Study of americium and plutonium chemistry in Mixed OXide fuel

The aim of this work is to follow the chemistry of uranium, plutonium and americium, and in particular their oxidation states, in MOX samples sintered under different oxygen potentials. To address this issue, X-ray Absorption Spectroscopy (XAS) is the ideally suited as it allows the quantitative determination of oxidation states for each cation using X-ray Absorption Near Edge Structure (XANES) and to outline potential discrepancies in actinide local environments using Extended X-ray Absorption Fine Structure (EXAFS) [3].
MOX samples with the following composition (U0.750Pu0.246Am0.004)O2-x, were manufactured at the LEFCA facility at CEA Cadarache (France). The process used is based on a direct co-milling of the oxides and leads to a homogeneous plutonium distribution [4]. Pellets were sintered at 1700°C under controlled atmosphere (moist Ar/5% H2) to obtain the following O/M ratios: 1.94, 1.97 and 2.00. These values were confirmed by thermogravimetric analysis.
XAS spectra at uranium, plutonium and americium LII,III edges were collected at the ROssendorf Beamline (ROBL) of the European Synchrotron Radiation Facility (Grenoble, France). XRD and thermogravimetric measurements were performed at the LEFCA facility.