Calculation of resonance self-shielding in 235U

The self-shielded fission rates for 235U measured by Czirr have been computed in the 0.464- to 464-eV range with the 235U resolved resonance parameters of the current version of ENDF/B-VI. The main purpose of describing the neutron cross sections of the fissile isotopes with resonance parameters is for the calculation of resonance self-shielding in reactors. Czirr has measured the relative self-shielded fission rate behind absorber thicknesses varying from 0.5 to 19 g/cm2 of uranium. These measurements have repeatedly been used to test the validity of sets of resonance parameters. However, previous calculations of these experiments were limited and inconclusive. An evaluation of the 235U resolved resonance region extending to 2.2 keV was recently completed and incorporated into ENDF/B-VI. The resonance parameters of this evaluation were used to compute the self-shielded fission rates for energy groups 0 to 8 (energies from 0.464 to 464 eV) of the Czirr measurement