Release of Evaluated 239Pu(n,f) Prompt Fission Neutron Spectra Including the CEA and Chi-Nu High-precision Experimental Data - Archive ouverte HAL Accéder directement au contenu
Pré-Publication, Document De Travail Année : 2022

Release of Evaluated 239Pu(n,f) Prompt Fission Neutron Spectra Including the CEA and Chi-Nu High-precision Experimental Data

Résumé

This report documents an evaluation of 239Pu 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 two 239Pu PFNS high- precision experiments: one measured by the Chi-Nu team of LANL and LLNL, and the second one by the CEA team using the liquid-scintillator Chi-Nu array. These two data sets are the first ones that cover the 239Pu PFNS for continuous incident-neutron energies of 1–20 MeV and broad outgoing-neutron energies with high precision. Chi-Nu covers outgoing-neutron energies from 10 keV–10 MeV, while CEA data are given for 0.25–11.3175 MeV. Previous data sets were either measured in a limited energy range or with less precision. Hence, these new CEA and Chi-Nu data provide decisive information for the evaluation. The resulting evaluated data correspond well to the new experimental PFNS, but are distinctly different than ENDF/B-VIII.0 values at all incident-neutron energies. These large differences compared to ENDF/B-VIII.0 can also be seen in the average mean energies computed from the new evaluated PFNS. However, the evaluated mean energies agree well with experimental data from Chi-Nu and CEA data, again, indicating that while the changes are large compared to ENDF/B-VIII.0, they are supported by experimental data. Due to those differences, large drops (e.g., -128 pcm for Jezebel or -114 for Flattop-Plutonium) in the predicted effective neutron multiplication factor, keff , of selected ICSBEP critical assemblies can be observed when these new PFNS are used compared to using ENDF/B-VIII.0. These large changes can be counter-balanced by considering, in addition to the new 239Pu PFNS, new evaluated data for the neutron-induced 239Pu fission cross section from the Neutron Data Standards project and the average prompt fission neutron multiplicity from an NCSP project. A further indication that the evaluated data describe high-precision experimental data well is that the the evaluated PFNS also produce 239Pu/235U PFNS in agreement with associated Chi-Nu data. Changes in the simulation of 239Pu LLNL pulsed-sphere neutron-leakage spectra are modest compared to ENDF/B-VIIII.0 PFNS
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Dates et versions

hal-03823245 , version 1 (20-10-2022)

Identifiants

  • HAL Id : hal-03823245 , version 1

Citer

Denise Neudecker,, Keegan J. Kelly, Paola Marini. Release of Evaluated 239Pu(n,f) Prompt Fission Neutron Spectra Including the CEA and Chi-Nu High-precision Experimental Data. 2022. ⟨hal-03823245⟩
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