The impact of the new nuclear data libraries on the isothermal reactivity coefficient determination

The impact of the new released evaluations for ²³⁵U, ²³⁸U, ¹⁶O, and S(α,β) for hydrogen bound water, in the determination of the isothermal reactivity coefficient of thermal reactors fueled with slightly enriched uranium is addressed in this work. The experiment to serve as a benchmark for this kind of reactor response is the inversion point of the isothermal reactivity coefficient of the IPEN/MB-01 reactor which was recently approved to be included in the IRPhE handbook. The theoretical analyses have been performed employing the coupled NJOY/AMPX-II/TORT systems. The analyses reveal that the major impacts are due to new data of ²³⁵U and to those of S(α,β) for hydrogen bound in water. The (C-E)/E values when considering the new data from these libraries show an excellent progress in the theoretical determination of this very important reactor response. The new data for ²³⁸U and ¹⁶O show very little impact on the analysis. This work supports the developments recently adopted in the generation of the new nuclear data libraries for ²³⁵U and for the S(α,β) for hydrogen bound in water. (authors)