The effect of coprecipitation in some key spent fuel elements

Performance assessment (PA) of high-level waste (HLW) repositories needs to know real aqueous concentrations of key radionuclides under repository con ditions for assuring the safety of the emplacement. The scarcity of these v alues under repository conditions leads to the use, in the PA studies, of t he solubility of pure phases, which is a conservative assumption. Coprecipi tation experiments are a very useful tool for giving realistic solubilities of key radionuclides. In this work, experimental data obtained from spent fuel (SF) and SIMFUEL coprecipitation tests under granite and saline condit ions are presented. The experimental concentrations measured for several el ements when equilibrium was achieved were much lower than expected consider ing only the solubility of pure phases. To explain this discrepancy, a tent ative approach for modelling these experimental leaching and precipitation results of uranium, plutonium, americium, and strontium taking into account solid solution formations was made. (C) 2001 Elsevier Science B.V. All rig hts reserved.