Characterization of Simulated Liquid Radioactive Waste in a New Type of Cement Mixture.

There is still a safety challenge for the long-term stabilization of nuclear waste. Due to its affordable price and easy manufacturing, cement is one of the most promising materials to immobilize a large volume of low- and intermediate-level radioactive liquid waste. To investigate the effect of borate on the cementation of radioactive evaporator concentrates and to provide more data for solidification formula optimization, simulated liquid waste in various concentrations was prepared. Different borate concentrations were solidified in ordinary Portland cement (OPC) and in two new cement compositions with water resistance and boron-binding additives. The chemical and mechanical properties were investigated for nine cementitious samples, together with three compositions in three concentrations. The leaching rate of the boron is lower in the case of a high strength cement mixture. The compressive strengths of the solidified waste correlate with the leaching rates of the boron. The leaching rates of Ca were changed with the cement composition and even with the boron concentrations; first, they were lower in the initial OPC in the case of the same boron concentration (50 g/L); second, they were lower at a higher boron concentration (250 g/L) for the OXY-B composition. The simulated liquid waste with higher boron concentrations solidified with newly developed cement composition (OXY-B) shows a homogeneous boron distribution in the volume of the cement cylinder both before and after leaching. The formulas of OXY and OXY-B developed in this application were effective for cementation of the simulated borate evaporator concentrates.