A method for calculating parameters of radionuclide bedrock fracture migration

Abstract

The present invention relates to a method for calculating the migration parameters of radioactive nuclides in bedrock fissures. The method aims to solve the technical problem that the existing technology generalizes the fractured rock mass that crosses each other into a network into an equivalent continuous medium, does not consider the exact position and size of each fracture, and averages the permeability of the fracture into the rock mass according to the flow equivalence principle, resulting in distortion of the calculation results of groundwater seepage and nuclides migration. The method disclosed in the present invention is to artificially manufacture a two-dimensional single fracture surface in the laboratory, start from the seepage characteristics of the single fracture surface, obtain the nuclides migration parameters of the single fracture surface, and then apply them to each single fracture in the fracture network to realize the network model calculation of bedrock fracture media. The radioactive nuclides migration parameters calculated by the method for calculating the migration parameters of radioactive nuclides in bedrock fissures described in the present invention have a high degree of fit with the actual situation, are scientific and rigorous, and have high reliability, which is of great significance to the site selection of nuclear power plants, nuclear radiation protection and pollution control.

Description

Technical Field

[0001] The invention belongs to the field of radiation protection, and in particular relates to a method for calculating radionuclide bedrock fissure migration parameters. Background Art

[0002] At present, in the study of the migration of radionuclides in bedrock fissure media, the fractured rock mass that intersects each other into a network is usually generalized as an equivalent continuous medium. The analysis is based on the mature porous media seepage theory, ignoring the exact position and size of each fracture, and the permeability of the fracture is averaged into the rock mass according to the flow equivalence principle. The discontinuity and anisotropy of water flow in the fracture are ignored, resulting in a considerable deviation between the theoretical calculation of groundwater seepage and radionuclide migration and the actual situation, and distorted evaluation results.

[0003] Therefore, in order to accurately and reasonably evaluate the migration behavior of radionuclides in bedrock fracture media, it is necessary to artificially create a two-dimensional single fracture surface in the laboratory, starting from the seepage characteristics of the single fracture surface, and obtaining the nuclide migration parameters of the single fracture surface. This can then be applied to each single fracture in the fracture network to realize the network model calculation of the bedrock fracture medium. Summary of the invention

[0004] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for calculating the migration parameters of radioactive nuclides in bedrock fractures. By artificially manufacturing a two-dimensional single fracture surface in the laboratory, starting from the seepage characteristics of the single fracture surface, the radionuclide migration parameters of the single fracture surface are obtained, which can then be applied to each single fracture in the fracture network to realize the network model calculation of the bedrock fracture medium.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is: a method for calculating the migration parameters of radioactive nuclides in bedrock fissures, the method comprising the following steps:

[0006] S1. forming a single fracture surface with specific requirements, designing water flow characteristic tests under different hydraulic gradients for the single fracture surface, and determining the relationship curve between the hydraulic gradient and the flow velocity value in the single fracture surface;

[0007] S2. Inject radioactive tracer nuclides into the injection holes of the single fracture surface under a set hydraulic gradient, regularly extract effluent from the sampling holes of the single fracture surface, measure the volume and the concentration data of the nuclides, and obtain the migration curves of the nuclides in the longitudinal and transverse directions;

[0008] S3, establishing a single fracture nuclide migration numerical model, and fitting and solving the migration parameters of the nuclide according to the longitudinal and transverse migration curves of the nuclide obtained in step S2.

[0009] Furthermore, step S3 also includes: establishing a corresponding single fracture nuclide migration numerical model according to the relationship curve between hydraulic gradient and flow velocity value in step S1 and the longitudinal and transverse migration curves of the nuclide obtained in the sampling hole in step S2.

[0010] Furthermore, the crack width of the single crack surface described in step S1 is much smaller than the length of the crack.

[0011] Furthermore, in step S1, an injection hole is arranged on the upper rock plate, and a plurality of sampling holes are arranged in the horizontal direction and the vertical direction, and the spacing between the sampling holes gradually widens from top to bottom in the vertical direction.

[0012] Further, step S1 includes designing different hydraulic gradients J by controlling the water level difference between the upper and lower overflow grooves on the single fracture surface, and measuring the water flow velocity V passing through the fracture width.

[0013] Furthermore, the water flow movement characteristics of the single fracture surface in step S1 are obtained by fitting the multiple sets of flow velocity V and hydraulic gradient J data to obtain a relationship curve between flow velocity V and hydraulic gradient J, and based on this, it is determined whether the water flow movement is laminar or turbulent.

[0014] Furthermore, the water level difference between the upper and lower overflow tanks on the single fracture surface is controlled to ensure that the hydraulic gradient in step S2 is J, and the hydraulic gradient J is the hydraulic gradient obtained in step S1 that conforms to the specific motion equation relationship.

[0015] Furthermore, the nuclide migration parameters in step S3 include the longitudinal dispersivity α L and the lateral dispersion α T .

[0016] Furthermore, in step S3, a triangular mesh is used to mesh the single fracture nuclide migration numerical model.

[0017] Further, in step S2, samples are taken from the longitudinal sampling holes N7 and N9, the effluent is measured, and the longitudinal migration curve of the nuclide is obtained, and samples are taken from the transverse sampling holes N1, N3, N12, and N14, the effluent is measured, and the transverse migration curve of the nuclide is obtained, wherein the transverse sampling holes N1 and N14 are symmetrically positioned, and the transverse sampling holes N3 and N12 are symmetrically positioned.

[0018] The effect of the present invention is that: the method for calculating the migration parameters of radioactive nuclides in bedrock fissures disclosed in the present invention obtains the migration parameters of radionuclides in the single fracture surface by artificially manufacturing a two-dimensional single fracture surface in the laboratory and starting from the seepage characteristics of the single fracture surface, and then applies it to each single fracture in the fracture network to realize the network model calculation of the bedrock fracture medium. The calculated migration parameters of radionuclides have a high degree of fit with the actual situation, are scientific and rigorous, and have high reliability, which is of great significance to the site selection of nuclear power plants, nuclear radiation protection and pollution control. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the position arrangement of injection holes and sampling holes on a single fracture surface in a method for calculating the migration parameters of radioactive nuclides in bedrock fractures according to the present invention;

[0020] Figure 2 It is a curve diagram showing the relationship between the hydraulic gradient and the flow velocity value in a single fracture surface obtained by fitting the data in Table 1 in a method for calculating the migration parameters of radioactive nuclides in bedrock fractures according to the present invention;

[0021] Figure 3 The nuclide obtained in the method for calculating the migration parameters of radioactive nuclides in bedrock fissures according to the present invention 3 Migration curve of H at the longitudinal and transverse sampling hole positions on a single fracture surface;

[0022] Figure 4 The method for calculating the migration parameters of radioactive nuclides in bedrock fissures according to the present invention is based on Figure 3 The longitudinal and transverse migration curves of the nuclide in the figure are fitted to solve the migration parameter diagram of the nuclide. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] Embodiment 1

[0025] The degree of development of bedrock fractures can be divided into single fracture scale, two-dimensional fracture network scale, and three-dimensional fracture network scale of fracture surfaces interacting with each other from simple to complex. A single fracture is the basis of the fracture network. A series of single fractures can form a fracture network. To study the complex seepage state in rock fractures, we must first start with the seepage characteristics of a single fracture surface. After obtaining the radionuclide migration parameters of a single fracture surface, we can apply them to each single fracture in the fracture network to realize the network model calculation of bedrock fracture media.

[0026] A method for calculating radionuclide bedrock fissure migration parameters disclosed in the present invention comprises the following steps:

[0027] S1: Form a single fracture surface with specific requirements, design water flow characteristic tests under different hydraulic gradients for the single fracture surface, and determine the relationship curve between the hydraulic gradient and the flow velocity value in the single fracture surface. In this embodiment, the single fracture surface is formed by using upper and lower bedrock slabs, and the fracture width of the single fracture surface is controlled. Taking the slightly weathered biotite granodiorite as an example, the dimensions of the upper and lower granite slabs are length × width × thickness = 1.2m × 0.8m × 0.1m, and the fracture width is controlled to be 2mm for illustration, but in fact, there is no limitation on this.

[0028] Injection holes are arranged on the upper slab of the slightly weathered biotite granodiorite to inject tracer nuclides; a certain number of sampling holes are arranged along the longitudinal and transverse directions of the upper slab to regularly extract effluent from the sampling holes and measure the volume and concentration of nuclides.

[0029] In this embodiment, one injection hole is arranged on the upper rock plate of the slightly weathered biotite granodiorite, four sampling holes are arranged in the longitudinal direction of the rock plate, and 10 sampling holes are arranged in the transverse direction, and the hole diameters are all 1.0 cm. Figure 1 As shown, the sampling holes N7 and N9 are arranged longitudinally, and the sampling holes N1, N3, N12, and N14 are arranged transversely. The transverse sampling holes N1 and N14 are symmetrically positioned, and the positions of N3 and N12 are symmetrical. Due to the diffusion effect, the concentration distribution range of the nuclides in the transverse direction increases, and the spacing between the sampling holes gradually widens from top to bottom.

[0030] The crack width is constant and much smaller than the crack length, ensuring that the single crack surface conforms to the two-dimensional plane model.

[0031] The key to the single fracture model is to determine whether the water flow is laminar or turbulent based on the relationship between flow velocity and hydraulic gradient. In laminar flow, the hydraulic gradient is linearly related to the flow velocity, which conforms to the Darcy equation; in turbulent flow, the hydraulic gradient is nonlinearly related to the flow velocity.

[0032] Different hydraulic gradients J were designed by controlling the water level difference of the upstream and downstream overflow tanks on the single fracture surface, and the water flow velocity V through the fracture width was measured. 11 different hydraulic gradients J were designed, and the flow velocity value V data under different hydraulic gradients were obtained as shown in Table 1. The results of the water flow characteristic experiment showed that within the hydraulic gradient range of 0.0033 to 0.0458, the flow velocity and hydraulic gradient were linearly related, belonging to laminar flow, and conforming to the Darcy equation. Figure 2 As shown, the data in Table 1 are fitted to obtain a relationship curve between flow velocity V and hydraulic gradient J. The permeability coefficient K is the slope K of the straight line, K=304.46 cm / s.

[0033] Table 1 Correspondence between hydraulic gradient J and flow velocity V

[0034]

[0035] S2: Under the set hydraulic gradient, the tracer radioactive nuclide is injected into the injection hole of the single fracture surface, the effluent is regularly extracted from the sampling hole of the single fracture surface, the volume and the concentration data of the nuclide are measured, and the migration curve of the nuclide in the longitudinal and transverse directions is obtained.

[0036] In this example, the nuclides considered 3 H, 3 H will penetrate quickly in a single fracture. In order to ensure that the effluent can be extracted in time in the sampling hole, the minimum hydraulic gradient of 0.0033 is selected for 3 H migration test. By instantaneous injection, 3 H is injected from the injection hole.

[0037] like Figure 3 As shown, samples are taken from the longitudinal sampling holes N7 and N9, and the effluent is measured to obtain the migration curve of the nuclide in the longitudinal direction. Samples are taken from the transverse sampling holes N1, N3, N12, and N14, and the effluent is measured to obtain the migration curve of the nuclide in the transverse direction. Among them, the transverse sampling holes N1 and N14 are symmetrically located, and the positions of N3 and N12 are symmetrical. In this embodiment, 0.5 mL is sampled each time, and the sampling time interval is 10s for example.

[0038] S3: Establish a single-crack nuclide migration numerical model, and according to the longitudinal and transverse migration curves of the nuclide obtained in the sampling hole in step S2, fit and solve the migration parameters of the nuclide.

[0039] According to the experimental results of water flow characteristics in step S1, the Darcy equation can be used to describe the movement of water flow in the single fracture surface. Using triangular meshing, the upper and lower granite slabs and the middle fracture are divided into 18 layers, generating a total of 186,211 nodes and 345,536 triangular meshes. Combined with the adsorption characteristics and decay of nuclides, a numerical model of nuclide migration in a single fracture is established.

[0040] like Figure 4 As shown, according to Figure 3 The longitudinal and transverse migration curves of the nuclide on a single fracture surface are obtained by fitting and calculating the key migration parameters of the nuclide such as the longitudinal dispersivity α L and the lateral dispersion α T In this embodiment, according to Figure 3 Medium nuclide 3 The longitudinal and transverse concentration migration curves of H on a single fracture surface give the longitudinal dispersion α L is 32.4 mm, and the lateral dispersion α T It is 2.72mm.

[0041] It can be seen from the above embodiments that the method for calculating the migration parameters of radioactive nuclides in bedrock fissures disclosed in the present invention is aimed at the existing problems that the fractured rock mass that crosses each other into a network is generalized as an equivalent continuous medium, the exact position and size of each fracture are not considered, the permeability of the fracture is homogenized into the rock mass according to the flow equivalence principle, and the discontinuity and anisotropy of the water flow in the fracture are ignored, resulting in a considerable deviation between the theoretical calculation of groundwater seepage and nuclide migration and the actual situation, and the technical problem of distorted evaluation results. The method disclosed in the present invention is to artificially manufacture a two-dimensional single fracture surface in the laboratory, start from the seepage characteristics of the single fracture surface, obtain the nuclide migration parameters of the single fracture surface, and then apply it to each single fracture in the fracture network to realize the network model calculation of the bedrock fracture medium. The calculated radioactive nuclide migration parameters have a high degree of fit with the actual situation, are scientific and rigorous, and have high reliability, which is of great significance to the site selection of nuclear power plants, nuclear radiation protection and pollution control.

[0042] The method described in the present invention is not limited to the embodiments described in the specific implementation manner. Those skilled in the art may derive other implementation manners based on the technical solution of the present invention, which also fall within the technical innovation scope of the present invention.

Claims

1. A method for calculating radionuclide bedrock fissure migration parameters, the method comprising the following steps: S1. forming a single fracture surface with specific requirements, designing water flow characteristic tests under different hydraulic gradients for the single fracture surface, and determining the relationship curve between the hydraulic gradient and the flow velocity value in the single fracture surface; S2. Inject radioactive tracer nuclides into the injection holes of the single fracture surface under a set hydraulic gradient, regularly extract effluent from the sampling holes of the single fracture surface, measure the volume and the concentration data of the nuclides, and obtain the migration curves of the nuclides in the longitudinal and transverse directions; S3, establishing a single fracture nuclide migration numerical model, and fitting and solving the migration parameters of the nuclide according to the longitudinal and transverse migration curves of the nuclide obtained in step S2.

2. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 1, characterized in that: Step S3 also includes: establishing a corresponding single fracture nuclide migration numerical model according to the relationship curve between hydraulic gradient and flow velocity value in step S1 and the longitudinal and transverse migration curves of the nuclide obtained in the sampling hole in step S2.

3. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 1, characterized in that: The crack width of the single crack surface described in step S1 is much smaller than the length of the crack.

4. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 1, characterized in that: Step S1 also includes arranging an injection hole on the upper rock plate, and setting a plurality of sampling holes in the horizontal direction and the vertical direction, wherein the spacing between the sampling holes gradually increases from top to bottom in the vertical direction.

5. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 1, characterized in that: Step S1 includes designing different hydraulic gradients J by controlling the water level difference between the upper and lower overflow channels on the single fracture surface, and measuring the water flow velocity V passing through the fracture width.

6. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 5, characterized in that: The water flow movement characteristics of the single fracture surface in step S1 are obtained by fitting the multiple sets of flow velocity V and hydraulic gradient J data to obtain a relationship curve between flow velocity V and hydraulic gradient J, and based on this, determine whether the water flow movement is laminar or turbulent.

7. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 6, characterized in that: The water level difference between the upper and lower overflow tanks on the single fracture surface is controlled to ensure that the hydraulic gradient in step S2 is J, and the hydraulic gradient J is the hydraulic gradient obtained in step S1 that conforms to the specific motion equation relationship.

8. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 1, characterized in that: The nuclide migration parameters in step S3 include the longitudinal dispersivity α L and the lateral dispersion α T .

9. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 1, characterized in that: In step S3, a triangular mesh is used to mesh the single fracture nuclide migration numerical model.

10. A method for calculating radionuclide bedrock fissure migration parameters as claimed in claim 1, characterized in that: In step S2, samples are taken from the longitudinal sampling holes N7 and N9, and the effluent is measured to obtain the longitudinal migration curve of the nuclide. Samples are taken from the transverse sampling holes N1, N3, N12, and N14, and the effluent is measured to obtain the transverse migration curve of the nuclide, wherein the transverse sampling holes N1 and N14 are symmetrically positioned, and the transverse sampling holes N3 and N12 are symmetrically positioned.

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