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	description	This application is the National Stage filing under 35 U.S.C. 371 of International Application No. PCT/KR2015/008636, filed on Aug. 19, 2015, which claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2014-0107928, filed on Aug. 19, 2014, the contents of which are all hereby incorporated by reference herein in their entirety. The present invention relates to facilities for preparing an accident mitigation of a nuclear power plant, and more particularly, a passive safety system, which uses a heat exchanger together with a thermoelectric element upon an occurrence of an accident of a nuclear power plant, and a nuclear power plant having the same. Types of reactors may be divided according to a configuration of a safety system and installation locations of main components. First, reactors are divided into active reactors using active power such as a pump, and passive reactors using passive power such as a gravity force, gas pressure or the like according to the configuration of the safety system. Next, reactors are divided according to the installation locations of the main components into loop type reactors (for example, Korean pressurized water reactor) in which main components (a steam generator, a pressurizer, a pump impeller, etc.) are installed at an outside of a reactor vessel, and integrated type reactors (for example, Korean SMART reactor) in which the main components are installed at an inside of the reactor vessel. In general, a containment structure for protecting an outside of the reactor vessel (or reactor coolant system of a loop type reactor) is referred to as a containment building (or reactor building) when the structure is constructed using reinforced concrete, and as a containment vessel (safeguard vessel for a small structure) when the structure is manufactured using a steel. In this specification, the containment building, the reactor building, the containment vessel, the safeguard vessel and the like, unless otherwise specified, are commonly referred to as “containment.” In a nuclear power plant industrial field, a passive containment cooling system (or containment cooling system) is widely used as a system of maintaining soundness of the containment by reducing pressure in a manner of condensing steam and cooling internal atmosphere, when internal pressure of the containment increases due to a discharge of coolant or steam, which results from a loss-of-coolant accident or steam line break accident occurred in various reactors including such integral reactor. As methods used for similar purposes to the passive containment cooling system, a method using a suppression tank in which steam discharged into the containment is induced into the suppression tank and condensates the steam (Commercial BWR, CAREM: Argentina, IRIS: U.S. Westinghouse, etc.), a method of applying a steel containment vessel and cooling (spray, air) an outer wall (AP1000: U.S. Westinghouse), and a method using a heat exchanger (SWR1000: Framatome ANP of France, AHWR: India, SBWR: GE of USA) and the like are currently used. A shell and tube type heat exchanger or condenser (SBWR: GE of USA, etc.) is generally applied as a heat exchanger of a passive containment cooling system related to the present invention, and the heat exchanger depends on natural circulation. In the nuclear power plant industrial field related to the present invention, a residual heat removal system (auxiliary feedwater system or passive residual heat removal system) is employed as a system for removing heat of the reactor coolant system (sensible heat in the reactor coolant system and residual heat of the core) when an accident occurs in various nuclear power plants including the integral reactor. Among those residual heat removal systems, two methods, such as a method of directly circulating primary coolant of the reactor coolant system to cool a reactor (AP1000: U.S. Westinghouse) and a method of indirectly circulating secondary coolant using a steam generator to cool a reactor (SMART reactor: Korea) are mostly used as fluid circulation methods of the passive residual heat removal system using natural circulation based on a density difference between steam and water, and a direct condensation method of injecting primary coolant into a tank (CAREM: Argentina) is partially used. Furthermore, as methods of cooling an outside of a heat exchanger (condensation heat exchanger) of the passive residual heat removal system, a water-cooling method (AP1000) applied to most of reactors, some air-cooling methods (WWER 1000: Russia), and a water-air hybrid cooling method (IMR: Japan) are currently used. A heat exchanger of the passive residual heat removal system performs a function of transferring heat delivered from a reactor to an outside (ultimate heat sink) through an emergency cooling tank or the like, and condensation heat exchangers using a steam condensation phenomenon with excellent heat transfer efficiency are widely employed as a heat exchanger type. In relation to the present invention, a printed circuit heat exchanger has been developed by the Heatric Ltd. in UK (U.S. Pat. No. 4,665,975, 1987), and is very variously used in general industrial fields. The printed circuit heat exchanger is a heat exchanger having a structure in which welding between plates of the heat exchanger is removed using a dense flow channel arrangement by a photo-chemical etching technique and diffusion bonding. Accordingly, the printed circuit heat exchanger is applicable to high-temperature and high-pressure conditions and has high accumulation and excellent heat transfer efficiency. The advantages of the printed circuit heat exchanger, such as durability against the high-temperature and high-pressure environments, the high accumulation and the excellent heat transfer efficiency, extend an application range of the printed circuit heat exchanger to various fields, such as an evaporator used in a very low temperature environment and the like, a condenser, a cooler, a radiator, a heat exchanger, a reactor, an air conditioning system, a fuel cell, a vehicle, a chemical process, a medical instrument, nuclear power plant, an information communication device. Meanwhile, a plate type heat exchanger, which is to be used as one of examples according to the present invention, has been widely applied in industrial fields over one hundred years. The plate type heat exchanger is generally configured such that plates are pressed out to form flow channels and then the pressed plates are joined to each other using gaskets or by typical molding or brazing. Accordingly, the plate type heat exchanger is similar to the printed circuit heat exchanger in view of an application field, but is more widely used under a low-pressure condition. Heat transfer efficiency of the plate type heat exchanger is lower than that of the printed circuit heat exchanger but higher than that of the shell and tube type heat exchanger. Also, the plate type heat exchanger is manufactured through more simplified processes than the printed circuit heat exchanger. The plate type heat exchanger disclosed herein, unless otherwise specified, is referred to as a heat exchanger when a difference is present in a method of manufacturing or bonding plates as well as the general plate type heat exchanger and the printed circuit heat exchanger. Meanwhile, thermoelectric phenomena involving a thermoelectric element or thermoelectric power generation disclosed herein include a Seebeck effect (1822), Peltier effect (1834), Thomson effect (1854) and the like. The Seebeck effect means a phenomenon in which electromotive force (electric power) is generated to cause a passage of the current when temperature difference exists between two contacts of a closed circuit formed by connecting two kinds of metals or semiconductors. This current is referred to as a thermoelectric current, and the electric power generated between metal lines is referred to as thermoelectromotive force (thermoelectric power). The magnitude of the thermoelectric current depends on the kinds of the paired metals and the temperature differences between the two contacts, and additionally is dependent on electric resistance of the metal lines. The Peltier effect, unlike the Seebeck effect, is a phenomenon in which the temperature difference is generated due to production and absorption of heat at two junctions when a current is applied. The Thomson effect is a phenomenon in which the Seebeck effect and the Peltier effect have correlation. A thermoelectric generator which is an energy conversion device of directly converting heat energy into electric energy can generate electricity (electric power) for use without a mechanical driving component when a heat source exists. The thermoelectric generation uses the Seebeck effect, in which electromotive force is generated due to a temperature difference between both ends of two different metals connected to each other, to cause the passage of the current by the production/absorption of heat of a thermoelectric module. The thermoelectric generation technology is a practical technology capable of reusing even low grade waste heat as electricity by converting even heat near room temperature into electricity, and is applied to an ocean thermal energy conversion (OTEC) power generation, a solar energy generation and the like. Accordingly, a usage range of the thermoelectric generation gradually becomes wide. The passive safety system for the nuclear power plant uses natural force that is generated by natural phenomena such as gravity force, gas pressure, density difference and the like, and thereby constructing the system is very limited. The passive safety system is driven using natural force by operating a safety system using power of a small battery required for opening a valve or the like when an emergency AC power source or an external power supply is not present. Therefore, the passive safety system is very excellent in view of safety. However, economical efficiency thereof is highly likely to be decreased due to a very limited design configuration option and very low driving force. For the heat exchanger, for example, a circulation flow of internal or external fluid of the heat exchanger depends on a natural circulation typically caused by a density difference. Accordingly, a heat exchange performance is decreased and thereby a size of the heat exchanger increases. Therefore, a configuration of a system having a compact size and providing higher efficiency than efficiency obtained when using the related art heat exchanger, by supplying circulating force to fluid using electricity produced by thermoelectric generation in a manner of additionally employing a thermoelectric element in a heat exchanger, which can be used in a passive safety system of a nuclear power plant. An aspect of the detailed description is to provide a passive safety system having a compact heat exchanger with high efficiency, using electricity produced by a thermoelectric power generation, and a nuclear power plant having the same. Another aspect of the detailed description is to provide a passive safety system with more improved economical efficiency and safety by generating electricity from waste heat generated upon an occurrence of an accident through a thermoelectric element and utilizing the generated electricity for a safety system, and a nuclear power plant having the same. To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a passive safety system, including a passive containment cooling system, a heat exchanger formed at a space inside or outside a hermetic containment, allowing heat exchange of internal atmosphere of the containment introduced therein, such that pressure or temperature of the internal atmosphere is reduced, when an accident occurs in a reactor coolant system or secondary system disposed within the containment, a thermoelectric element disposed within the heat exchanger and configured to produce electricity due to a temperature difference between the internal atmosphere and a cooling fluid, heat-exchanged with the internal atmosphere, when the cooling fluid performs the heat exchange with the internal atmosphere within the heat exchanger, and a fan unit or a pump unit connected to the thermoelectric element via an electricity path to receive the electricity produced from the thermoelectric element and configured to form a flow of fluid inside or outside the containment. In accordance with one embodiment disclosed herein, the fan unit may be configured to increase a flow rate of the internal atmosphere or cooling fluid passing through the heat exchanger, to facilitate the heat exchange between the internal atmosphere and the cooling fluid within the heat exchanger. Here, the heat exchanger may be arranged within the containment such that the internal atmosphere is introduced directly into the heat exchanger. Also, the passive safety system may further include an emergency cooling fluid storage section configured to store an emergency cooling fluid introduced into the heat exchanger for the heat exchange with the internal atmosphere upon an occurrence of an accident, and cooling fluid flow paths configured to connect the emergency cooling fluid storage section to the heat exchanger such that the emergency cooling fluid is introduced into the heat exchanger. The fan unit may be configured to blow the internal atmosphere toward the heat exchanger, to facilitate steam discharged from the reactor coolant system or secondary system to be introduced into the heat exchanger from a portion above the heat exchanger. The fan unit may be disposed outside the containment and configured to introduce an external cooling fluid of the containment into the heat exchanger through an external cooling fluid flow path connecting the heat exchanger to the outside of the containment. In accordance with another embodiment disclosed herein, the heat exchanger may be arranged outside the containment and include an internal atmosphere introduction flow path formed through the containment to connect the inside of the containment to the heat exchanger, such that the internal atmosphere is introduced into the heat exchanger. The heat exchanger may include a duct unit having at least part of a channel thereof narrowed toward an upper portion of the heat exchanger, such that the external cooling fluid is introduced into a lower portion of the heat exchanger and discharged out of the upper portion of the heat exchanger, and the fan unit may be located inside the containment and arranged on the internal atmosphere introduction flow path to introduce the internal atmosphere into the heat exchanger. The heat exchanger may include a duct unit having at least part of a flow channel thereof narrowed toward an upper portion of the heat exchanger, such that the external cooling fluid is introduced into a lower portion of the heat exchanger and discharged out of the upper portion of the heat exchanger, and the fan unit may be located in an upper or lower portion of the duct unit and configured to allow the external cooling fluid of the containment within the duct unit to be discharged through an upper portion of the duct unit such that the external cooling fluid flows much faster in the duct unit. Here, the passive safety system may further include an emergency cooling fluid storage section configured to store an emergency cooling fluid introduced into the heat exchanger for the heat exchange with the internal atmosphere upon an occurrence of an accident, and a circulation flow path configured to circulate the emergency cooling fluid through the heat exchanger. The fan unit may be located inside the containment and arranged on the internal atmosphere introduction flow path to introduce the internal atmosphere into the heat exchanger. In accordance with another embodiment of the present invention, a passive safety system may include a feedwater flow path forming a flow channel for injecting fluid into a steam generator provided within the containment, a steam flow path along which steam discharged from the steam generator flows toward a turbine system, a heat exchanger, a thermoelectric element disposed in the heat exchanger and configured to produce electricity due to a temperature difference between the steam and an external cooling fluid of the containment, heat-exchanged with the steam, while the external cooling fluid performs the heat exchange with the steam within the heat exchanger, a duct unit having at least part of a flow channel thereof narrowed toward an upper portion of the heat exchanger such that the external cooling fluid of the containment is introduced into a lower portion of the heat exchanger and discharged out of the upper portion of the heat exchanger, and a fan unit. The heat exchanger may be disposed outside the containment to reduce internal pressure or temperature of a reactor coolant system when an accident occurs in the reactor coolant system or secondary system disposed within the hermetic containment. The heat exchanger may receive the steam supplied through the steam flow path and discharge condensate, which has been passed through the heat exchanger, through the feedwater flow path. The fan unit may be arranged in an upper or lower portion of the duct unit, and configured to allow the external cooling fluid of the containment within the duct unit to be discharged through an upper portion of the duct unit such that the external cooling fluid flows much faster in the duct unit. The electricity path may be provided with a charging unit disposed on the electricity path to store the electricity produced from the thermoelectric element so as to supply the electricity to the fan unit. Here, the heat exchanger may be configured as a water-cooling or air-cooling type. The pump unit may facilitate a heat exchange between the internal atmosphere and an emergency cooling fluid within the heat exchanger or a flow of a cooling fluid for reducing temperature of the internal atmosphere. The electricity produced from the thermoelectric element arranged in the heat exchanger may allow the cooling fluid to be sprayed into the containment by the pump unit or allows cooling water to be injected into a safety system by the pump unit. In accordance with another embodiment disclosed herein, the passive safety system may further include an emergency cooling fluid storage section configured to store the emergency cooling fluid introduced into the heat exchanger for the heat exchange with the internal atmosphere, and a cooling fluid flow path configured to connect the emergency cooling fluid storage section to the heat exchanger such that the emergency cooling fluid is introduced into the heat exchanger. The pump unit may be disposed on the cooling fluid flow path such that the emergency cooling fluid is efficiently introduced into the heat exchanger, and allow the emergency cooling fluid to be supplied from the emergency cooling fluid storage section into the heat exchanger. In accordance with another embodiment disclosed herein, the passive safety system may further include a cooling fluid storage section disposed adjacent to the containment to store therein the cooling fluid for reducing the internal temperature of the containment, and a spray device disposed at an upper side within the containment and configured to spray the cooling fluid supplied from the cooling fluid storage section into the containment when an accident occurs within the containment. The pump unit may be disposed on a fluid supply flow path for connecting the cooling fluid storage section and the spray device to each other, to supply the cooling fluid into the spray device. In accordance with another embodiment disclosed herein, the passive safety system may further include a cooling fluid storage section disposed adjacent to the containment to store therein the cooling fluid for reducing the internal temperature of the containment, and a safety injection system configured to inject fluid into the reactor coolant system when an accident occurs in the reactor coolant system. The pump unit may be disposed on a fluid supply flow path for connecting the safety injection system to the cooling fluid storage section to supply the cooling fluid to the safety injection system such that the safety injection system injects the cooling fluid into the reactor coolant system. In accordance with another embodiment disclosed herein, the passive safety system may further include a cooling fluid storage section disposed adjacent to the containment to store therein the cooling fluid for reducing the internal temperature of the containment. The pump unit may be configured to introduce the cooling fluid stored in the cooling fluid storage section into the emergency cooling fluid storage section when a water level of the emergency cooling fluid storage section is decreased. To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a nuclear power plant, including a reactor coolant system having a core of a reactor, a steam generator, a containment surrounding the reactor coolant system to prevent a leakage of a radioactive material upon an occurrence of an accident, and a passive safety system configured to prevent an increase in internal pressure of the containment due to steam discharged from the reactor coolant system or secondary system. The passive safety system may include a heat exchanger formed at a space inside or outside a hermetic containment, and allowing heat exchange of internal atmosphere of the containment introduced therein, such that pressure or temperature of the internal atmosphere is reduced, when an accident occurs in a reactor coolant system or secondary system disposed within the containment, a thermoelectric element disposed within the heat exchanger and configured to produce electricity due to a temperature difference between the internal atmosphere and a cooling fluid, heat-exchanged with the internal atmosphere, when the cooling fluid performs the heat exchange with the internal atmosphere within the heat exchanger, and a fan unit connected to the thermoelectric element through an electricity path to receive the electricity produced from the thermoelectric element, and configured to increase a flow rate of the internal atmosphere or cooling fluid passed through the heat exchanger to facilitate the heat exchange between the internal atmosphere and the cooling fluid within the heat exchanger. To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a nuclear power plant, including a reactor coolant system having a core of a reactor, a steam generator, a containment surrounding the reactor coolant system to prevent a leakage of a radioactive material upon an occurrence of an accident, and a passive safety system configured to prevent an increase in internal pressure of the containment due to steam discharged from the reactor coolant system or secondary system. The passive safety system may include a heat exchanger formed at a space inside or outside a hermetic containment, and allowing heat exchange of internal atmosphere of the containment introduced therein, such that pressure or temperature of the internal atmosphere is reduced, when an accident occurs in a reactor coolant system or secondary system disposed within the containment, a thermoelectric element disposed within the heat exchanger to produce electricity due to a temperature difference between the internal atmosphere and an emergency cooling fluid, heat-exchanged with the internal atmosphere, while the emergency cooling fluid performs the heat exchange with the internal atmosphere within the heat exchanger upon an occurrence of an accident, an emergency cooling fluid storage section configured to store therein the emergency cooling fluid introduced into the heat exchanger for the heat exchange with the internal atmosphere, a cooling fluid flow path connecting the emergency cooling fluid storage section to the heat exchanger such that the emergency cooling fluid is introduced into the heat exchanger, and a pump unit connected to the thermoelectric element through an electricity path to receive the electricity produced from the thermoelectric element, and configured to facilitate the heat exchange between the internal atmosphere and emergency cooling fluid within the heat exchanger or a flow of a cooling fluid for reducing temperature of the internal atmosphere. According to the present invention with the configuration, a passive safety system which provides higher efficiency of a heat exchanger than that of the related art heat exchanger and has a more compact size, by providing circulating force to fluid (atmosphere or cooling fluid) using electricity produced by thermoelectric generation upon an occurrence of an accident, in a manner of further employing a thermoelectric element in the heat exchanger. According to the present invention, a thermoelectric element can be coupled to a heat exchanger (specifically, plate type heat exchanger) so as to provide circulating force to a flow path with a low heat transfer rate using electricity produced by thermoelectric generation upon an occurrence of an accident, thereby enhancing efficiency of the heat exchanger and reduce a capacity of the heat exchanger. According to the present invention, electricity produced through thermoelectric generation upon an occurrence of an accident can be used as fluid circulating force of a heat exchanger, thereby alleviating a great disadvantage of a plate type heat exchanger which exhibits very high heat transfer efficiency but great flow resistance. According to the present invention, when electricity produced in a heat exchanger of a passive safety system disclosed herein is used for facilities for supplying cooling water of a passive containment spray system, a passive residual heat removal system or a passive safety injection system, the passive safety system can be more easily implemented, thereby enhancing safety and economical efficiency. Hereinafter, description will be given in more detail of a passive safety system and a nuclear power plant having the same according to the present invention, with reference to the accompanying drawings. This specification employs like/similar reference numerals for like/similar components irrespective of different embodiments, so they all will be understood by the first description. The expression in the singular form in this specification will cover the expression in the plural form unless otherwise indicated obviously from the context. The present invention proposes various methods for improving economical efficiency or enhancing safety in a manner of supplying cooling water to a passive safety system, by constructing the system having a more compact size and providing higher efficiency than that obtained when using the related art heat exchanger, in a manner of additionally employing a thermoelectric element in a heat exchanger, which is capable of being used in a passive safety system of a nuclear power plant, to supply circulating force to fluid of the passive safety system using electricity produced through thermoelectric generation upon an occurrence of an accident. Specifically, a plate type heat exchanger-thermoelectric element coupling method, which is selectively proposed in the present invention, has a structure of facilitating coupling between the plate type heat exchanger and the thermoelectric element, and thus can be employed as a very useful configuration option, in view of generating electricity using passive energy such as residual heat generated inside a nuclear power plant, even without an external action, upon an occurrence of an accident. However, coupling methods of the heat exchanger and the thermoelectric element can be variously extended according to various types of a safety system heat exchanger, and thus the present invention may not be specifically limited to the plate type heat exchanger. A heat exchanger allows a heat transfer between two fluids. Therefore, when the two fluids are not the same type and do not have the same flowing condition, the two fluids have different heat transfer coefficients from each other. Accordingly, one of the two fluids having a small heat transfer coefficient becomes a factor deciding a size of the heat exchanger, thereby increasing the size of the heat exchanger. The present invention has provided a configuration option capable of improving economical efficiency by reducing the size of the heat exchanger or enhancing safety by stably providing a flow, by way of increasing a heat transfer rate, in a manner of inducing a forced flow in a flow path, in which fluid with a small heat transfer coefficient flows and a circulation flow is difficult to be generated, using a fan or pump by supplying electricity produced in the heat exchanger using waste heat generated upon an occurrence of an accident. Meanwhile, when the heat exchanger is reduced in size, problems of an arrangement inside and outside of a containment and a structure load can be remarkably alleviated. In order to apply a passive containment spray system, which is driven by gravity force, to a nuclear power plant to reduce internal pressure of the containment upon an occurrence of an accident, a very great quantity of water should be stored in an upper portion of the containment during a normal operation of the nuclear power plant. However, a large space is needed to store such a lot of water in the upper portion of the containment and a great load is applied to a structure due to the stored water. Therefore, it is realistically very difficult to install a water tank useable for a long term of time. Also, the similar issue is brought about in a passive residual heat removal system using an emergency cooling fluid storage section or a passive safety injection system when a method of using condensate (condensate water) proposed in the present invention is not applied. As aforementioned, upon applying the technology according to the present invention, electricity produced in the heat exchanger-thermoelectric element coupling manner of the passive safety system upon an occurrence of an accident can be used for improving efficiency of the heat exchanger, supplying cooling water of the passive safety system or ensuring a cooling water supply unit, which can contribute to improving safety and economical efficiency of a nuclear power plant. FIGS. 1A to 1C are conceptual views illustrating a detailed structure of a heat exchanger 20 in accordance with one embodiment of the present invention. (A) is a top view of a plate type heat exchanger 20, (b) is a front view, (c) is a sectional view taken along the line C-C of (a), (d) is a sectional view taken along the line D-D of (a) and (e) is a sectional view taken along the line E-E of (a). Referring to those drawings, cooling fluid and atmosphere inside a containment are introduced into an inlet/outlet pipe 2010 to be distributed into a plurality of heat transfer channels 2035 (plate channels). The cooling fluid and the atmosphere inside the containment distributed in the plate channels 2035 flow up or down along the heat exchanger 20 and then are discharged through an inlet/outlet pipe 2012 disposed at an opposite side. Here, to distribute the cooling fluid into the plurality of plate channels 2035, headers may also be provided at upper and lower portions of the heat exchanger 20, respectively. The heat exchanger 20 may be provided in plurality. The plurality of heat exchangers 20 may be closely adhered on one another. Also, each heat exchanger 20 may be provided with thermoelectric elements 20c (see (e)) arranged at both sides of each channel 2035. The thermoelectric element 20c will be described in detail with reference to FIG. 1B. An inlet header serves to distribute a flow rate of fluid supplied to the heat exchanger 20 into an inlet channel of the heat exchanger 20. An outlet header serves to collect a flow of fluid discharged into an outlet channel of the heat exchanger 20. In order to reduce temperature of atmosphere introduced into the plate channels 2035, cooling pins 2033 may surround the plate channels 2035. Or, unlike the structure illustrated in the drawing, a channel, which has a different shape from that of a channel adjacent to an arranged position of the cooling pins 2033 may also be formed (high temperature fluid flows along the channel when low temperature fluid flows along the adjacent channel, and low temperature fluid flows along the channel when high temperature fluid flows along the adjacent channel). As such, temperature and pressure of atmosphere inside the containment can fast be controlled by configuring the heat exchangers 20 by stacking the plurality of plate channels 2035 each forming a fine channel and combining a plurality of single heat exchangers 20 each surrounded by the cooling pins 2033. In addition, the plurality of plate channels 2035 may produce electricity using electric power, which is generated due to a temperature difference between the adjacent channels through adjacently-arranged thermoelectric elements 20c. FIGS. 1B and 1C are conceptual views illustrating channels formed in the heat exchanger 20 and thermoelectric elements arranged adjacent to the channels. First, referring to the left drawing of FIG. 1B, a high temperature channel part 20a along which high temperature fluid flows is shown at an upper portion of one heat exchanger 20, and a low temperature channel part 20b along which low temperature fluid flows is shown at a lower portion of the one heat exchanger 20. The right drawing of FIG. 1B illustrates a detailed view of the thermoelectric element 20c that is arranged adjacent to the channel parts to generate electric power due to a temperature difference. The low temperature channel part 20b along which the low temperature fluid flows is arranged at the left of the thermoelectric element 20c, and the high temperature channel part 20a along which the high temperature fluid flows is arranged at the right of the thermoelectric element 20c. The thermoelectric element 20c is interposed between the low temperature channel part 20b and the high temperature channel part 20a. The thermoelectric element 20c includes thermoelectric plates 20c1, semiconductors 20c2 generating the electric power, a power generating portion 20c3 connected to the semiconductors 20c2 to generate electricity, and an electricity path 20c4 connecting the semiconductors 20c2 and the power generating portion 20c3. The thermoelectric plates 20c1 come in contact with the high temperature channel part or the low temperature channel part, and the semiconductors 20c2 are interposed between the thermoelectric plates 20c1 arranged at both sides. The semiconductors 20c2 may be classified into N-type semiconductors and P-type semiconductors, which are alternately arranged in a spaced manner. The power generating portion 20c3 is connected to the N-type and P-type semiconductors by the electricity path 20c4, and electricity is produced in the power generating portion 20c3. The power generating portion 20c3 is formed at a different position from the positions of the channel parts 20a and 20b so as not to affect the channels. Also, the power generating portion 20c3 may be connected to such several semiconductors so as to produce a greater quantity of electricity. As illustrated, cooling pins 20c5 may be formed at the side of the high temperature channel part 20a. The cooling pins 20c5 may be formed to be brought into contact with fluid with an opposite attribute to fluid flowing in the adjacent channel 20b (i.e., to be brought into contact with low temperature fluid when high temperature fluid flows along the adjacent channel and with the high temperature fluid when the low temperature fluid flows along the adjacent channel). Next, referring to FIG. 1C, the high temperature channel part 20a along which the high temperature fluid flows is shown at the upper portion and the low temperature channel part 20b along which the low temperature fluid flows is shown at the lower portion. Comparing with FIG. 1B, the configurations illustrated in FIG. 1B and FIG. 1C are the same as each other in that the high temperature channel part 20a and the low temperature channel part 20b are alternately formed, but different from each other in the aspect of the formed positions of the channel parts. Thus, the configurations may be selectively specified during a process of fabricating the heat exchanger 20, if necessary. Referring to the right drawing of FIG. 1C, the power generating portion 20c3 that is connected to the N-type semiconductor and the P-type semiconductor to generate electricity is also shown. Besides, different methods of configuring the thermoelectric element can be employed, and thus the present invention may not be specifically limited to the illustrated method of configuring the thermoelectric element. Description of other components is similar/like to the description of FIG. 1B, and thus will be omitted for clarity of description. FIG. 2 is a conceptual view illustrating a passive safety system and a nuclear power plant having the same in accordance with one embodiment of the present invention. As illustrated in FIG. 2, a passive safety system, such as a passive containment cooling system, in accordance with one embodiment of the present invention includes a heat exchanger 120, a thermoelectric element 20c (see FIGS. 1B and 1C), and a fan unit 161a. The heat exchanger 120 is provided at an inner space of a hermetic containment 110, and configured to carry out a heat exchange of internal atmosphere of the containment 110 introduced therein so as to lower pressure or temperature of the atmosphere when an accident occurs in a reactor coolant system 112 or a secondary system arranged inside the hermetic containment 110. On the other hand, the heat exchanger 120 may selectively be arranged outside the containment 110, other than inside the containment 110. The thermoelectric element is arranged in the heat exchanger 120. As aforementioned, the thermoelectric element is arranged adjacent to the plate type heat exchanger 120. Also, the thermoelectric element produces electricity due to a temperature difference between the atmosphere and a cooling fluid 131 when the cooling fluid 131 and the atmosphere perform the heat exchange within the heat exchanger 120. That is, when an accident, such as an increase in temperature or pressure of the atmosphere inside the containment 110, occurs, the heat exchange between the atmosphere inside the containment 110 and the cooling fluid 131 is started in the heat exchanger 120. In this instance, the thermoelectric element arranged in the heat exchanger 120 generates electric power due to a temperature difference between the cooling fluid 131 and the atmosphere inside the containment 110. The generated electric power can be used as driving force for driving other components, which are provided for enhancing efficiency of the heat exchange or reducing the temperature or pressure of the atmosphere inside the containment 110, or driving force for operating other safety systems. The fan unit 161a is connected to the electricity path 163 such that the electricity produced from the thermoelectric element is supplied to the fan unit 161a. The fan unit 161a may be configured to increase a flow rate of the atmosphere inside the containment 110 or the cooling fluid outside the containment 110, which passes through the heat exchanger 120, so as to increase the heat transfer between the atmosphere and the cooling fluid 131 within the heat exchanger 120. In this embodiment, the heat exchanger 120 may be arranged inside the containment 110 such that the atmosphere inside the containment 110 is introduced directly into the heat exchanger 120. Also, the passive safety system according to this embodiment may further include an emergency cooling fluid storage section 130 and cooling fluid flow paths 141 and 142. The emergency cooling fluid storage section 130 is configured to store therein an emergency cooling fluid 131 which is introduced into the heat exchanger 120 for heat exchange with the atmosphere upon an occurrence of an accident. The cooling fluid flow paths 141 connect the emergency cooling fluid storage section 130 and the heat exchanger 120 to each other, such that the emergency cooling fluid 131 is introduced into the heat exchanger 120. Also, the fan unit 161a may be arranged above the heat exchanger 120 and blow the atmosphere inside the containment 110 into the heat exchanger 120, such that steam discharged from the reactor coolant system 112 or secondary system can be easily introduced into the heat exchanger 120 from a portion above the heat exchanger 120. That is, the fan unit 161a is disposed above the heat exchanger 120 and blows the atmosphere inside the containment 110 from the portion above the heat exchanger 120 toward the heat exchanger 120 when electric power is supplied. This is for increasing circulation efficiency of the atmosphere inside the containment 110 so as to enhance overall efficiency of the heat exchange carried out within the heat exchanger 120 because a heat exchange capability of the atmosphere inside the containment 110 is relatively lower than that of the emergency cooling fluid 131. Also, the heat exchanger 120 may further include an electricity path 163. The electricity path 163 is an electric line along which a current flows, such that the electricity is supplied from the thermoelectric element arranged in the heat exchanger 120 to be used for other components outside the heat exchanger 120. In addition, the electricity path 163 may include a charging unit 162 that is arranged on the electricity path 163 to store the electricity generated from the thermoelectric element and supply the stored electricity to the fan unit 161a. The charging unit 162 is disposed in a middle portion of the electricity path 163 along which the electricity generated from the thermoelectric element flows toward the fan unit 161a. When the electricity generated from the thermoelectric element is generated enough after supplying the fan unit 161a, the remaining electricity is stored in the charging unit 162. When the electricity generated from the thermoelectric element is less than electricity required for driving the fan unit 161a, a current sufficient for driving the fan unit 161a is supplied from the charging unit 162 to the fan unit 161a. Also, the charging unit 162 may be configured to drive the fan unit 161a at the beginning of an accident using the current stored therein before the accident, so as to allow a smooth operation of the heat exchanger 120 and thus mitigate the accident in an early stage. By the employment of the charging unit 162, the current can be sufficiently supplied in a stable state from the beginning of the heat exchange in the heat exchanger 120 to the long-term period of the heat exchange. Also, a nuclear power plant 100 according to one embodiment of the present invention includes a reactor coolant system 112 having a core of a reactor, a steam generator 113, a containment 110 protecting the reactor coolant system 112 to prevent a leakage of a radioactive material upon an occurrence of an accident, and a passive safety system, such as a passive containment cooling system, for preventing an increase in internal pressure of the containment 110 due to steam discharged from the reactor coolant system 112 or a secondary system upon the occurrence of the accident. The passive safety system includes a heat exchanger 120 disposed at an inner space of the containment 110, and configured to carry out a heat exchange of internal atmosphere of the containment 110 introduced therein so as to decrease pressure or temperature of the atmosphere when an accident occurs in the reactor coolant system 112 or a secondary system arranged inside the hermetic containment 110, a thermoelectric element disposed in the heat exchanger 120 and configured to produce electricity using a temperature difference between the atmosphere and the cooling fluid 131 when the cooling fluid 131 performs the heat exchange with the atmosphere within the heat exchanger 120, and a fan unit 161a connected to the thermoelectric element via an electricity path 163 to receive the electricity produced from the thermoelectric element and configured to increase a flow rate of the atmosphere inside the containment 110, which passes through the heat exchanger 120, so as to increase the heat exchange between the atmosphere and the cooling fluid 131 within the heat exchanger 120. A right figure of the drawing illustrates a normal operation state of the nuclear power plant, and a left figure of the drawing illustrates flows of various fluids and electricity upon an occurrence of an accident inside the containment 110. FIG. 3 is a conceptual view illustrating a passive safety system and a nuclear power plant having the same in accordance with another embodiment of the present invention. A passive safety system such as a passive containment cooling system according to this embodiment includes a heat exchanger 220, a thermoelectric element 20c (see FIG. 1B), an emergency cooling fluid storage section 230, cooling fluid flow paths 241 and 242 and a pump unit 261a. The heat exchanger 220, the thermoelectric element, the emergency cooling fluid storage section 230 and the cooling fluid flow paths 241 and 242 are similar/like to those illustrated in the foregoing embodiment, so description thereof will be omitted for clarity of explanation. The pump unit 261a of this embodiment is connected to the thermoelectric element via the electricity path 263 to receive the electricity produced from the thermoelectric element, and increase the heat exchange between the atmosphere and the emergency cooling fluid within the heat exchanger 220 or a flow of fluid which can lower the temperature of the atmosphere. The pump unit 261a is arranged on a cooling fluid flow path 241 as a flow channel along which the emergency cooling fluid 231 is introduced into the heat exchanger 220 from the emergency cooling fluid storage section 230. When the heat exchange is started in the heat exchanger 220, the electricity is supplied from the thermoelectric element disposed within the heat exchanger 220 to the pump unit 261a so as to drive the pump unit 261a such that the emergency cooling fluid 231 can be introduced at faster speed into the heat exchanger 220. In response to the pump unit 261a being driven, the emergency cooling fluid 231 is supplied well into the heat exchanger 220, and thus heat transfer efficiency between the emergency cooling fluid 231 and the atmosphere inside the containment 210 within the heat exchanger 220 is enhanced. Therefore, the temperature and pressure of the atmosphere inside the containment 210 can fast be reduced. The emergency cooling fluid supplied in the heat exchanger 220 is recirculated back into the emergency cooling fluid storage section 230 along the return cooling fluid flow path 242 that connects a top of the heat exchanger 220 to the emergency cooling fluid storage section 230 to allow the emergency cooling fluid to be returned into the emergency cooling fluid storage section 230. The returned emergency cooling fluid can be supplied again into the heat exchanger 220 by the pump unit 261a. Also, a nuclear power plant 200 according to this embodiment includes the reactor coolant system 212 having a core of a reactor, a steam generator 213, the containment 210 protecting the reactor coolant system 212 to prevent a leakage of a radioactive material upon an occurrence of an accident, and a passive safety system, such as a passive containment cooling system, for preventing an increase in internal pressure of the containment 210 due to steam discharged from the reactor coolant system 212 or a secondary system. The passive safety system includes a heat exchanger 220 disposed at an inner space of the containment 210, and configured to carry out a heat exchange of internal atmosphere of the containment 210 introduced therein so as to decrease pressure or temperature of the atmosphere when an accident occurs in the reactor coolant system 212 or a secondary system arranged inside the hermetic containment 210, a thermoelectric element disposed in the heat exchanger 220 and configured to produce electricity using a temperature difference between the atmosphere and the emergency cooling fluid, which performs heat exchange with the atmosphere upon an occurrence of an accident, when the emergency cooling fluid 231 performs the heat exchange with the atmosphere within the heat exchanger 220, an emergency cooling fluid storage section 230 storing therein the emergency cooling fluid introduced into the heat exchanger 220 for the heat exchange with the atmosphere, cooling fluid flow paths 241 and 242 connecting the emergency cooling fluid storage section 230 and the heat exchanger 220 to each other, respectively, such that the emergency cooling fluid is introduced into the heat exchanger 220, and a pump unit 261a connected to the thermoelectric element via an electricity path 263 to receive the electricity produced from the thermoelectric element, and configured to increase the heat exchange between the atmosphere and the emergency cooling fluid within the heat exchanger 220 or the flow of fluid for reducing the temperature of the atmosphere. Other components are similar/like to those of the foregoing embodiments, so description thereof will be omitted for clarity of explanation. FIG. 4 is a conceptual view illustrating a passive safety system and a nuclear power plant 300 having the same in accordance with another embodiment of the present invention. A passive safety system such as a passive containment cooling system according to this embodiment may be provided with a heat exchanger 320 that is disposed outside a containment 310 and configured to allow an introduction therein of atmosphere inside the containment 310 such that the atmosphere can perform a heat exchange. A fan unit 361a is disposed within the containment 310 to allow the atmosphere inside the containment 310 to be introduced into the heat exchanger 320. To this purpose, the passive safety system may include an internal atmosphere introduction flow path formed through the containment 310 to connect the inside of the containment 310 and the heat exchanger 320, such that the atmosphere inside the containment 310 can be introduced into the heat exchanger 320. Upon an occurrence of an accident inside the containment 310, the atmosphere inside the containment 310 is introduced into the heat exchanger 320 via the internal atmosphere introduction flow path. Also, the passive safety system may include an emergency cooling fluid storage section 330 storing therein an emergency cooling fluid 331 introduced into the heat exchanger 320 for the heat exchange with the atmosphere, and a circulation flow path 341, 342 along which the emergency cooling fluid circulates through the heat exchanger 320. Also, a fan unit 361a may be arranged within the containment 310 and located on the internal atmosphere introduction flow path through which the atmosphere inside the containment 310 is introduced into the heat exchanger 320. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described. When an accident occurs in the containment 310, temperature and pressure of the atmosphere inside the containment 310 may increase. In this instance, the atmosphere inside the containment 310 may be introduced into the heat exchanger 320 along the internal atmosphere introduction flow path, and the emergency cooling fluid storage section 330 may introduce the emergency cooling fluid into the containment 310 based on a related signal upon the occurrence of the accident. The atmosphere inside the containment 310 and the emergency cooling fluid perform the heat exchange within the heat exchanger 320, and electric power generated from the thermoelectric element arranged within the heat exchanger 320 is transferred to a charging unit 362 and the fan unit 361a. The fan unit 361a is arranged on the internal atmosphere introduction flow path within the containment 310 to blow fluid in one direction. The fan unit 361a is also configured to blow the atmosphere inside the containment 310 into the heat exchanger 320. Therefore, the atmosphere inside the containment 310 can be introduced well into the heat exchanger 320, and the heat exchange between the emergency cooling fluid and the atmosphere inside the containment 310 can be carried out more efficiently within the heat exchanger 320. Other components are similar/like to the foregoing embodiments, so description thereof will be omitted for clarity of explanation. FIG. 5 is a conceptual view illustrating a passive safety system and a nuclear power plant having the same in accordance with another embodiment of the present invention. A passive safety system such as a passive containment cooling system according to one embodiment, similar to the embodiment of FIG. 4, may include a heat exchanger 420 arranged outside the containment 410, and an internal atmosphere introduction flow path 464 formed through a containment 410 and connecting the inside of the containment 410 and the heat exchanger 420, such that atmosphere inside the containment 410 can be introduced into the heat exchanger 420. However, unlike the embodiment of FIG. 4, an emergency cooling fluid storage section and a cooling fluid flow path may not be provided. The passive safety system according to this embodiment may include a duct unit 329 having at least part of a flow channel thereof narrowed toward a portion above the heat exchanger 420, such that a cooling fluid outside the containment 410 is introduced into a lower portion of the heat exchanger 420 and flows through an upper portion of the heat exchanger 420. A fan unit 461a may be located inside the containment 410, and disposed on the internal atmosphere introduction flow path 464 such that the atmosphere inside the containment 410 is introduced into the heat exchanger 420. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described. Upon an occurrence of an accident, the atmosphere inside the containment 410 is introduced into the heat exchanger 420 through the internal atmosphere introduction flow path 464. A relatively low temperature cooling fluid outside the containment 410 (i.e., cooling fluid existing outside the containment to cool the internal atmosphere of the containment through heat exchange, in other words, external cooling fluid of the containment) is introduced into the heat exchanger 420 through the lower portion of the duct unit 429 surrounding the heat exchanger 420. Inside the heat exchanger 420, the heat exchange is performed between the atmosphere inside the containment 410 and the cooling fluid outside the containment 410. And, the heat-exchanged cooling fluid outside the containment 410 is discharged out through the upper portion of the duct unit 429. In this instance, as the upper portion of the duct unit 429 is formed such that the at least part of the flow channel is tapered, the cooling fluid outside the containment 410 is introduced well into the lower portion of the duct unit 429 according to a stack effect, and discharged out of the upper portion. When the heat exchange is started within the heat exchanger 420, electric power is generated from the thermoelectric element 20c (see FIG. 1B) arranged in the heat exchanger 420 due to a temperature difference between the atmosphere inside the containment 410 and the cooling fluid outside the containment 410. The generated electric power is transferred to the fan unit 461a and the charging unit 462 along the electricity path. Therefore, the fan unit 461a is driven. The fan unit 461a, as aforementioned, allows the atmosphere inside the containment 461a to be blown into the heat exchanger 420, so as to enhance the heat transfer efficiency within the heat exchanger 420. Other components are similar/like to those of the foregoing embodiments, so description will be given for clarity of explanation. FIG. 6 is a conceptual view illustrating a passive safety system and a nuclear power plant 500 having the same in accordance with another embodiment of the present invention. A nuclear power plant 500 disclosed herein includes a passive safety system such as a passive containment cooling system according to this embodiment. The passive safety system may include a fan unit 561a, a duct unit 529 and an atmosphere guiding unit 528. A heat exchanger 520 may be disposed inside a containment 510 and the fan unit 561a may be disposed outside the containment 510 such that a cooling fluid outside the containment 510 can be introduced into the heat exchanger 520 through an external cooling fluid flow path 564 which connects the heat exchanger 520 and the outside of the containment 510 to each other. In this embodiment, the cooling fluid which performs the heat exchange with the atmosphere inside the containment 510 (i.e., internal atmosphere of the containment) upon an occurrence of an accident corresponds to external atmosphere (i.e., external cooling fluid or external cooling atmosphere). The fan unit 561a blows the cooling fluid into a lower portion of the heat exchanger 520 arranged within the containment 510. The cooling fluid which has finished the heat exchange with the internal atmosphere of the containment 510 is discharged out of the containment 510 through an upper portion of the heat exchanger 520. The discharged cooling fluid is introduced into the duct unit 529 disposed outside the containment 510 and then discharged out of the duct unit 529. The lower portion of the duct unit 529 may be blocked. As the lower portion of the duct unit 529 is blocked, the external cooling fluid discharged into the duct unit 529 may be more effectively discharged through the upper portion of the duct unit 529. Also, since the upper portion of the duct unit 529 is formed high and the lower portion thereof is blocked, an effect similar to a stack effect may be generated, and accordingly, an amount of the external cooling fluid introduced into the heat exchanger 520 through the lower portion of the heat exchanger 520 may further increase. However, the duct unit 529 may not be installed according to a design characteristic of the nuclear power plant. Also, the passive safety system may further include the atmosphere guiding unit 528 which is formed at upper and lower sides of the heat exchanger 520 to allow the internal atmosphere of the containment 510 to be effectively introduced into or discharged out of the heat exchanger 520. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described. Upon an occurrence of an accident, high temperature or high pressure internal atmosphere of the containment 510 is introduced into the heat exchanger 520. And, external cooling fluid of the containment 510 is introduced into a lower portion of the heat exchanger 520. The introduced external cooling fluid and the internal atmosphere of the containment 510 perform the heat exchange within the heat exchanger 520. By virtue of the heat exchange, electric power is generated in the thermoelectric element 20c (see FIG. 1B) arranged within the heat exchanger 520. The generated electric power is supplied to the fan unit 561a, which is arranged on the external cooling fluid flow path 564 as a flow path along which the external cooling fluid of the containment 510 is introduced into the heat exchanger 520, and the charging unit 562. According to the generated electric power, the fan unit 561a is rotated by a motor 561b and the external cooling fluid of the containment 510 is introduced more well into the heat exchanger 520. The external cooling fluid increases in temperature while performing the heat exchange with the internal atmosphere of the containment 510 through the heat exchanger 520. The temperature-increased external cooling fluid is then discharged out of the containment 510 through the upper portion of the heat exchanger 520. The external cooling fluid discharged out of the containment 510 is introduced into the duct unit 529 arranged outside the containment 510 and discharged out through the upper portion of the duct unit 529. Other components are similar/like to those of the foregoing embodiments, so description will be given for clarity of explanation. FIGS. 7A and 7B are conceptual views illustrating a state during a normal operation and a state upon an occurrence of an accident, in relation to a passive safety system and a nuclear power plant 600 having the same in accordance with another embodiment of the present invention. FIG. 7A illustrates a normal operation state of the passive safety system and the nuclear power plant 600 according to one embodiment, and FIG. 7B is a conceptual view illustrating a state upon an occurrence of an accident in the embodiment illustrated in FIG. 7A. First, referring to FIG. 7A, a nuclear power plant according to one embodiment includes a passive safety system such as a passive containment cooling system. The passive safety system includes a heat exchanger 620 arranged within a containment 610, an emergency cooling fluid storage section 630, cooling fluid flow paths 641 and 642, and an external cooling fluid flow path 664 along which an external cooling fluid of the containment 610 is introduced into the heat exchanger 620, and a duct unit 629. Also, a fan unit 661a is disposed on the external cooling fluid flow path 664, such that the external cooling fluid of the containment 610 can be introduced into the heat exchanger 620. Other components are similar/like to those of the foregoing embodiments, so description will be given for clarity of explanation. Referring to FIG. 7B, a left drawing of FIG. 7B illustrates flows of fluid and electricity in the earliest stages of an accident, and a right drawing of FIG. 7B illustrates flows of fluid and electricity in the mid to late stages of the accident. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described, with reference to those drawings. in the earliest stages of the accident occurred within the containment 610, internal atmosphere of the containment 610 is introduced into the heat exchanger 620 and an emergency cooling fluid 631 stored in the emergency cooling fluid storage section 630 is introduced into the heat exchanger 620. Therefore, the emergency cooling fluid 631 can lower temperature and pressure of the internal atmosphere of the containment 610 at the beginning of the accident. Electric power generated from the thermoelectric element 20c (see FIG. 1B) through the heat exchange is supplied to the charging unit 662 and the fan unit 661a. In this instance, the emergency cooling fluid and the internal atmosphere of the containment 610 perform the heat exchange within the heat exchanger 620, and thus the fan unit 661a may not be driven. In the mid to late stages of the accident within the containment 610, the emergency cooling fluid stored within the emergency cooling fluid storage section 630 performs the heat exchange through the heat exchanger 620 and thereafter is totally discharged out of the containment 610 through a lower portion of the heat exchanger 620. Afterwards, the internal atmosphere of the containment 610 and an external cooling fluid of the containment 610 perform the heat exchange with each other. To this purpose, the fan unit 661a starts to be driven. As the fan unit 661a is driven, the external cooling fluid of the containment 610 is introduced more well into the heat exchanger 620, performs the heat exchange with the internal atmosphere of the containment 610 within the heat exchanger 620, and then is discharged out of the containment 610 through an upper portion of the heat exchanger 620. The external cooling fluid of the containment 610 discharged through the heat exchanger 620 is introduced into the duct unit 629 and then discharged out of an upper portion of the duct unit 629. The operations of the components and others are similar/like to those in the foregoing embodiments, so description thereof will be omitted for clarity of explanation. FIG. 8 is a conceptual view illustrating a state during a normal operation and a state upon an occurrence of an accident, in relation to a passive safety system and a nuclear power plant 700 having the same in accordance with another embodiment of the present invention. A nuclear power plant 700 according to this embodiment includes a passive safety system such as a combination of a passive residual heat removal system and a passive containment cooling system. The passive safety system includes a feedwater flow path 772, a steam flow path 774, a heat exchanger 720 disposed outside a containment 710, a duct unit 729 surrounding the heat exchanger 720 and having a flow channel with at least part narrowed (tapered) at an upper portion thereof, an internal atmosphere flow path along which internal atmosphere of the containment 710 is introduced into the heat exchanger 720, and a fan unit 761a disposed at an upper portion of the duct unit 729, to discharge internal atmosphere of the duct unit 729 to outside of the duct unit 729 so as to increase a flow rate of an external cooling fluid passing through the duct unit 729. Also, the passive safety system may further include a circulation increasing facility 780 facilitating an introduction of the internal atmosphere of the containment 710 into the heat exchanger 720. The feedwater flow path 772 forms a flow channel for injecting fluid into a steam generator 713 provided within the containment 710. The steam flow path 774 is a flow channel through which steam is discharged from the steam generator 713 to flow into a turbine system 773. The circulation increasing facility 780 may be a jet-pump type facility. The circulation increasing facility 780 may be configured to induce strong atmosphere flow (flow of steam) toward an inlet side of the internal atmosphere flow path such that the internal atmosphere of the containment 710 can be introduced into the heat exchanger 720 through the internal atmosphere flow path. Accordingly, non-condensable gas may not be accumulated around the heat exchanger 720 and a flow rate can increase, thereby remarkably increasing the efficiency of the heat exchanger 720. Also, an amount of circulated internal atmosphere of the containment 710 can greatly increase so as to effectively decrease the pressure and temperature. And, the aforementioned processes can bring about a circulation of the passive containment cooling system. In addition, the circulation increasing facility 780 may be connected to the steam flow path 774 as the flow channel of the turbine system 773 connected to the reactor coolant system 712. The circulation increasing facility 780 may receive the strong flow transferred from steam flow path 774. A condensed fluid storage section 750 may be provided below a discharge path 723 within the containment 710. The condensed fluid storage section 750 stores therein fluid condensed from atmosphere passed through the heat exchanger 720. The condensed fluid storage section 750 may be connected to the feedwater flow path 772 as a flow channel of a feedwater system 771 for injecting the fluid into the steam generator 713 provided within the reactor coolant system 712. Therefore, the fluid stored in the condensed fluid storage section 750 can be injected to the feedwater flow path 772. Through the aforementioned processes, a circulation of a secondary system of the passive residual heat removal system can be carried out. In detail, the condensed fluid stored in the condensed fluid storage section 750 is injected to the feedwater flow path 772, and thereafter transferred to the steam generator 713. In addition, steam generated in the steam generator 713 flows out along the steam flow path 774. The flowed-out steam is branched from the steam flow path 774 to flow into a flow path connected to the circulation increasing facility 780. Accordingly, the steam generated in the steam generator 713 can be supplied into the circulation increasing facility 780, so as to be introduced into an introduction flow path 764 through which the internal atmosphere of the containment 710 is introduced into the heat exchanger 720. Through the aforementioned processes, the internal atmosphere (or steam) of the containment 710 is introduced into the heat exchanger 720 together with the steam generated from the steam generator 713. And, the steam generated from the steam generator 713 and an external cooling fluid of the containment 710, which can perform heat exchange with the internal atmosphere of the containment 710, are introduced into the heat exchanger 720. The external cooling fluid is introduced into a lower portion of the duct unit 729 surrounding the heat exchanger 720, introduced into the heat exchanger 720 and then flows up along a flow path. The flowed-up external cooling fluid is discharged out of an upper portion of the heat exchanger 720 and then flows through an upper portion of the duct unit 729. In this instance, the fan unit 761a is disposed at the upper portion of the duct unit 729, to allow internal atmosphere of the duct unit 729 to be discharged out of the duct unit 729. The fan unit 761a may be driven by using electric power generated through the heat exchange within the heat exchanger 720. Also, the fan unit 761a may be arranged at an arbitrary appropriate position on the duct unit 729. The operations of the components and others are similar/like to those in the foregoing embodiments, so description thereof will be omitted for clarity of explanation. FIG. 9 is a conceptual view illustrating a state during a normal operation and a state upon an occurrence of an accident, in relation to a passive safety system and a nuclear power plant 800 having the same in accordance with another embodiment of the present invention. A nuclear power plant 800 according to another one embodiment includes a passive safety system such as a passive containment cooling system and a feedwater system. The passive safety system may include a heat exchanger 820 arranged within a containment 810, an emergency cooling fluid storage section 830 supplying a cooling fluid 831 to the heat exchanger 820 upon an occurrence of an accident, a cooling fluid storage section 891, a spray device 895, and a pump unit 861a. The cooling fluid storage section 891 is formed within the containment 810, and stores a cooling fluid 892 for reducing internal pressure or temperature of the containment 810. The cooling fluid storage section 891 is provided separate from the emergency cooling fluid storage section 830. The spray device 895 may be disposed at an upper side within the containment 810. And, when an accident occurs within the containment 810, the spray device 895 may receive the cooling fluid and spray the received cooling fluid into the containment 810. The pump unit 861a is arranged on a fluid supply channel 893 which connects the cooling fluid storage section 891 and the spray device 895. When the pump unit 861a is driven, the cooling fluid stored in the cooling fluid storage section 891 is supplied to the spray device 895 to be sprayed out. Also, a second cooling fluid storage section 894 in which the cooling fluid supplied from the cooling fluid storage section 891 by the pump unit 861a is temporarily stored may be formed at an upper portion of the spray device 895 within the containment 810. However, unlike the configuration illustrated in the drawing, the second cooling fluid storage section 894 may not be provided. In this instance, the fluid supplied by the pump unit 861a may immediately be supplied to the spray device 895 to be sprayed out. Other components are similar/like to those of the foregoing embodiments, so description will be omitted for clarity of explanation. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described. Upon an occurrence of an accident, a cooling fluid stored in the emergency cooling fluid storage section 830 is supplied into the heat exchanger 820. The internal atmosphere of the containment 810 is introduced into the heat exchanger 820 to perform a heat exchange with the cooling fluid. During this process, electric power generated by the thermoelectric element is supplied to the pump unit 861a and a charging unit disposed adjacent to the cooling fluid storage section 891. The cooling fluid supplied to the heat exchanger 820 is then supplied back to the emergency cooling fluid storage section 830 through a return flow path 842. The cooling fluid storage section 891 is connected to the second cooling fluid storage section 894 via the fluid supply channel 893. The pump unit 861a is arranged on the fluid supply channel 893. As the pump unit 861a is driven, the cooling fluid stored in the cooling fluid storage section 891 may be supplied into the second cooling fluid storage section 894. The cooling fluid supplied to the second cooling fluid storage section 894 may be sprayed into the containment 810 through the spray device 895. Internal temperature or pressure of the containment 810 can be decreased by virtue of the spraying of the spray device 895. The operations of the components and others are similar/like to those in the foregoing embodiments, so description will be omitted for clarity of explanation. FIG. 10 is a conceptual view illustrating a state during a normal operation and a state upon an occurrence of an accident, in relation to a passive safety system and a nuclear power plant 900 having the same in accordance with another embodiment of the present invention. A nuclear power plant 900 according to this embodiment includes a passive safety system such as a passive containment cooling system. The passive safety system is similar to that illustrated in the embodiment of FIG. 9. However, the passive safety system according to this embodiment does not include a spray device and a second cooling fluid storage section, but includes an emergency cooling fluid storage section 930, a heat exchanger 920 arranged within a containment 910, a cooling fluid storage section 991, a fluid supply channel 993, and a pump unit 961a arranged on the fluid supply channel 993. Also, the passive safety system further includes a condensate storage section 950 for storing condensate which is generated as temperature of the atmosphere inside the containment 910 supplied into the heat exchanger 920 is decreased. The fluid supply channel 993 is configured to connect the cooling fluid storage section 991 and the condensate storage section 950. Other components are similar/like to those of the foregoing embodiments, so description will be given for clarity of explanation. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described. Upon an occurrence of an accident, an emergency cooling fluid 931 stored in the emergency cooling fluid storage section 930 is introduced into a lower portion of the heat exchanger 920, discharged through an upper portion of the heat exchanger 920, and then returned back into the emergency cooling fluid storage section 930. The internal atmosphere of the containment 910 is introduced into an upper portion of the heat exchanger 920, and then discharged through a lower portion of the heat exchanger 920. The condensate is generated in response to temperature drop while the internal atmosphere of the containment 910 is introduced and discharged. The condensate is collected in the condensate storage section 950 arranged below the heat exchanger 920. Also, electric power generated from the heat exchanger 920 is supplied to the pump unit 961a, which are arranged on the fluid supply channel 993 connecting the cooling fluid storage section 991 and the condensate storage section 950 to each other, and a charging unit 962. When the pump unit 961a is driven, the cooling fluid stored in the cooling fluid storage section 991 is transferred to the condensate storage section 950. The condensate storage section 950 collects therein the condensate discharged from the heat exchanger 920 and the cooling fluid stored in the cooling fluid storage section 991. The collected fluid may be injected into the reactor cooling system through a safety injection system. However, unlike the configuration illustrated in the drawing, the condensate storage section 950 may not be provided. In this instance, the fluid supplied from the pump unit 961a may be directly supplied into the safety injection system, thereby being used for safety injection. FIG. 11 is a conceptual view illustrating a state during a normal operation and a state upon an occurrence of an accident, in relation to a passive safety system and a nuclear power plant 1000 having the same in accordance with another embodiment of the present invention. A nuclear power plant 1000 according to another embodiment includes a passive safety system such as a passive containment cooling system. The passive safety system includes a cooling fluid storage section 1091 installed outside a containment 1010, and a fluid supply channel 1093 connecting the cooling fluid storage section 1091 to an emergency cooling fluid storage section 1030. However, unlike configuration illustrated in the drawing, the cooling fluid storage section 1091 may also be installed inside the containment 1010. Other components are similar/like to those of the foregoing embodiments, so description will be given for clarity of explanation. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described. Upon an occurrence of an accident, the cooling fluid stored in the emergency cooling fluid storage section 1030 is introduced into a lower portion of the heat exchanger 1020, discharged through an upper portion of the heat exchanger 1020, and then returned back into the emergency cooling fluid storage section 1030. Internal atmosphere of the containment 1010 is introduced into the upper portion of the heat exchanger 1020 and then discharged through the lower portion of the heat exchanger 1020. Electric power generated during this process is supplied to a pump unit 1061a and a charging unit which are arranged on the fluid supply channel 1093 connecting the cooling fluid storage section 1091 to the emergency cooling fluid storage section 1030. When the pump unit 1061a is driven, the cooling fluid stored in the cooling fluid storage section 1091 is supplied into the emergency cooling fluid storage section 1030. The cooling fluid stored in the emergency cooling fluid storage section 1030 is returned after supplied into the heat exchanger 1020. However, temperature of the cooling fluid may increase during the heat exchange and thus the cooling fluid may be evaporated. Due to the evaporation, a water level of the cooling fluid stored in the emergency cooling fluid storage section 1030 may be decreased. In this instance, when the pump unit 1061a is driven, the cooling fluid stored in the cooling fluid storage section 1091 is supplied to the emergency cooling fluid storage section 1030. Also, when a predetermined water level of the cooling fluid within the emergency cooling fluid storage section 1030 is maintained, even though power can be supplied sufficiently to a charging unit 1062, the pump unit 1061a could not be driven by a related signal. This is for preventing the cooling fluid from flowing over the emergency cooling fluid storage section 1030 owing to the driving of the pump unit 1061a. Accordingly, an amount of the cooling fluid stored in the emergency cooling fluid storage section 1030 can be maintained for a long term of time, which may result in increasing a time for carrying out the heat exchange. The operations of the components and others are similar/like to those in the foregoing embodiments, so description will be omitted for clarity of explanation. FIG. 12 is a conceptual view illustrating a state during a normal operation and a state upon an occurrence of an accident, in relation to a passive safety system and a nuclear power plant 1100 having the same in accordance with another embodiment of the present invention. A nuclear power plant 1100 according to another embodiment includes a passive safety system such as a passive containment cooling system. The passive safety system includes a feedwater flow path 1172, a steam flow path 1174, a heat exchanger 1120 arranged outside a containment 1110, a duct unit 1129 surrounding the heat exchanger 1120, and a fan unit 1161a. The heat exchanger 1120 may be arranged outside the containment 1110. The heat exchanger 1120 may receive steam supplied along the steam flow path 1174 and discharge condensate, which has passed through the heat exchanger 1120, through the feedwater flow path 1172. The duct unit 1129 is configured such that an external cooling fluid is introduced into a lower portion of the heat exchanger 1120 to be discharged through an upper portion of the heat exchanger 1120. The duct unit 1129 may be formed such that at least part of a flow channel thereof is narrowed (tapered) toward an upper portion. The fan unit 1161a may be disposed within an upper portion of the duct unit 1129. The fan unit 1161a may allow the cooling fluid within the duct unit 1129 to be blown out through the upper portion thereof, such that the external cooling fluid of the containment 1110 can much faster flow within the duct unit 1129. This embodiment illustrates that the fan unit 1161a is disposed within the upper portion of the duct unit 1129, but the fan unit 1161a may alternatively be arranged at an appropriate position of the duct unit 1129 according to a design characteristic of the nuclear power plant. Other components are similar/like to those of the foregoing embodiments, so description will be given for clarity of explanation. Hereinafter, an operation of the passive safety system according to this embodiment upon an occurrence of an accident will be described. The heat exchanger 1120 is arranged outside the containment 1110. The steam flow path 1174 is connected directly to the upper portion of the heat exchanger 1120, such that steam can be introduced directly into the upper portion of the heat exchanger 1120 along the steam flow path 1174 upon an occurrence of an accident. And, the lower portion of the heat exchanger 1120 is connected directly to the feedwater flow path 1172 and thus the steam passed through the heat exchanger 1120 is discharged directly into the feedwater flow path 1172. The fan unit 1161a is arranged in an upper portion of the duct unit 1129. When electric power is supplied from the thermoelectric element arranged in the heat exchanger 1120, the fan unit 1161a blows air within the duct unit 1129 to be well discharged out of the duct unit 1129. Accordingly, a flow rate of the external cooling fluid which is introduced into the lower portion of the duct unit 1129 and then introduced into the heat exchanger 1120 increases, and efficiency of the heat exchanger 1120 is enhanced accordingly. The passive safety system and the nuclear power plant having the same described above may not be limited to the configurations and methods of the foregoing embodiments, but a part or all of the embodiments can selectively be combined to make various modifications. The embodiments of the present invention propose a passive safety system having a plate type heat exchanger provided therein a thermoelectric element producing electricity by a temperature difference, and a nuclear power plant having the passive safety system, and thus can be applied to various related industrial fields.
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	summary
045129398	description	DETAILED DESCRIPTION OF THE INVENTION A method for manufacturing oxidic sintered nuclear fuel bodies of the type mentioned at the outset is characterized according to the invention by the features that UO.sub.2 -starting powder is used for compacting which has a specific surface in the range of 2 to 4.5 m.sup.2 /g and/or a mean crystallite diameter in the range of 80 to 250 nm, and that the heat treatment is performed in the sintering atmosphere with reducing action at a temperature in the range of 1,500.degree. C. to 1,750.degree. C. It was found that UO.sub.2 -starting powder with such a relatively small specific surface and/or such a relatively large mean crystallite diameter which is not particularly fine-pore and therefore cannot be densified easily, shows a great readiness to be densified at relatively high heat treatment temperatures if it contains rare-earth oxide such as Gd.sub.2 O.sub.3 as an admixture. A heat treatment in a sintering atmosphere with oxidizing action before or also after the heat treatment in the sintering atmosphere with the reducing action can be omitted without impairing the sintering density of the sintered nuclear fuel bodies obtained from the UO.sub.2 -starting powder. While it is customary to process UO.sub.2 -starting powder into oxidic sintered nuclear fuel bodies containing rare earth elements, it was not possible to compact this UO.sub.2 -starting powder directly and to subject it to a heat treatment for sintering purposes. The UO.sub.2 -starting powder had to be milled first in order to obtain a high sintering density of the sintered nuclear fuel bodies, forming a mean surface larger than 4.5 m.sup.2 /g and a mean crystallite diameter larger than 250 nm, then mixed with rare-earth oxide in powder form, precompacted and subsequently granulated to fluid and extrudable granulates. Only these granulates were compacted into blanks which were finally subjected to a heat treatment for sintering purposes, forming the sintered nuclear fuel bodies. Such pregranulation of the UO.sub.2 -starting powder can likewise be eliminated, in contrast thereto, in the method according to the invention. The UO.sub.2 -starting powder which can be used for the method according to the invention may be ungranulated uranium dioxide powder directly obtained by the so-called ADU method according to "Gmelin Handbuch der Anorganischen Chemie", Uranium, Supplement Volume A3, pages 99 to 101, 1981. However, ungranulated uranium dioxide powder obtained by the so-called AUC method according to "Gmelin Handbuch der Anorganischen Chemie, Urnaium, Supplement Volume A3, pages 101 to 104, 1981, can also be used if the residence times of the powder under pyrohydrolysis conditions were chosen accordingly. It is economical to hold, in the method according to the invention, the temperature of the blanks during the heat treatment for a holding period in the range of one hour to ten hours. In this time period, an optimum density of the sintered nuclear fuel bodies is obtained; a heat treatment of longer duration does not improve this density but may, under some conditions, lead to a swelling of the sintered nuclear fuel bodies. It is furthermore advantageous to heat the blanks to the temperature of the heat treatment at a heating-up rate in the range of 1.degree. C./min to 10.degree. C./min. This assures sufficient time is provided for the densification processes which begin in the blanks already in the heating-up phase. The invention and its advantages will be explained in greater detail by a comparison example and two embodiment examples: As the comparison example, ungranulated UO.sub.2 -starting powder with a specific surface of 6.6 m.sup.2 /g and a mean crystallite diameter of 30 nm, obtained by the AUC method according to the Gmelin Handbuch, was mixed with 6.5% by weight Gd.sub.2 O.sub.3 -powder and compacted into blanks with a blank density of 5.6 g/cm.sup.3. These blanks were then heated in a sintering furnace in a pure hydrogen atmosphere with reducing action at a heating-up rate of 10.degree. C./min to 1,750.degree. C. and held at this temperature for two hours. After cooling down, the sintered nuclear fuel bodies obtained from the so-treated blanks had a density of 9.81 g/cm.sup.3, which corresponds to 91.7% of their theoretically possible density. As the first embodiment example, ungranulated UO.sub.2 -starting powder prepared by the AUC method according to the Gmelin Handbuch was likewise used, which, however, had been brought through an increased residence time under pyrohydrolysis conditions to a specific surface of 5.3 m.sup.2 /g and a mean crystallite diameter of 110 nm. This ungranulated UO.sub.2 starting powder was likewise compacted, after mixing with 6.5% by weight Gd.sub.2 O.sub.3 powder, into blanks with a density of 5.6 g/cm.sup.3, which were heated up and sintered under the same conditions as in the comparison example. From the blanks treated in this manner were obtained sintered nuclear fuel bodies with a density of 10 g/cm.sup.3, i.e., 93.4% of the theoretically possible density. In a second embodiment example, UO.sub.2 -starting powder obtained by the AUC method according to the Gmelin Handbuch was again used ungranulated, the dwelling or residence time under pyrohydrolysis conditions of which, however, was so long that a specific surface of 4.4 m.sup.2 /g and a mean crystallite diameter of 140 nm was obtained. This UO.sub.2 -starting powder was mixed with 6.5% by weight Gd.sub.2 O.sub.3 -powder and compacted into blanks with a density of 5.6 g/cm.sup.3, which were subsequently subjected to the same sintering conditions as in the comparison example and the first embodiment example. The sintered nuclear fuel bodies so obtained had a density of 10.17 g/cm.sup.3, which corresponds to 95.1% of their theoretically possible density.
	abstract	Chemical control system for a power plant including at least one coolant electrochemical indication sensor of a flow type electrically connected to the measurement data processing and transmission unit with its outlet connected to a central computer (CPC) controlling the actuator for injection of hydrogen and chemical reagents. The hydraulic inlet of the electrochemical sensor in use of the system is connected by a sampling tube to the power plant process circuit and its hydraulic outlet is hydraulically connected to the first heat exchanger and the first throttling device with a coolant supply circuit in series. The sampling tube is configured to pass a coolant sample to the coolant electromechanical sensor and the coolant supply circuit contains tubes and valves configured to reverse the flow of the coolant sample through the first throttling device.
053965256	summary	FIELD OF THE INVENTION The invention relates to a method and a device for repairing the internal surface of an adapter of tubular shape passing through the head of the vessel of a nuclear reactor cooled by pressurized water. BACKGROUND OF THE INVENTION Pressurized-water nuclear reactors generally comprise a vessel enclosing the core of the reactor which is immersed in the pressurized cooling water of the reactor. The vessel of the reactor of overall cylindrical shape comprises a head of hemispherical shape which may be attached onto its upper part. The head is pierced with openings in the region of each of which there is fastened, by welding, a tubular penetration piece constituting an adapter providing the passage for and controlling the movement of an extension of a control cluster for the reactivity of the core or a penetration passage for means for measurement inside the core, such as a thermocouple column. To the end parts of each of the adapters, there are fastened mechanisms for controlling movement of the control clusters for the reactivity of the core. Inside each of the tubular penetrations of the vessel head there is fastened, in a position which is coaxial with respect to the tubular penetration piece and with a certain radial clearance, a thermal sleeve which comprises a diametrically flared part coming to rest on a diametrically flared bearing surface located at the upper part of the bore of the tubular penetration piece and which is mounted to rotate freely inside the penetration piece. The extensions of the rods for controlling the reactivity of the nuclear reactor and the thermocouple columns pass through the vessel head inside thermal sleeves which are themselves arranged coaxially inside adapters for the control rods or more generally inside tubular penetration pieces of the head. In order to increase the reliability and operational safety of nuclear reactors and to extend the durability of these reactors, plant operators are led to carry out more and more numerous inspections of the various elements making up the nuclear reactor. In particular, it may be necessary to inspect the state of the penetration pieces of the head of the vessel in order to be sure of the integrity of these pieces after the reactor has been in operation for a certain time, in particular in the zone where these tubular pieces are welded to the head. As a function of the result of the inspection, detected faults may be repaired, by excavating the internal surface of the adapter in the zone having a fault and by building back up the cavity produced by excavation. In French Patent Application No. 92 02405 filed by FRAMATOME and Electricite de France on Feb. 28, 1992, it was proposed to carry out an inspection of the internal surface of the adapter using ultrasound or eddy currents, through a slit machined in the thermal sleeve in its longitudinal direction. It was also proposed to carry out excavation by machining through the slit, when a crack is detected on the internal surface of the adapter. In French Patent Application No. 92 02405, filed on Aug. 6, 1992 by FRAMATOME, it was also proposed to excavate zones having faults by machining the internal surface of the adapter to a slit made in the thermal sleeve using a jet of pressurized abrasive liquid. These methods make it possible to inspect and, if necessary, repair faults without dismantling the thermal sleeve arranged inside the adapter. However, such methods do not make it possible perfectly to characterise the faults detected and in particular to determine whether these faults extend deeply into the wall of the adapter, and, for this reason, whether they are likely to pass through this wall or to develop so as to become penetrant. By using the methods according to the prior art, one may be led to carry out repairs with excavation and building back up, which are not strictly necessary for the safety of the nuclear reactor. Neither do the inspections carried out make it possible to determine very precisely the location, extent and geometric shape of the faults detected. SUMMARY OF THE INVENTION The object of the invention is to propose a method for repairing the internal surface of an adapter of tubular shape passing through the head of the vessel of a nuclear reactor cooled by pressurized water and fastened to the head by a weld, which makes it possible to repair the adapter in, and only in, each zone of the internal wall of the adapter having faults likely to decrease the safety of the nuclear reactor. To this end: a detection and inspection of cracks on the internal surface of the adapter is carried out, at least in a zone close to the weld, using remote inspection operations comprising at least one dye penetration inspection with remote borescope examination of the cracks revealed by the dye penetration, PA1 at least one excavation cavity is made by machining to a specified depth of each of the zones of the internal surface of the adapter having a crack, and PA1 as a function of the result of the dye penetration inspection in each of the zone having a crack, the zone is or is not built back up after excavation. The invention also relates to a device for repairing the internal surface of an adapter comprising means making it possible successively to bring faults to light by dye penetration, to examine the faults brought to light using a borescope, to excavate the zones of the internal surface of the adaptor having faults and to build the zones back up after excavation.
	abstract	A zirconium alloy suitable for forming reactor components that exhibit reduced irradiation growth and improved corrosion resistance during operation of a light water reactor (LWR), for example, a boiling water reactor (BWR). During operation of the reactor, the reactor components will be exposed to a strong, and frequently asymmetrical, radiation fields sufficient to induce or accelerate corrosion of the irradiated alloy surfaces within the reactor core. Reactor components fabricated from the disclosed zirconium alloy will also tend to exhibit an improved tolerance for cold-working during fabrication of the component, thereby simplifying the fabrication of such components by reducing or eliminating subsequent thermal processing, for example, anneals, without unduly degrading the performance of the finished component.
	claims	1. A method operating in conjunction with a pressurized water reactor (PWR) including a nuclear reactor core comprising fissile material disposed in a reactor pressure vessel also containing primary coolant water, a pressurizer integral with or operatively connected with the reactor pressure vessel and configured to control pressure in the reactor pressure vessel, and a refueling water storage tank (RWST), the method comprising responding to a loss of heat sinking of the PWR by operations including:driving a turbine using steam piped from the pressurizer; anddriving a pump using the turbine to suction water from the RWST into the reactor pressure vessel. 2. The method of claim 1 wherein the driving of the pump comprises providing a common shaft mechanically connecting the turbine and the pump whereby the driven turbine rotates the common shaft to drive the pump. 3. The method of claim 1 further comprising:discharging steam piped from the pressurizer into a pressurized passive condenser; andconnecting the suction side of the pump to both the RWST and the pressurized passive condenser wherein the driving of the pump also suctions water from the pressurized passive condenser into the reactor pressure vessel.
058752218	claims	1. In a boiling-water reactor with a reactor core, a method of monitoring the reactor core for an unstable state caused by a local oscillation of a physical variable, the method which comprises: a) disposing a plurality of sensors each in a plurality of regions of a reactor core and measuring with the sensors a physical variable which is subject to local oscillations; combining output signals of the sensors into a given number of region channels and assigning to each region channel a region and the sensors disposed in the region for generating a region signal; b) combining the region channels into a given number of system channels and generating a system signal; and c) assigning the system signals to an output channel and generating an output signal in the output channel; d) setting, with monitoring stages and selection stages, an alarm output signal in each output channel if a monitoring criterion is satisfied in at least a predefined number of the system channels over a plurality of oscillation periods in a minimum number Nmp of the respective system channel; e) connecting the sensors such that an output signal of each sensor influences only a single region signal, and each region signal influences only a single system signal; and f) forming the region signals of each system channel from the output signals of those sensors which are located in regions distributed over a cross section of the reactor core in such a way that the regions which are respectively adjacent to such a region contain sensors, the output signals of which are assigned to region channels of other system channels. a system selection stage, a plurality of region selection stages connected to said system selection stage, a given number of region monitoring stages connected to each said region selection stage, and a sensor stage connected to each said region monitoring stage with a plurality of sensors strategically disposed in regions of a reactor core of a boiling water reactor, wherein a) measured signals supplied by said sensors to a respective said region monitoring stage are combined into a region signal for the physical variable; each said region signal is monitored in the respective said region monitoring stage in accordance with a monitoring criterion, and a region signal containing a region monitoring signal is output by each region monitoring stage; b) each region signal is connected to at least one of said region selection stages, and said region selection stages forming respective system monitoring signals from a predefined minimum number of region monitoring signals; and c) said region selections stages each outputting a respective system monitoring signal to said system selection stage, and said system selection stage outputting an output monitoring signal according to a predefined minimum number of systems. 2. In a boiling-water reactor having a reactor core, a device for monitoring the reactor core with respect to local oscillations of a physical variable causing an unstable state of the reactor, which comprises:
	summary
051005859	description	DETAILED DESCRIPTION OF THE INVENTION These and other objects of the invention for the recovery of strontium and technetium values from an aqueous nitric acid feed solution containing these and other fission product values may be met by preparing an extractant of about 0.2M bis-4,4'(5')[(t-butyl)cyclohexano]-18-Crown-6 (Dt-BuCH18C6) in 1-octanol as a diluent, contacting the extractant with the aqueous solution which is up to 6M in nitric acid, maintaining the contact for a period of time sufficient for the strontium and technetium values to be taken up by the extractant, and separating the extractant from the aqueous solution, thereby separating the strontium and technetium values from the aqueous solution. The macrocyclic polyether may be any of the dicyclohexano crown ethers such as dicyclohexano-18-Crown-6, dicyclohexano 21-Crown-7, or dicyclohexano-24-Crown-8. The preferred crown ethers have the formula: 4,4'(5')[(R,R')dicyclohexano]-18-Crown-6, where R and R' are one or more members selected from the group consisting of H and straight chain or branched alkyls containing 1 to 12 carbons. Examples include, methyl, propyl, isobutyl, t-butyl, hexyl, and heptyl. The preferred ethers include dicyclohexano-18-crown-6 (DCH18C6) and bis-methylcyclohexano-18-crown-6 (DMeCH18C6). The most preferred ether is bis-4,4'(5')[(t-butyl)cyclohexano]-18-Crown-6 (Dt-BuCH18C6). The amount of crown ether in the diluent may vary depending upon the particular form of the ether. For example a concentration of about 0.1 to 0.5M of the t-butyl form in the diluent is satisfactory, with 0.2M being the most preferred. When the hydrogen form is used, the concentration may vary from 0.25 to 0.5M. Concentrations above about 0.5M of the ether in the diluent will not improve strontium recovery when R and R' are H. The diluent is an organic compound which has a high boiling point, i.e. about 170.degree. to 200.degree. C., limited or no solubility in water, is capable of dissolving from about 0.5 to 6.0M water, and in which the crown ether is soluble. These diluents include alcohols, ketones, carboxylic acids and esters. Suitable alcohols include 1-octanol, which is most preferred, although 1-heptanol and 1-decanol are also satisfactory. The carboxylic acids include octanoic acid, which is preferred, in addition to heptanoic and hexanoic acids. Ketones which meet the criteria may be either 2-hexanone or 4-methyl-2-pentanone, while the esters include butyl acetate and amyl acetate. One required characteristic of the diluent is that it must be able to dissolve a minimum amount of water. This amount varies with the particular diluent. For alcohols and carboxylic acids the amount of water may vary from about 1.0 to 6.0M, while ketones and esters should dissolve from about 0.5 to 1.0M of water. Although diluents capable of dissolving larger quantities of water are satisfactory from the process standpoint, their use may result in greater losses of extractant and diluent during the process. While we do not wish to be bound by this explanation, it appears that the reason for the low distribution values of strontium in the non water-dissolving diluents is that the nitrate anion remains hydrated on extraction because of the low charge density of Sr.sup.2+. Hydrated anions are hydrophilic and thus will not readily transfer into a lipophilic medium. By the use of a diluent which can contain dissolved water, an environment is provided in which the anion need not dehydrate to be solvated. By avoiding anion dehydration, additional free energy of extraction is achieved. It is not necessary that the diluent be saturated with water before contact of the extractant with the aqueous nitric acid containing waste solution because the water for dissolution in the diluent is obtained from the aqueous waste feed solution. The volume ratio between the organic extractant and the aqueous acid feed solution depends upon the particular extractant system, i.e. the particular crown ether and diluent system. Generally these ratios may vary from about 1:1 to 1:4. For the extractant system consisting of bis-4,4'(5')[(t-butyl)cyclohexano]-18-Crown-6 in 1-octanol, the preferred ratio is 1:3. For dicyclohexano-18-crown-6, a 1:2 ratio is preferred. The extraction process is preferably run at ambient temperature since higher temperatures have little effecttion on extraction. Contact times at ambient temperature are short, typically on the order of about 0.5 minutes to provide complete extraction of the strontium and technetium values. Stripping the extracted strontium and technetium values from the extractant can be readily accomplished by contacting the extractant with water. A major advantage of the process of the invention is the stability of the crown ether-diluent systems to radiolysis. Exposure of DCH18C6 in octanol to an absorbed dose of 10 watt-hours/liter showed no change in strontium distribution ratios on extraction and stripping and on phase disengagement time. It is believed that any radiolytic degradation products formed are water soluble and therefore would be removed during extraction, scrubbing, and stripping cycles. The following examples are given to illustrate the invention but are not to be taken as limiting the scope of the invention which is defined in the appended claims. EXAMPLES The crown ethers dicyclohexano-18-crown-6 (DCH8C6) (99% pure), and bis-4,4'(5)[(t-butyl)cyclohexano]-18-crown-6 (Dt-BuCH18C6) were used without further purification. The extraction of HNO.sub.3 by the various solvents was measured by equilibrating the organic phase four times with a 1M HNO.sub.3 solution using an organic to aqueous phase ratio of 3. The resultant organic phase was stripped of acid by repeated water washings and the washings titrated with standard sodium hydroxide. All distributions of Sr were measured radiometrically. Prior to a distribution experiment, the organic phase was pre-equilibrated by contacting it 2-3 times with twice its volume of 1M HNO,. A 1.00 mL aliquot of this pre-equilibrated organic phase was then combined with an equal volume of fresh 1M HNO, spiked with .sup.85 Sr. The two phases were mixed using a vortex mixer for one minute, then centrifuged until complete phase separation was obtained. The .sup.85 Sr activity in each phase was measured by gamma counting using a Beckman Biogamma Counter. All measurements were performed at 25.+-.0.5.degree. C. EXAMPLE 1 A series of experiments were made to correlate the distribution of strontium with the molarity of water in a variety of diluents. 1 ml portions of 0.5M DCH18C6 or 0.1M Dt-BuCH18C6 in the various organic diluents were contacted with 1.0M HNO.sub.3 spiked with .sup.85 Sr. The results, grouped by diluent types, are shown in FIGS. 1 and 2 respectively. They show the positive effect of increasing water content in the diluent on the strontium extraction constant. EXAMPLE 2 Another series of experiments were run in the manner described above in order to determine the influence of acidity on the distribution ratios of the inert constituents and fissions products contained in a synthetic dissolved waste sludge (DWS) using 0.375M DCH18C6 and 0.125M Aliquat in octanoic acid. Aliquat 336, which is tricaprylylmethylammonium nitrate, was introduced into the organic phase to create an environment more favorable for ion pair formation. The results are shown in Table 1 below. TABLE 1 ______________________________________ Effect of Acidity Upon distribution Ratios of DSW Constituents System: 0.375 --M DCH18C6/0.125 --M Aliquat 336 in OA vs. DSW @ Various HNO.sub.3) Concentrations. Distribution Ratios 1 M 3 M 6 M ______________________________________ Inert Constituents Na 0.37 0.41 0.21 Mg 0.14 0.09 0.05 Al 0.14 0.10 0.06 Ca 0.15 0.17 0.19 Cr 0.14 0.10 0.06 Mn 0.14 0.10 0.06 Fe 0.14 0.10 0.06 Ni 0.14 0.10 0.06 Cu 0.14 0.10 0.06 Fission Products Sr 2.4 3.8 5.8 Y 0.14 0.09 0.06 Zr 0.09 0.10 0.12 Mo 0.15 0.12 <0.10 Ru 0.17 0.15 0.11 Rh 0.15 0.10 <0.06 Pd 0.20 <0.20 <0.24 Ag <0.20 <0.20 <0.20 Cd 0.14 <0.11 <0.13 Cs 0.27 0.16 0.03 Ba 1.4 1.9 2.2 La 0.14 0.10 0.08 Ce 0.14 0.12 0.08 Pr 0.14 0.09 0.07 Nd 0.17 0.13 0.10 Sm 0.13 0.07 0.05 Eu 0.14 0.10 0.07 ______________________________________ The data show that only Sr, Ba, and Zr distribution ratios increase with acidity: in all other cases D's decrease. EXAMPLE 3 The effect of changing diluent on D.sub.Sr was studied using solutions of DCH18C6 in using 2-ethylhexanol, n-octanol, and n-decanol. A comparison of D.sub.Sr using the above three alcohols and n-octanoic acid is shown in Table 2 below. TABLE 2 ______________________________________ Comparison of D.sub.sr using 0.1 --M DCH18C6 in octanoic acid, 2-ethylhexanol, n-octanol, and n-decanol, 25.degree. C. DSr Diluent 1M HNO3 3M HNO3 ______________________________________ octanoic acid 0.35 0.66 2-Ethylhexanol 0.57 2.0 n-octanol 0.71 3.1 n-decanol 0.36 1.6 ______________________________________ The results show that n-octanol is more effective in increasing D.sub.Sr than either 2-ethylhexanol or n-decanol and more effective than octanoic acid, especially at 3M HNO.sub.3. EXAMPLE 4 The extractant dependencies of D.sub.Sr with DCH18C6 in n-octanol from 1, 3, and 6M HNO.sub.3 at 25.degree. and 50.degree. C. are shown in FIG. 3. Under all conditions, the extractant dependencies are less than 1st power, although dependency increases as the concentration of DCH18C6 decreases. The D.sub.Sr extractant dependency is also slightly higher when the extraction takes place from 6M rather than 1M HNO.sub.3. Temperature is also shown to have little effect until the concentration of crown is less than 0.1M. EXAMPLE 5 The extractant dependencies of D.sub.Sr with DHC18C6, Dt-BuCH18C6, and bis-4,4'(5')-(methylcyclohexano)-l8-Crown-6 (DMeCH18C6) in n-octanol from 1M HNO.sub.3 at 25.degree. C. are shown in FIG. 4. As may be seen, each of the three extractants is equally effective at low contentration (about 0.01M). At concentrations high enough to yield acceptable D.sub.Sr values however, the di-t-butyl compound gives distribution ratios a factor of 5 or more greater than does DCH18C6 and at least twice those for the dimethyl compound. EXAMPLE 6 The distribution ratios of a number of inert constituents and fission products were measured at 40.degree. C. from synthetic dissolved sludge waste with 0.25M and 0.50M DCH18C6 in n-octanol using the experimental methods hereinbefore described. Measurements were also carried out using n-octanol without crown ether for comparison. The results are given in Table 3 below. TABLE 3 ______________________________________ Distribution Ratios of Inert Constituents and Fission Products from Dissolved Sludge Waste (1M HNO.sub.3 --0.5M Al) T = 40.degree. C. Distribution Ratios 0.25 --M DCH18C6 0.5 --M DCH18C6 n-Octanol in n-Octanol in n-Octanol ______________________________________ Inert Constituents Na 0.02 0.30 0.49 Mg 0.02 0.07 0.02 Al 0.02 0.07 0.02 Ca 0.03 0.15 0.18 Cr 0.03 0.07 0.02 Mn 0.03 0.07 0.02 Fe 0.03 0.07 0.02 Ni 0.03 0.08 0.02 Cu 0.03 0.08 0.03 Fission Products Sr 0.02 4.1 5.0 Y 0.02 0.08 0.02 Zr 0.04 0.10 0.06 Mo 0.15 0.26 0.18 Ru 0.25 0.52 0.53 Rh 0.03 <0.05 <0.05 Pd 0.21 0.47 0.71 Ag <0.05 <0.2 0.10 Cd 0.02 0.10 0.03 Cs -- (0.11) (0.33) Ba 0.03 1.3 1.5 La 0.03 0.08 0.02 R.E.'s 0.01-0.04 0.04-0.11 0.01-0.05 ______________________________________ () Radiometric Determination The data show that D is greater than one only for Sr and Ba. While Na, Ru, and Pd show some extractability, the distribution for the strontium is sufficiently higher to achieve complete separation. The data also show that selectivity is not significantly different for the two DCH18C6 concentrations and that n-octanol makes an appreciable contribution to the D's of all constituents except Sr and Ba. EXAMPLE 7 A series of experiments were run to study the affect of HNO.sub.3 concentration on the D's using 0.5M DCH18C6 solution. The results are shown in Table 4 below. TABLE 4 ______________________________________ Effect of Acidity Upon Distribution Ratios of DSW Constituents, 40.degree. C. System: 0.502 --M DCH18C6 in Octyl Alcohol vs. DSW @ Various HNO.sub.3 Concentrations Distribution Ratios 1 M 3 M 6 M ______________________________________ Inert Constituents Na 0.45 0.41 0.16 Mg 0.09 0.05 0.05 Al 0.09 0.06 0.06 Ca 0.15 0.23 0.24 Cr 0.09 0.06 0.06 Mn 0.09 0.06 0.06 Fe 0.09 0.06 0.06 Ni 0.09 0.06 0.06 Cu 0.09 0.06 0.06 Fission Products Sr 2.0 6.9 15.0 Y 0.09 0.06 0.06 Zr 0.10 0.12 0.21 Mo 0.20 0.23 0.27 Ru 0.40 0.41 0.23 Rh 0.12 0.09 0.06 Pd 0.67 0.58 0.29 Ag <0.2 <0.2 <0.2 Cd <0.1 <0.1 <0.13 Cs 0.34 0.18 0.03 Ba 0.91 2.6 3.6 La 0.10 0.07 0.08 Ce 0.10 0.08 0.08 R.E.'s Pr 0.09 0.06 0.07 Nd 0.12 0.10 0.10 Sm 0.07 0.03 0.05 Eu 0.10 0.06 0.07 ______________________________________ The data show clearly that the selectivity of Sr over every cationic constituent increases with an increase in acidity, which parallels the behavior of the corresponding octanoic acid system. EXAMPLE 8 Another series of experiments were run in the manner described above to determine the D.sub.Sr from nitric acid solutions with Dt-BuCH18C6 at several concentrations in n-octanol at 25.degree. and 50.degree. C. The results, as shown in FIGS. 5a and 5b, illustrate that Sr extraction continues to improve as the acidity of the aqueous phase increases up to 6M HNO.sub.3. The figures further illustrate that the temperature has little effect upon distribution ratios. EXAMPLE 9 The extraction of technetium from nitric acid solutions of various acidities using 0.20M Dt-BuHC18C6 in n-octanol was studied in the manner described above. The distribution ratios of Tc were measured radiometrically using liquid scintillation counting The results are given in Table 5 below. TABLE 5 ______________________________________ D.sub.TC using 0.20 D-t-BuCH18C6 in n-octanol at various acidities [HNO.sub.3 ] M D.sub.TC ______________________________________ 0.010 0.12 0.10 0.24 0.5 0.69 1.0 1.25 3.0 1.85 6.0 1.61 ______________________________________ The data from the table above show that, as with strontium, the D.sub.Tc increases with increasing nitric acid concentration. As has been shown by the preceding discussion and Examples, the process of the invention provides a safe and effective means for the recovery of Sr and Tc values from aqueous solutions up to 6 molar in nitric acid which contain these and other metal values.
	summary
	abstract	This invention deals with multi-component composite materials and techniques for improved shielding of neutron and gamma radiation emitting from transuranic, high-level and low-level radioactive wastes. Selective naturally occurring mineral materials are utilized to formulate, in various proportions, multi-component composite materials. Such materials are enriched with atoms that provide a substantial cumulative absorptive capacity to absorb or shield neutron and gamma radiation of variable fluxes and energies. The use of naturally occurring minerals in synergistic combination with formulated modified cement grout matrix, polymer modified asphaltene and maltene grout matrix, and polymer modified polyurethane foam grout matrix provide the radiation shielding product. These grout matrices are used as carriers for the radiation shielding composite materials and offer desired engineering and thermal attributes for various radiation management applications.
	summary
	abstract	During operation of the nuclear reactor, at specified time intervals, a neutron flux is measured using a set of neutron flux detectors which are fixed and arranged in the core (1) of the nuclear reactor, the maximum number n of detectors (8) being 15% of the number of fuel assemblies in the core. The measured signals are processed and the instantaneous distribution of neutron flux or of power throughout the entire core (1) is calculated from the measured signals. At least one core operating parameter is calculated from the instantaneous neutron flux distribution and an alarm is raised if at least one parameter exceeds a set range.
	description	This application claims priority based on International Patent Application No. PCT/FR2003/050199, entitled “Packaging for the Transport/Storage of Radioactive Material” by Jean-Pierre Bersegol, Benoît Alaurent and René Chiocca, which claims priority of French Application No. 02/16649, filed on Dec. 24, 2002, and which was not published in English. This invention relates to a container intended for transport/storage of radioactive materials. As can be seen in FIG. 1 representing a conventional container 1 according to prior art, this container 1 is provided with a container body 2 with an internal wall (not shown) delimiting a cavity inside which radioactive materials may be placed. Furthermore, the container 1 comprises a plurality of handling devices 8 also called <<handling trunnions>>. As can be seen in FIG. 1, each handling device 8 is provided with a main part 10 projecting outwards from the container body 2. The main part 10 is designed so that it can cooperate with a gripping mechanism (not shown) so that various handling operations of the container can be carried out. Furthermore, each handling device 8 is also provided with a base 12 fixed to the main part 10, this base being located in a base housing 30, delimited by a base housing wall 32 formed on the container body 2 of the container 1. Containers intended for transport/storage of radioactive materials may be loaded/unloaded under water in pools in nuclear installations during their life cycle. Thus, during immersion periods, the container is in contact with contaminated water in the pool, and therefore its outside surfaces might be contaminated. This is why regulation requirements impose that container surfaces in contact with water should not have any retention areas so that they can easily be decontaminated, for example using a high pressure water jet. Handling devices 8 are preferably arranged at an upper end portion 2a and a lower end portion 2b of the container body 2. Consequently, when the container is immersed in a loading/unloading pit, the handling devices 8 might also be contaminated. In this way, apart from the need to perform decontamination operations for each handling device 8, it is also essential to provide sealing means (not shown in FIG. 1) preventing water infiltrations between the base 12 of the handling device 8 and the base housing wall 32 provided on the container body 2 of the container 1. A first solution in prior art was to start by welding the handling device into its associated housing, thus providing a perfect seal of the assembly obtained. However, this first solution of an irreversible assembly was quickly abandoned because it was observed that repetitive handling operations could degrade these handling devices, such that it was sometimes necessary to replace them one or several times during the life cycle of the container. Thus, one assembly solution for easy assembly/disassembly of handling devices was then proposed. This solution consists of using a plurality of attachment screws distributed around the main part and fixing the base of the handling device onto the container body. For information, note that this solution was preferred to another solution that was also considered consisting of screwing the base into its associated housing directly. The choice of adopting a plurality of screws arranged on the base rather than providing a single thread on the outside surface of this base is explained particularly by the possibility of resisting high mechanical stresses, such as high bending/shear stresses encountered during handling operations. Nevertheless, with such an assembly, the sealing means must not only prevent water infiltrations, possibly of contaminated-water, between the base of the handling device and the base housing wall provided on the container body, but also prevent water from coming into contact with the attachment screws. Note that the geometry of the outside surfaces of attachment screws, and more specifically threaded surfaces, are such that their decontamination would be difficult because the time necessary to carry out the decontamination operations would be completely unreasonable. In prior art, a first embodiment of sealing means is known in which silicone or any other similar material is added into the different interstices of the assembly. In this respect, note that silicone is then put into place firstly between the base of the handling device and the base housing wall, and secondly between the attachment screws and the base. In the long term, this solution proved to be not very efficient in terms of the seal achieved, and a number of disadvantages appeared. Note firstly that application or repair operations on silicone seals need to be carried out by qualified personnel, due to a fairly complicated operating method. Furthermore, these operations are fairly long to carry out, which contributes towards increasing doses integrated by operators. Furthermore, the low observed efficiency of silicone seals in terms of the seal provided means that they have to be replaced regularly, consequently leading to the formation of large amounts of chemical/nuclear waste. Furthermore, note that these silicone seals also need to be replaced due to the fact that this material tends to fix contamination. Furthermore, sealing tests have to be carried out frequently, also due to the low efficiency achieved by silicone seals, which directly results in significant losses during operation. In this respect, note that tests are carried out by making <<pittings>> on seals, which can eventually cause degradation of the silicone and consequently necessitate a repair or replacement of the tested seals. In order to limit the quantity of silicone to be applied in the interstices, it has been proposed to replace the silicone seals initially provided at the attachment screws, by caps that cover each of these attachment screws individually. However, disassembly operations for such caps are long and tedious, which naturally does not help with concerns about doses integrated by operators. Furthermore, the caps used do not solve the problem related to the seal between the base of the handling device and the base housing wall, such that it is still necessary to use the silicone closing technique using sufficiently large quantities to be restrictive, introducing the many disadvantages described above. Finally, prior art also includes another type of sealing means that does not use silicone. This consists of a ring or two half-rings made of stainless steel assembled by welding onto the base of the handling device and onto the container body of the container. Thus, the resulting seal is very satisfactory such that there is no longer any need to make a sealing test. However, if it is required to replace an handling device, for example because it was degraded due to the repetition of handling operations, it is then necessary to grind the welds to remove the two half-rings and so that attachment screws can be accessed. Note that this necessity is also encountered when it is required to check the tightening torque of the attachment screws during maintenance operations. Thus, although it corrects some disadvantages related to the silicone closing technique, such as the poor seal obtained, this solution is relatively restrictive. The operation to disassemble the handling devices becomes long and difficult due to the need to grind the weld back strips holding the two half-rings together before the attachment screws of these handling devices can be accessed. Therefore, the purpose of the invention is to propose a container intended for the transport/storage of radioactive materials, the container comprising a container body and at least one handling device assembled on the container body using a plurality of attachment screws, the container at least partially correcting the disadvantages mentioned above related to embodiments according to prior art. More precisely, the object of the invention is to present a container with sealing means for each handling device designed so as to procure a sufficiently good seal such that when the container is loaded/unloaded in the pool, the contaminated water does not reach the interface between the handling device and the container body, nor the attachment screws for this handling device, the sealing means also being designed so that they can be assembled/disassembled more quickly and more easily than in embodiments according to prior art. To achieve this, the purpose of the invention is a container intended for transport/storage of radioactive materials, the container comprising a container body and at least one handling device assembled on the container body, each handling device being provided with a main part capable of cooperating with a gripping mechanism and projecting from the container body, and a base fixed to the main part and located in a base housing delimited by a base housing wall formed on the container body. The container also comprises firstly a plurality of attachment screws for each handling device distributed around the main part and attaching the base onto the container body, and secondly sealing means inserted between the base of the handling device and the container body of the container. According to the invention, the sealing means for each handling device comprise a sealing plate located in a plate housing delimited jointly by a plate housing wall provided on the base of the handling device and by a portion of the base housing wall, this sealing plate being installed removably in the plate housing so as to surround the main part of the handling device and to cover each attachment screw, the sealing means also including an external seal inserted between a peripheral wall external to the sealing plate and the portion of the base housing wall partially delimiting the plate housing, and an internal seal inserted between a peripheral wall internal to the same sealing plate and the plate housing wall. Advantageously, the sealing means used in the container according to the invention satisfactorily protect all sensitive areas present in the assemblies between a handling device and the container body of the container. These sealing means with a relatively simple design have an external seal preventing water infiltrations between the base of the handling device and the base housing wall provided on the container body, so as to prevent contamination of the interface between the handling device and the containers body. Furthermore, the sealing means comprise an internal seal that cooperates with a sealing plate and the external seal to prevent water from entering a space partially delimited by the sealing plate, inside which attachment screws of the handling device are located. Thus, the attachment screws are also protected from possible contamination. Furthermore, the sealing plate is advantageously installed removably, for example screwed or clipped into its associated plate housing, which provides speed and ease of assembly/disassembly of this sealing plate. In this way, assembly and disassembly operations of such a plate do not require any special training of operators, unlike sealing means previously used in some embodiments according to the state of the art. Furthermore, the reduction in the assembly/disassembly time of the sealing means results directly in a drop of doses integrated by operators during handling operations, and by significant savings in operation. Note also that the good seal obtained by the container sealing means according to the invention contributes firstly to provide an efficient barrier against contamination, but also to achieve further savings in operation due to the significant reduction to the number of repairs to be made, particularly compared with less reliable solutions using silicone seals. In this respect, note that the lack of silicone or similar materials eliminates the need for operators to worry about the harmful effects caused by the toxicity of such products, and also reduces the quantity of chemical/nuclear waste produced. Preferably, the external peripheral wall of the sealing plate comprises an external edge in contact with the external seal, and the internal peripheral wall of the sealing plate comprises an internal edge in contact with the internal seal. It is then possible for the external edge to have an external groove extending along the external edge inside which the external seal is located, and for the internal edge to have an internal groove extending along the internal edge and inside which the internal seal is located. Thus, the sealing means not yet assembled on the container advantageously form a single and compact block. Obviously, it would also be possible to place external and internal seals in grooves formed in the base housing wall and in the plate housing wall respectively, without going outside the scope of the invention. Preferably, each handling device is provided with a channels network for making a sealing test of the sealing means, the channels network communicating at least with an access orifice provided in the main part of the handling device so as to open up on the outside of this main part, each access orifice being closed off using a removable plug. Thus, sealing test operations can be done easily and quickly by removing the plug on an access orifice, then by connecting conventional test means to this access orifice. Consequently, the channels network provided on the handling device enables a reliable test to be carried out without damaging the tested sealing means. In this context, note that for each handling device, the sealing plate has an inside surface partially delimiting a space surrounding the main part of the handling device and partly filled in by the heads of the attachment screws. In this way, the channels network mentioned above may be arranged so as to enable communication between this space and at least one access orifice, so that a sealing test can be carried out. Furthermore, the base of each handling device is provided with a plurality of attachment screw passage holes. Thus, also in order to make a sealing test, the channels network can be arranged so as to enable communication between each passage hole and at least one access orifice. Naturally, the channels network formed in the handling device, can be made so that it is capable of fulfilling one or the other of the functions mentioned above, or both simultaneously. According to a first preferred embodiment of this invention, the sealing plate for each handling device is in the shape of a ring and the external and internal seals are each in the shape of an annular seal. Thus, the specific ring shape of the sealing plate is such that it can be installed screwed in the plate housing. To achieve this, it will be possible to have a threaded portion on the internal edge of the sealing plate and on the plate housing wall provided on the base of the handling device, cooperating with each other. Furthermore, the sealing plate then advantageously comprises an external surface on which there are gripping orifices capable of cooperating with an appropriate tool for fast assembly/disassembly by screwing/unscrewing the sealing plate. Note also that this first preferred embodiment is particularly but not exclusively adapted when the attachment screws are arranged so as to define a circle, and when the base of the handling device is cylindrically shaped with a circular section. According to a second preferred embodiment of this invention, the sealing plate for each handling device is installed clipped in the plate housing. To achieve this, the plate housing wall provided on the base of the handling device preferably comprises a shoulder, the internal, seal housed in the groove of the internal edge of the sealing plate bearing in contact with an inside surface of this shoulder, in order to maintain the sealing plate in the plate housing. In this configuration, the internal seal can also be compressed between the groove of the internal edge and a part of the maximum diameter of the shoulder, to enable assembly/disassembly of the sealing plate. Furthermore, in order to facilitate assembly/disassembly by clipping of the sealing plate, it will be possible for at least one access orifice provided in the main part of the handling device to be capable of holding pressurisation/vacuum creation means that can generate a pressure/vacuum inside the space partially delimited by the inside surface of the sealing plate and surrounding the main part of the handling device, through the channels network. Advantageously, the use of such an assembly/disassembly method no longer requires the presence of gripping orifices on the outside surface of the sealing plate. Obviously, this absence is an advantage, to the extent that decontamination of such orifices can be tedious. Furthermore, the lack of gripping orifices on the outside surface of the sealing plate advantageously contributes to giving a very good visual aspect to the container. Furthermore, assembly by clipping of the sealing plate can enable the sealing plate to be indifferently in the shape of a ring or a frame, unlike the screwing solution presented in the first preferred embodiment of this invention. Thus, when the sealing plate is in the shape of an arbitrary frame surrounding the main part of the handling device, the external and internal seals are also in the shape of a frame. Note that this frame shape is particularly but once again not exclusively suitable when the attachment screws that will be covered by the sealing plate are arranged so as to define a frame and not a circle, this specific arrangement particularly being used when the base of the handling device is in the shape of a rectangle parallelepiped. Other advantages and characteristics of the invention will become clear after reading the detailed non-limitative description given below. The container according to the invention is similar to the container 1 presented in FIG. 1 and already partially described above. Thus, the container 1 according to the invention comprises a plurality of handling devices 8 assembled on the container body 2. Note that the container body 2 has an external wall 7, preferably cylindrically shaped with a longitudinal axis 22. In the remainder of this description, this axis 22 will therefore be considered as being the longitudinal axis of the container body 2. The handling devices 8 are distributed circumferentially about the container body 2, for example at an upper end portion 2a and at a lower end portion 2b of the container body 2. With reference jointly to FIGS. 2 and 3, the figures show an assembly between the container body 2 and one of the handling devices 8 of a container 1 according to a first preferred embodiment of this invention. Obviously, in this preferred embodiment, all assemblies between the handling devices 8 and the container body 2 are preferably identical to the embodiment that will be described below. The handling device 8 has a main part 10 and a base 12, these two parts 10 and 12 being fixed and preferably made in a single piece of stainless steel. The main part 10 projects outwards from the container body 2, and its geometry is adapted so that it can easily cooperate with a gripping mechanism (not shown), in order to enable execution of handling operations. As an illustrative example, the main part 10 of the handling device 8 has a cylindrically shaped outside surface 24 with a circular section, with a longitudinal axis 26 approximately perpendicular to the longitudinal axis 22 of the container body 2. Furthermore, the main part 10 may comprise an end portion 28 in the shape of a shoulder, to prevent the gripping mechanism from escaping during handling operations. Furthermore, the base 12 of the handling device 8 is located in a base housing 30 delimited by a base housing wall 32, this wall being provided on the container body 2 of the container 1. Furthermore, the base 12 comprises an upper portion 12a and a lower portion 12b, the lower portion 12b preferably having a cylindrically shaped lateral surface 33 with a circular section and a longitudinal axis coincident with the longitudinal axis 26 of the outside surface 24 of the main part 10. The base housing wall 32 comprises a flat bottom 34 acting as a stop for the lower portion 12b of the base 12, and a cylindrically shaped lateral part 36 with a circular section and matching the entire lateral surface 33 of the same lower portion 12b. However, as can be seen in FIG. 2, note that the lower portion 12b of the base 12 only partially occupies the base housing 30, such that the lateral surface 33 of the lower portion 12b only matches a portion of the lateral part 36. Naturally, the lateral part 36 of the base housing wall 32 and the lateral surface 33 of the lower portion 12b of the base 12 could be in any other shape, provided that they are approximately complementary without going outside the scope of the invention. The base 12 of the handling device 8 is assembled in the base housing 30 using a plurality of attachment screws 38 distributed around the main part 10, and that can be screwed in the container body 2 of the container 1. To achieve this, the lower portion 12b of the base 12 is provided with screw head housings 40 preferably distributed concentrically around the longitudinal axis 26, each of these screw head housings 40 being capable of forming a stop for the head 42 of an attachment screw 38. Furthermore, each screw head housing 40 is prolonged by a passage hole 44, through which the threaded portion 46 of the attachment screw 38 passes. The assembly between the handling device 8 and the container body 2 also requires sealing means 48 arranged so as to provide a sufficiently satisfactory seal so that when the container 1 is loaded/unloaded in the pool, the contaminated water does not reach the interface between the handling device 8 and the container body 2, nor the attachment screws 38 of the same handling device 8. The sealing means 48 then comprise a sealing plate 50 in the shape of a ring preferably made of stainless steel, and located in a plate housing 52 so as to cover each of the attachment screws 38. As can be seen in FIG. 2, the plate housing 52 is delimited by a flat bottom 54 formed by the lower portion 12b of the base 12, by a plate housing wall 56 provided on the upper portion 12a of the base 12, and by a portion 58 of the lateral part 36 of the base housing wall 32. In this respect, note that the portion 58 of the lateral part 36 corresponds to the upper portion that is not in contact with the lateral surface 33 of the lower portion 12b of the base 12. Furthermore, note that the plate housing wall 56 is approximately cylindrically shaped with a longitudinal axis coincident with the longitudinal axis 26. The sealing plate 50 comprises an external peripheral wall 60, particularly with an external edge 62 corresponding to the external edge of the plate matching the portion 58 of the lateral part 36 of the base housing wall 32. The external edge 62 also has an external groove 64 inside which an annular external seal 66 is housed, this seal 66 also being in contact with the portion 58 of the lateral part 36 so as to prevent contamination from entering between the handling device 8 and the container body 2. Similarly, the sealing plate 50 comprises an internal peripheral wall 68 particularly with an internal edge 70 which corresponds to the internal edge of the plate matching the plate housing wall 56 provided on the upper portion 12a of the base 12. Furthermore, the internal edge 70 has an internal groove 72 inside which an internal annular seal 74 is housed, this seal 74 also being in contact with the plate housing wall 56. The combination of seals 66 and 74 prevents contamination from reaching the attachment screws 38. Note that the external and internal seals 66 and 74 are preferably made from an elastomer material. In order to make the sealing plate 50 perfectly removable, the internal edge 70 of the sealing plate is provided with a threaded portion 76 with a longitudinal axis coincident with the longitudinal axis 26, and capable of cooperating with a threaded portion 78 provided on the plate housing wall 56. In this way, the sealing plate 50 can be mounted screwed on the base 12. Note that the threaded portion 76 of the internal edge 70 is located along the prolongation of the portion of the same edge on which the groove 72 is formed, which is further outwards on the container body 2 than the threaded portion 76. Note as can be seen in FIG. 2 that the sealing plate 50 may comprise gripping orifices 80 formed on its outside surface 82 that will cooperate with an adapted tool (not shown), to facilitate screwing/unscrewing operations of this sealing plate. Note also that when the sealing plate 50 is assembled onto the base 12 of the handling device 8 by screwing, the inside surface 83 of this plate 50 stops in contact with the lower portion 12b of the base 12, and more precisely against the flat bottom 54 delimiting the plate housing 52. In this respect, note also that the inside surface 83 of the sealing plate 50 must be adapted to come into contact with the flat bottom 54 and not with the attachment screws 38, the heads 42 of these attachment screws 38 being capable of projecting outside the screw head housings 40. Consequently, the inside surface 83 preferably has an annular recess 85 facing the attachment screws 38 and designed such that the screw heads 42 can be partially inserted into this indentation 85 without forming stops, when the sealing plate 50 is assembled on the base 12 by screwing. Note also that when the sealing plate 50 is completely assembled, the outside surface 82 of this plate 50 is approximately continuous with the external wall 7 of the container body 2. Also with reference to FIGS. 2 and 3, the handling device 8 is provided with a channels network 84 for making a sealing test of the sealing means 48. The channels network 84 is made so as to communicate with an access orifice 86 provided at the end of the main part 10 of the handling device 8, this access orifice 86 opening outside this main part 10 and being closed off using a removable plug 88, preferably mounted screwed on the access orifice 86. The channels network 84 comprises firstly a longitudinal, channel 90 opening up in the access orifice 86 and having an axis coincident with the longitudinal axis 26 of the outside surface 24 of the main part 10, the channel 90 being formed so that it passes entirely through the handling device 8. A radial groove 92 is also provided on the lower portion 12b of the base 12, this groove 92 forming a radial channel 94 with the flat bottom 34 of the base housing wall 32, communicating with the channel 90 and being perpendicular to the longitudinal axis 26. Another longitudinal channel 96 starts from this radial channel 94 and extends approximately parallel to channel 90 in the direction of a space 98 surrounding the main part 10 of the handling device 8 and partially delimited by the recess 85 of the inside surface 83 of the sealing plate 50. Note that this space 98 is also partially delimited by the flat bottom 54 of the plate housing 52, and is partly filled in by the heads 42 of the attachment screws 38. Also starting from the radial channel 94, a circumferential channel 100 with an axis coincident with the longitudinal axis 26 extends so as to pass through all passage holes 44. In this respect, note that the circumferential channel 100 is made jointly using a circumferential groove 102 provided on the lower portion 12b of the base 12, and the flat bottom 34 of the base housing wall 32. Obviously, the channels network 84 may be adapted, always so as to enable communication between the space 98 and the access orifice 86 and/or so as to enable communication between each of the passage holes 44 and the access orifice 86, without going outside the scope of the invention. With reference to FIG. 4, the removable plug 88 is removed so that the conventional sealing test means 104 can communicate with the channels network 84, and so as to make a sealing test of the sealing means 48. Thus, this communication can be made quickly by screwing a perforated end piece 106 belonging to the control means 104, into the access orifice 86 of the main part 10. With reference jointly to FIGS. 5 to 7, the figures show an assembly between the container body 2 and one of the handling devices 8 of a container 1 according to a second preferred embodiment of this invention. Obviously, in this preferred embodiment, all assemblies between the handling devices 8 and the container body 2 are preferably identical to what is described below. In these FIGS. 5 to 7, elements marked with the same numeric references as those attached to the elements shown in FIGS. 1 to 4, correspond to identical or similar elements. In this respect, note that this assembly is fairly similar to that shown in the first preferred embodiment of this invention, except that the sealing plate 50 of the sealing means 48 is no longer installed into the plate housing 52 by screwing, but is clipped into it. To achieve this, the sealing plate 50 comprises an internal peripheral wall 268 in particular provided with an internal edge 270, this edge corresponding to the internal edge of the plate matching a plate housing wall 256 provided on the upper portion 12a of the base 12. Note that the shape of the plate housing wall 256 is not the same as the shape of the plate housing wall 56 in the first preferred embodiment, but it is still approximately cylindrical with a longitudinal axis coincident with the longitudinal axis 26. In this respect, note that the only difference between the sealing plates of the first and second preferred embodiments is at the internal edges 70 and 270. Similarly, note that the elements delimiting the plate housing 52 other than the plate housing wall 256, in other words the flat bottom 54 formed by the lower portion 12b of the base 12 and the portion 58 of the lateral part 36 of the base housing wall 32, are identical to those presented in the first preferred embodiment of this invention. Thus, the internal edge 270 is provided with an internal groove 272 inside which an annular internal seal 274 is housed, this seal 274 also being in contact with the plate housing wall 256 to prevent contamination from reaching the attachment screws 38. Note that the internal seal 274 is preferably made from an elastomer material. As can be seen in FIG. 6, the plate housing wall 256 comprises a shoulder 287 extending towards the inside of the plate housing 52. When the sealing plate 50 is installed on the base 12 of the handling device 8, the internal seal 274 housed in the groove 272 and projecting outside it bears in contact with an inside surface 289 of the shoulder 287, generally oriented towards the lower portion 12b of the base 12. Consequently, this particular configuration assures that the sealing plate 50 is held in place in the plate housing 52. As an illustrative example, the inside surface 289 of the shoulder 287 may be approximately perpendicular to the longitudinal axis 26, or it may be inclined so as to move away from this axis 26 as the distance from the lower portion 12b increases. Furthermore, the internal seal 274 is designed so that it is compressed between the groove 272 of the internal edge 270, and a part 291 of the shoulder 287 with maximum diameter, so that the sealing plate 50 can be assembled by clipping. Consequently, once the maximum diameter part 291 has been passed, the internal seal 274 can partially decompress, in particular so as to match the inside surface 289 of the shoulder 287. With reference particularly to FIGS. 5 and 7, the handling device 8 is provided with a channels network 284 to make a sealing test of the sealing means 48, this channels network 284 being different from the channels network 84 described in the first preferred embodiment. However, the channels network 284 may also be adapted, once again so as to enable communication between the space 98 and the access orifice 86, and/or to enable communication between each of the passage holes 44 and the access orifice 86, without going outside the scope of the invention. The channels network 284 firstly comprises the longitudinal channel 90 opening into the access orifice 86, the radial channel 94 formed jointly by the groove 92 and the flat bottom 34 of the base housing wall 32, the longitudinal channel 96 extending approximately parallel to the channel 90 towards the space 98 surrounding the main part 10, and the circumferential channel 100 formed jointly by the circumferential groove 102 and the flat bottom 34 of the base housing wall 32. Furthermore, the channels network 284 also comprises a plurality of radial channels 293 communicating with the channel 90, the radial channels 293 being formed partly using radial grooves 295 formed on the lower portion 12b of the base 12, and secondly using the flat bottom 34 of the base housing wall 32. Each of the radial channels 293 passes through a passage hole 44 and extends as far as the lateral surface 33 of the lower portion 12b of the base 12. Moreover, there is another circumferential channel 297 that communicates with each of the radial channels 293, the circumferential channel 297 being formed jointly by circumferential machining 299 formed on the lower portion 12b of the base 12, the flat bottom 34 of the base housing wall 32 and the lateral part 36 of the base housing wall 32. With the channels network 284 described above, it is possible not only to make sealing tests by connecting sealing test means 104 to the access orifice 86, but also to facilitate/perform assembly/disassembly operations of the sealing plate 50. The access orifice 86 is also capable of receiving pressurisation/vacuum creation means (not shown) that can generate a pressure/vacuum through the channels network 284, inside the space 98. Note that these pressurization/vacuum creation means are extremely useful particularly during the operation to compress the internal seal 274 between the shoulder 287 and the groove 272, which is difficult to do with a simple manual operation. Furthermore, this plate 50 can then be disassembled by a single pressurization of the space 98 without the need for any additional special tools or gripping orifices on the outside surface 82 of the sealing plate 50. Finally, note that with the clipping solution for assembly of the sealing plate 50, there is no longer any need to limit the shape of this sealing plate to a ring. Assembly by clipping does not require any particular shape, unlike assembly by screwing that requires a cylindrically shaped section. In this way, the sealing plate 50 can then be in the shape of any frame, provided with external and internal seals also in the shape of a frame, this possibility resulting directly in a wide choice of positions of the attachment screws 38 on the base 12, and a wide choice in the geometry of this base. Obviously, those skilled in the art could make many modifications to the container 1 that has been described, simply as non-limitative examples.
	description	The present application is a Divisional Application of application Ser. No. 10/896,092, filed Jul. 22, 2004 now abandoned, the contents of which are incorporated herein by reference. This invention relates to a technique for a preventive maintenance of boiling water nuclear power plant (hereinafter, referred to as “BWR”), and particularly to a method for mitigating a stress corrosion cracking (hereinafter, referred to as “SCC”) of nuclear power plant structural materials. In BWR, it is an important problem to suppress the SCC of the materials constructing the core structures and pressure boundaries (stainless steel, nickel-base alloys) from the viewpoint of improving the plant operating rate. SCC takes place when the three factors (materials, stress, environment) fall on one another. Accordingly, SCC can be mitigated by mitigating at least one of the three factors. When a plant is operated, the core cooling water is radioactively decomposed by the intense gamma and neutron rays emitted from the core. As its result, the structural materials constructing the in-core structures and pressure boundaries come to be exposed to the core cooling water containing oxygen and hydrogen peroxide (both are the products of radiolysis) in an amount of several hundreds ppb and having a high temperature (in this invention, a temperature of 100° C. or more is referred to as high temperature; and the outlet temperature of core is 288° C. at the time of normal power operation). FIG. 2 illustrates the relation between crack growth rate (hereinafter, referred to as “CGR”) and electrochemical corrosion potential (hereinafter, referred to as “ECP”). It is apparent from FIG. 2 that CGR decreases when ECP drops. FIG. 3 illustrates the results of measurement on the relation between the concentrations of oxygen and hydrogen peroxide and ECP of type 304 stainless steel (hereinafter, referred to as “304SS”) in high-temperature water. Both oxygen and hydrogen peroxide show a higher ECP at a higher concentration. Accordingly, for mitigating SCC of structural materials exposed to the cooling water of reactor, it is necessary to reduce ECP, or to lower the concentrations of oxygen and hydrogen peroxide present in the reactor water. As a technique for solving this problem, the technique of adding hydrogen from the feed water system (hereinafter, referred to as “hydrogen injection”) can be referred to. Hydrogen injection is a technique of reacting the injected hydrogen with the oxygen and hydrogen peroxide formed by the radiolysis of water to return them to water, and thereby decreasing the concentrations of oxygen and hydrogen peroxide in the reactor water. If the hydrogen injection is carried out, however, radioactive nitrogen 16 (hereinafter, referred to as “N-16”) formed by the radio-activation of water becomes readily migrating together with steam, and this N-16 enhances the dose rate of turbine building. FIG. 4 illustrates the relation between the concentration of hydrogen in the fed water and effective oxygen concentration ((oxygen concentration)+0.5×(hydrogen peroxide concentration)) and the relation between the concentration of hydrogen in the feed water and the relative value of main steam line dose rate. It is apparent from FIG. 4 that an increase in hydrogen concentration in the feed water brings about a rise in the relative value of main steam line dose rate, though it causes a decrease in the effective oxygen concentration. For solving this problem, a technique of making an element of the platinum group adhere to the surface of material and thereby accelerating the reaction between hydrogen and oxygen and hydrogen peroxide (for example, see: (1) JP Patent No. 2766422). By this technique, ECP can be decreased while suppressing the rise in the main steam line dose rate. If an element of the platinum group is made to adhere to the surface of a material in order to accelerate the reaction between hydrogen and oxygen and hydrogen peroxide, however, there arises a new problem that the concentration of radioactive cobalt Co-60 in the cooling water for the reactor rises. It is an object of this invention to provide a method for mitigating the stress corrosion cracking of reactor structural materials by which the rise in the main steam line dose rate can be suppressed without side reactions such as the elevation of radioactive cobalt Co-60 concentration in the cooling water of the reactor. A reductive nitrogen compound containing nitrogen having a negative oxidation number is injected into the reactor water of a boiling water nuclear power plant. By injecting a reductive nitrogen compound containing nitrogen having a negative oxidation number into the reactor water, the stress corrosion cracking of the structural material of the reactor can be mitigated without secondary effects such as the elevation of cobalt 60 (Co-60) concentration. Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 3 - - - Filter demineralizer for condensate; 5 - - - Feed water heating system; 6 - - - Feed water line; 8 - - - Bottom drain line; 10 - - - Reactor water clean up system line; 12 - - - Reactor water filter demineralizer; 16 - - - Primary loop re-circulation system line. Elevation of the main steam line dose rate is dependent on the hydrogen concentration in the reactor water. The decreasing effect of the effective oxygen concentration in the reactor pressure vessel bottom water on the hydrogen concentration in the fed water is dependent on the designed conditions of the plant. As shown in FIG. 4, however, the hydrogen concentration in the fed water at which the main steam line dose rate begins to rise is not greatly dependent on the kind of plant, and stays at about 0.4 ppm. This is for the reason that most of the boiling water type reactors are so designed that the ratio of flow rate of feed water to flow rate in the core (average steam quality) comes to about 13%, so that the amount of hydrogen injected into the reactor water is not greatly different from one plant to another so far as the concentration of the feed water is fixed. Accordingly, the chemical reactions participated by N-16 in the core progress roughly under the same conditions, and the change in the main steam line dose rate shows a similar behavior. Accordingly, when a compound decreasing the concentrations of oxygen and hydrogen peroxide in the reactor water without greatly affecting the hydrogen concentration and giving the changes of pH and electro conductivity falling in the standard of control is injected into the reactor water, ECP can be decreased and SCC can be suppressed without causing a rise in the main steam system does rate. The present inventors have discovered that nitrogen compounds containing a nitrogen atom having an oxidation number smaller than that in molecular nitrogen, such as hydroxylamine, carbohydrazide, hydrazine, ammonia, diazine and the like, (hereinafter, these nitrogen compounds are referred to as “reductive nitrogen compounds”) are reductants satisfying the above-mentioned conditions. As the first reason therefor, it can be mentioned that these compounds decrease ECP of the material by oxidation reduction reactions of the reductive nitrogen compounds themselves, even in the period in which dose rate of the irradiation is small. FIG. 5 illustrates results of measurement of ECP of 304SS in the presence of oxygen in water having a high temperature of 280° C., wherein the injected reductive nitrogen compound is hydrazine. As concentration of hydrazine becomes higher, ECP decreases. If hydrazine consumes oxygen and the decrease in oxygen concentration causes a decrease in ECP, ECP should decrease to −0.5 VvsSHE in the presence of excessive hydrazine. According to the result of actual measurement, nevertheless, there is seen a tendency of saturation at −0.2V (SHE), which is probably attributable to an oxidation reduction reaction of hydrazine. Further, from the results of the measurement, it has become apparent that ECP reaches a saturation when concentration of added hydrazine exceeds a definite value. This means that the time period of the hydrazine-oxygen reaction is in an order of second, in water of high temperature. Accordingly, it can be expected that, even in the case of BWR where it takes a time period of second order from entrance of the water to its arrival at the core, the decrease will show a tendency of saturation. Thus, the inventors have confirmed that ECP can be decreased by injecting a reductive nitrogen compound, and have found that ECP can be decreased economically by placing an upper limit on the amount of injection. As the second reason, it can be pointed out that a reductive nitrogen compound reduces oxygen and hydrogen peroxide according the (Equation 2) and (Equation 3), when the reductive nitrogen compound is oxidized to form a molecular nitrogen according to (Equation 1). In the time period when the irradiation has a high dose rate, this reaction is accelerated by formation of radials, etc.2N−n—R→N2+2ne−+R2n+ (Equation 1)O2+4H2O+4e−→4OH− (Equation 2)H2O2+2e−→2OH− (Equation 3)(R designates the residual part of the molecule of reductive organic compound.) As the reductive organic compound, hydrazine is preferable. This is for the following three reasons. (1) Hydrazine reacts with oxygen and hydrogen peroxide as expressed by (Equation 4) and (Equation 5) to form nitrogen molecule and water which do not affect pH and conductivity. Accordingly, no release of hydrogen takes place. If the compound contains carbon, carbon dioxide is formed, which forms carbonic acid causing subsidiary effects of a rise in electro conductivity and a decrease in pH. However, hydrazine contains no carbon, and therefore such a problem does not arise.N2H4+O2→N2+2H2O (Equation 4)N2H4+2H2O2→N2+4H2O (Equation 5)(2) Hydrazine is higher than hydrogen in the reaction rate with oxygen and hydrogen peroxide. Accordingly, hydrazine rapidly reacts to form nitrogen and water, and the rise in electric conductivity, caused by its residence, is suppressed.(3) Hydrazine is a liquid substance and chemically stable, so that it is easy to handle. It can be injected by means of a pump even into a site of high pressure. However, when subjected to γ ray irradiation, hydrazine undergoes the reaction of (Equation 6), and releases ammonia and hydrogen in addition to nitrogen.N2H4→NH3+(½)N2+(½)H2 (Equation 6) However, even in this case, due to the γ ray exposure, the reaction between N2H4 and radical forms a N2H3 radial which reacts with oxygen quite rapidly. The inventors have found that, so far as the amount of hydrazine is not excessive to oxygen or hydrogen peroxide, the quantities of ammonia and hydrogen formed by the reaction of (Equation 6) are only slight, and the influence on the water quality and main steam line dose rate can be minimized. In order to confirm the above-mentioned reaction, the inventors added hydrazine to oxygen-containing water having a high temperature of 280° C. and irradiated the system with Co-60, and followed the variations of oxygen concentration and by-product concentration based on hydrazine concentration. The results are shown in FIG. 6. When oxygen was excessive to the hydrazine concentration based on the stoichiometric quantities of the reaction of (Equation 4), the oxygen concentration decreased without formation of ammonia or hydrogen. On the other hand, when the concentration of hydrazine was excessive as compared with oxygen concentration, oxygen was consumed and at the same time ammonia and hydrogen were formed. From the results mentioned above, it was confirmed that, when oxygen is present in the system, hydrazine does not undergo the reaction of (Formula 6) even in exposure to γ ray, but the hydrazine reacts with oxygen to form nitrogen and water. Further, it became apparent that an excessive amount of hydrazine is decomposed into ammonia and hydrogen when exposed to γ ray. Based on this fact, the inventors found that the ammonia concentration in the cooling water in the reactor pressure vessel bottom can be used as an indication for controlling the amount of injected hydrazine. This is for the reason that existence of ammonia indicates that hydrazine is present at least in an amount enough for consuming the oxygen and hydrogen peroxide. Since ammonia forms ammonium ion and hydroxide ion in the neighborhood of room temperature, its existence can be indirectly confirmed by measuring conductivity or pH. On the other hand, when hydrazine is insufficient, ammonia is not formed. Accordingly, the ammonia concentration in the bottom of reactor is useful as an indication for judging the de-oxidant effect of hydrazine in the cooling water of reactor. The effect of injection of hydrazine can be surely evaluated by measuring ECP by the measurement of oxygen concentration in the cooling water at the bottom of reactor pressure vessel or by using an ECP sensor provided on the drain line led from the bottom of reactor pressure vessel, and thereby combining the effect of hydrazine injection with a monitor. The inventors have found that the concentration of oxygen and hydrogen peroxide in the reactor water can be decreased more economically and with smaller subsidiary effects by combining the injection of reductive nitrogen compound and the injection of hydrogen and appropriately controlling their concentrations. Although the concentration of oxygen and hydrogen peroxide in the reactor water can be reduced by merely injecting the reductive nitrogen compound, it can generally be said that the price per mole of reductive nitrogen compound is higher than that of hydrogen. Further, in this technique, a reductive nitrogen compound is injected at a high concentration, and therefore the excessive reductive nitrogen compound emits ammonia to make an adverse influence, unless the amount of reductive nitrogen compound is strictly controlled so as to become an optimum amount for consuming oxygen and hydrogen peroxide. Accordingly, it is most desirable to convert the residual parts of oxygen and hydrogen peroxide which has not been consumed by hydrogen injection into water with the reductive nitrogen compound, because this technique can minimize the necessary amount of reductive nitrogen compound and gives a room to the control. FIG. 7 illustrates the results of analysis of effective oxygen concentration in the upper part of reactor which has been subjected to hydrogen injection. It is apparent that, if hydrogen injection is carried out, the concentrations of oxygen and hydrogen peroxide in the upper part of reactor are decreased. This is for the reason that the hydrogen present in the cooling water at the bottom of reactor pressure vessel suppresses the formation of oxygen and hydrogen peroxide caused by the radiolysis of water in the core. This effect is not readily obtainable even if a reductive nitrogen compound is added. If the concentrations of oxygen and hydrogen peroxide in the upper part of reactor is lowered, the amount of reductive nitrogen compound necessary for consuming the oxygen and hydrogen peroxide in the reactor cooling water can be decreased. As has been mentioned above, an increase in the main steam line dose rate takes place when the hydrogen concentration in the feed water has exceeded about 0.4 ppm. Accordingly, when hydrogen concentration in feed water is 0.4 ppm or below, no rise in the main steam line dose rate takes place, and even if a reductive nitrogen compound is added, the hydrogen concentration in the reactor cooling water does not increase greatly, so that combination of hydrogen injection and addition of reductive nitrogen compound does not lead to an increase in the main steam line dose rate. Further, when injection of hydrogen and addition of reductive nitrogen compound are combined, there arises a merit that the nitrogen molecule formed from reductive nitrogen compound is not readily oxidized into compounds having a higher oxidation number such as nitrous acid, nitric acid, etc. When the amount of reductive nitrogen compound is smaller than that of oxygen or hydrogen peroxide, the unreacted oxygen and hydrogen peroxide and the formed nitrogen coexist in the down-stream of the site where the reductive nitrogen compound has reacted completely. In such a site, there is a possibility that the nitrogen is oxidized to form nitrous acid and nitric acid, in some cases. Nitrous acid and nitric acid are not desirable, because they make a cause of a rise in electric conductivity and a decrease in pH. Although these oxidative anions do not cause a marked acceleration of SCC, so far as they are present in the cooling water for reactor only in a small amount, there is a fear that they can cause a decrease in pH and thereby a decrease in the stability of the oxides present on the line surface or fuels, and they can exercise an influence on the radioactivity concentration of core water. It is preferable, accordingly, to use hydrogen injection in combination and thereby maintain the cooling water for reactor in a reductive atmosphere, even after the reductive nitrogen compound has become unable to react. The amount of hydrogen injection can be optimized by monitoring the main steam line dose rate or by measuring the hydrogen concentration in the cooling water at the bottom of reactor pressure vessel. Further, the inventors have found that alcohols (CnH2n+1OH; wherein n is a natural number) are compounds capable of decreasing the concentrations of oxygen and hydrogen peroxide in the reactor cooling water without greatly affecting the hydrogen concentration. An alcohol reacts with oxygen or hydrogen peroxide according to (Equation 7) or (Equation 8) to yield carbon dioxide and water.C2nH2n+1OH+(3n/2)O2→nCO2+(n+1)H2O (Equation 7)C2nH2n+1OH+3nH2O2→nCO2+(4n+1)H2O (Equation 8) However, unlike the case of hydrazine, the reactions of Equations 7 and 8 do not take place in the absence of γ ray irradiation. In order to confirm this fact, an alcohol (methyl alcohol) was injected into water of high temperature (280° C.) and ECP of 304SS was measured in the case of carrying out γ ray irradiation and in the case of not carrying out γ ray irradiation. The results are shown in FIG. 8. It is apparent from FIG. 3 that ECP of 304SS is about 0.1V (SHE) when the dissolved oxygen concentration is 300 ppb, and ECP decreases as the dissolved oxygen concentration decreases, and ECP reaches about −0.5V (SHE) when dissolved oxygen is 10 ppb or less. It is considered that, when γ ray irradiation is not carried out, oxygen remains without reacting with methanol and therefore ECP has become about 0.1V (SHE), while when γ ray irradiation is carried out, oxygen reacts with methanol to decrease the oxygen concentration so that ECP has become about −0.25V (SHE). Based on this result, it has been confirmed that methanol reacts with oxygen only when γ ray irradiation is carried out. On the other hand, when an alcohol reacts with oxygen and hydrogen peroxide, CO2 is formed, which reacts with water according to (Equation 9) to form carbonate ion.CO2+H2O→H2CO3→H++HCO3−→2H++CO32− (Equation 9) Thus, alcohols are disadvantageous in that they make higher the conductivity of reactor water and lower the pH value thereof. Accordingly, it is considered appropriate to use alcohols in combination with a reductive nitrogen compound such as hydrazine. Reductive nitrogen compounds such as hydrazine are reactive with oxygen and hydrogen peroxide even in the absence of γ ray irradiation, while alcohols such as methanol do not react with oxygen and hydrogen peroxide in the absence of γ ray irradiation. Therefore, it is considered that reductive nitrogen compounds such as hydrazine are higher in reactivity than alcohols such as methanol, and preferentially react with oxygen and hydrogen peroxide. Thus, by injecting a reductive nitrogen compound such as hydrazine in an amount somewhat smaller than the stoichiometric amount of the reaction with oxygen and hydrogen peroxide, and injecting the alcohol such as methyl alcohol in an amount needed for reacting the residual oxygen and hydrogen peroxide, the formation of ammonia which is a problem arising when a reductive nitrogen compound such as hydrazine is injected in itself alone can be suppressed. Further, there is a merit that pH can be returned to the neutral side by carbonate ion, even if the ammonia forms ammonium ion and shifts pH to the alkaline side. Additionally saying, it can be expected that, by adding an ion, an oxide or a hydroxide of manganese, zinc, molybdenum, tungsten or the like to the reactor water, an oxidation reduction reaction between these substances and reductive nitrogen compound takes place to accelerate the reactions of (Formula 4) and (Formula 5), and thereby the concentrations of oxygen and hydrogen peroxide are decreased, and thereby ECP is reduced. Next, BWR to which this invention is applied will be explained with reference to FIG. 1. In BWR, a condenser 13, a condensate filter demineralizer 3, a feed water pump 4, a feed water heater 5 and a reactor pressure vessel 1 charged with a nuclear fuel are connected by means of feed water line 6, and the reactor pressure vessel 1 and turbine 2 are connected by means of main steam line 14 to form a closed loop. Using water as the reactor coolant, water is converted to steam in the reactor pressure vessel 1. A turbine is rotated by the use of this steam, and thereby a generator (not shown in the figure) is rotated to generate electricity. The steam is returned to water in the condenser 13, made free from impurities in the condensate filter demineralizer 3, and returned to reactor pressure vessel 1 through feed water heater 5 by means of feed water pump 4. Apart from it, the lower part of reactor pressure vessel 1 and inlets of re-circulation pump 7 and jet pump 15 are connected by means of Primary Loop re-circulation system line 16. Heat output is increased by increasing the flow rate of cooling water flowing into the core by means of Primary Loop re-circulation pump 7. ABWR has no Primary Loop re-circulation system line 16, and the Primary Loop re-circulation pump 7, but has a structure of internal pump where the Primary Loop re-circulation pump 7 is provided in the pressure vessel 1. Hereinafter, an explanation will be made by referring to a reactor having a Primary Loop re-circulation system line 16. In this reactor, the upstream side of the Primary Loop re-circulation system line 16 and the reactor water clean up system 9, reactor water clean up system heat exchanger 11, reactor water filter demineralizer 12 and feed water system line 6 are connected by means of reactor water clean up system line 10, and the reactor water is passed to the reactor water filter demineralizer 12 by means of reactor water clean up system pump 9 to remove impurities from the reactor water. Further, a bottom drain line 8 is provided to connect the bottom of reactor pressure vessel 1 to the reactor water clean up system line 10. Further, in the upper part of the core of the reactor pressure vessel 1, there is provided an emergency core cooling system for injecting water into the rector core in order to cool the core at the time of emergency and a control rod drive hydraulic system for injecting cooling water to drive the control rod for controlling the nuclear reaction of the fuel in the reactor are provided (not shown in the figure). Further, water qualities in the system lines are monitored by means of water quality monitors 21 to 25, and the dose rate of the main steam line 14 is monitored by means of the main steam line dose rate measuring equipment 26. In the case of ABWR, there is provided a reactor water clean up system line 10 for drawing out a part of the reactor water from the upper part of reactor pressure vessel 1, cooling it by passing it through reactor water clean up system heat exchanger 11, removing the impurities from the reactor water in the reactor water clean up equipment and returning it to the feed water line 6. In the above-mentioned BWR, the time at which a reductive nitrogen compound is injected in order to mitigate SCC is roughly classified into the following two times, and the site of injection varies depending on the time of injection. (1) At the times of start up and shut down—The time period of start up operation of the reactor, namely from the drawing out of the control rod to the injection of cooling water from water feed system; and the time period of shut down, namely from the time of stopping the injection of feed water from the water feed system to the time of wholly inserting the control rod.(2) At the time of operation—The time period of starting up the reactor, the time period of normal operation, and the time period of shut down; provided that the period of (1) is excepted. The time periods of start up and shut down are period in which hydrogen and reductive nitrogen compound cannot be sent into the pressure vessel of the reactor, even if hydrogen and reductive nitrogen compound are injected into the cooling water from the feed water system. Therefore, it is necessary to inject hydrogen and reductive nitrogen compound into the cooling water flowing in at least one systems selected from the Primary Loop re-circulation system, reactor water clean up system, emergency core cooling system and control rod drive hydraulic system which can feed cooling water to reactor pressure vessel, for injecting hydrogen and reductive nitrogen compound into the reactor pressure vessel. At the time of start up and shut down, the radiation emitted from the core has a weak intensity, so that in the case of hydrogen injection, the efficiency of removal of oxygen and hydrogen peroxide is considered to be low. Thus, injection of reductive nitrogen compound reactive with oxygen and hydrogen peroxide even in the absence of the action of irradiation is particularly effective. Since steam flows into the condensation tank only when the steam flow rate is low and the turbine by-path valve is open, the influence of flying out of ammonia can also be neglected. Further, since the allowable range of ammonia concentration in the core water is broader than at the time of normal operation, the effect of injection of reductive nitrogen compound is very great in this period. On the other hand, at the time of normal operation, a reductive nitrogen compound is injected from at least one system selected from the water feed system, Primary Loop re-circulation system, reactor water clean up system, emergency core cooling system and control rod drive hydraulic system. Since the point of hydrogen injection is usually selected from the sucking-in side of the condensate pump having a low pressure, there is no problem in the positioning of hydrogen injection point and reductive nitrogen compound injection point, so that hydrogen injection and reductive nitrogen compound injection can be carried out simultaneously. The main place at which oxygen and hydrogen peroxide are formed by radiolysis of water is the core of the reactor. The emergency core cooling system and the control rod drive hydraulic system, capable of directly feed cooling water to the core, can directly inject hydrogen and reductive nitrogen compound into the generation source of oxygen and hydrogen peroxide, and therefore they have a merit of capable of decreasing oxygen and hydrogen peroxide in the early stage. Further, water is usually stagnated on the inner surface of emergency core cooling system and the surface is exposed to intense irradiation, as a result of which such areas are apt to generate SCC. Thus, if reductive nitrogen compound is passed constantly, SCC of the lines can be prevented and integrity of the system used at the time of emergency can be secured. In the case that a reductive nitrogen compound is injected from the feed water system line 6, it is preferable to feed the water to a downstream point of the feed water heater 5. Carbon steel is used as a material of the feed water system line 6, and oxygen is injected into the cooling water flowing therein in order to suppress corrosion of the pipe line. There is a possibility that the reaction with oxygen is catalyzed by the material surface, so that the reaction between oxygen and reductive nitrogen compound can be unnegligible at the position having a large surface area per unit volume of fluid as in the feed water heater 5, which can lead to a drop in utilization rate of the reductive nitrogen compound. Further preferably, it is desirable to inject the reductive nitrogen compound from downstream of water quality monitor 21 for the cooling water of feed water system line 6. In the water quality monitor 21, the impurities present in the cooling water taken into the reactor pressure vessel is monitored by checking electric conductivity. This is for the reason that, if the reductive nitrogen compound is injected into upstream thereof, the electric conductivity rises when the reductive nitrogen compound is dissociated into ions, and the presence of impurity becomes impossible to monitor. In the case where a reductive nitrogen compound is injected from the reactor water clean up system line 10, it is preferable to inject it from a down-stream point of the reactor cooling water filter demineralizer 12. This is for the reason that, when the reductive nitrogen compound is ionized, the ions are caught at the reactor water filter demineralizer 12, and the utilization rate of reductive nitrogen compound in the reactor pressure vessel 1 becomes lower. Further preferably, the reductive nitrogen compound is injected from the down-stream point of water quality monitor 24 which is located at downstream of the reactor water filter demineralizer 12. In the water quality monitor 24, the impurities in the cooling water passing through the reactor water filter demineralizer 12 are monitored by electric conductivity. If it is injected from the upstream thereof, the ionization of reductive nitrogen compound brings about a rise in electric conductivity, which makes it impossible to monitor the presence of impurities. Hereunder, examples relating to injection of reductive nitrogen compound into cooling water, according to this invention, will be mentioned. As the first example of this invention, an example in which only a reductive nitrogen compound is injected at the times of start up and shut down will be mentioned. At the times of start up and shut down, temperature is low and γ-ray exposure is small, so that the water-forming reaction between reductive nitrogen compound and oxygen and hydrogen peroxide does not take place readily. FIG. 5 illustrates hydrazine concentration dependence of ECP of 304SS, wherein hydrazine was added as a reductive nitrogen compound. If the ECP dependence of CGR shown in FIG. 2 is taken into consideration, it is necessary to add hydrazine in an amount of 50 ppb or more or further preferably in an amount of 100 ppb or more in order to reduce CGR to 1/10 of that in the case of no hydrazine injection. On the other hand, addition of 300 ppb or more brings about no change in the ECP-lowering effect. From the electric conductivity dependence of CGR shown in FIG. 2, it is apparent that, even when ECP is the same, a higher electric conductivity gives a greater CGR. Accordingly, it is not desirable to add hydrazine in an excessive amount in order to increase electric conductivity of cooling water. Based on the above-mentioned facts, it can be said that it is preferable to control the hydrazine concentration so as to come to 300 ppb or less or to control reductive nitrogen compound concentration so as to come to 9.4×10-6 mol/liter or less; and it is further preferable to control hydrazine concentration to 50 ppb to 300 ppb, namely to control the reductive nitrogen compound concentration so as to come to from 1.5×10-6 to 9.4×10-6 mol/liter. FIG. 1 illustrates one example of the system chart in a case that a reductive nitrogen compound solution stored in the reductive nitrogen compound solution tank 41 is injected into Primary Loop re-circulation system line 16 by means of reductive nitrogen compound solution injecting pump 42. In order to adjust the concentration of reductive nitrogen compound to a prescribed concentration, the reductive nitrogen compound of which amount is calculated by the following Equation 10 is injected:(Amount of injected reductive nitrogen compound)=(Prescribed concentration of reductive nitrogen compound)×(Amount of cooling water in the pressure vessel of reactor)÷(concentration of reductive nitrogen compound in the reductive nitrogen compound solution tank) (Equation 10) After once completing the injection, injection of the consumed amount of reductive nitrogen compound is enough for adjusting the reductive nitrogen compound concentration to the prescribed value. Concentration of the reductive nitrogen compound is determined by analyzing the concentration of reductive nitrogen compound in the sample taken out from the cooling water of the bottom part of reactor pressure vessel 1 through the water quality monitors 22 and 23. The amount to be re-injected is calculated from the following (Equation 11).(Amount of reductive nitrogen compound to be injected)={(Prescribed concentration of reductive nitrogen compound)−(Analyzed value of reductive nitrogen compound concentration)}×(Amount of cooling water in the reactor pressure vessel)÷(Concentration of reductive nitrogen compound in the reductive nitrogen compound solution tank) (Equation 11) By intermittently carrying out the above-mentioned procedures of analysis and re-injection, concentration of reductive nitrogen compound can be controlled so as to come to the prescribed value. It is also possible to carrying out a continuous monitoring by measuring the electric conductivity of the cooling water in place of intermittently analyzing the concentration of reductive nitrogen compound. This is for the reason that electric conductivity can be converted to concentration of reductive nitrogen compound by previously determining the coefficients a and b in (Equation 12) experimentally.(Concentration of reductive nitrogen compound)={(Electric conductivity)−b}÷a (Equation 12) In FIG. 1 is shown an example in which a reductive nitrogen compound injecting equipment is connected to the Primary Loop re-circulation system line 16. However, it is also possible to similarly control the injection of reductive nitrogen compound by connecting the reductive nitrogen compound injecting equipment to the reactor water clean up system line 10, as shown in FIG. 9. The other system lines are also similar. FIG. 10 illustrates one example of the reductive nitrogen compound injecting equipment preferably usable for the injection while controlling the amount of reductive nitrogen compound. This equipment is provided with a reductive nitrogen compound tank 51, in addition to which at least one of water level indicator 52, flowmeter 55 and integrated flowmeter 57 is provided. In addition to them, a reductive nitrogen compound solution injection pomp 54 for injecting a solution of reductive nitrogen compound into the cooling water, and a valve 53 and a check valve 56 for preventing erroneous injection of reductive nitrogen compound or back-flow of cooling water are equipped, and they are connected together by means of pipe lines. The tanks and lines are made of a steel material, the surfaces to be contacted with the reductive nitrogen compound are preferably coated with a resin material such as poly-tetrafluoroethylene resin to prevent a direct contact between steel material and reductive nitrogen compound. This is for the reason that a direct contact between steel material and reductive nitrogen compound can cause a decomposition of the reductive nitrogen compound. Further, there is a possibility that, if a reductive nitrogen compound comes into a direct contact with air, the reductive nitrogen compound can be decomposed. For preventing this decomposition, it is advisable to bubble the reductive nitrogen compound present in the tank with argon gas or to cover the liquid surface with argon or the like. Next, as the second example of this invention, an example in which only a reductive nitrogen compound is injected at the time of operation will be mentioned. Since temperature is high and γ-ray exposure is greatest at the time of operation, the water-forming reaction between reductive nitrogen compound and oxygen and hydrogen peroxide is accelerated. Accordingly it is necessary to inject the reductive nitrogen compound continuously. In FIG. 6 are shown the changes of oxygen and by-products in a case of adding hydrazine as a reductive nitrogen compound to high-temperature water containing dissolved oxygen and carrying out a γ ray irradiation. In case that the concentration of reductive nitrogen compound does not reach the amount needed for converting oxygen to water, a residual part of oxygen remains. In case that the concentration of reductive nitrogen compound is higher than the amount necessary for converting oxygen to water, oxygen is consumed and ammonia is formed. Based on these facts, the proper amount of injected reductive nitrogen compound can be controlled by using the concentrations of oxygen and ammonia contained in the reactor pressure vessel bottom water as indications. One example of the controlling method will be explained blow with reference to FIG. 11. If the amount of injection is increased stepwise, the oxygen concentration in the cooling water reactor pressure vessel bottom decreases at first so as to match the step. The target value of oxygen concentration is 10 ppb, and further preferably 5 ppb. So far as the oxygen concentration is lower than the target, ECP can be lowered sufficiently and CGR can be made small. If the amount of injection of reductive nitrogen compound is stepwise increased, ammonia becomes detectable in the cooling water of reactor pressure vessel bottom. Since ammonia increases the load of reactor water filter demineralizer and leads to a rise in electric conductivity, a lower ammonia concentration is desirable. FIG. 12 shows the relations between ammonia concentration and pH at room temperature and electric conductivity. From the viewpoint of water quality management criteria of BWR, it is required that pH at room temperature is 5.6 to 8.6, and electric conductivity does not exceed 1 μS/cm. Accordingly, it is preferable that ammonia concentration in the reactor water does not exceed 4.2×10-6 mol/liter. The oxygen concentration can be analyzed by means of a dissolved oxygen meter; while the ammonia concentration can be analyzed by means of ion meter, calorimetric analysis or ion chromatography. It is also allowable to use electric conductivity or pH as an indication in place of analyzing ammonia concentration, because electric conductivity and pH can be converted to ammonia concentration based on FIG. 12. As above, the amount of injection of reductive nitrogen compound is stepwise increased, and the amount of injection of reductive nitrogen compound at which the ammonia concentration or the electric conductivity and pH comes to lower than the target value is previously determined. After that time of the operation, the designed amount of reductive nitrogen compound is injected. Otherwise, the range of amount of injection is determined, and reductive nitrogen compound is injected in that concentration range. It is also allowable to alter the amount of injection manually in the light of measured values of pH and ammonia, or to provide a control system into which measured values are fed back and thereby control the amount of injection. In this example, the mount of reductive nitrogen compound which must be injected has been determined by taking oxygen concentration as an indication. It is also possible to use ECP of the plant-constructing material immersed in the cooling water as an indication. This is for the reason that, as shown in FIG. 3, oxygen concentration has a 1:1 correlation with ECP, oxygen concentration can be determined from ECP. Next, as the third example of this invention, an example in which hydrogen and a reductive nitrogen compound are injected into the cooling water will be mentioned. In case that hydrogen is injected, the hydrogen concentration in the cooling water at the bottom of reactor pressure vessel increases. If the hydrogen concentration exceeds a definite value, dose rate of the main steam line can increase. Accordingly, it is necessary to control the amount of injected hydrogen together with the reductive nitrogen compound to obtain an optimum condition. Since hydrogen is usually cheaper in price than reductive nitrogen compound, it is preferable to increase the amount of hydrogen and decrease the amount of reductive nitrogen compound. FIG. 13 diagrammatically illustrates the changes of concentrations of oxygen, hydrogen and ammonia in the cooling water at the bottom of reactor pressure vessel, and the dose rate of main steam line, in the case of changing the amount of injection of reductive nitrogen compound while keeping the injection of hydrogen constant. In FIG. 13 is simultaneously shown a case of changing the amount of hydrogen injection. The dose rate of main steam line is taken to increase when the hydrogen concentration in the cooling water at the bottom of reactor has exceeded a definite value. In FIG. 13, a and d denote the amount of injection of reductive nitrogen compound at which dose rate of main steam line increases; while b and c are amount of injection of reductive nitrogen compound where oxygen concentration reaches the lowered target (b) by injection of reductive nitrogen compound. In the case of (2) where the injection of hydrogen is large, a small amount of reductive nitrogen compound is enough for reaching the lowered target of oxygen concentration (b), but the dose rate of main steam line begins to increase before reaching that amount of injection of reductive nitrogen compound (a). On the other hand, when the amount of injected hydrogen is small (1), the injected amount of reductive nitrogen compound is larger than that in the case of (2), but at such an amount the dose rate of main steam line does not rise (d). From the economical point of view, it is preferable to determine the maximum (1) as in the case of hydrogen injection (1). By stepwise changing the injected amounts of hydrogen and reductive nitrogen compound and determining the relation of FIG. 13, proper ranges of the injected amounts of hydrogen and reductive nitrogen compound can be determined. On the other hand, it is expected from the relation shown in FIG. 13 that, if the amount of injection of hydrogen is decreased, the amount of injection of reductive nitrogen compound necessary for reducing the oxygen concentration will increase. By utilizing this fact, proper ranges of injection of hydrogen and reductive nitrogen compound can be determined more efficiently. This method will be explained below by referring to FIGS. 14 and 15. As shown in FIG. 14, a reductive nitrogen compound and hydrogen are stepwise injected, by taking the oxygen concentration and ammonia concentration in the coolant in the reactor pressure vessel bottom as indications. Concretely saying, according to the flow chart of FIG. 15, the amount of injected hydrogen and the amount of injected reductive nitrogen compound are varied. At first, injection of hydrogen is carried out at the critical amount of hydrogen injection giving a dose rate, in the main steam line, not exceeding the lower limit of target value. Subsequently, the concentration of reductive nitrogen compound is stepwise increased. When main steam line dose rate has exceeded in this process, the amount of injected hydrogen is decreased by a definite amount. The concentration of reductive nitrogen compound is increased while aiming at that the oxygen concentration will reach a value not exceeding the lower limit of target. By this procedure, the amount of injection of the reductive nitrogen compound giving an oxygen concentration not exceeding the target value can be determined. Further, in the same manner as in Example 2, the amount of injected reductive nitrogen compound is stepwise increased to determine the range of the amount of injected reductive nitrogen compound giving an ammonia concentration not exceeding the upper limit. By the procedure mentioned above, an amount of injection of reductive nitrogen compound giving an oxygen concentration not exceeding the lower limit of target is taken as a minimum value, and the amount of injection just before the ammonia concentration exceeds the aimed upper limit is taken as the upper limit. In the subsequent period of operation, hydrogen and reductive nitrogen compound concentrations are so controlled as to come to the values determined above. It is also allowable to control the hydrogen injection by using the hydrogen concentration in the reactor pressure vessel bottom as an indication, in place of main steam line dose rate. In this case, injection of hydrogen only is previously carried out, and the relations of main steam line dose rate and hydrogen concentration in the bottom of reactor pressure vessel to the amount of hydrogen injection are determined, and further the relation between main steam line dose rate and hydrogen concentration in the bottom of reactor pressure vessel is determined. Hydrogen concentration can be continuously monitored by the use of dissolved hydrogen concentration meter. Further, it is also possible to use ECP of the plant-structural material dipped in cooling water as an indication, as has been mentioned in Example 2. Next, as the fourth example of this invention, a method of injecting hydrogen, a reductive nitrogen compound and an alcohol into cooling water will be mentioned. When hydrogen is injected, there is a possibility that the hydrogen concentration in the reactor pressure vessel bottom water increases, and if it exceed a definite value, main steam line dose rate increases, in the same manner as in Example 3. When an alcohol is injected, there is a possibility that, due to the carbonate ion, pH becomes low or electric conductivity becomes high. Accordingly, it is necessary to control the amounts of injection of alcohol and hydrogen together with reductive nitrogen compound, and optimize the condition. After determining the amount of injection of reductive nitrogen compound and hydrogen according to the method mentioned in Example 3, alcohol is injected so as to replace the reductive nitrogen compound and alcohol. Its amount is calculated according to the following equation 13:(Concentration of injected alcohol)=(Molar number of alcohol necessary for reacting with 1 mol of hydrogen peroxide)/(Molar number of reductive nitrogen compound necessary for reacting with 1 mol of hydrogen peroxide)×(Concentration of injected reductive nitrogen compound to be subtracted) (Equation 13) Concretely saying, it is advisable to replace the reductive nitrogen compound and alcohol stepwise while confirming that the change of electric conductivity of cooling water becomes smaller than the target value, as shown in FIG. 16. Otherwise, it is also allowable to determine the amount of alcohol injection giving an electric conductivity smaller than the target value and thereafter to inject the reductive nitrogen compound stepwise, as shown in FIG. 17. The concentration of dissolved CO2 formed from the alcohol can be calculated according to (Equation 7) and (Equation 8). From the relation between dissolved CO2 concentration and pH at room temperature and electric conductivity shown in FIG. 18, the concentration of dissolved CO2 giving an electric conductivity smaller than the target value can be read out. Accordingly, the alcohol concentration giving an electric conductivity not exceeding the target can be determined. However, since there is a possibility that the reductive nitrogen can be consumed prior to the alcohol, it is advisable to confirm the effect by taking the oxygen concentration in the cooling water and ECP of plant-structural material dipped in the cooling water as an indication. It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. According to this invention, a stress corrosion cracking of nuclear power plant structural material can be mitigated without secondary effects such as rise in the cobalt-60 concentration and the like, by injecting a reductive nitrogen compound containing a nitrogen having a negative oxidation number into a reactor water.
	description	This invention relates to tropospheric volume elements enriched with vital elements and/or protective substances as well as the procedures for their production and application. The term “vital elements” applies to all matter supporting the development of life within the earth's biosphere and the term “protective substances” means all those substances which contribute directly or indirectly to the prevention of harmful effects on the earth's biosphere and in particular on man. Tropospheric volume elements according to the invention are enriched with vital elements and/or protective substances. Tropospheric volume elements in the form of clouds which contain contaminants and which can escape from industrial facilities due to damage or malfunction are enriched with protective substances which prevent the organism from taking in radioactive elements and minimize the extent of the area affected by the clouds and possess additional warning and identification properties. Enriched tropospheric volume elements may offer numerous advantageous effects, the most important of which are: Climate cooling and climate stabilization Increase of food production Production of methane hydrate and kerogen as renewable energy sources Reduction in all sorts of air pollutants Increase of precipitation and Reduction of the extent of damage and the number of victims due to nuclear reactor accidents. The components of the environment include the populated and the unpopulated parts of the earth's surface and neighboring areas, including the atmosphere, the surface of the earth, ground, sediment, sediment surface, stretches of water and ecological systems. These components are linked with each other by cycles of material exchange which are all connected to each other by partly instable flux exchange balances. Consequently, the complex system may exist in differing, more or less stable phases. Relatively minor causes may trigger off the transition from one phase to another. Climate phase transitions are recognized as being particularly disadvantageous. The geological climate history of the ice age has shown us that the transition of the earth's climate from the ice age's cold climate to the warm age's hot climate may only take a few years to be completed. At present, we are experiencing the transition from the moderate to the hot climate phase. This is a result of the rise in the quantities of greenhouse gases methane and CO2 which has been caused by man since the early 19th century, whereby the methane content growth is also coupled with the troposphere's diminishing power of self-purification. The increase in methane in the troposphere is also coupled with the decomposition of solid methane hydrate in the tundra moor sediments and in the ocean sediments to free quantities of methane due to the rise in temperature. There has been a demand for large-scale geo-engineering projects (P. J. Crutzen, Nature, Vol. 415 of Jan. 3, 2002) for a lasting correction of the climate development in the near future. There have been various proposals on how to prevent the transition to the hot climate phase; the enrichment of the stratosphere with aerosols with sulfur dioxide (M. Budyko) or soot (P. J. Crutzen) is supposed to cool the troposphere. The costs for such a project are estimated to be more than 20 billion US $ (Graedel, T. E., Crutzen, P. J.: Chemie der Atmosphäre, Spektrum Ahademischer Verlag, Heidelberg/Berlin/Oxford [1994], pages 457, 458). At present, attempts are being made to come to international agreements to reduce the release of carbon dioxide by limiting the combustion of fossil energy sources. However, the attempts to gain acceptance of the so-called Kyoto protocol have shown that such a measure cannot be put into practice world-wide. Without intervention, the warming of the troposphere will continue. The result will be an increase in food scarcity and an increase in the area of land which is salted and devastated. The continuous growth of the world's population will cause a rise in distribution conflicts. Overgrazing, fire clearance and ground erosion will accelerate this negative development. In spite of an increase in the utilization of sea area for fish farming, over-fishing of the oceans has already prompted a dramatic recession in food production. In the near future, fossil fuel resources are also expected to run short. A compensation by extension of alternative energy sources and energy-saving measures cannot be enforced in the world's poorer regions due to the required investments. The Chernobyl disaster was triggered off due to the nuclear fission of nuclear fuel in the reactor running out of control; the cloud of radioactive flue gas released by the nuclear reaction and the fire the nuclear reaction caused in the reactor and moderator unit struck large parts of Europe. Terror acts, such as crashing civilian large capacity aircraft onto the towers in New York, have shown that catastrophes repeat themselves. Safety scenarios which have not considered this, have since lost their validity. In all of the nuclear power plants world-wide, there are no safety installations which are capable of reducing the spread of radioactive clouds, which can occur when a nuclear reactor runs out of control, which can limit their effects and which can mark the emission visibly for everybody at the affected spots. The argument that nuclear power plants will be put out of operation world-wide within a few decades is unacceptable, as even the German authorities have guaranteed the operation of at least some nuclear power plants for more than thirty years to come. In Europe, the erection of new nuclear power plants continues, the latest examples of which are the nuclear power plant built in Temelin and another planned in Finland. There are also no safety installations for the treatment and identification of toxic clouds in those industrial facilities which handle highly toxic materials or dangerous microbes. According to the invention, the bundle of problems pictured above is solved by the production of definite tropospheric volume elements enriched with vital elements and/or protective substances. Here, “vital elements” means all elements which support the development of life within the earth's biosphere and “protective substances” means all those substances which contribute directly or indirectly to the prevention of harmful effects on the earth's biosphere and the life-forms it contains. The production of tropospheric volume elements enriched with protective substances and/or vital elements, which may be of global, regional or local extent, is carried out preferably by releasing flue gases according to the invention into the tropospheric air space above the desired area to be affected. The purpose of the addition of flue gases according to the invention is the distribution of protective substances and/or vital elements in the troposphere over the desired area to be affected, to have them remain there for a period of time before they finally sink down onto the surface of the ground and/or water. The flue gases according to the invention used for this purpose are enriched with protective substances and/or vital elements. Belonging to the substances under the term protective substances are also those substances which will develop into protective properties in particular in the troposphere. The production of the flue gases may occur by combustion of fuels containing vital elements and/or containing other materials which on their combustion form protective substances. However, it is also possible to enrich the flue gases with vital elements and/or protective substances after they have been produced. Post-combustion enrichment of flue gases with vital elements and/or protective substances is preferred if the respective substances are sensitive to temperature or if they cannot be produced by combustion. For many applications, it is advantageous to use customary fuels for the production of the flue gases according to the invention, e. g. oil or petrol. Additives, which on combustion form a vital element composite fraction and/or a protective composite fraction in the flue gas which has developed, preferably exist in the form of oil- or petrol-soluble compounds in a molecular-dispersed distribution. Table 1 lists examples of substances which may be utilized as fuels or fuel additives to produce the flue gases according to the invention. Table 2 lists examples of protective substances which may be added to the flue gas after combustion and table 3 lists examples of protective substances and/or substances containing vital elements as flue gas components produced by combustion. Table 4 contains further examples of protective substances. Table 5 lists examples of those substances from which protective substances in the troposphere can be autonomously formed. The production of the flue gases according to the invention may take place by combustion in any type of combustion apparatus. Production may also take place by means of vehicles driven by fuels according to the invention, in particular by means of aircraft, ships and motor vehicles. Production may also take place by means of devices which are constructed to exclusively serve this purpose. The production of tropospheric volume elements according to the invention by the release of customary available protective substances and vital elements is not preferred if the materials are solid materials. The protective substances and vital elements of finest granulation available on the market are so-called pyrogenic oxides. Examples of these types of commercial products are “Aerosil” (=silicon dioxide) and titanium oxide pigments (the latter lacking the protective coating which prevents the production of hydroxyl radicals). Even if released in the finest granulation available, these dusts have the disadvantageous property that they only remain for a short time because they settle quickly. Contrary thereto, certain applications permit the advantageous distribution of gaseous protective substances and gaseous vital elements in a tropospheric volume element even without the aid of flue gas. Examples of vital elements are, for instance, phosphorus, nitrogen, silicon and iron which are essential for the existence of living organisms. Examples of protective substances are those substances which directly trigger off destruction, removal or neutralization of hazardous substances, or substances which enable living organisms to avoid contact with hazardous substances. Substances belonging to the protective substances are, for example, hydroxyl radicals in the troposphere because they cause the decomposition of dangerous reductive substances such as e. g. methane, smog and flue gases. Substances belonging to the protective substances are also those substances which stimulate the production of hydroxyl radicals in the troposphere, e. g. oxides containing titanium. Substances belonging to the protective substances are also contaminant-sorbents such as soot, pyrogenous silicic acid, iron(III)-oxide, fog and substances forming fog. Also belonging to the protective substances are warning substances which due to color, smell or irritating effects stop living organisms and man in particular from coming close to a dangerous substance or from eating food or drinking water contaminated by the dangerous substance. Also belonging to the protective substances are, for instance, the color pigments soot and red iron oxide, the intensively smelling substances ethyl mercaptan and pyridine, the irritants chloracetophenone and trichloronitromethane, taste-intensive substances or aromatic substances and substances which cause disgust or nausea. Some examples of the volume elements enriched with vital elements and/or protective substances according to the invention, are: the tropospheric volume element over the sea which is preferably enriched with aerosols containing vital elements e. g. iron and phosphorus in oxide bonding for the growth of phyto-plankton, and protective substances e. g. titanium in oxide and/or nitride bonding which may trigger off the photolytic production of hydroxyl radicals to decompose methane and other undesirable tropospheric gases. The aerosols contribute directly or indirectly to the increase in the troposphere's retro-radiating effect (Albedo). The advantageous effect of this tropospheric volume element on the climate, energy supply and world nutrition is explained by way of example in FIG. 1. In FIG. 1: The flow path indicated by bold-type arrows in FIG. 1 represents the non-tectonic share of the earth's short-term carbon cycle which is maintained by the photosynthesis of the phyto-plankton. Compared to the presently existing transient equilibrium, the transient equilibrium achieved by the tropospheric volume element according to the invention is marked by a lower atmospheric carbon dioxide level, a considerable rise is carbon load quantity and by a shorter carbon cycle completion period. The fossil energy resources will become less important when the use of kerogene sediment and methane sediment as renewable energy sources begins. the tropospheric volume element over land or coastline regions marked by high levels of traffic and industry emissions is preferably enriched with aerosols containing protective substances such as titanium in oxide bonding, which stimulates here the photolytic decomposition of smog, nitrogen oxides, carbon monoxide, halogen and nitric aromatics and other undesirable combustion and emission products, and also protective substances such as iron in oxide bonding which causes the absorbent bonding of the emission products originating from the wear of friction-coating materials, in particular of carcinogenic antimony and toxic lead. the enclosed and artificially illuminated tropospheric volume element in tunnels or multi-storey car parks and underground car parks which is preferably enriched with aerosols containing protective substances such as titanium and cerium in oxide bonding which here also trigger off the photolytic decomposition of nitrogen oxides, carbon monoxide and other undesirable combustion products, and also, for example, absorb the emission products antimony and lead originating from the wear of friction-coating materials such as e. g. iron in oxide bonding. the tropospheric volume element over land and coastline regions marked by a deficiency of essential elements, e. g. iodine, selenium, manganese and molybdenium, which is preferably enriched with gases and/or aerosols containing the missing vital elements. The essential elements are preferably linked by absorptive or chemical-absorptive bonding to aerosol carriers, e. g. soot or iron oxides produced by combustion. Belonging to the tropospheric volume elements enriched with protective substances according to the invention are also those clouds which have been produced by the most devastating nuclear power plant accidents, such as were produced by the nuclear power plant at Chernobyl, which float in the troposphere and are enriched with radioactive elements. This also includes other clouds enriched with radioactive elements which may escape from other sources due to an uncontrollable nuclear reaction; some examples are, for instance, nuclear waste dumps, nuclear fuel rod depots, nuclear reactors for powering ships, nuclear weapons and their storage facilities, enriched uranium and plutonium depots. Flue clouds from fires or clouds of highly toxic or pathogenic potential which may exist in the troposphere due to accidents or disasters in depots and production facilities for poison gas, bacteriological weapons or laboratories and technological facilities handling these sorts of toxic or pathogenic materials are also among the tropospheric volume elements enriched with protective substances according to the invention. The protective substances used for this purpose can be classified with one or more substances from the substance groups for marking materials, absorbents, substances stimulating precipitation, substances supporting condensation, substances supporting particle-agglomeration and substances which obstruct an intake of matter in the organism. The clouds carrying contaminants and enriched with protective substances and the contaminated sediment which has fallen from them or the contaminated water that has made contact with them may be identified by anybody due to one ore more protective substances from the pigment, smell, taste and irritant substance groups by sight, by smell, by taste and also by skin irritation and can thereby be avoided. Restricted to smell and skin irritation, the same also applies to animals. Several examples for these kinds of marking materials are given in table 2. In addition, these contaminated tropospheric volume elements are preferably enriched with protective substances which bind the pollutants, stimulate their precipitation and directly obstruct their intake by the organism. According to the invention, the clouds containing contaminants are enriched with protective substances. These directly or indirectly obstruct or prevent the intake of radioactive, toxic or virulent substances by human or animal organisms, and even by plants. This considerably lowers the effects of the toxic emissions released. In case of an accident, the production of tropospheric volume elements enriched with protective substances is carried out by safety installations specifically constructed for this purpose. The operation of such safety installations is described below by using an accident with released radioactive emissions from an uncontrollable nuclear reaction in a nuclear power plant as an example. This sort of accident is known by the term MCA (maximum credible accident). The buoyant hot gases released due to nuclear fission reactions of this kind can be classified as flue gases, due to the participation of high-temperature chemical combustion processes. One major risk emerging from an MCA is the release of radioactive iodine isotopes. To minimize the risk potential of the iodine emissions containing radioactivity, the fuel according to the invention and/or the fuel additive with iodine as protective substance are stored inside the nuclear power plant. In case of an MCA, the fuel may be burnt near to the focus of the open nuclear fuel reaction. This may be done, for example, by injection of liquid fuel doped with iodine by means of one or more jet lances arranged in the direct vicinity of the point of nuclear fuel reaction, whereby the heat of the nuclear reaction will inflame the liquid fuel. It is also possible to use natural gas enriched with hydroiodic acid as fuel and to burn this off accordingly. Hereby, the flue gases according to the invention mix with the flue gases produced by the MCA. The safety installation may also be realized by a customary combustion device by using customary oil and gas burners to release the combustion products according to the invention and containing iodine from the fuel and fuel additives. As fuels, fuel oils or oil additives doped with iodine are preferred. The emission of radioactive iodine from the MCA flue gases into the troposphere is preferably exceeded many times over, in relation to the amount of radioactive iodine released in a certain period of time into the troposphere, by the emission of iodine with the flue gases according to the invention to minimize the hazard of persons taking in radioactive iodine isotopes when they come into contact with the emissions at the location of the emissions. The enrichment of the emitted contaminant cloud with protective substances from the category of solid and/or liquid absorbents enables an additional reduction in the intake of harmful substances from the contaminated cloud. Soot has the capacity to absorb gaseous radioactive substances. It may easily be produced as flue gas containing soot by the incomplete combustion of soot oil. Iron in organic bonding and/or manganese contained in the fuel result in flue gases enriched with iron and/or manganese oxides which are excellent absorbents of radioactive heavy metals. In the buoyant hot flue gases buoyant from the core melt and on its way to the troposphere, the soot aerosol will be oxidized superficially. Soot oxidized in this manner has the additional capacity of binding parts of the heavy radioactive elements. Raising the contaminated cloud's steam content and/or the content level of substances which form fog will support the bonding of radioactive metals to the absorbent protective substances. The bonding of radioactive heavy metals, metalloids and earth-alkali with the oxidized soot-particle protective substances and/or oxide-particle protective substances succeeds most advantageously in the watery phase because this phase induces the production of dissolved ions which may be more easily absorbed by the absorbents soot and iron oxides. To enable the production of watery protective substance aerosols even in a dry tropospheric environment, the contaminated cloud may be enriched additionally with protective substances which form fog. The fog-forming substances can be produced by combustion as well as by injection of the fog-forming substances into the hot flue gases. Apart from water, the fog-forming substances are, for example, volatile acids, volatile bases, volatile hydrolytic salts and thermally decomposing salts as well as hygroscopic substances or also those substances which may transform into one or more fog-forming substances in the cloud which is enriched with protective substances. Belonging to the fog-forming substances are those substances which are listed by example in tables 3 and 4. Fog-forming substances can also be directly produced from fuels, for example, phosphorus acid from the combustion of trikresylphosphate and sulfuric acid from the combustion of carbon disulfide. In a cloud, these substances or their oxidation products and/or hydrolysis products produce watery fog droplets of protective substance. The forming of fog has the advantage that it aggregates the aerosol particles in the cloud into flakes by agglomeration. This increases the sinking speed of the particles up to them forming precipitation. Preferably, water-soluble hygroscopic protective substances are used to form protective substance fog whereby ammonium chloride, calcium chloride, magnesium chloride or zinc chloride are preferred. The combination of volatile bases with volatile acids also results in advantageous and stable protective substance fogs. The combustion of metal dusts such as zinc, aluminum, iron or magnesium or mixtures of these substances with organic compounds of high chlorine content also permits the production of stable protective substance fogs. It is of advantage to choose a high charging density of protective substances to enrich the contaminated cloud. On the one hand, this measure causes the majority of the inherent contaminants to bond and on the other, it causes the protective substance aerosols to agglomerate and sedimentate faster than the cloud without protective substances. This results in the advantage of restricting the region which is affected by fall-out to a many times smaller area than would have been struck without applying the described measure. The protective substances according to the invention, soot and iron oxide, possess pigment characteristics and therefore offer a simple method of visibly marking the fall-out area with black or red fall-out color. The contaminant bonding to the protective substances has the further advantage that the radioactive particles can be easily separated from the contaminated air by means of air purification devices and the contamination of water due to dissolved radioactive substances can be reduced. In addition, protective substances which are identifiable by smell and/or skin irritation are suitable as sensory marking means for the radioactive cloud and its emissions. Examples of these substances may be found in the groups of smell-intensive and/or skin-irritating substances. These are, for instance, mercaptans (smell-intensive), pyridine (smell-intensive), halogen ketones (skin-irritating), halogen nitrites (skin-irritating), cyanogen halides (skin-irritating), trichloronitromethane (skin-irritating), halogen-nitro aromatic substances (skin-irritating), oxazepine (skin-irritating) and similar substances. Another way to prevent humans and animals from drinking water affected by the fall-out is to add aromatic substances with an intensive disgusting taste as protective substances. These protective substances, which would decompose if exposed to high temperatures, are preferably injected as gas or spray mist into the active hot flue gas current after the above-mentioned flue gases according to the invention with the protective substances have been added. Examples of protective substances having the described signal and protection properties which may be released into the flue gas of an MCA are listed in table 2. To protect the substances sensitive to temperature and oxidation in the cloud from decomposition by UV-radiation and oxidation, it is of advantage if the flue gas current contains light-refracting or light-absorbing pigments e. g. soot and oxides because the protective substances adsorbed by such pigments are better protected from chemical decomposition. The interactive mechanisms, described in the example where the radioactive cloud caused by an accident is enriched with the protective substances according to the invention, may also be applied correspondingly to accidents where gas clouds are released which contain toxics or viruses or microbes. In those cases where an accident causes a gas release without fire or explosion and where there is no influence by thermal convection, it may be helpful in an urban neighborhood to start a fire to produce the flue gases containing protective substances to provide the gas cloud with thermal lifting power which lifts the gas cloud up and away from the most endangered localities. The local tropospheric volume elements enriched with protective substance aerosols in which the production of hydroxyl radicals is stimulated by radiation can make the customary catalysts systems, serving to purify the exhaust gases of motor vehicles, obsolete. The effect of the fine distribution of aerosols according to the invention is better than the effects of solid-bedded catalysts because the aerosols can keep on taking effect within the flue gas cloud, wherever this may go, even after having left the vehicle's exhaust. The smog components ozone, NOx and peroxyacetylnitrate are thereby decomposed by the hydroxyl radicals produced or, in environments where the daytime concentration of OH-radicals exceeds the usual level significantly, cannot even be formed at all. Protective substance aerosols containing iron in oxide-bonding securely bind carcinogenic antimony and toxic lead from the wear of clutch and brake pads even after precipitation washes them away and they are sedimentated with the protective substance particles or they are washed into the sewage system with the rainwater. Protective aerosols which settle from the air onto the surfaces of vegetation, buildings and the ground can continue to produce hydroxyl radicals due to radiation and can continue their purifying function. The release of flue gases which produce protective substances could be subsidized, for instance, by introducing a fuel tax exemption or fuel tax reduction for motor vehicles which are mainly used during the day for these particular fuels so that fuels which produce flue gases containing protective substances may find widespread use as an alternative to catalysts. Equipping vehicles with catalytic devices for exhaust gas purification, as is the regulation particularly for cars with gasoline engines, would then not be necessary. To achieve a lasting climate stabilization in the moderate phase and to increase food production and renewable energy sources, it would suffice just to make use of the tropospheric volume element enriched with vital elements and protective substances over the sea. Therefore, controlling and monitoring the enrichment of the tropospheric volume elements over the sea with vital elements and/or protective substances is particularly important because as the addition of vital elements increases, the throughput in the non-geogenic carbon cycle increases, whereby the lasting stability of the transient equilibrium of the carbon cycle must be secured. The increase in the carbon load conveyed in this part of the carbon cycle therefore requires that the carbon load taken from the troposphere by the mass growth of phyto-plankton resulting from the enrichment of the tropospheric volume element, according to the invention, over the sea must be replaced to a sufficient extent. In the transitive phase, replacement may take place by the combustion of fossil fuels. After this phase, the products arising from the increased production of phyto-plankton, namely kerogen hydrate sediments and methane hydrate sediments, should be integrated in the energy production of the anthropogenic material economy. Otherwise, there is a danger that due to the falling concentration of carbon dioxide in the troposphere, the climate could slip into a cold phase. The system components of the carbon cycle, which may be modified by human intervention in order to sustain a stable carbon transient equilibrium, as a result of the enrichment of the oceanic tropospheric volume element with vital elements and protective substances are underlined below: (1) Carbon dioxide load form the sources: Combustion of renewable energy carriers and volcanic exhalation→(2) (2) Carbon dioxide sinks: Assimilated carbon dioxide load in phyto-plankton, geogenic bonding in the course of the decaying process as limestone sediment and limestone sediment subduction in the earth's crust and the earth's mantle→(3a), (3b) (3a) Phyto-plankton load into the food pyramid (3b) Phyto-plankton load into the oceanic sediment fermentation→(4) (4) Kerogen sediment load and methane hydrate sediment load from sediment fermentation→(5) (5) Kerogen sediment load and methane hydrate sediment load by sediment mining to be fed into the anthropogenic material cycle→(6) (6) Combustion of the kerogen sediment load and methane hydrate sediment load for anthropogenic energy gain→(1) A number of examination parameters permit controlling the stability of the carbon cycle's transient equilibrium with the increased carbon load rate induced. These examination parameters are preferably gained from ecological systems which are directly influenced and from other environmental systems which are affected. Controlling of the carbon load rate takes place by raising or lowering the content of vital elements and/or protective elements in the tropospheric volume element and/or protective substances according to the invention. This is achieved according to the invention by the continuous or sporadic dosage of the additive agents distributed via the airspace and by determining the position of the respective location of distribution depending strictly on the actual status and change in the respective parameters recorded. Such parameters are for example: regional, hemispheric and global contents of methane and dimethyl sulfide measured at different heights in the troposphere and above the tropopause; regional and hemispheric contents of protective substances and/or vital elements in the air, on/in vegetation, on/in the ground and in waters; average covering of cloud in the tropospheric volume element; carbon dioxide contents measured in the air and sea water, globally, in the hemisphere and in the tropospheric volume element; concentration of phyto-plankton below the tropospheric volume element; oxygen content of sea water beneath the tropospheric volume element at different depths; content of turbid matter in sea water beneath the tropospheric volume element at different depths; sedimentation rates in the sea beneath the tropospheric volume element at different depths; studying the ecological systems beneath the tropospheric volume element; measuring global temperature in the troposphere, on the surface of the ground and on the surface of the sea. The concentration of vital elements and/or protective substances in the tropospheric volume element, the volume of the tropospheric volume element and the surface covered by the tropospheric volume element influence the carbon throughput. Potential ways to influence the parameters of tropospheric volume elements charged with vital elements and/or protective substances exist in considerable variety. The average distribution, duration of stay and concentration of the substances released into the tropospheric volume element with the flue gases are here important quantities. Some examples of what can be controlled are: the location over which the flue gas is released; the extent of the area over which the flue gas is released; the height above ground or sea level at which the flue gas is released; the concentration of substances in the flue gas; the dosage of flue gas released; the composition of the substances released with the flue gas; the intervals at which the flue gas is released; the size of the particles of the substances in the flue gas. Regarding the size of the particles in the aerosols in the flue gas, the size of the secondary particles is the preferred measured quantity because the diameter of the secondary aerosol particles has an essential and decisive influence on their sinking velocity. The secondary particles consist of agglomerated primary particles. The diameters of the secondary particles are a function of the aerosol concentration in the flue gas. The aerosol concentration itself is a function of the concentration of the aerosol-forming inflammable substance in the fuel: the higher the concentration, the coarser the secondary particles in the flue gas will be and the faster they will sink in the troposphere. Similar control mechanisms may be used with the dosage of additive agents, applicable for accidents. These control mechanisms are oriented, for example, according to the status of the data on the contaminant load constantly supplied to the cloud which in the case of a nuclear power plant accident can be assessed quite accurately from the radiation temperature of the core melt and/or the height of the thermal convection column and/or from the column's radioactive radiation intensity. From the spectrum of the radioactive radiation intensity and the knowledge of the nuclear fuel type used, it is possible to conclusively identify the active composites present in the emission. These criteria are also suitable for determining the necessary amounts of load of the protective substances. It may also be decided from case to case if all the protective substances or only a certain fraction of the protective substances are to be used. Tropospheric volume elements with an increased content of vital elements have the specific advantage that the distribution of the vital elements latter over sea or land is lasting and extensive. Attempts which have been made to release vital elements in the form of iron salts which were directly released into the sea were only able to stimulate mass growth of phyto-plankton in small areas. It is also possible to separate flue gases according to the invention, which have been released in closed buildings, from the air which has been treated accordingly by utilizing the flue gases' aerosols which contain titanium and/or iron which form hydroxyl radicals under the influence of sunlight or artificial light sources after they have fulfilled their task of neutralizing harmful gases by means of the commonly known processing steps of air purification by dust extraction. By using this method, the flue gases may also be used to purify waste air or fresh air containing harmful gases. With the enrichment of the oceanic tropospheric volume element with vital elements and/or protective substances according to the invention, it is possible to ward off the climate crisis threatening mankind on a lasting basis. A selection of individual effects are: Lowering the troposphere's CO2 content (leads to climate cooling); Albedo increase directly effected by the aerosols according to the invention (leads to climate cooling); Albedo increase by cloud formation caused by increased dimethyl sulfide emissions from phyto-plankton metabolism (leads to climate cooling); Decomposition of tropospheric methane by the production of hydroxyl radicals (leads to climate cooling); Decomposition of substances which are difficult to decompose, e. g. poly-chlorinated biphenyls, halogenated dibenzodioxins and dibenzofurans, DDT, phthalates, polycyclic aromatics, by the production of hydroxyl radicals; Increase of necrotized phyto-plankton sedimentation (leads to the production of kerogen hydrate sediments and methane hydrate sediments as a source for renewable energy products); Increase of protein production in the oceanic ecological system by increasing the mass of phyto-plankton in sea water (leads to an increase in protein food resources). The mixed oxides and nitrides required to produce the additives to be released into the tropospheric volume elements are all non-toxic and, in the applicable concentrations, they do not have a negative effect on the lungs or on the digestive system. They do not cause toxic effects on the environment either. At least, there is no evidence that natural particles of similar constitution—such as may be released in considerable quantities from the tropospheric hydrolysis of iron halogenics, silicon halides and titanium halides contained in volcanic gas exhalations—have ever caused damage to the health. No negative effects have become known so far from the operation of stationary domestic heating systems fuelled with oils containing iron either. Neither the ubiquitous iron oxides and manganese oxides nor the various oxides, nitrides and oxide-nitrides, which can result from combustion of the elements silicon, titanium, zirconium and iron, which are preferably used elements, possess toxic qualities. Only the quartz modifications of the corresponding silicon compounds and titanium compounds have been proven to be harmful to the health. The aerosols released into the troposphere due to the commonly known combustion of silicon, titanium, silane, titanium acid esters and silicic acid esters are non-crystalline. There are also no hazardous effects known to emanate from non-crystalline silicon dioxide aerosols. The titanates, ferrates, zirconates, zirconium dioxide and cerium dioxide which may be used as composites of the aerosols according to the invention also have, to a great extent, disordered non-crystalline grid structures which belong to the inert substances in chemical/biological terms. In sandy sediments of decayed crystalline and volcanic rocks and in volcanic ashes, these elements sporadically in the decay-resistant fraction of heavy minerals as rutile, anatase, brookite, ilmenite, titanite and zircon. Harmful effects of these substances when taken into the digestive system are therefore not known and are not to be expected. The natural burden due to the wind-borne fraction of fine-dust aerosols can be expected to increase worldwide, if the enrichment of the tropospheric volume elements with vital elements and/or protective substances according to the invention is not put into practice, due to the continuing growth of deserts and steppes. In many regions, the natural wind-borne aerosols contain crystalline composites, in particular quartz and serpentine, which when inhaled are harmful to the health. Particularly, the natural fine-dust aerosols coming from desert belts and moraine belts which occasionally spread to central Europe can be classed as being harmful to the health due to their content of quartz. In particular, the fine dusts containing serpentine fiber which are blown out of natural serpentine deposits in dry zones are recognized as being harmful to the health. Particularly, the organic compounds of titanium, silicon, phosphorus and iron required for the production of the fuels and fuel additives for producing the flue gases enriched with vital elements and/or protective substances can be produced on a large scale at low costs. Moreover, titanium and iron are not scarce elements in the earth's crust, but belong to the most frequent elements. The continental earth's crust has an average content of iron of 42 g pro kg and an average content of titanium of 5 g pro kg. According to the 1992 volume of the Federal German statistical almanac, the fuel consumption of motor vehicles, aircraft and diesel engines in 1990 amounted to about 457,000,000 metric tons just in the U.S.A. Assuming that about one fifth of this quantity has been used for appropriate purposes (air traffic, shipping) about 10,000 metric tons of doping elements could have been released by a medium concentration of doping elements of 10−4 parts pro unit of fuel. TABLE 1Examples of substances used as fuels or fuel-additives withwhich flue gases can be produced by combustion permitting theenrichment of tropospheric volume elements with vital elementsand/or protective substancesExample of substances;Element symbolPropertiesof the effective elements in the flue gasof the effective substancescontaining additive agentsapplied to the flue gasPhosphorus acid ester; Pa, pPhosphoric acid ester; Pa, pWhite phosphorus; Pa, pMagnesium phosphide; Pa, pCalcium phosphide; Pa, pSilicic acid ester; Si, NaTetramethyl silane; Si, NaSilane compounds; Si, NaHalogene silane compounds; Si, NaSilicon-magnesium alloys; Si, NaTitanocene; Ti, Na, dTetramethyl titanium; Ti, Na, dHydrolysis-resistant titanium acida, desters; Ti, Na, dCondensates of carboxylic acid -a, dtitanium acid; Ti, Na, dTitanium acetylacetonates; Ti, Na, dTitanium phthalocyanines; Ti, Na, dTitanium; Ti, NMagnesium-titanium alloys; Ti, NIron carbonyls; Fea, d, p, sFerrocene; Fea, d, p, sDekamethyl ferrocene; Fea, d, p, sIron oleates; Fea, d, p, sFatty acidic iron salts; Fea, d, p, sIron-acethylacetonate Fea, d, p, sIron rhodanide; Fea, d, p, sAromatic N-heterocyclics containinga, d, p, siron; Fea, d, p, sIron-silicon-magnesium alloys; Fe, SiTricyclopentadienyl-cerium; CedCerium heptane dionate; CedCerium acetyl acetonate; CedIron-cerium-titanium alloys; Fe, Ce, Tia, d, p, sIodine methane; Ia, rDiiodine methane; Ia, rTetraiodine methane; Ia, rIodine; Ia, rIodine dissolution in soot oil; I, Ca, p, r, sDiphenyl selenide; SeaDiphenyl selenium dioxide; SeaDiphenyl selenium oxide; SeaSelenium dissolution in soot oil; Se, Ca, p, sDiphenyl selenide with ferrocene; Se,a, p, sFeSoot oil; Cp, sSoot oil with ferrocene anda, p, stetraiodine methane; C, Se, FeSoot oil with ferrocene; C, Fep, sProperty a) vital element,Property d) protective substance; production of hydroxyl radicalsProperty p) protective substance; absorbentProperty r) protective substance; minimization of the intake of radioactive iodine by the organismProperty s) protective substance; marking the toxic fall-out from a contaminated cloud by visible pigmentation TABLE 2a) Examples of protective substances as direct additives or asflue gas additives which are to be released into contaminantclouds caused by accidentb) Examples of the flue gases usedDirect andindirectpropertiesof theprotectivesubstancesin thecontaminateda) Protectivecloudsubstances addedand its fall-to flue gasb) Flue gas exampleouta) Chlorineb) Flue gas: Gas mixture containingp, r, s, u, tacetophenonesoot, hydroiodic acid and iron (III)oxide at a temperature of 150° C.Flue gas from the waste gases of theseparate combustion of soot oilmethyl-iodide solution and ferroceneoil solutiona) Ethane thiolb) Flue gas: Flue gas containing sootp, s, tfrom the combustion of soot oila) Pyridineb) Flue gas: Gas and aerosol convectiontcurrent which swirls up due to theuncontrolled reaction of the core meltProperty p) absorptive bonding to a protective substanceProperty r) minimizing the intake of radioactive iodine by the organismProperty s) protective substance: marking the toxic fall-out from a contaminated cloud by visible pigmentationProperty t) marking the toxic emissions in the air and the toxic fall-out on the ground and in waters by smell or tasteProperty u) marking the toxic emissions in the air and the toxic fallout on the ground and in waters by skin irritation or other irritation TABLE 3Examples of vital elements and protective substances in the fluegas and the effects in the tropospheric volume element doped withthemExamplesEffect in dopedof substances containing vital elementsSymbol(s) oftroposphericand/or protective substances andthe effectivevolumethe effective elements contained thereinelement(s)elementPyrophosphorus acidsPa, pMixed phosphorus acids fogAmmonium phosphatesSilicon-dioxide-aerosolSiaSilicon nitride-oxynitride-aerosolNTitanium-dioxide-aerosola, d, sTitanium-oxynitride-aerosolTi, Si, Zr, NTitanium-silicon-mixoxide-aerosolTitanium-silicon-mixoxynitride-aerosolTitanium-silicon-zirconium-mixoxide-aerosolTitanium-silicon-zirconium-mixoxynitride-aerosolIron (III) oxide-aerosolFea, p, sIron-silicon-magnesium-mixoxide-Fe, Si, Mg, Na, p, saerosolSilicon nitride-oxidnitride-aerosolCerium-dioxide-aerosolCedThinned iodine gasa, p, r, sThinned iodine-hydrogen gasI, CSoot aerosols containing iodineThinned selenium-dioxide gasSea,Selenium-dioxide-iron(III)oxide-Se, Fea, p, saerosolsSoot aerosols containing seleniumSe, Ca, p, sProperty a) vital elementProperty d) protective substance; production of hydroxyl radicalsProperty p) protective substance; absorbentProperty r) protective substance; minimization of the intake of radioactive iodine by the organismProperty s) protective substance; marking the toxic fall-out from contaminated clouds by visible pigmentation TABLE 4Examples of fog-forming substances as protective substances asdirect additives or as flue gas additives which are to be releasedinto contaminant clouds caused by accidentWaterHydrochloric acidAmmonia waterAmmonia gasMethyl amineEthyl amineSodium carbonateAmmonium carbonateCalcium chlorideMagnesium chlorideAluminum chlorideIron(III) chlorideAmmonium hydrogencarbonateAmmonium chlorideMethyl ammonium chlorideAmmonia hydrogen sulfateChlorine sulfonic acidSulfur trioxidePyridinium chloridePhosphorus pentoxide TABLE 5Examples of substances which convert into fog-formingprotective substances only within the contaminant clouds causedby accidentExamples of substances whichconvert into fog-formers inFog-formers which are produced fromthe contaminant cloudsubstances in the contaminant cloudHydrogen sulfideSulfuric acidAmmonium sulfideAmmonium sulfateSulfur dioxideSulfuric acidCarbon disulfideSulfuric acidPhosphorus trichloridePhosphorus acid, Hydrochloric acidPhosphorus oxychloridePhosphorus acid, Hydrochloric acidPhosphorus pentachloridePhosphorus acid, Hydrochloric acidSulfur dichlorideSulfuric acid, Hydrochloric acidSulfuryl chlorideSulfuric acid, Hydrochloric acidAluminum chlorideHydrochloric acid, AluminumIron (III) chloridehydroxideBoron trichlorideHydrochloric acid, Iron (III)Titanium tetrachloridehydroxideSilicon tetrachlorideHydrochloric acid, Boric acidChlorine silaneTitanium acid, Hydrochloric acidSilicic acid, Hydrochloric acidSilicic acid, Hydrochloric acid
	description	1. Field of the Invention The present invention relates to methods for performing radiosurgery on a patient using microbeam radiation. 2. Description of the Related Art Nearly two decades ago, a radiosurgery method was patented by Slatkin et al. (see U.S. Pat. No. 5,339,347, the disclosure of which is incorporated herein by reference). This radiosurgery method employs sub-millimeter beams of X-rays, termed microbeams. An advantageous feature of this radiosurgery technique is that the microbeams, while successfully destroying targeted diseased tissue, do not destroy the functionality of normal healthy tissue surrounding the target. Scientific studies using cell cultures and animal models show that although the normal tissue cells directly in the path of a microbeam are destroyed, the region of destruction is sufficiently small in width that the adjacent normal tissue is capable of healing the damaged region (see Dilmanian et al., Experimental Hematology, Vol. 35, 2007, pp. 69-77, the disclosure of which is incorporated herein by reference). Normal tissue heals when microbeams are less than 700 um in size (see Dilmanian et al., Proceedings of the National Academy of Sciences, Vol. 103, 2006, pp. 9709-9714, the disclosure of which is incorporated herein by reference). Diseased tissue is destroyed by cross firing from other directions, thereby creating sufficiently broad regions of damage that a healing response by adjacent tissue cannot be mounted. Unfortunately, the great promise of microbeam radiosurgery has yet to be realized. There are two major problems. First, the only source of microbeam radiation capable of providing sufficient dose rate for radiosurgery until now has been a synchrotron. A synchrotron is a very large and expensive device. The synchrotron source which has been used for most microbeam radiosurgery studies is the European Synchrotron Radiation Facility located in Grenoble, France. The storage ring associated with this synchrotron is 300 m in diameter, and the facility cost approximately $900 M to construct. These characteristics of a synchrotron source are prohibitive. This first problem is likely to be resolved by a new type of radiation source which utilizes the physical phenomenon of inverse Compton scattering to generate high energy X-ray photons. Such a source promises to provide the necessary dose rate, while requiring a much smaller footprint (less than 5 m in diameter) and much lower cost to construct (approximately $15 M) than a synchrotron (see Adler et al., U.S. patent application Ser. No. 13/453,338, the disclosure of which is incorporated herein by reference). The second problem with conventional microbeam radiosurgery is the restriction of the X-ray photons comprising the microbeams to energies less than 200 keV. This restriction arises from the requirement that the dose deposition in tissue have a lateral profile (i.e., a profile in a direction orthogonal to the direction of beam propagation) with very sharp edges; that is, the lateral energy deposition in tissue must fall from the peak value abruptly (see Dilmanian et al., Experimental Hematology, cited above). Referring to FIG. 1, the percentage lateral dose profile 10 in tissue required by conventional microbeam radiosurgery is shown. (Note: A percentage dose profile is obtained from a dose profile by dividing the dose at all positions by the maximum dose in the profile, and multiplying by 100.) It is preferred that the transition 14 from the peak dose value 12 to the valley dose value 16 have an 80% to 20% fall length of no more than a few tens of microns. A percentage lateral dose profile such as shown in FIG. 1 requires incident photons of less than 200 keV because of the physical process known as Compton scattering. Compton scattering is the primary mechanism by which incident X-ray photons with energies between 100 keV and 10 MeV interact with the atoms comprising the tissues of a patient. Referring to FIG. 2, the physical phenomenon of Compton scattering is shown. When a high energy photon 20 collides with a low energy atomic electron 22, the result is an ionized high energy electron 24 and a scattered reduced energy photon 26. Most energy deposition within the tissue of a patient is a result of secondary collisions of the high energy electron 24 with other atoms in the patient. The higher the initial energy of the electron 24, the farther the electron 24 can travel. In order to keep the width of energy deposition less than a few tens of microns within the patient, the incident X-ray photon 20 must have energy less than 200 keV. Referring to FIG. 3, the percentage lateral dose profile associated with a 200 keV incident X-ray beam is shown. The percentage lateral flux profile 31 of the incident X-ray beam in air before striking the patient is extremely sharp, having a transition region 35 with an 80% to 20% fall length of 5 um. The associated percentage lateral dose profile 30 at a depth of 1 cm in the patient is also relatively sharp, having a transition region 34 from the peak dose value 32 to the valley dose value 36 with an 80% to 20% fall length of 25 um. (The percentage lateral dose profile 30 is obtained from Monte Carlo calculations of the Compton scattering process in water, which is a good model for the tissues of a patient.) Referring to FIG. 4, the percentage lateral dose profile associated with a 400 keV incident X-ray beam is shown. The percentage lateral flux profile 41 of the incident X-ray beam in air before striking the patient is again very sharp, having a transition region 45 with an 80% to 20% fall length of 5 um. The associated percentage lateral dose profile 40 at a depth of 1 cm in the patient is not sharp, however, having a transition region 44 from the peak dose value 42 to the valley dose value 46 with an 80% to 20% fall length of 110 um. Referring to FIG. 5, the percentage lateral dose profile associated with a 2 MeV incident X-ray beam is shown. The percentage lateral flux profile 51 of the incident X-ray beam in air before striking the patient is sharp, having a transition region 55 with an 80% to 20% fall length of 5 um. The associated percentage lateral dose profile 50 at a depth of 1 cm in the patient is very broad, having a transition region 54 from the peak dose value 52 to the valley dose value 56 with an 80% to 20% fall length of 275 um. Requiring X-ray photon energies to be less than 200 keV results in insufficient dose to tissues deep within a patient. Such low energy photons are quickly absorbed by tissues near the surface of the body. Referring to FIG. 6, the percentage dose profiles along the direction of beam propagation (i.e., in the direction of depth into the patient) for various X-ray photon energies are shown. The percentage depth dose profiles 62, 64, and 66 are those of X-ray photons of 200 keV, 400 keV, and 2 MeV, respectively. For all curves, the beam physical size is 500 um in diameter. It can be seen from FIG. 6 that the 2 MeV beam penetrates much deeper into a patient than the 200 keV and 400 keV beams. In general, the higher the photon energy, the deeper the beam penetrates into a patient. In accordance with the presently claimed invention, a method of performing microbeam radiosurgery on a patient provides for irradiating target tissue within a patient with high energy electromagnetic radiation via one or more microbeam envelopes with photons having respective energy magnitudes in excess of 200 keV, and maximum defined beam widths sufficiently narrow to yield a biological damage width which does not exceed a predetermined value. The following detailed description is of example embodiments of the presently claimed invention with references to the accompanying drawings. Such description is intended to be illustrative and not limiting with respect to the scope of the present invention. Such embodiments are described in sufficient detail to enable one of ordinary skill in the art to practice the subject invention, and it will be understood that other embodiments may be practiced with some variations without departing from the spirit or scope of the subject invention. Referring to FIG. 7, the concepts of graded percentage lateral dose profile and biological damage width are shown. For a graded percentage lateral dose profile 70, the transition 74 from the peak dose 72 to the valley dose 76 is not abrupt. The 80% to 20% fall length may be as large as a few hundred microns. The width of the percentage lateral dose profile 73 above a threshold value 77 is defined as the biological damage width. For doses above the threshold value 77, significant damage is done to tissue. The requirements for a graded percentage lateral dose profile are twofold. First, the peak dose 72 must be sufficiently larger than the threshold dose 77 to destroy target tissue. It is anticipated that a peak-to-threshold dose ratio (D72/D77) greater than or equal to 10 is preferred. Second, the biological damage width 73 is preferably less than or equal to 700 um, which is the maximum damage width that can be healed by surrounding normal tissue. To achieve a biological damage width less than or equal to 700 um for X-ray photon energies above 200 keV, the width of the incident X-ray beam is made considerably smaller than 700 um. The width of the incident X-ray beam is made sufficiently small that, upon accounting for the Compton scattering process, the biological damage width is within the desired range. Referring to FIG. 8, the graded percentage lateral dose profile associated with a 100 um wide incident 2 MeV X-ray beam is shown. The percentage lateral flux profile 81 of the incident X-ray beam in air before striking the patient is extremely sharp, having a transition region 85 with an 80% to 20% fall length of 5 um. The associated graded percentage lateral dose profile 80 at a depth of 1 cm in the patient has a transition region 84 from the peak dose value 82 to the valley dose value 86 with an 80% to 20% fall length of 70 um. For a peak-to-threshold dose ratio of 10, the biological damage width 83 is 400 um in width. In accordance with a preferred embodiment, target tissue in a patient is irradiated with X-ray microbeams from one or more directions. For any given direction, one or more X-ray microbeams are used. Each X-ray microbeam has a maximum defined beam width sufficiently narrow to yield a biological damage width not exceeding a predetermined value. For the case of irradiation with multiple X-ray microbeams from a given direction, the microbeams are substantially mutually parallel and are mutually separated by a minimum defined inter-beam spacing to provide an undamaged tissue width sufficient to promote healing of damaged non-target tissue. Various other modifications and alternatives in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and the spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.
	abstract	Disclosed are a nuclear fuel pellet having enhanced thermal conductivity and a method of manufacturing the same, the method including (a) a step of manufacturing a mixture including a nuclear fuel oxide powder and a thermally conductive plate-shaped metal powder; and (b) a step of molding and then heat-treating the thermally conductive plate-shaped metal powder to have an orientation in a horizontal direction in the mixture, thereby forming a pellet.
052767191	summary	BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a hydraulic control rod drive for a nuclear reactor, in particular for a heating reactor, with a piston/cylinder drive for a respective control rod and a reactor plenum enclosing the drive. Heating reactors are designed for a relatively low primary pressure of, for instance, 15 bar; the primary medium or working fluid circulates in the reactor pressure vessel by the natural circulation principle. The fuel element bundle of such a heating reactor and the flow box are preferably embodied mechanically separate from one another, whereby the flow box is as long as dictated by the stack height necessary for natural circulation. Four fuel element bundles respectively are combined within such a box, the core box, including the associated control rod with drive. The control rods are moved within cross-like guides, which are disposed in the box of the reactor core. The integration of the control rod drives in the primary system necessitates a drive system which is compatible with the primary coolant, i.e. with water. The low nuclear power density due to the natural circulation principle and the corresponding control requirements make it possible to use a hydraulic drive which is operated with primary water as the working fluid. The fuel element bundle and the actual control rod are thereby preferably embodied as they are known from boiling water reactors. In general, a heating reactor has characteristics of a boiling water reactor as well as of a pressurized water reactor. A hydraulic control rod drive for a nuclear reactor is known from German Published, Non-Prosecuted application 34 30 929, entitled "Boiling Water Reactor Control Rod Drive Using Coolant as Hydraulic Fluid With Ultrasonic Locating Probe for Rod Position". In that device, the position of the control rods is determined by way of an ultrasonic measurement device with a supersonic transducer, which serves as an ultrasonic sender and receiver. The transducer is disposed in a linear channel between the control rod drive and the upper fill level of the reactor coolant. The invention starts out with the appreciation that gas bubbles in the drive system can under certain circumstances lead to oscillations of the control element and thus to undesireable reactivity fluctuations. The above-mentioned prior art teaching does not provide for venting any gas bubbles from the drive system. Regarding a venting opening provided in the context of this invention, working fluid leaks through the opening which corresponds approximately to the core inlet temperature. Due to heat conduction and heating by gamma radiation absorption, the working medium temperature in the guide shaft of the associated fuel element may be up to about 30.degree. C. above the temperature of the partial fluid currents through the venting opening. Accordingly, eddies with varying water density can form in the opening region of the venting openings, which eddies impair the ultrasonic distance measurement. It is accordingly an object of the invention to provide a hydraulic control rod drive for a nuclear reactor, and particularly for a heating reactor, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and taking the afore-mentioned dangers into account. The invention is based on the object to improve the control rod drive of the above-mentioned kind in its operational functionality in a sense that, on the one hand, the piston-cylinder drive is effectively vented of gas bubbles and that, on the other hand, the partial fluid flows exiting from the venting opening cannot impair the ultrasonic distance measurement. With the foregoing and other objects in view there is provided, in accordance with the invention, in a nulcear reactor having a fuel assembly with a control rod and a reactor plenum enclosing the fuel assembly, a hydraulic control rod drive, comprising a movable cylinder having control rod elements disposed thereon; a stationary piston rigidly mounted in the fuel assembly, the piston having a bottom, an open top, and an axial opening formed therein for allowing communication between the bottom and the open top; the cylinder being disposed coaxially around the piston and defining a gap therebetween so as to allow axial movement of the cylinder; means for supplying a working fluid to the piston for lifting, lowering or suspending the cylinder; means for measuring a vertical displacement of the cylinder; and means for venting the gap between the piston and the cylinder. In accordance with another feature of the invention, the control rod drive measuring means include an ultrasonic reflector disposed on the cylinder, and an ultrasonic transducer rigidly mounted above the cylinder in alignment with a longitudinal axis of the cylinder. In accordance with again another feature of the invention, the venting means are in the form of a venting channel formed in an upper end of the cylinder for allowing working fluid with gas bubbles to escape from the cylinder. The invention is embodied in a hydraulic control rod drive for a nuclear reactor, in particular a heating reactor, of the above-mentioned structure, which provides the following further features, in accordance with the invention, for solving the object as presented: a) besides a cylinder, a piston is also formed as a hollow body, b) a first one of the two hollow bodies is stationary and serves to supply the working fluid, c) the second one of the two hollow bodies is coaxially mounted around the first hollow body with an annular gap in between and is movable upward and downward and forms a carrier body for control elements of the control rod, d) the working fluid can be supplied into the two hollow bodies via a supply channel in the lower region of the first hollow body for mass flow-dependent lifting, lowering or suspending the second hollow body and can be removed from the inner space of the two hollow bodies via a throttle passage, preferably an annular gap, e) an ultrasound reflector is attached at the upper, head end of the second hollow body, which reflector forms a positional measurement system with an ultrasonic measurement path together with an ultrasonic transducer rigidly mounted above and remote from the second hollow body, f) the second hollow body has a venting channel configuration in the region of its upper end for venting the second hollow body, which configuration opens into the reactor plenum at a security distance a1, a2 from the ultrasonic measurement path which is great enough such that the ultrasonic measurement remains virtually unaffected by density fluctuations in the working fluid. The advantages attained with the invention are mainly seen in the fact that, on the one hand, an effective venting of the inner space of the control element, or hollow cylinder/hollow piston is provided and, on the other hand, the partial venting currents associated with this venting can have no or virtually no disadvantageous effect on the ultrasonic distance measurement of the control element. In a preferred embodiment of the invention the first of the two hollow bodies is preferably a hollow piston open on the top and, correspondingly, the second hollow body is a hollow cylinder, which covers the hollow piston coaxially and with an annular gap, whereby the axial position of the hollow cylinder relative to the hollow piston can be determined by the amount of working fluid supplied through the hollow piston into the interior of the hollow cylinder. According to an advantageous further development of the invention and in the case when the control elements are embodied as cross-shaped absorber plates, a cross-shaped attachment part for forming the venting channel configuration is attached at the head end of the hollow cylinder. Radial channels of the venting configuration originate from a central channel part communicating with the hollow cylinder interior, extend through the cross legs of the attachment part, and open into the reactor plenum approximately in the region of the absorber plate tips. According to another advantageous embodiment of the hydraulic drive, whereby cross-shaped absorber plates are likewise assumed, there is provided for the venting channel configuration to be formed by a head plate whose diameter corresponds approximately to that of the hollow cylinder and which has a venting channel configuration disposed therein which is approximately T-shaped in axial section. The outlet pipes with outlet openings are inserted into the channels and the outlet openings are disposed at a security distance from the ultrasonic measurement path. When the pressure of the hydraulic working fluid within the piston/cylinder drive relative to the reactor plenum is not more than about 1.5 bar, it is suggested that the channels of the venting channel configuration opening into the reactor plenum extend at a slight rise of, for instance, 5.degree. to 10.degree. with the horizontal. In accordance with a concomitant feature of the invention, the control rod drive is embodied such that the first hollow body on its outer circumference and the second hollow body on its inner periphery are provided with first annular protrusions and recesses and with cooperating second annular recesses and protrusions, wherein an annular gap is defined between the first protrusions and recesses and the second recesses and protrusions. The annular gap forms a throttle passage for the working fluid from the inner space of the two hollow bodies into the reactor plenum. 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 hydraulic control rod drive for 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 of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of the specific embodiment when read in connection with the accompanying drawings.
041522052	summary	The invention relates to a spacer or spacer support, especially for water-cooled nuclear reactor fuel assemblies formed of a grid of edgewise disposed sheetmetal webs of material having minimal neutron absorption, preferably a zirconium alloy, and of resilient or springy contact elements of other materials which are applied therein and extend in the axial or longitudinal direction of the mesh of the grid. Such spacers have become known, heretofore, for example, from the German Published Prosecuted Application DT-AS 1,489,632, wherein use was made of the principle, known also from considerably earlier publications, of making the spacer grid per se of a material that absorbs as few neutrons as possible and to fabricate the resilient contact elements of a correspondingly harder material which can have a considerably higher absorption cross section. Since it is difficult to join such different materials metallurgically, a simple plug connection was proposed, the loosening of which was supposed to be prevented by a bent-over end of the resilient contact strip. This construction, however, posed great difficulties in assembly as well as in accurately establishing the radial insertion location as seen from the fuel rod, not to mention that also the axial support of the contact springs during the operation of the reactor might be very unreliable. The problem therefore arose of finding a spacer construction with parts of different materials, with which these difficulties are circumvented, and which furthermore permits the use of the generally known "three-point support" (note the German Published Non-Prosecuted Application DT-OS 1,589,051). It is accordingly an object of the invention to provide a spacer or spacer support for nuclear reactor fuel assemblies which meets the latter requirements. With the foregoing and other objects in view, there is provided, in accordance with the invention, in a nuclear reactor fuel element, a spacer comprising a grid formed of edgewise disposed sheetmetal webs of material having minimal neutron absorption, and resilient contact elements of different material applied to the grid and extending in axial direction of the mesh of the grid, the mesh of the grid being defined by mesh walls formed with rectangular openings extending in longitudinal direction of the fuel element, the resilient contact elements comprising respective resilient strips self-lockingly snapped into the openings and including a wave-shaped part thereof extending from one to the other side of the mesh walls and respective parts that are not wave-shaped connected to opposite ends of the wave-shaped part thereof and contacting respective webs of the grid. In accordance with other features of the invention, the fuel element is for a water-cooled nuclear reactor and the material having minimal neutron absorption is formed of zirconium alloy. In accordance with additional features of the invention, at least one of the parts that are not wave-shaped is bent about the edge of the respective web or is suspended therefrom. In accordance with a concomitant feature of the invention, the parts that are not wave-shaped and contact the respective webs of the grid are formed with rigid contact projections i.e. either provided therewith or constructed therewith. 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 spacer support for water-cooled nuclear reactor fuel elements, 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.
	summary