THERMODYNAMIC DATABASE FOR ACTINIDE AQUEOUS INORGANIC COMPLEXES

All available published results of experimental investigations of the solubility, hydrolysis, and complex formation processes occurring in aqueous actinide-bearing systems were collected and analyzed within the framework of the ''DiaNIK'' database. The results of critical evaluations of the data published before early 1989 were adopted from Fuger et al. (J. Fuger, I.L. Khodakovsky, E.I. Sergeyeva, V.A. Medvedev and J.D. Navratil, in V.A. Medvedev, M.H. Rand and E.F. Westrum, Jr., (eds.), The Chemical Thermodynamics of Actinide Elements and Compounds, Part 12, The Actinide Aqueous Inorganic Complexes, International Atomic Energy Agency, Vienna, 1992). The most reliable experimental values of the equilibrium constants were selected and the values of corresponding thermodynamic constants recommended. In many cases thermodynamic equilibrium constants are not recommended owing to the lack of experimental data or discrepancies between the data available. Probable sources of discrepancies between the experimental data, obtained by various researchers, and the results of thermodynamic calculations are analyzed using examples. The necessity of further studies of the solubility of actinide compounds and refinement of the values of standard entropy of UO22+, U4+, and Th4+ aqueous ions is substantiated.