Speaker
Description
From fission yield measurements to evaluation: correlations of multi-observable analysis
S.M. Cheikh 1, G. Kessedjian 1, A. Chebboubi 1, O. Serot 1 and C. Sage 2
1 CEA, DES, IRESNE, DER, SPRC, LEPh, Cadarache center, F-13108 Saint Paul lez Durance, France
2 LPSC, Université Grenoble-Alpes, CNRS/IN2P3, 38026 Grenoble, France
Topics for submission: Fission yield evaluation
Keywords: fission yields, evaluation, variance-covariance matrix
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 inconsistencies in the evaluations. For instance, the mass yield uncertainties are drastically overestimated while this observable is the best known. This last decade, different covariance matrices have been proposed but the experimental part of those are neglected. A consistent covariance matrix depends on the evaluation process. This consistency is deeply entangled to the statistical agreement between each data sets. Moreover, the experimental covariance data are crucial in the evaluation process and covariance of model parameters does not represent the only contribution to the covariance matrix associated to evaluation. A large range of data are present in the EXFOR data bank but most of them cover partial mass range, for different incident neutron energy, without necessarily an absolute mass or isotopic identification. Thus, the mix of data could lead to several solutions, which then has to be ranked.
The LEPh Laboratory of CEA Cadarache develops a new methodology in the field of the fission products for the future version of the JEFF-library. Statistical test of datasets and data ranking are requested in order to define the confident region of the fission yield knowledge. A complete evaluation of the mass and independent fission product yields of the 235U(nth,f) reaction will be presented with the associated covariance matrix their impact on nuclear reactor calculations.