Proposed re-evaluation of the 154Eu thermal n, γ capture cross-section based on spent fuel benchmarking studies. (January 2017)

• Record Type: Journal Article
• Authors: Skutnik, Steven E.
• Is Part Of: Annals of nuclear energy. Volume 99(2017:Jan.)
• Page Start: 80
• Page End: 107
• Publication Date: 2017-01
• Subjects: Eu-154 -- Nuclear data -- ENDF -- Burnup -- Nuclear fuel depletion; Nuclear energy -- Periodicals; Nuclear engineering -- Periodicals; 621.4805
• DOI: 10.1016/j.anucene.2016.09.003
• Languages: English
• ISSNs: 0306-4549

Abstract

Highlights: Spent fuel benchmark calculations indicate a bias in the 154 Eu ( n, γ ) 155 Eu cross-section. This bias appears to be located in the thermal-energy (<1 eV) region. This bias is present in the ENDF/B-VII.0, ENDF/B-VII.1, and JEFF-3.2 evaluations Due to this bias, 154 Eu is consistently overestimated in calculations by ≈10–15 Corrections to the thermal-region 154 Eu cross-section ameliorate these overestimates. Abstract: 154 Eu is a nuclide of considerable importance to both non-destructive measurements of used nuclear fuel assembly burnup as well as for calculating the radiation source term for used fuel storage and transportation. However, recent evidence from code validation studies of spent fuel benchmarks have revealed evidence of a systemic bias in predicted 154 Eu inventories when using ENDF/B-VII.0 and ENDF/B-VII.1 nuclear data libraries, wherein 154 Eu is consistently over-predicted on the order of 10% or more. Further, this bias is found to correlate with sample burnup, resulting in a larger departure from experimental measurements for higher sample burnups. In this paper, the bias in 154 Eu is characterized across eleven spent fuel destructive assay benchmarks from five different assemblies. Based on these studies, possible amendments to the ENDF/B-VII.0 and VII.1 evaluations of the 154 Eu n, γ 155 Eu are explored. By amending the location of the first resolved resonance for the 154 Eu radiative capture cross-section (centered at 0.195 eV in ENDF/B-VII.0 and VII.1) to 0.188 eV and adjusting the neutron capture width proportional to 1 / E, the amended cross-section evaluation was found to reduce the bias in predicted 154 Eu inventories by approximately 5–7%. While the amended capture cross-section still results in a residual over-prediction of 154 Eu (ranging from 2% to 9%), the effect is substantially attenuated compared with the nominal ENDF/B-VII.0 and VII.1 evaluations.