PNNL

Abstract

Studtite, [UO2(?2-O2)(H2O)2]·2H2O and metastudtite [UO2(?2-O2)(H2O)2] are important phase alteration of UO2 in a spent nuclear fuel repository and has previously been shown to react with Np(V). In this work we extend the study to Am(V) on a tracer scale and show spectroscopic evidence that the Am is incorporated into the structure of studtite as Am(III). A computational study on the possible mechanisms for incorporation of Np and Am shows that protonation of the -yl oxygen is the favoured route and the calculated incorporation energies are large and positive. The results suggest that Am is less favoured compared to Np but energetically more favoured to incorporate both actinide ions into metastudtite rather than studtite. Finally, we have shown that once incorporated, Am readily leaches into water but spectroscopic measurements suggest subtle changes in the structure of studtite.