Cementation of a low-level radioactive waste of complex chemistry

Abstract A cement-based grout formulation was investigated to immobilize low-level radioactive evaporator concentrates with widely variable chemical composition. The objective was to determine the sensitivity of the solidified waste forms characteristics on a variation in the concentrations of four components of the waste (boron, chloride, sulfate and phosphate). Providing adequate changes of variables, the problem was shown to amount to a mixture study with constraints placed on each factor. Experimental design methodology enabled to build empirical models (special cubic models in the canonical form), which gave a satisfactory description of the responses (viscosity of the grout, heat of hydration of cement, compressive strength and expansion of 4×4×16 cm specimens after 90 days of wet curing) within the region of the experimental data, and which could be used as prediction tools. High contents of phosphate in the waste (>25 g·l−1) were shown to improve most properties of the elaborated materials. In particular, setting time, rate of heat production and swelling under water were decreased, while grout workability was enhanced.

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