Neptunium-237 is a major concern for the long-term disposal of nuclear waste in a geological repository owing to its 2.14 million year half-life and its solubility in water as the neptunyl ion under oxidizing conditions. We have examined incorporation of Np(V) into a variety of uranyl minerals that may form due to the alteration of nuclear waste in a repository, and find that uptake is dependent on the details of the specific target structure as well as the synthesis conditions. We have also examined incorporation of Np(V) into several carbonate, borate, and sulfate minerals in order to determine the specific uptake mechanisms, including site selectivity and charge-balance mechanisms. In general, we find that uptake is strongly dependent on the details of the available crystallographic sites in the minerals for substitution, as well as the specifics of charge-balance mechanisms. We have compared Np(V) uptake in low-temperature minerals with that of U(VI), and find significant differences in uptake levels under identical experimental conditions.

Incorporation of neptunium into uranyl minerals and various non-actinide low-temperature minerals

248th National Meeting (2014)

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