Evaluation of neutron-induced reactions on ²³⁸U nucleus

Advanced modelling of neutron-induced reactions on ²³⁸U nucleus using the EMPIRE system is aimed at improving our knowledge of the neutron scattering leading to better nuclear data for nuclear power applications. Capture and fission channels in n + ²³⁸U reaction are well constrained by available experimental data and IAEA neutron standard evaluations allowing to focus on the impact of elastic and inelastic scattering in evaluated cross-sections. The reaction model includes: i) a new rotational-vibrational dispersive optical model that couples the low-lying collective bands of vibrational character observed in even-even actinides; ii) the Engelbrecht-Weidenmüller transformation allowing inclusion of compound-direct interference effects enhanced by a dispersive treatment of the optical model potential; iii) a multi-humped fission barrier with absorption in the secondary well described within the optical model for fission. Impact of the advanced modelling on inelastic scattering cross-section and corresponding uncertainties is being assessed both by comparison with selected microscopic experimental data and integral criticality benchmarks including measured reaction rates (e.g. FLATTOP, JEMIMA, BIGTEN, MASURCA, PROFIL and PROFIL-2). Additionally, neutron scattering yields on ²³⁸U measured accurately at RPI by the time-of-flight technique at 29°, 60°, 112° and 153° have been used as a further constraint on the incident energy dependence of elastic and inelastic scattering of neutrons. Benchmark calculations provided feedback to improve the reaction modelling. The improvement of scattering cross-sections in existing libraries is discussed.