Chemical reactions between liquid sodium and urania-plutonia solid solutions - the threshold plutonium valency for reaction

Experimental determinations of the threshold plutonium valency above which reactions occur between urania-plutonia solutions with plutonia concentrations between 10 and 30 mol.% and liquid sodium are reviewed. Some discrepancies were found between these values obtained using different experimental techniques. In particular, the data obtained from the direct measurement of the thermodynamic oxygen potential of the three phase assemblage, sodium, urania-plutonia and sodium uranoplutonate do not show adequate agreement with the values of the threshold valency obtained from measurements of the lattice parameters of the oxide phase and the amount of swelling of dense pellets of the oxide. The review has indicated that the threshold valency of plutonium decreases with increasing temperature and plutonia concentration of the solid solution and that there are some inadequacies in the thermodynamic data for urania-plutonia solid solutions. (orig.)