Speaker
Description
A comprehensive reevaluation of $^{239}$Pu transport cross sections from subthermal energies up to 30 MeV within the INDEN collaboration is presented. Softer prompt fission neutron spectra (PFNS) for thermal neutron-induced fission with an average energy of 2.08 MeV from the IAEA evaluation is combined with new resonance parameters and new nubar evaluation to preserve the good criticality performance of the ENDF/B-VIII.0 evaluation for plutonium thermal solution (PST) benchmarks. A new LANL PFNS evaluation, based on ChiNu and CEA data, is used in the fast energy region above 500 keV. A new evaluation of the fast neutron cross sections based on updated Neutron Standard fit for the fission channel (including fissionTPC data and covariances updated with templates of expected measurement uncertainties) and EMPIRE nuclear reaction modeling was undertaken. A soft rotator optical model potential that couples the ground state rotational band with K$^{\pi}$=1/2+ and the octupolar rotational band with K$^{\pi}$=1/2- starting at 469 keV is employed to obtain consistent scattering cross sections in the fast neutron range. DWBA inelastic scattering to the continuum is included to get a better agreement with 14 MeV Kammerdiener double differential cross section data. The calculated (n,2n) cross section is in good agreement both with latest CEA measurements by Meot et al and with ENDF/B-VIII.0 evaluation.
This new INDEN evaluation is shown to improve benchmark performance for Livermore 14-MeV Pulsed Spheres compared to ENDF/B-VIII.0 (Fig. 1) and preserve the good criticality performance of the ENDF/B-VIII.0 file.
Fig. 1: The INDEN evaluation p27 performs better in predicting LLNL pulsed sphere neutron spectra for a Pu sphere than ENDF/B-VIII.0 and INDEN p26 compared with data (UCID-16372).