Evaluation of Neutron Nuclear Data for Uranium-233

Abstract

Neutron nuclear data of 233 U have been evaluated in the energy range from 10-5 eV to 20 MeV. Evaluated quantities are the total, fission, capture, elastic and inelastic scattering, (n, 2n) and (n, 3n) reaction cross sections, and the average numbers of prompt and delayed neutrons emitted per fission. The thermal and resonance cross sections have been evaluated on the basis of the measured data. The resolved resonance parameters are given up to 100eV and the unresolved resonance parameters between 100eV and 30keV. The total and fission cross sections have been evaluated in the higher energy region on the basis of the recently measured data, while the theoretical calculation with the optical, statistical and evaporation models has been used for evaluation of the other cross sections. The presently adopted optical potential parameters have reproduced well the experimental total cross section in the entire energy range as well as the measured data of the s-wa ve strength function. The structure observed in the vp values below 1 MeV is reproduced by the semi-empirical formula based on the fission fragment kinematics. The presently evaluated fission cross section is considerably lower than that of ENDF /8-IV between 10 and 50 keY. This low fission cross section is expected to resolve the kef! discrepancy pointed out from the benchmark tests in 233 U critical assemblies.