Use of integral experiments for the assessment of a new 235U IRSN-CEA evaluation

The Working Party on International Nuclear Data Evaluation Co-operation (WPEC) subgroup 29 (SG 29) was established to investigate an issue with the U-235 capture cross-section in the energy range from 0.1 to 2.25 keV, due to a possible overestimation of 10% or more. To improve the U-235 capture crosssection, a new U-235 evaluation has been proposed by the Institut de Radioprotection et de Surete Nucleaire (IRSN) and the CEA, mainly based on new time-of-flight U-235 capture cross-section measurements and recent fission cross-section measurements performed at the n_TOF facility from CERN. IRSN and CEA Cadarache were in charge of the thermal to 2.25 keV energy range, whereas the CEA DIF was responsible of the high energy region. Integral experiments showing a strong U-235 sensitivity are used to assess the new evaluation, using Monte-Carlo methods. The k(eff) calculations were performed with the 5.D.1 beta version of the MORET 5 code, using the JEFF-3.2 library and the new U-235 evaluation, as well as the JEFF-3.3T1 library in which the new U-235 has been included. The benchmark selection allowed highlighting a significant improvement on k(eff) due to the new U-235 evaluation. The results of this data testing are presented here.