Disposal structure design method and disposal structure design system

Abstract

To provide a disposal structure design method and a disposal structure design system for optimizing the performance of a natural barrier and the performance of an artificial barrier, suppressing the increase of costs required for a disposal structure, and achieving the shortening of a construction period and the reduction of an environmental load.SOLUTION: A disposal structure design method according to an embodiment includes a step of storing a relationship between a capacity of a natural barrier which is a radioactive substance movement suppression function of an underground bedrock and a capacity of an artificial barrier which is a radioactive substance movement suppression function of an artificially produced barrier structure, a step of setting a capacity of the natural barrier which satisfies a radiation dose regulation and a regulation satisfaction range A1 which is a range of the capacity of the artificial barrier in the relationship, a step of setting a capacity B1 of the artificial barrier, and a step of setting a capacity of the natural barrier which corresponds to the set capacity B1 of the artificial barrier and is within the regulation satisfaction range A1 in the relationship.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a disposal structure design method and disposal structure design system for disposing of radioactive waste in underground bedrock. [Background technology]

[0002] Patent Document 1 describes a system for evaluating leakage of radioactive nuclides from disposal facilities. Radioactive waste disposal sites are planned to be designed and operated as geological disposal sites both in Japan and overseas. Geological disposal sites consist of an engineered barrier made of artificial materials such as concrete and buffer materials to prevent leakage of radioactive materials, and a natural barrier consisting of bedrock surrounding the engineered barrier.

[0003] The natural barrier is a hard rock such as granite or hard bedrock that has low water permeability. The engineered barrier is installed so that it is buried in the natural barrier. The engineered barrier is made of concrete, corrosion-resistant materials, etc. The engineered barrier comprises an overpack, which is a steel structure in which the waste is embedded, and bentonite that covers the overpack. The waste is immobilized with glass.

[0004] The leakage evaluation system has a calculation unit that performs various calculations. The calculation unit has a radionuclide leakage rate calculation unit, a nuclide concentration calculation unit, and an exposure dose calculation unit. The radionuclide leakage rate calculation unit calculates the radionuclide leakage rate based on the elapsed time of the radioactive waste disposal site to be evaluated, constants related to the decay of nuclides, etc., and the time the nuclide source exists.

[0005] The nuclide concentration calculation unit calculates the retardation coefficient, porosity of the natural barrier, true density of the natural barrier, effective diffusion coefficient, Darcy flow velocity, leakage rate of the nuclide from the engineered barrier, and nuclide concentration in the liquid phase of the nuclide to be evaluated. The exposure dose calculation unit calculates the radionuclide leakage rate based on the nuclide concentration in the liquid phase, and calculates the exposure dose based on the calculated radionuclide leakage rate and the radionuclide dose coefficient. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-277584 Summary of the Invention [Problem to be solved by the invention]

[0007] Geological disposal of radioactive waste involves confining it deep underground in rock and isolating it from the human environment. Geological disposal employs a multi-barrier system that combines natural and engineered barriers to adequately contain highly radioactive nuclides.

[0008] In the design of a radioactive waste disposal structure in a multi-barrier system, it is sometimes required to maximize the performance of the natural and engineered barriers in order to maximize safety. However, from the perspective of ensuring safety, it is sometimes not necessary to maximize the performance of the natural and engineered barriers.

[0009] For example, if the underground rock mass where radioactive waste will be placed is very deep, the permeability of the underground rock mass is very low, and the performance of the natural barrier is very high, it may not be necessary to maximize the performance of the engineered barriers. In such cases, there is a concern that excessively increasing the performance of the engineered barriers will increase the cost of the disposal structure. Therefore, it is necessary to optimize the performance of the natural barriers and the engineered barriers to prevent increases in the cost of the disposal structure, shorten the construction period, and reduce the environmental impact.

[0010] The present disclosure aims to provide a disposal structure design method and system that can optimize the performance of the natural barrier and the engineered barrier, suppress increases in the cost of the disposal structure, shorten construction time, and reduce environmental impact. [Means for solving the problem]

[0011] (1) The disposal structure design method according to the present disclosure is a disposal structure design method for disposing of radioactive waste in underground bedrock. The disposal structure design method includes the steps of: memorizing the relationship between the performance of the natural barrier, which is the function of the underground bedrock to suppress the migration of radioactive materials, and the performance of the engineered barrier, which is the function of the artificially constructed barrier structure to suppress the migration of radioactive materials; setting, within this relationship, the performance of the natural barrier that satisfies radiation dose regulations and a regulatory satisfaction range, which is the range of the performance of the engineered barrier; setting the performance of the engineered barrier; and setting, within the relationship, the performance of the natural barrier that corresponds to the set performance of the engineered barrier and is within the regulatory satisfaction range.

[0012] In this disposal structure design method, the relationship between the performance of the natural barriers and the performance of the engineered barriers is stored. By storing the relationship between the performance of the natural barriers and the performance of the engineered barriers, it is possible to determine the appropriate level of performance for the engineered barriers when the performance of the natural barriers is at a certain level. This prevents excessive increases in the performance of the engineered barriers, thereby preventing increases in the cost of the disposal structure, shortening the construction period, and reducing the environmental impact. Among the above relationships, the performance of the natural barriers that satisfies radiation dose regulations and the regulatory satisfaction range, which is the range of the performance of the engineered barriers, are set, and the performance of the engineered barriers is then set. Then, the performance of the natural barriers that corresponds to the set performance of the engineered barriers and falls within the regulatory satisfaction range are set. Therefore, the performance of the natural barriers that corresponds to the set performance of the engineered barriers and falls within the regulatory satisfaction range are set. Therefore, the appropriate performance of the natural barriers that corresponds to the set performance of the engineered barriers is set, allowing the performance of the engineered barriers and the performance of the natural barriers to be optimized.

[0013] (2) In the above (1), the disposal structure design method may include a step of setting excessive ranges within the regulatory satisfaction range, which are ranges of excessive natural barrier performance and excessive engineered barrier performance, and excluding the excessive ranges from the regulatory satisfaction range. In the step of setting the natural barrier performance, upper and lower limits of the natural barrier performance may be set that correspond to the set engineered barrier performance and are within the regulatory satisfaction range in the above relationship. In this case, since upper and lower limits of the natural barrier performance are set, the appropriate natural barrier performance can be understood as a range from the upper limit to the lower limit.

[0014] (3) In the above (1) or (2), the disposal structure design method may include a step of lowering the performance of the engineered barriers within the regulatory compliance range after the step of setting the performance of the natural barriers. In this case, the performance of the engineered barriers can be lowered to the minimum necessary within the regulatory compliance range, thereby reducing the cost of the disposal structure.

[0015] (4) In the above (3), the step of reducing the performance of the engineered barriers may involve reducing the amount of excavation required to place radioactive waste in the underground rock mass. In this case, reducing the performance of the engineered barriers reduces the amount of excavation required to place radioactive waste in the underground rock mass, thereby reducing the environmental load.

[0016] (5) In any of the above (1) to (4), the step of setting the performance of the natural barrier may set an allowable value for the groundwater migration time, which is the time it takes for groundwater in the underground bedrock to migrate. In this case, since the allowable value for the groundwater migration time can be set as the performance of the natural barrier, it is easy to select underground ground that will serve as a natural barrier that satisfies the performance.

[0017] (6) In the step (5) above, in the step of determining the performance of the natural barrier, the groundwater migration time may be determined based on at least one of the depth of the radioactive waste to be placed in the underground bedrock, the permeability coefficient of the underground bedrock, and the hydraulic gradient of the underground bedrock. In this case, the groundwater migration time can be determined with higher accuracy.

[0018] (7) In any of the above (1) to (6), the step of setting the performance of the natural barrier may include a step of setting a lower limit of the performance of the natural barrier. The step of setting the lower limit of the performance of the natural barrier may include calculating the minimum allowable groundwater migration time based on the Darcy flow rate. In this case, the allowable migration time of radioactive materials from the location of the radioactive waste in the underground bedrock to the living environment can be calculated, making it possible to select a natural barrier that can more reliably ensure safety in the living environment.

[0019] (8) In any of the above (1) to (7), the step of setting the performance of the natural barrier may include a step of setting an upper limit of the performance of the natural barrier. The step of setting the upper limit of the performance of the natural barrier may include calculating the time required for the radioactivity emitted by the radioactive waste to fall below an allowable value. In this case, the upper limit of the performance of the natural barrier is calculated as the time required for the emitted radioactivity to fall below an allowable value, making it possible to select a natural barrier that can more reliably ensure safety in the living environment.

[0020] (9) A disposal structure design system according to the present disclosure is a disposal structure design system for disposing of radioactive waste in underground bedrock. The disposal structure design system includes: a memory unit that stores the relationship between the performance of the natural barrier, which is the radioactive material migration suppression function of the underground bedrock, and the performance of the engineered barrier, which is the radioactive material migration suppression function of an artificially constructed barrier structure; a regulation satisfaction range setting unit that sets, within this relationship, the natural barrier performance that satisfies radiation dose regulations and the regulation satisfaction range, which is the range of the engineered barrier performance; an engineered barrier setting unit that sets the engineered barrier performance; and a natural barrier setting unit that sets the natural barrier performance that corresponds to the set engineered barrier performance and is within the regulation satisfaction range, within the above relationship.

[0021] In this disposal structure design system, the memory unit stores the relationship between the performance of the natural barriers and the performance of the engineered barriers, making it possible to determine the appropriate level of performance for the engineered barriers when the natural barrier performance is at a certain level. Therefore, as with the above-described disposal structure design method, excessively enhancing the performance of the engineered barriers can be avoided, thereby suppressing increases in disposal structure costs, shortening construction time, and reducing environmental impact. The regulatory satisfaction range setting unit sets the natural barrier performance that satisfies radiation dose regulations and the regulatory satisfaction range, which is the range of the engineered barrier performance, from the above relationship, and the engineered barrier setting unit sets the engineered barrier performance. The natural barrier setting unit then sets the natural barrier performance that corresponds to the set engineered barrier performance and is within the regulatory satisfaction range. Therefore, the natural barrier performance is set so that it corresponds to the set engineered barrier performance and is within the regulatory satisfaction range, and the natural barrier performance is set to an appropriate level within the regulatory satisfaction range. Therefore, as with the above-described disposal structure design method, the performance of the engineered barriers and the performance of the natural barriers can be optimized. [Effects of the Invention]

[0022] According to the present disclosure, the performance of the natural barrier and the engineered barrier can be optimized, thereby suppressing increases in costs associated with the disposal structure, shortening construction time, and reducing the environmental burden. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a disposal structure according to an embodiment. [Figure 2] FIG. 2 is an enlarged perspective cross-sectional view of the disposal structure of FIG. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an engineered barrier according to an embodiment. [Figure 4] Figure 4 is a cross-sectional view showing a schematic diagram of the engineered barriers, natural barriers, and living environment. [Figure 5] FIG. 5 is a block diagram showing the functions of the disposal structure design system according to the embodiment. [Figure 6]Fig. 6(a) is a graph for explaining the setting of the regulation satisfaction range, and Fig. 6(b) is a graph for explaining the elimination of the excess range. [Figure 7] Figure 7(a) is a graph illustrating the setting of upper and lower limits of the performance of the natural barrier, and Figure 7(b) is a graph illustrating the degradation of the performance of the engineered barrier. [Figure 8] 8(a) and 8(b) are graphs illustrating an example of how to set a lower limit on the performance of the natural barrier. [Figure 9] FIG. 9 is a cross-sectional view illustrating an example of a method for reducing the performance of the engineered barrier. [Figure 10] 10(a) and 10(b) are flowcharts showing example steps of a disposal structure design method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the disposal structure design method and disposal structure design system according to the present disclosure will be described with reference to the drawings. In the description of the drawings, identical or corresponding elements are designated by the same reference numerals, and duplicate explanations will be omitted as appropriate. The drawings may be partially simplified or exaggerated to facilitate understanding, and the dimensional proportions and the like are not limited to those shown in the drawings.

[0025] FIG. 1 is a diagram showing an example of a disposal structure 1 for radioactive waste. The disposal structure 1 includes, for example, facilities for performing geological disposal of radioactive waste. The disposal structure 1 includes, for example, a building H provided on the ground G, and a waste disposal section 2 and a tunnel 3 buried in underground bedrock B. The building H is a building provided at the entrance to the disposal structure 1. The building H is connected to the tunnel 3 that leads to the waste disposal section 2.

[0026] FIG. 2 is a cross-sectional perspective view showing the waste placement unit 2. As shown in FIGS. 1 and 2, the waste placement unit 2 includes, for example, an underground tunnel 2b having a radioactive waste disposal site. The underground tunnel 2b is provided at a depth of 300 m or more (for example, a depth of 300 m or more and 1000 m or less) underground in underground bedrock B. A plurality of holes 2c dug downward are formed in the bottom surface of the tunnel of the underground tunnel 2b. The plurality of holes 2c are aligned along the longitudinal direction of the underground tunnel 2b.

[0027] Figure 3 is an enlarged cross-sectional view of hole 2c. As shown in Figures 2 and 3, disposal structure 1 has metal container 4 disposed inside hole 2c and buffer material 5 disposed inside hole 2c so as to surround metal container 4. Metal container 4 stores radioactive waste inside.

[0028] The radioactive waste stored inside the metal container 4 may be low-level radioactive waste or high-level radioactive waste. As a specific example, the metal container 4 has a vitrified waste 4b in which high-level radioactive waste (HLW) is solidified together with glass, and an overpack 4c that encloses the vitrified waste 4b.

[0029] In the vitrified waste 4b, the radioactive waste is trapped in the molecular network structure of the glass. In the vitrified waste 4b, since the glass is difficult to dissolve in water, even if the radioactive waste trapped in the glass comes into contact with groundwater, the radioactive waste only dissolves very slowly. For example, the diameter of the vitrified waste 4b is 40 cm, and the length (height) of the vitrified waste 4b is 130 cm. The vitrified waste 4b is housed, for example, in a canister (stainless steel container).

[0030] The overpack 4c is a metal container. The material of the overpack 4c is carbon steel. For example, the thickness of the overpack 4c is 20 cm. The overpack 4c is provided to prevent groundwater from coming into contact with the vitrified waste 4b. The metal container 4 has a gripping portion 4d that can be gripped by heavy machinery, for example. The gripping portion 4d protrudes upward from the overpack 4c.

[0031] The buffer material 5 is interposed between the underground bedrock B and the metal container 4. The buffer material 5 functions as an engineered barrier that blocks the influence of the radioactive waste inside the metal container 4 on the underground bedrock B. The buffer material 5 is made of a water-permeable material. The buffer material 5 prevents the metal container 4 from being exposed to groundwater.

[0032] The buffer material 5 has the function of buffering external forces acting on the metal container 4 from the surrounding underground bedrock B during an earthquake or the like. The buffer material 5 is, for example, a bentonite-based engineered barrier material or a cement-based engineered barrier material. As an example, the buffer material 5 is a bentonite-based engineered barrier material. In this case, the buffer material 5 is made of an earthen material in which bentonite and sand are mixed. For example, the length (height) of the buffer material 5 is 3.1 m, and the width of the buffer material 5 is 2.2 m. For example, the 2.2 m width of the buffer material 5 is hollow. The buffer material 5 is, for example, made up of a plurality of blocks. For example, the length (height) of each block is 35 cm, and the thickness of each block is 70 cm.

[0033] When radioactive waste is disposed of in a landfill, first, a buffer material 5 is installed inside the hole 2c. At this time, an installation hole is formed in the buffer material 5, into which the metal container 4 is to be installed. Then, the metal container 4 is inserted into the installation hole using heavy machinery, and the metal container 4 is installed in the buffer material 5, and the buffer material 5 is filled up to the top of the hole 2c so as to cover the top of the metal container 4. In this way, the metal container 4 is buried in the buffer material 5. After one metal container 4 has been buried in each hole 2c, the tunnels of the underground tunnel 2b are filled with ground material M.

[0034] As shown in Figure 4, radioactive waste is confined in underground bedrock B and isolated from the living environment E. The disposal structure design method and disposal structure design system according to this embodiment use a multi-barrier system that combines natural and engineered barriers. In this embodiment, the natural barrier is underground bedrock B.

[0035] Deep underground in the natural barrier, underground bedrock B, there is very little oxygen, which makes it difficult for corrosion of the metal container 4 to progress and for radioactive waste to dissolve in groundwater W. Furthermore, deep underground in the underground bedrock B, the movement of groundwater W is extremely slow, and radioactive waste tends to be easily adsorbed by the underground bedrock B, so the movement of radioactive waste in the underground bedrock B is extremely slow. The engineered barriers are installed inside the natural barriers. The engineered barriers consist of a metal container 4 and a buffer material 5 that contain the radioactive waste. By using a multiple barrier system, the radioactive waste can be isolated and contained from the human living environment E for a long period of time.

[0036] However, it cannot be denied that after thousands or tens of thousands of years, radioactive waste will pass through the engineered barriers and migrate together with groundwater W into the living environment E. The disposal structure design method and disposal structure design system according to this embodiment consider the progress of this migration and calculate the extent of the impact on the human living environment E through analysis.

[0037] Examples of safety assessments for radioactive waste to date include a model in which groundwater W transports radioactive waste to the surface E1 (or river E2), and a model in which groundwater W comes into contact with vitrified waste 4b several thousand years after the closure of disposal structure 1, causing radioactive waste to leach out. Furthermore, a model has been created in which the occurrence of a fault that crosses disposal structure 1 causes the function of the engineered barriers and the natural barriers to be lost, causing radioactive waste to be transported to the surface E1 by groundwater W.

[0038] The performance of the natural barrier and the engineered barrier are evaluated using the above model. When designing the disposal structure 1, it may be necessary to maximize the performance of the natural barrier and the engineered barrier in order to maximize safety. However, from the perspective of ensuring safety, there are cases where it is not necessary to maximize the performance of the natural barrier and the engineered barrier. For example, if the performance of the natural barrier is significantly high, it may not be necessary to increase the performance of the engineered barrier as much. In such cases, excessively increasing the performance of the engineered barrier may result in unnecessary increases in costs for the production of the metal container 4 and buffer material 5.

[0039] The disposal structure design system and disposal structure design method according to this embodiment optimize the performance of the natural barrier and the engineered barrier, thereby making it possible to suppress the increase in costs mentioned above, shorten the construction period, and reduce the environmental impact. The performance of the natural barrier is the function of the underground bedrock B to suppress the migration of radioactive materials, and the performance of the engineered barrier is the function of the artificially constructed barrier structure to suppress the migration of radioactive materials. The artificially constructed barrier structure is, for example, the metal container 4 and buffer material 5 mentioned above.

[0040] The performance of the natural barrier is, for example, the groundwater migration time, which is the time it takes for groundwater in underground rock mass B to migrate. In this case, the longer the groundwater migration time, the higher the performance of the natural barrier, and the shorter the groundwater migration time, the lower the performance of the natural barrier. The performance of the natural barrier may also be the depth of the underground rock mass B in which the radioactive waste is placed. In this case, the greater the depth, the higher the performance of the natural barrier, and the shallower the depth, the lower the performance of the natural barrier. The performance of the natural barrier may also be the permeability coefficient of the underground rock mass B. In this case, the greater the permeability coefficient of the underground rock mass B, the lower the performance of the natural barrier, and the smaller the permeability coefficient of the underground rock mass B, the higher the performance of the natural barrier.

[0041] For example, the permeability coefficient of underground rock mass B is 10 -12 (m / sec) or more and 10 -6 (m / sec) or less. In this case, the hydraulic conductivity is 10 -12The closer the underground rock mass B is to the permeability coefficient, the higher the natural barrier performance. -6 The closer the underground rock mass B is to (m / sec), the lower the performance of the natural barrier becomes.

[0042] The performance of the natural barrier may be the hydraulic gradient of groundwater W in underground rock mass B. In this case, the greater the hydraulic gradient, the lower the performance of the natural barrier, and the smaller the hydraulic gradient, the higher the performance of the natural barrier. The hydraulic gradient of groundwater W in underground rock mass B is, for example, 0.0001 or more and 0.2 or less. In this case, the closer the hydraulic gradient of underground rock mass B is to 0.0001, the higher the performance of the natural barrier, and the closer the hydraulic gradient is to 0.2, the lower the performance of the natural barrier.

[0043] The performance of the engineered barrier is, for example, the thickness of the overpack 4c. The thicker the overpack 4c, the higher the performance of the engineered barrier, and the thinner the overpack 4c, the lower the performance of the engineered barrier. If the performance of the engineered barrier can be reduced, the cost of the engineered barrier can be reduced.

[0044] One way to improve the performance of the engineered barrier is to increase the thickness of the overpack 4c from 20 cm to a value greater than 20 cm (for example, 40 cm). The performance of the engineered barrier may also depend on the material of the overpack 4c. For example, the performance of the engineered barrier may be improved by changing the material of the overpack 4c from iron to copper.

[0045] The performance of the engineered barrier may be determined by the material, composition, or amount of the buffer material 5. For example, the performance of the engineered barrier may be determined by at least one of the material, thickness, and hydraulic conductivity of the buffer material 5. The hydraulic conductivity of the buffer material 5 may be, for example, 10 -13 (m / sec), but the permeability coefficient of the buffer material 5 is 10 -14 (m / sec) or more and 10 -6The performance of the engineered barrier may be adjusted by adjusting the thickness of the buffer material 5 within a range of 1 / 2 m / s or less. The performance of the engineered barrier may be reduced by making the thickness of the buffer material 5 less than 70 cm (for example, 20 cm or more and less than 70 cm), or the performance of the engineered barrier may be increased by making the thickness of the buffer material 5 greater than 70 cm (for example, greater than 70 cm and less than 100 cm).

[0046] As described above, the disposal structure design system and disposal structure design method according to this embodiment achieve a good balance between the performance of the natural barriers and the performance of the engineered barriers by adjusting them at the time of construction of the disposal structure 1 (for example, before construction of the disposal structure 1). The disposal structure design system according to this embodiment will be described below.

[0047] 5 is a block diagram showing the functional configuration of a disposal structure design system 10 as an example of this embodiment. The disposal structure design system 10 is a system for designing a disposal structure 1 that disposes of radioactive waste in underground bedrock B. The disposal structure design system 10 may be a distributed processing system made up of multiple computers, a client-server system, or a cloud system.

[0048] The disposal structure design system 10 may include a disposal structure design program. The disposal structure design system 10 according to this embodiment includes, for example, a main module, a data acquisition module, a determination module, and an output module. The functional elements of the disposal structure design system 10 function when the data acquisition module, the determination module, and the output module are executed. For example, the disposal structure design system 10 may be provided in a state where it is permanently recorded on a tangible storage medium such as a CD-ROM, a DVD-ROM, or a semiconductor memory. The disposal structure design program may also be provided via a communication network as a data signal superimposed on a carrier wave.

[0049] For example, disposal structure design system 10 includes information terminal 11 and server 20. Server 20 is capable of communicating with information terminal 11. As an example, server 20 includes a processor (e.g., CPU) that executes an operating system and software (applications), a main memory unit configured with ROM and RAM, an auxiliary memory unit configured with a hard disk or flash memory, etc., a communication control unit configured with a network card or wireless communication module, an input device such as a keyboard or mouse, and an output device such as a monitor. However, the configuration of server 20 is not limited to the above and can be changed as appropriate.

[0050] Each functional element of server 20 is realized by loading software into a processor or memory unit (e.g., the main memory unit or auxiliary memory unit) and executing the software. The processor operates the communication control unit, input device, or output device in accordance with the software, and reads and writes data from and to the memory unit. Data or databases used in the processing of server 20 are stored in the memory unit.

[0051] The information terminal 11 is, for example, a device capable of executing the functions of the server 20. The information terminal 11 is, for example, a mobile terminal. The "mobile terminal" refers to a portable terminal such as a mobile phone including a smartphone, a tablet, or a laptop computer. The information terminal 11 may be a terminal other than a mobile terminal, for example, a personal computer.

[0052] For example, the server 20 includes, as functional components, a regulation satisfaction range setting unit 21, an excess range setting unit 22, an artificial barrier setting unit 23, a natural barrier setting unit 24, a first threshold setting unit 25, a second threshold setting unit 26, a display control unit 27, and a memory unit 28. The functions of each of the regulation satisfaction range setting unit 21, excess range setting unit 22, artificial barrier setting unit 23, natural barrier setting unit 24, first threshold setting unit 25, second threshold setting unit 26, display control unit 27, and memory unit 28 will be described below.

[0053] The display control unit 27 is, for example, one type of output module described above. The display control unit 27 displays, for example, an operation screen for operating the functions of the disposal structure design system 10 (or disposal structure design program) on the display 11b of the information terminal 11. For example, when a user of the disposal structure design system 10 operates the operation screen displayed on the display 11b, the performance of the natural barrier and the range of performance of the engineered barrier are displayed on the display 11b.

[0054] The memory unit 28 is a functional element that stores data in, for example, the main memory unit or auxiliary memory unit described above. The memory unit 28 stores data transmitted and received from the information terminal 11 by the disposal structure design system 10 (or the disposal structure design program). The memory unit 28 stores the relationship between the performance of the natural barriers and the performance of the engineered barriers.

[0055] As shown in Figure 6(a), for example, the memory unit 28 stores Table D, which shows the range of performance of the natural barrier and the range of performance of the engineered barrier, as the above relationship. Table D shows the range of performance of the natural barrier and the range of performance of the engineered barrier. As described above, the performance of the natural barrier is at least one of the groundwater migration time, the depth of the radioactive waste placement location in the underground bedrock B, the permeability coefficient of the underground bedrock B, and the hydraulic gradient of the groundwater W in the underground bedrock B. The performance of the engineered barrier is at least one of the thickness of the overpack 4c, the material of the overpack 4c, and the material, composition, amount used, thickness, and permeability coefficient of the buffer material 5.

[0056] In this case, the performance of the natural barrier is at least one of the groundwater migration time, the depth of the radioactive waste placement location in underground bedrock B, the permeability coefficient of underground bedrock B, and the hydraulic gradient of groundwater W in underground bedrock B. The performance of the engineered barrier is at least one of the thickness of overpack 4c, the material of overpack 4c, the material, composition, amount used, thickness, and permeability coefficient of buffer material 5.

[0057] The regulation satisfaction range setting unit 21 sets a regulation satisfaction range A1, which is the range of natural barrier performance and engineered barrier performance that satisfies radiation dose regulations within the relationship between the performance of the natural barrier and the performance of the engineered barrier. For example, the regulation satisfaction range A1 indicates the range of natural barrier performance and engineered barrier performance within which the radiation dose from radioactive waste to the living environment E is estimated to be below a certain value. The regulation satisfaction range A1 indicates the range of natural barrier performance and engineered barrier performance that satisfies the dose assessment guidelines.

[0058] As shown in Figure 6(b), the excess range setting unit 22 sets an excess range A2, which is a range of excessive natural barrier performance and excessive engineered barrier performance, within the regulatory satisfaction range A1. The excess range setting unit 22 excludes the excess range A2 from the regulatory satisfaction range A1. The excess range A2 indicates a range of natural barrier performance and engineered barrier performance that satisfies the dose assessment guidelines but is excessive and unreasonable. The excess range A2 may also indicate a range of natural barrier performance and engineered barrier performance that is excessive and meaningless.

[0059] The engineered barrier configuration unit 23 sets the engineered barrier performance B1 as shown in Figure 7(a). As an example, the engineered barrier performance B1 indicates the current engineered barrier performance. As an example, the current engineered barrier performance is the metal vessel 4 and buffer material 5 shown in Figure 3. For example, the metal vessel 4 and buffer material 5 are as shown in Figure 3, which have not changed for over 20 years.

[0060] 7(a), the natural barrier setting unit 24 sets the performance of the natural barrier that corresponds to the set engineered barrier performance B1 and is within the regulation satisfaction range A1 in the relationship between the performance of the natural barrier and the performance of the engineered barrier (Table D in this embodiment). The natural barrier setting unit 24 may also set an allowable value for the groundwater migration time, which is the time it takes for groundwater W in the underground bedrock B to migrate.

[0061] The natural barrier setting unit 24 may set the groundwater migration time from at least one of the depth of the radioactive waste to be placed in the underground bedrock B, the permeability coefficient of the underground bedrock B, and the hydraulic gradient of the underground bedrock B. For example, the natural barrier setting unit 24 sets the range of the performance of the natural barrier between an upper limit C2 and a lower limit C1 of the performance of the natural barrier.

[0062] For example, the first threshold setting unit 25 sets a lower limit C1 of the performance of the natural barrier. The first threshold setting unit 25 calculates the minimum allowable time for groundwater migration based on the Darcy flow velocity as the lower limit C1 of the performance of the natural barrier. For example, the Darcy flow velocity is the product of the permeability coefficient and the hydraulic gradient. For example, the first threshold setting unit 25 calculates the Darcy flow velocity (groundwater migration time) from the location where the radioactive waste is located in the underground bedrock B to the evaluation location (e.g., living environment E). As an example, this calculation is performed for multiple cases (e.g., 3,000 cases).

[0063] Figures 8(a) and 8(b) are graphs showing the simulation results obtained by inputting parameters for underground rock mass B. The simulation results shown in Figures 8(a) and 8(b) were obtained by performing calculations using a portion of underground rock mass B under the most severe conditions (e.g., closest to living environment E) as a model. In this simulation, the minimum and maximum values ​​of the migration distance of groundwater W per unit time, the density of fractures in underground rock mass B, and the number of fractures per unit volume were input, and the Darcy flow velocity and groundwater migration time were calculated from the input values.

[0064] Figure 8(a) is a graph showing the relationship between the logarithm (common logarithm) of groundwater migration time and satisfaction rate for highly oxidizing underground rock mass B. Figure 8(b) is a graph showing the relationship between the logarithm of groundwater migration time and satisfaction rate for normal (not highly oxidizing) underground rock mass B. The satisfaction rate for groundwater migration time indicates the proportion of cases in which the target radiation exposure dose is below a certain value among the multiple cases mentioned above. In the graphs of Figures 8(a) and 8(b), the solid line indicates the satisfaction rate for a target radiation exposure dose of 100 (μsV / year) or less, and the dashed line indicates the satisfaction rate for a target radiation exposure dose of 10 (μsV / year) or less.

[0065] For example, the first threshold setting unit 25 may set the groundwater migration time at which the satisfaction rate is equal to or greater than a certain value as the allowable value (lower limit C1) for the groundwater migration time. In the examples of Figures 8(a) and 8(b), when the logarithm of the groundwater migration time is 4.5 or greater (groundwater migration time is 30,000 years), the satisfaction rate at which the target exposure dose is 10 μsV / year is 0.8 or greater, so the first threshold setting unit 25 sets the groundwater migration time of 30,000 years as the lower limit C1 for the performance of the natural barrier.

[0066] For example, the second threshold setting unit 26 calculates the time until the radioactivity emitted by the radioactive waste falls below an allowable value as the upper limit C2 of the natural barrier's performance. The upper limit C2 of the natural barrier's performance is, for example, the upper limit of the groundwater migration time. The second threshold setting unit 26 calculates the time until the amount of uranium radioactivity equivalent to 1 ton of fuel falls below a certain value as the upper limit C2. This certain value is, for example, the total amount of radioactivity in the uranium ore from which the fuel is made. As an example, the second threshold setting unit 26 calculates the time until the amount of uranium radioactivity equivalent to 1 ton of fuel falls below a certain value as the upper limit C2. 3 The time it takes for the carbon dioxide to fall below 100,000 GBq is calculated as the upper limit C2. In this case, the upper limit C2 is 100,000 years.

[0067] For example, the first threshold setting unit 25 sets a lower limit C1 of the natural barrier performance, the second threshold setting unit 26 sets an upper limit C2 of the natural barrier performance, and the natural barrier setting unit 24 sets the range between the upper limit C2 and the lower limit C1 as the range of the natural barrier performance. However, as shown in Figure 7(b), the natural barrier setting unit 24 does not have to set the natural barrier performance as a range.

[0068] In this case, the artificial barrier setting unit 23 sets the performance of the artificial barriers, and the natural barrier setting unit 24 sets the performance of the natural barriers, and then the artificial barrier setting unit 23 reduces the performance of the artificial barriers within the regulation satisfaction range A1. In the example of Figure 7(b), the natural barrier setting unit 24 sets the upper limit C2 of the natural barrier performance, and then the artificial barrier setting unit 23 reduces the performance of the artificial barriers from performance B1 to performance B2.

[0069] For example, the engineered barrier construction unit 23 reduces the performance of the engineered barriers by reducing the amount of excavation of underground rock mass B when placing radioactive waste in underground rock mass B. Figure 9 shows an example of a disposal structure 1A in which the amount of excavation of underground rock mass B is reduced compared to Figures 2 and 3. As shown in Figure 9, the disposal structure 1A does not have the buffer material 5 described above.

[0070] In the disposal structure 1A, a borehole 6 is formed large enough to accommodate the metal container 4 (for example, having an inner diameter slightly larger than the outer diameter of the metal container 4), and after the metal container 4 is placed in the borehole 6, a shielding material 7 is filled on top of the metal container 4 inside the borehole 6. The material of the shielding material 7 is, for example, the same as the material of the buffer material 5 described above. Because the inner diameter of the borehole 6 is smaller than the inner diameter of the hole 2c (see Figure 3) described above, the amount of excavation of the underground bedrock B can be reduced.

[0071] Next, an example of the steps of the disposal structure design method according to this embodiment will be described. Figure 10(a) is a flowchart showing an example of the steps of the disposal structure design method according to this embodiment. Below, an example of a method for designing a disposal structure 1 for disposing of radioactive waste in underground bedrock B will be described.

[0072] First, the memory unit 28 stores the relationship between the performance of the natural barrier and the performance of the engineered barrier (storing step). For example, the memory unit 28 stores Table D, which shows the range of performance of the natural barrier and the range of performance of the engineered barrier, as shown in Fig. 6(a). The regulation satisfaction range setting unit 21 sets, from the above relationship, a regulation satisfaction range A1, which is the range of performance of the natural barrier and the engineered barrier that satisfies the radiation dose regulation (step S1, step of setting the regulation satisfaction range).

[0073] 6(b), the excess range setting unit 22 sets an excess range A2, which is a range of excessive natural barrier performance and excessive engineered barrier performance, within the regulation satisfaction range A1 (step S2).The excess range setting unit 22 then excludes the excess range A2 from the regulation satisfaction range A1 (a step of excluding the excess range from the regulation satisfaction range).

[0074] As shown in Figure 7(a), the engineered barrier design unit 23 sets the performance of the engineered barriers (step S3 for setting the performance of the engineered barriers). The engineered barrier design unit 23 sets the performance B1 of the current engineered barriers (the metal container 4 and buffer material 5 shown in Figure 3, which have not changed for over 20 years).

[0075] After the performance of the engineered barriers has been set, the natural barrier setting unit 24 sets the performance of the natural barriers in accordance with the above relationship, which corresponds to the set performance B1 of the engineered barriers and is within the regulation satisfaction range A1 (the process of setting the performance of the natural barriers). At this time, the natural barrier setting unit 24 sets the upper limit C2 and lower limit C1 of the natural barriers in accordance with the above relationship, which correspond to the set performance B1 of the engineered barriers and are within the regulation satisfaction range A1.

[0076] When the natural barrier setting unit 24 sets the performance of the natural barrier, for example, a permissible value for groundwater migration time is set. For example, the natural barrier setting unit 24 sets the groundwater migration time from at least one of the depth of the radioactive waste to be placed in the underground bedrock B, the permeability coefficient of the underground bedrock B, and the hydraulic gradient of the underground bedrock B.

[0077] For example, the first threshold setting unit 25 sets a lower limit C1 of the performance of the natural barrier (step of setting a lower limit of the performance of the natural barrier, step S4). At this time, the first threshold setting unit 25 calculates the minimum allowable time of groundwater migration based on the Darcy flow velocity as the lower limit C1. For example, as shown in Figures 8(a) and 8(b), the first threshold setting unit 25 sets the groundwater migration time at which the satisfaction rate for achieving the target radiation exposure dose of 10 (μsV / year) is equal to or greater than a certain value (for example, 0.8) as the lower limit C1.

[0078] Note that the order of steps S4 and S5 may be reversed, and is not particularly limited. For example, the second threshold setting unit 26 sets an upper limit C2 for the performance of the natural barrier (step of setting an upper limit for the performance of the natural barrier, step S5). At this time, the second threshold setting unit 26 sets the time until the radioactivity emitted by the radioactive waste falls below an allowable value as the upper limit C2. For example, if the radioactive waste contains uranium, the second threshold setting unit 26 calculates the time until the amount of uranium radioactivity falls below a certain value (for example, 100,000 years) as the upper limit C2.

[0079] As described above, the first threshold setting unit 25 sets the lower limit C1 of the natural barrier performance, and the second threshold setting unit 26 sets the upper limit C2 of the natural barrier performance, and then the natural barrier setting unit 24 sets the range between the upper limit C2 and the lower limit C1 as the range of the natural barrier performance (step S6). For example, underground bedrock B, which has a natural barrier performance with a groundwater migration time of more than 30,000 years and less than 100,000 years, is selected as the disposal site for radioactive waste. After the performance of the engineered barriers and the performance of the natural barriers have been set in this way, the series of steps in the disposal structure design method are completed.

[0080] Next, a modified example of the steps of the disposal structure design method according to this embodiment will be described. Figure 10(b) is a flowchart showing the steps of the disposal structure design method according to this modified example. The step in which the regulation satisfaction range setting unit 21 sets the regulation satisfaction range A1 (step S11), the step in which the excess range setting unit 22 sets and excludes the excess range A2 (step S12), and the step in which the engineered barrier setting unit 23 sets the engineered barrier performance B1 (step S13) are the same as the steps S1, S2, and S3 described above, respectively.

[0081] After the engineered barrier setting unit 23 sets the engineered barrier performance B1 in step S13, the natural barrier setting unit 24 sets the performance of the natural barrier as shown in Figure 7(b) (step S14). For example, the natural barrier setting unit 24 selects the performance of the natural barrier from within the regulation satisfaction range A1. As an example, the natural barrier setting unit 24 sets an upper limit C2 of the natural barrier performance within the regulation satisfaction range A1.

[0082] Thereafter, the engineered barrier design unit 23 reduces the performance of the engineered barriers within the regulatory satisfaction range A1 (the step of reducing the performance of the engineered barriers). For example, as described above, the engineered barrier design unit 23 reduces the performance of the engineered barriers by reducing the amount of excavation of the underground bedrock B during the disposal of radioactive waste.

[0083] The engineered barrier design unit 23 may also lower the performance of the engineered barrier by adjusting the thickness of the overpack 4c of the metal container 4, the material of the overpack 4c, the material of the buffer material 5, the composition of the buffer material 5, the amount of buffer material 5 used, and the thickness of the buffer material 5. The engineered barrier design unit 23 then sets the lowered engineered barrier performance B2. Through the above steps, the series of steps in the disposal structure design method is completed.

[0084] Next, the effects obtained by the disposal structure design method and disposal structure design system 10 according to this embodiment will be described. As shown in Figures 6(a), 6(b), 7(a), and 7(b), the disposal structure design method and disposal structure design system 10 according to this embodiment store the relationship between the performance of the natural barriers and the performance of the engineered barriers. Storing this relationship between the performance of the natural barriers and the performance of the engineered barriers makes it possible to determine the appropriate level of performance for the engineered barriers given the level of performance of the natural barriers. Therefore, excessively increasing the performance of the engineered barriers can be avoided, thereby preventing increases in the cost of the disposal structure, shortening the construction period, and reducing the environmental impact.

[0085] In the above relationship, a regulation satisfaction range A1, which is the range of the natural barrier performance and engineered barrier performance that satisfies the radiation dose regulations, is set, and then the engineered barrier performance B1 is set. Then, the natural barrier performance is set so that it corresponds to the set engineered barrier performance B1 and is within the regulation satisfaction range A1. Therefore, the natural barrier performance is set so that it corresponds to the set engineered barrier performance B1 and is within the regulation satisfaction range A1. Therefore, the appropriate natural barrier performance that corresponds to the set engineered barrier performance B1 is set, and the engineered barrier performance and the natural barrier performance can be optimized.

[0086] As described above, the disposal structure design method according to this embodiment may include a step of setting an excess range A2, which is a range of excessive natural barrier performance and excessive engineered barrier performance within the regulatory satisfaction range A1, and excluding the excess range A2 from the regulatory satisfaction range A1. In the step of setting the natural barrier performance, an upper limit C2 and a lower limit C1 of the natural barrier performance may be set in accordance with the above relationship, which correspond to the set engineered barrier performance B1 and are within the regulatory satisfaction range A1. In this case, the upper limit C2 and lower limit C1 of the natural barrier performance are set so that they correspond to the set engineered barrier performance B1 and are within the regulatory satisfaction range A1, and therefore the appropriate natural barrier performance can be understood as a range from the upper limit C2 to the lower limit C1.

[0087] As described above, the disposal structure design method according to this embodiment may include a step of lowering the performance of the engineered barriers within the regulatory satisfaction range A1 after the step of setting the performance of the natural barriers. In this case, the performance of the engineered barriers can be lowered to the minimum necessary within the regulatory satisfaction range A1, thereby reducing the cost of the disposal structure 1.

[0088] As described above, the step of reducing the performance of the engineered barriers may involve reducing the amount of excavation of underground rock mass B when placing radioactive waste in underground rock mass B. In this case, reducing the performance of the engineered barriers results in a reduction in the amount of excavation of underground rock mass B, thereby reducing the environmental load.

[0089] As described above, in the step of setting the performance of the natural barrier, an allowable value for the groundwater migration time, which is the time it takes for the groundwater W in the underground rock mass B to migrate, may be set. In this case, since the allowable value for the groundwater migration time can be set as the performance of the natural barrier, it is possible to easily select an underground rock mass B that will become a natural barrier that satisfies the performance.

[0090] As described above, in the step of setting the performance of the natural barrier, the groundwater migration time may be set from at least one of the depth in the underground rock mass B of the radioactive waste to be placed in the underground rock mass B, the permeability coefficient of the underground rock mass B, and the hydraulic gradient of the underground rock mass B. In this case, the groundwater migration time can be set with higher precision.

[0091] As described above, the step of setting the performance of the natural barrier may include the step of setting a lower limit C1 of the performance of the natural barrier. The step of setting the lower limit C1 of the performance of the natural barrier may include calculating the minimum allowable groundwater migration time based on the Darcy flow rate. In this case, the allowable migration time for radioactive materials from the location of the radioactive waste in the underground bedrock B to the living environment E can be calculated, making it possible to select a natural barrier that can more reliably ensure safety in the living environment E.

[0092] As described above, the step of setting the performance of the natural barrier may include the step of setting an upper limit C2 of the performance of the natural barrier. The step of setting the upper limit C2 of the performance of the natural barrier may involve calculating the time required for the radioactivity emitted by the radioactive waste to fall below an allowable value. In this case, the upper limit C2 of the performance of the natural barrier is calculated as the time required for the emitted radioactivity to fall below an allowable value, making it possible to select a natural barrier that can more reliably ensure safety in the living environment E.

[0093] The above describes embodiments and various examples of the disposal structure design method and disposal structure design system according to the present disclosure. However, the disposal structure design method and disposal structure design system according to the present disclosure are not limited to the above-described embodiments or various examples, and may be further modified within the scope of the gist described in the claims. In other words, the content and order of the steps of the disposal structure design method according to the present disclosure, as well as the configuration and function of each part of the disposal structure design system, may be modified as appropriate within the scope of the above-described gist.

[0094] For example, in the above-described embodiment, an example was described in which the memory unit 28 stores Table D, which indicates the ranges of performance for the natural barrier and the engineered barrier. However, the memory unit may also store a table indicating the ranges of performance for the natural barrier, the ranges of performance for the engineered barrier, and the ranges of an environmental load index. One example of an environmental load index is the excavation volume of underground rock mass B mentioned above. In this case, an environmental load index can be set along with the performance of the natural barrier and the engineered barrier. This makes it possible to design natural and engineered barriers with environmental load taken into consideration.

[0095] In the above-described embodiment, the disposal structure design system 10 includes a server 20 having a regulation satisfaction range setting unit 21, an excess range setting unit 22, an engineered barrier setting unit 23, a natural barrier setting unit 24, a first threshold setting unit 25, a second threshold setting unit 26, a display control unit 27, and a memory unit 28. However, the disposal structure design system may not include any of the regulation satisfaction range setting unit 21, the excess range setting unit 22, the engineered barrier setting unit 23, the natural barrier setting unit 24, the first threshold setting unit 25, the second threshold setting unit 26, the display control unit 27, and the memory unit 28. For example, the disposal structure design method according to the present disclosure may not require the excess range A2 to be set. In this case, the excess range setting unit 22 may be unnecessary. In this manner, the configurations of the disposal structure design system and disposal structure design method may be modified as appropriate. [Explanation of symbols]

[0096] 1,1A...disposal structure, 2...waste placement section, 2b...underground tunnel, 2c...hole, 3...tunnel, 4...metal container, 4b...vitrified waste, 4c...overpack, 4d...gripping section, 5...buffering material, 6...borehole, 7...shielding material, 10...disposal structure design system, 11...information terminal, 11b...display, 20...server, 21...regulatory satisfaction range setting section, 22...excess range setting section, 23...engineered barrier setting section, 24...natural barrier setting section, 25...first threshold setting section, 26...second threshold setting section, 27...display control section, 28...memory section, A1...regulatory satisfaction range, A2...excess range, B...underground bedrock, B1,B2...performance, C1...lower limit, C2...upper limit, E...living environment, E1...surface, H...building, M...geomaterial, W...groundwater.

Claims

1. A disposal structure design method for disposing of radioactive waste in underground bedrock, comprising: a step of memorizing the relationship between the performance of a natural barrier, which is the radioactive material migration suppression function of the underground rock mass, and the performance of an engineered barrier, which is the radioactive material migration suppression function of an artificially constructed barrier structure; a step of determining a regulatory satisfaction range, which is a range of the performance of the natural barrier and the performance of the engineered barrier that satisfies radiation dose regulations, in the relationship; establishing the performance of the engineered barrier; establishing a performance of the natural barrier that corresponds to the established performance of the engineered barrier and is within the regulatory compliance range in the above relationship; Equipped with Disposal structure design methods.

2. a step of setting an excess range within the regulation satisfaction range, which is a range of excessive performance of the natural barrier and excessive performance of the engineered barrier, and excluding the excess range from the regulation satisfaction range; In the step of setting the performance of the natural barrier, upper and lower limits of the performance of the natural barrier are set in the relationship so as to correspond to the set performance of the engineered barrier and to fall within the range of compliance with the regulations. The disposal structure design method according to claim 1.

3. a step of lowering the performance of the engineered barrier within the regulation satisfaction range after the step of setting the performance of the natural barrier; The disposal structure design method according to claim 1 or 2.

4. the step of reducing the performance of the engineered barrier comprises reducing the amount of excavation of the underground rock mass when the radioactive waste is placed in the underground rock mass; The disposal structure design method according to claim 3.

5. In the step of setting the performance of the natural barrier, an allowable value for groundwater migration time, which is the time it takes for groundwater in the underground bedrock to migrate, is set. The disposal structure design method according to claim 1 or 2.

6. In the step of setting the performance of the natural barrier, the groundwater migration time is set based on at least one of the depth of the radioactive waste placed in the underground rock mass, the permeability coefficient of the underground rock mass, and the hydraulic gradient of the underground rock mass. The disposal structure design method according to claim 5.

7. setting the performance of the natural barrier includes setting a lower limit of the performance of the natural barrier; In the step of setting a lower limit of the performance of the natural barrier, a minimum allowable time for groundwater migration based on Darcy flow velocity is calculated. The disposal structure design method according to claim 1 or 2.

8. setting the performance of the natural barrier includes setting an upper limit for the performance of the natural barrier; In the step of setting an upper limit of the performance of the natural barrier, a time required for the radioactivity emitted by the radioactive waste to fall below an allowable value is calculated. The disposal structure design method according to claim 1 or 2.

9. A disposal structure design system for disposing of radioactive waste in underground bedrock, comprising: a memory unit that stores the relationship between the performance of a natural barrier, which is the underground rock mass's function of suppressing the migration of radioactive materials, and the performance of an engineered barrier, which is the function of suppressing the migration of radioactive materials, which is an artificially constructed barrier structure; a regulation satisfaction range setting unit that sets a regulation satisfaction range, which is a range of the performance of the natural barrier and the performance of the engineered barrier that satisfies the radiation dose regulation, in the relationship; an engineered barrier setting unit that sets the performance of the engineered barrier; a natural barrier setting unit that sets the performance of the natural barrier so that the performance of the engineered barrier corresponds to the set performance and is within the range of the regulation satisfaction in the above relationship; Equipped with Disposal structure design system.

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