Long-term field tests of cemented aqueous radioactive wastes in an experimental mound type surface repository were carried out at Moscow Scientific and Industrial Association “Radon” from 1965 to 2004. Aqueous radioactive wastes of different compositions containing short-lived radionuclides including 90Sr and 137Cs at concentrations from 0.34 to 1.8 MBq/L were immobilized using cementation technology. Water solution to cement ratio was 0.66, grout mixing time 10-15 minutes, and cement paste hardening time 7 days. 73 cement blocks with a volume of 0.027 m3 were disposed of for long-term tests in a simple mound type surface repository. The atmospheric precipitates, which contacted radioactive cement blocks, were collected and analyzed for the content of radionuclides. In August 2004 the experimental repository was opened, cemented blocks, underlying and covering materials were retrieved for analyses. XRD analyses showed that along with amorphous tobermorite gel the main crystal phases in cements are calcite and portlandite. Both visual inspection and radiometric analyses demonstrate that cemented blocks are in good condition and that the cement paste has retained radionuclides from the wastes. Thus after 39 years of storage in the mound type repository the cemented aqueous wastes are reliable immobilized.
Cemented wastes to be stored for a long time are investigated using physicochemical and microbiological methods of analysis. It is determined that the cement compound containing radioactive wastes conforms to the regulations pertaining to strength and radionuclide leach rate. No effects due to natural factors in the form of filtering waters and temperature differentials on the change in the properties of the cement compounds were found.The most widely used, technically most effective, and most cost-effective technology for conditioning low-and medium-level wastes is cementing [1]. Diverse wastes are cemented: liquid, containing salts (nitrates, chlorides, sulfates, borates); solid, including metallic and with cellulose; construction debris and household refuse; soil; mud; spent oils; and organic solvents. It has been shown that high-level wastes with specific activity up to 22 GBq/kg can be cemented [2]. Combined cementing of liquid and solid radioactive wastes is most often used in practice [1]: for this, the liquid wastes are mixed with cement and the solution obtained is allowed to permeate solid wastes. As a rule, cemented low-and medium-level wastes are placed in surface repositories. According to the regulations [3], the properties of the cemented wastes which are to be transported or stored for a long period of time, must have high mechanical strength, be chemically stable and structurally uniform, and so forth. Cemented wastes must keep their primary properties during the period of time over which they reach a safe level of radioactivity as the radionuclides decay or for the storage time specified in the regulations. Conformance to requirements is determined on the basis of investigations of the parameters of the cement compound that characterize its properties. Basic parameters include the leach rate of radionuclides, mechanical strength under compression, frost resistance, and stability when standing in water for a long time [1,3].The best method for evaluating the properties and predicting the behavior of the cemented wastes during long-term storage is to study them under conditions close to the actual conditions, i.e., in experimental near-surface repositories with periodic sampling of the material being tested and ground waters. Site tests of cemented wastes are being conducted at the Moscow Scientific and Industrial Association Radon under different storage conditions: open method and in experimental mound and burial (no additional engineered barriers in the cover loams) type repositories. The experimental repositories simulate the climatic, hydrogeological, and microbiological conditions of storage in industrial surface repositories.The objective of the present work is to evaluate the properties of cemented wastes during long-term storage and to confirm the conformance of cemented low-and medium-level wastes to the regulatory requirements.The results of investigations of cemented wastes from a mound-type experimental repository built in 1965 are presented in the present article [4]. The foundation ...
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