Uncertainty and sensitivity analysis in the neutronic parameters generation over the coupled thermalhydraulic-neutronic nuclear power plant simulations

This paper presents a study of the influence of the uncertainty in the macroscopic neutronic information that describes a three-dimensional BWR core model on the most relevant results of the simulation of a Reactivity Induced Accident (R1A). The analysis of the BWR-R1A has been carried out with a three-dimensional thermal-hydraulic and neutronic model for the coupled system TRACE-PARCS. The cross section information has been generated by the SIMTAB methodology based on the joint use of CASMO-SIMULATE. The Best Estimate analysis consists of a coupled thermal-hydraulic and neutronic description of the nuclear system's behaviour, uncertainties from both aspects should be included and jointly propagated. The statistically based methodology performs a Monte-Carlo kind of sampling of the uncertainty in the macroscopic cross sections. The size of the sampling is determined by the characteristics of the tolerance intervals by applying the Noether-Wilks formulas. A number of simulations equal to the sample size is carried out in which the cross sections used by PARCS are directly modified with uncertainty, and non-parametric statistical methods are applied to the resulting sample of the values of the output variables to determine their intervals of tolerance.