LAUSR

Combined cement matrixes are proposed for petrification of organic liquid radioactive liquid wastes (spent tributyl phosphate in hydrocarbon solvent, process oil) containing radionuclides 137Cs and 90Sr. The high level of filling of the matrixes with waste is achieved by premixing thermally expanded graphite with the latter. To confine cesium firmly, bentonite clay additions with a montmorillonite content not less than 65 vol % should be included in the compounds. It is demonstrated that the desired content of extracting agent in the compound is 25 vol % and that of oil is 20 vol %. The minimum time of aging of the compounds before transportation for long-term storage or burial should be not less than 42 days from the moment of cement mixing. The moisture-resistant enamel coating of the surface of compounds does not prevent substantial diffusion of 137Cs. However, it slows down the water absorption by the cement, thus postponing the beginning of transition 137Cs and other radionuclides to the liquid phase. The strength of the compounds obtained in the paper complies with the standardized values (GOST R 51883-2002). The average leaching rate of 137Cs is not more than 1 mg/(cm2 day) and that of 90Sr + 90Y is not more than 0.1 mg/(cm2 day). The leaching kinetics of cesium radionuclides from the compound has a diffusive character. The leaching kinetics of strontium and yttrium radionuclides from the compound has a sorption-desorption character. The leaching rates of radionuclides of elements of groups I, II, and III form the following series: R(137Cs) > R(90Sr) ≫ R(90Y).