Aggregate Delayed Neutron Intensities and Spectra Using Augmented ENDF/B-V Precursor Data

Abstract

The evaluated nuclear data files (ENDF/B-V) have been used for 105 precursors, augmented with experimental spectral data for 29 emitters and recent model calculations for the remaining 76 emitters, in aggregate summation calculations. The equilibrium-delayed neutron intensities and spectra in the conventional six time groups for 11 fissionable nuclides were calculated. Normalized experimental neutron spectra for 29 emitters were supplied by Rudstam. Augmentation of the spectra uses data calculated with a recently developed code, BETA. Fission yields of the precursors and their delayed neutron branching fractions, P_n, are from ENDF/B-V. Results are compared where possible with corresponding group and total evaluations of aggregate measurements. The intent of these calculations is to examine the adequacy of precursor data for inclusion in ENDF/B-VI. Most of the results, particularly with the added model parameters, are sufficiently accurate to be of direct interest to the reactor community. The total delayed neutron yield per neutron absorption, , for ²³⁸U and ²³²Th suggests that either an improvement in ENDF/B fission yields is needed or the evaluated experimental values are in significant error.