Use of integral experiments for the assessment of the ²³⁵U capture cross section within the CIELO project

A new ²³⁵U capture cross-section evaluation, evaluated by ORNL and the CEA Bruyeres-le-Chatel has been proposed within the CIELO (Collaborative International Evaluated Library Organization) project. IRSN, who participates in the CIELO project, contributes with data testing and has carried out benchmark calculations using few benchmarks, extracted from the ICSBEP database, for testing the new ²³⁵U evaluation. The benchmarks have been selected by privileging the experiments showing small experimental uncertainties and a significant sensitivity to ²³⁵U capture cross-section. The k_eff calculations were performed with both the MCNP 6 code and the 5.C.1 release of the MORET 5 code, using the ENDF/B-VII.1 library for all isotopes except ²³⁵U, for which both the ENDF/B-VII.1 and the new ²³⁵U evaluation was used. The benchmark selection allowed highlighting a significant effect on k_eff of the new ²³⁵U capture cross-section: the impact varies from about +370 pcm to about -1000 pcm for all the selected benchmarks