Propagation of Uncertainty in System Parameters of a LWR Model by Sampling MCNPX Calculations – Burnup Analysis

¹ Centro de Desenvolvimento da Tecnologia Nuclear/CNEN
² Departamento de Engenharia Nuclear, Universidade Federal de Minas Gerais/UFMG Av. Presidente Antônio Carlos, 6627, Cidade Universitia - Pampulha - Belo Horizonte - MG - Brazil

^* Daniel de A. M. Campolina, E-mail: campolina@cdtn.br

Abstract

For all the physical components that comprise a nuclear system there is an uncertainty. Assessing the impact of uncertainties in the simulation of fissionable material systems is essential for a best estimate calculation that has been replacing the conservative model calculations as the computational power increases. The propagation of uncertainty in a simulation using a Monte Carlo code by sampling the input parameters is recent because of the huge computational effort required. In this work a sample space of MCNPX calculations was used to propagate the uncertainty. The sample size was optimized using the Wilks formula for a 95^th percentile and a two-sided statistical tolerance interval of 95%. Uncertainties in input parameters of the reactor considered included geometry dimensions and densities. It was showed the capacity of the sampling-based method for burnup when the calculations sample size is optimized and many parameter uncertainties are investigated together, in the same input.