The Geochemical Behaviour of Nickel in the Repository Environment

Abstract

Abstract59Ni may make significant contributions to calculated doses in performance assessment (PA) studies of geological repositories for radioactive waste, due principally to the adoption of relatively high near-field solubilities. Ni concentration values used in PA are typically 1–6 orders of magnitude greater than those measured in natural groundwaters. This difference is a result of the utilisation in PA of solubility data for pure nickeliferous solids, and in some instances, the selection of solids chemically incompatible with the disposal environment. The geochemical behaviour of Ni is reviewed. It is considered highly unlikely that Ni will form discrete pure solids in the repository near-field, so that partition as a trace element into solid solutions should be considered. Henry’s law behaviour of trace elements is discussed and geochemically-realistic Ni solubility values for HLW and L/ILW disposal scenarios calculated. It is concluded that Ni will behave according to the chemical conditions of the disposal environment, which should be reflected in the choice of solubility data for PA. The adoption of solid solution modelling for other elements of interest to PA should be considered.