High-level waste disposal pit multi-field coupling condition full cycle simulation system and test method

Abstract

The application discloses a high-level radioactive waste disposal pit multi-field coupling condition full cycle simulation system and a test method, and relates to the field of rock mechanics tests.The system comprises a true triaxial dynamic and static loading device, which can bear a fractured rock sample to be tested, and can move the fractured rock sample to a set position, and can apply dynamic and static loads in multiple directions to the fractured rock sample; a vertical excavation and tunneling device can realize simulation of an excavation process of dynamic disturbance drilling of the center of the fractured rock sample under a deep geostress environment; a disposal pit reaction source device is placed in the disposal pit to simulate a nuclide leakage process under conditions of decay heat release, corrosion and gas production of a high-level radioactive waste tank; and a fractured seepage control device can apply a water head difference to left and right end surfaces of the fractured rock sample in a horizontal direction through a rock sample pad to drive seepage solution to flow along original fractures in the fractured rock sample.The application can truly reproduce disposal pit full cycle disturbance effects, integrate multiple barrier coupling boundary conditions, and consider seepage influence on storage tank surface corrosion differences.

Description

Technical Field

[0001] This invention relates to the field of rock mechanics testing technology, and in particular to a full-cycle simulation system and testing method for multi-field coupling conditions in high-level radioactive disposal pits. Background Technology

[0002] Deep geological disposal is a nuclear waste treatment technology that buries high-level radioactive waste in geological layers 500-1000 meters below the surface. High-level radioactive waste deep geological disposal repositories, i.e., high-level radioactive disposal pits, will be subjected to the coupled effects of multiple factors during their thousands of years of operation, from excavation and formation to permanent closure. These factors include disturbance from excavation machinery, heat release from the decay of high-level radioactive waste, expansion of the bentonite buffer layer, erosion from groundwater seepage, and potential earthquakes and geological tectonic activities. These effects can easily induce the initiation and expansion of micro-fractures in the surrounding rock, a sudden increase in rock permeability, and even the breakthrough of engineering barriers, forming radionuclide migration channels and seriously damaging the radionuclide isolation function of the multi-barrier system. Therefore, conducting simulation tests of the surrounding rock response under the multi-field coupling effects throughout the entire life cycle of high-level radioactive disposal pits is an important technical support for the safety assessment and engineering design of high-level radioactive waste deep geological disposal repositories.

[0003] Currently, the industry mainly relies on traditional rock mechanics testing equipment to conduct indoor simulation tests for deep geological repositories of high-level radioactive waste. This equipment attempts to simulate the mechanical, thermal, and seepage characteristics of the repositories from the perspective of single or partial physical mechanisms. For example, some test devices can apply single-factor or dual-factor loads such as temperature and confining pressure, and some devices can simulate the triaxial high-temperature seepage process of rock mass, providing certain experimental data support for related research on repositories.

[0004] However, existing indoor testing methods and equipment for simulating high-level radioactive waste repositories still have many significant shortcomings, making it difficult to meet the engineering requirements for simulating the multi-field coupling effects throughout the entire lifecycle of the disposal pit. Specifically, these shortcomings are as follows: First, existing equipment mostly focuses on simulating single physical mechanisms, generally using pre-drilled holes to simulate the disposal pit, replacing the actual mechanical excavation process. This ignores the impact of excavation disturbance on the initial micro-cracks and stress redistribution of the surrounding rock, resulting in significant distortion between the simulation results of the initial state of the disposal pit and the actual engineering situation. Second, the testing process lacks continuity. Only some equipment can simulate local processes such as triaxial high-temperature seepage, and it is impossible to continuously simulate the entire lifecycle evolution process of excavation, heat, seepage, dynamic load, and radionuclide leakage on the same rock sample. It is necessary to conduct tests by segmented sample preparation and equipment replacement, resulting in a lack of correlation in the test data and making it difficult to reflect the true multi-field coupling effects throughout the entire lifecycle of the disposal pit. Third, there is a lack of consideration for endogenous boundary conditions such as gas generation and radionuclide leakage from high-level radioactive waste containers. The collaborative simulation did not consider the uneven corrosion caused by the different distribution of seepage fissures on the tank surface, ignored the correspondence between gas release and seepage location, and the positive feedback non-uniform effect of increased local permeability due to intensified corrosion. It could not reproduce the real thermal, water, mechanical and chemical coupling behavior of the disposal pit after closure. Fourth, the existing test systems generally do not integrate dynamic loading capabilities, and cannot apply dynamic loads such as earthquakes and tectonic activities. It is difficult to assess the activation effect of extreme dynamic loads on the existing damaged area of ​​the surrounding rock during the 10,000-year operation cycle, and cannot support the complete simulation analysis of the physical mechanism of the disposal pit throughout its entire life cycle. Fifth, the simulation of the coupling boundary conditions of multiple barriers is insufficient. It failed to realistically reproduce the interaction of the composite boundary system composed of high-level radioactive waste tank, bentonite buffer layer and near-field surrounding rock. It did not consider key factors such as the contact confining pressure generated by the expansion of bentonite when it comes into contact with water and the impact of the accumulation of corrosive gas pressure on the boundary contact state, resulting in a significant deficiency in the simulation of the coupling effect of the barrier system.

[0005] Therefore, there is an urgent need for a technical solution that can realistically reproduce the full-cycle disturbance effect of the treatment pit, integrate multiple barrier coupled boundary conditions, and consider the differences in surface corrosion of the storage tank caused by seepage. Summary of the Invention

[0006] The purpose of this invention is to provide a full-cycle simulation system and test method for multi-field coupling conditions in high-level radioactive disposal pits, in order to solve the problems existing in the prior art. This system can realistically reproduce the full-cycle disturbance effect of the disposal pit, integrate multiple barrier coupling boundary conditions, and consider the differences in surface corrosion of the storage tank due to seepage.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits, comprising: The true triaxial dynamic and static loading device is equipped with a movable bearing mechanism, which can carry the fractured rock sample to be tested and move the fractured rock sample to a set position. The true triaxial dynamic and static loading device is equipped with multiple dynamic and static loading mechanisms, which can apply dynamic and static loads in multiple directions to the fractured rock sample. A vertical excavation device is connected to the bottom of the dynamic and static loading mechanism at the top of the true triaxial dynamic and static loading device to realize a simulated excavation process of dynamic disturbance drilling on the center of fractured rock samples under deep geostress environment. A disposal pit reaction source device is placed within the disposal pit formed by excavating the fractured rock sample. The device is used to seal the radionuclide solution and can regulate its temperature and pressure to simulate the radionuclide leakage process under conditions of radioactive decay exothermics and corrosion gas generation in high-level radioactive waste containers. The fissure seepage control device includes a rock sample pad installed on the outer wall of the fissure rock sample. It can apply a hydraulic head difference to the left and right end faces of the fissure rock sample in the horizontal direction through the rock sample pad, and drive the seepage solution to seep along the original fissures in the fissure rock sample.

[0008] In one embodiment, the true triaxial dynamic and static loading device includes a host reaction frame, on which the dynamic and static loading mechanism is installed at the top, left and right sides and front and rear sides, and the movable bearing mechanism is provided in the internal cavity of the host reaction frame.

[0009] In one embodiment, the dynamic and static loading mechanism includes a static load hydraulic cylinder, a dynamic hydraulic cylinder connected to the side of the static load hydraulic cylinder away from the mobile bearing mechanism, and the bottom of the piston rod of the static load hydraulic cylinder located at the top of the host reaction frame is connected to the vertical excavation and drilling device; the piston rod ends of the static load hydraulic cylinder located on the left and right sides and the front and rear sides of the host reaction frame are connected to force transmission rods, and the ends of the force transmission rods abut against the rock sample pads in the mobile bearing mechanism to apply dynamic and static loads in multiple directions to the fractured rock sample.

[0010] In one embodiment, an adjustment space is provided between the piston rod end of the static load hydraulic cylinder located on the front side of the host reaction frame and the force transmission rod located on the front side of the host reaction frame. A lifting guide rod is provided at the adjustment space. When the lifting guide rod rises to be coaxial with the piston rod of the static load hydraulic cylinder on the front side of the host reaction frame, both ends of the lifting guide rod can be connected to the piston rod end of the static load hydraulic cylinder on the front side of the host reaction frame and the outer side of the force transmission rod on the front side of the host reaction frame, respectively.

[0011] In one embodiment, the mobile support mechanism includes a sample box for placing a fractured rock sample and a fracture seepage control device; the sample box is placed on the surface of a sample box platform, the sample box platform is fixedly installed on a sample box moving mechanism, the sample box moving mechanism is located within the host reaction frame, and the sample box moving mechanism can drive the sample box platform and the sample box to move synchronously to a set position.

[0012] In one embodiment, the vertical drilling device includes a vertical drilling spindle. The top end of the vertical drilling spindle is magnetically attached to the piston rod end of the dynamic and static load hydraulic cylinder at the top of the host reaction frame via a magnetic base. A tapered cutterhead is connected to the bottom of the vertical drilling spindle. A torque servo motor is mounted on the piston rod of the dynamic and static load hydraulic cylinder at the top of the host reaction frame. The torque servo motor is connected to the vertical drilling spindle via a transmission belt. A rotating bearing is fixedly connected to the top of the vertical drilling spindle. The rotating bearing is engaged in a groove in the magnetic base and is axially limited by the vertical drilling spindle. The rotating bearing can rotate horizontally within the groove. The interior of the vertical drilling spindle is hollow to form a rock cuttings discharge channel. A guide pipe is connected to the upper part of the rock cuttings discharge channel. The guide pipe is located inside the magnetic base and is externally connected to an air suction device.

[0013] In one embodiment, the vertical excavation device further includes an outer housing with openings at both ends. The upper part of the outer housing contacts a magnetic base, a fixed support is placed on the top of the fractured rock sample, and the lower part of the outer housing passes through the fixed support. The drilling spindle is located inside the outer housing, and a slot is opened on the upper side wall of the outer housing. The transmission belt connects the torque servo motor to the vertical drilling spindle through the slot.

[0014] In one embodiment, the reaction source device in the treatment pit is a columnar structure, which, from the inside out, comprises a pressure chamber, an inner stainless steel wall layer of the storage tank, an electrothermal ceramic layer, an outer stainless steel wall layer of the storage tank, a fiber optic grating surface temperature measuring layer, and compacted bentonite blocks. The inner stainless steel wall layer of the storage tank has multiple horizontally arranged micropores and horizontally arranged radionuclide liquid isolation gas chambers spaced vertically. A piston push rod displacement gauge is connected to the inner side of the micropores of the inner stainless steel wall layer of the storage tank, and the data line of the piston push rod displacement gauge is led out through the pressure chamber. A radionuclide liquid injection channel is provided between the inner stainless steel wall layer and the electrothermal ceramic layer of the storage tank. An exhaust valve is connected to the bottom of the radionuclide liquid injection channel, and the radionuclide liquid injection channel communicates with the micropores of the inner stainless steel wall layer of the storage tank. A diaphragm is provided on the side of the radionuclide liquid isolation gas chamber closest to the micropores of the inner stainless steel wall layer of the storage tank, and a radionuclide liquid isolation gas chamber piston passes through the side of the radionuclide liquid isolation gas chamber away from the diaphragm. The radionuclide liquid isolation gas chamber piston and the piston push... A rod displacement gauge is connected. The outer side of the piston in the nuclide solution isolation chamber is connected to the pressure chamber. When the pressure chamber is filled with air, it pushes the piston in the nuclide solution isolation chamber to move towards the diaphragm. The air pressure in the nuclide solution isolation chamber can push the diaphragm outward to block the nuclide solution injection channel, thereby separating the nuclide solution injection channel. Micropores corresponding to the micropores in the stainless steel wall layer of the tank are opened on the electrothermal ceramic layer, the outer stainless steel wall layer of the tank, and the surface temperature measuring layer of the fiber optic grating. The micropores in the outer stainless steel wall layer of the tank are filled with a mixture of nano-zero valent iron and bentonite. A compacted bentonite block is provided on the side of the outer stainless steel wall layer away from the electrothermal ceramic layer. The top and bottom of the outer stainless steel wall layer of the tank are provided with extended plates to fix the compacted bentonite block. The surface temperature measuring layer of the fiber optic grating is located between the compacted bentonite block and the side wall of the outer stainless steel wall layer away from the electrothermal ceramic layer.

[0015] In one embodiment, the rock sample pad of the fracture seepage control device is installed at the four side wall positions of the fractured rock sample. The rock sample pad has a seepage liquid cavity. The internal space of the rock sample pad near the fractured rock sample is provided with an S-shaped heating pipeline. The upper surface of the rock sample pad has an opening. The opening is connected to the seepage liquid cavity through a seepage pipeline and a gas pipeline. The gas pipeline is nested outside the seepage pipeline.

[0016] The present invention also provides an experimental method based on the above-described high-level radioactive waste disposal pit multi-field coupling condition full-cycle simulation system, comprising the following steps: During the excavation phase, the fractured rock sample is placed in the sample box and moved to the loading position by the sample box moving mechanism; the dynamic and static loading mechanisms located on the front, rear and left and right sides of the host reaction frame apply confining pressure to the fractured rock sample through the rock sample pad; at the same time, the heating pipeline in the rock sample pad simulates the deep temperature conditions where the fractured rock sample is located. Driven by a torque servo motor, the vertical drilling spindle rotates the tapered cutterhead. Excavation thrust is applied through the static hydraulic cylinder at the top of the host reaction frame, and excavation disturbance force is applied through the dynamic hydraulic cylinder at the top of the host reaction frame. This simulates the excavation process of dynamically disturbing the center of the fractured rock sample under deep geostress conditions. Rock cuttings generated during the drilling process enter the rock cuttings discharge channel inside the vertical drilling spindle through the tapered cutterhead opening and are discharged from the top of the guide tube by air extraction. After drilling is completed, the static load hydraulic cylinder at the top of the host reaction frame is raised, the tapered cutter head is withdrawn, and a treatment pit is formed; During the sealing phase, the confining pressure conditions and heating conditions of the rock sample pads from the previous phase are maintained. The reaction source device of the treatment pit is placed into the treatment pit, and the radionuclide solution is injected through the radionuclide solution injection channel at the top of the reaction source device. The gas in the radionuclide solution injection channel is discharged through the exhaust valve at the bottom. After the radionuclide solution is injected, the pressure chamber is pressurized, and under the action of pressure, the diaphragm of the radionuclide solution isolation chamber seals the radionuclide solution injection channel. The heating of the electrothermal ceramic layer is transmitted through the stainless steel wall layer outside the tank to the temperature measuring layer on the surface of the fiber optic grating, and finally conducted to the fractured rock sample after passing through the compacted bentonite block. The seepage pump pipeline applies a head difference to the horizontal left and right ends of the fractured rock sample through the rock sample pad, driving the seepage solution to seep along the original fractures in the fractured rock sample. As the seepage penetrates along the fractures into the compacted bentonite block and reacts with the nano-zero valent iron in the micropores of the stainless steel wall layer outside the tank, the permeability of the micropores increases. The gas pressure chamber pushes the piston of the radionuclide liquid isolation gas chamber to move outward, increasing the leakage rate of the radionuclide solution in the injection channel. The generated gas will form microchannels in the compacted bentonite block, increasing the seepage flow rate. Due to the high heat exchange efficiency of seepage, the temperature measuring layer on the fiber optic grating surface will detect the local high temperature zone outside the corrosion zone. The seeped gas is discharged through the micropores of the rock sample pad around the fractured rock sample and is discharged from the gas pipeline above the seepage liquid chamber, realizing gas-liquid separation.

[0017] The present invention achieves the following technical effects compared to the prior art: This invention achieves full-cycle simulation of multi-field coupling conditions in high-level radioactive waste disposal pits. Based on an integrated architecture of vertical drilling, central heat / gas / nucleus release, fracture seepage control, and true triaxial dynamic and static loading, it can reproduce the entire process of multi-physics coupling effects from excavation disturbance, decay heat release, waste tank gas production to seismic activation on fractured rock samples. This overcomes the limitations of traditional experiments that rely on pre-drilled holes, segmented loading, and the inability to simulate long-term evolution chains, achieving full-cycle coverage of near-field surrounding rock damage evolution in disposal pits. By integrating controllable heating and gas / nucleus solution release functions at the center of the disposal pit, it simultaneously simulates decay heat release, corrosion gas production, and nucleus leakage from high-level radioactive waste tanks, and couples the contact pressure effect of bentonite self-expansion on the surrounding rock, realistically reproducing the complex boundary conditions of the buffer layer and surrounding rock interface in a closed environment. The rate of corrosion gas production and nucleus leakage in this invention's device is controlled by the degree of corrosion on the lower surface through seepage, realistically reflecting the uneven corrosion and leakage situation of high-level radioactive waste storage tanks in actual engineering. This solves the problem that existing equipment cannot simulate the actual distribution of nucleus leakage. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the overall structure of the full-cycle simulation system for multi-field coupling conditions in a high-level radioactive waste disposal pit, as shown in one or more embodiments of the present invention. Figure 2 This is a lateral cross-sectional view of the full-cycle simulation system for multi-field coupling conditions in a high-level radioactive waste disposal pit, as described in one or more embodiments of the present invention. Figure 3 This is a front cross-sectional view of a full-cycle simulation system for multi-field coupling conditions in a high-level radioactive waste disposal pit, as described in one or more embodiments of the present invention. Figure 4 This is a schematic diagram of the vertical excavation device of the full-cycle simulation system for multi-field coupling conditions in a high-level radioactive waste disposal pit, as shown in one or more embodiments of the present invention. Figure 5 This is a side cross-sectional view of the reaction source device in the high-level radioactive disposal pit multi-field coupling condition full-cycle simulation system in one or more embodiments of the present invention. Figure 6 This is a lateral cross-sectional view of a rock sample pad from a full-cycle simulation system for multi-field coupling conditions in a high-level radioactive disposal pit, as shown in one or more embodiments of the present invention.

[0020] In the diagram: 1-True three-axis dynamic and static loading device; 2-Z-axis dynamic hydraulic cylinder; 3-Z-axis static hydraulic cylinder; 4-X-axis static hydraulic cylinder; 5-X-axis dynamic hydraulic cylinder; 6-X-axis force transmission rod; 7-Y-axis static hydraulic cylinder; 8-Y-axis lifting guide rod; 9-Y-axis force transmission rod; 10-Sample box platform; 11-Sample box; 12-Sample box moving mechanism; 13-Vertical excavation device; 14-Vertical drilling spindle; 15-Magnetic base; 16-Transmission belt; 17-Reducing cutterhead; 18-Outer housing; 19-Fixed support; 20-Torque servo motor; 21-Reaction source device for the treatment pit; 22-Pressure chamber; 23-Inner stainless steel wall layer of the storage tank; 24-Electrically heating ceramic layer; 25-Outer stainless steel wall layer of the storage tank; 26-Surface temperature measuring layer of fiber optic grating; 27-Compacted bentonite block; 28-Isolation gas chamber for nuclide solution; 29-Piston push rod displacement gauge; 30-Nuclide solution injection channel; 31-Exhaust valve; 32-Fracture seepage control device; 33-Rock sample pad; 34-Seepage liquid chamber; 35-Seepage pipeline; 36-Gas pipeline; 37-Heating pipeline; 38-Fracture rock sample; 39-Main unit reaction frame. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The purpose of this invention is to provide a full-cycle simulation system and test method for multi-field coupling conditions in high-level radioactive disposal pits, in order to solve the problems existing in the prior art. This system can realistically reproduce the full-cycle disturbance effect of the disposal pit, integrate multiple barrier coupling boundary conditions, and consider the differences in surface corrosion of the storage tank due to seepage.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Full-cycle damage evolution of surrounding rock in the disposal pit: The cumulative damage development process of the surrounding rock under the combined effects of multiple disturbances during the excavation and closure of the high-level radioactive waste disposal pit includes: (1) initial microcracks and stress redistribution caused by excavation disturbance; (2) thermal crack propagation caused by the decay heat of high-level radioactive waste; (3) the influence of the accumulation of corrosive gas pressure and bentonite expansion on the boundary contact state in the closed environment; and (4) the activation of the existing damaged zone by dynamic loads caused by external earthquakes or tectonic activities. Each evolution process is realized by the collaborative simulation of the vertical drilling device, the true triaxial dynamic-static coupling loading device and the disposal pit reaction source device in the high-level radioactive waste disposal pit simulation system.

[0025] Multiple Barrier Coupled Boundary Conditions: In a high-level radioactive waste disposal environment, a complex boundary system is formed by a central high-level radioactive waste storage tank (serving as a decay heat source and gas release source), a bentonite buffer layer (which exerts contact pressure on the surrounding rock due to its high adsorption, low permeability, and water-induced self-swelling properties), and the near-field surrounding rock. This system achieves a realistic simulation of the complex boundaries between the waste storage tank and bentonite, and between bentonite and surrounding rock, through a reaction source device in the disposal pit.

[0026] Multi-field coupling effect of surrounding rock in the closed stage disposal pit: After the high-level radioactive waste disposal pit is backfilled and sealed, the surrounding rock undergoes a thermo-hydraulic-mechanical response under the combined action of in-situ high confining pressure, decay heat and sparse fractures. This coupling effect controls the evolution of fracture aperture, the development of permeability anisotropy and the formation of radionuclide migration paths, and is the core physical link in the simulation and evaluation of the experimental device.

[0027] Corrosion of tank surfaces in disposal pits: Located in deep geological environments, disposal tanks are subject to chemical corrosion reactions with groundwater due to seepage and temperature changes, generating H2 and accelerating the release of radionuclides. Due to variations in the distribution of seepage fissures, the surface corrosion of the tanks is uneven. Areas with severe corrosion produce more gas, and the external bentonite more easily creates seepage channels that facilitate gas leakage, accelerating radionuclide outflow and groundwater infiltration. Therefore, the uneven distribution of surface corrosion directly affects the tank's sealing performance and the accuracy of radionuclide leakage analysis.

[0028] Based on the above, this invention provides a full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits, with reference to... Figures 1-6As shown, the system includes a true triaxial dynamic and static loading device 1, a vertical excavation and excavation device 13, a treatment pit reaction source device 21, and a fracture seepage control device 32. The true triaxial dynamic and static loading device 1 is equipped with a movable bearing mechanism capable of carrying the fractured rock sample 38 to be tested and moving it to a set position. The true triaxial dynamic and static loading device 1 has multiple dynamic and static loading mechanisms that can apply dynamic and static loads to the fractured rock sample 38 in multiple directions. The vertical excavation and excavation device 13 is connected to the bottom of the dynamic and static loading mechanisms at the top of the true triaxial dynamic and static loading device 1 to achieve testing of the fractured rock sample 38 under deep geostress conditions. The 8th center implements a simulated excavation process of dynamic disturbance drilling; the disposal pit reaction source device 21 is placed in the disposal pit formed by excavating the fractured rock sample 38. The disposal pit reaction source device 21 is used to seal the radionuclide solution and can regulate its temperature and pressure to simulate the radionuclide leakage process under the conditions of high radioactive waste can decay heat release and corrosion gas generation; the fracture seepage control device 32 includes a rock sample pad 33 installed on the outer wall of the fractured rock sample 38. It can apply a water head difference to the left and right side faces of the fractured rock sample 38 in the horizontal direction through the rock sample pad 33, and drive the seepage solution to seep along the original fractures in the fractured rock sample 38. This invention continuously reproduces the full-cycle damage evolution of the surrounding rock, the multi-barrier coupled boundary conditions, and the multi-field coupling effects in the post-closure stage of the disposal pit on a single fractured rock sample 38, without the need for segmented sample preparation or equipment replacement. The system can realistically simulate the damage effects of key physical processes such as decay heat release, gas production, radionuclide leakage, and seismic disturbance of high-level radioactive waste canisters on the surrounding rock, as well as the analysis of radionuclide diffusion.

[0029] In one embodiment, the true triaxial dynamic and static loading device 1 includes a main reaction frame 39, which is a U-shaped high-strength alloy casting structure. Dynamic and static loading mechanisms are installed on its top, left and right sides, and front and rear sides. Mounting plates are fixedly connected to the front and rear sides of the main reaction frame 39 via horizontally arranged connecting rods. The dynamic and static loading mechanisms on the front and rear sides are mounted on the corresponding mounting plates. The space between the mounting plates and the main reaction frame 39 forms an adjustment space, which can be used for placing or removing fractured rock samples 38. Before the test, the fractured rock sample 38 is placed into the main reaction frame 39 through this space. In this embodiment, the top, left and right sides, and front and rear sides are all... Figure 1The following is an example from the perspective of the main reaction frame 39; a movable bearing mechanism is provided inside the internal cavity of the main reaction frame 39. The dynamic and static loading mechanism of this embodiment includes a static load hydraulic cylinder, and a dynamic hydraulic cylinder is connected to the side of the static load hydraulic cylinder away from the movable bearing mechanism. The bottom of the piston rod of the static load hydraulic cylinder located at the top of the main reaction frame 39 is connected to a vertical excavation device 13; the piston rod ends of the static load hydraulic cylinders located on the left, right and front and rear sides of the main reaction frame 39 are connected to force transmission rods, and the ends of the force transmission rods abut against the rock sample pad 33 in the movable bearing mechanism to apply dynamic and static loads in multiple directions to the fractured rock sample 38. The movable bearing mechanism of this embodiment includes a sample box 11, which is used to place the fractured rock sample 38 and the fracture seepage control device 32; the sample box 11 is placed on the surface of the sample box platform 10, and the sample box platform 10 is fixedly installed on the sample box moving mechanism 12. The sample box moving mechanism 12 is located inside the main reaction frame 39, and the sample box moving mechanism 12 can drive the sample box platform 10 and the sample box 11 to move synchronously to a set position.

[0030] In one embodiment, with Figure 1 The left and right sides are defined as the X direction, the front and back sides are defined as the Y direction, and the vertical direction is defined as the Z direction. In this embodiment, the static load hydraulic cylinders include an X-direction static load hydraulic cylinder 4, a Y-direction static load hydraulic cylinder 7, and a Z-direction static load hydraulic cylinder 3. The dynamic hydraulic cylinders include a Z-direction dynamic hydraulic cylinder 2 and an X-direction dynamic hydraulic cylinder 5. The Z-direction static load hydraulic cylinder 3 is installed on the top of the main reaction frame 39, and the upper end of the piston rod of the Z-direction static load hydraulic cylinder 3 is connected to the Z-direction dynamic hydraulic cylinder 2. The X-direction static load hydraulic cylinders 4 are symmetrically installed on the left and right sides of the main reaction frame 39. The X-direction static load hydraulic cylinders 4 are applied to the rock sample pads 33 on the left and right sides inside the sample box 11 via X-direction force transmission rods 6. The rear end of the X-direction static load hydraulic cylinder 4 is connected to the X-direction dynamic hydraulic cylinder 5. The Y-direction static load hydraulic cylinders 7 are installed on the front and back sides of the main reaction frame 39. A lifting guide rod is provided at the adjustment space position on the front side. In this embodiment, the lifting guide rod is a Y-direction lifting guide rod 8. The Y-direction lifting guide rod 8 rises to the position of the Y-direction static load hydraulic cylinder on the front side of the main reaction frame 39. When the piston rod of 7 is coaxial, the two ends of the Y-direction lifting guide rod 8 can be connected to the piston rod end of the Y-direction static load hydraulic cylinder 7 on the front side of the host reaction frame 39 and the outer side of the Y-direction force transmission rod 9 on the front side of the host reaction frame 39, respectively. Thus, the Y-direction static load hydraulic cylinder 7 on the front side of the horizontal Y direction is applied to the rock sample pad 33 on the front side of the sample box 11 through the Y-direction lifting guide rod 8 and the Y-direction force transmission rod 9, and the Y-direction static load hydraulic cylinder 7 on the rear side of the horizontal Y direction is applied to the rock sample pad 33 on the rear side of the sample box 11 through the Y-direction force transmission rod 9.

[0031] In one embodiment, the vertical drilling device 13 includes a vertical drilling spindle 14 and an outer housing 18 with openings at both ends. The top end of the vertical drilling spindle 14 is attached to the piston rod end of the dynamic and static load hydraulic cylinder at the top of the host reaction frame 39 via a magnetic base 15. A tapered cutterhead 17 is connected to the bottom of the vertical drilling spindle 14. A torque servo motor 20 is provided on the piston rod of the dynamic and static load hydraulic cylinder at the top of the host reaction frame 39. The torque servo motor 20 is connected to the vertical drilling spindle 14 via a transmission belt 16. A rotating bearing is fixedly connected to the top of the vertical drilling spindle 14. The rotating bearing is inserted into the groove of the magnetic base 15. The rotating bearing is axially limited in the vertical drilling spindle 14 and can rotate horizontally in the groove. The interior of the vertical drilling spindle 14 is hollow to form a rock cuttings discharge channel. A conduit is connected to the upper part of the rock cuttings discharge channel. The conduit is located inside the magnetic base 15 and is connected to an air suction device. In this embodiment, the upper part of the outer shell 18 contacts the magnetic base 15, a fixed support 19 is placed on the top of the fractured rock sample 38, and the lower part of the outer shell 18 passes through the fixed support 19; the drilling spindle is located inside the outer shell 18, and a slot is opened on the upper side wall of the outer shell 18. The transmission belt 16 connects the torque servo motor 20 to the vertical drilling spindle 14 through the slot.

[0032] In one embodiment, the disposal pit reaction source device 21 is used to simulate a high-level radioactive waste storage tank. It has a columnar structure, and from the inside out, it is provided with a pressure chamber 22, an inner stainless steel wall layer 23, an electrothermal ceramic layer 24, an outer stainless steel wall layer 25, a fiber optic grating surface temperature measuring layer 26, and compacted bentonite blocks 27. The inner stainless steel wall layer 23 has multiple horizontally arranged micropores and horizontally arranged radionuclide liquid isolation gas chambers 28 spaced vertically. A piston push rod displacement gauge 29 is connected to the inner side of the micropores of the inner stainless steel wall layer 23. The piston push rod displacement gauge 29... The data line is led out through the air pressure chamber 22; a radionuclide solution injection channel 30 is provided between the stainless steel wall layer 23 and the electric heating ceramic layer 24 inside the tank. The bottom of the radionuclide solution injection channel 30 is connected to the exhaust valve 31. The radionuclide solution injection channel 30 is connected to the micropores of the stainless steel wall layer 23 inside the tank. A diaphragm is provided on the side of the radionuclide solution isolation chamber 28 near the micropores of the stainless steel wall layer 23 inside the tank. A piston of the radionuclide solution isolation chamber 28 is provided on the side of the radionuclide solution isolation chamber 28 away from the diaphragm. Its displacement is measured by the piston push rod displacement gauge 29. The piston of the radionuclide solution isolation chamber 28 and the piston push rod are connected. The rod displacement gauge 29 is connected, and the piston outside the nuclide liquid isolation gas chamber 28 is connected to the pressure chamber 22. When the pressure chamber 22 is filled with air, it pushes the piston of the nuclide liquid isolation gas chamber 28 to move closer to the diaphragm. The air pressure in the nuclide liquid isolation gas chamber 28 can push the diaphragm to move outward to block the nuclide solution injection channel 30, thereby separating the nuclide solution injection channel 30. The electrothermal ceramic layer 24, the stainless steel wall layer 25 of the tank, and the fiber optic grating surface temperature measuring layer 26 are all provided with micropores that correspond one-to-one with the micropores of the stainless steel wall layer 23 inside the tank. The micropores of the outer stainless steel wall layer 25 are filled with a mixture of nano-zero valent iron and bentonite. A compacted bentonite block 27 is provided on the side of the outer stainless steel wall layer 25 away from the electrothermal ceramic layer 24. The top and bottom of the outer stainless steel wall layer 25 are provided with plates extending horizontally outward. The top and bottom of the compacted bentonite block 27 are respectively attached to the plate at the corresponding positions, so that the plate is used to fix the compacted bentonite block 27. The fiber optic grating surface temperature measuring layer 26 is located between the compacted bentonite block 27 and the side wall of the outer stainless steel wall layer 25 away from the electrothermal ceramic layer 24.

[0033] In one embodiment, the rock sample pad 33 of the fracture seepage control device 32 is installed at the four side wall positions of the fractured rock sample 38. The rock sample pad 33 is provided with micro-fractures, and a seepage liquid cavity 34 is opened inside the rock sample pad 33. An S-shaped heating pipeline 37 is provided in the internal space of the rock sample pad 33 near the fractured rock sample 38. The upper surface of the rock sample pad 33 has an opening, and the opening is connected to the seepage liquid cavity 34 through a seepage pipeline 35 and a gas pipeline 36, and the gas pipeline 36 is nested outside the seepage pipeline 35.

[0034] The present invention also provides an experimental method based on the above-mentioned full-cycle simulation system of multi-field coupling conditions in high-level radioactive waste disposal pits, comprising the following steps: During the excavation stage, the fractured rock sample 38 is placed in the sample box 11 and moved to the loading position by the sample box moving mechanism 12; the dynamic and static loading mechanisms located on the front, rear and left and right sides of the host reaction frame 39 apply confining pressure to the fractured rock sample 38 through the rock sample pad 33; at the same time, the heating pipeline 37 in the heated rock sample pad 33 simulates the deep temperature conditions where the fractured rock sample 38 is located. Driven by the torque servo motor 20, the vertical drilling spindle 14 drives the tapered cutterhead 17 to rotate. The excavation thrust is applied by the static hydraulic cylinder at the top of the host reaction frame 39, and the excavation disturbance force is applied by the dynamic hydraulic cylinder at the top of the host reaction frame 39. This realizes the simulated excavation process of dynamic disturbance drilling on the center of the fractured rock sample 38 under deep geostress environment. The rock cuttings generated during the drilling and excavation process enter the rock cuttings discharge channel inside the vertical drilling spindle 14 through the opening of the tapered cutterhead 17, and are discharged from the top of the guide tube by air extraction. After drilling is completed, the static load hydraulic cylinder at the top of the host reaction frame 39 is raised, the tapered cutter head 17 is withdrawn, and a treatment pit is formed. During the sealing stage, the confining pressure conditions and heating conditions of the rock sample pad 33 in the previous stage are maintained. The reaction source device 21 of the treatment pit is placed into the treatment pit, and the radionuclide solution is injected through the radionuclide solution injection channel 30 at the top of the reaction source device 21. The gas originally in the radionuclide solution injection channel 30 is discharged through the exhaust valve 31 at the bottom. After the nuclide solution is injected, pressure is applied to the gas pressure chamber 22. Under the action of gas pressure, the piston of the nuclide solution isolation gas chamber 28 moves closer to the diaphragm, increasing the gas pressure in the nuclide solution isolation gas chamber 28. Under the action of gas pressure, the diaphragm of the nuclide solution isolation gas chamber 28 expands outward, blocking the nuclide solution injection channel 30 at the location, so that the nuclide solution injection channel 30 is no longer connected. The electric heating ceramic layer 24 heats the material, which then travels through the stainless steel wall layer 25 of the tank to the fiber optic grating surface temperature measuring layer 26, and finally through the compacted bentonite block 27 to the fractured rock sample 38. An external seepage pump pipeline applies a head difference to the left and right ends of the fractured rock sample 38 through the rock sample pad 33, driving the seepage solution to seep along the original fractures in the fractured rock sample 38. As the seepage penetrates along the fractures into the compacted bentonite block 27, it reacts with the nano-zero valent iron in the micropores of the stainless steel wall layer 25 of the tank, increasing the permeability of the micropores. The pressure chamber 22 pushes the piston of the nuclide liquid isolation chamber 28 to move outward, increasing the leakage rate of the nuclide solution in the nuclide solution injection channel 30. The generated gas will form microchannels in the compacted bentonite block 27, increasing the seepage flow. Due to the high heat exchange efficiency of seepage, the fiber optic grating surface temperature measuring layer 26 will detect the local high temperature zone outside the corrosion zone. The seeped gas is discharged through the micropores of the rock sample pad 33 around the fractured rock sample 38 and is discharged from the gas pipeline 36 above the seepage liquid chamber 34, achieving gas-liquid separation. The Z-axis dynamic hydraulic cylinder 2 or the X-axis dynamic hydraulic cylinder 5 can be activated in combination to simulate the impact of seismic loads during long-term evolution, effectively assess the reactivation effect of dynamic disturbance on the permeability of existing fractures and the long-term damage evolution law of the surrounding rock of the treatment pit; finally, through the multi-field synergistic effect of the full-cycle simulation of high-level radioactive treatment pit excavation-heat-permeability coupling, the key process from excavation to closure on a ten-thousand-year scale can be continuously reproduced indoors.

[0035] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits, characterized in that: include: The true triaxial dynamic and static loading device is equipped with a movable bearing mechanism, which can carry the fractured rock sample to be tested and move the fractured rock sample to a set position. The true triaxial dynamic and static loading device is equipped with multiple dynamic and static loading mechanisms, which can apply dynamic and static loads in multiple directions to the fractured rock sample. A vertical excavation device is connected to the bottom of the dynamic and static loading mechanism at the top of the true triaxial dynamic and static loading device to realize a simulated excavation process of dynamic disturbance drilling on the center of fractured rock samples under deep geostress environment. The disposal pit reaction source device is placed in the disposal pit formed by excavating the fractured rock sample. The disposal pit reaction source device is used to seal the radionuclide solution and can regulate its temperature and pressure to simulate the radionuclide leakage process under the conditions of decay heat release and corrosion gas generation in the high-level radioactive waste canister. as well as The fissure seepage control device includes a rock sample pad installed on the outer wall of the fissure rock sample. It can apply a hydraulic head difference to the left and right end faces of the fissure rock sample in the horizontal direction through the rock sample pad, and drive the seepage solution to seep along the original fissures in the fissure rock sample.

2. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 1, characterized in that: The true triaxial dynamic and static loading device includes a host reaction frame, on which the dynamic and static loading mechanism is installed at the top, left and right sides and front and rear sides, and the movable bearing mechanism is provided in the internal cavity of the host reaction frame.

3. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 2, characterized in that: The dynamic and static loading mechanism includes a static load hydraulic cylinder, and a dynamic hydraulic cylinder is connected to the side of the static load hydraulic cylinder away from the mobile bearing mechanism. The bottom of the piston rod of the static load hydraulic cylinder located at the top of the host reaction frame is connected to the vertical excavation and excavation device. The piston rod ends of the static load hydraulic cylinders located on the left, right and front and rear sides of the host reaction frame are connected to force transmission rods. The ends of the force transmission rods abut against the rock sample pads in the mobile bearing mechanism to apply dynamic and static loads in multiple directions to the fractured rock sample.

4. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 3, characterized in that: An adjustment space is provided between the piston rod end of the static load hydraulic cylinder located on the front side of the host reaction frame and the force transmission rod located on the front side of the host reaction frame. A lifting guide rod is provided at the adjustment space. When the lifting guide rod rises to be coaxial with the piston rod of the static load hydraulic cylinder on the front side of the host reaction frame, both ends of the lifting guide rod can be connected to the piston rod end of the static load hydraulic cylinder on the front side of the host reaction frame and the outer side of the force transmission rod on the front side of the host reaction frame, respectively.

5. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 2, characterized in that: The mobile support mechanism includes a sample box, which is used to place fractured rock samples and fracture seepage control devices. The sample box is placed on the surface of the sample box platform, which is fixedly installed on the sample box moving mechanism. The sample box moving mechanism is located within the host reaction frame and can drive the sample box platform and the sample box to move synchronously to a set position.

6. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 3, characterized in that: The vertical drilling device includes a vertical drilling spindle. The top of the vertical drilling spindle is magnetically attached to the piston rod end of the dynamic and static load hydraulic cylinder at the top of the host reaction frame via a magnetic base. A tapered cutterhead is connected to the bottom of the vertical drilling spindle. A torque servo motor is mounted on the piston rod of the dynamic and static load hydraulic cylinder at the top of the host reaction frame. The torque servo motor is connected to the vertical drilling spindle via a transmission belt. A rotating bearing is fixedly connected to the top of the vertical drilling spindle. The rotating bearing is engaged in a groove in the magnetic base and is axially limited by the vertical drilling spindle. The rotating bearing can rotate horizontally within the groove. The interior of the vertical drilling spindle is hollow to form a rock cuttings discharge channel. A guide pipe is connected to the upper part of the rock cuttings discharge channel. The guide pipe is located inside the magnetic base and is externally connected to an air suction device.

7. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 6, characterized in that: The vertical excavation device also includes an outer shell with openings at both ends. The upper part of the outer shell contacts the magnetic base. A fixed support is placed on the top of the fractured rock sample. The lower part of the outer shell passes through the fixed support. The drilling spindle is located inside the outer shell. A slot is opened on the upper side wall of the outer shell. The transmission belt connects the torque servo motor to the vertical drilling spindle through the slot.

8. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 2, characterized in that: The reaction source device in the treatment pit is a columnar structure, which, from the inside out, consists of a pressure chamber, an inner stainless steel wall layer, an electrothermal ceramic layer, an outer stainless steel wall layer, a fiber optic grating surface temperature measuring layer, and compacted bentonite blocks. The inner stainless steel wall layer has multiple horizontally arranged micropores and horizontally arranged radionuclide liquid isolation chambers spaced vertically. A piston push rod displacement gauge is connected to the inner side of the micropores in the inner stainless steel wall layer, and the data line of the piston push rod displacement gauge is led out through the pressure chamber. A radionuclide liquid injection channel is located between the inner stainless steel wall layer and the electrothermal ceramic layer. An exhaust valve is connected to the bottom of the radionuclide liquid injection channel, which communicates with the micropores in the inner stainless steel wall layer. A diaphragm is located on the side of the radionuclide liquid isolation chamber closest to the micropores in the inner stainless steel wall layer, and a piston for the radionuclide liquid isolation chamber is located on the side away from the diaphragm. The piston for the radionuclide liquid isolation chamber is connected to the piston push rod displacement gauge. The connection is as follows: the outer side of the nuclide liquid isolation gas chamber piston is connected to the pressure chamber. When the pressure chamber is filled with air, pushing the nuclide liquid isolation gas chamber piston to move along the nuclide liquid isolation gas chamber towards the diaphragm, the air pressure in the nuclide liquid isolation gas chamber can push the diaphragm outward to block the nuclide solution injection channel, thereby separating the nuclide solution injection channel; micropores corresponding to the micropores of the inner stainless steel wall layer of the tank are opened on the electrothermal ceramic layer, the outer stainless steel wall layer of the tank, and the fiber optic grating surface temperature measuring layer. The micropores of the outer stainless steel wall layer of the tank are filled with a mixture of nano-zero valent iron and bentonite. A compacted bentonite block is provided on the side of the outer stainless steel wall layer away from the electrothermal ceramic layer. The top and bottom of the outer stainless steel wall layer of the tank are provided with extended plates to fix the compacted bentonite block; the fiber optic grating surface temperature measuring layer is located between the compacted bentonite block and the side wall of the outer stainless steel wall layer away from the electrothermal ceramic layer.

9. The full-cycle simulation system for multi-field coupling conditions in high-level radioactive waste disposal pits according to claim 2, characterized in that: The rock sample pad of the fracture seepage control device is installed at the four side wall positions of the fractured rock sample. The rock sample pad has a seepage liquid cavity. The internal space of the rock sample pad near the fractured rock sample is provided with an S-shaped heating pipeline. The upper surface of the rock sample pad has an opening. The opening is connected to the seepage liquid cavity through a seepage pipeline and a gas pipeline. The gas pipeline is nested outside the seepage pipeline.

10. An experimental method for a full-cycle simulation system of multi-field coupling conditions in a high-level radioactive disposal pit as described in any one of claims 1 to 9, characterized in that: Includes the following steps: During the excavation phase, the fractured rock sample is placed in the sample box and moved to the loading position by the sample box moving mechanism; the dynamic and static loading mechanisms located on the front, rear and left and right sides of the host reaction frame apply confining pressure to the fractured rock sample through the rock sample pad; at the same time, the heating pipeline in the rock sample pad simulates the deep temperature conditions where the fractured rock sample is located. Driven by a torque servo motor, the vertical drilling spindle rotates the tapered cutterhead. Excavation thrust is applied through the static hydraulic cylinder at the top of the host reaction frame, and excavation disturbance force is applied through the dynamic hydraulic cylinder at the top of the host reaction frame. This simulates the excavation process of dynamically disturbing the center of the fractured rock sample under deep geostress conditions. Rock cuttings generated during the drilling process enter the rock cuttings discharge channel inside the vertical drilling spindle through the tapered cutterhead opening and are discharged from the top of the guide tube by air extraction. After drilling is completed, the static load hydraulic cylinder at the top of the host reaction frame is raised, the tapered cutter head is withdrawn, and a treatment pit is formed; During the sealing phase, the confining pressure conditions and heating conditions of the rock sample pads from the previous phase are maintained. The reaction source device of the treatment pit is placed into the treatment pit, and the radionuclide solution is injected through the radionuclide solution injection channel at the top of the reaction source device. The gas in the radionuclide solution injection channel is discharged through the exhaust valve at the bottom. After the radionuclide solution is injected, the pressure chamber is pressurized, and under the action of pressure, the diaphragm of the radionuclide solution isolation chamber seals the radionuclide solution injection channel. The heating of the electrothermal ceramic layer is transmitted through the stainless steel wall layer outside the tank to the temperature measuring layer on the surface of the fiber optic grating, and finally conducted to the fractured rock sample after passing through the compacted bentonite block. The seepage pump pipeline applies a water head difference to the left and right end faces of the fractured rock sample through the rock sample pad, driving the seepage solution to seep along the original fractures in the fractured rock sample; As the seepage penetrates along the fissures into the compacted bentonite block and reacts with the nano-zero-valent iron in the micropores of the stainless steel wall layer outside the tank, the permeability of the micropores increases. The gas pressure chamber pushes the piston of the radionuclide liquid isolation gas chamber outward, increasing the leakage rate of the radionuclide solution in the injection channel. The generated gas will form microchannels in the compacted bentonite block, increasing the seepage flow. Due to the high heat exchange efficiency of the seepage, the temperature measuring layer on the surface of the fiber optic grating will detect the local high temperature zone outside the corrosion zone. The seeped gas is discharged through the micropores of the rock sample pad around the fissure rock sample and is discharged from the gas pipeline above the seepage liquid chamber, realizing gas-liquid separation.

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