The reliability of solubility data: Results from a limited literature survey focusing on Ni, Pd and Np

The performance assessment (PA) of, e.g., repositories for spent nuclear waste needs data that relies on databases containing large amounts of chemical thermodynamic data. It is evident that the quality of such data should be good, in the sense that its uncertainties and origin, etc. should be well documented. The presence of erroneous data might make the outcome of the PA doubtful, in the worst case even partly worthless. However, the task of checking the quality of data is far from effortless and demands a considerable amount of time and money. The objective of this work was to examine, within limited resources, the solubility data for three elements of interest, for example, in the safety analyses of repositories for nuclear waste. The elements studied were nickel, palladium, and neptunium. In order to delimit the topic, this report deals only with a small number of relevant species; the discussions of the solubilities of nickel, palladium and neptunium are mainly restricted to sulphides, oxide/hydroxide, and phosphates, respectively. The report discusses some general difficulties associated with "data evaluation", and presents the outcome of a minor literature survey on the solubility studies for nickel, palladium, and neptunium, respectively. The results indicate that in the case of palladium, few published data exist. This is however not alarming since palladium, being a member of the platinum group metals, is known to have considerable stability in the environment. In the cases of nickel and neptunium, it was found that there is a lack of proper solubility data. The report does not discuss whether this is serious or not, since this depends on the system studied and the conditions considered.