Device for simulating migration of nuclide in multi-scale fracture system and application of device in calculation of nuclide migration parameters

Abstract

The invention provides a device for simulating migration of nuclides in a multi-scale fracture system and a method for calculating migration parameters of the nuclides in the multi-scale fracture system. The device comprises an injection pump, a fracture system and an automatic collector which are hermetically connected through a silicone tube. The fracture system comprises a rock block and four thin plates, n equal-thickness sections are formed in the middle of the rock block to serve as fracture water flow channels, all the sections start from the same side face of the rock block and end at the opposite side face of the side face, n sections penetrating through the whole rock block are formed, and n is a positive integer. The four thin plates cover the four side faces of the rock block and are used for blocking cracks of the four side faces, the thin plates and the rock block are fixed through sealant, and a crack water flow channel is blocked into a closed space. The device can simulate the migration process of nuclides in multi-scale fracture systems such as a single fracture, a cross fracture and a fracture grid, thereby calculating the migration parameters of the nuclides in the multi-scale fracture systems, and clarifying the migration characteristics of the nuclides in a heterogeneous fracture channel.

Description

Technical Field

[0001] This invention belongs to the field of radionuclide processing technology, and particularly relates to a device for simulating the migration of nuclides in a multi-scale fracture system and its application in calculating nuclide migration parameters. Background Technology

[0002] Deep geological disposal is internationally recognized as the most effective solution for disposing of high-level radioactive waste. Engineering barriers (such as steel containers and cement-solidified structures) and natural barriers (the surrounding rock and geological formations outside the engineering barriers) isolate high-level radioactive waste from the human living environment. Once the engineering barriers fail, natural barriers become the last line of defense against radionuclides entering the biosphere. Natural barriers contain numerous heterogeneous fracture channels, including single fractures at the micrometer-centimeter scale, intersecting fractures at the decimeter-meter scale, and fracture networks at the hundred-meter-kilometer scale. These heterogeneous fracture channels are the primary means by which radionuclides migrate into the biosphere via groundwater. Conducting research on the migration patterns of radionuclides in different fracture channels and understanding the transport characteristics and patterns of radionuclides in fracture systems is a crucial issue related to the development of the nuclear industry and national nuclear safety. Chinese patent CN116819041A discloses a simulation device for the migration of radionuclides in a single-fracture rock mass. This device features a detachable structure for easy cleaning, is easy to manufacture, and allows for adjustment of the fracture width according to the experimental plan. It has significant research value for simulating and predicting the migration characteristics of radionuclides. Chinese patent CN118670929A discloses an experimental device and method for simulating the migration of nuclides in a multi-scale single-fracture system. This device overcomes the scale dependence of nuclide migration parameters in laboratory fracture systems, providing important reference value for understanding the scale effects of nuclides in complex fracture systems.

[0003] However, the migration characteristics of nuclides differ across fracture systems. For example, the migration of nuclides in a single-fracture system is primarily influenced by the interaction and mass exchange between the nuclide and the matrix. In a cross-fracture system, migration is dominated by convection and dispersion, but also involves mass exchange between the fracture and the matrix. Furthermore, the migration of nuclides in a fracture network must consider factors such as local preferential flows and dominant channels. Currently, existing techniques generally explain the migration patterns of nuclides in fracture systems by simulating their migration characteristics in single-fracture systems. To investigate the migration patterns of nuclides in single fractures, cross-fractures, and fracture grids, and to elucidate the migration characteristics of nuclides in heterogeneous fracture channels, it is urgent to develop a device and method for simulating nuclide migration in multi-scale fracture systems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an apparatus for simulating the migration of radionuclides in a multi-scale fracture system and a method for calculating the migration parameters of radionuclides in a multi-scale fracture system. By controlling the type, angle, and thickness of the fracture system, the apparatus of this invention can adjust the experimental scale of radionuclide migration in fractures, thereby enabling the study of the migration characteristics of radionuclides in single-fracture systems, cross-fracture systems, and fracture grid systems, providing a foundation for exploring the migration laws of radionuclides in heterogeneous fracture channels.

[0005] In a first aspect, the present invention discloses an apparatus for simulating the migration of nuclides in a multi-scale fracture system. The apparatus includes an injection pump, a fracture system, an automatic collector, and a silicone tube. The outlet of the injection pump is connected to the inlet of the fracture system via the silicone tube, and the outlet of the fracture system is connected to the automatic collector via the silicone tube. The fracture system includes a rock block and four thin plates. The rock block has n equal-thickness cross-sections in its center as fracture water flow channels. Each cross-section begins on the same side of the rock block and terminates on the opposite side, forming n fracture water flow channels that penetrate the entire rock block. The four thin plates cover the four sides of the rock block to seal the fractures on the four sides. The thin plates are fixed to the rock block with sealant, sealing the fracture water flow channels into a closed space. Inlets and outlets are respectively opened along the fractures on one side of the rock block and on its opposite side of the thin plates; where n ≥ 1.

[0006] Furthermore, the thickness of the cross-section is 0.2 mm, 0.6 mm, or 1 mm.

[0007] Furthermore, the thin plate is made of plexiglass, and the sealant is made of silicone weather-resistant sealant.

[0008] Furthermore, the fracture system is a single fracture system, with a cross-section of equal thickness in the middle of the rock block as a fracture water flow channel. The cross-section starts from one side of the rock block and ends at the opposite side of the side, so as to form a fracture water flow channel that runs through the entire rock block. An inlet and an outlet are respectively opened along the fracture on the thin plate on one side and the opposite side of the rock block.

[0009] Furthermore, the fracture system is an intersecting fracture system, with two intersecting equal-thickness cross sections in the middle of the rock block serving as fracture water flow channels. The cross sections all start from the same side of the rock block and end at the opposite side of the same side, forming two fracture water flow channels that run through the entire rock block. Two inlets and two outlets are respectively opened along the two fractures on the thin plates on one side and the opposite side of the rock block.

[0010] Furthermore, the included angle between the two intersecting equal-thickness sections is 30° to 60°.

[0011] Furthermore, the fracture system is a fracture network system, with 2N equal-thickness cross-sections in the middle of the rock block serving as fracture water flow channels. Each cross-section starts from the same side of the rock block and terminates on the opposite side, forming 2N fracture water flow channels that run through the entire rock block. Among them, N cross-sections are arranged parallel to each other and intersect with another N parallel cross-sections. T inlets and (2N-T) outlets are opened along the 2N fractures on a thin plate on one side of the rock block, and 2N outlets are opened along the 2N fractures on a thin plate on the opposite side of the rock block. Wherein, N is an integer not less than 2, and 2≤T≤2N.

[0012] Furthermore, the included angle between the two intersecting sections is 30° to 60°.

[0013] Furthermore, integer N=2, integer T=2.

[0014] Secondly, the present invention also discloses a method for calculating the migration parameters of nuclides in a multi-scale fracture system. The method uses the apparatus described in the first aspect of the present invention to simulate the migration of nuclides in a multi-scale fracture system for calculation. The method includes: 1. Experimental Preparation Connect the injection pump and the automatic collector to the power supply, and set the injection flow rate of the injection pump and the time interval for the automatic collector to automatically collect samples; 2. Penetration test A tritium solution is loaded into the injection pump and injected into the fracture system at the set injection flow rate. Subsequently, deionized water is continuously injected into the fracture system through the injection pump at the set injection flow rate. The automatic collector automatically collects samples at pre-set time intervals, measures the tritium concentration of each sample, and plots the tritium penetration curve of the fracture system. 3. Nuclide migration experiment The radionuclide source solution is loaded into the injection pump and injected into the fracture system at the preset injection flow rate. Subsequently, deionized water is continuously injected into the fracture system through the injection pump at the preset injection flow rate. The automatic collector automatically collects samples at pre-set time intervals, measures the nuclide concentration of each sample, and plots the migration curves of the nuclides in the fracture system. 4. Multivariate repeated experiments By changing the geometric properties and / or water chemistry properties of the fracture system, including the number, angle, and thickness of the cross sections, and the water chemistry properties including the injection flow rate, pH value of the deionized water, and ionic strength in the deionized water, the experimental preparation, penetration experiment, and nuclide migration experiment were repeated to obtain the penetration curves of tritium in different fracture systems and the migration curves of nuclides in different fracture systems. 5. Data Processing Based on the penetration curves of tritium in different fracture systems, the time of the tritium concentration peak and the cumulative outflow at that moment are determined, the Darcy velocity is calculated, and the hydrodynamic dispersion of the multi-scale fracture system is obtained. Based on the migration curves of nuclides in different fracture systems, a nuclide migration numerical model is established, the nuclide migration curve is fitted, and the distribution coefficient of the nuclide in the multi-scale fracture system is solved.

[0015] This invention provides an apparatus for simulating the migration of nuclides in a multi-scale fracture system and a method for calculating the migration parameters of nuclides in such systems. This invention is a research result of the National Natural Science Foundation of China project: Study on the scale effect of nuclide migration in multi-scale fracture systems (Project No. U226721). Compared with existing technologies, the apparatus of this invention can simulate the migration process of nuclides in single fractures, intersecting fractures, and complex fracture grids. The apparatus and method of this invention can calculate the migration parameters of nuclides in multi-scale fracture systems, thereby elucidating the migration characteristics of nuclides in heterogeneous fracture channels. This provides a model basis for studying the migration laws of nuclides in fracture systems and provides a guarantee for the development of my country's nuclear industry and nuclear safety protection. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the single-crack system migration simulation device of the present invention.

[0018] Figure 2 This is a top view of the single-crack system of the present invention.

[0019] Figure 3 This is an exploded view of the single-crack system of the present invention.

[0020] Figure 4 This is a schematic diagram of the migration simulation device for the cross-crack system of the present invention.

[0021] Figure 5 This is a top view of the cross-crack system of the present invention.

[0022] Figure 6 This is an exploded view of the cross-crack system of the present invention.

[0023] Figure 7 This is a schematic diagram of the rock block structure in the cross-fracture system of the present invention.

[0024] Figure 8 This is a schematic diagram of the migration simulation device for the fracture network system of the present invention.

[0025] Figure 9 This is a perspective view of the fracture network system of the present invention.

[0026] Figure 10 This is an exploded view of the fracture network system of the present invention.

[0027] Figure 11 This is a schematic diagram of the rock block structure in the fracture network system of the present invention.

[0028] Explanation of reference numerals in the attached figures: 1. Injection pump, 2. Fracture system, 3. Automatic collector, 4. Silicone tubing, 5. Injection pump outlet, 6. Inlet, 7. Outlet, 8. Rock block, 9. Cross-section, 10. Upper side plate, 11. Lower side plate, 12. Left side plate, 13. Right side plate. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] Unless otherwise specified, the preferred embodiments of the present invention can be freely combined as needed. Those skilled in the art will understand that the data and various parameters described in the embodiments are merely exemplary and do not constitute a limitation of the present invention. The devices used in the following embodiments are all devices known in the art, and all devices used in the present invention can be obtained commercially.

[0031] Example 1 This embodiment provides a device for simulating the migration of nuclides in a single-crack system, such as... Figure 1As shown, the device includes a syringe pump 1, a fissure system 2, an automatic collector 3, and a silicone tube 4. The fissure system is a single-fissure system. The syringe pump outlet 5 is connected to the fissure system inlet 6 via the silicone tube 4, and the fissure system outlet 7 is connected to the automatic collector 3 via the silicone tube 4. In this embodiment, the syringe pump 1 is equipped with two 60mL syringes, and the syringe outlet is the syringe pump outlet 5. The flow rate adjustment range of the syringe pump 1 is 0.00001~20mL / min. The automatic collector 3 in this embodiment can be set to automatically collect samples at set time intervals, supporting up to 40 sample positions. The silicone tube 4 used in this embodiment has an inner diameter of 4mm, is chemically resistant, and is used to connect the syringe pump 1, the fissure system 2, and the automatic collector 3 to form a closed flow path.

[0032] like Figure 2 and 3 As shown, the single fracture system includes a rock block 8 and four thin plates. A cross-section 9 of equal thickness is opened in the middle of the rock block 8 as a fracture water flow channel. The thickness of the cross-section 9 is 0.6 mm. The cross-section 9 starts from the left side of the rock block 8 and ends at the right side of the rock block 8. Alternatively, it can be described as starting from the upper side of the rock block 8 and ending at the lower side of the rock block 8, thus forming a fracture water flow channel that runs through the entire rock block 8.

[0033] The upper side plate 10 and the lower side plate 11 of the four thin plates cover the upper and lower sides of the rock block 8, respectively, and the left side plate 12 and the right side plate 13 cover the left and right sides of the rock block 8, respectively, thereby sealing the cracks on the four sides of the rock block 8. The four thin plates are fixedly connected to the rock block 8 with sealant, sealing the water flow channels in the cracks into a closed space.

[0034] An inlet 6 is provided along the fissure on the left side plate 12 on the left side of rock block 8, located at the top of the left side plate 12; an outlet 7 is provided along the fissure on the right side plate 13 on the right side of rock block 8, located at the bottom of the right side plate 13. To realistically simulate the process of nuclides penetrating the barrier and migrating downwards through groundwater to the biosphere after barrier failure, in this embodiment and subsequent embodiments, the inlet of the fissure system is located at the top, and the outlet is located at the bottom, thus realistically simulating the downward migration process of nuclides. In this embodiment, rock block 8 is made of granite; however, other rock types can be used to realistically simulate different types of fissure systems. In this embodiment, all four thin plates are made of plexiglass; however, other chemically inert materials can also be used, with transparent materials being preferred for easy observation of the water flow in the fissure system. In this embodiment, ultra-high performance silicone weather-resistant sealant is used.

[0035] Example 2 This embodiment provides a device for simulating the migration of nuclides in a cross-crack system, such as... Figure 4 As shown, the device includes a syringe pump, a fissure system, two automatic collectors, and silicone tubing. The fissure system is a cross-fissure system. The syringe pump outlet is connected to the fissure system inlet via silicone tubing, and the fissure system outlet is connected to the automatic collectors via silicone tubing. The syringe pump in this embodiment is equipped with two 60mL syringes, and the syringe outlet is the syringe pump outlet. The flow rate of the syringe pump is adjustable from 0.00001 to 20mL / min. The automatic collectors in this embodiment can be set to automatically collect samples at set time intervals, supporting up to 40 sample positions. The silicone tubing used in this embodiment has an inner diameter of 4mm, is chemically resistant, and is used to connect the syringe pump, fissure system, and automatic collectors to form a closed flow path.

[0036] like Figure 5-7 As shown, the intersecting fracture system includes a rock block and four thin plates. Two intersecting sections of equal thickness are formed in the middle of the rock block as fracture water flow channels. The included angle between the two intersecting sections is 30°, and the thickness of each section is 0.6 mm. Both sections start from the left side of the rock block and end at the right side of the rock block. Alternatively, they can be described as starting from the upper side of the rock block and ending at the lower side of the rock block, thus forming two fracture water flow channels that run through the entire rock block.

[0037] The upper and lower side plates of the four thin plates cover the upper and lower sides of the rock block, respectively, while the left and right side plates cover the left and right sides of the rock block, respectively, thereby sealing the cracks on the four sides of the rock block. The four thin plates are fixedly connected to the rock block with sealant, sealing the water flow channels in the cracks into a closed space.

[0038] Two water inlets are provided along two fissures on the left side plate of the left side of the rock block, both located at the top of the left side plate; two water outlets are provided along two fissures on the right side plate of the right side of the rock block, both located at the bottom of the right side plate. In this embodiment, the rock block is made of granite, the four thin plates are all made of plexiglass, and the sealant is ultra-high performance silicone weather-resistant sealant.

[0039] Example 3 This embodiment provides a device for simulating the migration of nuclides in a cross-crack system. This device is identical to that in Embodiment 2, except that the included angle between the two intersecting, equally thick sections in the cross-crack system is 45°, and the thickness of each section is 0.2 mm. Figure 7 As shown.

[0040] Example 4 This embodiment provides a device for simulating the migration of nuclides in a cross-crack system. This device is identical to that in Embodiment 2, except that the included angle between the two intersecting, equally thick sections in the cross-crack system is 60°, and the thickness of each section is 0.6 mm. Figure 7 As shown.

[0041] Example 5 This embodiment provides a device for simulating the migration of nuclides in a fractured network system, such as... Figure 8 As shown, the device includes a syringe pump, a fissure system, six automatic collectors, and silicone tubing. The fissure system is a fissure network system. The syringe pump outlet is connected to the fissure system inlet via silicone tubing, and the fissure system outlet is connected to the automatic collectors via silicone tubing. In this embodiment, the syringe pump is equipped with two 60mL syringes, and the syringe outlet is the syringe pump outlet. The syringe pump flow rate is adjustable from 0.00001 to 20mL / min. The automatic collectors in this embodiment can be set to automatically collect samples at set time intervals, supporting up to 40 sample positions. The silicone tubing used in this embodiment has an inner diameter of 4mm, is chemically resistant, and is used to connect the syringe pump, fissure system, and automatic collectors to form a closed flow path.

[0042] like Figure 9-11 As shown, the fracture network system includes a rock block and four thin plates. Four equal-thickness sections are formed in the middle of the rock block as fracture water flow channels. All four sections begin on the left side and end on the right side of the rock block; alternatively, they can be described as beginning on the upper side and ending on the lower side, thus forming four fracture water flow channels that run through the entire rock block. Two sections are parallel to each other and intersect with two other parallel sections. The angle between any two intersecting equal-thickness sections is 30°, and each section has a thickness of 0.6 mm.

[0043] The upper and lower side plates of the four thin plates cover the upper and lower sides of the rock block, respectively, while the left and right side plates cover the left and right sides of the rock block, respectively, thereby sealing the cracks on the four sides of the rock block. The four thin plates are fixedly connected to the rock block with sealant, sealing the water flow channels in the cracks into a closed space.

[0044] Two water inlets and two water outlets are respectively opened at the four fissures on the left side plate of the left side of the rock block. The two water inlets are located at the top of the left side plate, and the two water outlets are located at the bottom of the left side plate. Four water outlets are opened at the four fissures on the right side plate of the right side of the rock block, and all four water outlets are located at the bottom of the right side plate. In this embodiment, the rock block is made of granite, the four thin plates are all made of plexiglass, and the sealant is ultra-high performance silicone weather-resistant sealant.

[0045] Example 6 This embodiment provides a device for simulating the migration of nuclides in a fracture network system. This device is identical to that in Embodiment 5, except that the included angle between any two intersecting equal-thickness sections in the fracture network system is 45°, and the thickness of each section is 1 mm. Figure 11 As shown.

[0046] Example 7 This embodiment provides a device for simulating the migration of nuclides in a fracture network system. This device is identical to that in Embodiment 5, except that the included angle between any two intersecting equal-thickness sections in the fracture network system is 60°, and the thickness of each section is 0.6 mm. Figure 11 As shown.

[0047] Example 8 This embodiment provides a method for calculating the migration parameters of nuclides in a multi-scale fracture system. The method uses the apparatus of this invention to simulate the migration of nuclides in a fracture system for calculation, including: 1. Experimental Preparation Assemble the device used in Example 1 to simulate the migration of nuclides in a single-crack system (0.6 mm), ensuring that the interface is sealed and leak-free; Using U-238 as the research object, a certain volume of U-238 source solution with a concentration of 150 Bq / mL was prepared; a certain volume of H-3 solution with a concentration of 700 Bq / mL was prepared. Connect the syringe pump and the automatic collector to the power supply. The injection flow rate of the syringe pump is adjustable from 10 to 40 mL / d. Set the injection flow rate to 10 mL / d and the automatic collector to automatically collect samples at a time interval of 2 hours. 2. Penetration test 10 mL of H-3 solution was loaded into the injection pump, and the injection pump injected the H-3 solution into the fracture system at the set injection flow rate; subsequently, the injection pump continuously injected deionized water with pH 3 and NaCl concentration of 0.001 mol / L into the fracture system at the set injection flow rate. The automatic collector automatically collects samples at pre-set time intervals, and the H-3 concentration in each sample is determined by a liquid scintillation counter to plot the H-3 penetration curve for the single fracture system. 3. Nuclide migration experiment 10 mL of U-238 source solution was loaded into the injection pump, and the source solution was injected into the fracture system at the set injection flow rate. Subsequently, deionized water with pH 3 and NaCl concentration of 0.001 mol / L was continuously injected into the fracture system at the set injection flow rate. The automatic collector automatically collects samples at pre-set time intervals, and the concentration of U-238 in each sample is determined by ICP-OES. The migration curve of U-238 in the single fracture system is plotted. 4. Multivariate repeated experiments (1) Change the number of cross sections: In this embodiment, the single fracture system (0.6 mm) is changed to a cross fracture system (45° / 0.6 mm) and a fracture network system (45° / 0.6 mm). Based on the changed fracture type, the above experimental preparation, penetration experiment and nuclide migration experiment were repeated to obtain the penetration curves of H-3 in different fracture systems and the migration curves of U-238 in different fracture systems. (2) Change the cross-sectional angle: In this embodiment, the single fracture system (0.6 mm) is changed to a cross fracture system (30° / 0.6 mm, 45° / 0.6 mm, 60° / 0.6 mm) and a fracture network system (30° / 0.6 mm, 45° / 0.6 mm, 60° / 0.6 mm). Based on the changed fracture angle, the above experimental preparation, penetration experiment and nuclide migration experiment were repeated to obtain the penetration curves of H-3 in different fracture systems and the migration curves of U-238 in different fracture systems. (3) Change the cross-sectional thickness: In this embodiment, the single fracture system (0.6 mm) is changed to a single fracture system (0.2 mm, 1 mm), a cross fracture system (45° / 0.2 mm, 45° / 0.6 mm, 45° / 1 mm), and a fracture network system (45° / 0.2 mm, 45° / 0.6 mm, 45° / 1 mm). Based on the changed fracture width, the above experimental preparation, penetration experiment and nuclide migration experiment were repeated to obtain the penetration curves of H-3 in different fracture systems and the migration curves of U-238 in different fracture systems. (4) Change the water chemical parameters: The single-fracture system (0.6 mm; 10 mL / d) in this embodiment can be changed to a single-fracture system (0.6 mm; 20 mL / d, 40 mL / d), a cross-fracture system (45° / 0.6 mm; 10 mL / d, 20 mL / d, 40 mL / d), or a fracture network system (45° / 0.6 mm; 10 mL / d, 20 mL / d, 40 mL / d). The single-fracture system (0.6 mm; pH=3) in this embodiment is changed to a single-fracture system (0.6 mm; pH=5, pH=8), a cross-fracture system (45° / 0.6 mm; pH=3, pH=5, pH=8), and a fracture network system (45° / 0.6 mm; pH=3, pH=5, pH=8). The single-fracture system (0.6 mm; NaCl concentration 0.001 mol / L) in this embodiment is changed to a single-fracture system (0.6 mm; NaCl concentration 0.01 mol / L, NaCl concentration 0.1 mol / L), a cross-fracture system (45° / 0.6 mm; NaCl concentration 0.001 mol / L, NaCl concentration 0.01 mol / L, NaCl concentration 0.1 mol / L), and a fracture network system (45° / 0.6 mm; NaCl concentration 0.001 mol / L, NaCl concentration 0.01 mol / L, NaCl concentration 0.1 mol / L). Based on the modified water chemistry parameters, the above experimental preparation, penetration experiment and nuclide migration experiment were repeated to obtain the penetration curves of H-3 in different fracture systems and the migration curves of U-238 in different fracture systems. 5. Data Processing Based on the penetration curves of H-3 in different fracture systems, the time of the H-3 concentration peak and the cumulative outflow at that moment are determined, the Darcy velocity is calculated, and the hydrodynamic dispersion of the multi-scale fracture system is obtained. Based on the migration curves of U-238 in different fracture systems, a nuclide migration numerical model was established, the nuclide migration curves were fitted, and the distribution coefficients of the nuclide in the multi-scale fracture system were solved.

[0048] In summary, this invention provides an apparatus for simulating the migration of nuclides in multi-scale fracture systems, as well as a method for calculating the migration parameters of nuclides in multi-scale fracture systems. The apparatus of this invention can simulate the migration process of nuclides in multi-scale fracture systems such as single fractures, intersecting fractures, and complex fracture grids. Through the apparatus and method of this invention, the migration parameters of nuclides in multi-scale fracture systems can be calculated, thereby elucidating the migration characteristics of nuclides in heterogeneous fracture channels. This provides a model basis for studying the migration laws of nuclides in fracture systems and provides a guarantee for the development of my country's nuclear industry and nuclear safety protection.

[0049] The materials and equipment used in this invention are all commercially available. The above description is only a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for simulating the migration of nuclides in a multi-scale fracture system, characterized in that, The device includes an injection pump, a fissure system, an automatic collector, and a silicone tube; the outlet of the injection pump is connected to the inlet of the fissure system via the silicone tube, and the outlet of the fissure system is connected to the automatic collector via the silicone tube. The fracture system includes a rock block and four thin plates. The rock block has n equal-thickness cross sections in the middle as fracture water flow channels. The cross sections all start from the same side of the rock block and end at the opposite side of the side, so as to form n fracture water flow channels that run through the entire rock block. Four thin plates are applied to the four sides of the rock block to seal the cracks on the four sides. The thin plates are fixed to the rock block with sealant to seal the water flow channels in the cracks into a closed space. Water inlets and outlets are respectively opened on the thin plates on one side and the opposite side of the rock block along the cracks. Where n≥1.

2. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 1, characterized in that, The thickness of the cross section is 0.2 mm, 0.6 mm, or 1 mm.

3. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 1, characterized in that, The thin plate is made of plexiglass, and the sealant is made of silicone weather-resistant sealant.

4. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 1, characterized in that, The fracture system is a single fracture system. A cross-section of equal thickness is opened in the middle of the rock block as a fracture water flow channel. The cross-section starts from one side of the rock block and ends at the opposite side of the side to form a fracture water flow channel that runs through the entire rock block. An inlet and an outlet are respectively opened along the fracture on the thin plate on one side and the opposite side of the rock block.

5. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 1, characterized in that, The fracture system is an intersecting fracture system, with two intersecting equal-thickness cross sections in the middle of the rock block serving as fracture water flow channels. The cross sections all start from the same side of the rock block and end at the opposite side of the same side, forming two fracture water flow channels that run through the entire rock block. Two inlets and two outlets are respectively opened along the two fractures on the thin plates on one side and the opposite side of the rock block.

6. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 5, characterized in that, The included angle between the two intersecting sections of equal thickness is 30° to 60°.

7. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 1, characterized in that, The fracture system is a fracture network system. 2N equal-thickness cross-sections are formed in the middle of the rock block as fracture water flow channels. Each cross-section starts on the same side of the rock block and terminates on the opposite side, forming 2N fracture water flow channels that run through the entire rock block. N cross-sections are arranged parallel to each other and intersect with another N parallel cross-sections. T inlets and (2N-T) outlets are opened along the 2N fractures on a thin plate on one side of the rock block, and 2N outlets are opened along the 2N fractures on a thin plate on the opposite side of the rock block. N is an integer not less than 2, and 2 ≤ T ≤ 2N.

8. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 7, characterized in that, The included angle between the two intersecting sections is 30° to 60°.

9. The apparatus for simulating the migration of nuclides in a multi-scale fracture system according to claim 7, characterized in that, Integer N=2, integer T=2.

10. A method for calculating the migration parameters of nuclides in a multi-scale fracture system, characterized in that, The method uses the apparatus for simulating the migration of nuclides in a multi-scale fracture system as described in any one of claims 1-9 for calculation, and the method includes:

1. Experimental Preparation Connect the injection pump and the automatic collector to the power supply, and set the injection flow rate of the injection pump and the time interval for the automatic collector to automatically collect samples; 2. Penetration test A tritium solution is loaded into the injection pump and injected into the fracture system at the set injection flow rate. Subsequently, deionized water is continuously injected into the fracture system through the injection pump at the set injection flow rate. The automatic collector automatically collects samples at pre-set time intervals, measures the tritium concentration of each sample, and plots the tritium penetration curve of the fracture system.

3. Nuclide migration experiment The radionuclide source solution is loaded into the injection pump and injected into the fracture system at the preset injection flow rate. Subsequently, deionized water is continuously injected into the fracture system through the injection pump at the preset injection flow rate. The automatic collector automatically collects samples at pre-set time intervals, measures the nuclide concentration of each sample, and plots the migration curves of the nuclides in the fracture system.

4. Multivariate repeated experiments By changing the geometric properties and / or water chemistry properties of the fracture system, including the number, angle, and thickness of the cross sections, and the water chemistry properties including the injection flow rate, pH value of the deionized water, and ionic strength in the deionized water, the experimental preparation, penetration experiment, and nuclide migration experiment were repeated to obtain the penetration curves of tritium in different fracture systems and the migration curves of nuclides in different fracture systems.

5. Data Processing Based on the penetration curves of tritium in different fracture systems, the time of the tritium concentration peak and the cumulative outflow at that moment are determined, the Darcy velocity is calculated, and the hydrodynamic dispersion of the multi-scale fracture system is obtained. Based on the migration curves of nuclides in different fracture systems, a nuclide migration numerical model is established, the nuclide migration curve is fitted, and the distribution coefficient of the nuclide in the multi-scale fracture system is solved.

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