阅读说明：本技术 用于高放废物处置库中的缓冲回填材料及其制备方法 (Buffer backfill material for high-level radioactive waste disposal warehouse and preparation method thereof ) 是由 伍涛 童艳花 李金英 于 2018-05-10 设计创作，主要内容包括：本发明属于高放废物地质处置技术领域,具体涉及用于高放废物处置库中的缓冲回填材料及其制备方法。该制备方法依次包括如下步骤,(1)改性：将膨润土、碱土金属盐按比例混合,并加水搅拌；膨润土、碱土金属盐的混合比例为：膨润土60～80重量份、碱土金属盐1～5重量份；混合物过滤后在80～120℃条件下烘干；(2)配料：在烘干后的混合物中加入石英砂10～20重量份、黄铁矿1～5重量份；(3)筛分：将混合物经孔径为0.002mm～5mm的筛网筛分；(4)压实成型：将筛分后的混合物均匀混合后,放入耐压容器中压实至混合料密度为1500～1900kg/m<Sup>3</Sup>,即制得回填材料。该回填材料能与地下水中的阴离子生成沉淀,达到阻滞弱吸附性核素的扩散的目的。(The invention belongs to the technical field of high-level waste geological disposal, and particularly relates to a buffer backfill material for a high-level waste disposal warehouse and a preparation method thereof. The preparation method sequentially comprises the following steps of (1) modification: mixing bentonite and alkaline earth metal salt in proportion, adding water and stirring; the mixing proportion of the bentonite and the alkaline earth metal salt is as follows: 60-80 parts of bentonite and 1-5 parts of alkaline earth metal salt; filtering the mixture and drying at 80-120 ℃; (2) preparing materials: adding 10-20 parts by weight of quartz sand and 1-5 parts by weight of pyrite into the dried mixture; (3) screening: sieving the mixture by a screen with the aperture of 0.002 mm-5 mm; (4) compacting and forming: uniformly mixing the sieved mixture, putting the mixture into a pressure-resistant container, and compacting until the density of the mixture is 1500-1900 kg/m 3 And finally, preparing the backfill material. The backfill material can generate precipitation with anions in underground water to retard the diffusion of weakly adsorbed nuclideThe purpose of (1).)

1. A buffering backfill material for high level waste disposal storehouse which characterized in that: comprises the following components in parts by weight:

2. The buffer backfill material for use in high level waste disposals of claim 1, wherein: the bentonite is sodium bentonite or calcium bentonite.

3. The buffer backfill material for use in high level waste disposals of claim 1, wherein: the alkaline earth metal salt is any one of soluble calcium salt, soluble strontium salt and soluble barium salt, or a mixture of any two of the soluble calcium salt, the soluble strontium salt and the soluble barium salt, or a mixture of the soluble calcium salt, the soluble strontium salt and the soluble barium salt.

4. the buffer backfill material for use in high level waste disposals according to claim 3, characterized by: the soluble calcium salt comprises anhydrous CaCl₂，Ca(NO₃)₂·4H₂O，CaCl₂·2H₂O; the soluble strontium salt comprises SrCl₂，SrCl₂·6H₂O，Sr(NO₃)₂(ii) a The soluble barium salt comprises BaCl₂·2H₂O，Ba(C₂H₃O₂)₂，Ba(NO₃)₂。

5. The buffer backfill material for use in high level waste disposals of claim 1, wherein: the fineness of the quartz sand is that the quartz sand completely passes through a 200-mesh sieve, and the mud content is less than 3%.

6. The preparation method of the buffer backfill material used in the high level waste disposal warehouse is characterized by comprising the following steps: the method sequentially comprises the following steps of,

(1) Modification: mixing bentonite and alkaline earth metal salt in proportion, adding water and stirring; the mixing proportion of the bentonite and the alkaline earth metal salt is as follows: 60-80 parts of bentonite and 1-5 parts of alkaline earth metal salt; filtering the mixture and drying at 80-120 ℃;

(2) preparing materials: adding 10-20 parts by weight of quartz sand and 1-5 parts by weight of pyrite into the dried mixture;

(3) Screening: sieving the mixture by a screen with the aperture of 0.002 mm-5 mm;

(4) Compacting and forming: uniformly mixing the sieved mixture, putting the mixture into a pressure-resistant container, and compacting until the density of the mixture is 1500-1900 kg/m³and finally, preparing the backfill material.

7. the method for preparing a buffer backfill material for use in a high level waste disposal warehouse according to claim 6, characterized by: in the step (1), the adding mass of water is 40-60 times of the total mass of bentonite and alkaline earth metal salt.

8. The method for preparing a buffer backfill material for use in a high level waste disposal warehouse according to claim 6, characterized by: in the step (1), the stirring time is 1-3 hours.

9. the method for preparing a buffer backfill material for use in a high level waste disposal warehouse according to claim 6, characterized by: in the step (1), the bentonite is sieved by a screen with the aperture of 0.002 mm-5 mm before being mixed with the alkaline earth metal salt.

Technical Field

The invention belongs to the technical field of high-level waste geological disposal, and particularly relates to a buffer backfill material for a high-level waste disposal warehouse and a preparation method thereof.

background

The spent fuel of the nuclear power station contains a large amount of actinides and schizophragma elements which have strong radioactivity, long half-life period and high toxicity, and must be reliably isolated from the human living environment for a long time. The best method for treating the spent fuel at present is to establish a high-level waste geological disposal library, and the design year is more than 1 ten thousand years. The design concept of a multiple barrier system is adopted, and the design concept is mainly divided into an engineering barrier and a natural barrier. Granite has high strength and low permeability, and is selected as a natural barrier by many countries. The engineering barrier is filled between the high-level radioactive waste tank and the geologic body and plays an important role in engineering barrier, chemical barrier, radioactive waste decay heat conduction and the like.

Radioactive waste is carried by groundwater and migrates through fissures, pores and voids of "engineered barriers" and "natural barriers" towards the biosphere. As a final artificial barrier, the backfill material must have a low permeability such that the migration of radioactive waste is dominated by diffusion; and secondly, the underground water treatment device has good expansibility, and when underground water enters the treatment reservoir along the granite cracks, the underground water can absorb water to expand, so that the cracks are reduced as much as possible, and the underground water is retarded. It is further desired to have a high cation exchange capacity, to block a large number of radionuclides, and to have good stability, low cost, radiation resistance, and the like. Bentonite is therefore often chosen as the cushioning backfill material. However, the mechanical properties and heat conductivity of bentonite are poor, and most of researchers at home and abroad add quartz sand to enhance the mechanical properties. In addition, the application No. 200810044755.6 adds zeolite or/and attapulgite in bentonite to improve mechanical properties, and adds pyrite to improve heat conductivity.

Despite the existing formulations for a large number of long-lived strongly adsorbed nuclides, such as actinides, contained in spent fuels²³⁸U、²³⁷Np、²³⁹The nuclides such as Pu have good blocking capability. But it is difficult to block weakly adsorbed species with long lifetimes, e.g.⁹⁹Tc，¹²⁹I，⁷⁹Migration of a nuclear species such as Se. The research aims to carry out inorganic modification on the bentonite on the basis of not changing the performance of the existing backfill material, so that the surface of the bentonite particle is provided with alkaline earth metal ions. When the natural barrier is invalid, the underground water enters the engineering barrier, contains a large amount of sulfate radicals, carbonate radicals and phosphate ions, and the anions and alkaline earth metal cations generate precipitates to block the pores among bentonite particles, which are main diffusion channels of weakly adsorbed nuclides, so that the migration of the weakly adsorbed nuclides is retarded. The research project is supported by the natural science fund (project number: LY18B070006) in Zhejiang province.

disclosure of Invention

the invention aims to overcome the defects and provides a buffer backfill material for a high-level radioactive waste disposal warehouse and a preparation method thereof. The characteristics of low permeability, high expansibility, high cation exchange capacity, irradiation resistance and the like of the bentonite are utilized. The surface of the bentonite is subjected to inorganic modification, so that cations on the surface of bentonite particles can generate precipitates with anions in underground water, and a diffusion channel of weakly adsorbing nuclide is blocked, so that the purpose of retarding the migration of the weakly adsorbing nuclide is achieved, and the buffer backfill material for building the high-level waste geological disposal library is obtained.

in order to achieve the purpose, the technical scheme of the invention is as follows:

The buffer backfill material for the high level waste disposal warehouse comprises the following components in parts by weight:

As an improvement, the bentonite is sodium bentonite or calcium bentonite.

as an improvement, the alkaline earth metal salt is any one of soluble calcium salt, soluble strontium salt and soluble barium salt, or a mixture of any two of the soluble calcium salt, the soluble strontium salt and the soluble barium salt, or a mixture of the soluble calcium salt, the soluble strontium salt and the soluble barium salt.

As a further improvement, the soluble calcium salt comprises anhydrous CaCl₂，Ca(NO₃)₂·4H₂O，CaCl₂·2H₂O; the soluble strontium salt comprises SrCl₂，SrCl₂·6H₂O，Sr(NO₃)₂(ii) a The soluble barium salt comprises BaCl₂·2H₂O，Ba(C₂H₃O₂)₂，Ba(NO₃)₂。

As an improvement, the fineness of the quartz sand is that the quartz sand completely passes through a 200-mesh sieve, and the mud content is less than 3%.

The invention also provides a preparation method of the buffer backfill material used in the high level waste disposal warehouse, which sequentially comprises the following steps,

(1) Modification: mixing bentonite and alkaline earth metal salt in proportion, adding water and stirring; the mixing proportion of the bentonite and the alkaline earth metal salt is as follows: 60-80 parts of bentonite and 1-5 parts of alkaline earth metal salt; filtering the mixture and drying at 80-120 ℃;

(2) Preparing materials: adding 10-20 parts by weight of quartz sand and 1-5 parts by weight of pyrite into the dried mixture;

(3) Screening: sieving the mixture by a screen with the aperture of 0.002 mm-5 mm;

(4) Compacting and forming: uniformly mixing the sieved mixture, putting the mixture into a pressure-resistant container, and compacting until the density of the mixture is 1500-1900 kg/m³and finally, preparing the backfill material.

In the step (1), the added mass of the water is 40-60 times of the total mass of the bentonite and the alkaline earth metal salt.

As an improvement, in the step (1), the stirring time is 1-3 hours.

In the step (1), the bentonite is sieved by a screen with the aperture of 0.002 mm-5 mm before being mixed with the alkaline earth metal salt.

The invention has the beneficial effects that:

(1) The alkaline earth metal salt is fully mixed with the bentonite, the original crystal structure of the bentonite is not changed, namely the properties of the bentonite, including permeability, expansibility, cation exchange capacity, irradiation resistance and the like, are not changed. The chemical stability of the alkaline earth metal salt is good, and the performance of the prepared backfill material can not be greatly changed within the design period.

(2) The quartz sand can enhance the mechanical property of the backfill material, the montmorillonite in the bentonite is still the main component in the backfill material, and the migration speed of the radioactive waste can not be obviously changed. The pyrite not only serves to increase the thermal conductivity of the backfill material, but also provides a reducing atmosphere for the 'engineering barrier', and the pyrite also increases the retarding performance on radioactive wastes due to the weakened migration capability of most radioactive wastes under reducing conditions.

(3) The backfill material for the high-level waste address disposal warehouse is prepared by adopting cheap raw materials and simple mixing mechanical compaction, is easy to realize engineering application, and meets the design and construction requirements of the disposal warehouse.

(4) The backfill material prepared by the invention has good engineering performance and permeability resistance, and can not only be used for weakly adsorbed nuclides such as⁹⁹Tc，¹²⁹I，⁷⁹Nuclides such as Se and the like have good blocking capability; for strongly adsorbed nuclides, e.g. actinides²³⁸U、²³⁷Np、²³⁹Nuclides such as Pu also have good blocking capability.

Detailed Description

The present invention provides a method for preparing a buffer backfill material for a high level waste disposal warehouse, which is a clear technical solution for the purpose of the invention, but can not be understood as a limitation to the protection scope of the invention, and the insubstantial modifications and adjustments made by the person skilled in the art according to the present disclosure still belong to the protection scope of the invention.