Bridging the Gap in the Chemical Thermodynamic Database for Nuclear Waste Repository: Studies of the Effect of Temperature on Actinide Complexation, in Nuclear Energy and the Environment;

Recent results of thermodynamic studies on the complexation of actinides (UO22+, NpO2+ and Pu4+) with F-, SO42- and H2PO4-/HPO42- at elevated temperatures are reviewed. The data indicate that, for all systems except the 1:1 complexation of Np(V) with HPO42-, the complexation of actinides is enhanced by the increase in temperature. The enhancement is primarily due to the increase in the entropy term (T\u394S) that exceeds the increase in the enthalpy (\u394H) as the temperature is increased. These data bridge the gaps in the chemical thermodynamic database for nuclear waste repository where the temperature could remain significantly higher than 25\ub0C for a long time after the closure of the repository