Database development of chemical thermodynamics of plutonium for performance assessment of HLW geological disposal system

Shibutani, Tomoki; Shibutani, Sanae

In the performance assessment of geological disposal system of high-evel radioactive waste(HLW), solubility and speciation of radioactive elements are important to estimate their migration behavior from vitrified HLW in engineered and natural barrier system. The solubility and speciation of radioactive elements are calculated by using thermodynamic data and geochemical code, so development of reliable thermodynamic data base is important to built confidence for performance assessment. In this report, reaction constants of plutonium oxidation/reduction, hydrolysis, complexation for carbonate, sulphate, phosphate, nitrate, fluoride and chloride are discussed and selected. For the development of the PNC-TDB, existing literature data were surveyed and realistic thermodynamic data were selected under consideration of chemical properties, chemical analogy of other actinide element and the internal consistency with the hole PNC-TDB. Solubilities of plutonium were studied by several researchers, and these measurement have been compared with geochemical calculation for validation of the PNC-TDB. Calculated results shows that the experimental results can be interpreted by geochemical calculation by using the PNC-TDB.