Ruthenium Volatilisation from Reprocessed Spent Nuclear Fuel – Studying the Baseline Thermodynamics of Ru(III)

Abstract

Ruthenium is a fission product possessed of two relatively long lived isotopes, 103 Ru and 106 Ru, both of which form part of the Highly Active (HA) waste raffinate during spent nuclear fuel reprocessing. During reprocessing ruthenium, which may be in the form of the RuNO 3+ complex, encounters temperatures conducive to volatilization. Due rutheium's high specific radioactivity it is important to understand the mechanism by which volatilisation occurs. Here we use combined CV, RDE and electrochemical microgravimetry experiments in a study of the the RuCl 3 system for the first time. We do this in the interest of establishing NO-free Ru(III) baseline behaviour so as to support future studies on NO complexed ruthenium. Using wide aqueous solvent window carbon electrodes we have observed discrete oxidations to a solution phase Ru(III)-Ru(IV)-Ru(III) trimer, to solid RuO 2 and volatile RuO 4 . We have also observed and assigned discrete reductions of solid RuO 2 back to Ru(III) and Ru(III) reduction to ruthenium metal.