Combined matrixes for solidification of organic radioactive liquid wastes containing Cs-137 and Sr-90

详细

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).