JP6665258B1 - External pressure load device, test method for irradiated fuel pellets - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high compression force (external pressure) load mechanism composed of a relatively small and simple mechanism that can be installed in a radiation shielding cell and does not require high pressure gas, and a test method using the same mechanism. . SOLUTION: A concave container 1 for storing a test piece, heat resistant particles 5 filled in the concave container, a heater 21 for heating the heat resistant particles, and a concave part of the concave container are fitted, A push rod 2 that applies an external pressure to the heat-resistant particles, an atmosphere protection container 6 that encloses the concave container, an atmosphere adjustment system 8 that supplies an atmosphere adjustment gas into the atmosphere protection container, and the test piece is released. And a detector 26 for detecting a substance to be released, wherein the test piece is embedded in the heat-resistant particles, the heat-resistant particles are heated by the heater, and the heat-resistant particles are converted into the heat-resistant particles by the push rod. A characteristic of the test piece is detected by applying an external pressure and detecting a release substance released from the test piece when the external pressure is unloaded by the detector. [Selection diagram] Fig. 1

Description

  The present invention relates to an external pressure loading device and an external pressure loading method for testing the behavior and characteristics of a test piece when pressure is unloaded from a high-temperature high-pressure state, and particularly to a test of irradiated fuel pellets used in a nuclear reactor. To apply to effective technology.

The nuclear fuel used in a nuclear reactor is a fuel rod which is obtained by baking and solidifying a powdered nuclear fuel material such as uranium dioxide (UO ₂ ) into a ceramic shape and filling it in a metal fuel cladding tube to form a sealed fuel rod. It is used as a "fuel assembly" consisting of ten fuel rods.

  Under accident conditions, such as a loss of coolant in a nuclear reactor, the fuel cladding temperature of a nuclear fuel rod in use may rise rapidly to its softening temperature, causing the fuel pellets to lose their binding force from the cladding and When fission products (FP gas: Fission Products) are released from the pellets, the pellets shatter and become finer, rearrange in the fuel rods, and when the fuel cladding breaks, the fragmented fuel material flows into the reactor water However, there is a concern that problems may arise in the stability, safety, and maintenance of the reactor.

  The gas (FP gas) generated during the nuclear fission of uranium during use in a nuclear reactor accumulates in the nuclear fuel pellets. As mentioned above, if an accident such as a loss of coolant occurs in an operating nuclear reactor, it is possible that the accumulated FP gas may pulverize and refine the fuel pellets. In order to do this, a test in which the fuel rods (fuel pellets) are at a high temperature and a high pressure is required.

  In addition, since the test piece contains a large amount of radioactive material, it is necessary to perform the test by remote control in a strong radiation shielding room.

  Conventionally, with respect to nuclear fuel rods, there are few examples in which the temperature is raised to a high temperature at which the cladding tube of about 1000 ° C. or more is softened and the pressure is simultaneously raised to a high compression pressure of, for example, 100 MPa or more. There are no standard technical specifications for test techniques and test equipment.

JP-A-5-39504

Japan Society for Technology of Plasticity, “Powder Forming and Processing”, Corona, July 25, 1994 Nobuyasu Kawai, et al., “Current State of Hot Isostatic Pressing (HIP) Technology”, “Iron and Steel”, Iron and Steel Institute of Japan, 67 (1981), No. 9, p. 25-32 S. Kashibe, et al., “Effect of external restraint on bubble swelling in UO2 fuels”, Journal of Nuclear Materials, 247 (1997), p. 138-146 Ken. H. Yueh, et al., “Fuel Fragmentation Data Review and Separate Effects Testing”, WRFPM 2014, Sep. 14-17, 2014, No. 100117 S. Yagnik, 6 others, “An Investigation into Fuel Pulverization with Specific Reference to High Burn-up LOCA”, WRFPM 2014, Sep. 14-17, 2014, No. 100145

  As a conventional technology in the general industry that can achieve a temperature and pressure environment close to the above conditions, for example, a hot press as disclosed in Patent Literature 1 and Non-Patent Literature 1 is known. Hot pressing is a method of sintering into a product shape while applying pressure to a molding powder at a high temperature. The powder is filled in a mold called a carbon die, and sintered by applying a pressure of 10 MPa to 30 MPa with a push rod.

  Since graphite dies and graphite heating elements are used, sintering cannot be performed in the air, and it must be performed in combination with atmosphere control. In addition, a uniaxial compression load acts on the molding material powder in the compression direction of the push rod, and it is difficult to obtain a uniform density distribution. In addition, it is said that high-temperature molding and production of large products are difficult due to restrictions on the temperature and dimensions due to the material strength of the mold.

Furthermore, since hot pressing is a powder molding technique, high temperature and high pressure can be achieved. However, a compressive load is uniformly applied to a test specimen containing UO ₂ pellets baked in a cladding tube such as a nuclear fuel rod. This is not possible and is difficult to apply to testing of nuclear fuel rods.

  In the hot press described above, the pressure is basically applied only from the uniaxial direction in order to apply the press pressure. On the other hand, hot isostatic pressing (HIP) as in Non-Patent Document 2 is used. The process of increasing the sintering pressure by using gas pressure, and simultaneously applying a high temperature of several hundred degrees Celsius to 2000 degrees Celsius and an isotropic pressure of several tens MPa to 200 MPa to the object to be processed. Widely used.

  A typical HIP device includes a) a pressure vessel for holding a high-pressure gas, b) a furnace internal structure such as a heater built in the pressure vessel, a heating power supply and a control device, and c) compression for supplying the high-pressure gas to the pressure vessel. And d) a device for storing a gas of a pressure medium, and e) a safety device. Usually, an inert gas such as argon (Ar) is used.

  In the case of HIP, since the pressurized medium is a gas as compared to a hot press, pressure is uniformly applied to the object to be processed, and the shape after pressurization does not change significantly from the initial shape of the object to be processed, and sometimes changes. HIP is applied to various fields by taking advantage of this characteristic that it shrinks in a similar manner and that there are relatively few restrictions on product processing.

  In the HIP method, since a uniform compressive load acts on the test piece due to the gas pressure, the HIP method is also used for a high-temperature compression test of a nuclear fuel rod with strong radioactivity as in the prior art shown in FIG. Research on the release behavior of fission gas (FP gas) from fuel pellets under such high pressure and high temperature has been published.

  In the conventional external pressure load device shown in FIG. 4, a heater 21 adjacent to the irradiated nuclear fuel pellet small piece (test piece 20) and a heat insulating material 22 adjacent to the outer periphery thereof are arranged. It is stored in. The entire high-pressure vessel 23 is surrounded by a radiation shielding wall (not shown), and the inside of the wall is controlled at a negative pressure so that radioactive substances are not released.

  The high-pressure container 23 is filled with an inert gas such as argon gas supplied from a high-pressure gas storage cylinder of the high-pressure gas supply system 24 via a compression pump of the high-pressure gas supply system 24. Both the high-pressure container 23 and the high-pressure gas supply system 24 correspond to a high-pressure gas manufacturing facility defined by the High Pressure Gas Safety Law, and are required to satisfy various safety standards.

  At the time of the test, for example, the gas pressure is increased to 100 MPa, the pressure is checked with a pressure gauge 25, and the temperature (for example, 1500 ° C.) detected by an in-furnace thermometer (not shown) is recorded through a trace gas release valve while being recorded. The radioactivity concentration in the gas is recorded in the radioactivity concentration meter 26 while the pressure is lowered, and the effect of the gas pressure and the temperature on the release behavior of the fission gas (FP gas) in the pellet (test piece 20). Checking the relationship.

  In the external pressure loading device shown in FIG. 4, the irradiated fuel pellets (test pieces 20) are stored in a pressure-resistant container 23 and a high pressure is applied to perform the test at a high temperature. Since the space for accommodating the test piece 20 is small and the size of the sample is restricted from the viewpoint of securing various safety specified by law, the size of the fuel pellet is limited to about several mm, Testing on large volumes and highly radioactive samples, such as those containing fuel pellets, was not possible.

  Further, in the gas pressure loading method in the high pressure container 23, it is necessary to rapidly release gas in order to simulate a sudden decrease in compression force in the event of a fuel rod accident. For example, a compressed state of 100 MPa is required. In order to rapidly reduce the pressure to the atmospheric pressure, it is necessary to instantaneously release a gas having a volume of about 1000 times the volume in the sealed container (high pressure container 23) into another container which is controlled under a negative pressure. The release of large amounts of gas containing strong radioactive materials was not practical from the viewpoint of safety management of fuel handling facilities.

  In order to determine the release behavior of fission gas (FP gas) from fuel pellets with high reliability, it is preferable to use a long (about 20 mm long) fuel rod as the test material. The test should be conducted under high-pressure conditions using a small room equipped with remote control equipment in a radiation shielding facility called "radiation shielding facility". However, since it is practically difficult to install a device that satisfies the high pressure resistance conditions defined in the High Pressure Gas Safety Act in a cell, the fuel rod is heated to a high temperature under atmospheric pressure as an alternative as in Non-Patent Document 4. In some cases, the release behavior of FP gas from fuel pellets was investigated.

  The present invention has been made in view of the above-described deficiencies of the related art, and an object thereof is to provide a relatively small and simple mechanism that can be installed in a radiation shielding cell and does not require high-pressure gas. It is an object of the present invention to provide a configured high compression force (external pressure) load device and a test method using the same.

  In order to achieve the above object, the present invention provides a concave container for accommodating a test piece, heat-resistant particles filled in the concave container, a heater for heating the heat-resistant particles, and a concave portion of the concave container. A push rod fitted with the heat-resistant particles to apply an external pressure, an atmosphere protection container containing the concave container, an atmosphere adjustment system for supplying an atmosphere adjustment gas into the atmosphere protection container, and the test piece. A detector for detecting a substance to be released, wherein the test piece is embedded in the heat-resistant particles, the heat-resistant particles are heated by the heater, and the heat-resistant particles are pressed by the push rod. An external pressure is applied to the test piece, and a characteristic of the test piece is detected by detecting a substance released from the test piece when the external pressure is released by the detector.

  Further, the present invention provides a cylindrical container for accommodating a test piece, heat-resistant particles filled in the cylindrical container, a heater for heating the heat-resistant particles, and inserted into a cylinder of the cylindrical container. A first push rod that applies an external pressure to the heat-resistant particles from one side, a second push rod that applies an external pressure to the heat-resistant particles from the other side, and an atmosphere protection container that includes the cylindrical container. An atmosphere adjustment system that supplies an atmosphere adjustment gas into the atmosphere protection container, and a detector that detects a substance released from the test piece, wherein the test piece is embedded in the heat-resistant particles. The heat-resistant particles are heated by a heater, and an external pressure is applied to the heat-resistant particles by the first push rod and the second push rod, and released from the test piece when the external pressure is released. Emitted substance to the detector By detecting Ri, and detects a characteristic of the test piece.

  Further, the present invention is the method for testing irradiated fuel pellets, wherein the test piece is an irradiated fuel pellet.

  According to the present invention, the following effects can be obtained.

  Because a test piece consisting of fuel pellets, which is a strong radioactive substance, is embedded in a concave container along with heat-resistant particles, and the heat-resistant particles are compressed by a hydraulic press through a push rod to apply a compressive force to the test piece. It is not necessary to store test specimens in a high-pressure gas container and does not use a high-pressure gas supply source.Therefore, there is no regulation under the High Pressure Gas Safety Law, so it is not only economically advantageous but also safe for radioactive handling facilities. This has the effect of contributing to improved performance and ease of management.

  Furthermore, the mechanism that compresses the heat-resistant particles with a hydraulic press, the unloading speed of the press at the time of releasing the hydraulic pressure is high, and the compressed gas method significantly increases the volume expansion, making it difficult to maintain and maintain the negative pressure of the facility. However, the method using particle compression has an important additional effect that rapid unloading becomes possible.

  This provides a high compression force (external pressure) load device that can be installed in the radiation shielding cell and has a relatively small and simple mechanism that does not require high-pressure gas, and a test method using the same. be able to.

  Problems, configurations, and effects other than those described above will be apparent from the following description of the embodiments.

It is a sectional view showing the schematic structure of the external pressure load device concerning one embodiment of the present invention. (Example 1) It is a sectional view showing the schematic structure of the external pressure load device concerning one embodiment of the present invention. (Example 2) It is a sectional view showing the schematic structure of the external pressure load device concerning one embodiment of the present invention. (Example 3) It is sectional drawing which shows schematic structure of the conventional external pressure load device. It is a figure which shows notionally the compression force measuring method of a test piece.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and detailed description of overlapping portions will be omitted.

  First Embodiment An external pressure load device and an external pressure load method according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing a schematic configuration of the external pressure load device of the present embodiment.

As shown in FIG. 1, the external pressure load device according to the present embodiment includes a used nuclear fuel rod 20 cut into a length of about 20 mm, which is a test piece, in a concave container 1 made of a heat-resistant material such as tungsten (W). Is filled with heat-resistant particles 5 (here, zirconia (zirconium dioxide: ZrO ₂ ), particle size of about 0.1 mmφ) so as to cover the entire outer surface, and filled with push rod 2 made of a heat-resistant material. It is inserted so as to be in close contact.

  In addition, when filling the heat-resistant particles 5 and the test piece 20 into the concave container 1, the fluidity of the particles was improved by externally applying vibration to the container. The container 1 is disposed between a press housing 4 (an upper press housing 4a and a lower press housing 4b) and a hydraulic piston 7 constituting a press structure, and a heat insulator 3 (an upper heat insulator 3a and a lower heat insulator 3b). And a mechanism for compressing the heat-resistant particles 5 via the push rod 2.

  Further, the concave container 1 is sealed by a container 6 for protecting the atmosphere inside the container, and a sample heater 21 and a heat insulating material 22 are arranged on the outer periphery thereof, and the temperature is maintained at a high temperature while detecting the temperature with a thermometer (not shown). Is done.

  In the test, the press structure (between the upper press housing 4a and the lower press housing 4b) was passed while flowing the in-vessel atmosphere adjusting gas 8 containing an inert gas as the main composition (main component) into the vessel 6 for protecting the in-vessel atmosphere. ), A predetermined high compression force (for example, 100 MPa) is applied to the heat-resistant particles 5 via the push rod 2, and the concave container 1 and the test piece 20 are heated to a high temperature (for example, 1500 ° C.). The radioactive substance contained in the atmospheric gas flowing out of the concave container 1 is measured by a detector (radioactive concentration measuring instrument 26), and the relationship between the temperature, the pressure, and the lapse of time is recorded, so that the sample (the specimen 20) can be measured. The information on the release behavior of fission products (FP gas) is obtained.

  Further, when simulating the fuel crushing phenomenon at the time of an accident, the pressure of the hydraulic piston 7 is rapidly (or gradually) released, and the press pressure and the compression pressure of the particles (heat-resistant particles 5) are rapidly (or alternatively). The radioactive substance contained in the atmospheric gas flowing out of the concave container 1 is measured by a detector (radioactive concentration measuring device 26) at that time, and the temperature, pressure and time elapse are measured. Is recorded, information on the release behavior of fission products (FP gas) in the sample (test piece 20) is obtained. Further, after the heating test, the concave container 1 is disassembled, and a phenomenon in which fine FP gas bubbles contained in the fuel pellet (test piece 20) burst due to rapid release of the compression pressure and the accompanying fuel pellet (test piece 20). Observe the presence and degree of the crushing phenomenon in ()).

  As described above, the external pressure load device according to the present embodiment includes the concave container 1 for storing the test piece 20, the heat-resistant particles 5 filled in the concave container 1, and the heater 21 for heating the heat-resistant particles 5. And a push rod 2 fitted in the concave portion of the concave container 1 and applying an external pressure to the heat-resistant particles 5, an atmosphere protection container containing the concave container 1 (a container 6 for protecting the atmosphere in the container), and an atmosphere protection container. An atmosphere adjusting system (ambient atmosphere adjusting gas 8 in the container) for supplying an atmosphere adjusting gas into the chamber 6 and a detector (radioactivity concentration measuring instrument 26) for detecting a substance released from the test piece 20 are provided. The piece 20 is embedded in the heat-resistant particles 5, the heat-resistant particles 5 are heated by the heater 21, and an external pressure is applied to the heat-resistant particles 5 by the push rod 2. Detector (radioactivity) By detecting the degree meter 26), detecting a property of the test piece 20.

  According to the present embodiment, a high compression force (external pressure) load device that can be installed in a radiation shielding cell and is composed of a relatively small and simple mechanism that does not require high-pressure gas, and irradiation using the same device A test method for spent fuel pellets can be realized.

  When irradiated nuclear fuel rods or fuel pellets are used as the test pieces 20, at least one of the heating temperature of the heater 21 and the external pressure (compression force) of the push rod 2 is changed to change the irradiated nuclear fuel rods. By grasping (detecting) the release behavior of fission product gas (FP gas) released from rods and fuel pellets, it is possible to simulate the fuel crushing phenomenon at the time of the accident.

  Second Embodiment With reference to FIG. 2, an external pressure load device and an external pressure load method according to a second embodiment of the present invention will be described. FIG. 2 is a sectional view showing a schematic configuration of the external pressure load device of the present embodiment.

  As shown in FIG. 2, in the external pressure load device of this embodiment, heat-resistant particles (coarse particles) 27 having a larger particle diameter than the heat-resistant particles 5 are arranged between the push rod 2 and the heat-resistant particles 5. This is different from the external pressure load device of the first embodiment. Other points are the same as in the first embodiment.

  In Example 1, heat-resistant particles (fine particles) 5 having a particle diameter of about 0.1 mmφ are used as a pressurizing medium. A diameter gap of about 0.05 mm is formed between the inner diameter of the heat-resistant container (concave container 1) and the push rod 2, but after pressurization, heat-resistant particles (fine particles) are formed in the gap between the push rod 2 and the inner diameter of the container. 5 are firmly pinched, and it is extremely difficult to remove the push rod 2 after the test.

  Therefore, in this embodiment, as shown in FIG. 2, the filler (heat-resistant particles (fine particles)) is formed on the contact surface between the push rod 2 and the heat-resistant particles (fine particles) 5 having a particle diameter of about 0.1 mmφ as the filler. The heat-resistant particles (coarse particles) 27 having a diameter larger than the diameter of the particles 5) are interposed. That is, between the push rod 2 and the heat-resistant particles 5, a coarse-grained particle layer composed of coarse-grained particles (heat-resistant particles 27) having a larger particle diameter than the heat-resistant particles 5 is provided.

  In this embodiment, heat-resistant particles (coarse particles) having a particle diameter of about 1.0 mmφ overlap one or more layers (preferably 2 to 3 layers) on heat-resistant particles (fine particles) having a particle diameter of about 0.1 mmφ. In addition, the diameter gap between the push rod 2 and the inner diameter of the container is set to be equal to or less than the diameter of the interposed coarse particles (heat-resistant particles 27) (preferably, a value close to 0.5 mm). That is, the diameter gap between the push rod 2 and the inner diameter of the concave container 1 is larger than the particle size of the heat-resistant particles (fine particles) 5 and smaller than the particle size of the coarse particles (heat-resistant particles 27).

  As described above, according to the present embodiment, in addition to the effect of the first embodiment, the push rod 2 is easily disassembled after pressurization because the diameter gap between the push rod 2 and the inner diameter of the container is as large as about 0.5 mm. It is possible, and even if a compressive surface pressure of 100 MPa is applied, there is no leakage of the fine particles (heat-resistant particles 5) and the coarse particles (heat-resistant particles 27) of the pressurized medium from the gap, and the test work up to disassembly is performed. Workability can be significantly improved.

  Third Embodiment An external pressure load device and an external pressure load method according to a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a sectional view showing a schematic configuration of the external pressure load device of the present embodiment.

  Although the concave container 1 is used in the first embodiment, the external pressure load device of the present embodiment uses a cylindrical container 28 made of a heat resistant material instead of the concave container 1 as shown in FIG. The rod 2 is different from the external pressure load device of the first embodiment in that the rod 2 is constituted by an upper push rod 2a and a lower push rod 2b. Other points are the same as in the first embodiment.

  In the present embodiment, the heat-resistant particles 5 as the filler and the spent nuclear fuel rod pieces (test pieces 20) are housed in a cylindrical container 28, and the upper heat rods 2a and the lower push rods 2b vertically move the heat resistant particles. 5 is compressed.

  The external pressure load device of the present embodiment includes a cylindrical container 28 for storing the test piece 20, the heat-resistant particles 5 filled in the cylindrical container 28, the heater 21 for heating the heat-resistant particles 5, An upper push rod 2a (first push rod) that is inserted into the cylinder of the container 28 and applies external pressure to the heat-resistant particles 5 from one side, and a lower push rod 2b (first push rod) that applies external pressure to the heat-resistant particles 5 from the other side. 2), an atmosphere protection container (container 6 for protecting the atmosphere in the container) containing the cylindrical container 28, and an atmosphere adjustment system (atmosphere adjustment gas in the container) for supplying an atmosphere adjustment gas into the atmosphere protection container 6. 8) and detecting a substance released from the test piece 20 (radioactivity concentration measuring instrument 26). The test piece 20 is embedded in the heat-resistant particles 5, and the heat-resistant particles 5 are Is heated, and the upper push rod 2a (first An external pressure is applied to the heat-resistant particles 5 by a push rod and a lower push rod 2b (a second push rod), and a substance released from the test piece 20 when the external pressure is unloaded is detected by a detector (radioactive concentration). The characteristics of the test piece 20 are detected by the detection by the measuring device 26).

  According to the present embodiment, in addition to the effects of the first embodiment, the workability of the disassembly work after the test (such as the work of removing the heat-resistant particles 5 and the spent nuclear fuel rod pieces (test pieces 20)) can be improved. it can.

  In FIG. 3, the lower push rod 2b and the lower heat insulating material 3b may be combined (integrated) to form a lower push rod with a disk.

<< Operation of the Invention >>
The operation of the present invention will be described more specifically with reference to FIG. FIG. 5 is a diagram conceptually showing a method for measuring the compressive force of a test piece.

  In order to confirm that compressing the specimen with the compressed particles generates a compressive force that can suppress or control the release of fission products (FP gas) from fuel pellets at high temperatures, A surface pressure measuring element 32 having a structure in which a pressure film (PRESCALE: manufactured by FUJIFILM) for displaying the contact surface pressure in color was sandwiched between metal disks was produced, and was arranged in a recess of the container 30 as shown in FIG. It is predicted that the generated surface pressure has direction dependency, and the surface pressure measuring element 32 is set in a direction in which the surface pressure in the compression direction (vertical direction) and the lateral direction (radial direction) can be detected at each depth position in the container 30. Was placed.

  The push rod was compressed by a press so as to obtain a nominal compression surface pressure of 100 MPa by dividing the compression load by the cross-sectional area of the container. The test was repeated several times, and the surface pressure was determined by comparing the degree of color development of the pressure measurement film with the standard color. The average value of the obtained surface pressures and the range of the obtained data are shown in FIG.

  It was confirmed that when a nominal compressive force of 100 MPa was applied from the surface pressure shown in FIG. 5, a compressive stress of particles produced a compressive stress of 50 MPa at the minimum and 90 MPa at the maximum. Regarding nuclear fuel pellets actually used in a reactor, as described in Non-Patent Document 5, when an external pressure load of 40 MPa to 60 MPa is applied at a high temperature, release of fission gas (FP gas) may stop. Since the zirconia particles having a high softening temperature of about 2700 ° C. are known, the compressive force is considered to be equal to room temperature even in a high-temperature test at 1500 ° C., and the press structure (external pressure load) in each of the above examples is considered. Since the load can be uniformly applied to the test pieces, such as the spent nuclear fuel rod pieces and the fuel pellets, the device can be said to be applicable to a test for grasping the release characteristics of fission gas (FP gas) without any problem.

  In each of the above embodiments, the tip of the push rod 2 (2a, 2b) and the bottom of the container have been described as being flat, but their shapes are not necessarily limited to flat. An example of a shape in which the inner diameter of the container is constant is shown, but a shape in which the inner diameter varies is also included.

  The material and gas composition of the container, the material and dimensions (size) of the heat-resistant particles, and the size of the gap (diameter gap) between the push rod 2 (2a, 2b) and the inner wall of the container are, of course, the same as those in the above embodiment. It is not limited.

  Furthermore, in each embodiment, an example is shown in which the container 6 for protecting the atmosphere in the container is disposed on the center side (inside) of the heater 21 and the heat insulating material 22. However, the heater 21 and the heat insulating material 22 are provided for protecting the atmosphere in the container. A similar effect can be obtained with a structure included inside the container 6 of FIG.

  Further, the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described above. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. Also, for a part of the configuration of each embodiment, it is possible to add, delete, or replace another configuration.

  INDUSTRIAL APPLICABILITY The present invention can be applied to evaluation of radioactive gas release behavior from nuclear fuel rods and fuel pellets having radioactivity for nuclear power generation.

  In addition, a test piece from which a release substance is released by heating and pressurizing can be applied to the property evaluation and behavior evaluation of industrial materials other than nuclear fuel rods and fuel pellets.

  DESCRIPTION OF SYMBOLS 1 ... Concave container (made of heat resistant material), 2 ... Push rod (made of heat resistant material), 2a ... Top push rod, 2b ... Bottom push rod, 3 ... Insulation material, 3a ... Insulation material, 3b ... Bottom Insulating material, 4 ... Press housing, 4a ... Upper pressing housing, 4b ... Lower pressing housing, 5 ... Heat-resistant particles (fine particles), 6 ... Container for protecting the atmosphere in the container, 7 ... Hydraulic piston, 8 ... (In the container) Atmosphere adjusting gas, 20: test piece (spent nuclear fuel rod piece or fuel pellet), 21: (sample) heater, 22: heat insulating material, 23: high pressure container (high pressure container), 24: high pressure gas Supply system, 25: pressure gauge, 26: radioactivity concentration meter, 27: heat-resistant particles (coarse particles), 28: cylindrical container (made of heat-resistant material), 29: base, 30: (cylindrical) container , 31 ... filler (heat-resistant particles), 32 ... surface pressure gauge.

Claims (6)

A concave container for storing the test piece,
Heat-resistant particles filled in the concave container,
A heater for heating the heat-resistant particles,
A push rod fitted into the concave portion of the concave container and applying an external pressure to the heat-resistant particles,
An atmosphere protection container containing the concave container,
An atmosphere adjustment system for supplying an atmosphere adjustment gas into the atmosphere protection container,
A detector for detecting a substance released from the test piece,
Embedding the test piece in the heat-resistant particles, heating the heat-resistant particles by the heater, and applying an external pressure to the heat-resistant particles by the push rod, when the external pressure is unloaded, An external pressure load device, wherein characteristics of the test piece are detected by detecting a substance released from the test piece by the detector. The external pressure load device according to claim 1,
An external pressure load device comprising a coarse particle layer made of coarse particles having a larger particle diameter than the heat resistant particles, between the push rod and the heat resistant particles. The external pressure load device according to claim 2,
An external pressure loading device, wherein a diameter gap between the inner diameter of the push rod and the inner diameter of the concave container is larger than the particle size of the heat-resistant particles and smaller than the particle size of the coarse particles. A cylindrical container for storing the test piece,
Heat-resistant particles filled in the cylindrical container,
A heater for heating the heat-resistant particles,
A first push rod that is inserted into the cylinder of the cylindrical container and applies external pressure to the heat-resistant particles from one side, and a second push rod that applies external pressure to the heat-resistant particles from the other side,
An atmosphere protection container containing the cylindrical container,
An atmosphere adjustment system for supplying an atmosphere adjustment gas into the atmosphere protection container,
A detector for detecting a substance released from the test piece,
The test piece is embedded in the heat-resistant particles, the heat-resistant particles are heated by the heater, and an external pressure is applied to the heat-resistant particles by the first push rod and the second push rod. An external pressure loading device, wherein the detector detects a substance released from the test piece when the external pressure is unloaded, thereby detecting characteristics of the test piece.   The method for testing irradiated fuel pellets using an external pressure load device according to any one of claims 1 to 4, wherein the test piece is an irradiated fuel pellet. A method for testing irradiated fuel pellets according to claim 5 ,
By changing at least one of the heating temperature by the heater and the external pressure by the push rod, detecting the release behavior of the fission product gas released from the irradiated fuel pellet, Test method.

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