Actinide M4,5 edge HR-XANES study of the actinide redox states in spent nuclear fuel

Advanced spectroscopy methods, which provide precise actinide (An) oxidation state and electronic structure information are needed to understand in details redox processes in complex actinide materials. The An M4,5 edge high energy resolution X-ray absorption near edge structure HR-XANES experimental technique has been extensively developed and applied over the last decade. We report here applications of the An M4,5 edge HR-XANES and RIXS methods in a oxidation states study of U, Pu, Np and/or Am in spent nuclear fuel (SNF). All samples are prepared in the facilities of the European Joint Research Centre – Karlsruhe. The HR-XANES and RIXS experiments are carried out at the ACT station of the CAT-ACT beamline at the Karlsruhe Research Accelerator (KARA), Karlsruhe Institute of Technology. Karlsruhe, Germany.
The aim of our study is to gain understanding of the An oxidation states in SNF when exposed to air. We investigated the U, Pu, Np and Am oxidation states across a SNF pellet applying the An M4,5 edge HR-XANES and RIXS techniques. The fuel was irradiated in the Grohnde pressurized water reactor and has an average burn-up of 67 GWd/tHM. ... mehrWe isolated particles from three different radial positions of the SNF pellet and cut a piece of the zircaloy cladding with still attached to it fuel material. It will be shown that the U and the Np oxidation states depend on the radial position of the SNF pellet, whereas the redox states of Am and Pu do not change. Different redox mechanisms and the interdependency between the An oxidation states and the SNF morphology as well as the level of burn-up will be discussed.