Evaluation of Uranium-238 Neutron Cross Sections from Spectral Measurements

The neutron spectra on the central axis of a massive block of uranium depleted in the ²³⁵U isotope have been measured using spherical proton-recoil and ³He semiconductor-sandwich spectrometers. The experimental spectra are compared to calculated multigroup spectra obtained with a 208-group constant cross-section set which is based on KEDAK cross sections. By parametric variation of all relevant nuclear data, the sensitivity of the spectra to changes in the ²³⁸U cross sections is determined. The ²³⁸U capture and inelastic scattering cross sections are adjusted to bring the calculations in line with the experiment. It is shown that the resulting adjusted ²³⁸U cross sections also lead to considerably better agreement between experimental and theoretical results for other fast assemblies which are sensitive to changes in the ²³⁸U cross sections.