Evaluation of the²³⁵U resonance parameters to fit the standard recommended values

Abstract

Abstract.A great deal of effort has been dedicated to the revision of the standard values in connection with the neutron interaction for some actinides. While standard data compilation are available for decades nuclear data evaluations included in existing nuclear data libraries (ENDF, JEFF, JENDL, etc.) do not follow the standard recommended values. Indeed, the majority of evaluations for major actinides do not conform to the standards whatsoever. In particular, for the n + 235 U interaction the only value in agreement with the standard is the thermal fission cross section. A resonance re-evaluation of the n + 235 U interaction has been performed to address the issues regarding standard values in the energy range from 10 −5 eV to 2250 eV. Recently, 235 U fission cross-section measurements have been performed at the CERN Neutron Time-of-Flight facility (TOF), known as n TOF, in the energy range from 0.7 eV to 10 keV. The data were normalized according to the recommended standard of the fission integral in the energy range 7.8 eV to 11 eV. As a result, the n TOF averaged fission cross sections above 100 eV are in good agreement with the standard recommended values. The n TOF data were included in the 235 U resonance analysis that was performed with the code SAMMY. In addition to the average standard values related to the fission cross section, standard thermal values for fission, capture, and elastic cross sections were also included in the evaluation. This paper presents the procedure used for re-evaluating the 235 U resonance parameters including the recommended standard values as well as new cross section measurements.

High-resolution evaluation of the U5(n,f) cross section from 3 keV to 30 keV

“…Concerning the 235 U neutron-induced fission cross-section, below 150 keV this cross section is only included as Standard at the thermal point and recently its integral value between 7.8 eV and 11 eV [1]. The resolved resonance region, spanning up to 2.25 keV, has been re-evaluated in this energy range with high resolution in the last ENDF/B-VIII release [2] and a SAMMY resonance analysis was done by L. Leal et al [3] after including the work of Paradela el al., presented at WONDER-2015 [4], and taken into account the IAEA Reference file. This result of L. Leal has been included in the last up-dating version ,…”