Including 238U(n,f)/235U(n,f) and 239Pu(n,f)/235U(n,f) NIFFTE fission TPC Cross-sections into the Neutron Data Standards Database
The primary purpose of this report is to document how the 238U/235U and 239Pu/235U neutron induced fission cross-section ratios, 238U(n,f)/235U(n,f) and 239Pu(n,f)/235U(n,f), respectively, measured by the NIFFTE fission Time Projection Chamber (fissionTPC) were included in the most recent database (termed GMA) underlying Neutron Data Standards (NDS) evaluations. This report shows and discusses NDS input files, and underlying assumptions regarding the uncertainty estimate and necessary for including these data. This uncertainty estimate and the resulting files were based on information provided by fissionTPC experimentalists, R.J.Casperson, N.S. Bowden, L. Snyder and K.T. Schmitt for the 238U ratio, and by L. Snyder for the 239Pu ratio. The fissionTPC data were included twice, by D. Neudecker and V. Pronyaev, to counter-check results and exclude possible mistakes in their inclusion. It is shown in both evaluations that including fissionTPC 239Pu(n,f)/235U(n,f) data points to a lower evaluated 239Pu(n,f) cross section above 10 MeV than the currently released NDS data. This raises the question whether a part of a previous dataset by Tovesson et al., that was previously rejected above 13 MeV for having low values, should be included in the NDS evaluation after all. The evaluated 238U(n,f) cross section only changes significantly close to the threshold. The impact on the 235U(n,f) cross section is minimal. fissionTPC data reduce evaluated uncertainties on both observables by 0–12% of the GMA evaluated uncertainties. However, the currently released NDS data contain in addition to these GMA evaluated uncertainties “Unrecognized Sources of Uncertainties” (USU) of 1.2%. It needs to be further discussed within the NDS project, whether the new fissionTPC data should also reduce USU.
- 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:
- 1788383
- Report Number(s):
- LA-UR-21-24093; TRN: US2216234
- Country of Publication:
- United States
- Language:
- English
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