Criticality Safety Evaluation of a Swiss wet storage pool using a global uncertainty analysis methodology
Uncertainty quantification is a key component in the Criticality Safety Evaluation (CSE) of spent nuclear fuel systems. An important source of uncertainties is caused by manufacturing and technological parameter tolerances. In this work, such class of uncertainties are evaluated for a Swiss wet storage pool. The selected configuration corresponds to a case where the target criticality eigenvalue is close to the upper criticality safety limits. Although current PSI CSE safety criteria are fulfilled, it is reasonable to apply uncertainty quantification methodologies in order to provide the regulatory authorities with additional information relevant for safety evaluations. The MTUQ (Manufacturing and Technological Uncertainty Quantification) methodology, based on global stochastic sampling was the selected tool for the analysis. Such tool is specifically designed for the treatment of geometrical/material uncertainties for any target system. In particular the MTUQ advanced modelling capability allows the implementation of realistic boundary condition, with a resulting detailed evaluation of statistical quantities of interest in CSE. Therein, the computational code implemented is the MCNP Monte Carlo based neutron transport code. The analysis showed the benefits in using realistic modelling compared to the traditional one-factor-at-time methodology applied to system modelled using repeated structures. A detailed comparison between the 2 approaches is also presented. Finally, it is discussed the role of asymmetrical probability distribution functions to feed the global statistical methods. (C) 2015 Elsevier Ltd. All rights reserved.