RU2757782C1 - Method for forming an anti-filtration barrier for radioactive waste storage facilities - Google Patents

Abstract

FIELD: nature protection.SUBSTANCE: invention relates to the field of environmental protection, in particular to methods for disposal of liquid radioactive waste, and can be used at enterprises storing radioactive waste (RW) in various types of storage facilities, in areas of radiation contamination with potential release of RW components into the environment, as well as for protection from contamination with radioactive substances of underground drinking water, grounds and soils in storage areas. An adhesive, a gel-forming composition and water are successively injected into the wells with one or more rims until an anti-filtration barrier is obtained.EFFECT: invention makes it possible to increase the reliability of the disposal of radioactive waste and safety during the operation and liquidation of ground and underground RW storage facilities.5 cl, 1 tbl, 4 dwg

Description

The invention relates to the field of environmental protection, in particular to methods of disposal of liquid radioactive waste, and can be used at enterprises storing radioactive waste (RW) in storage facilities of various types, in areas of radiation contamination with the potential release of RW components into the environment, as well as to protect ground drinking water, soil and soil in storage areas from radioactive contamination.

At all stages of radioactive waste management, it is necessary to minimize environmental pollution, therefore, special measures for handling them are currently envisaged. The most urgent problem is the problem of safe disposal. The methods of radioactive waste disposal used during and after the formation of the nuclear industry in Russia and the United States have led to the formation of a significant number of storage facilities that do not have protective barrier systems currently recommended by the IAEA. Existing underground and surface storage facilities pose a risk of environmental contamination with radioactive isotopes.

The national operator for radioactive waste management (NO RAO) received a license for the construction of a radioactive waste disposal facility near the closed city of Seversk. Work is scheduled to begin in 2021. A near-surface disposal facility for liquid radioactive waste is to be built in Seversk. The total capacity of the facility will be about 150 thousand cubic meters. The facility will be used to store waste from the current activities of the Siberian Chemical Combine (SCC).

Clay-based barrier materials are known. Clay materials, due to their unique properties, are extremely common for use as materials for safety barriers [https://www.atomic-energy.ru/articles/2020/02/13/101415].

The known method of immobilization of radionuclides, as well as biodegradation of macrocomponents of radioactive waste in situ in areas adjacent to waste storage, which can be an additional barrier for modern storage, designed in accordance with the concept of multi-barrier protection (patent No. 2547812). The disadvantages are the high cost of the used reagents and carriers, as well as the use of strains that do not have a high efficiency of immobilizing processes.

A known method of creating an artificial geochemical barrier to retain heavy metals migrating in technogenic polluted streams [RF Patent No. 2050334]. On the path of flow migration, an absorption barrier is created by drilling a chain of wells at a distance of 4-5 m, into which solutions are injected with a gelation time of 1-1.5 h, forming a gel, for example, oxal-aluminosilicate, absorbing heavy metals. The disadvantage of this method is that the barrier is partially permeable to a liquid flow (filtration coefficient 1⋅10 ^-2 -5⋅10 ^-3 m / day) and sorption saturation occurs rather quickly, in 50-85 days, which limits the duration of this barrier for its intended purpose.

In terms of the technical essence and the achieved effect, the closest to the claimed technical solution is RF patent No. 2316068, which we have taken as a prototype. As a gelling solution, a solution of acid decomposition of rocks of the ijolite group - urtite, containing ions of aluminum, alkaline and alkaline earth elements and orthosilicic acid is used. An anti-filtration barrier is created by injecting a gel-forming solution into the wells. The formation of a dense gel in the pore space of the rock occurs due to the polymerization of orthosilicic acid. The polymerization time of the solution is regulated by the degree of dilution of the solution, the pH of the solution and is set based on the conditions of use. The diffusion coefficients (Da) constitute (m ² / sec) for Th - 1,4⋅10 ^{-8, 90} Sr - 6,5⋅10 ^{-9, 137} Cs - 7,9⋅10 ^{-10, 239} Pu - 3 , 4⋅10 ^-11 , which is comparable with the data obtained for dense clay screens. The disadvantage of this solution is the duration of the gel formation. At 12 ° C, it takes 48 hours for the polymer gel to form completely.

The objective of the present invention is to create a method of forming an anti-filtration safety barrier in a porous horizon for storage of radioactive waste with improved anti-filtration and anti-migration properties.

The technical result consists in reducing the filtration of water in a porous medium and reducing the migration of radioactive waste through the impervious barrier, thereby increasing the reliability of disposal of radioactive waste and safety during operation and liquidation of ground and underground storage facilities for radioactive waste.

The technical result is achieved by the fact that an adhesive, a gel-forming composition and water are sequentially injected into the wells with one or more slugs until an anti-seepage barrier is obtained.

The method differs in that, as an adhesive, a 2.0-30.0% borax solution is used, as a gel-forming composition, a composition with the following content of components, wt%:

Polyvinyl alcohol 3.0-7.0 Boric acid 0.5-1.0 Water rest

The method differs in that, as an adhesive, an 11.0-20.0% NaCl solution is used, as a gel-forming composition, a composition with the following content of components, wt%:

Methylcellulose 1.0-1.5 Urea 2.0-5.0 NaCl 10.0-11.0 Water rest

or

Methylcellulose 1.0-1.5 Potassium alum (AlK (SO ₄ ) ₂ ⋅12H ₂ O) 3.0-7.0 NaCl: 5.0-6.0 Water rest

The method differs in that, as an adhesive, a 6.0-20.0% solution of hexamethylenetetramine is used, as a gel-forming composition, a composition with the following content of components, wt%:

Aluminum salt (AlCl ₃ ⋅6H ₂ O or hydroxychloride aluminum AQUA-AURAT-30) 4.0-7.5 Urea 6.0-16.0 Hexamethylenetetramine 6.0-8.0 Water rest

In the experiments, thermotropic gel-forming compositions based on water-soluble polymers are used: polyvinyl alcohol (PVA), methylcellulose (MC) and inorganic aluminum hydroxopolymer, capable of forming gels at temperatures of 10-30 ° C, in which anti-filtration and anti-migration properties are provided due to preliminary injection of adhesives - formulations for faster gelation and fixation of the gel barrier.

Examples of specific implementation.

The filtration characteristics of gel-forming systems and gel screens are investigated under thermobaric conditions, simulating water filtration through the aeration zone in the area of surface storage facilities of the SCC in the first aquifer from the surface. Low-viscosity gel-forming compositions are pumped into the model porous medium, which directly in the porous medium are transformed into gels by the mechanism of hydroxopolycondensation of aluminum ions and phase transitions "solution-gel" of polymers with lower and upper critical dissolution temperatures with the formation of anti-filtration barriers. The anti-migration properties of gels in relation to radionuclides are investigated by filtering aqueous solutions of simulators of the most mobile radioactive contaminants through the formation rock with gels. For this, before and after the formation of gels in the rock model by pumping gel-forming compositions, simulators of radioactive contaminants are injected, the concentration of which is determined at the exit from the model. The following salts are used as simulants in the form of solutions in fresh water:

- cesium nitrate - 0.5 wt%, cesium content - 3343 mg / dm ³ or 25 mg-eq / dm ³ ;

- strontium chloride - 0.5 wt.%, strontium content - 1643 mg / dm ³ or 19 mg-eq / dm ³ .

Example 1. To 490.0 g of fresh water add 10.0 g of boric acid, then after stirring to the resulting solution add 500.0 g of PVA solution with a concentration of 10.0 wt.% After thorough mixing receive 1000.0 g of a composition containing 5.0 wt.% PVA, 1.0 wt.% Boric acid and 94.0 wt% water. An adhesive - a composition for faster gelation and fixation of the gel barrier is prepared as follows: 20.0 g of borax is dissolved in 980.0 g of water, and after stirring, 1000.0 g of a solution is obtained containing 2.0 wt% borax and 98.0 wt% water. Through a model of disintegrated natural material with an initial gas permeability of 8.958 μm (Fig. 1), after water filtration, a portion of simulators is injected to evaluate the filtration properties of the rock itself, then a portion of a 2% borax solution and again simulators to evaluate the filtration properties of the rock impregnated with the solution borax, then gel-forming composition 1 based on PVA (5.0 wt.% PVA, 1.0 wt.% boric acid), water, 2% borax solution are injected, and after holding for gelation, simulators are again injected to evaluate the anti-migration properties of the gel screen. The alternate injection into the model of the rock from a disintegrated natural material with an initial gas permeability of 8.958 μm solutions: 2% borax, water, a composition based on PVA, water and again a 2% borax solution at a temperature of 20 ° C led to the creation of an anti-seepage screen. The pressure drop during the breakthrough of the gel was 5 atm / m, water filtration through the model was carried out at a pressure drop of 1.3 atm / m, then a decrease in the pressure drop to 0.45 atm / m was observed, Fig. 1.

Alternate injection into the model of rock from a disintegrated natural material with an initial gas permeability of 5.712 μm ² at a temperature of 20 ° C solutions: 2% borax, water, a composition based on PVA (5.0 wt.% PVA, 1.0 wt.% Boric acid), water and again 2% borax, fig. 2, led to the creation of an anti-filtration screen, water filtration through which was carried out at a pressure drop of 13 atm / m. Injection of another slug of the PVA-based composition led to the formation of an almost impermeable screen, water filtration through which was not achieved even with an increase in the pressure drop to 149.5 atm / m, Fig. 2.

Example 2. In 920.0 g of fresh water with a temperature of 70-90 ° C with constant stirring is placed 10.0 g of boric acid, then 70.0 g of polyvinyl alcohol and stirred until a homogeneous solution is obtained. A composition is obtained containing 7.0 wt% polyvinyl alcohol, 1.0 wt% boric acid and 92.0 wt% water. An adhesive - a composition for faster gelation and fixation of the gel barrier is prepared as follows: 300.0 g of borax is dissolved in 700.0 g of hot water, and after stirring, 1000.0 g of a solution is obtained containing 30.0 wt% borax and 70.0 wt% water. To improve the adhesion of the PVA-based composition to the rock, pre-impregnation of the rock with a borax solution is used. Filtration through a rock model with an initial gas permeability of 6.808 μm ^{2 of a} hot 30% borax solution, and then a composition based on PVA (7 wt.% PVA, 1 wt.% Boric acid), Fig. 3, at a temperature of 20 ° C leads to the formation of an almost impenetrable screen - filtration was not observed with an increase in the pressure drop to 17 atm / m.

Example 3. 20.0 g of carbamide and 100.0 g of NaCl are dissolved in 380.0 g of fresh water, then 500.0 g of methylcellulose (MC) solution with a concentration of 3.0 wt% is added to a homogeneous solution. After thorough mixing, 1000.0 g of a composition containing 1.5 wt% is obtained. MC, 2.0 wt% carbamide, 10% NaCl, and 86.5 wt% water. An adhesive - a composition for faster gelation and fixation of the gel barrier is prepared as follows: 110.0 g of NaCl is dissolved in 890.0 g of water, and after stirring, 1000.0 g of a solution is obtained containing 11.0 wt% NaCl and 89.0 wt% water. The adhesive, the gelling composition and water are pumped in successively. The results of measuring the viscosity of compositions based on MC and the resulting gels showed that the solutions themselves are low-viscosity, they can be easily pumped over with a pump and moved over a sufficiently long distance. When gels are formed, the viscosity of the composition increases by 7.5-30.0 times. Complexones, oxidizing agents - reducing agents, co-precipitating agents, ion exchangers or dispersed fillers, which can retain radionuclides, that is, endow the impervious screen with additional protective functions, can also be added to the composition of the gel-forming composition.

Example 4. 50.0 g of potassium alum AlK (SO ₄ ) ₂ ⋅12H ₂ O and 50.0 g of NaCl are dissolved in 400.0 g of fresh water, then 500.0 g of MC solution with a concentration of 2.0 wt% is added to the homogeneous solution.After thorough mixing, 1000.0 g of the composition is obtained containing 1.0 wt% MC, 5.0 wt% potassium alum AlK (SO ₄ ) ₂ ⋅12H ₂ O, 5.0% NaCl, and 89.0 wt% water. An adhesive - a composition for faster gelation and fixation of the gel barrier is prepared as follows: 110.0 g of NaCl is dissolved in 890.0 g of water, and after stirring, 1000.0 g of a solution is obtained containing 11.0 wt% NaCl and 89.0 wt% water. Adhesive, water, then the resulting composition based on MC, water, composition based on MC, and after exposure to gelation, simulators are pumped into a model made of disintegrated natural material with an initial gas permeability of 7.954 μm to evaluate the anti-migration properties of the gel screen (Fig. 4). When analyzing samples at the outlet of a model consisting of a disintegrated natural material with a permeability of 7.954 μm, an anti-filtration screen formed by a composition based on MC and potassium alum, the content of cesium and strontium cations was determined using the method of capillary electrophoresis on a Kapel 103 R device ( production of NPF "Lumex", St. Petersburg). The anti-filtration gel barrier made of the gel-forming composition has anti-migration properties, absorbing 47% of cesium ions and 71% of strontium ions.

Example 5. 60.0 g of aluminum hydroxychloride AQUA-AURAT-30 and 80.0 g of carbamide are dissolved in 360.0 g of fresh water, thoroughly mixed to obtain 500.0 g of a homogeneous solution containing 12.0 wt.% Aluminum hydroxochloride AQUA-AURAT-30, 16.0 wt.% Carbamide and 72.0 wt% water. To 440.0 g of water add 60.0 g of hexamethylenetetramine. After stirring, 500.0 g of a solution containing 12.0 wt% is obtained. hexamethylenetetramine and 88.0 wt% water. By mixing the prepared solutions, 1000.0 g of a composition containing 6.0 wt% AQUA-AURAT-30 aluminum hydroxychloride, 8.0 wt% carbamide, 6.0 wt% hexamethylenetetramine, and 80.0 wt% water are obtained. An adhesive - a composition for faster gelation and fixation of the gel barrier is prepared as follows: 200.0 g of hexamethylenetetramine is dissolved in 800.0 g of water, and after stirring, 1000.0 g of a solution is obtained containing 20.0 wt% of hexamethylenetetramine and 80.0 wt% of water. An adhesive, a gel-forming composition based on an aluminum salt and water are alternately pumped into the rock model from a disintegrated natural material with two fringes until an anti-filtration barrier is obtained.

Example 6. 72.0 g of AlCl ₃ ⋅6H ₂ O and 160.0 g of carbamide are dissolved in 268.0 g of fresh water, thoroughly mixed to obtain 500.0 g of a homogeneous solution containing 14.4 wt% AlCl ₃ ⋅6H ₂ O, 32.0 wt% of carbamide and 53.6 wt% water. To 440.0 g of water add 60.0 g of hexamethylenetetramine. After stirring, 500.0 g of a solution is obtained containing 12.0 wt% hexamethylenetetramine and 88.0 wt% water. By mixing the prepared solutions, 1000.0 g of a composition is obtained containing 7.2 wt% AlCl ₃ ⋅6H ₂ O, 16.0 wt% carbamide, 6.0 wt% hexamethylenetetramine, and 70.8 wt% water. An adhesive - a composition for faster gelation and fixation of the gel barrier is prepared as follows: 200.0 g of hexamethylenetetramine is dissolved in 800.0 g of water, and after stirring, 1000.0 g of a solution containing 20.0 wt% of hexamethylenetetramine and 80.0 wt% of water is obtained. Alternating injection into the rock model from a disintegrated natural material of an adhesive, a gel-forming composition based on an aluminum salt and water with one slug leads to the formation of an anti-seepage barrier.

The table (in the graphical part) shows the properties of the gel-forming compositions that were used to create impervious screens in columns made of natural material that simulate the rock in the aeration zone in the area of ground storage facilities of the Siberian Chemical Combine in the first aquifer from the surface. All compositions are low-viscosity: the viscosity of the composition based on polyvinyl alcohol with a PVA concentration of 5.0 wt% is 36.0-45.0 mPa⋅s, with a PVA concentration of 7.0 wt% - 96.0-140.0 mPa⋅s; the viscosity of compositions based on a water-soluble polymer of methylcellulose MC is in the range of 26.5-54.4 mPa⋅s; the viscosity of the composition based on aluminum salts (1.4-1.6 mPa⋅s) is comparable to the viscosity of water. The compositions of the gel-forming compositions are selected so that at a temperature of 16-24 ° C after a certain time they form gels directly in the formation model. The viscosity of the gels themselves (without rock) is in the range from 120 to 1045 mPa · s.

The strength properties of impervious screens are characterized by their elasticity. The elasticity of gels without soil and with soil was studied in the ratio soil: gel-forming composition 2: 1 (table). The elasticity of gels with soil increases in comparison with the elasticity of the gels themselves (without soil) by 8-26 times.

The proposed compositions, when pumped into wells, form a bulk gel with high rheological characteristics, the elasticity of which remains constant over time, the gels are harmless to humans and environmentally friendly, they are an effective plugging agent that significantly reduces water filtration in a porous medium. All original compositions are low-viscosity. The compositions of the gel-forming compositions are selected so that at a temperature of 16-25 ° C after a certain time they form gels directly in the formation. By varying the concentration of the components of the gel-forming composition, the size and number of rims, the sequence of injection of the composition, water and reagents affecting the rate of gelation and adhesion of the gel to the rock, it is possible to create an anti-filtration screen with certain properties.

Thus, the anti-filtration and anti-migration properties of the formed gel screens can be controlled by the amount of the injected gel-forming solution, the concentration of the components of the compositions, the number and sequence of rims, and various technological methods that modify the surface of the rock.

Claims (9)

1. A method of forming an anti-filtration barrier for disposal of radioactive waste by injecting a gel-forming composition through the wells, characterized in that an adhesive, a gel-forming composition and water are sequentially pumped into the wells with one or more slugs to obtain an anti-filtration barrier. 2. The method according to claim 1, characterized in that a 2.0-30.0% borax solution is used as an adhesive, and a composition with the following ratio of components, wt%, as a gel-forming composition: Polyvinyl alcohol 3.0-7.0 Boric acid 0.5-1.0 Water Rest 3. The method according to claim 1, characterized in that 11.0-20.0% NaCl solution is used as an adhesive, and a composition with the following ratio of components, wt%, as a gel-forming composition: Methylcellulose 1.0-1.5 Urea 2.0-5.0 NaCl 10.0-11.0 Water Rest 4. A method according to claim 3, characterized in that a composition with the following ratio of components, wt% is used as a gel-forming composition: Methylcellulose 1.0-1.5 Potassium alum (AlK (SO ₄ ) ₂ ⋅12H ₂ O) 3.0-7.0 NaCl 5.0-6.0 Water Rest 5. The method according to claim 1, characterized in that a 6.0-20.0% solution of hexamethylenetetramine is used as an adhesive, and a composition is used as a gel-forming composition with the following ratio of components, wt%: Aluminum salt (AlCl ₃ ⋅6Н ₂ О or hydroxychloride aluminum AQUA-AURAT-30) 4.0-7.5 Urea 6.0-16.0 Hexamethylenetetramine 6.0-8.0 Water Rest

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