Influence of nuclear data parameters on integral experiment assimilation using Cook's distance

In order to utilize the past critical experimental data to the reactor design work, a typical procedure for the nuclear data adjustment is based on the Bayesian theory (least-square technique or Monte-Carlo). In this method, the nuclear data parameters are optimized by the inclusion of the experimental information using a Bayesian inference. The Bayesian inference is a mathematical framework that allows one to assimilate information from measurements (microscopic and integral) and from a prior knowledge of the parameters, in order to reduce the uncertainties of these parameters and modify their values if necessary. The selection of integral experiments is based on the availability of well-documented specifications and experimental data. Data points with large uncertainties or large residuals (outliers) may affect the accuracy of the adjustment. Hence, in the adjustment process, it is very important to study the influence of experiments as well as of the prior nuclear data on the adjusted results. In this work, the influence of each individual reaction (related to nuclear data) is analyzed using the concept of Cook's distance. Cook's distance provides an overall measurement of the change in all parameter estimates. The concept of Cook's distance is a good measure of the influence of an observation and is proportional to the sum of the squared differences between predictions made with all observations in the analysis and predictions made by removing the observation in question. The selection of integral experiments is based on the availability of well-documented specifications and experimental data. Data points with large uncertainties or large residuals (outliers) may affect the accuracy of the adjustment. Hence, in the adjustment process, it is very important to study the influence of experiments as well as of the prior nuclear data on the adjusted results. First, JEZEBEL (Pu²³⁹, Pu²⁴⁰ and Pu²⁴¹) integral experiment is considered for data assimilation and then the transposition of results on ASTRID fast reactor concept is discussed