From fission yield measurements to evaluation: Propositions of ²³⁵U(n_th,f) Fission Yields for JEFF-4

Abstract

The study of fission yields has a major impact on the characterization and understanding of the fission process and its applications. The fission products have a direct influence on the amount of neutron poisons that limit the fuel burnup and on the evaluation of the decay heat of the reactor after shutdown. Fission yield evaluation represents the synthesis of experimental and theoretical knowledge in order to perform the best estimation of mass and independent fission product yields. Today, the lack of correlations between the different fission observables induces some inconsistencies in the evaluations. For instance, the mass yield uncertainties are drastically overestimated while this observable is the best known. In this last decade, different covariance matrices have been proposed but the experimental part of those are neglected. A consistent covariance matrix depends on the global process of evaluation from data up to the models used. The collaboration develops a new methodology in the field of fission products for the future version of the JEFF-library coupling the analyses of the CEA and NNL institutes.