From fission yield measurements to evaluation: status on statistical methodology for the covariance question

Abstract

Studies on fission yields have a major impact on the characterization and the understanding of the fission process and are mandatory for reactor applications. Fission yield evaluation represents the synthesis of experimental and theoretical knowledge to perform the best estimation of mass, isotopic and isomeric yields. Today, the output of fission yield evaluation is available as a function of isotopic yields. Without the explicitness of evaluation covariance data, mass yield uncertainties are greater than those of isotopic yields. This is in contradiction with experimental knowledge where the abundance of mass yield measurements is dominant. These last years, different covariance matrices have been suggested but the experimental part of those are neglected. The collaboration between the LPSC Grenoble and the CEA Cadarache starts a new program in the field of the evaluation of fission products in addition to the current experimental program at Institut Laue-Langevin. The goal is to define a new methodology of evaluation based on statistical tests to define the different experimental sets in agreement, giving different solutions for different analysis choices. This study deals with the thermal neutron induced fission of 235 U. The mix of data is non-unique and this topic will be discussed using the Shannon entropy criterion in the framework of the statistical methodology proposed. *

Status of fission fragment observables measured with the LOHENGRIN spectrometer

“…The program on fission yields with the LOHENGRIN spectrometer at ILL has been initiated for several years [1][2] and we developed different methodologies to obtain absolute fission yields with the description of the Probability Density Function (PDF) and the covariance matrices associated to the measurements [3]. This information on measurements is required in order to consider statistical tests as the cornerstone of the evaluation program [4][5].…”

A study of the construction of the correlation matrix of 241Pu(nth,f) isobaric fission yields

“…Considering this approach, the Exp.2 is taken as reference for the rest of this work. Work is in progress in order to construct an observable quantifying the quality of the information depending on the reference, similarly to the work presented in [19]. A new analysis of the 2013 data is in progress and is expected to give results with lower uncertainties.…”

Generation and analysis of independent fission yield covariances based on GEF model code

“…The inventories of fission products determine the calculation accuracy of macro parameters of reactor physics, such as eigenvalue. The fission yield data are mainly obtained through theoretical model evaluation [1]. During the evaluation process, imperfect model parameters propagate uncertainties to fission yields.…”