Comparison of solubility databases used for HLW performance assessment

Elemental solubility limits are employed in many performance assessment studies of the disposal of high-level radioactive waste. A comparison of solubility databases used in a number of recent assessments from Canada, Finland, Japan, Sweden, Switzerland and the U.S.A. is presented. Despite similarities in the chemical conditions under which such solubilities are defined, there are very large ranges in the values selected for most elements (several orders of magnitude). In some cases, differences in solubilities can be attributed to differences in the thermodynamic databases used but, due to generally incomplete documentation, both of such databases and the criteria for data selection, detailed analysis of the reason for such discrepancies is precluded. A key factor, however, is the fairly subjective choice of the solid phase considered to be “solubility-limiting”. Procedures are recommended which would increase the transparency of solubility database compilation in future analyses.