A refined model for 235U(n,f) prompt fission neutron multiplicity and spectrum calculation with validation in integral benchmarks

The prompt fission neutron multiplicity and spectra of the n+U235 reaction are calculated for the first time with a refined model that takes into account the entire fission fragment range with a point-by-point treatment. At higher incident neutron energies, the treatment of neutrons evaporated prior to scission is improved by the use of the (n,xn) spectra obtained in the frame of the cross-section calculation (compound nucleus and pre-equilibrium mechanisms). The new prompt fission neutron multiplicity and spectra up to 30 MeV incident neutron energy, included in the U-235 BRC/JEFF3.1t evaluation, lead to very good Keff results with the fast and thermal integral benchmarks.