Producing ENDF/B-quality Evaluations of 239Pu(n,f) and 235U(n,f) Average Prompt Neutron Multiplicities using the CGMF Model
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
This report documents evaluations of the neutron-induced 239Pu and 235U average prompt neutron multiplicities, $$\overline{v}_p$$, using the CGMF model developed at LANL. These evaluations are not updates of existing ENDF/B-VIII.0 nuclear data, but were both re-done from "scratch". That is, all experimental data were extracted from EXFOR, re-normalized to the newest nuclear data representing monitor observables, and detailed uncertainties were estimated from information in EXFOR as well as from templates of expected measurement uncertainties. We also included experimental data that were not yet available for ENDF/B-VIII.0, for instance, the data of Marini et al. for 239Pu(n,f) $$\overline{v}_p$$ or the data of Khoklov et al. for 235U(n,f) $$\overline{v}_p$$. Finally, we include the CGMF model; it computes $$\overline{v}_p$$ based on model parameters that at the same time calculate fission fragments as a function of mass, Y (A), the average total kinetic energy as a function of incident-neutron energy, $$\langle TKE \rangle$$(Einc), etc. Such a detailed fission model that ties together many fission quantities has not been used to date for any $$\overline{v}_p$$ evaluation in ENDF/B. Here, we show that we can get evaluated 235U(n,f) and 239Pu $$\overline{v}_p$$ that not only correspond well to experimental $$\overline{v}_p$$, but that the associated evaluated model parameters also yield parameterizations of Y (A), $$\langle TKE \rangle$$(Einc), etc., that correspond well to their respective experimental data. The new evaluated 239Pu(n,f) $$\overline{v}_p$$ was also combined into a 239Pu test file with the newest nuclear data for the 239Pu prompt-fission neutron spectrum and fission cross sections. This new 239Pu file performed reasonably well in predicting PU-MET-FAST assemblies, reaction rates in Jezebel and Flattop and three LLNL pulsed spheres. Due to that, the new 239Pu(n,f) $$\overline{v}_p$$ evaluation presented here is being considered for ENDF/B-VIII.1. Hence, we can show here that CGMF is able to produce ENDF/B quality $$\overline{v}_p$$ nuclear data.
- 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:
- 1897963
- Report Number(s):
- LA-UR-21-29906; TRN: US2309410
- Country of Publication:
- United States
- Language:
- English
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