Actinide Thermodynamics at Elevated Temperatures

摘要

The postclosure chemical environment in the proposed Yucca Mountain repository is expected to experience elevated temperatures. Predicting potential migration of actinides would be more robust if sufficient reliable thermodynamic data on hydrolysis and complexation are available for these temperatures. Data are scarce and scattered for 25C, and nonexistent for elevated temperatures. Current modeling of actinide migration makes conservative assumptions to compensate for this lack of data, particularly at elevated temperatures. This collaborative project between LBNL and PNNL collects thermodynamic data at elevated temperatures on actinide complexes with inorganic ligands that may be present in Yucca Mountain. The ligands include hydroxide, fluoride, sulfate, phosphate and carbonate. Thermodynamic parameters of complexation, including stability constants, enthalpy, entropy and heat capacity of complexation, are measured with a variety of techniques including solvent extraction, potentiometry, spectrophotometry and calorimetry.