Effect of cement water on UO2 solubility

Abstract

To assess the stability of spent fuel in the highly alkaline chemical environment of the Belgian Supercontainer design, static leach experiments were performed with depleted UO2 and 238Pu-doped UO2 at different SA/V ratios for 1.5 years in cement waters (11.7< pH < 13.5) at ambient temperature and under argon atmosphere. The influence of the calcium concentration on the uranium release was also investigated. While the ultrafiltered U(IV) concentration was 10−9–10−8 mol.L−1 and independent of the pH, the U(VI) release from the UO2 surface was enhanced by the OH concentration, leading to soluble U concentrations up to 10−5 mol.L−1 at high SA/V and under the influence of radiolysis. Together with the high Ca concentration, this can lead to the formation of Ca-U(VI) colloids as precursor of Ca-U(VI) secondary phases, decreasing the soluble U concentration. The precipitation of Ca-U secondary phases was however not clearly evidenced by surface analyses.

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Acknowledgements

This work was performed as part of the program of the Belgian Agency for Radioactive Waste and Enriched Fissile Materials (NIRAS/ONDRAF) on the geological disposal of high-level/long-lived radioactive waste. The authors gratefully acknowledge the technical support from Ben Gielen and Regina Vercauter.

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Cachoir, C., Mennecart, T. & Lemmens, K. Effect of cement water on UO2 solubility. MRS Online Proceedings Library 1665, 267–273 (2014). https://doi.org/10.1557/opl.2014.654

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