Current Issues in Nuclear Data Evaluation Methodology: {sup 235}U Prompt Fission Neutron Spectra and Multiplicity for Thermal Neutrons

Journal Article · Thu Jan 15 04:00:00 EST 2015 · Nuclear Data Sheets

DOI:https://doi.org/10.1016/J.NDS.2014.12.003· OSTI ID:22436751

Capote, R. ^[1]; Pronyaev, V. G. ^[2]

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1. Nuclear Data Section, International Atomic Energy Agency, A-1400 Vienna (Austria)
2. Institute of Physics and Power Engineering, Obninsk (Russian Federation)

Issues in evaluation methodology of the prompt fission neutron spectra (PFNS) and neutron multiplicity for the thermal-neutron-induced fission of the {sup 235}U are discussed. The inconsistency between the experimental differential and integral data is addressed. By using differential data as ”shape data” good consistency was achieved between available sets of differential data. Integral dosimetry data have been used to define the PFNS slope at high outgoing neutron energies, where the quality of the differential data is poor. The inclusion into the fit of measured integral (spectrum-averaged) cross sections had a very small impact in the region where differential PFNS data are abundant and accurate, but removed the discrepancy with integral data at higher neutron emission energies. All experimental data are consistently fitted giving a PFNS average energy of 2.008 MeV. The impact on criticality prediction of the newly evaluated PFNS was tested. The highly enriched {sup 235}U solution assemblies with high leakage HEU-SOL-THERM-001 and HEU-SOL-THERM-009 benchmarks are the most sensitive to the PFNS. Criticality calculations for those solutions show a significant increase in reactivity if the average neutron energy of the fission neutrons is reduced from the ENDF/B-VI.5 value of 2.03 MeV. The proposed reduction of the PFNS average energy by 1.1% can be compensated by reducing the average number of neutrons per fission ν{sup ¯} at the thermal energy to the Gwin et al. measured value. The simple least-squares PFNS fit was confirmed by a more sophisticated combined fit of differential PFNS data for {sup 233,235}U, {sup 239}Pu and {sup 252}Cf nuclides with the generalised least-squares method using the GMA and GANDR codes.

• OSTI ID: 22436751
• Journal Information: Nuclear Data Sheets, Journal Name: Nuclear Data Sheets Vol. 123; ISSN NDTSBA; ISSN 0090-3752
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
CALIFORNIUM 252
DATA
EVALUATION
FISSION NEUTRONS
LEAST SQUARE FIT
MEV RANGE
NEUTRON SPECTRA
PLUTONIUM 239
THERMAL NEUTRONS
URANIUM 233
URANIUM 235