JP2005201735A - Test method for simulating actual utilization of new type fuel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure safety of new type fuel having no or least utilization experience for using in a reactor. <P>SOLUTION: The whole of a single new type fuel element 30 for testing is installed in capsules 34a and 34b and held by a shroud tube 32. The capsules are independently contained in a compartment 14 to be a coolant flow path. A plurality of compartments are arranged around middle tie-rod 12 and its surrounding is covered with a wrapper tube 18 to be a capsule type irradiation fuel assembly 10 for testing. By loading this and irradiating with neutrons in a reactor, the use of the new type fuel elements in a commercial reactor is simulated while ensuring safety in the reactor by the capsule. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a simulation test method for practical use of a new type fuel in a nuclear reactor, and a test irradiation fuel assembly used therefor. More specifically, the present invention relates to a method for obtaining approval including a test of a new type fuel, and an irradiation fuel assembly for performing the test.

  In research and development of nuclear reactor materials and nuclear fuel, irradiation tests are conducted in which material specimens are placed in the nuclear reactor and exposed to radiation. For example, in a creep rupture strength test of a material in a liquid coolant under a high-temperature radiation environment, a cylindrical specimen with a fixed shape filled with high-pressure gas is stored in an irradiation capsule and inserted into a nuclear reactor. Then, the time until the test piece breaks in the liquid in the radiation environment is measured (see, for example, Patent Document 1). In the case of a relatively small test piece, this method does not cause any particular problem.

However, the above method is a single material test, and another problem arises in the assembled fuel element test. When the test fuel element is used in a nuclear reactor,
(1) Even if fuel melting or cladding breakage occurs in the test fuel element, it does not affect other fuel elements, and (2) Fuel fragment or FP (fission generation due to damage to the cladding tube of the test fuel element) To prevent excessive diffusion of
Is necessary to ensure safety. That is, the test fuel element must itself have the ability to ensure such safety. However, there is no guarantee that such safety can be ensured when test fuel elements with little or no use are used in a nuclear reactor.

Therefore, in Japan's safety review concerning permission for the use of fuel in nuclear reactors, a record of use in overseas advanced reactors has been required in order to confirm the validity of safety design within the scope of permission. For this reason, it takes a long time to use fuel with little or no use (hereinafter referred to as “new fuel”) in a nuclear reactor, making it difficult to test a wide variety of new fuels. It was.
Japanese Patent Laid-Open No. 9-145891

  The problem to be solved by the present invention is that it is difficult to use a new fuel with little or no use record in a nuclear reactor, and therefore it takes a long time to put the new fuel into practical use.

  In the present invention, an entire new fuel element for testing is loaded into a capsule, and a plurality of the capsules are held in an array to form a capsule-type irradiation fuel assembly. The capsule-type irradiation fuel assembly is placed in a nuclear reactor. This is a practical test method for the practical use of a new fuel, characterized by simulating the use of a new fuel element in a practical reactor while ensuring safety in the reactor with a capsule by loading and neutron irradiation. .

  The present invention also relates to an irradiated fuel assembly used in the above-described practical simulation test method for a new fuel, wherein the entire new fuel element for testing is held in a shroud tube and loaded into the capsule, and the capsule is independently In a compartment that forms a coolant flow path, a plurality of compartments arranged around the center tie rod, covered with a trumpet tube, a handling head at the upper end, and an entrance nozzle at the lower end This is a capsule-type irradiation fuel assembly for use.

The present invention is a simulation test method for practical application of a new fuel as described above, and a capsule-type irradiation fuel assembly for testing used therefor. By using this technology, it is possible to safely use a new fuel with little or no use record. The test can be performed while securing the property. For example, the new fuel can be used in the fast experimental reactor “Joyo”, and the following effects can be obtained.
(1) In the development for the practical application of fast breeder reactors, irradiation tests of various target fuels (minor actinide-added fuel, bipack fuel, etc.) can all be performed in the fast experimental reactor “Joyo” .
(2) With regard to preparations for the start of the use of new fuels, including prior irradiation in overseas reactors, the required period can be shortened by about 4 years.
(3) Since it is not necessary to limit the enrichment level of plutonium, which is a part of the fuel composition, it is possible to support irradiation tests that contribute to research and development of plutonium combustion furnaces using uranium-free fuel.
(4) It is possible to respond to various irradiation needs including GEN-IV (4th generation nuclear power generation system) by the United States etc. as one of the few fast neutron irradiation fields in the world.
(5) This technology will be applicable not only to fuel bodies but also to the use of nuclear fuel materials and materials containing RI.

  As described above, when using a test fuel element in a nuclear reactor, it is necessary to ensure the safety of the test fuel element even if fuel melt or cladding breakage occurs in the test fuel element. And “preventing excessive diffusion of fuel fragments and FP due to breakage of the cladding tube of the test fuel element”. For this reason, even in the case of using a test fuel element that has not been used or few, a test fuel that has been conventionally provided with the ability to satisfy the above conditions so as to ensure the safety of the nuclear reactor. Instead of elements, in the present invention, the idea is changed so that the assembly component has the ability. For this reason, a capsule-type irradiation fuel assembly having a built-in capsule for loading a test fuel element has been developed, and the test fuel element can be safely loaded into the reactor by using it.

  Specifically, a whole new fuel element for testing is held by a shroud tube and loaded into a capsule, and the capsule is stored in a compartment serving as an independent coolant flow path. Are arranged around the tie rod, covered with a trumpet tube, a handling head at the upper end, and an entrance nozzle at the lower end to provide a test capsule type irradiated fuel assembly. By loading the capsule-type irradiated fuel assembly into the reactor and performing neutron irradiation, the use of the new fuel element in the practical reactor is simulated while ensuring safety in the reactor by the capsule.

  FIG. 1 is an explanatory view showing an embodiment of a capsule-type irradiated fuel assembly according to the present invention. A is the entire structure of the capsule-type irradiated fuel assembly, B is a cross section, C is a compartment, D is an open type capsule, and E is a sealed type capsule. The capsule-type irradiation fuel assembly 10 has six compartments 14 arranged around a central tie rod 12, which are held at both upper and lower ends and fixed by lock nuts 16. It is the structure covered with. A handling head 20 is disposed at the upper end of the capsule-type irradiated fuel assembly, an entrance nozzle 22 is disposed at the lower end, and a spacer pad 24 is disposed around the periphery. The capsule-type irradiation fuel assembly 10 has the same shape as the fuel assembly for operation, and can be loaded into the core in place of it.

  One of the new test fuel elements 30 is held by a shroud tube 32 and loaded into the thick-walled capsules 34a and 34b. The capsules 34a and 34b function to prevent the pressure generated when the cladding tube of the new fuel element 30 is damaged from being transmitted to the outside of the capsule and to prevent the propagation of damage to other fuel elements. There are an open type (inner wall structure container) and a sealed type (sealed structure container). In the case of the open type capsule 34a, strainers 38 are installed above and below the container body 36, and open portions are formed vertically. In the case of the sealed capsule 34b, a sealing structure is formed by installing a closing plate 40 above and below the container body 36 in place of the strainer.

  Such an open type capsule 34a or a sealed type capsule 34b is stored in the compartment 14 one by one. The compartment 14 ensures an independent coolant channel for each new fuel element. Therefore, the compartment 14 has an inner / outer dual structure, and a gas layer is formed between the outer tube 42 and the inner tube 44, and the gas layer is filled with a gas having a high heat insulating effect, thereby securing an independent coolant channel. In addition, it is possible to make each new fuel element thermally independent. A coolant inflow hole 50 is opened at the lower end portion, an orifice 52 is provided, and a number of small holes 54 are opened at the upper end portion, which serve as a coolant outflow portion.

  The container bodies of the capcells 34a and 34b are made of thick-walled pipes, so that the capsules can withstand the pressure generated when the cladding tube of the new fuel element is broken. Capsule is not only limited to the contents of the test but also has a more stringent safety review than before, so the material and thickness are limited. For example, a material obtained by improving JIS SUS316 (a material used for a cladding tube or a trumpet tube of a fast breeder reactor “Monju”) is used, and the wall thickness is 2.8 mm or more.

  By the way, when the types of fuel elements are different, it is the diameter and the total length that may greatly differ. The diameter affects the radial size of the holding means of the fuel element, and the total length affects the axial position of the holding means. Capsules can be made to match the diameter and length of the new fuel element for testing, but the capsule must be dimensioned to withstand the pressure generated when the cladding of the new fuel element breaks. Therefore, there is a situation where it is not possible to manufacture the capsule according to the diameter and the total length of the fuel element. Therefore, the present invention employs a structure in which another tube called a shroud tube is provided in the capsule, and this is used as a spacer for maintaining the space between the fuel element and the capsule. As the name suggests, the shroud tube is tubular, and has an inner diameter that matches the diameter of the fuel element to be held and a length that matches the overall length of the fuel element to be held. Therefore, only the shroud tube is designed exclusively for the fuel element. Although the shroud tube is fixed in the capsule, since the fixing position and the fixing method can be the same even if the fuel elements are different, it is possible to use the same capsule even if the types of the fuel elements are different.

  As described above, as the capsule, there is an open-type capsule 34a, and a sealed-type capsule 34b that can confine all the fuel pieces and fission products (FP) released due to breakage of the cladding of the test fuel element.

  The open-type capsule 34a has an advantage that the primary coolant sodium can be introduced into the inside as a thermal bond material by the furnace interior load because the top and bottom of the capsule are open. Can be assembled and reloaded. However, it is not possible to confine all the fuel pieces and FP released due to breakage of the cladding tube of the test fuel element. For this reason, open-type capsules can be used only when the soundness of the cladding of the test fuel element can be secured even during abnormal transient changes during plant operation. In order to prevent excessive diffusion of the fuel pieces and FP that are released when the cladding tube is broken, strainers 38 are installed in the open portions above and below the capsule.

  By taking such a structure, for example, when performing a test for melting oxide fuel (other than oxide fuel is not melted), even if a cladding tube accident occurs, the molten fuel and coolant By designing to have sufficient strength against the pressure generated by contact, there is no possibility of adversely affecting the health of other fuel elements.

  Here, the strainer 38 is a perforated plate made of stainless steel, and has a hole so that sodium, which is a primary coolant, can be introduced into the open-type capsule 34a as a material for transferring heat. However, it should be of a certain size so that the small pieces generated in the event of a breakage of the cladding of the new fuel element will not get caught in any part of the primary system of the reactor and obstruct the coolant flow. For the purpose of catching, it has a small-diameter porous.

  Normally, the open type capcell 34a as described above is used. However, when the design is to allow the opening of the cladding tube, such as when the cladding tube is intentionally designed to break, the sealed type capsule 34b is used. use. The fission product gas and fuel released when the cladding tube is opened are confined in a sealed capsule 34b to prevent diffusion into the reactor.

  In the present invention, the encapsulated irradiation fuel assembly is loaded on the core and tested in place of the operating fuel assembly. Therefore, the position where the capsule-type irradiation fuel assembly is loaded is the position where the operating fuel assembly is located. The number of encapsulated irradiated fuel assemblies to be loaded is limited to a maximum of about 7 from the viewpoint of safety and the like.

  The design life of the capsule-type irradiation fuel assembly in the nuclear reactor is, for example, about 750 days. However, the loading period of new fuel elements often exceeds 1500 days. In such a case, an irradiation test is performed while connecting a plurality of capsule-type irradiation fuel assemblies.

  In the practical use simulation test of the present invention, even if the integrity of the new fuel element used in the irradiation test is lost due to the accident of the reactor, an event caused by this will occur in the capsule-type irradiated fuel assembly. If it converges at, it can be determined that the new fuel element is safe (permitted).

  By doing in this way, even if the soundness of the test fuel element stored in the capsule is lost due to an accident in the plant, the soundness of the capsule is ensured and there is no possibility of adversely affecting the plant. Since the capsule will ensure safety even in the event of an accident, the design policy, design method and limit values should be set so that the integrity of the capsule will not be affected in the design of the test fuel element at the time of installation permission. It is only necessary to clarify the concept of setting, and a new license acquisition method has been established that does not require physical property data of fuel materials and coating materials (no need for actual use).

  Needless to say, the method of the present invention can be implemented not only in a fast breeder reactor but also in all reactors.

Explanatory drawing which shows one Example of the capsule-type irradiation fuel assembly which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Capsule type irradiation fuel assembly 12 Tie rod 14 Compartment 18 Trumpet pipe 20 Handling head 22 Entrance nozzle 30 New fuel element 32 Shroud pipe 34a Open type capsule 34b Sealed type capsule

Claims (2)

  A whole new fuel element for testing is loaded into a capsule, and a plurality of capsules are held in an array to form a capsule-type irradiation fuel assembly. The capsule-type irradiation fuel assembly is loaded into a nuclear reactor and irradiated with neutrons. A practical test method for the practical use of a new fuel, characterized in that the use of a new fuel element in a practical reactor is simulated while ensuring safety in the reactor by a capsule. An irradiated fuel assembly for use in the practical test method for practical application of a new fuel according to claim 1, wherein one whole new fuel element for test is held in a shroud tube and loaded into the capsule, and the capsule is made independent. For testing, which is housed in a compartment that serves as a coolant flow path, and multiple compartments are arranged around the center tie rod, covered with a trumpet tube, a handling head at the upper end, and an entrance nozzle at the lower end Capsule type irradiation fuel assembly.

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