Method for determining deterioration of cushioning material and cushioning body

Abstract

To provide a buffer material deterioration determination method and buffer, which improve accuracy of buffer material deterioration determination.SOLUTION: A method of determining deterioration of a buffer material provided in a buffer of a radioactive material storage container is provided, the method comprising generating a deterioration determination map containing determination values corresponding to state quantities of the buffer material, acquiring a detected value of the state quantity of the buffer material, and determining the degree of deterioration of the buffer material using the detected value and the deterioration determination map.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a method for determining deterioration of a buffer material provided in a buffer that protects a radioactive material storage container, and the buffer. [Background technology]

[0002] At nuclear facilities, radioactive waste such as spent fuel generated in reactors and other facilities is stored in radioactive material storage containers and transported to storage facilities, reprocessing facilities, etc., for storage or reprocessing. A radioactive material storage container consists of a cylindrical body with an open top and a bottom, and a lid that is fixed to the top of the body and closes the opening. A buffer body is provided at the axial end of the radioactive material storage container. The buffer body deforms to absorb impact when the radioactive material storage container is dropped, tipped over, or hit.

[0003] The buffer body is configured by disposing a buffer material inside a support member. The buffer material may deteriorate over long periods of use depending on the material used and the environment in which it is used, so it is preferable to monitor the deterioration state of the buffer material. For example, Patent Document 1 below describes a technology for monitoring the deterioration state of the buffer material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-11603 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned Patent Document 1, a deterioration monitoring member made of a material with the same deterioration characteristics as the buffer material is arranged around the radioactive material storage container. However, the buffer body is configured by placing the buffer material in a sealed state inside a support member, and since the environment in which the radioactive material storage is placed is different, there is a possibility that this may affect the deterioration judgment of the buffer material.

[0006] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a method for determining deterioration of a cushioning material and a cushioning body that improves the accuracy of determining deterioration of the cushioning material. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the method for determining deterioration of buffer material disclosed herein is a method for determining deterioration of buffer material provided in a buffer of a radioactive material storage container, and includes the steps of creating a deterioration determination map having determination values ​​corresponding to the state quantities of the buffer material, obtaining detection values ​​of the state quantities of the buffer material, and determining the degree of deterioration of the buffer material using the detection values ​​and the deterioration determination map.

[0008] In addition, the buffer body of the present disclosure includes a support member having a hollow shape and provided on the outside of the radioactive material storage container, a buffer material that is disposed inside the support member and absorbs impact by deforming, and an observation window that is provided in the support member and allows the buffer material to be observed from the outside. [Effects of the Invention]

[0009] According to the method for determining deterioration of a cushioning material and the cushioning body of the present disclosure, it is possible to improve the accuracy of determining deterioration of a cushioning material. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view of a radioactive material storage container with a part cut away. [Figure 2] FIG. 2 is a plan view showing a radioactive substance storage container equipped with a buffer body. [Figure 3] FIG. 3 is a front view showing the radioactive substance storage container with the buffer body attached in an upright position. [Figure 4] FIG. 4 is a front view showing a state in which the radioactive substance storage container with the buffer body attached is placed horizontally. [Figure 5] FIG. 5 is a cross-sectional view showing the internal structure of the buffer body. [Figure 6]FIG. 6 is a flowchart showing a method for determining deterioration of a cushioning material according to the first embodiment. [Figure 7] FIG. 7 is a deterioration determination map showing the compressive strength relative to the amount of residual gas. [Figure 8] FIG. 8 is a front view of a buffer body used in the method for determining deterioration of a buffer material according to the second embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing a main part of the cushioning material. [Figure 10] FIG. 10 is a schematic diagram for explaining a method for determining the deterioration of a cushioning material. [Figure 11] FIG. 11 is a flowchart showing a method for determining deterioration of a cushioning material according to the second embodiment. [Figure 12] FIG. 12 is a deterioration determination map showing the compression strength relative to the color difference. [Figure 13] FIG. 13 is a cross-sectional view showing a main part of a buffer body used in a method for determining deterioration of a buffer material according to the third embodiment. [Figure 14] FIG. 14 is a flowchart showing a method for determining deterioration of a cushioning material according to the third embodiment. [Figure 15] FIG. 15 is a first deterioration determination map showing the degree of deterioration relative to pH. [Figure 16] FIG. 16 is a second deterioration determination map showing the compressive strength relative to the deterioration degree. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes configurations that combine the embodiments. Furthermore, the components in the embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially identical, and those that are within the so-called equivalent range.

[0012] [First embodiment] <Radioactive material storage container> FIG. 1 is a perspective view of a radioactive substance storage container of the first embodiment, with a part cut away.

[0013] As shown in FIG. 1, a cask 11 serving as a radioactive material storage container includes a trunk portion 12 and a lid portion 13. The trunk portion 12 has a container body 21. The container body 21 is cylindrical (in this embodiment, cylindrical), has an opening 22 formed at the upper end, and is closed at the lower end. The container body 21 has a cavity 23 therein, and a basket 24 is provided in the cavity 23. The basket 24 is provided with a plurality of cells 25 that can independently store radioactive material (e.g., spent fuel assemblies). The container body 21 is a forged product made of carbon steel that has a gamma ray shielding function, but stainless steel can also be used instead of carbon steel. The container body 21 can also be a cast product made of spheroidal graphite cast iron, carbon steel cast steel, or the like.

[0014] In the trunk 12, an outer cylinder 26 is disposed on the outer peripheral surface of the container body 21 with a predetermined gap therebetween. The container body 21 is provided with a plurality of copper heat transfer fins 27 in the circumferential direction, which perform heat conduction between the outer peripheral surface and the inner peripheral surface of the outer cylinder 26. In the space surrounded by the outer cylinder 26 and the heat transfer fins 27, the container body 21 is provided with a resin (neutron shielding body) 28, which is a polymer material containing a large amount of hydrogen and contains boron or a boron compound that has a neutron shielding function.

[0015] The body 12 is provided with a bottom 29 that protrudes below the closed lower end of the container body 21. The bottom 29 is formed to have dimensions smaller than the outer diameter of the container body 21. The bottom 29 has a space surrounded by the closed lower end of the container body 21, and a resin (neutron shielding body) is provided in the space.

[0016] The barrel 12 is provided with a trunnion 30 for lifting the cask 11 on the vessel body 21. The trunnion 30 is provided penetrating the outer cylinder 26 from the vessel body 21, and protrudes most outward from the cask 11.

[0017] The lid portion 13 is provided at the opening 22 of the vessel body 21, and closes the opening 22 to hermetically seal the vessel body 21 (torso portion 12). The lid portion 13 is composed of a primary lid 31 and a secondary lid 32. The primary lid 31 is formed in a disk shape from a material such as carbon steel or stainless steel that shields against gamma rays. The secondary lid 32 covers the primary lid 31 and appears on the outside of the cask 11, and like the primary lid 31, is also formed in a disk shape from a material such as carbon steel or stainless steel that shields against gamma rays. A resin (neutron shield) 28 may be provided between the primary lid 31 and the secondary lid 32. In addition, a tertiary lid may be provided on the lid portion.

[0018] The primary lid 31 is fixed to a first step 22a formed at the opening 22 of the container body 21 with bolts (not shown) made of carbon steel or stainless steel, and is attached to the container body 21. The secondary lid 32 is fixed to a second step 22b formed at the opening 22 of the container body 21 with bolts (not shown) made of carbon steel or stainless steel, and is attached to the container body 21. Although not shown, metal gaskets are provided between the primary lid 31 and the first step 22a and between the secondary lid 32 and the second step 22b. The metal gaskets ensure sealing between the primary lid 31 and the first step 22a and between the secondary lid 32 and the second step 22b.

[0019] The barrel 12 surrounds the secondary lid 32 at the opening 22 of the vessel body 21, and has a cylindrical upper edge 22c that appears on the outside of the cask 11. The upper surface of the upper edge 22c is located higher than the surface of the secondary lid 32, and surrounds the secondary lid 32. The upper surface of the upper edge 22c has a plurality of bolt holes 33 spaced apart in the circumferential direction for attaching a buffer body A, which will be described later.

[0020] <Buffer> FIG. 2 is a plan view showing a radioactive material storage container equipped with a protective device of the first embodiment, and FIG. 3 is a front view showing a state in which the radioactive material storage container equipped with a protective device is placed upright.

[0021] 2 and 3, the cask 11 includes a buffer body 41. The buffer body 41 is attached to the cask 11 that has been transported to a storage facility, which is, for example, a storage location.

[0022] In a nuclear power plant, the cask 11 contains, for example, spent fuel assemblies stored in cells 25 of a basket 24 of a vessel body 21, and is sealed by a lid 13. The cask 11 is transported, for example, from a nuclear power plant to a storage facility. A transport buffer (not shown) is attached to the cask 11 during transportation. When the cask 11 is transported to the storage facility, which is the storage location, the transport buffer is removed and the cask 11 is stored upright on the floor F with the lid 13 facing upward, and a buffer 41 is attached to the lid 13 side. During storage, the bottom 29 of the cask 11 is fitted into a frame 37 installed on the floor F, or the trunnion is fastened to the frame, and the cask 11 is stored in an upright position with the central axis O aligned vertically.

[0023] The buffer body 41 includes a support member 42 and a buffer material 43 .

[0024] The support member 42 has a disk portion 51 and a cylindrical portion 52. The cylindrical portion 52 is integrally formed on the radially outer side of the disk portion 51. The support member 42 is hollow and made of a metal plate such as a steel plate, and is deformable under a predetermined load. The predetermined load is the load of an anticipated falling object or the load that would be applied to the cask 11 when it hits the floor F if the cask 11 standing on the floor F were to tip over. The disk portion 51 is disposed above the lid portion 13 of the cask 11, along the surface of the secondary lid 32 that is exposed on the outside of the lid portion 13. The disk portion 51 is disposed so as to cover the surface of the secondary lid 32 and the surface of the upper edge 22c of the vessel body 21. The disk portion 51 is fixed to the vessel body 21 by bolts (not shown) attached to bolt holes 33 provided in the upper edge 22c. In addition, when a tertiary lid is provided as the lid portion, the disc portion 51 is arranged along the surface of the tertiary lid that appears on the outside of the lid portion 13, and is arranged so as to cover the surface of the tertiary lid and the surface of the upper edge 22c of the container body 21.

[0025] The cylindrical portion 52 is disposed so as to surround the outside of the upper edge 22c of the body portion 12. That is, the cylindrical portion 52 is disposed radially outward from the lid portion 13 and protrudes radially outward from the body portion 12.

[0026] The buffer material 43 is disposed inside and supported by the support member 42. The buffer material 43 deforms under a predetermined load. The buffer material 43 is made of wood, a foam material, or a polymer compound.

[0027] FIG. 4 is a front view showing a state in which the radioactive material storage container equipped with the protective device is placed horizontally.

[0028] 4, the cask 11 may also be stored horizontally with its central axis O aligned horizontally. The cask 11 is stored vertically with its body 12 fitted into a stand 38 installed on the floor F, with its central axis O aligned vertically. In this case, a buffer 41 is attached to one side of the cask 11 along the central axis O (the lid 13 side), and a buffer 46 is attached to the other side of the cask 11 along the central axis O (the bottom 29 side). The buffer 46 has a configuration similar to that of the buffer 41.

[0029] <Internal structure of the buffer body> FIG. 5 is a cross-sectional view showing the internal structure of the protection device.

[0030] 5, the buffer 41 has a support member 42 and a buffer material 43, and the buffer material 43 is disposed inside the hollow support member 42. The buffer material 43 is configured by combining a first buffer material 43a, a second buffer material 43b, and a third buffer material 43c. The first buffer material 43a, the second buffer material 43b, and the third buffer material 43c are formed by combining multiple blocks of wood.

[0031] The first buffer material 43a is provided along the circumferential direction on the outer side of the peripheral surface side member 53 and the outer side of the end surface side member 54 of the support member 42. The first buffer material 43a is made up of a plurality of blocks divided in the circumferential direction of the buffer body 41.

[0032] The second buffer material 43b is provided adjacent to the first buffer material 43a along the circumferential direction on the outer side of the peripheral surface side member 53 and on the upper side of the end surface side member 54 of the support member 42. The second buffer material 43b is composed of a plurality of blocks divided into blocks in the circumferential direction of the buffer body 41.

[0033] The third buffer material 43c is provided adjacent to the second buffer material 43b along the inner periphery of the second buffer material 43b. The third buffer material 43c is composed of a plurality of blocks divided in the circumferential direction of the buffer body 41.

[0034] The first material constituting the first buffer material 43a has the highest compressive strength of all the materials constituting the buffer material 43, and is, for example, oak. The second material constituting the second buffer material 43b has a lower compressive strength than the first material, and is, for example, red cedar. The third material constituting the third buffer material 43c has a lower compressive strength than the second material, and is, for example, balsa. Here, compressive strength refers to the Young's modulus or compressive strength when the buffer material 43 is compressed.

[0035] The buffer material 43 is not limited to a wooden block, but may be, for example, a foam material or a polymer compound other than wood.

[0036] <How to determine the deterioration of cushioning materials> FIG. 6 is a flowchart showing the method for determining deterioration of a cushioning material according to the first embodiment, and FIG. 7 is a deterioration determination map showing the compressive strength relative to the amount of residual gas.

[0037] 3, the method for determining deterioration of a buffer material according to the first embodiment is a method for determining deterioration of a buffer material 43 provided in a buffer body 41 of a cask 11. The method for determining deterioration of a buffer material includes the steps of creating a deterioration determination map having determination values ​​according to state quantities of the buffer material 43, acquiring detected values ​​of the state quantities of the buffer material 43, and determining the degree of deterioration of the buffer material 43 using the detected values ​​and the deterioration determination map.

[0038] Here, the degree of deterioration of the buffer material 43 is the degree of decrease in the compressive strength of the buffer material 43. That is, in the method for determining deterioration of the buffer material, the deterioration determination map represents the compressive strength of the buffer material 43 as a determination value for the state quantity of the buffer material 43, and the compressive strength of the buffer material for the detected value is found using the deterioration determination map, and the degree of deterioration is determined based on the found compressive strength.

[0039] As shown in Fig. 6, in step S11, a deterioration determination map having determination values ​​corresponding to the state quantities of the buffer material 43 is created. As shown in Fig. 7, the deterioration determination map of the first embodiment is the compressive strength of the buffer material 43 relative to the amount of gas remaining in the buffer material 43. The deterioration determination map is created by conducting experiments or the like in advance.

[0040] As shown in FIG. 3 , the buffer 41 has a buffer material 43 supported inside a support member 42. That is, the buffer material 43 is covered by a hollow support member 42. The support member 42 is preferably made of a steel material such as stainless steel, and hermetically covers the buffer material 43. If the buffer material 43 is made of wood, a foam material, a polymer compound, or the like, it will deteriorate over time due to exposure to the outside air. In the buffer 41 of this embodiment, the buffer material 43 is covered by the support member 42, so deterioration over time is suppressed. However, if the buffer material 43 is hermetically covered by the support member 42, the buffer material 43 will not be exposed to the outside air, and deterioration over time will occur mainly due to temperature. By hermetically covering the buffer material 43 with the support member 42, the main cause of deterioration over time can be limited to temperature.

[0041] Therefore, in the first embodiment, a buffer material 43 of a predetermined size is first heat-treated alone at a predetermined temperature for a predetermined time to simulate a state in which the buffer material 43 is disposed within the support member 42 and the buffer body 41 is fixed to the cask 11 for a predetermined period of time. In this case, the buffer material 43 may be heat-treated at the actual temperature for the actual period of time, or may be heat-treated at a temperature higher than the actual temperature for a shorter period of time. The buffer material 43 heat-treated at the predetermined temperature for the predetermined period of time is subjected to thermogravimetric calorimetry to determine the type and amount of gas generated. Here, the amount of gas generated from the buffer material 43 of a predetermined size is the amount of gas remaining in the buffer material 43. In this case, it is preferable to determine the amount of remaining gas for each type of gas as well as the total amount of all types of gas. Then, buffer materials 43 heat-treated at different heating temperatures and heating times are produced.

[0042] If the buffer material 43 is made of wood, the gases shown below will be generated, and the residual gas amount for each type of gas, the total residual gas amount for specified types of gas, and the total residual gas amount for all types of gas will be calculated. Hydroxyacetone Propionic acid 2-Cyclopenten-1-one acetic acid Furfural 5-Methyl-2-furaldehyde butyric acid 3-Methyl-1,2-cyclopentanedione guaiacol Methylguaiacol (4-methylguaiacol) Maltol phenol 2-(Methoxy-4-ethylphenol) Cresol (p-Cresol) Isoeugenol (cis and trans isioeugenol) Eugenol 5-Hydroxymethylfurfural vanillin Hydrogen (H) Water (H2O) Carbon monoxide (CO) Carbon dioxide (CO2) Methane (CH4) Ethylene (C2H4) Ethane (C2H6)

[0043] Furthermore, when the cushioning material 43 is a rigid urethane foam, the gases shown below are generated, and the residual gas amount for each type of gas, the total residual gas amount for the specified types of gas, and the total residual gas amount for all types of gas are calculated. Water (H2O) Carbon monoxide (CO) Nitrogen (N2) Carbon dioxide (CO2) Propylene dichloride Aniline Methylaniline Trimethylsilyl (Tris Phosphate) Nitrogen compounds Methylenedianiline

[0044] Next, a deterioration assessment test is conducted on a plurality of buffer materials 43 that have been heat-treated at different heating temperatures and times. In the deterioration assessment test, the compressive strength is obtained by a uniaxial compression test on the buffer material 43. In the uniaxial compression test, for example, the buffer material 43 is placed inside a restraining ring, and only the buffer material 43 is compressed. In this case, the restraining ring is made of wood that has not deteriorated over time, as it serves as a boundary condition for the buffer material 43. Furthermore, the uniaxial compression test is conducted at room temperature to be performed under stable conditions. Alternatively, the test may be conducted at a high temperature equivalent to the temperature environment of the buffer body 41.

[0045] Once the residual gas amounts for the plurality of buffer materials 43 are determined and the compressive strengths for the plurality of buffer materials 43 are determined, a calibration curve of compressive strength versus residual gas amount for the buffer materials 43 can be determined, as shown in FIG. 7. The deterioration determination map is a calibration curve of compressive strength versus residual gas amount for the buffer materials 43. The calibration curve of the deterioration determination map is such that the compressive strength increases as the residual gas amount increases. Here, a service limit stress at which the buffer materials 43 can be used continuously is set.

[0046] 6, in step S12, a test piece of the buffer material 43 for which deterioration is to be determined is removed from the buffer body 41 provided in the cask 11. In this case, for example, an opening is formed by cutting a part of the support member 42 of the buffer body 41, and a part of the buffer material 43 for which deterioration is to be determined is cut out from the opening. However, it is also possible to store a test piece made of the same material as the buffer body 41 inside the support member 42 together with the buffer body 41, and remove this test piece as part of the buffer material 43 for which deterioration is to be determined.

[0047] In step S13, the type of gas generated and the amount of gas generated (detected value) are determined by thermogravimetric calorimetry for the test piece of buffer material 43 removed from buffer 41. The gas generated from the test piece of buffer material 43 is gas that remained in buffer material 43. In step S14, the amount of remaining gas for each type of gas generated by thermogravimetric calorimetry is determined, as well as the total amount of remaining gas for all types of gas.

[0048] Then, in step S15, the determined amount of residual gas is applied to the deterioration determination map to estimate the compressive strength of the test piece of buffer material 43 and determine the degree of deterioration. That is, as shown in FIG. 7, for example, the compressive strength of the test piece of buffer material 43 is determined using the calibration curve of the deterioration determination map for the amount of residual gas of all types of gas generated from the test piece of buffer material 43. The determined compressive strength of the test piece of buffer material 43 is compared with a preset determination value to determine deterioration. For example, when the compressive strength of the test piece of buffer material 43 estimated from the calibration curve falls below the determination value (limit stress for use), it is determined that the buffer material 43 has deteriorated.

[0049] The buffer 41 is formed by combining different types of first buffer material 43a, second buffer material 43b, and third buffer material 43c inside the support member 42. Therefore, it is preferable to create a deterioration determination map for each of the buffer materials 43a, 43b, and 43c.

[0050] The method for determining deterioration of the buffer material according to the first embodiment involves conducting a preliminary experiment to create a deterioration determination map of compressive strength versus residual gas amount in the buffer material 43, applying the detected residual gas amount in the buffer material 43 to the deterioration determination map to determine the compressive strength, and determining the degree of deterioration of the buffer material 43 based on the compressive strength. The degree of deterioration of the buffer material 43 can be determined with high accuracy simply by determining the residual gas amount of a small amount of test piece taken from the buffer material 43 using a thermogravimetric analyzer and a gas chromatograph. The degree of deterioration of the buffer material 43 is determined, for example, by drop analysis or the like to determine whether the buffer material 43 has enough shock absorption performance to maintain the integrity of the cask 11, even when taking into account the results (degree of deterioration) of the compression test obtained in the deterioration determination test.

[0051] [Second embodiment] <Cushioning material> Fig. 8 is a front view of a buffer body used in the method for determining deterioration of a buffer material of the second embodiment, Fig. 9 is a cross-sectional view showing the main part of the buffer material, and Fig. 10 is a schematic diagram for explaining the method for determining deterioration of a buffer material. Note that members having the same functions as those in the first embodiment described above are given the same reference numerals and detailed descriptions thereof will be omitted.

[0052] As shown in FIG. 8, a buffer body 41A of the second embodiment includes a support member 42, a buffer material 43, and an observation window 61.

[0053] The observation window 61 is provided in the support member 42, allowing observation of the buffer material 43 from the outside. The buffer material 43 is composed of a combination of a first buffer material 43a, a second buffer material 43b, and a third buffer material 43c. Therefore, the observation window 61 is provided with multiple observation windows 61a, 61b, and 61c corresponding to the buffer materials 43a, 43b, and 43c, which have different compressive strengths. That is, the observation window 61a is provided corresponding to the first buffer material 43a. The second observation window 61b is provided corresponding to the second buffer material 43b. The third observation window 61c is provided corresponding to the third buffer material 43c. Furthermore, multiple observation windows 61a, 61b, and 61c are provided for each of the buffer materials 43a, 43b, and 43c. Note that the observation windows 61a, 61b, and 61c are preferably provided at the position of the support member 42, which is the hottest part of the buffer 41.

[0054] Here, the structures of the observation windows 61a, 61b, and 61c will be described. However, since the structures of the observation windows 61a, 61b, and 61c are almost the same, only the structure of the observation window 61a will be described and a description of the structures of the observation windows 61b and 61c will be omitted.

[0055] As shown in FIG. 9 , a gap is formed between the inner surface of the support member 42 and the outer surface 43a1 of the first buffer material 43a. An opening 42a is formed in a predetermined position of the support member 42. The opening 42a is rectangular, but may be circular. The opening 42a can be opened and closed by a lid portion 62. The lid portion 62 is rectangular, but may be circular. That is, it is desirable that the lid portion 62 has the same shape as the opening 42a. The lid portion 62 is larger than the opening 42a and can close the opening 42a. The lid portion 62 is rotatably supported on the support member 42 by a hinge portion 63. In this case, it is desirable to provide a locking mechanism between the lid portion 62 and the support member 42 or a metal seal to prevent leakage of water vapor from inside the support member 42.

[0056] 10, when the lid portion 62 is opened at the observation window 61a, the outer surface 43a1 of the first cushioning material 43a is exposed to the outside. In the second embodiment, the degree of deterioration of the cushioning material 43 is determined based on the amount of discoloration of the first cushioning material 43a (the cushioning material 43). Here, the amount of discoloration of the first cushioning material 43a is detected using a colorimeter 64. The colorimeter 64 measures the color difference ΔE*ab of the outer surface 43a1 of the first cushioning material 43a.

[0057] After the lid 62 of the observation window 61a is opened and the color difference ΔE*ab of the first buffer material 43a is measured using the colorimeter 64, the lid 62 of the observation window 61a is closed to seal the window again. At this time, it is preferable to remove the air inside the support member 42 by evacuating it and then fill the interior with nitrogen. Furthermore, the observation window 61a may be configured as a transparent window that cannot be opened, rather than opening the lid 62.

[0058] <How to determine the deterioration of cushioning materials> FIG. 11 is a flowchart showing a method for determining deterioration of a cushioning material according to the second embodiment, and FIG. 12 is a deterioration determination map showing compressive strength relative to color difference.

[0059] As shown in Fig. 11, in step S21, a deterioration determination map is created having determination values ​​corresponding to the state quantities of the cushioning material 43. As shown in Fig. 12, the deterioration determination map of the second embodiment is the compressive strength of the cushioning material 43 relative to the amount of discoloration in the cushioning material 43. The deterioration determination map is created by conducting experiments or the like in advance.

[0060] In the second embodiment, similar to the first embodiment, first, a buffer material 43 of a predetermined size is heat-treated alone at a predetermined temperature for a predetermined time to simulate a state in which the buffer material 43 is disposed in a support member 42 and the buffer body 41 is fixed to the cask 11 for a predetermined period of time. In this case, buffer materials 43 are produced by heat-treating them at different heating temperatures and heating times. Then, the color difference of the surfaces of the multiple buffer materials 43 is measured using a colorimeter. Next, a deterioration determination test is performed on the multiple buffer materials 43. The deterioration determination test is similar to that in the first embodiment.

[0061] Once the color differences and compressive strengths of the multiple buffer materials 43 are determined, the correlation between the color differences and compressive strengths of the buffer materials 43 can be determined, as shown in FIG. 12. The deterioration determination map is the correlation between the color differences and compressive strengths of the buffer materials 43. The correlation in the deterioration determination map is such that the compressive strength decreases as the color differences increase. Here, a service limit stress at which the buffer materials 43 can be used continuously is set.

[0062] Returning to FIG. 11, in step S22, the cover 62 of the observation window 61a is opened to expose the outer surface 43a1 of the first buffer material 43a to the outside. In step S23, the colorimeter 64 is used to measure the amount of discoloration in the first buffer material 43a, i.e., the color difference ΔE*ab of the first buffer material 43a. In step S24, the color difference ΔE*ab of the first buffer material 43a is obtained. Then, in step S25, the determined color difference is applied to a deterioration determination map to estimate the compressive strength of the first buffer material 43a and determine the degree of deterioration. That is, as shown in FIG. 12, for example, the estimated compressive strength of the first buffer material 43a is obtained using the correlation of the deterioration determination map with respect to the color difference of the first buffer material 43a. The determined compressive strength of the first buffer material 43a is compared with the service limit stress (determination value) to determine deterioration. For example, when the estimated compressive strength of the first buffer material 43a is lower than the service limit stress, it is determined that the first buffer material 43a has deteriorated.

[0063] The buffer 41 is a combination of first, second, and third buffer materials 43a, 43b, and 43c, which are different types of buffer material, arranged inside the support member 42. Therefore, it is preferable to create a deterioration determination map for each of the buffer materials 43a, 43b, and 43c. Furthermore, since the temperature of the buffer material 43 differs depending on the position on the support member 42, it is preferable to create a deterioration determination map for each different position.

[0064] The method for determining deterioration of a cushioning material according to the second embodiment involves conducting a preliminary experiment to create a deterioration determination map of compressive strength relative to the color difference of the cushioning material 43, applying the detected color difference of the cushioning material 43 to the deterioration determination map to determine the compressive strength, and determining the degree of deterioration of the cushioning material 43 based on the compressive strength. The degree of deterioration of the cushioning material 43 can be determined with high accuracy simply by determining the amount of discoloration (color difference) of the cushioning material 43.

[0065] [Third embodiment] <Buffer> 13 is a cross-sectional view showing the main part of a buffer body used in the method for determining deterioration of a buffer material according to the third embodiment. Note that members having the same functions as those in the first embodiment described above are given the same reference numerals and detailed descriptions thereof will be omitted.

[0066] As shown in FIG. 13, a buffer body 41B of the third embodiment includes a support member 42, a buffer material 43, and an observation window 71.

[0067] The observation window 71 is provided in the support member 42 so that the buffer material 43 can be observed from the outside. As in the second embodiment, a plurality of observation windows 71 are provided corresponding to the buffer materials 43a, 43b, and 43c (see FIG. 8) having different compressive strengths.

[0068] A gap is formed between the inner surface of the support member 42 and the outer surface 43a1 of the first buffer material 43a. An observation window 71 is provided in a predetermined position on the support member 42. The observation window 71 is a transparent window 72, and preferably has heat resistance above a predetermined temperature. The transparent window 72 is made of, for example, glass, polycarbonate, or polyvinyl chloride. It is preferable that the observation window 71 be provided with a wiper for cleaning the inner surface.

[0069] In the third embodiment, the degree of deterioration of the buffer material 43 is determined based on the acid concentration of the component released from the first buffer material 43a (buffer material 43). Here, the acid concentration of the component released from the first buffer material 43a in the first buffer material 43a is detected using test paper (e.g., litmus paper) 73. The test paper 73 is fixed to the inside of a transparent window 72 by a support member 74. A gap is formed between the test paper 73 and the outer surface 43a1 of the first buffer material 43a. The test paper 73 changes color to measure the acid concentration of the component released from the first buffer material 43a in the first buffer material 43a, i.e., pH. Note that the acid concentration of the component released from the first buffer material 43a may be detected using, for example, an indicator instead of the test paper 73.

[0070] <Method for determining deterioration of cushioning material> FIG. 14 is a flowchart showing a method for determining deterioration of a cushioning material according to the third embodiment, FIG. 15 is a first deterioration determination map showing the degree of deterioration relative to pH, and FIG. 16 is a second deterioration determination map showing the compressive strength relative to the degree of deterioration.

[0071] As shown in Fig. 14, in step S31, a deterioration determination map having determination values ​​corresponding to the state quantities of the buffer material 43 is created. As shown in Fig. 15 and Fig. 16, the deterioration determination map of the third embodiment is the compressive strength of the buffer material 43 relative to the acid concentration of components released from the buffer material 43. The deterioration determination map is created in advance by conducting experiments or the like.

[0072] In the third embodiment, similar to the first embodiment, a buffer material 43 of a predetermined size is first heat-treated alone at a predetermined temperature for a predetermined time to simulate a state in which the buffer material 43 is disposed within the support member 42 and the buffer body 41 is fixed to the cask 11 for a predetermined period of time. In this case, buffer materials 43 are produced by heat-treating the buffer material 43 at different heating temperatures and heating times. The acid concentration (pH) of the components released from the buffer material 43 is then measured using test paper, and the thermal history (deterioration level) is determined. Next, once the acid concentration (pH) and the thermal history (deterioration level) for the multiple buffer materials 43 are determined, the relationship between the acid concentration (pH) of the components released from the buffer material 43 and the thermal history (deterioration level) can be determined, as shown in FIG. 15 . The first deterioration determination map shows the correlation between the acid concentration (pH) of the components released from the buffer material 43 and the thermal history (deterioration level). The correlation in the first deterioration determination map is such that the thermal history (degree of deterioration) increases with an increase in acid concentration (decrease in pH). Here, a usage limit is set for the buffer material 43, within which it can be used continuously.

[0073] Next, a deterioration determination test is performed on the plurality of buffer materials 43. The deterioration determination test is the same as that in the first embodiment. Then, once the thermal history (degree of deterioration) of the plurality of buffer materials 43 and the compressive strength of the plurality of buffer materials 43 are determined, it is possible to determine the correlation between the thermal history (degree of deterioration) and the compressive strength of the buffer materials 43, as shown in FIG. 16. The second deterioration determination map is the correlation between the thermal history (degree of deterioration) and the compressive strength of the buffer materials 43. The correlation in the second deterioration determination map is such that the compressive strength decreases as the thermal history (degree of deterioration) increases. Here, a service limit stress at which the buffer materials 43 can be continuously used is set.

[0074] Returning to FIG. 14, in step S32, the color of the test paper 73 is measured. In step S33, the pH is obtained using the test paper 73. In step S34, the thermal history (degree of deterioration) of the buffer material 43 is estimated using the first deterioration determination map. Then, in step S35, the compressive strength of the first buffer material 43a is estimated using the second deterioration determination map to determine the degree of deterioration. That is, as shown in FIG. 16, for example, the estimated compressive strength of the first buffer material 43a is obtained using the first and second deterioration determination maps for the pH of the first buffer material 43a. The obtained compressive strength of the first buffer material 43a is compared with the service limit stress (determination value) to determine deterioration. For example, when the estimated compressive strength of the first buffer material 43a is lower than the service limit stress, it is determined that the first buffer material 43a has deteriorated.

[0075] The buffer 41 is a combination of first, second, and third buffer materials 43a, 43b, and 43c, which are different types of buffer material, arranged inside the support member 42. Therefore, it is preferable to create a deterioration determination map for each of the buffer materials 43a, 43b, and 43c. Furthermore, since the temperature of the buffer material 43 differs depending on the position on the support member 42, it is preferable to create a deterioration determination map for each different position.

[0076] The method for determining deterioration of a buffer material according to the third embodiment involves conducting a preliminary experiment to create a deterioration determination map of compressive strength versus the acid concentration of components released from the buffer material 43, applying the detected acid concentration of components released from the buffer material 43 to the deterioration determination map to determine the compressive strength, and determining the degree of deterioration of the buffer material 43 based on the compressive strength. Simply by determining the acid concentration of components released from the buffer material 43, the degree of deterioration of the buffer material 43 can be determined with high accuracy.

[0077] In the third embodiment, a first deterioration determination map of thermal history (degree of deterioration) versus acid concentration (pH) of components released from buffer material 43 and a second deterioration determination map of compressive strength versus thermal history (degree of deterioration) of buffer material 43 were used, but a deterioration determination map of compressive strength versus acid concentration (pH) of components released from buffer material 43 may also be used.

[0078] [Effects of this embodiment] The method for determining deterioration of a cushioning material according to the first aspect includes the steps of creating a deterioration determination map having a determination value according to the state quantity of the cushioning material 43, obtaining a detection value of the state quantity of the cushioning material 43, and determining the degree of deterioration of the cushioning material 43 using the detection value and the deterioration determination map.

[0079] According to the method for determining deterioration of a cushioning material according to the first aspect, a deterioration determination map having determination values ​​corresponding to the state quantities of the cushioning material 43 is created in advance, and the degree of deterioration of the cushioning material 43 is determined at a desired time using the acquired detected values ​​of the state quantities of the cushioning material 43 and the deterioration determination map. As a result, it is possible to confirm the soundness of the cushioning material 43 during storage, and to maintain the soundness of the cushioning material 43. Furthermore, when determining the degree of deterioration of the cushioning material 43, it is only necessary to detect the state quantities of the cushioning material 43, which improves workability and also improves the accuracy of determining the deterioration of the cushioning material 43.

[0080] The method for determining deterioration of a buffer material according to the second aspect is the same as the method for determining deterioration of a buffer material according to the first aspect, and further, the degree of deterioration of the buffer material 43 is the degree of decrease in the compressive strength of the buffer material 43. This makes it possible to determine the deterioration of the buffer material 43 with high accuracy.

[0081] The method for determining deterioration of a cushioning material according to the third aspect is the method for determining deterioration of a cushioning material according to the first or second aspect, and further includes a deterioration determination map that represents the compressive strength of the cushioning material 43 as a determination value for a state quantity of the cushioning material 43, and the deterioration determination map is used to determine the compressive strength of the cushioning material 43 for a detected value, and the degree of deterioration is determined based on the determined compressive strength. In this way, it is sufficient to detect the compressive strength of the cushioning material 43 as the state quantity of the cushioning material 43, and the degree of deterioration of the cushioning material 43 can be easily determined using the deterioration determination map.

[0082] A method for determining deterioration of a cushioning material according to a fourth aspect is the method for determining deterioration of a cushioning material according to any one of the first to third aspects, further comprising: the deterioration determination map representing the compressive strength of the cushioning material 43 relative to the amount of gas remaining in the cushioning material 43; the detected value representing the amount of gas remaining in the cushioning material 43; and the detected value for the amount of gas remaining and the deterioration determination map being used to determine the degree of deterioration of the cushioning material 43. Thus, by detecting the amount of gas remaining in the cushioning material 43 as the state quantity of the cushioning material 43, the degree of deterioration of the cushioning material 43 can be determined with high accuracy.

[0083] The method for determining deterioration of a buffer material according to the fifth aspect is the method for determining deterioration of a buffer material according to the fourth aspect, and further, the amount of residual gas is the amount of all gases generated when the buffer material 43 is subjected to thermogravimetric analysis, or the amount of a specific gas generated. This improves the workability of detecting the amount of residual gas.

[0084] A method for determining deterioration of a cushioning material according to a sixth aspect is the method for determining deterioration of a cushioning material according to any one of the first to fifth aspects, further comprising: the deterioration determination map representing the compressive strength of the cushioning material 43 relative to the amount of discoloration in the cushioning material 43; the detected value representing the amount of discoloration in the cushioning material 43; and the detected value of the amount of discoloration and the deterioration determination map being used to determine the degree of deterioration of the cushioning material 43. Thus, by detecting the amount of discoloration in the cushioning material 43 as the state quantity of the cushioning material 43, the degree of deterioration of the cushioning material 43 can be determined with high accuracy.

[0085] The method for determining deterioration of a cushioning material according to the seventh aspect is the same as the method for determining deterioration of a cushioning material according to the sixth aspect, and further, the amount of discoloration is the color difference of the surface of the cushioning material 43. This can improve the workability of the work of detecting the color difference of the surface.

[0086] A method for determining deterioration of a buffer material according to an eighth aspect is the method for determining deterioration of a buffer material according to any one of the first to seventh aspects, further comprising: the deterioration determination map representing the compressive strength of the buffer material relative to the acid concentration in the buffer material 43; the detected value representing the acid concentration in the buffer material 43; and the deterioration determination map being used to determine the degree of deterioration of the buffer material 43. Thus, by detecting the acid concentration in the buffer material 43 as the state quantity of the buffer material 43, the degree of deterioration of the buffer material 43 can be determined with high accuracy.

[0087] The buffer according to the ninth aspect includes a support member 42 having a hollow shape and provided outside a cask (container for storing radioactive material) 11, a buffer material 43 that is disposed inside the support member 42 and absorbs shock by deforming, and observation windows 61, 71 that are provided in the support member 42 and allow observation of the buffer material 43 from the outside. This makes it possible to detect the state quantity of the buffer material 43 using the observation windows 61, 71, thereby improving workability and improving the accuracy of determining deterioration of the buffer material 43. [Explanation of symbols]

[0088] 11 Cask (container for storing radioactive materials) 12 Torso 13 Lid 31 Primary lid 32 Secondary lid 41,46 Buffer 42 Support member 43 Cushioning material 43a 1st buffer material 43b Second buffer material 43c 3rd buffer material 51 Disc 52 Cylindrical part 61 Observation window 61a First observation window 61b Second observation window 61c Third observation window 62 Lid 63 Hinge part 64 Colorimeter 71 Observation window 72 Transparent Window 73 Test Paper 74 Support member

Claims

1. A method for determining deterioration of a buffer material provided in a buffer of a radioactive material storage container, comprising: creating a deterioration determination map having a determination value corresponding to the state quantity of the cushioning material; acquiring a detected value of the state quantity of the buffer material; determining a degree of deterioration of the cushioning material using the detected value and the deterioration determination map; A method for determining deterioration of a cushioning material.

2. The degree of deterioration of the buffer material is the degree of decrease in compressive strength of the buffer material. The method for determining deterioration of a cushioning material according to claim 1 .

3. the deterioration determination map represents the compressive strength of the buffer material as the determination value for the state quantity of the buffer material, and the compressive strength of the buffer material for the detected value is obtained using the deterioration determination map, and a deterioration degree is determined based on the obtained compressive strength. The method for determining deterioration of a cushioning material according to claim 2.

4. the deterioration determination map is a compressive strength of the buffer material relative to the amount of gas remaining in the buffer material, the detected value is the amount of gas remaining in the buffer material, and the degree of deterioration of the buffer material is determined using the detected value of the amount of gas remaining and the deterioration determination map. The method for determining deterioration of a cushioning material according to claim 3.

5. The residual gas amount is the amount of all gases generated when the buffer material is subjected to thermogravimetric analysis, or the amount of a specific gas generated. The method for determining deterioration of a cushioning material according to claim 4.

6. the deterioration determination map is a compressive strength of the cushioning material relative to an amount of discoloration of the cushioning material, the detected value is an amount of discoloration of the cushioning material, and the degree of deterioration of the cushioning material is determined using the detected value of the amount of discoloration and the deterioration determination map. The method for determining deterioration of a cushioning material according to claim 3.

7. The discoloration amount is a color difference of the surface of the buffer material. The method for determining deterioration of a cushioning material according to claim 6.

8. the deterioration determination map is a compressive strength of the buffer material relative to an acid concentration in the buffer material, the detected value is an acid concentration in the buffer material, and the deterioration degree of the buffer material is determined using the detected value of the acid concentration and the deterioration determination map. The method for determining deterioration of a cushioning material according to claim 3.

9. a support member having a hollow shape and provided on the outside of the radioactive material storage container; a buffer material that is disposed inside the support member and deforms to absorb impact; an observation window provided in the support member through which the buffer material can be observed from the outside; A buffer body comprising:

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