RU2231842C2 - Method of incorporating radioactive ion-exchange resins into portland cement binder - Google Patents

Abstract

FIELD: radioactive materials disposal.

SUBSTANCE: radioactive ion-exchange resins are incorporated into Portland cement binder by mixing both mentioned components with sorption clay additive, cement, and tempering solution followed by solidification, said tempering solution being radioactive concentrate of salts of natural hydrocarbonate waters.

EFFECT: increased percentage of incorporation of radioactive waste in Portland cement binder and reduced leaching of radionuclides from solidified materials.

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Description

The invention relates to the field of processing of radioactive ion exchange resins (IOS) by cementing.

Spent cation-exchange and anion-exchange resins are the most radioactive (up to 10 ^-3 Ci / kg and more) waste generated during the operation of nuclear power plants (NPPs) [1]. Therefore, their inclusion in a binder, reliably insulating from the environment, is an important environmental task.

A known method of incorporating radioactive IOS into an inorganic binder based on Portland cement. In Portland cement, it is recommended to include no more than 10% of IOS (by weight of dry resin) with a water-cement ratio of about 0.5 [2]. Moreover, low-salt (less than 1 g / l) floor drain solutions, which are natural waters used for water supply and contaminated with radionuclide leaks from the NPP circuit, are used for hydrotransport and subsequent solidification of IOS by cementing [1].

The disadvantage of this method is the unacceptably high leachability of radiocaesium from Portland cement compounds (more than 10 ^-3 -10 ^-4 g / cm ² · day).

A known method, including the introduction of Portland cement during the curing of IOS, the addition of clay sorbents (vermiculite, bentonite clay, etc.), which reduces the rate of leaching of radionuclides to values of 10 ^-4 g / cm ² · day [3]. This method in its technical essence and the achieved effect is closest to the claimed and selected as a prototype.

The disadvantages of this method are the low degree of inclusion of radioactive waste in Portland cement compounds, the low strength of the cured products and the insufficiently low leachability of radionuclides.

According to domestic technical requirements of RD 95 10497-93, the mechanical strength of radioactive cement compounds should be at least 50 kgf / cm ² (and the compounds are considered waterproof if they retain a strength of at least 50 kgf / cm ² and after exposure to water for 90 days) and the leachability of radiocesium is less than 10 ^-3 g / cm ² · day [4]. At the same time, to exclude the possibility of the destruction of radioactive cement blocks during transportation in case of an emergency, according to the IAEA, it is necessary that the strength of the cement compound be at least 100 kgf / cm ² [2]. The burial of radioactive cement blocks in the simplest soil burial grounds is considered quite safe only when the radionuclides are leached less than 1 · 10 ^-4 g / cm ² · day [5].

The problem solved by this invention is to increase the degree of inclusion of radioactive waste in the Portland cement binder and reduce the leachability of radiocaesium from cured products while maintaining their high strength.

The essence of the invention lies in the fact that in the method of incorporating radioactive IOS into a Portland cement binder with a sorption clay additive, radioactive concentrates of salts of natural bicarbonate waters are used to mix cement.

Hydrocarbonate (carbonate) solutions of natural waters are formed in the processes of chemical weathering of igneous rocks or are genetically related to sedimentary rocks. This species includes the waters of most rivers, lakes, as well as groundwater, which are used to supply nuclear power plants as "technical waters". Therefore, when radionuclides leak from the NPP circuit into them, the salt composition of liquid radioactive waste - LRW sent to the ladder (with the exception of spent reagent solutions: deactivating, regenerating, etc.) is mainly determined by hydrocarbonate anions (mixed with sulfates and chlorides) and calcium, sodium and magnesium cations [6]. The purification of such solutions by evaporation or membrane methods leads to the formation of hydrocarbonate concentrates of LRW, the curing of which is carried out by cementing or bitumen [1]. Cementing LRW concentrates is economically feasible with a salinity of at least 50 g / l, and with a salinity of more than 200 g / l, bitumen is more preferable [7].

The method is as follows.

Radioactive IOS is mixed with a sorption clay admixture (about 10% by weight of cement) and Portland cement, which is closed with radioactive concentrates of natural hydrocarbonate salts (salinity of at least 50 g / l) at a solution-cement ratio of about 0.5. At the same time, the content of IOS (by dry weight) in the cement mixture should not exceed 10%, since otherwise the cured products lose their water resistance (they are destroyed after exposure to water for 90 days).

The mixture is stirred until a homogeneous mass, and then utverjdayut within 28 days to gain strength sufficient for safe transportation (not less than 100 kg / cm ² ). These Portland cement compounds with a high degree of filling with radioactive waste (more than 10% of the total dry residue of salts and IOS) have a sufficiently high water resistance (retain strength at least 100 kg / cm ² even after 90 days in water) and leach after 90 days less 10 ^-4 g / cm ² · day, which ensures their safe burial in the simplest soil repositories.

Compared with the known methods for incorporating radioactive IOS into a Portland cement binder, the use of a solution of LRW hydrocarbonate concentrates as cement hardening cement provides a decrease in the leachability of radionuclides to a level sufficient for burial in soil repositories (less than 10 ^-4 g / cm ² · day), while maintaining high strength cement compounds (not less than 100 kg / cm ² ). At the same time, the water resistance of cement compounds is ensured with a total degree of filling of the dry residue of radioactive waste (IOS and salts) of more than 10%, which does not follow explicitly from the prior art (the introduction of salt concentrates in cement reduces the quality of cured products [7]), ie . the proposed method meets the criteria of an inventive step.

Examples of specific performance.

Example 1. (Analog). A mixture of KU-2 radioactive cation exchangers (in the Na ⁺ form) and anion exchangers (in SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ form) in a ratio of 1: 1 was mixed with 400 grade Portland cement and a solution of 0.5 g / l of natural hydrocarbonate salts (floor drain water) at a water-cement ratio of 0.5 until a homogeneous mass was obtained and solidified for 28 days. Cement compounds were tested for strength according to GOST 310.4-81 and leachability in accordance with GOST 29114-91. The characteristics of cement compounds are given in the table.

Example 2. (Prototype). It differs from example 1 in that a sorption clay admixture was added to the mixture in an amount of 10% by weight of cement. The characteristics of cement compounds are given in the table.

Example 3. (The inventive method). It differs from example 2 in that the cement was closed with a hydrocarbonate LRW concentrate with a salt content of 50 g / l at a mortar-cement ratio of 0.5. The characteristics of cement compounds are given in the table.

From the data given in the table, it follows that when Portland cement is mixed with industrial water without clay addition, cement compounds with a degree of filling of 10 wt.% On a dry IOS have ¹³⁷ Cs leachability exceed 1.0 · 10 ^-3 g / cm ² · day, t .e. does not meet the rules for safe disposal even in concrete storage facilities. The introduction of clay into the compound of the sorption additive reduces the leachability by an order of magnitude (up to 2.4 · 10 ^-4 g / cm ² · day), but decreases the strength almost to the safety limit (about 50 kgf / cm ² ). At the same time, the use of a concentrate of salts of hydrocarbonate natural waters for mixing Portland cement allows you to include up to 11.4 wt.% Dry radioactive residue (IOS and salts) to obtain high-strength (more than 100 kgf / cm ² ), waterproof compounds with a leachability of ¹³⁷ Cs less than 1 , 0 · 10 ^-4 g / cm ² · day, which ensures their safety even in emergency situations during transportation and the possibility of burial in the simplest soil burial grounds.

The proposed method can be carried out on the same equipment as the prototype, does not require additional consumption of materials and allows to reduce the total amount of landfill waste (provides joint curing of spent IOS and salt concentrates), i.e. the method is industrially applicable and economically viable. The application of this method increases the environmental safety of transportation and disposal of solidified radioactive waste, which satisfy not only domestic but also international requirements of the IAEA [2]. In addition, this method allows the solidified waste to be disposed of in simple ground repositories (with a specific activity of not more than 10 ^-5 Ci / kg [5].

Sources of information

1. Nikiforov A.S., Kulichenko V.V., Zhikharev M.I. Neutralization of liquid radioactive waste. - M .: Energoatomizdat, 1985, p. 110-111.

2. Bonnevie-Svendsen M., Tallberg K., Aittola P., e.a. Studies on the incorporation of spent ion-exchange resins from nuclear power plants into bitum and cement. - In: Symposium on the ion-site management of power reactor wastes, Zurich, 26-30 Marh, 1979, Paris, 1979, p. 155-174.

3. Byckley L.H., Speranzini R.A. Evaluation of matrica for immijbiliting ion-exchange resins, AECL - 6971, jule 1980.

4. The quality of the compounds formed by cementing liquid radioactive waste of low and medium levels of activity. - Technical requirements. - RD 95 10497-93. M .: Minatom of the Russian Federation, 1993.

5. Bazhenov Yu.M., Volkova OI, Dukhovich F.S. and others. Safety conditions during storage of radioactive cements. - Isotopes in the USSR, 1970, v. 17, p. 17-22.

6. Kuznetsov Yu.V., Schebetkovsky V.N., Trusov A.G. Basics of water purification from radioactive contamination. - M.: Atomizdat, 1974.

7. Sobolev I.A., Khomchik L.M. Disposal of radioactive waste at centralized sites. - M .: Energoatomizdat, 1983.

Claims (1)

The method of incorporating radioactive ion-exchange resins into a Portland cement binder, including mixing them with a clay sorption additive, cement and a grout followed by curing, characterized in that radioactive concentrates of salts of natural bicarbonate water are used as a grout.