ELECTROCHEMICAL PROPERTIES AND THERMODYNAMIC STABILITY OF PU AND NEIGHBORING ACTINIDES IN THE (IV) AND (V) OXIDATION-STATES IN AQUEOUS ALKALINE MEDIA AND RADWASTES

In alkaline media Pu(V) is reduced to Pu(IV) and Pu(III) at a mercury electrode at -0.72 and -1.1V/S.H.E. respectively, while Am(V) is reduc ed to hydrolysed Am(IV) at a Pt cathode at +0.2V. The apparent redox p otential Am(V)/Am(IV) is consistent with earlier published data, while that of Pu(V)/ Pu(IV) = -0.72 V differs significantly from the publis hed data between +0.4 and +0.9 V. Our data are consistent with the rep orted high stability of Pu(V) in alkaline media. It is concluded that Pu(V) cannot disproportionate in these conditions. Electrochemical red uction of U(V) and Np(V) is not observed in 1 to 10M NaOH solutions at significantly negative potentials. Hence the estimations of (V)/(IV) potentials for U and Np in 1 M NaOH should also be corrected. A simila r study has been undertaken at a pH closer to neutrality and the stabi lity of pentavalent actinides at this pH is also discussed.