Improved Mixed Oxide Fuel Calculations with the Evaluated Nuclear Data Library JEFF-3.2

International audienceAn overestimation of the $k_{eff}$ values for MOX fuels was identified with Monte-Carlo (TRIPOLI4) and deterministic (APOLLO2) calculations based on the Evaluated Nuclear Data Library JEFF. The overestimation becomes sizeable with the Pu-ageing, reaching a reactivity change of $\Delta_ \rho$ $\simeq$ $+$700 pcm for integral measurements carried out with MOX fuel containing a large amount of Americium. This bias was observed on various critical configurations performed in the zero power reactor EOLE of the CEA Cadarache, France. The present work focuses on the improvements achieved with the new $^{239}$Pu and $^{241}$Am Evaluated Nuclear Data Files available in the latest version of the JEFF library (JEFF-3.2). The Resolved Resonance Range of the plutonium evaluation was re-evaluated at ORNL (Oak Ridge National Laboratory) with the SAMMY code in collaboration with the CEA Cadarache. The resonance parameters of the Americium evaluation were obtained with the REFIT code in collaboration with the research institutes IRMM (Institute for Reference Materials and Measurements, Geel, Belgium) and Irfu (Institut de recherche sur les lois fondamentales de l’Univers, Saclay, France)