Measurement of partial (n, n'gamma) reaction cross -sections on highly radioactive nuclei of interest for energy production

In the context of the development of Gen. IV nuclear reactors, the GIF (Generation IV. International Forum) has selected six innovative technologies. Among them, one can highlight the concept of breeding for Th-232/U-233 and U-238/Pu-239 fuel cycles. But those nuclei, crucial for such cycles, suffer from a lack of precise knowledge (nuclear structure, reaction cross sections). In particular, it has been demonstrated that neutron inelastic scattering reaction cross sections are not known with sufficient precision for the isotopes U-238 and Pu-239, and not known at all experimentally for U-233. In order to perform simulations of innovative reactor cores for the development of those technologies, the knowledge of the reaction cross section has to be improved which implies that new measurements have to be done. The GRAPhEME (GeRmanium array for Actinides PrEcise MEasurements) experimental setup, developed by the IPHC laboratory from CNRS and installed at the EC-JRC-Geel GELINA facility is a powerful tool to answer this need [1, 2]. Combining the prompt gamma-ray spectroscopy and the time-of-flight methods, it measures partial (n, xn gamma) reaction cross sections. This paper reports on the improvements made on the GRAPhEME setup and data analysis methodology to tackle the challenge of (n, xn gamma) cross section measurements on high activity actinides. Results obtained so far on U-233 are presented compared to TALYS calculations.