Study on the properties of cement composites for immobilization of evaporator concentrates

The disposal of evaporator concentrates (EC) as an intermediate-level radioactive waste requires reliable immobilization in a solid matrix, such as cement. Six types of cement composites were studied in terms of drying and saturation cycling, water absorption, mechanical properties and leaching to assess their suitability to EC immobilization. Composites differed in the binder composition - five of them were based on a mixture of non gypsum cement with Ordinary Portland cement (NP)/metakaolin (NM) and admixtures of natural zeolite and metakaolin (NP_M, NP_Z, NM_Z). Sulpho-aluminate cement (SAC) was chosen for comparison. SAC composite exhibited superior parameters of compressive strength and water absorption in the reference state, however after cycling severe cracks and disintegration appeared causing this matrix inappropriate for EC immobilization. NM based mixtures showed highest Cs+ retention capacity, however less resistance to cycling and lower mechanical parameters than NP based composites. In terms of leachability, all mixtures met the requirements according to ANSI/ANS-16.1-2003.