Probability Density Functions with Correlations of Experimental and Evaluated ²³⁵U(n_th,f) Fission Yields and Their Impacts on Reactivity Loss with Burnup

The study of fission yields has a major impact on the characterization and understanding of the fission process and its applications. For the latter, it is crucial to provide fission yields with their associated correlation matrix in order to estimate precisely the uncertainties of crucial quantities, such as the reactivity loss. In the last decade, different works have been proposed to estimate the correlations of the independent fission yields satisfying the consistency of the cumulative yield evaluations. In these previous works, only model parameters and conservation laws have driven the correlations.

The novelty of the present work consists of new complete and consistent evaluations of ²³⁵U(n_th,f) independent and cumulative yields and their correlation matrices, starting from experimental data. The characterization of the probability density functions of fission yields validates the multivariate Gaussian assumption and constitutes a major issue in the validation of the uncertainty propagation tools of the applications. In addition, the new ²³⁵U(n_th,f) fission yield covariance data have resulted in a decrease in nuclear data related to uncertainty in associated burnup calculations.