Method for determining design parameter index of cushioning material based on effective density of montmorillonite

Abstract

The present invention discloses a method for determining buffer material design parameter indicators based on the effective density of montmorillonite. In response to the current situation of high-level radioactive waste geological disposal repositories in my country, the average dry density and saturated density parameters of the buffer material installed in the disposal hole are obtained based on the effective dry density of montmorillonite in bentonite, thereby obtaining buffer material design parameter indicators that meet the design requirements of high-level radioactive waste deep geological disposal repositories. Since the montmorillonite content in bentonite has a wide distribution range, the complexity and diversity of indoor bentonite testing increase. However, the method of the present invention is simple, facilitates the preparation of test samples, and reduces the experimental workload. In the absence of experimental data, the method can be directly applied to the parameter design of buffer materials with different montmorillonite contents based on a general calculation method proposed based on basic soil theory. The method is highly scientific, economical, practical, and convenient, and provides a reliable basis and technical input for the design of buffer materials in high-level radioactive waste geological disposal repositories.

Description

Technical Field

[0001] The present invention relates to the technical field of high-level radioactive waste disposal, and in particular to a method for calculating design parameter indicators of buffer materials with different montmorillonite contents in a vertical disposal mode of a deep geological repository for high-level radioactive waste based on the effective dry density of montmorillonite. Background Art

[0002] A deep geological repository for high-level radioactive waste (HLW) is a specialized facility for the permanent disposal of HLW. my country currently utilizes a multi-barrier deep geological disposal method to protect humans and the environment from the harmful effects of ionizing radiation. The engineering barriers at these HLW repositories primarily consist of the HLW itself, the disposal container, and buffer materials. Buffer materials are a crucial component of the repository's multi-barrier system. Bentonite, due to its extremely low permeability and excellent radionuclide adsorption properties, has been selected as a buffer material in numerous countries. my country has initially selected bentonite from Gaomiaozi, Inner Mongolia, as its buffer material. Determining the design parameters for buffer materials is crucial; however, research on determining these parameters prior to installation is limited and complex. Summary of the Invention

[0003] In view of the above technical problems existing in the prior art, the purpose of the present invention is to provide a calculation method for determining the design parameter indicators of buffer materials with different montmorillonite contents in the vertical disposal mode of high-level radioactive waste disposal repository based on the effective density of montmorillonite.

[0004] To achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows: a method for determining the design parameter index of a buffer material based on the effective density of montmorillonite, comprising the following steps:

[0005] (1) First, a type of bentonite is selected. Under the condition that the design index requirements of the buffer material (including permeability and swelling) are met, the standard value of the dry density of the buffer material before installation prepared by this bentonite is determined.

[0006] (2) calculating the effective dry density of the montmorillonite in the bentonite based on the standard value of the dry density of the buffer material before installation prepared from the bentonite and the standard value of the montmorillonite content in the bentonite;

[0007] (3) calculating the dry density of the buffer material before installation with different montmorillonite contents based on the effective dry density of the montmorillonite obtained above;

[0008] (4) Based on the dry density of the buffer material before installation obtained above, the average dry density of the buffer material blocks after installation is obtained by calculating and analyzing various working conditions during the treatment process.

[0009] (5) Based on the average dry density of the buffer material blocks after installation obtained above, calculate the saturated density of the buffer material blocks after installation that meets the functional requirements and design requirements of the high-level radioactive waste geological disposal repository for buffer materials.

[0010] Furthermore, in step (1), a type of bentonite is selected, and combined with the indoor test results of the bentonite, the test takes into account factors such as the gap inside the disposal hole of the disposal repository, the gap outside the disposal hole, the allowable deviation of the dry density of the buffer material blocks and the bentonite particles filling the gap, while meeting the requirements of the buffer material design indicators such as permeability and expansibility, and determining the standard value of the dry density of the buffer material before installation prepared from the bentonite.

[0011] Furthermore, in step (3), for the same bentonite, the montmorillonite content is different, but the effective dry density of the montmorillonite is a constant; the dry density of the buffer material with different montmorillonite contents is calculated based on the effective dry density of the montmorillonite; the effective dry density of the montmorillonite is a quantitative indicator for characterizing the montmorillonite content in the material, which refers to the ratio of the mass of montmorillonite in the buffer material to the sum of the volume of the buffer material and the pore volume.

[0012] Furthermore, in step (4), the installed buffer material blocks include solid buffer material blocks and annular buffer material blocks; the solid buffer material blocks are located at the top and bottom of the disposal container; and the annular buffer material blocks are located around the disposal container.

[0013] Furthermore, in step (5), the dry density of the buffer material blocks after installation and the relationship between the porosity ratio and the dry density are obtained according to different working conditions of the disposal process in the disposal repository to obtain the saturated density of the buffer material blocks after installation in the disposal hole.

[0014] The technical solution adopted by the present invention has the beneficial effects of determining the design parameter index of the buffer material based on the effective density of montmorillonite, selecting a bentonite as the buffer material, and obtaining the average dry density and saturated density parameters of the buffer material blocks after installation based on the effective dry density of montmorillonite in the bentonite in view of the development status of the existing high-level radioactive waste geological disposal repositories in China, thereby obtaining the design parameter index of the buffer material that meets the design requirements of the high-level radioactive waste deep geological disposal repositories; since the montmorillonite content in bentonite has a wide distribution range, the complexity and diversity of indoor tests of bentonite are increased, while the method of the present invention is simple, easy to prepare test samples, and reduces the workload of the test; in the absence of test data, the general calculation method proposed based on the basic theory of soil can be directly applied to the design of the parameters of the buffer material blocks of bentonite with different montmorillonite contents; the method has high scientificity, economy, practicality and convenience, and can provide reliable data support for the design of buffer materials in high-level radioactive waste geological disposal repositories. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flow chart of a method for determining design parameter indicators of a buffer material based on the effective density of montmorillonite according to the first embodiment of the present invention;

[0016] Figure 2 This is a schematic structural diagram of a vertical disposal hole for a high-level radioactive waste deep geological repository according to a first embodiment of the present invention;

[0017] Figure 3 1 is a schematic cross-sectional view of a vertical disposal hole of a deep geological repository for high-level radioactive waste according to a first embodiment of the present invention;

[0018] Figure 4 is the relationship between the montmorillonite content of the solid building blocks of the buffer material and the average dry density of the solid building blocks of the buffer material after installation in Example 2 of the present invention;

[0019] Figure 5 This is the relationship between the montmorillonite content of the solid building blocks of the buffer material and the saturation density of the solid building blocks of the buffer material after installation of the second embodiment of the present invention.

[0020] Among them, there are a solid building block 1 of the post-installation buffer material, a ring-shaped building block 2 of the post-installation buffer material, a disposal container 3, an outer gap 4, and an inner gap 5. DETAILED DESCRIPTION

[0021] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0022] The reference design for buffer materials is based on an analysis of factors such as the functional requirements of the buffer material and the properties of the barrier system. The dry density of the bentonite used in the repository is determined based on permeability and swelling requirements. Since the swelling and permeability of bentonite in the repository are primarily determined by its montmorillonite content, there is a correlation between montmorillonite content and bentonite density.

[0023] Example 1

[0024] Refer to the attached Figure 1 、 2 The method for determining the design parameter index of a buffer material based on the effective density of montmorillonite according to the first embodiment of the present invention comprises the following steps:

[0025] (1) First, based on a bentonite, combined with the indoor test results of the bentonite, and considering the main influencing factors in the vertical disposal method (mainly including the gap outside the disposal hole, the allowable deviation of the dry density of the buffer material blocks and particles), under the condition that the design index requirements of the buffer material (including permeability and expansibility) are met, the standard value of the dry density of the buffer material prepared by the bentonite before installation is obtained;

[0026] (2) calculating the effective dry density ρ' of the montmorillonite in the bentonite based on the standard value of the dry density of the buffer material before installation and the standard value of the montmorillonite content in the bentonite;

[0027] (3) Taking the standard value of the dry density of the buffer material before installation as the reference value, the dry density ρ of the buffer material before installation prepared from bentonite with different montmorillonite contents was calculated in combination with the effective dry density ρ' of montmorillonite and the content of montmorillonite in bentonite. db ;

[0028] (4) According to the dry density ρ of the buffer material before installation obtained above db By calculating and analyzing various working conditions during the disposal process, the average dry density of the buffer material blocks after installation is obtained. d ;

[0029] (5) Based on the average dry density of the buffer material blocks after installation obtained above, calculate the saturated density ρ of the buffer material blocks after installation that meets the functional requirements and design requirements of the high-level radioactive waste geological disposal repository for buffer materials. sat .

[0030] Refer to the attached Figure 3 Preferably, in the step (1), the dry density allowable deviation factor of the outer gap 4, the inner gap 5, the buffer material and the bentonite particles filling the gap is taken into account in the calculation, while meeting the requirements for the permeability and expansion of the buffer material, and determining the dry density ρ of the buffer material before installation db The outer gap 4 is the gap between the surrounding rock of the disposal hole and the buffer material after installation, and the inner gap 5 is the gap between the disposal container 3 and the buffer material after installation.

[0031] Preferably, the disposal container 3 is located in the disposal hole, and the type of waste inside the disposal container 3 is high-level radioactive waste glass solidification body.

[0032] Preferably, the width of the outer gap 4 is 25-80 mm, the width of the inner gap 5 is 5-10 mm, and the cross-sectional width of the buffer material annular building block 2 after installation is about 350 mm.

[0033] The reference design of the buffer material is based on the functional requirements of the repository for the buffer material and the properties of the barrier system. The dry density of the bentonite is determined based on the permeability and swelling requirements. The swelling and permeability of the bentonite are mainly determined by the montmorillonite content. The average dry density of the saturated buffer material in the disposal hole should meet the requirement of the buffer material permeability coefficient of ﹤10 -12 m / S, expansion force 2~10Mpa.

[0034] Preferably, in step (2), the effective dry density ρ' of the montmorillonite is obtained by formula (I), which is:

[0035]

[0036] Wherein, ρ' is the effective dry density of montmorillonite in bentonite; R is the mass ratio of non-swelling clay in bentonite; 1-R is the ratio of montmorillonite content in bentonite; ρ db is the dry density of the buffer material block before installation; ρ 非c Lay is the dry density of non-swelling clay, 2.780 g / cm 3 .

[0037] Preferably, in step (3), the effective dry density of the same bentonite and montmorillonite is a constant, and the dry density of the buffer material before installation with different montmorillonite contents is calculated using the effective dry density of the montmorillonite by formula (I).

[0038] Preferably, in step (4), the post-installation buffer material blocks include post-installation buffer material solid blocks 1 and post-installation buffer material annular blocks 2; the post-installation buffer material solid blocks 1 are located at the top and bottom of the disposal container 3; the post-installation buffer material annular blocks 2 are located around the disposal container 3.

[0039] The disposal container 3 is located in the disposal hole of the disposal repository. The cross-sectional area of the disposal hole at the upper and lower heights of the disposal container 3 is composed of the cross-sectional area of the solid building block 1 of the buffer material after installation and the outer gap 4; the cross-sectional area of the disposal hole at the middle height of the disposal container 3 is composed of the cross-sectional area of the disposal container 3, the inner gap 5, the annular building block 2 of the buffer material after installation, and the outer gap 4. According to the single variable principle, the embodiment of the present invention divides the working conditions into: the influence of the change of the outer gap 4, the change of the buffer material size, the change of the density of the loose particles of bentonite, the change of the dry density of the buffer material (including the change of the dry density of the solid building block 1 of the buffer material after installation and the change of the dry density of the annular building block 2 of the buffer material after installation), and the relationship between the dry density boundary value and the gap width (including the outer gap 4 and the inner gap 5) on the saturated density of the installed thick buffer material block.

[0040] Assuming that the buffer material is fully saturated, the materials in the inner gap 5 (initial air), initial buffer material and outer gap 4 (bentonite particle filling) areas reach a homogeneous state; the dry density of the buffer material in the cross section of the buffer material of the disposal hole (the middle of the disposal container 3, the top / bottom height position) is homogenized and calculated.

[0041] Preferably, the average dry density ρ of the solid building block 1 of the buffer material after installation and the average dry density ρ of the annular building block 2 of the buffer material after installation are calculated based on the relevant parameters of the buffer material and the bentonite particles filled in the inner and outer gaps respectively. d .

[0042] The average dry density ρ of the buffer material annular building block 2 after installation d It is calculated by formula (II), which is:

[0043]

[0044] Among them, ρ d is the average dry density of the buffer material annular block 2 after installation; ρ db is the dry density of the buffer material before installation; ρ dp is the dry density of loose bentonite particles; S c is the cross-sectional area of the outer gap 4; S t The difference between the cross-sectional area of the disposal hole and the cross-sectional area of the disposal container 3; d s It is the ratio of the internal gap 5 in the disposal hole to the cross-sectional area of the buffer material annular building block 2 after installation.

[0045] The average dry density ρ of the solid building block 1 of the buffer material after installation d The ratio of the internal gap 5 to the cross-sectional area of the solid building block 1 of the buffer material after installation is zero, as calculated by formula (III):

[0046]

[0047] Among them, ρ d is the average dry density of the solid building block 1 of the buffer material after installation; ρ db is the dry density of the buffer material before installation; ρ dp is the dry density of loose bentonite particles; S c is the cross-sectional area of the outer gap 4; S t It is the difference between the cross-sectional area of the disposal hole and the cross-sectional area of the disposal container 3.

[0048] Preferably, in step (5), the saturated density ρ of the buffer material block after installation in the disposal hole is obtained according to the relationship between the average dry density, porosity and dry density of the buffer material in the disposal hole obtained under the above different working conditions. sat , the saturation density of the buffer material block after installation ρ sat It is obtained by formula (IV), which is:

[0049]

[0050] Among them, ρ sat is the saturation density of the buffer material after installation, ρ d is the average dry density of the buffer material after installation; e is the porosity ratio; ρ w The density of water in soil at 4°C is 1 g / cm 3 .

[0051] The porosity ratio e is obtained by formula (V), which is:

[0052]

[0053] Among them, G s is the particle density of bentonite; ρ d is the average dry density of the buffer material blocks after installation; ρ w The density of water in soil at 4°C is 1 g / cm 3 .

[0054] Example 2

[0055] The method according to the first embodiment of the present invention takes sodium bentonite from Gaomiaozi, my country as an example to calculate the design parameters of the solid building block 1 of the buffer material, including the following steps:

[0056] (1) According to the functional and design requirements of the high-level waste underground disposal repository for buffer materials, the relevant experimental data of bentonite were selected, and the standard value of the dry density of the solid buffer material before installation was initially selected as 1.700g / cm 3 , at this time the montmorillonite content is 75%;

[0057] Specifically, assuming that the buffer material blocks are fully saturated after installation, the materials in the inner gap (initial air), initial buffer material blocks, and outer gap (particle filling) areas are homogeneous; the calculation variable is the dry density of the solid block 1 of the buffer material (i.e., the variable is the montmorillonite content), and the constants are the dry density of the filled bentonite particles, the gap outside the treatment hole, and the geometric dimensions of the blocks. The average dry density and saturated density of the solid block 1 of the buffer material after installation in the treatment hole under this working condition are calculated; the parameters for determining the standard value of the dry density of the solid block 1 of the buffer material before installation are shown in Table 1;

[0058] Table 1 Calculation parameters of montmorillonite content change in solid blocks

[0059]

[0060] (2) According to the standard value of the dry density of the solid building block 1 of the buffer material before installation and the content of montmorillonite, the effective dry density ρ' of the montmorillonite in the buffer material is calculated according to formula (I) to be 1.505 g / cm 3 ; Based on the bentonite test data, the standard value of montmorillonite content selected here is 75%;

[0061] (3) According to formula (1), the dry density ρ of the solid building block 1 of the buffer material before installation with different montmorillonite contents is obtained: db Values, Table 2;

[0062] Table 2 Dry density of blocks corresponding to different montmorillonite contents

[0063]

[0064] (4) The embodiment of the present invention divides the working conditions for the disposal work in the vertical disposal hole into: ① The geometric dimensions of the disposal hole (external gap 4) change, and the others remain unchanged; ② The width of the buffer material block changes after installation (solid block dry density, annular block dry density), and the others remain unchanged; ③ The dry density of the block before installation changes, that is, the montmorillonite content changes, and the others remain unchanged; ④ The dry density of the loose bentonite particles filling the gap changes, and the others remain unchanged; ⑤ The influence of the relationship between the dry density boundary value and the gap width on the saturated density of the buffer material block after installation; the width of the buffer material annular block after installation is 350 mm.

[0065] According to formula (III), the average dry density ρ of the solid building block 1 of the buffer material after installation under the working condition is obtained: d , see Table 3;

[0066] Table 3 Changes in dry density of blocks (different montmorillonite content) and density of buffer materials after installation

[0067]

[0068] (5) According to the relationship between the average dry density, porosity and dry density of the solid block 1 of the buffer material in the disposal hole (i.e. after installation) under different working conditions, the particle density Gs of sodium bentonite in Gaomiaozi, my country is 2.66 g / cm 3 According to formula (IV) and (V), the saturation density ρ of the solid block 1 of the buffer material after installation is calculated sa t, see Table 3.

[0069] Refer to the attached Figure 4 、 5 ,Table 3,Verify the functional requirements and design requirements of buffer material blocks based on the underground disposal repository for high-level radioactive waste.

[0070] According to the test results of the relationship between the expansion force and dry density of GMZ13 and GMZ24 bentonite in my country, combined with the design and functional requirements of buffer materials in my country, and the calculation results of the other four working conditions, it can be seen that when the montmorillonite content is 70% to 78%, it meets the requirements. After installation, the saturated density of the solid block 1 of the buffer material is 1.930 to 2.030 / cm 3 The allowable variation range of the dry density of the solid block 1 of the buffer material before installation is 1.700±0.03g / cm 3 .

[0071] Before conducting disposal tests / projects in vertical disposal holes of high-level radioactive waste underground disposal repositories, the engineering design parameters of the buffer material blocks calculated according to the method of the embodiment of the present invention can be used to directly prepare buffer material blocks using bentonite that meets the requirements, thereby providing a reliable basis and technical input for the construction of high-level radioactive waste underground disposal repositories in my country.

[0072] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for determining design parameter indicators of a cushioning material based on the effective density of montmorillonite, characterized by: The following steps are involved: (1) Conducting an indoor test of bentonite based on a selected bentonite, and selecting a standard value of the dry density of the buffer material before installation prepared with bentonite according to the test results, vertical disposal method, and buffer material design index requirements; (2) The effective dry density ρ' of the montmorillonite in the bentonite is calculated based on the standard value of the dry density of the buffer material before installation prepared from the bentonite and the standard value of the montmorillonite content in the bentonite. The calculation formula for the effective dry density ρ' of the montmorillonite is: Wherein, ρ' is the effective dry density of montmorillonite in bentonite; R is the mass ratio of non-swelling clay in bentonite; 1-R is the ratio of montmorillonite content in bentonite; ρ db is the dry density of the buffer material before installation; ρ 非clay The dry density of non-swelling clay is 2.780 g / cm 3 ; (3) For the same type of bentonite, the effective dry density of montmorillonite is a constant. Based on the standard value of the dry density of the buffer material before installation, the effective dry density ρ' of montmorillonite, and the montmorillonite content in the bentonite, the dry density ρ of the buffer material before installation with different montmorillonite contents can be calculated using the above formula. db ; (4) Dry density ρ of the buffer material before installation according to different montmorillonite contents db , various working conditions during the installation process, and the average dry density ρ of the buffer material blocks after installation that meets the requirements of the disposal repository is obtained d ; (5) The saturated density ρ of the installed buffer material blocks that meets the requirements of the high-level radioactive waste deep geological disposal repository for buffer materials is calculated based on the average dry density of the installed buffer material blocks. sat .

2. The method for determining design parameter indicators of a cushioning material based on the effective density of montmorillonite according to claim 1, characterized in that: In the step (4), the average dry density of the buffer material annular building block (2) after installation is d It is calculated by the formula, which is: Among them, ρ d is the average dry density of the buffer material annular block (2) after installation in the disposal hole; ρ db Dry density of the buffer material before installation; ρ dp is the dry density of loose bentonite particles; S c is the cross-sectional area of the outer gap (4); S t is the difference between the cross-sectional area of the disposal hole and the cross-sectional area of the disposal container (3); d s It is the ratio of the internal gap (5) in the disposal hole to the cross-sectional area of the buffer material annular building block (2) after installation.

3. The method for determining design parameter indicators of a cushioning material based on the effective density of montmorillonite according to claim 1, characterized in that: In the step (3), the average dry density of the solid building block (1) of the buffer material after installation in the disposal hole is d The ratio of the internal gap (5) to the cross-sectional area of the solid building block (1) of the buffer material after installation in the disposal hole is zero, as calculated by the formula: Among them, ρ d is the average dry density of the solid blocks (1) of the buffer material after installation in the disposal hole; ρ db is the dry density of the buffer material before installation; ρ dp is the dry density of loose bentonite particles; S c is the cross-sectional area of the outer gap (4); S t It is the difference between the cross-sectional area of the disposal hole and the cross-sectional area of the disposal container (3).

4. The method for determining design parameter indicators of a cushioning material based on the effective density of montmorillonite according to any one of claims 1 to 3, characterized in that: The post-installation buffer material blocks include the post-installation buffer material solid blocks (1) and the post-installation buffer material annular blocks (2); the post-installation buffer material solid blocks (1) are located at the top and bottom of the disposal container (3); and the post-installation buffer material annular blocks (2) are located around the disposal container (3).

5. The method for determining design parameter indicators of a buffer material based on the effective density of montmorillonite according to any one of claims 1 to 3, characterized in that: The outer gap (4) is the gap between the surrounding rock of the disposal hole and the buffer material block after installation; the inner gap (5) is the gap between the disposal container (3) and the buffer material block after installation; the width of the outer gap (4) is 25 to 80 mm, and the width of the inner gap (5) is 5 to 10 mm.

6. The method for determining design parameter indicators of a cushioning material based on the effective density of montmorillonite according to claim 1, characterized in that: In the step (5), the saturation density ρ of the buffer material block after installation in the treatment hole is sa t is obtained by the formula: Among them, ρ sat is the saturation density of the buffer material block after installation, ρ d is the average dry density of the buffer material blocks after installation; e is the porosity ratio; ρ w The density of water in soil at 4°C is 1 g / cm 3 .

7. The method for determining design parameter indicators of a cushioning material based on the effective density of montmorillonite according to claim 6, characterized in that: The porosity ratio e is obtained by the formula: Among them, G s is the loose particle density of bentonite; ρ d is the average dry density of the buffer material blocks after installation; ρ w The density of water in soil at 4°C is 1 g / cm 3 .

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