Including Chi-Nu 235U PFNS Experimental Data into an ENDF/B-VIII.1 Release Candidate Evaluation
This report documents an evaluation of 235U prompt fission neutron spectra (PFNS) that is a release candidate for the upcoming U.S. nuclear data library, ENDF/B-VIII.1. This evaluation differs from its predecessor, ENDF/B-VIII.0, mainly by the inclusion of 235U PFNS measured by the Chi-Nu team of LANL and LLNL. This data set is the first one that covers the 235U PFNS for continuous incident-neutron energies of 1⁻20 MeV and outgoing-neutron energies from 10 keV⁻10 MeV with high precision. Previous data sets were either measured in a limited energy range or with less precision. Hence, these new Chi-Nu data provide decisive information for the evaluation. The resulting evaluated data correspond well to the new experimental PFNS. The evaluated PFNS also produce average mean energies and 239Pu/235U PFNS in agreement with associated Chi-Nu data. If one uses the new evaluated data to predict the neutron multiplication factor, keff, of selected ICSBEP critical assemblies, the differences of simulated values compared to those using ENDF/B-VIII.0 is modest (less than 55 pcm). This difference in keff can be easily accommodated by changes in the 235U average prompt fission neutron multiplicity that is currently being re-evaluated. In addition to that, the new PFNS predict on average 235U LLNL pulsed-sphere neutron-leakage spectra better than ENDF/B-VIIII.0 PFNS.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
- DOE Contract Number:
- 89233218CNA000001
- OSTI ID:
- 1855106
- Report Number(s):
- LA-UR-22-22220; TRN: US2302986
- Country of Publication:
- United States
- Language:
- English
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