Synchrotron investigation of actinide (U and Pu) speciation during ADOA gel-to-oxide conversion

Actinide co-conversion is a central challenge for developing Gen IV reactors and MOx fuels. The Advanced Thermal Denitration with Organic Additives (ADOA) route is especially promising, as it ensures homogeneous trapping of U and Pu cations in polymer gels, later converted into oxides without valence adjustment. However, little is known about actinide speciation and redox states at the gel stage, although these parameters strongly influence the final oxide. This proposal aims to investigate U and Pu oxidation states and local environments in gels and xerogels obtained by ADOA under varied synthesis conditions. Using EXAFS and HERFD-XANES at the ROBL beamline, we will probe actinide coordination and redox chemistry, and compare with oxide references. These results will clarify how polymerization and gelation control speciation and will guide optimization of the ADOA process toward homogeneous, fuel-relevant U₁₋ₓPuₓO₂ materials, improving nuclear fuel recycling.