part has RC reception channels, where RC=[N,2N,3N . . . pN], N being an integer larger than or equal to 1, and comprises M high-voltage isolation circuits, RC amplifiers, RC ADCs and a beamformer electrically connected in said order. The method being characterized in that, M low-voltage analog switches and a network of resistors are serially connected between the M high-voltage isolation circuits and the RC amplifiers, the M low-voltage analog switches are configured to electrically connect RC array elements of the M array elements in the probe and the RC corresponding reception channels in the ultrasonic reception part as the scan lines of the ultrasonic system change; the network of resistors is configured to connect the RC reception channels connected by the M low-voltage analog switches with the RC amplifiers, the network of resistors comprises M inputs IN[1, 2, 3, . . . , M] connected to the outputs of the low-voltage analog switches and RC outputs OUT[1, 2, . . . , RC] connected to the inputs of the amplifiers, the structure of the network of resistors is expressed by the following formula; OUT[jj]=IN[jj+kkRC], indicating that the output OUT[jj] and the input IN[jj+kkRC] of the network of resistors are connected through resistors, where 1≦jj≦RC, 0≦kk≦INT(M/RC), INT denotes taking the integer part, if j+kkRC>M, since such an input does not exist, there is no resistor connecting the input and the output of the network of resistors; and a digital reordering unit included in the reception beamformer comprises a plurality of 2:1 multiplexers and a plurality of DFFs coupled thereto correspondingly, the method comprising the steps of: (1) emitting pulses by the ultrasonic transmission part with transmission parameters, to activate the currently selected transmission array elements in the probe of the ultrasonic system to transmit ultrasonic waves; (2) receiving echoes of the ultrasonic waves and converting them into electric signals by the currently selected reception array elements in the probe; (3) receiving the electric signals from the probe by the high-voltage isolation circuits in the ultrasonic reception part; (4) electrically connecting, by the M low-voltage analog switches in the ultrasonic reception part, RC array elements of the M array elements in the probe and RC corresponding reception channels in the ultrasonic reception part as the scan lines of the ultrasonic diagnostic system change; (5) connecting, by the network of resistors, the RC reception channels connected by the M low-voltage analog switches with the RC amplifiers; (6) amplifying and AD converting the received electric signals by the amplifiers and the ADCs in the ultrasonic reception part; and (7) digital reordering the reception parameters or the received signals, and beam forming by the beamformer in the ultrasonic reception part. In an embodiment, the step (1) further comprises the substeps of: (1a) setting and storing, by the transmission beamformer in the ultrasonic transmission part, a set of ordered transmission parameters corresponding to the transmission channels; and (1b) providing, by the transmission beamformer, a binary control parameter B[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change; the parameter controls an array of 2:1 multiplexers to convert the ordered transmission parameters into parameters for the current transmission channels; the array of 2:1 multiplexers comprises a plurality of stages each having M 2:1 multiplexers, each bit of the parameter controls M 2:1 multiplexers at a corresponding stage, where 2K+1≧M, K being an integer larger than or equal to 0; the inputs at the 0th stage are the ordered transmission parameters for the M transmission channels; each bit of the parameter B is used to control M 2:1 multiplexers at a corresponding stage: if the bit is 0, the data on from “0” inputs of the 2:1 multiplexers are output, otherwise, the data on the “1” inputs of the 2:1 multiplexers are output; the signals on the “1” inputs of the array of 2:1 multiplexers are shifted 2K units rightward, for example, the signals on the inputs of the multiplexers at the B[0] stage are shifted 1 unit rightward, the signals on the inputs of the multiplexers at the B[1] stage are shifted 2 units rightward, the signals on the inputs of the multiplexers at the B[2] stage are shifted 4 units rightward, the signals on the inputs of the multiplexers at the B[3] stage are shifted 8 units rightward, . . . , and the signals on the inputs of the multiplexers at the B[K] stage are shifted 2K units rightward, the shift complies with the binary coding format, and the outputs from the 2:1 multiplexers at the last stage are M digitally reordered transmission parameters. There are two types of digital reordering at the step (7): first, conduct digital reordering on the received signals while no digital reordering on the reception parameters; second, conduct digital reordering on the reception parameters while no digital reordering on the received signals. In an embodiment, for the reception parameters, the digital reordering and beam forming at the step (7) comprises the substeps of: (7a) setting and storing a set of ordered reception parameters corresponding to the reception channels, by the reception beamformer in the ultrasonic reception part: and (7b) providing, by the reception beamformer, a binary control parameter C[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change, the control parameter controlling an array of 2:1 multiplexers to convert the ordered reception parameters into parameters for the current reception channels; the array of 2:1 multiplexers comprises multiple stages each having PN 2:1 multiplexers, each bit of the parameter controls PN 2:1 multiplexers at a corresponding stage, where 2K+1≧PN. K being an integer larger than or equal to 0, wherein all the inputs of the PN 2:1 multiplexers at the 0th stage are the reception parameters for the corresponding reception channels; each bit of the parameter C is used to control 2:1 multiplexers at a corresponding stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers are output; the signals on the “1” inputs of the whole array of 2:1 multiplexers are shifted 2K units rightward, for example, the signals on the “1” inputs of the multiplexers at the C[0] stage are shifted 1 unit rightward, the signals on the “1” inputs of the multiplexers at the C[1] stage are shifted 2 units rightward, the signals on the “1” inputs of the multiplexers at the C[2] stage are shifted 4 units rightward, . . . , and the signals on the “1” inputs of the multiplexers at the C[K] stage are shifted 2K units rightward. In an embodiment, for the received signals, the digital reordering and beam forming at the step (7) comprises a substep of: providing, by the reception beamformer, a binary control parameter C[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change, the control parameter controls an array of 2:1 multiplexers; the array of 2:1 multiplexers includes k+1 stages each having PN 2:1 multiplexers, where 2K+1≧PN, K being an integer larger than or equal to 0, wherein signals from the ADCs are received by the inputs of the PN 2:1 multiplexers at the 0th stage, each bit of the control parameter C is used to control PN 2:1 multiplexers at a corresponding stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers are output; the signals on the “1” inputs of the array of 2:1 multiplexers are shifted 2K units rightward, for example, the signals on the inputs of the multiplexers at the C[0] stage are shifted 1 unit rightward, the signals on the inputs of the multiplexers at the C[1] stage are shifted 2 units rightward, the signals on the inputs of the multiplexers at the C[2] stage are shifted 4 units rightward, the signals on the inputs of the multiplexers at the C[3] stage are shifted 8 units rightward, . . . , and the signals on the inputs of the multiplexers at the C[K] stage are shifted 2K units rightward, the shift complies with the binary coding format, and the outputs from the 2:1 multiplexers at the last stage are PN digitally reordered signals. The aforementioned technical solutions lead to implementation of a high-speed and real-time ultrasonic system, improvement in the compatibility for the ultrasonic front-end of the ultrasonic system and cost saving for the ultrasonic system. Detailed descriptions will be made below to the invention with reference to embodiments shown in accompanying drawings. FIG. 7 is a schematic diagram showing the configuration of a digital reordering unit 45 according to one embodiment of the invention. As shown in the figure, the digital reordering unit 45 comprises a plurality of 2:1 multiplexers 51 and a plurality of DFFs 52 coupled thereto correspondingly. FIG. 8 is a block diagram showing the configuration of an ultrasonic front-end device 3 in an ultrasonic diagnostic system 1 according to one embodiment of the invention. As shown in the figure, the ultrasonic system 1 mainly comprises a probe 2, an ultrasonic front-end 3, a detector 4, a DSC (Digital Scan Conversion) unit 5, a display 6 and a primary controller 7. The probe 2 has M array elements, where M is an integer larger than or equal to 1. The ultrasonic front-end 3 is equipped with an ultrasonic transmission part 31 comprising a transmission beamformer 311 and M transmission driving units 312, and has M transmission channels, and an ultrasonic reception part 32 comprises a high-voltage isolation circuit 322, RC amplifiers 324, RC ADCs 325 and a reception beamformer 326 electrically connected in said order and has RC reception channels, wherein RC=[N,2N,3N . . . pN], N being an integer larger than or equal to 1. The ultrasonic front-end device characterizes in that M low-voltage analog switches 327 and a network of resistors 328 are seriallyconnected between the high-voltage isolation circuit 322 and the RC amplifiers 324. The M low-voltage analog switches 327 are configured to electrically connect RC array elements of the M array elements in the probe 2 and the RC corresponding reception channels in the ultrasonic reception part 3 as the scan lines of the ultrasonic diagnostic system change. The network of resistors 328 is configured to connect the RC reception channels connected by the M low-voltage analog switches 327 and the RC amplifiers 324, as shown in FIG. 7 and FIG. 8. The network of resistors 328 is used to be compatible with a system having P types of reception channels, comprising M inputs IN[1, 2, 3, . . . , M] connected to the outputs of the low-voltage analog switches 326 and RC outputs OUT[1, 2, . . . , RC] connected to the inputs of the amplifiers 324. The structure of the network of resistors can be expressed by OUT[jj]=IN[jj+kkRC], indicating that the output OUT[jj] and the input IN[jj+kkRC] of the network of resistors 328 are connected through resistors, where 1≦jj≦RC, 0≦kk≦INT(M/RC), INT denotes taking the integer part. If jj+kkRC>M, since such an input does not exist, there is no resistor connecting the input and the output of the network of resistors 328. A digital reordering unit included in the reception beamformer 326 comprises a plurality of 2:1 multiplexers 51 and a plurality of DFFs 52 coupled thereto correspondingly. The ultrasonic front-end device 3 may be implemented on a PCB. For an ultrasonic diagnostic system 1 having a different number of reception channels, a different network of resistors 328 may be soldered on the PCB of the ultrasonic front-end device 3 and a corresponding number of amplifiers 324 and ADCs 325 may be soldered on the PCB. In this way, compatibility with an ultrasonic diagnostic system 1 having P types of and a different number (RC) of reception channels may be implemented by means of the same PCB. The low-voltage analog switches 327 comprise a plurality of single-stage analog switches connected to the respective reception array elements in the probe through the isolation circuit 321 and are under the control of the primary controller 7. Assume the number of the reception array elements in the probe 2 is M, when the scan lines of the ultrasonic system 1 change, the corresponding reception channels change accordingly. By means of these analog switches 327, the ultrasonic system 1 may select RC out of the M array elements for reception and disable the other array elements not involved in the reception. The connection between the network of resistors 328 and the low-voltage analog switches 327 and the amplifiers 324 is implemented through resistors, wherein based on the number of RC, the corresponding resistors in the network of resistors 328 are soldered with the low-voltage analog switches 327 and the amplifiers 324. As shown in FIG. 9, the network of resistors 328 implements electrical connection between the selected array elements and the respective reception channels, accordingly it comprises M inputs and RC outputs. When the maximum number of ultrasonic systems 1 that the ultrasonic front-end 2 can accommodate is P, the network of resistors 328 designed in accordance with the electrical connection relationship allows the ultrasonic system 1 to be compatible with an ultrasonic front-end having reception channel numbers of N, 2N, 3N, . . . , or PN. The electrical connection may be implemented by resistors. As shown in FIG. 10, when RC=N, the outputs OUT[1, 2, 3, . . . , N] and the inputs IN[1,2,3, . . . , M] of the network of resistors 328 are electrically connected by resistors (the connections are shown by dots), while OUT[N+1, N+2, . . . , PN] are not electrically connected. When RC=2N, the rectangular boxes represent the electrical connection between the outputs OUT[1,2,3, . . . , 2N] and the inputs IN[1,2,3, . . . , M], while OUT[2N+1,2N+2, . . . , PN] are not electrically connected. When RC=the maximum number of channels PN, the circles represent the electrical connection between the outputs OUT[1,2,3, . . . , PN] and the inputs IN[1,2,3, . . . , M]. In this way, in design of the same PCB, when the network of resistors 328 is designed to meet the requirement of an ultrasonic system having different number of reception channels, the union set of the connection relationships of the resistors in various compatible ultrasonic systems may be used to design the connection between the network of resistors, to remove redundancy and reduce the number of resistors. In this manner, for an ultrasonic system having N reception channels, the amplifiers 324 and the ADCs located after the network of resistors 328 need to have only N paths soldered. For an ultrasonic system having 2N reception channels, the amplifiers 324 and the ADCs located after the network of resistors 328 need to have only 2N paths soldered. For an ultrasonic system having PN reception channels, the amplifiers 324 and the ADCs located after the network of resistors 328 need to have only PN paths solder. Therefore, the compatibility with an ultrasonic diagnostic system having P types of reception channels may be achieved by using a single PCB, which improves the compatibility of the ultrasonic front-end device 3 of the ultrasonic system 1 and reduces the cost of the ultrasonic system 1. For the transmission beamformer 311 that performs digital reordering on the transmission parameters, its digital reordering unit comprises a plurality of delay parameter digital reordering units 3111. For the transmission beamformer that performs digital reordering on the transmission signals, its digital reordering unit is a single digital reordering unit 3118, comprising a plurality of 2:1 multiplexers 51 and a plurality of DFFs 52 coupled thereto correspondingly. As shown in FIG. 12, the transmission beamformer 311 is configured to store a set of ordered transmission parameters corresponding to the respective transmission channels, to provide a binary control parameter B[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change, for controlling an array of 2:1 multiplexers 51 to convert the ordered transmission parameters into parameters for the current transmission channels. The array of 2:1 multiplexers 51 comprises a plurality of stages 41 each having M 2:1 multiplexers. Each bit of the parameter controls M 2:1 multiplexers at a corresponding stage, wherein 2K+1≧M and K is an integer larger than or equal to 0. The inputs at the 0th stage are the transmission parameters for the M transmission channels. Each bit of the parameter B is used to control M 2:1 multiplexers at a stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers are output. The signals on the “1” inputs of the array of 2:1 multiplexers are shifted 2K units rightward, for example, the signals on the “1” inputs of the multiplexers at the B[0] stage are shifted 1 unit rightward, the signals on the “1” inputs of the multiplexers at the B[1] stage are shifted 2 units rightward, the signals on the “1” inputs of the multiplexers at the B[2] stage are shifted 4 units rightward, signals on the “1” the inputs of the multiplexers at the B[3] stage are shifted 8 units rightward, . . . , and the signals on the “1” inputs of the multiplexers at the B[K] stage are shifted 2K units rightward. The shift is in accordance with the binary coding format and the outputs from the 2:1 multiplexers at the last stage are M digitally reordered transmission parameters. The reception beamformer 326 may be classified into two types. A reception beamformer 326 for performing digital reordering on the received parameters, comprises delay units 3261, a delay parameter read controller 3262, a delay parameter digital reordering unit 3263, apodization units 3264, an apodization parameter read controller 3266, an apodization parameter digital reordering unit 3266 and an adding unit 3267. The reception beamformer 326 delays, apodises, reorders and adds the signals received from the ADCs 325, to synthesize the received beam signals. The delay parameter digital reordering unit 3263 and the apodization parameter digital reordering unit 3266 each comprises multiple stages each of which has PN 2:1 multiplexers 51 followed with PN corresponding DFFs 52. A reception beamformer 326 for performing digital reordering on the received signals comprises a digital reordering unit 3268, delay units 3261, a delay parameter read controller 3282, apodization units 3264, an apodization parameter read controller 3265 and an adding unit 3267. The reception beamformer 326 reorders, delays, apodises and adds the signals received from the ADC 325, to synthesize the received beam signals. The signal digital reordering unit 3288 comprises multiple stages each having PN 2:1 multiplexers 51 followed by the corresponding DFFs 62. As shown in FIG. 13, when digitally reordering the reception parameters, the reception beamformer 326 is configured to store a set of ordered reception parameters corresponding to the reception channels. The parameter controls an array of 2:1 multiplexers to convert the ordered reception parameters into parameters for the current reception channels. The array of 2:1 multiplexers comprises multiple stages, each of which has PN 2:1 multiplexers 51. Each bit of the parameter is used to control PN 2:1 multiplexers 51 at a corresponding stage, where 2K+1≧PN, and K is an integer larger than or equal to 0. The inputs of the PN 2:1 multiplexers 51 at the 0th stage is set to the ordered reception parameters for the corresponding reception channels. Each bit of the parameter C is used to control 2:1 multiplexers 51 at a stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers are output. The signals on the “1” inputs of the whole array are shifted rightward, the multiplexers at the C[0] stage shifted 1 unit rightward, the signals on the “1” inputs of the multiplexers at the C[1] stage are shifted 2 units rightward, the signals on the “1” inputs of the multiplexers at the C[2] stage are shifted 4 units rightward, the signals on the “1” inputs of the multiplexers at the C[3] stage are shifted 8 units rightward, . . . , and the signals on the “1” inputs of the multiplexers at the C[K] stage are shifted 2K units rightward. The shift complies with the binary coding format and the outputs from the 2:1 multiplexers 51 at the last stage are PN digitally reordered parameters. When digitally reordering the received signals, signals from the ADCs 325 are received at the input of the reception beamformer 326, which performs digital reordering on the received signals in a manner similar to digital reordering on the reception parameters. The reception beamformer 326 outputs ordered channel signals. FIG. 11 is a flowchart showing a method of using an ultrasonic front-end device 3 in an ultrasonic system 1 according to one embodiment of the invention. As shown in FIG. 8, the ultrasonic front-end device 3 is connected between a probe 2 and a detector 4 of the ultrasonic system 1 and controlled by a primary controller 7 of the ultrasonic system. The probe 2 has M array elements. The ultrasonic front-end device 3 has an ultrasonic transmission part 31 and an ultrasonic reception part 32, wherein the ultrasonic transmission part 31 comprises a transmission beamformer 311 and a transmission driving unit 312, while the ultrasonic reception part 32 has RC reception channels and comprises a high-voltage isolation circuit 322, RC amplifiers 324, RC ADCs 325 and a beamformer 326 electrically connected in said order, where RC=[N,2N,3N . . . pN], N being an integer larger than or equal to 1. The ultrasonic front-end device characterizes in that M low-voltage analog switches 327 and a network of resistors 318 are serially connected between the high-voltage isolation circuit 322 and the RC amplifiers 324, wherein the M low-voltage analog switches 327 is configured to electrically connect RC array elements of the M array elements in the probe 2 and RC respective reception channels in the ultrasonic reception part 3 as the scan lines of the ultrasonic system change. The network of resistors 328 is configured to connect the RC reception channels connected by the M low-voltage analog switches 327 and the RC amplifiers 324. The network of resistors 328 comprises M inputs IN[1, 2, 3, . . . , M] connected to the outputs of the low-voltage analog switches 327 and RC outputs OUT[1, 2, . . . , RC] connected to the inputs of the amplifiers 324. The structure of the network of resistors can be expressed by OUT[jj]=IN[jj+kkRC], indicating that the output OUT[jj] and the input IN[jj+kkRC] of the network of resistors 328 are connected through resistors, where 1≦jj≦RC, 0≦kk≦INT(M/RC), INT denotes taking the integer part. If j+kkRC>M, since such an input does not exist, there is no resistor connecting the input and the output of the network of resistors 328. A digital reordering unit included in the reception beamformer 326 comprises a plurality of 2:1 multiplexers 51 having a “0” input and a “1” input and the DFFs 52 coupled thereto correspondingly, the method comprising the steps of: 1. emitting pulses by the ultrasonic transmission part 31 with transmission parameters, to activate the currently selected transmission array elements in the probe 2 of the ultrasonic system 2 to transmit ultrasonic waves; 2. receiving echoes of the ultrasonic waves and converting them into electric signals by the currently selected reception array elements in the probe 2; 3. receiving electric signals from the probe by the high-voltage isolation circuit; 4. electrically connecting, by the M low-voltage analog switches 321 in the ultrasonic reception part 32, RC array elements of the M array elements in the probe 2 and RC corresponding reception channels in the ultrasonic reception part 32 as the scan lines of the ultrasonic system 1 change: 5. connecting, by the network of resistors 328, the RC reception channels connected by the M low-voltage analog switches 327 with the RC amplifiers 324; 6. amplifying and AD converting the received electric signals by the amplifiers 324 and the ADCs 325 in the ultrasonic reception part 32; and 7. digital reordering and beamforming the reception parameters or the received signals by the beamformer 326 in the ultrasonic reception part 32. Step 1 comprises the substeps of: (1a) setting and storing a set of ordered transmission parameters corresponding to the M transmission channels, by the transmission beamformer 311 in the ultrasonic transmission part 31; and (1b) providing, by the transmission beamformer 311, a binary control parameter B[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system change. The parameter controls an array of 2:1 multiplexers to convert the ordered transmission parameters into parameters for the current transmission channels. The array of 2:1 multiplexers comprises a plurality of stages each having M 2:1 multiplexers 51. Each bit of the parameter controls M 2:1 multiplexers 51 at a corresponding stage, wherein 2K+1≧M, K is an integer larger than or equal to 0, The inputs at the 0th stage are the ordered transmission parameters for the M transmission channels. Each bit of the parameter B is used to control M 2:1 multiplexers 51 at a stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers 51 are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers 61 are output. The signals on the “1” inputs of the array of 2:1 multiplexers are shifted 2K units rightward, for example, the signals on the inputs of the multiplexers 51 at the B[0] stage are shifted 1 unit rightward, the signals on the inputs of the multiplexers 51 at the B[1] stage are shifted 2 units rightward, the signals on the inputs of the multiplexers 61 at the B[2] stage are shifted 4 units rightward, the signals on the inputs of the multiplexers 51 at the B[3] stage are shifted 8 units rightward, . . . , and the signals on the inputs of the multiplexers 51 at the B[K] stage are shifted 2K units rightward. The shift complies with the binary coding format and the outputs from the 2:1 multiplexers at the last stage are M digitally reordered transmission parameters. There are two types of digital reordering at the step 7: first, conduct digital reordering on the received signals while no digital reordering on the reception parameters; second, conduct digital reordering on the reception parameters while no digital reordering on the received signals. For the reception parameters, the digital reordering and beam forming at the step 7 comprise the substeps of: (7a) setting and storing a set of ordered reception parameters corresponding to the reception channels, by the reception beamformer 326 in the ultrasonic reception part 32; and (7b) providing, by the reception beamformer 326, a binary control parameter C[K K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system 1 change. The control parameter controls an array of 2:1 multiplexers to convert the ordered reception parameters into parameters for the current reception channels. The array of 2:1 multiplexers comprises multiple stages, each of which has PN 2:1 multiplexers 51. Each bit of the parameter controls PN 2:1 multiplexers at a corresponding stage, where 2K+1≧PN and K is an integer larger than or equal to 0, wherein the inputs of the PN 2:1 multiplexers 51 at the 0th stage are the reception parameters for the corresponding reception channels. Each bit of the parameter C is used to control 2:1 multiplexers 51 at a corresponding stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers 51 are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers 51 are output. The signals on the “1” inputs of the whole array of 2:1 multiplexers 51 are shifted 2K units rightward, for example, the signals on the “1” inputs of the multiplexers 51 at the C[0] stage are shifted 1 unit rightward, the signals on the “1” inputs of the multiplexers 51 at the C[1] stage are shifted 2 units rightward, the signals on the “1” inputs of the multiplexers 51 at the C[2] stage are shifted 4 units rightward, . . . , and the signals on the “1” inputs of the multiplexers 51 at the C[K] stage are shifted 2K units rightward. For the received signals, the digital reordering and beam forming at the step 7 comprises the substeps of: providing, by the reception beamformer 326, a binary control parameter C[K, K−1,K−2, . . . , 0] which varies as the scan lines of the ultrasonic system 1 change. The control parameter controls an array of 2:1 multiplexers, the array of 2:1 multiplexers including k+1 stages, each stage having PN 2:1 multiplexers 61, where 2K+1≧PN, and K is an integer larger than or equal to 1. Signals from the ADCs are received at the inputs of the PN 2:1 multiplexers 51 at the 0th stage. Each bit of the parameter C is used to control M 2:1 multiplexers 51 at a stage: if the bit is 0, the data from the “0” inputs of the 2:1 multiplexers 51 are output, otherwise, the data from the “1” inputs of the 2:1 multiplexers 51 are output. The signals on the “1” inputs of the array of 2:1 multiplexers 51 are shifted 2K units rightward, for example, the signals on the “1” inputs of the multiplexers 51 at the C[0] stage are shifted 1 unit rightward, the signals on the “1” inputs of the multiplexers 51 at the C[1] stage are shifted 2 units rightward, the signals on the “1” inputs of the multiplexers 51 at the C[2] stage are shifted 4 units rightward, the signals on the “1” inputs of the multiplexers 51 at the C[3] stage are shifted 8 units rightward, . . . , and the signals on the “1” inputs of the multiplexers 51 at the C[K] stage are shifted 2K units rightward. The shift complies with the binary coding format and the outputs from the 2:1 multiplexers 51 at the last stage are P*Nof digitally reordered signals. The above-mentioned various solutions provide compatibility for an ultrasonic front-end device in an ultrasonic system and reduce the cost of the ultrasonic system. The digital reordering unit for use in the ultrasonic front-end has advantages in being highly real time and less consumption of hardware resources. The inventive method is tested in experiments, leading to implementation of a high-speed and real-time ultrasonic system as well as improvement in the compatibility for the ultrasonic front-end of the ultrasonic system and cost saving for the ultrasonic system. Preferred embodiments of the present invention have thus been shown and described. It would be apparent to one of ordinary skill in the art, however, that various variations, alternatives and alterations may be made to the embodiments herein disclosed without departing from the spirit or scope of the invention.
	summary
060318937	claims	1. A stray radiation grid comprising: a carrier; a plurality of lamellae disposed on said carrier forming radiation absorption elements, said lamellae being disposed in a plurality of rows in a grid, with said rows being spaced from each other and proceeding substantially parallel to each other, each of said lamellae having a width and said grid having a middle region and edge regions; said rows being spaced from each other at a spacing at said edge regions of said grid which is larger than a spacing of said rows from each other in said middle region of said grid; and the width of lamellae disposed in said edge regions of said grid being larger than the width of lamellae disposed in said middle of said grid. 2. A stray radiation grid as claimed in claim 1 wherein a spacing of said rows of lamellae increases continuously from row to row proceeding from the middle region of the grid to the edge regions of said grid. 3. A stray radiation grid as claimed in claim 2 wherein each of said lamellae has a width continuously increasing from said middle region of said grid toward said edge regions of said grid. 4. A stray radiation grid as claimed in claim 3 wherein said width increases substantially proportionally relative to an increase in spacing between said rows. 5. A stray radiation grid as claimed in claim 3 wherein said width increases sub-proportionally relative to an increasing spacing between said rows. 6. A stray radiation grid as claimed in claim 3 wherein said stray radiation grid is subjected to incident radiation striking said stray radiation grid at a plurality of incident angles, each of said lamellae having a local incident angle, among said plurality of incident angles, respectively associated therewith, and wherein the spacing between neighboring rows increases from said middle region of said grid to said edge regions of said grid dependent on the respective local incident angles of said radiation. 7. A stray radiation grid as claimed in claim 3 wherein said stray radiation grid is subjected to incident radiation striking said stray radiation grid at a plurality of incident angles, each of said lamellae having a local incident angle, among said plurality of incident angles, respectively associated therewith, and wherein the width of each of said lamellae rows increases from said middle region of said grid to said edge regions of said grid dependent on the respective local incident angles of said radiation. 8. A stray radiation grid as claimed in claim 3 wherein said stray radiation grid is subjected to incident radiation striking said stray radiation grid at a plurality of incident angles, each of said lamellae having a local incident angle, among said plurality of incident angles, respectively associated therewith, and wherein the spacing between neighboring rows and the width of each of said lamellae increase from said middle region of said grid to said edge regions of said grid dependent on the respective local incident angles of said radiation. 9. A stray radiation grid as claimed in claim 1 wherein each of said lamellae has a width continuously increasing from said middle region of said grid toward said edge regions of said grid. 10. A stray radiation grid as claimed in claim 9 wherein said width increases substantially proportionally relative to an increase in spacing between said rows. 11. A stray radiation grid as claimed in claim 9 wherein said width increases sub-proportionally relative to an increasing spacing between said rows. 12. A stray radiation grid as claimed in claim 9 wherein said stray radiation grid is subjected to incident radiation striking said stray radiation grid at a plurality of incident angles, each of said lamellae having a local incident angle, among said plurality of incident angles, respectively associated therewith, and wherein the width of each of said lamellae rows increases from said middle region of said grid to said edge regions of said grid dependent on the respective local incident angles of said radiation. 13. A stray radiation grid as claimed in claim 1 wherein said grid comprises a plurality of grid regions proceeding from said middle region of said grid to said edge regions of said grid, each of said grid regions having a spacing of the rows therein which is constant within that grid region, and the respective spacings of the rows in the respective grid regions increasing from grid region to grid region proceeding from said middle region of said grid to said edge regions of said grid. 14. A stray radiation grid as claimed in claim 13 wherein the width of said lamellae is substantially constant within each of said grid regions, and the respective widths of the lamellae in respective regions increasing from region to region, proceeding from said middle region of said grid to said edge regions of said grid. 15. A stray radiation grid as claimed in claim 8 wherein said width increases substantially proportionally relative to the increase in said spacing from grid region to grid region. 16. A stray radiation grid as claimed in claim 8 wherein said width increases substantially sub-proportionally relative to the increase in said spacing from grid region to grid region. 17. A stray radiation grid as claimed in claim 14 wherein said stray radiation grid is subjected to incident radiation which is incident on said stray radiation grid at a plurality of local incident angles, each of said grid regions having one of said local incident angles respectively associated therewith, and wherein the spacing between said rows in each grid region is dependent on the local incident angle respectively associated with that grid region. 18. A stray radiation grid as claimed in claim 14 wherein said stray radiation grid is subjected to incident radiation which is incident on said stray radiation grid at a plurality of local incident angles, each of said grid regions having one of said local incident angles respectively associated therewith, and wherein the width of each of said lamellae in each grid region is dependent on the local incident angle respectively associated with that grid region. 19. A stray radiation grid as claimed in claim 14 wherein said stray radiation grid is subjected to incident radiation which is incident on said stray radiation grid at a plurality of local incident angles, each of said grid regions having one of said local incident angles respectively associated therewith, and wherein the spacing between said rows and the width of each of said lamellae in each grid region is dependent on the local incident angle respectively associated with that grid region.
	description	The United States Government has certain rights in this invention pursuant to Contract No. DE-AC07-05-ID14517 between the United States Department of Energy and Battelle Energy Alliance, LLC. This application is related to co-pending U.S. patent application Ser. No. 12/770,178 to Meikrantz et al., entitled “METHODS OF PRODUCING AND RECOVERING PLUTONIUM-238,” filed on Apr. 29, 2010. The invention, in various embodiments, relates generally to methods of producing and recovering radioisotopes. More specifically, the invention, in various embodiments, relates to methods of producing cesium-131 (“131Cs” ) from a barium source. In the medical field, various radioisotopes such as 131Cs, iodine-125, and palladium-103 are used for diagnostics and for treating various forms of cancer. For instance, 131Cs has been investigated for use in cancer research and treatments, such as in brachytherapy. 131Cs is a beta emitter and is produced by radioactive decay from neutron irradiated, naturally occurring barium-130 (“130Ba”). When irradiated, 130Ba captures a neutron, becoming 131Ba, which decays to 131Cs with an 11.5 day half-life. 131Cs decays to xenon-130 with a 9.7 day half-life. However, upon continued exposure to neutrons, 131Cs is converted to cesium-132 (“132Cs”) which is a gamma emitter. To be effective in treating cancers, the 131Cs should be substantially pure, such as greater than approximately 99.9% 131Cs. For instance, the 131Cs should include substantially no impurities, such as 130Ba, 131Ba, or 132Cs. Conventional processes for producing 131Cs are time consuming, costly, and inefficient. As described in U.S. Pat. No. 7,479,261 to Bray et al., solid barium carbonate is irradiated in a nuclear reactor to produce a barium target. The irradiated barium carbonate target is removed from the nuclear reactor after 7-21 days to limit the formation of undesirable by-products, such as 132Cs. The irradiated barium carbonate target is stored for several days to limit exposure of personnel to the radiation, and then is dissolved in nitric acid to form a solution of cesium nitrate, barium nitrate, water, and carbon dioxide. The solution is concentrated to remove excess water, additional nitric acid is added, and the solution is dried to near dryness. The solution includes cesium nitrate, which is soluble in the nitric acid, and barium nitrate, which is insoluble in the nitric acid. The barium nitrate remaining in the solution is removed by precipitation. The cesium nitrate is separated from the barium nitrate by filtration or centrifugation. After removing the 131Cs and unwanted 132Cs, the irradiated barium carbonate target is stored to enable pure 131Cs to grow in. The process described above is then repeated periodically to recover the additional 131Cs. As such, multiple acts, which are time consuming and costly, are utilized in this process for producing and recovering the 131Cs from the irradiated barium carbonate target. In addition, the 9.7 day half-life of 131Cs provides significant decay loss of product in this multiple step process. It would be desirable to produce and recover 131Cs of a high purity in a process including fewer acts and higher purity. It would also be desirable to eliminate the time, cost, and hazards to personnel associated with using a solid barium target. A method of producing 131Cs is disclosed. The method comprises dissolving at least one non-irradiated barium source in water or a nitric acid solution to produce a barium target solution. The barium target solution is irradiated with neutron radiation to produce 131Cs, which is removed from the barium target solution. In another embodiment, the method comprises irradiating a barium target solution comprising at least one non-irradiated barium-130 compound to produce 131Cs. The 131Cs is complexed with a calixarene compound and the 131Cs is separated from the 130Ba compound. In another embodiment, the method comprises irradiating a barium target solution to produce an irradiated barium target solution. After barium in the irradiated barium target solution decays for an amount of time sufficient to produce 131Cs, the 131Cs is continuously separated from the irradiated barium target solution. In another embodiment, the method comprises dissolving at least one non-irradiated barium source in an aqueous solution to produce a barium target solution. The barium target solution is irradiated in a nuclear reactor to produce 131Cs. The irradiated barium target solution is flowed through at least one separation device to remove the 131Cs. A method of producing and recovering 131Cs is disclosed. The 131Cs is recovered in the form of a 131Cs ion, such as Cs1+. The 131Cs is produced by neutron decay from a barium source. The barium source is dissolved, before being exposed to neutron irradiation, to produce a barium target solution containing the barium source. The barium target solution is circulated through a neutron field and irradiated to produce 131Ba, which decays to 131Cs. The 131Cs is selectively removed from the irradiated barium target solution using a calixarene compound and recovered, providing the 131Cs of high purity. The method utilizes fewer separation or purification acts than conventional processes for producing the 131Cs. The method also eliminates the time and cost associated with preparation of a solid barium target. In addition, the resulting 131Cs has a higher purity than that produced by conventional techniques. The barium source may be a compound of naturally occurring barium or may be a compound enriched in 130Ba, such as a barium compound or combination of barium compounds. As used herein, the term “naturally occurring barium” means and includes barium including a mixture of seven stable barium isotopes: 130Ba (0.1%), 132Ba (0.1%), 134Ba (2.4%), 135Ba (6.6%), 136Ba (7.9%), 137Ba (11.2%), and 138Ba (71.7%). The natural abundance of each of the barium isotopes is indicated in parenthesis. The term “enriched barium” means and includes barium having an abundance of 130Ba that is greater than 0.1%. By way of non-limiting example, the enriched barium may include from 0.2% to 50% 130Ba, such as from 30% to 50% 130Ba. The barium source may be a high purity, barium salt or other barium compound that is substantially soluble in water or a nitric acid solution. The barium source may include, but is not limited to, barium carbonate (BaCO3), barium chlorate (Ba(ClO3)2.H2O), barium chloride (BaCl2), barium formate (Ba(CHO2)2), barium fluoride (BaF2), barium nitrate (Ba(NO3)2), barium metal, barium oxide (BaO), or combinations thereof. Natural barium compounds suitable for use as the barium source are commercially available from various sources, such as Sigma-Aldrich Co. (St. Louis, Mo.), Trace Sciences International (Wilmington, Del.), or other chemical suppliers. The barium source may have a purity of greater than approximately 95%, such as approximately 100%. Such barium compounds are inexpensive relative to the cost of enriched barium targets used in conventional processes. The barium source may be dissolved in water or a nitric acid solution to form a barium target solution. The barium source dissolved in the barium target solution may be non-irradiated. The term “non-irradiated” is used herein to mean and include a barium source that has not been exposed to neutron radiation. Rather, the barium source is a compound of naturally occurring barium or enriched barium. The barium target solution may include a minimum barium concentration of approximately 0.5 M barium. The maximum concentration of barium in the barium target solution may be the solubility limit of the barium source in the water or nitric acid solution. By way of non-limiting example, the barium target solution may include from approximately 0.5 M to approximately 1 M of the barium source. The nitric acid solution used in the barium target solution may be an aqueous solution having a nitric acid concentration of from approximately 1 M to approximately 3 M. After dissolving the barium source in the water or nitric acid solution, the barium target solution may be subjected to neutron radiation. To irradiate the barium source, the barium target solution 2 may be introduced into an isotope production system 4, as shown in FIGS. 1 and 2. In one embodiment, shown in FIG. 1, the isotope production system 4 includes an inlet (not shown) through which the barium target solution 2 is introduced, a neutron source 6, a liquid loop 8, a separator 10, and an outlet (not shown) through which a 131Cs solution 12 exits the isotope production system 4. In another embodiment, shown in FIG. 2, the isotope production system 4 includes the barium target solution 2, the neutron source 6, the liquid loop 8, and the separator 10. In the embodiment of FIG. 2, the 131Cs is recovered from the separator 10 as described in more detail below. As used herein, the term “liquid loop” means and includes means for transporting or circulating the barium target solution 2, irradiated barium target solution 2′, or extracted barium target solution 2″ throughout the isotope production system 4. The structure of the liquid loop 8 may be formed from a material that is capable of containing the barium target solution 2, irradiated barium target solution 2′, and extracted barium target solution 2″, and is substantially non-reactive with the components of the barium target solution 2, irradiated barium target solution 2′, and extracted barium target solution 2″. By way of non-limiting example, components of the liquid loop 8 may be formed from stainless steel, aluminum, zirconium, or other corrosion-resistant, neutron-transparent alloy or material. To assist in circulating the barium target solution 2, irradiated barium target solution 2′, and extracted barium target solution 2″, the isotope production system 4 may include additional features, such as a pump. The pump may be a conventional device that is capable of transporting the barium target solution 2, irradiated barium target solution 2′, and extracted barium target solution 2″ through the liquid loop 8 and neutron source 6. The pump may also circulate the irradiated barium target solution 2′ to the separator 10. The pump may be formed from a material compatible with the barium target solution 2, irradiated barium target solution 2′, and extracted barium target solution 2″. The isotope production system 4 may also include a heat exchanger if heating or cooling of the barium target solution 2, irradiated barium target solution 2′, or extracted barium target solution 2″ is desired. The heat exchanger, if present, may be a conventional device that transfers heat away from the barium target solution 2, irradiated barium target solution 2′, or extracted barium target solution 2″. The isotope production system 4 may also include openings, such as vents, to enable offgasing of byproducts. These additional features of the isotope production system 4 are not shown in FIG. 1 for simplicity and clarity. The barium target solution 2 and extracted barium target solution 2″ may be subjected to neutron irradiation by continuously flowing the barium target solution 2 or extracted barium target solution 2″ through the neutron source 6. The neutron source 6 may be a device capable of producing thermal neutron irradiation, such as a nuclear reactor. The nuclear reactor may be a conventional nuclear reactor capable of producing neutrons and continuously irradiating the barium target solution 2 or the extracted barium target solution 2″ with the neutrons. By way of non-limiting example, the nuclear reactor may be a pool-type reactor including, but not limited to, a TRIGA® reactor. Since the neutron source 6 is conventional, specific details of its design and configuration are not described or illustrated herein. As the barium target solution 2 or extracted barium target solution 2″ flows through the isotope production system 4, a portion of the barium target solution 2 or extracted barium target solution 2″ may enter the neutron source 6 and be irradiated with neutrons, forming the irradiated barium target solution 2′. Since the barium target solution 2 or extracted barium target solution 2″ circulates throughout the isotope production system 4, the entire volume of the barium target solution 2 or extracted barium target solution 2″ may, over time, be irradiated with neutrons. Even though only a portion of the barium target solution 2 or extracted barium target solution 2″ passes through the neutron source 6 at a given time, for simplicity, the process is described herein as applying to the barium target solution 2 or extracted barium target solution 2″, rather than a portion of the barium target solution 2 or extracted barium target solution 2″. As the barium target solution 2 or extracted barium target solution 2″ passes through the neutron source 6, the barium target solution 2 or extracted barium target solution 2″ may be exposed to radiation of a sufficient energy for the 130Ba to capture neutrons, forming 131Ba, which decays to 131Cs. The energy conditions utilized for irradiating the barium target solution 2 or extracted barium target solution 2″ are conventional and, therefore, are not described in detail herein. By way of non-limiting example, the barium target solution 2 or extracted barium target solution 2″ may be exposed to thermal neutrons having a mean energy of approximately 0.025 eV and a velocity of approximately 2200 m/s. Once irradiated, the irradiated barium target solution 2′ may be circulated by way of the liquid loop 8 to the separator 10 of the isotope production system 4. Since the irradiated barium target solution 2′ is not manually transported from the neutron source 6, such as for separation and purification of the 131Cs, exposure of personnel to radiation is greatly reduced in comparison to conventional techniques for producing 131Cs. The irradiated barium target solution 2′ may include 131mBa and 131Ba, or 131mBa, 131Ba, and 131Cs depending on the amount of time that has elapsed since the irradiation of the barium target solution 2. After a sufficient amount of time has elapsed, the 130Ba in the irradiated barium target solution 2′ may be converted to 131Ba, which subsequently decays to 131Cs with a half-life of 11.5 days. The rate of production of the 131Ba may depend on the initial concentration of 130Ba in the barium target solution 2, the neutron fluence, the neutron capture cross section of the 130Ba, and the irradiation time. For instance, immediately before irradiation of a fresh volume of the barium target solution 2, no radioactivity may be present in the barium target solution 2. However, after the irradiation, the radioactivity in the irradiated barium target solution 2′ may be substantially due to 131mBa and 131Ba. In addition, trace amounts of other radioisotopes may be present. As the 131Ba decays, 131Cs may begin to appear in the irradiated barium target solution 2′. As such, the irradiated barium target solution 2′ may include the radioactive isotopes 131Ba, 131mBa, and 131Cs before the 131Cs is selectively removed in the separator 10. As the 131Cs begins to accumulate, the 131Cs may be continuously removed from the irradiated barium target solution 2′ using the separator 10. The separator 10 may include at least one separation device 10A that utilizes a calixarene compound to selectively remove the 131Cs while the 131Ba remains in the irradiated barium target solution 2′. The 131Cs is removed relative to the 131Ba, which is also present in the irradiated barium target solution 2′. The calixarene compound may form a complex with the 131Cs, enabling its selective removal from the irradiated barium target solution 2′. Since the 131Cs in the irradiated barium target solution 2′ has a valence state of +1 and the 130Ba and 131Ba have a valence state of +2, the 131Cs may coordinate or complex with the calixarene compound, while the 130Ba and 131Ba do not coordinate or complex with the calixarene compound. The separation device 10A may be a device capable of conducting a liquid:liquid extraction using the calixarene compound as an extractant, as shown in FIG. 1, or an extraction chromatography device capable of using the calixarene compound as a stationary phase, as shown in FIG. 2. By way of non-limiting example, the separation devices 10A, 10B, 10C may be liquid:liquid extraction devices, such as centrifugal separators or annular centrifugal contactors (“ACC”). Examples of ACCs include those described in U.S. Pat. Nos. 5,571,070, 5,591,340, and 7,157,061 to Meikrantz et at and U.S. Pat. No. 4,959,158 to Meikrantz, the disclosure of each of which is incorporated by reference herein in its entirety. ACCs are commercially available, such as from Costner Industries Texas LP (Houston, Tex.), and provide a high throughput method of performing the liquid-liquid extraction. The separation devices 10A, 10B, 10C may also be extraction chromatography columns that contains the calixarene compound coated on a solid support. For instance, the calixarene compound may be used as a stationary phase in an extraction chromatography column. In addition, combinations of ACCs and extraction chromatography columns may be used as the separation devices 10A, 10B, 10C. While three separation devices 10A, 10B, 10C are illustrated in FIGS. 1 and 2, the separator 10 may include more than three or less than three separation devices 10A, 10B, 10C depending on the desired purity of the 131Cs. For instance, the irradiated barium target solution 2′ may be flowed through one or two separation devices 10A, 10B. To protect personnel from the radiation emitted by the irradiated barium target solution 2′, the separation devices 10A, 10B, 10C may be enclosed in a containment device, such as a glove box and/or shielded cell. The 131Cs may be continuously separated from the 130Ba and 131Ba by flowing the irradiated barium target solution 2′ through the separation devices 10A, 10B, 10C of the separator 10. If the separation devices 10A, 10B, 10C are liquid:liquid extraction devices, such as ACCs, the irradiated barium target solution 2′ may be contacted with a calixarene extractant solution that includes the calixarene compound. The components of the calixarene extractant solution are described in detail below. The calixarene extractant solution may function in the liquid:liquid extraction device as an organic phase, while the irradiated barium target solution 2′ may function as an aqueous phase. When the irradiated barium target solution 2′ and the calixarene extractant solution are contacted and agitated with one another, the 131Cs may partition into the calixarene extractant solution (organic phase), while the 130Ba and 131Ba remain in the irradiated barium target solution 2′ (aqueous phase). As such, the 131Cs is removed or forward extracted from the irradiated barium target solution 2′. After extracting the 131Cs, the irradiated barium target solution 2′ may be substantially depleted of 131Cs while the calixarene extractant solution includes substantially all of the 131Cs. The irradiated barium target solution 2′ and the calixarene extractant solution containing the 131Cs may then be separated from one another by conventional techniques, such as by conventional liquid-liquid separation techniques. Since the calixarene extractant solution includes one predominant isotope, 131Cs, minimal recovery and purification acts are used to recover the 131Cs compared to conventional 131Cs processes. The calixarene extractant solution containing the 131Cs may be removed from the separation device 10A once sufficient radioactivity has accumulated, and is referred to herein as 131Cs solution 12. However, to increase the amount of 131Cs removed from the irradiated barium target solution 2′, the irradiated barium target solution 2′ from separation device 10A may be passed through separation devices 10B, 10C in which additional liquid:liquid extractions are conducted. The calixarene extractant solution containing the 131Cs may exit the separation devices 10B, 10C as 131Cs solution 12 once sufficient radioactivity has accumulated. The 131Cs solution 12 may be periodically removed from the separation devices 10A, 10B, 10C, such as weekly or monthly. The 131Cs may be removed from the irradiated barium target solution 2′ at a sufficient efficiency to prevent the formation of 132Cs from 131Cs. By continuously removing the 131Cs, the 131Cs is no longer exposed to neutrons, which substantially prevents the production of 132Cs. Therefore, continuously removing the 131Cs from the irradiated barium target solution 2′ may maximize the 131Cs recovery rate. The irradiated barium target solution 2′ including the 131Cs maybe continuously passed through the liquid:liquid extraction device to continuously remove the 131Cs as it is produced. The 131CS may be continuously removed from the irradiated barium target solution 2′ by continuously contacting the irradiated barium target solution 2′ with the calixarene extractant solution, enabling the 131Cs to distribute into the calixarene extractant solution. Once desired levels of 131Cs are achieved in the separator 10, the 131Cs solution 12 may be removed from the separator 10 and further purified, if desired. Additional purification of the 131Cs from the 131Cs solution 12 may be conducted outside the separator 10, such as by passing the 131Cs solution 12 through extraction chromatography columns, ion exchange columns, or by filtering the 131Cs solution 12. The 131Cs may then be concentrated, such as to dryness, by evaporation. After the irradiated barium target solution 2′ and calixarene extractant solution containing the 131Cs are separated in the liquid:liquid extraction device, the extracted barium target solution 2″, which lacks the 131Cs, may be circulated through the isotope production system 4 for an amount of time sufficient for any 130Ba remaining in the extracted barium target solution 2″ to be activated to 131Ba and for additional 131Cs to grow in. The extracted barium target solution 2″ may be flowed through the neutron source 6 and exposed to neutron irradiation, producing the irradiated barium target solution 2′. As the 131Cs accumulates in the irradiated barium target solution 2′ and is continuously removed by the separator 10, as described above, the resulting 131Cs solution 12 may be removed outside the continuous process system for further purification whenever the radioactive quantity desired is reached. After a sufficient amount of the 130Ba is depleted from the barium source, additional 130Ba may be introduced into the isotope production system 4 to produce additional 131Cs by adding additional barium to the isotope production system 4. By way of non-limiting example, additional 130Ba, in the form of the natural barium source, may be dissolved into the extracted barium target solution 2″ and passed through the isotope production system 4. The 131CS solution 12 may be further processed to recover the 131Cs in the form of a 131Cs ion. The 131Cs may be removed or stripped from the 131Cs solution 12 by adjusting the pH of the calixarene extractant solution with an aqueous acid solution. The aqueous acid solution may be an aqueous nitric acid solution having from approximately 0.001 M HNO3 to approximately 0.5 M HNO3, such as approximately 0.01 M HNO3. The 131Cs solution 12 and the aqueous acid solution may be contacted and agitated such that the 131Cs partitions from the 131Cs solution 12 and into the aqueous acid solution. The 131Cs solution 12, which is now depleted of 131Cs, and the aqueous acid solution, which now contains the 131Cs, may then be separated by conventional liquid:liquid separation techniques. While the 131Cs solution 12 is being stripped, a fresh volume of the calixarene extractant solution may be contacted with the irradiated barium target solution 2′ in the isotope production system 4 to provide a continuous process for recovering the 131Cs. The aqueous acid solution containing the 131Cs may be used or further purified. For instance, the aqueous acid solution containing the 131Cs may be concentrated, such as to dryness, by evaporating the aqueous acid solution. The resulting 131Cs may then be used in brachytherapy seeds, which are administered to patients having cancerous tumors. The brachytherapy seeds may be formed by conventional techniques, which are not described in detail herein. To shorten the processing time, the brachytherapy seeds may be produced at the same facility where the 131Cs is recovered, enhancing the therapeutic value of the 131Cs brachytherapy seeds, which have a half-life of 9.7 days. The calixarene extractant solution includes at least one calixarene compound and at least one modifier dissolved in a diluent. The calixarene compound may be a calix[4]arene-crown ether compound, such as a derivative of a calix[4]arene-crown-6 ether including, but not limited to, a mono- or bis-crown-6-derivative of 1,3 calix[4]arene or a dialkyloxycalix[4]arenebenzo-crown-6 compound. The calixarene compound may be one of the compounds described in U.S. Pat. No. 7,291,316 to Meikrantz et al., or in U.S. patent application Ser. No. 12/268,189 to Peterman et al., filed Nov. 10, 2008, and entitled “Extractant Compositions for Co Extracting Cesium and Strontium, A Method of Separating Cesium and Strontium from An Aqueous Feed, Calixarene Compounds, and An Alcohol Modifier.” The disclosure of each of the above-mentioned documents is incorporated by reference herein in its entirety. The calixarene compound may be in cone, partial cone, 1,2 alternate, or 1,3 alternate conformations. The calixarene compound may be present in the calixarene extractant solution from approximately 0.0025 M to approximately 0.025 M. In one embodiment, the calixarene compound is calix[4]arene-bis-(tert-octylbenzo)-crown-6 (“BOBCalixC6”). BOBCalixC6 is available from IBC Advanced Technologies, Inc. (American Fork, Utah) and has a molecular weight of 1149.52 g/mol, BOBCalixC6 has the following structure: In another embodiment, the calixarene compound is a dialkyloxycalix[4]arenebenzocrown-6 compound having a general chemical structure as shown below: where each of R1 and R2 is an alkyl group and R1 and R2 may be the same or different. The alkyl group may be a saturated, straight, or branched hydrocarbon including from three carbon atoms to fourteen carbon atoms. Examples of the alkyl groups include, but are not limited to, propyl, methylethyl, butyl, methylpropyl, dimethylethyl, pentyl, methylbutyl, dimethylpropyl, trimethylethyl, ethylpropyl, hexyl, methylpentyl, dimethylbutyl, ethyltutyl, trimethylpropyl, heptyl, methylhexyl, dimethylpentyl, ethylpentyl, propylbutyl, trimethylbutyl, octyl, methylheptyl, dimethylhexyl, ethylhexyl, propylpentyl, trimethylpentyl, nonyl, methyloctyl, dimethylheptyl, ethylheptyl, propylhexyl, trimethylhexyl, decyl, methylnonyl, dimethyloctyl, ethyloctyl, propylheptyl, trimethylheptyl, butylhexyl, tetramethylhexyl, undecyl, methyldecyl, dimethylnonyl, ethylnonyl, propyloetyl, trimethyloctyl, butylheptyl, tetramethylheptyl, pentylhexyl, dodecyl, methylundecyl, dimethyldecyl, ethyldecyl, propylnonyl, trimethylnonyl, butyloetyl, tetramethyloctyl, pentylheptyl, tridecyl, methyldodecyl, dimethyl undecyl, ethylundecyl, propyldecyl, trimethyldecyl, butylnonyl, tetramethylnonyl, pentyloctyl, hexylheptyl, tetradecyl, methyltridecyl, dimethyldodecyl, ethyldodecyl, propylundecyl, trimethylundecyl, butyldecyl, pentylnonyl, or hexyloctyl. Specific examples of dialkyloxycalix[4]arenebenzocrown-6 compounds that may be used in the calixarene extractant solution include, but are not limited to: MC-8: 1,3-alternate-25,27-di(octyloxy)calix[4]arenebenzocrown-6, MC-10: 1,3-alternate-25,27-di(decyloxy)calix[4]arenebenzocrown-6, MC-12: 1,3-alternate-25,27-di(dodecyloxy)calix[4]arenebenzocrown-6, MC-8B: 1,3-alternate-25,27-di(2-ethylhexyl-1-oxy)calix[4]arenebenzocrown-6, MC-10B: 1,3-alternate-25,27-di(3,7-dimethyloctyl-1-oxy)calix[4]arenebenzocrown-6, MC-12B: 1,3-alternate-25,27-di(4-butyloctyl-1-oxy)calix[4]arenebenzoerown-6, and combinations thereof Structural isomers or constitutional isomers of MC-8B, MC-10B, and MC-12B may also be used in the calixarene extractant solution, alone or in combination with one or more of the above-mentioned structures. The dialkyloxycalix[4]arenebenzocrown-6 compounds described above may be synthesized as described in the above-mentioned U.S. patent application Ser. No. 12/268,189 to Peterman et al. The at least one modifier may be an alcohol modifier, trioctylamine (“TOA”), tri-n-butyl phosphate (“TBP”), or combinations thereof The modifier used in the calixarene extractant solution may be one of the modifiers described in the above-mentioned U.S. Pat. No. 7,291,316 to Meikrantz et al., or U.S. patent application Ser. No. 12/268,189 to Peterman et al. In one embodiment, the modifier is 3-[4-(tert-octyl)phenoxy]-1-propanol (“Cs-4”), 3-[4-(sec-butyl)phenoxy]-1-propanol (“Cs-4SB”), 3-[4-(tert-octyl)phenoxy]-2-methyl-1-propanol (“Cs-5”), 3-[4-(sec-butyl)phenoxy]-2-methyl-1-propanol (“Cs-5SB”), or 1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (“Cs-7SB”). The modifier may be present in the calixarene extractant solution at from approximately 100 mM to approximately 3.0 M. The modifier may increase the calixarene compound's ability to extract the cesium and may enable a lower concentration of the calixarene compound to be used in the calixarene extractant solution. The modifier may also prevent the formation of a third phase during the extraction. In addition, the modifier may improve stripping efficiency of the cesium, enabling the cesium to be effectively removed or stripped from the calixarene extractant solution. If the calixarene compound is sufficiently soluble in the modifier, the modifier may be used as both a modifier and a diluent. The diluent may be an inert diluent, such as a straight chain hydrocarbon diluent. For instance, the diluent may be an isoparaffinic hydrocarbon diluent, such as ISOPAR® L or ISOPAR® M. ISOPAR® L includes a mixture of C10-C12 isoparaffinic hydrocarbons and is available from Exxon Chemical Co. (Houston, TX). ISOPAR® M includes a mixture of C12-C15 isoparaffinic hydrocarbons and is available from Exxon Chemical Co. (Houston, TX). The calixarene extractant solution may be prepared by combining the calixarene compound and the modifier with the diluent to form a mixture. Initially, a portion of a final volume of the diluent may be added to the calixarene compound and the modifier to lower the viscosity of the mixture. The mixture may be stirred overnight and the remainder of the diluent may then be added. As shown in FIG. 2, if the separation devices 10A, 10B, 10C are chromatography devices, such as extraction chromatography columns, the calixarene compound may be coated on a solid support of the chromatography column. The solid support may be silica or an organic polymer. The calixarene compound may be one of the compounds discussed above and may function as a stationary phase of the extraction chromatography column. Extraction chromatography columns and techniques for immobilizing the calixarene compound on the solid support are known in the art and, therefore, are not described in detail herein. As the irradiated barium target solution 2′ passes through the extraction chromatography column, the 131Cs may come into contact with the calixarene compound and form a complex with the calixarene compound. Since the 131Cs is to be continuously removed, the irradiated barium target solution 2′ may be continuously flowed through extraction chromatography columns that function as separation devices 10A, 10B, 10C. The extracted barium target solution 2″ that exits the extraction chromatography column is substantially depleted of the 131Cs. If, however, additional 131Cs is present, the extracted barium target solution 2″ may be flowed through additional extraction chromatography columns as desired. The extracted barium target solution 2″, which lacks the 131Cs, may be circulated through the isotope production system 4 for an amount of time sufficient for any 130Ba remaining in the extracted barium target solution 2″ to be activated to 131Ba and for additional 131Cs to grow. The extracted barium target solution 2″ may be flowed through the neutron source 6 and exposed to neutron irradiation, producing the irradiated barium target solution 2′. As the 131Cs accumulates in the irradiated barium target solution 2′ and is passed through the extraction chromatography columns, the 131Cs complexes with the calixarene compound. The 131Cs is eluted from the extraction chromatography columns, as described below. The 131Cs complexed to the calixarene compound may be eluted from the extraction chromatography column using an aqueous acid solution as a mobile phase. To reduce exposure of personnel to radiation, the extraction chromatography column having the 131Cs complexed to the calixarene compound may be removed from the separator 10 and transported to a different location for elution of the 131Cs. For instance, if the separation devices 10A, 10B, 10C are extraction chromatography columns, the extraction chromatography columns may be removed from the isotope production system 4 before eluting the 131Cs. The aqueous acid solution used to elute the 131Cs may be an aqueous nitric acid solution having from approximately 0.001 M HNO3 to approximately 6 M HNO3, such as from 0.001 M HNO3 to approximately 0.5 M HNO3. By way of non-limiting example, the aqueous acid solution may have approximately 0.01 M HNO3. The aqueous acid solution exiting the extraction chromatography column may be collected and includes substantially all of the 131Cs. The aqueous acid solution containing the 131Cs may be concentrated and taken to dryness, such as by evaporating the aqueous acid solution. The aqueous acid solution containing the 131Cs may also be farther purified by subjecting the aqueous acid solution to filtration, ion exchange chromatography, extraction chromatography, or other conventional techniques. The resulting 131Cs may then be used in brachytherapy seeds, as previously described. Since 131Cs is the only isotope to be removed by the separation devices 10A, 10B, 10C (liquid:liquid extraction device or extraction chromatography column), 131Cs having higher purity may be achieved by the method of the invention compared to conventional techniques. By way of non-limiting example, the 131Cs produced by the method of the invention may be greater than 99.9% pure. In addition, since the 131 Cs is continuously removed from the irradiated barium target solution 2′ before subsequent neutron capture can occur, the resulting 131Cs is substantially free of 132Cs. The described method of producing 131Cs also provides isolating cesium-131 with fewer separation acts. In addition to selectively removing the 131Cs from the irradiated barium target solution 2′ using calixarene compounds, the 131Cs may be removed using an inorganic ion exchange composite as described in Tranter et al., Solvent Extr. and Ion Exch., 27:219-243 (2009), the disclosure of which is incorporated by reference herein in its entirety. The inorganic ion exchange composite includes ammonium molybdophosphate synthesized within hollow aluminosilicate microspheres. The 131Cs may also be intermittently removed from the isotope production system 4, such as if the isotope production system 4 is taken offline for maintenance. Before restarting the neutron source 6 after the isotope production system 4 has been offline, any 131Cs that has accumulated in the irradiated barium target solution 2′ and extracted barium target solution 2″ may be removed, as described above, to prevent the formation of 132Cs. After removing the 131Cs, the isotope production system 4 may be put back online. By utilizing a liquid target of the barium source, the irradiated barium target solution 2′ may be continuously circulated through the isotope production system 4 until substantially all of the 130Ba is depleted and has been converted to the recovered 131Cs. In contrast, conventional processes of producing 131Cs use a solid barium target, which leads to incomplete use of available 130Ba. In addition, since the irradiated barium target solution 2′ is a liquid, the irradiated barium target solution 2′ may be easily transported between the neutron source 6 and the separator 10 by way of the liquid loop 8, with minimal exposure of personnel to irradiation. The irradiated barium target solution 2′ may be circulated through a single system, the isotope production system 4, to achieve both irradiation of the 130Ba and separation of the 131Cs. This is in contrast to conventional processes of producing 131Cs where the barium target is a solid material that is manually loaded into the nuclear reactor for irradiation. The irradiated solid target is then manually removed from the nuclear reactor for isolation and purification of the 131Cs. However, the loading and unloading of the solid target is time consuming, costly, and exposes personnel to irradiation. The following example serves to explain embodiments of the present invention in more detail. This example is not to be construed as being exhaustive or exclusive as to the scope of this invention. The growth of 131Ba, 131Cs, and 132Cs from 1 mole (137.33 g) of natural barium carbonate irradiated in a neutron flux of 5×1012 n/cm2 s for 55 days in 5 day increments was calculated. The natural barium carbonate used was 100% pure. The calculations assumed no removal of 132Cs from the irradiated material. The 131Ba, 131Cs, and 132Cs growth was calculated using ORIGEN2 version 2.2, a depletion and radioactive decay computer code developed by Oak Ridge National Laboratory. Plots showing the growth of 131Ba, 131Cs, and 132Cs as a function of days of irradiation are shown in FIGS. 3-5, respectively. FIGS. 3-5 illustrate that from the start of irradiation, the liquid loop activities grow steadily such that the 131Ba reaches about 0.6 curies per mole of natural barium target after 30 days. The 131Cs level is about 0.4 curies at this time, and increases to about 0.6 curies after 55 days of operation. Thus, using the isotope production system 4 and process described above, a liquid loop target containing between 4 moles and 5 moles of natural barium is estimated to be able to produce several curies of recoverable 131Cs several times per month. The efficiency of the cesium/barium separation precludes the added neutron capture on 131Cs and minimizes 132Cs formation to acceptable levels in the recovered isotope product. While the invention is susceptible to various modifications, as well as alternative forms and implementations, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, the invention is not intended to be limited to the particular forms and embodiments disclosed. Rather, the invention, in various embodiments, is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the following appended claims and their legal equivalents.
050227882	description	DESCRIPTION OF THE PREFERRED EMBODIMENT In respect of the following and previously set out description and explanation, it should be understood that while the information given is considered to be correct, such explanations are necessarily somewhat speculative since the amount of factual information relating to the earth's crust and deep mantle is limited. Applicant would not want to be bound, therefore, by the following explanations if, subsequently, new and better information becomes available. The explanations hereinafter given are made for the purpose of full and complete disclosure of the invention but the qualification given above should be borne in mind. With reference now to the drawings, FIG. 1 illustrates the locations of subduction zones and plates throughout the world. The Pacific Plate 10 subducts the Indo-Australian Plate 11 on the North Island of New Zealand 12. The Explorer Plate 13 subtends the North American Plate 14 opposite the Canadian located Brooks Peninsula and Scott Islands generally illustrated at 15. The Gorda Plate 20 subtends the North American Plate 14 opposite the United States site of Cape Mendecino generally shown at 16. The four locations set out above are the only naturally occurring sites where the topography would allow a viable tunnelled access using current technology to the subduction zone where the tectonic plate descends adjacent the non-descending earth's crust. All other subduction zones are associated with deep ocean trenches and/or are situated far enough from land, that accessing them by a tunnel would be impractical. One exception is the Himalayas Subduction Zone. The truncated nature of the Himalayas Subduction Zone 40, however, where the continental crust subtends another continental crust makes India a less desirable location to dispose of high-level radioactive waste than the four locations set forth above. A typical subduction zone generally illustrated at 30 is shown in FIG. 2. The descending tectonic plate generally illustrated at 21 includes the sedimentary layer 22, the oceanic crust 23, the continental crust 42 and some semi-plastic rock mass 24. The subduction zone 30 denotes the boundary between the tectonic plate 21 and the non-descending plate 31. The tectonic plate 21 descends at a rate of about 6 cm per year into the earth's mantle 32. This phenomena is a result of the generation of the oceanic crust 23 by the rising plume of low-viscosity asthenosphere 34 at an oceanic ridge 41. The oceanic crust 23 which forms into a portion of the tectonic plate 21 moves to the left as indicated by the arrows in FIG. 2. The continental crust 42 of the tectonic plate 21 does not exist off the North American coast but could represent, for example, the Hawaiian Islands as they move towards subduction at the Japan Trench 43 (FIG. 1), or the Mariana Islands as they move towards subduction at the Phillipine Trench (not shown). The tectonic plate 21 is covered with ocean water 50 and comprises the sedimentary layer 22, the oceanic crust 23 and the continental crust 42. It descends back into the center of the earth at the subduction zone 30. It is contemplated that tens of millions of years would pass for the material in the tectonic plate 21 at the subduction zone 30 to descend downwardly as a solid, melt at a depth of approximately 700 kilometers, mix and become part of the liquid rock currents in the mantle 32 and, thereafter, migrate and return to the surface of the earth at the oceanic ridge 41. This time, of course, is far in excess of the time required for nuclear or other toxic waste materials to become harmless. It is calculated, for example, that Plutonium 239 placed in repositories in the tectonic plate 21 at the subduction zone 30 will reach a depth 51 of about fifteen (15) kilometers when it becomes radioactively harmless at an estimated subduction rate of about 6 cm per year and the approximately 250,000 years needed for Plutonium 239 to become radioactively harmless. The heat and pressure within the earth are also effective in reducing the toxicity of non-nuclear waste. At the subduction zone 30, the abrasion of the tectonic plate 21 against the non-descending plate 31 will cause portions of the sedimentary layer 22 to be scraped off the tectonic plate 21 which sediment is added to the non-descending plate 31 although some sediment may later be dragged into the mantle 32 by the tectonic pate 21 by the same abrasive action. At a depth of 100 kilometers illustrated at 52, the subducted sediment undergoes a phase change as heat and pressure drive water from the crystal structure. Some of the sediment will malt and rise to the surface as andesitic volcanoes 53. As the tectonic plate 21 descends further into the earth, it thins due to partial plasticizing and an increase in the rate of descent due to the current flow within the mantle 32. A section illustrating the ocean 50, sediment 22 and oceanic crust 23 is shown in FIG. 3. The oceanic crust. 23 comprises the basalt lava 25, the basalt dykes 26, the gabbro 27, the layered peridotite 28 and the peridotite 29. The combination of the sedimentary layer 22 and the oceanic crust 23 comprises the tectonic plate 21. The illustration is based on seismic velocity interpretations, evidence from dredged samples and comparisons with outcrops of rocks thought to have once been parts of ocean floors. At most subductior zones, the ocean 50 is deep as subduction zones are typically associated with trenches which reach depths as great as seven (7) miles. The Cascadia Subduction Zone 54 (FIG. 1), however, lays typically beneath only one (1) mile of water and thus the subducting tectonic plate 21 could be accessed by a tunnel from the non-descending plate 31 which, in this event, for example, would be the Brooks Peninsula, the Scott Island or Cape Mendicino. The thickness of sedimentary layer 22 over the oceanic crust 23 ranges from zero at the oceanic ridge 41 where the oceanic crust 23 is formed from the rising plume of the mantle 32 to an average of 3 to 4 kilometers near continental edges where the oceanic crust 23 is typically subducted. The further a plate has spread from its originating oceanic ridge 41, the older it is assumed to be and thus the thicker is the sediment 22 overlaying it having regards to the fact that the sedimentary layer 22 is built up over millions of years by debris raining onto the ocean floor. The Cascadia Subduction Zone 54 (FIG. 1) is only 550 kilometers from the Juan de Fuca Ridge 60 at its widest point. It is assumed, therefore, that the sedimentary layer over the Explorer Plate 13, the Juan de Fuca Plate (not shown) and the Gorda Plate 20 which are all subducted at the Cascadia Subduction Zone 54 would be considerably thinner than three (3) kilometers in depth. Accordingly, the sedimentary layer 22 could be tunnelled through using a method similar to conventional mining techniques such as those which have operated in South Africa to a depth of 9300 feet. If the sedimentary layer 22 proves to be three (3) to four (4) kilometers thick at the Cascadia Subduction Zone 54, however, it is: contemplated that tunneling to the bottom of the sedimentary layer 22 and radiating repositories at that depth as set forth in more detail hereafter should allow a sufficient overlaying buffer from the effects of abrasion and volcanism suffered by the sediments in the upper regions of the sedimentary layer 22 during subduction. Preferably, however, a tunnel would be driven into the oceanic crust 23 beneath the sedimentary layer 22 before waste repositories are radiated from the tunnel access. The accessing tunnel 61 envisioned according to the invention in a first embodiment traverses the subduction zone 30 (FIG. 5) from the non-descending plate 31 and bores into the descending tectonic plate 21. Alternatively, and in a second embodiment, the tunnel 61 could originate from the continental crust 42, including a natural or man-made island, on the descending side of the subduction zone 30. In either case, repositories 63 radiate outwardly from the tunnel 61 as shown more clearly in FIG. 4. The repositories 63 would be filled with the most hazardous wastes 64 in the distal reaches of the respective repository and the least hazardous wastes 70 such as low-level radioactive waste could act as a buffer between the high level radiation and thermal heat of the high-level radioactive wastes 64 and the plug 39, thereby better isolating both types of waste from the biosphere. As viewed in FIG. 5 a caisson 62 could also be used to access the tectonic plate 21 via the access tunnel 61. It can also be seen in FIG. 5 that in a preferred embodiment of this invention, the access tunnel 61 would have a sufficiently large cross section to permit the simultaneous removal of tailings from repositories 63 undergoing excavation as well as importation of wastes into the repositories 63. The following describes the approximate volume of high level radioactive waste to be disposed of having in mind current waste stockpiles. If the amount of radioactive waste stockpiled at present is assumed to be approximately 135,000 feet, it is calculated that the repositories required would have a width and height of approximately 15 ft.times.15 ft, the repositories having a lineal distance of about 600 feet being required to dispose of the current U.S. stockpile. If the waste is shielded before being brought to the disposal site, and assuming this adds five (5) times the volume to the waste, approximately 3000 lineal feet of repository would be required which is well within current technological abilities. Besides the use of an access tunnel to allow the deposit of wastes in a subtending tectonic plate, it is also contemplated that the use of an access tunnel or borehole across the subduction zone could be utilized for installing and monitoring instrumentation which could be used to determine the movement of the subtending tectonic plate relative to the non-descending plate in the subduction zone. This possibly, could be useful for more accurately determining the onset of earthquakes at various locations on the earth's surface which could bear some relationship to the movement of the plates at the subduction zone. While a specific embodiment of the invention has been described, many modifications will readily occur to those skilled in the art to which the invention relates. Accordingly, such description should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims.
039416526	claims	1. Apparatus for locating failed fuel assemblies in a nuclear reactor cooled by upward flow of liquid coolant through the fuel assemblies, comprising gas source means for supplying gas at a pressure greater than the pressure of liquid coolant at the outlet of each assembly, emulsion producing means for producing an emulsion between the gas and the liquid coolant, the emulsion producing means including an enclosed flow path for each assembly adapted to receive a portion of the liquid coolant flowing from the outlet thereof, the emulsion producing means further including gas diffusion means connected to the flow path and adapted to receive gas from the gas source means and introduce the gas into liquid coolant flowing through the flow path, selector means for successively supplying gas to each gas diffusion means one at a time, means for separating the gas from the liquid coolant, and means for detecting the presence of radioactivity in the separated gas, each flow path including a tube with one end near the outlet of a fuel assembly, said tube being adapted to enable the liquid coolant to flow upwardly therein, the gas diffusion means including a gas chamber bounded on one side by said tube and on the other side by a supporting plate connected to the selector means, the portion of the tube that bounds the gas chamber being laterally disposed and including a plurality of gas inlet apertures therein. 2. An apparatus as set forth in claim 1, wherein said laterally disposed portion of the tube is frusto-conical and co-operates with a bore in the supporting plate to bound the gas chamber. 3. An apparatus as set forth in claim 2, wherein the tube is formed below the apertures with a tip which is of smaller diameter than that through which the emulsion flows and is formed with inlet slots or apertures for coolant coming from the fuel assembly. 4. An apparatus as set forth in claim 3, wherein each said tip projects into an upwardly flared passage of a plate disposed above the assemblies. 5. An apparatus as set forth in claim 1, wherein said means for separating is a shallow tank and disposed at a level such that the emulsion has a free surface in the tank. 6. An apparatus as set forth in claim 5, wherein anti-splash plates are disposed in the tank and each confronts one of the vertical tubes. 7. An apparatus as set forth in claim 1, wherein the means for separating is connected via a single outlet to said means for detecting and said later-named means is disposed outside the reactor shield.
	summary
060581530	summary	BACKGROUND OF THE INVENTION The present invention relates to a preventive maintenance apparatus for structural members in a nuclear pressure vessel and, more particularly, to a preventive maintenance apparatus for structural members in a nuclear pressure vessel capable of preventing occurrence of stress corrosion cracks of structural members by adding compressive remaining stress to surfaces of the structural members. The present invention relates to an apparatus of preventive maintenance for structural members in a nuclear pressure vessel suitable for adding compressive residual stress to a surface of a welded portion and a heat affected zone in each of core internals of, preferably, a boiling water reactor (BWR) such as a core shroud, a shroud support cylinder, a shroud support leg, a shroud support plate and a jet pump diffuser. Japanese Patent Application Laid-Open No.62-63614 discloses a method of releasing tensile remaining stress in a welded portion which may become a cause of occurrence of stress corrosion cracks. In the method, a high pressure water shot peening apparatus is inserted inside of a heat transfer tube of a heat exchanger to peen an inner surface of the heat transfer tube by axial kinetic pressure energy of a high pressure water jet (kinetic pressure energy of a confined water jet in the axial direction). Tensile remaining stress having existed near the inner surface of the heat transfer tube is converted into compressive remaining stress by the peening. The high pressure water shot peening apparatus comprises a rotating nozzle portion for discharging a high pressure liquid jet. Further, Japanese Patent Application Laid-Open No.5-78738 discloses an improving method of converting tensile remaining stress on a surface of a core shroud in a reactor pressure vessel into compressive remaining stress by water jet peening. The water jet peening is performed by arranging a traveling cart mounting a vertical driving apparatus on a flange in a top end portion of the reactor pressure vessel. An upper mast and a lower mast having a water jet discharging head in the top end are mounted onto the vertical driving apparatus. A high pressure water jet is discharged from a water jet discharging nozzle of the water jet discharging head to generate cavitation. Air bubbles generated by the cavitation are hit on a surface of the shroud. Furthermore, Japanese Patent Application Laid-Open No.7-270591 discloses a method in which preventive maintenance apparatuses comprising a nozzle unit having an upper attachment, a lower attachment and a drive mechanism for a discharging nozzle and a main apparatus body are arranged in a top end portion of a CRD housing and a lower core support plate inside a reactor pressure vessel to generate cavitation bubbles by discharging a high pressure jet from the discharging nozzle. The method also discloses a method of improving remaining stress by water jet peening. The cavitation bubbles are hit onto the surfaces of a lower barrel of the core shroud, a core shroud support cylinder and so on. Tensile remaining stress in the surfaces of the lower barrel of the core shroud, the core shroud support cylinder and so on is converted to compressive remaining stress. The method of the prior art disclosed in Japanese Patent Application Laid-Open No.62-63614 is effective as a method of releasing the remaining stress in a heat exchanger and the like. The axial kinetic pressure of the water jet in this method can be effectively used in the work under atmospheric pressure. However, when the high pressure shot peening apparatus of the prior art is used under water, an effective peening effect cannot be obtained because the axial kinetic pressure of the water jet is substantially decayed under water. In order to obtain an axial kinetic pressure equivalent to that under a condition of air atmosphere under a condition of water using the high pressure shot peening apparatus, a water jet of ultra high pressure discharge is necessary. Accordingly, the pump and the related components used need to have structures capable of withstanding the ultra high pressure. In order to avoid such structures, it is required to discharge the high pressure liquid jet under air atmosphere by lowering a core water level inside the reactor pressure vessel. Since lowering of the core water level causes an increase in the environmental radiation dose, radiation exposure to workers may be increased. On the other hand, the method of improving remaining stress by the water jet peening disclosed in Japanese Patent Application Laid-Open No.5-78738 is effective as a method of improving remaining stress in core internals such as a core shroud. However, since the traveling cart having the mast is placed on the top end portion of the reactor pressure vessel, the mast becomes long in order to apply the method of improving remaining stress by water jet peening to the lower barrel of the core shroud, the core shroud support cylinder and so on. In addition to this, the apparatus is difficult to be handled. It cannot be said that this is preferable from the viewpoint of workability. The method of improving remaining stress by the water jet peening disclosed in Japanese Patent Application Laid-Open No.7-270591 is an effective technology aiming to improve the workability which is the problem in the method of improving remaining stress described in Japanese Patent Application Laid-Open No.5-78738 since the apparatus does not have any long mast. However, application of the method in Japanese Patent Application Laid-Open No.7-270591 is limited within a small field of preventive maintenance work since the preventive maintenance apparatus is attached to the top end portion of the CRD housing and the lower core support plate inside the reactor pressure vessel. Therefore, it is necessary that the preventive maintenance apparatus is detached and moved from one CRD housing after completion of the preventive maintenance work to a portion existing in the inner surface of the core shroud to be set to another CRD housing. SUMMARY OF THE INVENTION An object of the present invention is to provide a preventive maintenance apparatus for structural members in a reactor pressure vessel which is capable of being easily arranged on a core shroud and easily moving a discharging nozzle to a portion to perform preventive maintenance. A first invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel which comprises a ring-shaped guide rail having a plurality of lugs, the guide rail being placed on an upper flange of a core shroud provided inside a reactor pressure vessel, at least of the plurality of lugs engaging a plurality of guide rods provided on an inner surface of the reactor pressure vessel; a turntable rotatable on the guide rail; a discharging nozzle moving apparatus for moving a discharging nozzle in a radial direction of the core shroud and in an axial direction of the core shroud, the discharging nozzle moving apparatus being placed on the turntable; and a high pressure water supply apparatus for supplying high pressure water to the discharging nozzle. Since the guide rail has the plurality of lugs engaging with the plurality of guide rods provided in the inner surface of the reactor pressure vessel, the guide rail can be easily moved downward up to the upper portion of the core shroud along the guide rods. Therefore, the guide rail can be easily placed on the upper flange without being interfered with main steam line plugs which are inserted into opening portions of main steam pipes. In addition to this, since the turntable can be rotated, the discharging nozzle can be easily moved to a portion to perform preventive maintenance. Since the turntable is rotated on the guide rail placed on the upper flange, the turntable does not contact the upper flange. Accordingly, the upper flange can be prevented from being damaged by the rotation of the turntable. A second invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel which comprises a first discharging nozzle moving apparatus for moving a discharging nozzle in a radial direction of the core shroud and in an axial direction of the core shroud, the discharging nozzle discharging high pressure water to add compressive remaining stress to an outer surface of the core shroud, the discharging nozzle moving apparatus being placed on the turntable; and a second discharging nozzle moving apparatus for moving a discharging nozzle in a radial direction of the core shroud and in an axial direction of the core shroud, the discharging nozzle discharging high pressure water to add compressive remaining stress to an inner surface of the core shroud, the discharging nozzle moving apparatus being placed on the turntable. Since the first and the second discharging nozzle moving apparatuses are installed in the turntable, compressive remaining stress can be added to both of the outer surface and the inner surface of the core shroud. Therefore, it is possible to shorten the time for performing preventive maintenance to the core shroud. A third invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel in which the second discharging nozzle moving apparatus comprises an arm member movable in a horizontal direction; a pole member movable in an axial direction of the core shroud provided in the arm member; a multi-joint arm attached to the pole member; and the discharging nozzle provided in a top end portion of the multi-joint arm. Since the multi-joint arm is provided, it is possible to insert the discharging nozzle into a narrow portion formed between the core shroud and an upper core grid plate placed on the core shroud. Therefore, compressive remaining stress can be added to the inner surface of the core shroud in the narrow portion. A fourth invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel in which the first discharging nozzle moving apparatus comprises an arm member movable in a horizontal direction; a pole member movable in an axial direction of the core shroud provided in the arm member, the pole member being inserted between the reactor pressure vessel and the core shroud; a vertically moved body attached to the pole member, the vertically moved body being movable in a vertical direction; and the discharging nozzle provided in a top end portion of the vertically moved body. Since the vertically moved body having the discharging nozzle can be vertically moved along the pole member, it is possible to easily add compressive remaining stress to a welded portion of the core shroud and the vicinity. A fifth invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel which comprises a water supply apparatus for cleaning reactor water and supplying the water to a high pressure water supply apparatus. Since the reactor water is cleaned to be supplied to the high pressure supply apparatus, the water discharged from the discharging nozzle becomes the reactor water again. Accordingly, an amount of the reactor water inside the reactor pressure vessel and the reactor well is never increased even when the high pressure water is discharged from the discharging nozzle during preventive maintenance work. Therefore, radioactive disposal liquid cannot be produced even when the high pressure water is discharged from the discharging nozzle. A sixth invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel which comprises a crud sucking apparatus for sucking crud suspending in reactor water. Since it is possible to remove crud suspended in the reactor water during preventive maintenance work, visibility under the reactor water can be improved. Therefore, it is possible to clearly monitor a portion under preventive maintenance work using an image in a monitoring camera. A seventh invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel which comprises a bubble collecting apparatus for collecting bubbles reaching a water surface in a reactor well, the bubble collecting apparatus being placed near the water surface. Since the bubble collecting apparatus is provided, it is possible to prevent radioactive materials floating up in the reactor water accompanied by the bubbles from being dispersed. Therefore, it is possible to suppress radiation exposure to workers. An eighth invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel in which the first discharging nozzle moving apparatus comprises an arm member movable in a horizontal direction; a plurality of pole members provided in the arm member, the pole member being inserted between the reactor pressure vessel and the core shroud; vertically moved bodies respectively attached to the pole members, the vertically moved body being movable in a vertical direction; and the discharging nozzles respectively provided in the vertically moved bodies. Since the vertically moved bodies capable of respectively and vertically moving the plurality of pole members are provided, it is possible to perform preventive maintenance work to different positions on the outer surface of the core shroud at the same time. Therefore, it is possible to further shorten the time required for the preventive maintenance work. A ninth invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel which comprises a rotating apparatus for rotating a metal fitting for bundling a plurality of hoses and a plurality of cables, the plurality of hoses and the plurality of cables being connected to the first discharging nozzle moving apparatus and the second discharging nozzle moving apparatus. Since the rotating apparatus for rotating the metal fitting for bundling the plurality of hoses and the plurality of cables is provided, the rotating apparatus can be rotated when the turntable mounting the first discharging nozzle moving apparatus and the second discharging nozzle moving apparatus is rotated during preventive maintenance work. Therefore, it is possible to prevent the plurality of hoses and the plurality of cables from being intertwined by rotation of the turntable. A tenth invention to attain the above-mentioned object is characterized by a preventive maintenance apparatus for structural members inside a reactor pressure vessel in which the first discharging nozzle moving apparatus and the second discharging nozzle moving apparatus respectively comprise a discharging nozzle for discharging high pressure water for adding compressive remaining stress to an outer surface of the core shroud and a discharging nozzle for discharging high pressure water for adding compressive remaining stress to an inner surface of the core shroud, and the preventive maintenance apparatus further comprises an apparatus for moving the discharging nozzles. Since the first discharging nozzle moving apparatus and the second discharging nozzle moving apparatus respectively comprise the discharging nozzle for discharging high pressure water for adding compressive remaining stress to an outer surface of the core shroud and the discharging nozzle for discharging high pressure water for adding compressive remaining stress to an inner surface of the core shroud, it is possible to perform preventive maintenance work to four positions in the inner and outer surfaces of the core shroud at the same time. Therefore, it is possible to substantially shorten the time required for the preventive maintenance work to the core shroud.
046408134	summary	CROSS REFERENCE TO RELATED APPLICATION Reference is hereby made to the following copending U.S. application dealing with related subject matter and assigned to the assignee of the subject application: "Light Water Moderator Filled Rod For A Nuclear Reator"; by P. K. Doshi et al; assigned U.S. Ser. No. 654,709; and filed Sept. 26, 1984. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactors and, more particularly, is concerned with a unique design of a soluble burnable absorber rod for use in a nuclear reactor which achieves substantially complete absorber burnup and has reduced fabrication cost. 2. Description of the Prior Art In a typical nuclear reactor, the reactor core includes a large number of fuel assemblies each of which is composed of top and bottom nozzles with a plurality of elongated transversely spaced guide thimbles extending between the nozzles and a plurality of transverse grids axially spaced along the guide thimbles. Also, each fuel assembly is composed of a plurality of elongated fuel elements or rods transversely spaced apart from one another and from the guide thimbles and supported by the grids between the top and bottom nozzles. The fuel rods each contain fissile material and are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A liquid coolant is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work. Since the rate of heat generation in the reactor core is proportional to the nuclear fission rate, and this, in turn, is determined by the neutron flux in the core, control of heat generation at reactor start-up, during its operation and at shutdown is achieved by varying the neutron flux. Generally, this is done by absorbing excess neutrons using control rods which contain neutron absorbing material. The guide thimbles, in addition to being structural elements of the fuel assembly, also provide channels for insertion of the neutron absorber control rods within the reactor core. The level of neutron flux and thus the heat output of the core is normally regulated by the movement of the control rods into and from the guide thimbles. Also, it is conventional practice to design an excessive amount of neutron flux into the reactor core at start-up so that as the flux is depleted over the life of the core there will still be sufficient reactivity to sustain core operation over a long period of time. In view of this practice, in some reactor applications burnable poison rods are inserted within the guide thimbles of some fuel assemblies to assist the control rods in the guide thimbles of other fuel assemblies in maintaining the neutron flux or reactivity of the reactor core relatively constant over its lifetime. The burnable poison rods, like the control rods, contain neutron absorber material. They differ from the control rods mainly in that they are maintained in stationary positions within the guide thimbles during their period of use in the core. The overall advantages to be gained in using burnable poison at stationary positions in a nuclear reactor core are described in U.S. Pat. No 3,510,398 to Wood. Heretofore, rods containing burnable poison intended to be stationarily positioned within the reactor core have been of the "fixed" type. By a rod being of the fixed type, it is meant that the absorber content of the burnable poison at any axial elevation on the rod is fixed by the initial loading of the material during manufacture of the rod. The burnable poison rod in the Wood patent is representative of the fixed type. A major disadvantage of the fixed type absorber rod, such as the one illustrated and described in this patent, is that not all of the poison material in the rod burns up completely or depletes evenly. The shape of the axial depletion curve for the fixed type absorber rod is approximately the same as the axial neutron flux distribution curve averaged over the core life cycle. However, because of the lack of correspondence between the average axial distribution of neutron flux and some of the neutron flux peaks occurring in the reactor core over the life cycle of core operation, poison material at certain axial locations of the fixed type burnable poison rod depletes more rapidly than at other locations. This results in incomplete absorber depletion at the other locations, which means there is a substantial residual absorber penalty at the end of the cycle. Consequently, a need exists for a burnable poison rod design which will have an improved fuel cycle cost benefit over the previous fixed design, as represented by the rod design in the Wood patent, in terms of fabrication costs and increased length of core cycle. SUMMARY OF THE INVENTION The present invention provides a soluble burnable poison or neutron absorber rod designed to satisfy the aforementioned needs. Unlike the prior art rod, the absorber content of the material at any axial location of the rod of the present invention is not fixed at the time of manufacture nor at any time thereafter. Instead, the absorber material can circulate so that axial zones which are depleted faster than the average (due to neutron flux peaks) can be replenished with absorber material from other axial regions of the rod having lower depletion rates. Underlying the present invention is the recognition that by simply providing the absorber material in mobile rather than fixed form, it will be driven into circulation within the rod by thermal gradients which are normally present along the height of the rod. No external driving source is required. Thus, the absorber content tends to maintain a constant value over the full height of the rod of the invention as it is depleted rather than burning out faster at certain local elevations. Since during the manufacture of the rod the amount of absorber material required is calculated for the peak neutron flux location, the fixed absorber rod type requires more absorber material than the circulating type of the present invention. In contrast to the substantial residual absorber penalty at the end of the core cycle in the case of the fixed absorber type, the circulating type of the invention can be entirely depleted over its full length so there is no significant residual absorber penalty associated with it. In summary, therefore, as compared to the prior fixed type of absorber rod, the circulating absorber rod extends the burnup and thereby results in an increased cycle length. Also, it is felt that its fabrication costs would be less. Accordingly, the present invention sets forth in a fuel assembly for a nuclear reactor including a plurality of guide thimbles and a plurality of nuclear fuel rods spaced apart from one another and from the guide thimbles and grouped together in an array organized to generate a neutron flux in the fuel assembly, an improved burnable absorber rod for insertion into at least one of the guide thimbles for regulating the reactor neutron flux. The improved burnable absorber rod is composed of: (a) an elongated hollow tubular member having opposite ends and a hermetically sealed chamber defined therein between its ends; (b) a neutron absorber material in liquid form contained in the sealed chamber within the tubular member; (c) means providing a hydride sink disposed at one end of the tubular member and in communication with the sealed chamber; and (d) means providing a hydrogen getter disposed at the other end of the tubular member and in communication with the sealed chamber. More particularly, the tubular member is formed by a tubular body of thin wall construction and a pair of end plugs attached to the opposite ends of the body so as to hermetically seal the same. The tubular body has one or more reinforcing convolutions formed therein which enhance the structural rigidity and integrity of the rod so as to enable it to better withstand both high internal and external pressures acting thereon. The reinforcing convolutions can take on the shape of a recess or groove formed in the body so as to extend along a spiraling path between the ends of the tubular member. Or, alternatively, the convolutions can be a series of ring-like circular grooves formed in the body so as to extend circumferentially about and be spaced axially along the tubular member between the ends thereof. Still further, some combination of both can be used. The liquid neutron absorber material is preferably composed of boron dissolved in water with the boron enriched with B-10 over the proportion naturally contained therein. Also, since the rod is designed to have absorber material at full core height during operation, the column of liquid absorber material in the rod is reduced during non-operating periods. Thus, there will be some empty vapor space left within the chamber of the tubular member. Further, more specifically, the material composing the tubular body and end plugs of the tubular member is preferably Zircaloy-4. To reduce corrosion of the inside of the tubular member, the material is beta quenched. This also reduces the hydride pickup in the member due to free hydrogen from the oxidation or burn process. The solid lower end plug provides the means serving as the hydride sink and has an outer end portion of reduced diameter adapting it to fit into a dashpot in the lower end of the guide thimble. The upper end plug of the tubular member is an attachment fitting and disposed adjacent thereto is the means providing the hydrogen getter which takes the form of a Zircaloy sponge adaped to remove hydrogen from the vapor space in the chamber of the tubular member. The sponge is retained at the upper end against the fitting by a disc which has a central opening for allowing passage of the hydrogen gas to the sponge and is held against the sponge by a circumferential bulge formed in the body of the tubular member. Finally, the sealed chamber of the tubular member is prepressurized with helium gas so that at core operating temperature the internal pressure of the chamber will be in equilibrium with the external pressure in the core. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.
	abstract	A retainer provided at lower portion of a pump beam of a jet pump for circulating cooling water to a reactor core or a bolt for fastening the retainer is cut through an underwater-remote control to remove the bolt and the retainer is removed through the underwater-remote control.
	abstract	A digital radiographic tool with drive car for moving along track sections attached longitudinally to a pipe is shown. The drive car carries (1) a collimator on one side of the pipe for projecting x-rays or gamma rays on said pipe and (2) a linear digital array on an opposing side of the pipe for collecting x-rays or gamma rays that have passed through the pipe. The collected rays are processed to indicate any defects in the pipe. The digital radiographic tool is adjustable to allow inspection of pipes that have obstructions adjacent thereto.
	claims	1. A combined radiation therapy and magnetic resonance unit, comprising:a magnetic resonance diagnosis part with an interior within which a main magnet generates a main magnet field, said interior being limited in a radial direction about an axis by the main magnet, and a radiation therapy part for irradiation of an irradiation area within the interior, said radiation therapy part comprising an electron beam accelerator which provides an electron beam directed parallel to the main magnet field;at least parts of the radiation therapy part comprising a beam deflection enclosure defining an enclosed volume entirely radially surrounding the electron beam and deflecting the electron beam in a single plane and along a two dimensional trajectory lying within said plane and toward the axis from an initial trajectory parallel to the axis, said enclosure being arranged within the interior; andsaid beam deflection enclosure comprising a magnetic arrangement creating first and second magnetic fields, the first magnetic field being of magnitude equal to a magnitude of the main magnet field in a region of the beam deflection enclosure, but of opposite direction, and effective to cancel the main magnet field in the region of the beam deflection enclosure, and the second magnetic field in the region of the beam deflection enclosure and directed perpendicular to said two dimensional trajectory of the electron beam throughout said two dimensional trajectory to cause the electron beam to be deflected inward into the interior and towards the axis. 2. The combined radiation therapy and magnetic resonance unit as claimed in claim 1 wherein the beam deflection enclosure is configured to deflect the electron beam through 90° radially inward. 3. The combined radiation therapy and magnetic resonance unit as claimed in claim 1 wherein the beam deflection enclosure comprises at least one electromagnet. 4. The combined radiation therapy and magnetic resonance unit as claimed in claim 1 wherein the beam deflection enclosure comprises at least one permanent magnet. 5. The combined radiation therapy and magnetic resonance unit as claimed in claim 1 wherein the beam deflection enclosure comprises at least one pulsed magnet. 6. The combined radiation therapy and magnetic resonance unit as claimed in claim 1 wherein the first magnetic field is generated within the enclosed volume. 7. The combined radiation therapy and magnetic resonance unit as claimed in claim 6 wherein the beam deflection enclosure is tubular, and shaped to contain an arcuate path of the electron beam as it is deflected towards the axis. 8. The combined radiation therapy and magnetic resonance unit as claimed in claim 7 wherein the beam deflection enclosure carries conductors in such a pattern that a DC current flowing through the conductors generates the first magnetic field and the second magnetic field. 9. The combined radiation therapy and magnetic resonance unit as claimed in claim 1 wherein the beam deflection enclosure is tubular, and shaped to contain an arcuate path of the electron beam as it is deflected towards the axis. 10. The combined radiation therapy and magnetic resonance unit as claimed in claim 9 wherein the beam deflection enclosure carries conductors in such a pattern that a DC current flowing through the conductors generates the second magnetic field.
053368940	claims	1. A controller for an infrared heat source capable of being programmed to act as a target for a missile target seeker, in a system for testing a guidance and control section of missiles of different types, with a missile mounted on a stand with the infrared heat source; wherein the infrared heat source includes a black body, a shutter, filter means, and an aperture wheel having a plurality of apertures, a motor coupled to the aperture wheel to rotate it to select an aperture, and position detecting means for the aperture wheel, the motor and position detecting means being electrically coupled to the controller; solenoid means for operating the shutter and the filter means; means on the stand for sending to the controller temperature data, aperature data, shutter-filter data and missile identification data; wherein the controller comprises; a CPU comprising a microprocessor, input/output ports, and a read only memory coupled together, with the read only memory having a program stored therein for the microprocessor; aperture control means including means in the CPU for receiving signals from the position detecting means, means for reading aperture data from the stand, means for comparing the signals from the position detecting means to the aperture data, means for sending signals to operate the motor to select an aperture such that the means for comparing indicates equality, and means for sending an aperature ready signal from the controller to the stand; means for reading the missile identification data so that subsequent operation may be controlled depending on missile type; temperature control means including means in the CPU, a resistance bridge circuit comprising first, second, third and fourth legs, with the black body forming resistance of the first leg is series with a resistor forming the second leg, a resistor forming the third leg, means including electronic switching means for selecting resistance means to form the fourth leg with a variable value of resistance, a power supply having first and second terminals, means including electronic device means coupled between said first terminal and a junction of the first and third legs for supplying power to the black body at different power levels, with a junction of the second and fourth legs connected to said second terminal, an instrumentation amplifier having non-inverting and inverting inputs, with the non-inverting input connected to a junction of the third and fourth legs and the inverting input connected to a junction of the first and second legs, with the voltage at the non-inverting input used as a reference voltage, means for reading temperature data designating a temperature value from the stand to the CPU, means in the CPU for converting the temperature data to a temperature code and using it to control said electronic switching means so that the reference voltage is a function of said temperature value, means coupling an output of the instrumentation amplifier to an input of the electronic device means so that a differential voltage between the non-inverting and inverting inputs of the instrumentation amplifier is used to control power supplied to the black body from said power supply, and the differential voltage is approximately zero when the black body is at the designated 55 temperature; means for reading shutter-filter data from the stand into the CPU, and means including the CPU for using the shutter-filter data to generate signals to control the solenoid means, depending on the missile type and the shutter-filter data, to thereby move the shutter and the filter means in and out of position. wherein the temperature ready means includes black body protection means for disabling said power supply in response to the temperature detected by the temperature detection means exceeding a given value; and fuse means for the power supply for disabling the power supply in response to excessive current to thereby protect the black body. wherein said electronic device means comprises power pass transistor means, wherein said means coupling an output of the instrumentation amplifier to an input of tile electronic device means comprises an operational amplifier followed by an emitter follower transistor circuit. wherein the temperature ready means includes black body protection means having buffer means coupled between an output of the last said memory means and an input of a solid state relay, with output of the solid state relay connected in an input to a transformer of the power supply for disabling said power supply in response to the temperature detected by the temperature detection means exceeding a given value; and fuse means for the power supply for disabling the power supply in response to excessive current to thereby protect the black body. 2. A controller according to claim 1, further including temperature ready means coupled to a temperature detection means integrated into the black body for indicating to the CPU whether the black body is heating, cooling, or stabilized, with means for generating a temperature-ready signal when the temperature has stabilized, and for sending the temperature-ready signal to the stand; 3. A controller according to claim 1, wherein the position detecting means for the aperture wheel comprises a potentiometer having a wiper mechanically coupled to the aperture wheel and the motor, wherein the means for receiving signals from the position detecting means comprises an analog-to-digital converter which converts a voltage from the potentiometer to a digital value, outputs of the converter being coupled to a set of flip-flops for storing the digital value, with outputs of the flip-flops being used by said means for comparing the signals from the position detecting means to the aperture data. 4. A controller according to claim 1, wherein said electronic switching means of the temperature control means comprises a plurality of MOSFETs, each MOSFET having a source, a gate and a drain, with the drain of each MOSFET connected to said second terminal of the power supply, wherein the fourth leg of the bridge has a resistor connected between the non-inverting input of the instrumentation amplifier and a multiple connection point, each MOSFET having resistance means connected between its source and the multiple connection point, wherein the means using the temperature code from the CPU to control the electronic switching means includes a temperature decoder having a set of inputs coupled to the CPU for the temperature code, and wherein the temperature decoder has outputs coupled via buffers to the gates of the MOSFETs so that only one of the MOSFETs is turned on at a time; 5. A controller according to claim 4, further including temperature ready means coupled to a thermocouple integrated into the black body, wherein the temperature ready means comprises an instrumentation amplifier having inputs coupled to the thermocouple, with an output of the last said instrumentation amplifier coupled via a Butterworth filter which includes an operational amplifier having an output coupled to an analog-to-digital converter which provide address inputs to a memory unit, with data from the last said memory unit indicating to the CPU whether the black body is heating, cooling, or stabilized, with means for generating a temperature-ready signal when the temperature has stabilized, and for sending the temperature-ready signal to the stand;
	abstract	A portable electronic device (10) has a customizable housing (20) where a “skin” (22, 72) is provided, wherein the texture and/or color can be changed by a consumer. The portable electronic device (10) is positioned within an apparatus (41, 51, 61) providing a power source for supplying radiant energy such as heat and/or light to the material. The method of customizing a housing (20) encasing electronics of a portable electronic device (10) includes treating the skin (22, 72) within the housing (20) with heat and/or light, and thereby creating at least one of a texture and a color within the skin (22, 72).
	claims	1. A method of controlling reactivity of a nuclear fission reaction in a fast spectrum, molten salt reactor comprising:sustaining a nuclear fission reaction with fast neutrons in an unmoderated nuclear reactor core, the fast neutrons generated by a molten fuel salt within the unmoderated nuclear reactor core, thereby generating heated molten fuel salt in the unmoderated nuclear reactor core;removing heat from the molten fuel salt by circulating the molten fuel salt between the unmoderated nuclear reactor core and one or more heat exchangers in which heated molten fuel salt is cooled;monitoring one or more reactivity parameters indicative of reactivity of the molten fuel salt within the nuclear reactor core, the one or more reactivity parameters including a first parameter; andwhen the first parameter indicative of reactivity indicates that the reactivity has increased above an upper threshold of reactivity, reducing the reactivity by replacing a first volume of the molten fuel salt with a second volume of a feed material that does not contain any fissile material. 2. The method of claim 1 wherein the first volume and the second volume are the same. 3. The method of claim 1 wherein the feed material consists of a mixture of a selected fertile material and salt. 4. The method of claim 1 wherein the replacing comprises:inserting one or more volumetric displacement bodies into the molten fuel salt within the molten salt reactor. 5. The method of claim 1 further comprising:determining the second volume of the feed material to be added to the nuclear reactor core necessary to bring the first parameter within the selected range. 6. The method of claim 1 wherein the first parameter indicative of reactivity of the molten fuel salt within the nuclear reactor core is keff and the selected range of nominal reactivity is from 1.0 to 1.035. 7. The method of claim 1 wherein the first parameter indicative of reactivity of the molten fuel salt within the nuclear reactor core is keff and the selected range of nominal reactivity is from 1.001 to 1.005. 8. The method of claim 1 wherein the first parameter indicative of reactivity of the molten fuel salt within the nuclear reactor core is keff and the selected range of nominal reactivity is from 1.0 to 1.01. 9. The method of claim 1 further comprising:monitoring the one or more reactivity parameters indicative of reactivity of the nuclear reactor core; andcontrolling exchange of the first volume of the molten fuel salt with the second volume of a feed material, wherein the feed material consists of a mixture of a selected fertile material and salt based on the one or more reactivity parameters. 10. The method of claim 1 wherein the feed material consists of UCl3 and one or more of UCl4, NaCl, MgCl2, CaCl2, BaCl2, KCl, SrCl2, VCl3, CrCl3, TiCl4, ZrCl4, ThCl4, AcCl3, NpCl4, PuCl3, AmCl3, LaCl3, CeCl3, PrCl3, and/or NdCl3.

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